Patent Publication Number: US-2021169852-A1

Title: Protein recognizing drug moiety of antibody-drug conjugate

Description:
TECHNICAL FIELD 
     The present invention relates to a protein that recognizes a drug moiety of an antibody-drug conjugate having a derivative of exatecan as a component; a method for quantifying the concentration in plasma of the antibody-drug conjugate in a mammal administered with the antibody-drug conjugate by using the protein; and a method for determining a tissue distribution thereof. 
     BACKGROUND ART 
     An antibody-drug conjugate (ADC) having a drug with cytotoxicity conjugated to an antibody which binds to an antigen expressed on the surface of cancer cells and is also capable of cellular internalization can deliver the drug selectively to the cancer cells, and is thus expected to cause accumulation of the drug within cancer cells and to kill the cancer cells (Non-Patent References 1 to 5). 
     In developing antibody-drug conjugates into pharmaceutical products, similarly to development of small molecule compounds and antibodies, a pharmacokinetic study (PK study) is indispensable. This is because information useful for planning of clinical trial design and considering effectiveness and safety in humans can be obtained by carrying out a PK study in humans based on understanding of the correlation between PK study results and pharmacological study results and safety test result in animals. 
     The PK study of an antibody-drug conjugate is basically carried out by quantifying the concentration in plasma of the antibody-drug conjugate administered. As the method for quantifying the concentration in plasma of an antibody-drug conjugate, ELISA method can be exemplified. For example, the concentration in plasma of an antibody-drug conjugate can be quantified through the steps of: (1) contacting an antibody-drug conjugate with a plate having an antigen immobilized thereon to form a complex, (2) contacting a protein capable of recognizing the antibody-drug conjugate and labeled with a marker with the complex to form a further complex; and then, (3) detecting the marker based on color/light produced by enzymatic reactions. 
     However, if a protein that recognizes an antibody moiety of an antibody-drug conjugate is used, plasma-concentration including not only the concentration of antibody-drug conjugate retaining the drug but also the concentration of antibody-drug conjugate from which the drug is released (more specifically, substantially the antibody moiety, alone) is quantified by calculation, and a determination cannot be accurately made. 
     A method for quantifying the concentration in plasma of an antibody-drug conjugate by ELISA method using a protein that recognizes a drug moiety of an antibody-drug conjugate, is known (Non Patent References 6 to 11). 
     As one of antibody-drug conjugates, an antibody-drug conjugate having an antibody and a derivative of exatecan, which is a topoisomerase I inhibitor, as its components, is known (Patent References 1 to 7, Non Patent References 12 to 15). Since these antibody-drug conjugates exert a particularly superior antitumor effect and have safety, they are currently under clinical studies. 
     A method for quantifying the concentration in plasma of an antibody-drug conjugate having a derivative of exatecan as a component while retaining a drug, has not yet been known. 
     CITATION LIST 
     Patent Literature 
     
         
         [Patent Reference 1] International Publication No. WO 2014/057687 
         [Patent Reference 2] International Publication No. WO 2014/061277 
         [Patent Reference 3] International Publication No. WO 2015/098099 
         [Patent Reference 4] International Publication No. WO 2015/115091 
         [Patent Reference 5] International Publication No. WO 2015/146132 
         [Patent Reference 6] International Publication No. WO 2015/155976 
         [Patent Reference 7] International Publication No. WO 2015/155998 
       
    
     Non Patent Literature 
     
         
         [Non Patent Reference 1] Ducry, L., et al., Bioconjugate Chem. (2010) 21, 5-13. 
         [Non Patent Reference 2] Alley, S. C., et al., Current Opinion in Chemical Biology (2010) 14, 529-537. 
         [Non Patent Reference 3] Damle N. K. Expert Opin. Biol. Ther. (2004) 4, 1445-1452. 
         [Non Patent Reference 4] Senter P. D., et al., Nature Biotechnology (2012) 30, 631-637. 
         [Non Patent Reference 5] Howard A. et al., J Clin Oncol 29: 398-405. 
         [Non Patent Reference 6] Xie H. et al., J Pharmacol Exp Ther. (2004) 308 (3), 1073-1082. 
         [Non Patent Reference 7] Sanderson RJ. et al., Clinical Cancer Research (2005) Vol. 11, 843-852. 
         [Non Patent Reference 8] Stephan JP. et al., Bioconjugate Chem. 2008, 19, 1673-1683. 
         [Non Patent Reference 9] Stephan JP. et al., Bioanalysis (2011) 3 (6), 677-700. 
         [Non Patent Reference 10] Kaur S. et al., Bioanalysis (2013) 5 (2), 201-226. 
         [Non Patent Reference 11] Dere R. et al., Bioanalysis (2013) 5 (9), 1025-1040. 
         [Non Patent Reference 12] Ogitani Y. et al., Clinical Cancer Research (2016) 22 (20), 5097-5108. 
         [Non Patent Reference 13] Ogitani Y. et al., Cancer Science (2016) 107, 1039-1046. 
         [Non Patent Reference 14] Doi T, et al., Lancet Oncol 2017; 18: 1512-22. 
         [Non Patent Reference 15] Takegawa N, et al., Int. J. Cancer: 141, 1682-1689 (2017). 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     An object of the present invention is to provide a protein that recognizes a drug moiety of an antibody-drug conjugate having a derivative of exatecan as a component; a method for quantifying the concentration in plasma of the antibody-drug conjugate in a mammal administered with the antibody-drug conjugate by using the protein; and a method for determining a tissue distribution thereof. 
     Solution to Problem 
     As a result of diligent studies in order to solve the above problems, the present inventors have found that a protein obtained by specific immunoscreening specifically recognizes a drug moiety of an antibody-drug conjugate having a derivative of exatecan as a component. Further, they established a method for quantifying the concentration in plasma of the antibody-drug conjugate in a mammal administered with the antibody-drug conjugate by using the protein; and a method for determining a tissue distribution thereof. 
     Thus, the present invention provides the following [1] to [51]. 
     [1] A protein that recognizes a drug moiety of an antibody-drug conjugate in which a drug represented by the following formula: 
     
       
         
         
             
             
         
       
     
     is conjugated to an antibody via a linker.
 
[2] The protein according to [1], wherein a drug-linker in the antibody-drug conjugate is represented by the following formula:
 
     
       
         
         
             
             
         
       
     
     wherein A represents a connecting position to the antibody, and
 
the drug-linker is conjugated to the antibody via a thioether bond.
 
[3] The protein according to [1], wherein the drug-linker in the antibody-drug conjugate is represented by the following formula:
 
     
       
         
         
             
             
         
       
     
     wherein A represents a connecting position to the antibody, and
 
the drug-linker is conjugated to the antibody via a thioether bond.
 
[4] The protein according to [1], wherein the drug-linker in the antibody-drug conjugate is represented by the following formula:
 
     
       
         
         
             
             
         
       
     
     wherein A represents a connecting position to the antibody, and
 
the drug-linker is conjugated to the antibody via a thioether bond.
 
[5] The protein according to [1], wherein the antibody-drug conjugate is represented by the following formula:
 
     
       
         
         
             
             
         
       
     
     wherein the drug-linker is conjugated to the antibody via a thioether bond and n represents the average number of units of the drug-linker conjugated per antibody molecule.
 
[6] The protein according to [1], wherein the antibody-drug conjugate is represented by the following formula:
 
     
       
         
         
             
             
         
       
     
     wherein the drug-linker is conjugated to the antibody via a thioether bond and n represents the average number of units of the drug-linker conjugated per antibody molecule.
 
[7] The protein according to [1], wherein the antibody-drug conjugate is represented by the following formula:
 
     
       
         
         
             
             
         
       
     
     wherein the drug-linker is conjugated to the antibody via a thioether bond and n represents the average number of units of the drug-linker conjugated per antibody molecule.
 
[8] The protein according to any one of [1] to [7], wherein the average number of units of the drug-linker conjugated per antibody molecule in the antibody-drug conjugate is in the range of from 2 to 8.
 
[9] The protein according to any one of [1] to [8], wherein the antibody in the antibody-drug conjugate is an anti-HER2 antibody, an anti-HER3 antibody, an anti-TROP2 antibody, an anti-B7-H3 antibody, an anti-GPR20 antibody or an anti-CDH6 antibody.
 
[10] The protein according to any one of [1] to [9], wherein the recognition property of the protein to the antibody-drug conjugate is substantially independent of any difference in the average number of units of the drug-linker conjugated per antibody molecule in the antibody-drug conjugate.
 
[11] A protein that recognizes a drug represented by the following formula:
 
     
       
         
         
             
             
         
       
     
     [12] A protein that recognizes a drug represented by the following formula: 
     
       
         
         
             
             
         
       
     
     [13] A protein that recognizes a drug represented by the following formula: 
     
       
         
         
             
             
         
       
     
     [14] A protein that recognizes a drug represented by the following formula: 
     
       
         
         
             
             
         
       
     
     [15] The protein according to any one of [1] to [14], wherein the protein is an antibody.
 
[16] The protein according to [15], wherein the protein is
 
     a) an antibody consisting of a heavy chain comprising CDRH1 consisting of an amino acid sequence represented by SEQ ID NO: 1, CDRH2 consisting of an amino acid sequence represented by SEQ ID NO: 2, and CDRH3 consisting of an amino acid sequence represented by SEQ ID NO: 3; and a light chain comprising CDRL1 consisting of an amino acid sequence represented by SEQ ID NO: 4, CDRL2 consisting of an amino acid sequence represented by SEQ ID NO: 5, and CDRL3 consisting of an amino acid sequence represented by SEQ ID NO: 6, 
     b) an antibody consisting of a heavy chain comprising CDRH1 consisting of an amino acid sequence represented by SEQ ID NO: 7, CDRH2 consisting of an amino acid sequence represented by SEQ ID NO: 8, and CDRH3 consisting of an amino acid sequence represented by SEQ ID NO: 3; and a light chain comprising CDRL1 consisting of an amino acid sequence represented by SEQ ID NO: 4, CDRL2 consisting of an amino acid sequence represented by SEQ ID NO: 5, and CDRL3 consisting of an amino acid sequence represented by SEQ ID NO: 6, 
     c) an antibody consisting of a heavy chain comprising CDRH1 consisting of an amino acid sequence represented by SEQ ID NO: 9, CDRH2 consisting of an amino acid sequence represented by SEQ ID NO: 10, and CDRH3 consisting of an amino acid sequence represented by SEQ ID NO: 3; and a light chain comprising CDRL1 consisting of an amino acid sequence represented by SEQ ID NO: 4, CDRL2 consisting of an amino acid sequence represented by SEQ ID NO: 5, and CDRL3 consisting of an amino acid sequence represented by SEQ ID NO: 6, or 
     d) an antibody consisting of a heavy chain comprising CDRH1 consisting of an amino acid sequence represented by SEQ ID NO: 11, CDRH2 consisting of an amino acid sequence represented by SEQ ID NO: 12, and CDRH3 consisting of an amino acid sequence represented by SEQ ID NO: 13; and a light chain comprising CDRL1 consisting of an amino acid sequence represented by SEQ ID NO: 14, CDRL2 consisting of a tripeptide represented by WAS, and CDRL3 consisting of an amino acid sequence represented by SEQ ID NO: 6. 
     [17] The protein according to [16], wherein the protein is an antibody consisting of a heavy chain comprising a heavy chain variable region consisting of an amino acid sequence consisting of amino acid residues 20 to 141 of SEQ ID NO: 15, and a light chain comprising a light chain variable region consisting of an amino acid sequence consisting of amino acid residues 21 to 127 of SEQ ID NO: 16.
 
[18] The protein according to [17], wherein the protein is a mouse antibody.
 
[19] The protein according to [17], wherein the protein is an antibody consisting of a heavy chain consisting of an amino acid sequence consisting of amino acid residues 20 to 477 of SEQ ID NO: 15, and a light chain consisting of an amino acid sequence consisting of amino acid residues 21 to 234 of SEQ ID NO: 16.
 
[20] The protein according to [17], wherein the protein is a chimeric antibody.
 
[21] The protein according to [17], wherein the protein is a rabbit chimeric antibody.
 
[22] The protein according to [17], wherein the protein is an antibody consisting of a heavy chain consisting of an amino acid sequence consisting of amino acid residues 20 to 464 of SEQ ID NO: 19, and a light chain consisting of an amino acid sequence consisting of amino acid residues 21 to 233 of SEQ ID NO: 20.
 
[23] The protein according to [15], wherein the protein is an antibody in which a lysine residue at the carboxyl terminus of the heavy chain of the antibody according to [19] or [22] is deleted.
 
[24] The protein according to [15], wherein the protein is an antibody consisting of an amino acid sequence having at least 95% identity with the amino acid sequence of the antibody according to [19] or [22].
 
[25] The protein according to [15], wherein the protein is an antibody consisting of an amino acid sequence having at least 99% identity with the amino acid sequence of the antibody according to [19] or [22].
 
[26] The protein according to [15], wherein the protein is an antibody that competes with the antibody according to [19] or [22] for the recognition property to the drug.
 
[27] The protein according to any one of [1] to [14], wherein the protein is an antigen binding fragment of the antibody according to any one of [15] to [26].
 
[28] The protein according to [27], wherein the antigen binding fragment of the antibody is Fab, F(ab′)2, Fab′ or Fv.
 
[29] A method for quantifying the concentration in plasma of an antibody-drug conjugate in a mammal to which the antibody-drug conjugate has been administered, by using the protein according to any one of [1] to [28].
 
[30] The method according to [29], comprising the steps of: (1) contacting an antibody-drug conjugate in plasma with a plate having a target antigen for the antibody-drug conjugate immobilized thereon to form a complex; (2) contacting the protein according to any one of [1] to [28] labeled with a marker with the complex to form a further complex; and then (3) detecting the marker.
 
[31] The method according to [29], comprising the steps of: (1) contacting an antibody-drug conjugate in plasma with a plate having a protein according to any one of [1] to [28] immobilized thereon to form a complex; (2) contacting a second protein that is capable of recognizing an antibody moiety of the antibody-drug conjugate and is labeled with a marker with the complex to form a further complex; and then (3) detecting the marker.
 
[32] A method for quantifying the concentration in plasma of a drug released from an antibody-drug conjugate in a mammal to which the antibody-drug conjugate has been administered, by using the protein according to any one of [1] to [28].
 
[33] The method according to [32], comprising the steps of: (1) contacting a drug released from the antibody-drug conjugate in plasma with a plate having the protein according to any one of [1] to [28] immobilized thereon, in the presence of a competitive drug labeled with a marker, to form a complex; and (2) detecting the marker.
 
[34] A method for identifying a tissue distribution of an antibody-drug conjugate and/or a drug released from the antibody-drug conjugate in a mammal to which the antibody-drug conjugate has been administered, using a protein according to any one of [1] to [28].
 
[35] The method according to [34], comprising the steps of: (1) contacting an antibody-drug conjugate and/or a drug released from the antibody-drug conjugate in a tissue with a protein according to any one of [1] to [28] to form a complex, (2) contacting a second protein that is capable of recognizing the protein according to any one of [1] to [28] and is labeled with a marker with the complex to form a further complex, and then (3) detecting the marker.
 
[36] The method according to [34], comprising the steps of: (1) contacting an antibody-drug conjugate and/or a drug released from the antibody-drug conjugate in a tissue with the protein according to any one of [1] to [28] labeled with a marker to form a complex; and then (2) detecting the marker.
 
[37] The method according to [30], [31], [33], [35] or [36], wherein the marker is a chromogenic reagent, and the detection of the marker is performed by sensing a color of the marker.
 
[38] The method according to [30], [31], [33], [35] or [36], wherein the marker is an enzyme, and the detection of the marker is performed by sensing luminescence or color development caused by a reaction between a substrate and the enzyme.
 
[39] The method according to [30], [31], [33], [35] or [36], wherein the marker is a luminescent substance, and the detection of the marker is performed by sensing the luminescence of the marker based on an electrochemical reaction.
 
[40] A polynucleotide encoding the protein according to any one of [1] to [28].
 
[41] A vector comprising the polynucleotide according to [40].
 
[42] A transformed host cell comprising the polynucleotide according to [40].
 
[43] A transformed host cell comprising the vector according to [41].
 
[44] A method for producing the protein according to any one of [1] to [28], comprising the steps of: culturing the host cell according to [42] or [43]; and then purifying a protein from a cultured product obtained in the culturing step.
 
[45] A composition comprising the protein according to any one of [1] to [28].
 
[46] A kit comprising the protein according to any one of [1] to [28] or the composition according to [45].
 
[47] The kit according to [46] for quantifying the concentration in plasma of an antibody-drug conjugate and/or a drug released from the antibody-drug conjugate in a mammal to which the antibody-drug conjugate has been administered.
 
[48] The kit according to [46] for identifying the tissue distribution of an antibody-drug conjugate and/or a drug released from the antibody-drug conjugate in a mammal to which the antibody-drug conjugate has been administered.
 
[49] An antibody comprising a heavy chain comprising a heavy chain variable region consisting of an amino acid sequence consisting of amino acid residues 20 to 141 of SEQ ID NO: 15, and a light chain comprising a light chain variable region consisting of an amino acid sequence consisting of amino acid residues 21 to 127 of SEQ ID NO: 16.
 
[50] The antibody according to [49], comprising a heavy chain consisting of an amino acid sequence consisting of amino acid residues 20 to 477 of SEQ ID NO: 15, and a light chain consisting of an amino acid sequence consisting of amino acid residues 21 to 234 of SEQ ID NO: 16.
 
[51] The antibody according to [49], comprising a heavy chain consisting of an amino acid sequence consisting of amino acid residues 20 to 464 of SEQ ID NO: 19, and a light chain consisting of an amino acid sequence consisting of amino acid residues 21 to 233 of SEQ ID NO: 20.
 
     Advantageous Effects of Invention 
     The present invention provided a protein that recognizes a drug moiety of an antibody-drug conjugate having a derivative of exatecan as a component; a method for quantifying the concentration in plasma of the antibody-drug conjugate in a mammal administered with the antibody-drug conjugate, by using the protein; and a method for determining a tissue distribution thereof. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows an amino acid sequence (SEQ ID NO: 15) of a heavy chain of mouse antibody 1A3. 
         FIG. 2  shows an amino acid sequence (SEQ ID NO: 16) of a light chain of mouse antibody 1A3. 
         FIG. 3  shows a nucleotide sequence (SEQ ID NO: 17) encoding the amino acid sequence of a heavy chain variable region of mouse antibody 1A3. 
         FIG. 4  shows a nucleotide sequence (SEQ ID NO: 18) encoding the amino acid sequence of a light chain variable region of mouse antibody 1A3. 
         FIG. 5  shows an amino acid sequence (SEQ ID NO: 19) of a heavy chain of rabbit chimeric antibody 1A3. 
         FIG. 6  shows an amino acid sequence (SEQ ID NO: 20) of a light chain of rabbit chimeric antibody 1A3. 
         FIG. 7  shows an amino acid sequence (SEQ ID NO: 21) of a heavy chain of an anti-HER2 antibody. 
         FIG. 8  shows an amino acid sequence (SEQ ID NO: 22) of a light chain of an anti-HER2 antibody. 
         FIG. 9  shows an amino acid sequence (SEQ ID NO: 23) of a heavy chain of an anti-HER3 antibody. 
         FIG. 10  shows an amino acid sequence (SEQ ID NO: 24) of a light chain of an anti-HER3 antibody. 
         FIG. 11  shows an amino acid sequence (SEQ ID NO: 25) of a heavy chain of an anti-TROP2 antibody. 
         FIG. 12  shows an amino acid sequence (SEQ ID NO: 26) of a light chain of an anti-TROP2 antibody. 
         FIG. 13  shows an amino acid sequence (SEQ ID NO: 27) of a heavy chain of an anti-B7-H3 antibody. 
         FIG. 14  shows an amino acid sequence (SEQ ID NO: 28) of a light chain of an anti-B7-H3 antibody. 
         FIG. 15  shows calibration curves of HER2-ADC (I) (DAR8) and HER2-ADC (I) (DAR4) when mouse antibody 1A3 was used as a capture reagent. 
         FIG. 16  shows calibration curves of HER2-ADC (I) (DAR8) and HER2-ADC (I) (DAR4) when mouse antibody 8B2 was used as a capture reagent. 
         FIG. 17  shows calibration curves of HER2-ADC (I) (DAR8) and HER2-ADC (I) (DAR4) when mouse antibody 11B1 was used as a capture reagent. 
         FIG. 18  shows calibration curves of HER2-ADC (I) (DAR8) and HER2-ADC (I) (DAR4) when mouse antibody 1A3 was used as a detection reagent. 
         FIG. 19  shows calibration curves of HER2-ADC (I) (DAR8) and HER2-ADC (I) (DAR4) when mouse antibody 8B2 was used as a detection reagent. 
         FIG. 20  shows calibration curves of HER2-ADC (I) (DAR8) and HER2-ADC (I) (DAR4) when mouse antibody 11B1 was used as a detection reagent. 
         FIG. 21  shows calibration curves of B7-H3-ADC(I) (DAR8) and B7-H3-ADC(I) (DAR4) when mouse antibody 1A3 was used as a detection reagent. 
         FIG. 22  shows calibration curves of B7-H3-ADC(I) (DAR8) and B7-H3-ADC(I) (DAR4) when mouse antibody 8B2 was used as a detection reagent. 
         FIG. 23  shows calibration curves of B7-H3-ADC(I) (DAR8) and B7-H3-ADC(I) (DAR4) when mouse antibody 11B1 was used as a detection reagent. 
         FIG. 24  shows a calibration curve for quantifying the concentration in plasma of HER2-ADC (I) in a mouse. 
         FIG. 25  shows a calibration curve for quantifying the concentration in plasma of HER3-ADC (I) in a monkey. 
         FIG. 26  shows a calibration curve for quantifying the concentration in plasma of TROP2-ADC (I) in a monkey. 
         FIG. 27  shows a calibration curve for quantifying the concentration in plasma of B7-H3-ADC (I) in a monkey. 
         FIG. 28  shows a nucleotide sequence (SEQ ID NO: 29) encoding the amino acid sequences of a human light chain signal sequence and a human κ chain constant region. 
         FIG. 29  shows a nucleotide sequence (SEQ ID NO: 30) encoding the amino acid sequence of a heavy chain of rabbit chimeric antibody 1A3. 
         FIG. 30  shows a nucleotide sequence (SEQ ID NO: 31) encoding the amino acid sequence of a light chain of rabbit chimeric antibody 1A3. 
         FIG. 31  shows an amino acid sequence (SEQ ID NO: 32) of a heavy chain of an anti-GPR20 antibody. 
         FIG. 32  shows an amino acid sequence (SEQ ID NO: 33) of a light chain of an anti-GPR20 antibody. 
         FIG. 33  shows an amino acid sequence (SEQ ID NO: 34) of a heavy chain of an anti-CDH6 antibody. 
         FIG. 34  shows an amino acid sequence (SEQ ID NO: 35) of a light chain of an anti-CDH6 antibody. 
         FIG. 35  shows immunologically stained images using rabbit chimeric antibody 1A3. Immunologically stained images of nude mice, to which human head and neck cancer cell line FaDu was subcutaneously transplanted and administered separately with TROP2-ADC (I) and Anti-TROP2 Ab, are compared. 
         FIG. 36  shows immunologically stained images using rabbit chimeric antibody 1A3. Images of nude mice, to which GPR20 overexpressing human gastrointestinal stromal tumor cell line GIST-T1/GPR20 was subcutaneously transplanted and administered with GPR20-ADC (I) and not administered with GPR20-ADC (I), are compared. 
         FIG. 37  shows immunologically stained images using rabbit chimeric antibody 1A3. Images of nude mice, to which a tumor tissue taken from a patient with clear cell renal cell carcinoma was subcutaneously transplanted and administered with CDH6-ADC (I) and not administered with CDH6-ADC (I), are compared. 
         FIG. 38  shows immunologically stained images using rabbit chimeric antibody 1A3. Images of nude mice, to which a tumor tissue taken from a patient with clear cell renal cell carcinoma was subcutaneously transplanted, administered with CDH6-ADC (I) and stained with a mixture of mouse antibody 1A3 and a compound (2) or a mixture of mouse antibody 1A3 and SN-38 previously prepared or not prepared, are compared. 
         FIG. 39  shows a calibration curve for quantifying the concentration in plasma of GPR20-ADC (I) in a mouse. 
         FIG. 40  shows a calibration curve for quantifying concentration in plasma of HER2-ADC (I) in a human. 
         FIG. 41  shows the inhibition rates of compounds competitively inhibiting recognition of mouse antibody 1A3 to HER2-ADC (I). 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, preferred modes for carrying out the present invention are described. The embodiments described below are given merely for illustrating one example of a typical embodiment of the present invention and are not intended to limit the scope of the present invention. 
     1. Definition 
     In the present invention, “protein” is synonymous with “peptide” or “polypeptide”. 
     In the present invention, “protein” is preferably an antibody or an antigen binding fragment of an antibody. As long as it has a function to recognize an antigen similarly to an antibody, the “protein” may be any protein other than an antibody and an antigen binding fragment of an antibody (antibody alternative). Examples of the antibody alternative include scaffold proteins such as Fibronectin, Protein A, Lipocalin, TrxA, A-domain, Ankyrin repeat, APPI and Ras-binding AF-6 (Kasper Binz H. et al., Current Opinion in Biotechnology 2005, 16: 459-469, Kasper Binz H. et al., Nature Biotechnology 23 (10) 2005, 1257-1268, Skerra A., Current Opinion in Biotechnology 2007, 18: 295-304, Nygren P., FEBS Journal 275 (2008) 2668-2676, Gronwall C. et al., Journal of Biotechnology 140 (2009) 254-269). 
     In the present invention, “antibody” refers to a glycoprotein having a function to recognize a specific antigen. Examples of the antibody include a polyclonal antibody, a monoclonal antibody, a chimeric antibody, a rabbit type antibody, a humanized antibody and a human antibody. 
     In the present invention, “antigen” is sometimes used in the meaning of “immunogen”. 
     In the present invention, “antigen binding fragment of an antibody” refers to a partial fragment of an antibody having a function to recognize an antigen and is synonymous with “functional fragment of an antibody”. Examples of the antigen binding fragment of an antibody include, but are not limited to, Fab, F(ab′)2, scFv, Fab′ and a single-strand immunoglobulin. The functional fragment of an antibody may be obtained by treating a full-length antibody molecule with an enzyme such as papain and pepsin. Besides this, the functional fragment of an antibody may be a recombinant protein produced in an appropriate host cell using a recombinant gene. 
     The phrase that the protein of the present invention “recognizes” an antigen means that the protein of the present invention binds to an antigen through intermolecular force (such as electrostatic interaction, van der Waals force and hydrogen bond). “Recognition” of an antigen by the protein of the present invention can be checked, for example, by detecting signals generated by various immunochemical methods. 
     The phrase that the “recognition property” of the protein of the present invention to an antigen are different means that binding strength and behavior of the protein of the present invention to antigens substantially differ. Whether the “recognition property” of the protein of the present invention to an antigen are different or not can be checked, for example, by comparing the intensities of signals produced by various immunochemical methods and/or comparing calibration curves representing the concentration of an antigen and the intensity of a signal. 
     The “moiety” recognized by the protein of the present invention refers to a specific partial structure in a target recognized by the protein of the present invention. The target recognized by the protein of the present invention is referred to as an “antigen” and the specific moiety recognized by the protein of the present invention is sometimes referred to as “epitope”. 
     It is known that each heavy chain and light chain of an antibody has three complementarity determining regions (CDR). The complementarity determining region is also referred to as a hypervariable region (hypervariable domain), which is a site present within the variable region of each heavy chain and light chain of an antibody and having a particularly high primary-structure mutation rate. The CDR is usually present in three discrete sites on the primary structure of each of the polypeptide chains of a heavy chain and a light chain. In the present invention, complementarity determining regions of an antibody are expressed as follows: the complementarity determining regions in a heavy chain are expressed as CDRH1, CDRH2 and CDRH3 sequentially from the amino terminus of the heavy chain amino acid sequence; whereas, the complementarity determining regions in a light chain are expressed as CDRL1, CDRL2 and CDRL3 sequentially from the amino terminus of the light chain amino acid sequence. In the tertiary structure, these regions are present close to each other and involved in determination of specificity to an antigen. 
     In the present invention, “gene” refers to a nucleotide comprising a nucleotide sequence encoding amino acids of a protein or a complementary strand thereof, for example, a polynucleotide, an oligonucleotide, DNA, mRNA, cDNA and cRNA, which are nucleotides comprising a nucleotide sequence encoding amino acids of a protein or a complementary strand thereof, are included in the meaning of “gene”. The gene as mentioned above consists of nucleotides of a single strand, double strand or triple strand or larger. A pair of a DNA strand and an RNA strand, ribonucleotide (RNA) and deoxyribonucleotide (DNA) co-present on a single nucleotide chain, and a double strand or triple strand or larger comprising such a nucleotide chain are included in the meaning of “gene”. 
     In the present invention, “nucleotide” is synonymous with “nucleic acid”; for example, DNA, RNA, a probe, an oligonucleotide, a polynucleotide and a primer are included in the meaning of “nucleotide”. Such a nucleotide is a nucleotide consisting of a single strand, double strand or triplet strand or larger. A pair of a DNA strand and an RNA strand, ribonucleotide (RNA) and deoxyribonucleotide (DNA) co-present on a single nucleotide chain and a pair of a double strand or triple strand or larger comprising such a nucleotide chain are included in the meaning of “nucleotide”. 
     In the present invention, “cells” include various cells derived from animals, subcultured cells, primary cultured cells, cell strains, recombinant cells and microorganisms. 
     2. Antibody-Drug Conjugate 
     In the present invention, “antibody-drug conjugate” refers to a conjugate obtained by conjugating an antibody and a drug via a linker. 
     In the present invention, “drug-linker” refers to a partial structure of an antibody-drug conjugate and consisting of a linker and a drug. 
     The protein of the present invention is characterized by recognizing a drug moiety of an antibody-drug conjugate (hereinafter referred to as “the antibody-drug conjugate according to the present invention”) in which a drug (hereinafter referred to as “compound (1)”) represented by the following formula: 
     
       
         
         
             
             
         
       
     
     and an antibody are conjugated via a linker. 
     Compound (1) is an antitumor drug called exatecan (which can be also expressed by IUPAC name: (1S,9S)-1-amino-9-ethyl-5-fluoro-1,2,3,9,12,15-hexahydro-9-hydroxy-4-methyl-10H,13H-benzo[de]pyrano[3′,4′:6,7]indolizino[1,2-b]quinoline-10,13-dione, or chemical name: (1S,9S)-1-amino-9-ethyl-5-fluoro-2,3-dihydro-9-hydroxy-4-methyl-1H,12H-benzo[de]pyrano[3′,4′:6,7]indolizino[1,2-b]quinoline-10,13 (9H,15H)-dione) and known to have topoisomerase I inhibitory activity. 
     Note that, the protein of the present invention can also recognize compound (1), itself. 
     Examples of the antibody in the antibody-drug conjugate according to the present invention include, but are not particularly limited to, an anti-HER2 antibody, an anti-HER3 antibody, an anti-TROP2 antibody, an anti-B7-H3 antibody, an anti-CD3 antibody, an anti-CD30 antibody, an anti-CD33 antibody, an anti-CD37 antibody, an anti-CD56 antibody, an anti-CD98 antibody, an anti-DR5 antibody, an anti-EGFR antibody, an anti-EPHA2 antibody, an anti-FGFR2 antibody, an anti-FGFR4 antibody, an anti-FOLR1 antibody, an anti-VEGF antibody, an anti-CD20 antibody, an anti-CD22 antibody, an anti-CD70 antibody, an anti-PSMA antibody, an anti-CEA antibody, an anti-Mesothelin antibody, an anti-A33 antibody, an anti-CanAg antibody, an anti-Cripto antibody, an anti-G250 antibody, an anti-MUC1 antibody, an anti-GPNMB antibody, an anti-Integrin antibody, an anti-Tenascin-C antibody, an anti-SLC44A4 antibody, an anti-GPR20 antibody and an anti-CDH6 antibody. Further, an anti-HER2 antibody, an anti-HER3 antibody, an anti-TROP2 antibody, an anti-B7-H3 antibody, an anti-GPR20 antibody, and anti-CDH6 antibody can be preferably exemplified. 
     In the present invention, “anti-HER2 antibody” refers to an antibody which binds specifically to HER2 (Human Epidermal Growth Factor Receptor Type 2; ErbB-2), and preferably has an activity of internalization in HER2 expressing cells by binding to HER2. 
     Examples of the anti-HER2 antibody include trastuzumab (U.S. Pat. No. 5,821,337) and pertuzumab (International Publication No. WO 01/00245). Preferably, trastuzumab can be exemplified. 
     In the present invention, “anti-HER3 antibody” refers to an antibody which binds specifically to HER3 (Human Epidermal Growth Factor Receptor Type 3; ErbB-3), and preferably has an activity of internalization in HER3 expressing cells by binding to HER3. 
     Examples of the anti-HER3 antibody include patritumab (U3-1287), U1-59 (International Publication No. WO 2007/077028), MM-121 (seribantumab), anti-ERBB3 antibody described in International publication No. WO 2008/100624, RG-7116 (lumretuzumab) and LJM-716 (elgemtumab). Preferably, patrizumab and U1-59 can be exemplified. 
     In the present invention, “anti-TROP2 antibody” refers to an antibody which binds specifically to TROP2 (TACSTD2: Tumor-associated calcium signal transducer 2; EGP-1), and preferably has an activity of internalization in TROP2 expressing cells by binding to TROP2. 
     Examples of the anti-TROP2 antibody include hTINA1-Hill (International Publication No. WO 2015/098099). 
     In the present invention, “anti-B7-H3 antibody” refers to an antibody which binds specifically to B7-H3 (B cell antigen #7 homolog 3; PD-L3; CD276), and preferably has an activity of internalization in B7-H3 expressing cells by binding to B7-H3. 
     Examples of the anti-B7-H3 antibody include M30-H1-L4 (International Publication No. WO 2014/057687). 
     In the present invention, “anti-GPR20 antibody” refers to an antibody which binds specifically to GPR20 (G Protein-coupled receptor 20), and preferably has an activity of internalization in GPR20 expressing cells by binding to GPR20. 
     Examples of the anti-GPR20 antibody include h046-H4e/L7 (International Publication No. WO 2018/135501). 
     In the present invention, “anti-CDH6 antibody” refers to an antibody which binds specifically to CDH6 (Cadherin-6), and preferably has an activity to internalize in CDH6 expressing cells by binding to CDH6. 
     Examples of the anti-CDH6 antibody include H01L02 (International Publication No. WO 2018/212136). 
     The protein of the present invention is characterized by specifically recognizing a drug moiety of, preferably, an antibody-drug conjugate (hereinafter referred to as “antibody-drug conjugate (I)”) having a drug-linker represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein A represents a connecting position to an antibody, and the drug-linker is conjugated to the antibody via a thioether bond; 
     an antibody-drug conjugate (hereinafter referred to as “antibody-drug conjugate (II)”) having a drug-linker represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein A represents a connecting position to an antibody, and the drug-linker is conjugated to the antibody via a thioether bond; or 
     an antibody-drug conjugate (hereinafter referred to as “antibody-drug conjugate (III)”) having a drug-linker represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein A represents a connecting position to an antibody, the drug-linker is conjugated to the antibody via a thioether bond. 
     Each of the drug-linkers of the antibody-drug conjugates (I) to (III) connects to a thiol group (in other words, a sulfur atom of a cysteine residue) formed at an interchain disulfide bond site (two sites between heavy chains, and two sites between a heavy chain and a light chain). 
     The protein of the present invention is more preferably characterized by specifically recognizing the drug moiety of antibody-drug conjugate (I). 
     Antibody-drug conjugate (I) can also be represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein the drug-linker is conjugated to the antibody via a thioether bond. The meaning of n is the same as that of what is called the average number of conjugated drug molecules (DAR; Drug-to-Antibody Ratio), and indicates the average number of units of the drug-linker conjugated per antibody molecule. 
     Note that, the average number of conjugated drug molecules per antibody molecule of the antibody-drug conjugate according to the present invention can be determined, for example, by a method of calculation based on measurement of UV absorbance for the antibody-drug conjugate and the conjugation precursor thereof at two wavelengths of 280 nm and 370 nm (UV method), or a method of calculation based on quantification through HPLC measurement for fragments obtained by treating the antibody-drug conjugate with a reducing agent (HPLC method). 
     After migrating into cancer cells, antibody-drug conjugate (I) is cleaved at the linker portion to release the compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     (hereinafter referred to as “compound (2)”). 
     The compound (2) is inferred to be formed by decomposition of an aminal structure of a compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     (hereinafter referred to as “compound (3)”) which is inferred to be formed by cleavage of the linker part of the antibody-drug conjugate used in the present invention. 
     Compound (2) is inferred to be the original source of the antitumor activity of antibody-drug conjugate (I) and has been confirmed to have a topoisomerase I inhibitory effect (Ogitani Y. et al., Clinical Cancer Research, 2016, Oct. 15;22 (20): 5097-5108, Epub 2016 Mar. 29). 
     Note that, the protein of the present invention can also recognize compound (2) itself released from antibody-drug conjugate (I). 
     Antibody-drug conjugate (II) can also be represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein the drug-linker is conjugated to an antibody via a thioether bond. The meaning of n is the same as that of what is called DAR and indicates the average number of units of the drug-linker conjugated per antibody molecule. 
     After migrating into cancer cells, antibody-drug conjugate (II) is cleaved at the linker portion to release a compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     (hereinafter referred to as “compound (4)”) 
     Note that, the protein of the present invention can also recognize compound (4) itself released from the antibody-drug conjugate (II). 
     The antibody-drug conjugate (III) can also be represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein the drug-linker is conjugated to an antibody via a thioether bond. The meaning of n is the same as that of what is called DAR and indicates the average number of units of the drug-linker conjugated per antibody molecule. 
     After migrating into cancer cells, antibody-drug conjugate (III) is cleaved at the linker portion to release the compound (hereinafter referred to as “compound (5)”) represented by the following formula: 
     
       
         
         
             
             
         
       
     
     Note that, the protein of the present invention can also recognize compound (5) itself released from the antibody-drug conjugate (III). 
     In the present invention, “anti-HER2 antibody-drug conjugate” refers to an antibody-drug conjugate such that the antibody in the antibody-drug conjugate according to the present invention is an anti-HER2 antibody. 
     The anti-HER2 antibody is preferably an antibody comprising a heavy chain consisting of the amino acid sequence consisting of amino acid residues 1 to 449 of SEQ ID NO: 21 and a light chain consisting of the amino acid sequence consisting of amino acid residues 1 to 214 of SEQ ID NO: 22, or an antibody comprising a heavy chain consisting of the amino acid sequence represented by SEQ ID NO: 21 and a light chain consisting of the amino acid sequence represented by SEQ ID NO: 22. 
     The average number of units of the drug-linker conjugated per antibody molecule in the anti-HER2 antibody-drug conjugate is preferably 2 to 8, more preferably 3 to 8, even more preferably 7 to 8, even more preferably 7.5 to 8, and even more preferably about 8. 
     The anti-HER2 antibody-drug conjugate can be produced with reference to descriptions in Publications such as International Publication No. WO 2015/115091. 
     In the present invention, “anti-HER3 antibody-drug conjugate” refers to an antibody-drug conjugate such that the antibody in the antibody-drug conjugate according to the present invention is an anti-HER3 antibody. 
     The anti-HER3 antibody is preferably an antibody comprising a heavy chain consisting of CDRH1 consisting of amino acid sequence of amino acid residues 26 to 35 of SEQ ID NO: 23, CDRH2 consisting of amino acid sequence of amino acid residues 50 to 65 of SEQ ID NO: 23 and CDRH3 consisting of amino acid sequence of amino acid residues 98 to 106 of SEQ ID NO: 23, and a light chain consisting of CDRL1 consisting of amino acid sequence of amino acid residues 24 to 39 of SEQ ID NO: 24, CDRL2 consisting of amino acid sequence of amino acid residues 56 to 62 of SEQ ID NO: 24 and CDRL3 consisting of amino acid sequence of amino acid residues 95 to 103 of SEQ ID NO: 24; more preferably an antibody comprising a heavy chain comprising a heavy chain variable region consisting of amino acid sequence of amino acid residues 1 to 117 of SEQ ID NO: 23 and a light chain comprising a light chain variable region consisting of amino acid residues 1 to 113 of SEQ ID NO: 24; and even more preferably, an antibody comprising a heavy chain consisting of amino acid sequence represented by SEQ ID NO: 23 and a light chain consisting of amino acid sequence represented by SEQ ID NO: 24 or a variant of the antibody in which a lysine residue at the carboxyl terminus of the heavy chain is deleted. 
     The average number of units of the drug-linker conjugated per antibody molecule in the anti-HER3 antibody-drug conjugate is preferably 2 to 8, more preferably 3 to 8, even more preferably 7 to 8, even more preferably 7.5 to 8 and even more preferably about 8. 
     The anti-HER3 antibody-drug conjugate can be produced with reference to descriptions in publications such as International Publication No. WO 2015/155998. 
     In the present invention, “anti-TROP2 antibody-drug conjugate” refers to an antibody-drug conjugate such that the antibody in the antibody-drug conjugate according to the present invention is an anti-TROP2 antibody. 
     The anti-TROP2 antibody is preferably an antibody comprising a heavy chain consisting of CDRH1 consisting of amino acid sequence of amino acid residues 50 to 54 of SEQ ID NO: 25, CDRH2 consisting of amino acid sequence of amino acid residues 69 to 85 of SEQ ID NO: 25, and CDRH3 consisting of amino acid sequence of amino acid residues 118 to 129 of SEQ ID NO: 25, and a light chain comprising CDRL1 consisting of amino acid sequence of amino acid residues 44 to 54 of SEQ ID NO: 26, CDRL2 consisting of amino acid sequence of amino acid residues 70 to 76 of SEQ ID NO: 26, and CDRL3 consisting of amino acid sequence of amino acid residues 109 to 117 of SEQ ID NO: 26; 
     more preferably an antibody comprising a heavy chain comprising a heavy chain variable region consisting of amino acid sequence of amino acid residues 20 to 140 of SEQ ID NO: 25 and a light chain comprising a light chain variable region consisting of amino acid residues 21 to 129 of SEQ ID NO: 26; and 
     even more preferably, an antibody comprising a heavy chain consisting of amino acid sequence of amino acid residues 20 to 470 of SEQ ID NO: 25 and a light chain consisting of amino acid sequence of amino acid residues 21 to 234 of SEQ ID NO: 26 or a variant of the antibody in which a lysine residue at the carboxyl terminus of the heavy chain is deleted. 
     The average number of units of the drug-linker conjugated per antibody molecule in the anti-TROP2 antibody-drug conjugate is preferably 2 to 8, more preferably 3 to 5, even more preferably 3.5 to 4.5, and even more preferably about 4. 
     The anti-TROP2 antibody-drug conjugate can be produced with reference to descriptions in publications such as International Publication No. WO 2015/098099. 
     In the present invention, “anti-B7-H3 antibody-drug conjugate” refers to an antibody-drug conjugate such that the antibody in the antibody-drug conjugate according to the present invention is an anti-B7-H3 antibody. 
     The anti-B7-H3 antibody is preferably an antibody comprising a heavy chain comprising CDRH1 consisting of amino acid sequence of amino acid residues 50 to 54 of SEQ ID NO: 27, CDRH2 consisting of amino acid sequence of amino acid residues 69 to 85 of SEQ ID NO: 27 and CDRH3 consisting of amino acid sequence of amino acid residues 118 to 130 of SEQ ID NO: 27, and a light chain consisting of CDRL1 consisting of amino acid sequence of amino acid residues 44 to 53 of SEQ ID NO:28, CDRL2 consisting of amino acid sequence of amino acid residues 69 to 75 of SEQ ID NO: 28 and CDRL3 consisting of amino acid sequence of amino acid residues 108 to 116 of SEQ ID NO: 28; 
     more preferably, an antibody comprising a heavy chain containing a heavy chain variable region consisting of amino acid sequence of amino acid residues 20 to 141 of SEQ ID NO: 27 and a light chain comprising a light chain variable region consisting of amino acid residues 21 to 128 of SEQ ID NO: 28; and 
     even more preferably, an antibody comprising a heavy chain consisting of amino acid sequence of amino acid residues 20 to 471 of SEQ ID NO: 27 and a light chain consisting of amino acid sequence of amino acid residues 21 to 233 of SEQ ID NO: 28 or a variant of the antibody in which a lysine residue at the carboxyl terminus of the heavy chain is deleted. 
     The average number of units of the drug-linker conjugated per antibody molecule in the anti-B7-H3 antibody-drug conjugate is preferably 2 to 8, more preferably 3 to 5, even more preferably 3.5 to 4.5, and even more preferably about 4. 
     The anti-B7-H3 antibody-drug conjugate can be produced with reference to descriptions in publications such as International Publication No. WO 2014/057687. 
     In the present invention, “anti-GPR20 antibody-drug conjugate” refers to an antibody-drug conjugate such that the antibody in the antibody-drug conjugate according to the present invention is an anti-GPR20 antibody. 
     The anti-GPR20 antibody is preferably an antibody comprising a heavy chain consisting of CDRH1 consisting of amino acid sequence of amino acid residues 45 to 54 of SEQ ID NO: 32, CDRH2 consisting of amino acid sequence of amino acid residues 69 to 78 of SEQ ID NO: 32 and CDRH3 consisting of amino acid sequence of amino acid residues 118 to 131 of SEQ ID NO:32, and a light chain consisting of CDRL1 consisting of amino acid sequence of amino acid residues 44 to 54 of SEQ ID NO:33, CDRL2 consisting of amino acid sequence of amino acid residues 70 to 76 of SEQ ID NO: 33 and CDRL3 consisting of amino acid sequence of amino acid residues 109 to 117 of SEQ ID NO: 33; 
     more preferably, an antibody comprising a heavy chain containing a heavy chain variable region consisting of amino acid sequence of amino acid residues 20 to 142 of SEQ ID NO: 32 and a light chain containing a light chain variable region consisting of amino acid residues 21 to 129 of SEQ ID NO: 33; and 
     even more preferably, an antibody comprising a heavy chain consisting of amino acid sequence of amino acid residues 20 to 472 of SEQ ID NO: 32 and a light chain consisting of amino acid sequence of amino acid residues 21 to 234 of SEQ ID NO: 33 or a variant of the antibody in which a lysine residue at the carboxyl terminus of the heavy chain is deleted. 
     The average number of units of the drug-linker conjugated per antibody molecule in the anti-GPR20 antibody-drug conjugate is preferably 2 to 8, more preferably 3 to 8, even more preferably 7 to 8, even more preferably 7.5 to 8, and even more preferably about 8. 
     The anti-GPR20 antibody-drug conjugate can be produced with reference to descriptions in publications such as International Publication No. WO 2018/135501. 
     In the present invention, “anti-CDH6 antibody-drug conjugate” refers to an antibody-drug conjugate such that the antibody in the antibody-drug conjugate according to the present invention is an anti-CDH6 antibody. 
     The anti-CDH6 antibody is preferably an antibody comprising a heavy chain consisting of CDRH1 consisting of amino acid sequence of amino acid residues 45 to 54 of SEQ ID NO: 34, CDRH2 consisting of amino acid sequence of amino acid residues 69 to 78 of SEQ ID NO: 34 and CDRH3 consisting of amino acid sequence of amino acid residues 118 to 130 of SEQ ID NO: 34, and a light chain consisting of CDRL1 consisting of amino acid sequence of amino acid residues 44 to 54 of SEQ ID NO:35, CDRL2 consisting of amino acid sequence of amino acid residues 70 to 76 of SEQ ID NO: 35 and CDRL3 consisting of amino acid sequence of amino acid residues 109 to 116 of SEQ ID NO: 35; 
     more preferably an antibody comprising a heavy chain comprising a heavy chain variable region consisting of amino acid sequence of amino acid residues 20 to 141 of SEQ ID NO: 34 and a light chain comprising a light chain variable region consisting of amino acid residues 21 to 128 of SEQ ID NO: 35; and 
     even more preferably, an antibody comprising a heavy chain consisting of amino acid sequence of amino acid residues 20 to 471 of SEQ ID NO: 34 and a light chain consisting of amino acid sequence of amino acid residues 21 to 233 of SEQ ID NO: 35 or a variant of the antibody in which a lysine residue at the carboxyl terminus of the heavy chain is deleted. 
     The average number of units of the drug-linker conjugated per antibody molecule in the anti-CDH6 antibody-drug conjugate is preferably 2 to 8, more preferably 3 to 8, even more preferably 7 to 8, further more preferably 7.5 to 8, and even more preferably about 8. 
     The anti-CDH6 antibody-drug conjugate can be produced with reference to descriptions in publications such as International Publication No. WO 2018/212136. 
     3. Production of the Protein of the Present Invention 
     The protein of the present invention can be preferably obtained as an antibody (hereinafter referred to as “the antibody of the present invention”). The antibody of the present invention can be obtained by immunizing animals with an antigenic protein obtained by conjugating compound (1) or a derivative thereof and a carrier protein via a linker, and collecting the antibodies produced in vivo and then, purifying it. 
     As the antigen protein, a protein prepared by adding a carrier protein to the compound represented, for example, by the following formula: 
     
       
         
         
             
             
         
       
     
     (hereinafter referred to as “compound” (6)) can be used. 
     The carrier protein is not particularly limited as long as it can induce immune response even if it is a small antigen such as a lower molecule compound or a peptide. For example, bovine thyroglobulin and bovine serum albumin (BSA) and Keyhole limpet hemocyanin (KLH) can be used. 
     From the antiserums obtained, an antiserum having desired properties can be selected by ELISA method using a positive control and a negative control. 
     As the positive control, for example, compound (1), compound (2) and compound (6) can be exemplified. Antiserum having a high inhibition effect can be selected using these as positive controls. 
     Note that, it is known that equilibrium of the lactone ring of compound (1) shifts toward a closed ring in an acidic aqueous solvent (for example, about pH3); whereas the ring shifts towards an open ring in a basic aqueous solvent (for example, about pH10). In order to select an antibody recognizing the basic skeleton of the compound (1) itself no matter whether a lactone ring is opened or closed, a compound having a reduced lactone ring, for example, a compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     (hereinafter referred to as “compound (7)”) can be also used as a positive control. The antiserum having a high inhibition effect can be selected as the positive control. Note that, in order to select an antibody recognizing compound (1) and compound (7) at the same level, it is preferable to exclude an antibody moiety particularly highly recognizing compound (7) rather than compound (1). 
     The antibody-drug conjugate according to the present invention (preferably, antibody-drug conjugates (I), (II) and (III)) can be used as a positive control. Antiserum having a high inhibition effect can be selected using these as positive controls. 
     In order to exclude an antibody recognizing a part distantly positioned from the basic skeleton of compound (1), for example, a compound consisting of a cyclohexane ring, a partial structure near a linker and represented by the following formula: 
     
       
         
         
             
             
         
       
     
     (hereinafter referred to as “compound (8)”) can be used as a negative control. Antiserum exhibiting a high inhibition effect can be excluded using this as a negative control. 
     The cells producing the antibody of the present invention can be obtained by cloning the antiserum selected as mentioned above. 
     In accordance with a method known in the art (for example, Kohler and Milstein, Nature (1975) 256, p. 495-497, Kennet, R. ed., Monoclonal Antibodies, p. 365-367, Plenum Press, N.Y. (1980)), cells producing the antibody of the present invention are fused with myeloma cells to establish hybridoma cells, from which monoclonal antibodies can be obtained. Examples of such a method are more specifically described in International Publication No. WO 09/48072 published Apr. 16, 2009) and WO10/117011 (published Oct. 14, 2010). 
     The antibody obtained can be uniformly purified. For separation and purification of the antibody, customary separation and purification methods used for protein may be used. The antibody can be separated and purified appropriately selecting and combining, for example, column chromatography, filtration by filter, ultrafiltration, salting out, dialysis, polyacrylamide gel electrophoresis for preparation and isoelectric point electrophoresis (Strategies for Protein Purification and Characterization: A Laboratory Course Manual, Daniel R. Marshak et al. eds., Cold Spring Harbor Laboratory Press (1996), Antibodies: A Laboratory Manual. Ed Harlow and David Lane, Cold Spring Harbor Laboratory (1988); however, the separation and purification methods are not limited to these. 
     Examples of the chromatography include affinity chromatography, ion exchange chromatography, hydrophobic chromatography, gel filtration chromatography, reversed-phase chromatography and adsorption chromatography. These chromatographic methods can be carried out using liquid chromatography such as HPLC and FPLC. Examples of the column to be used in affinity chromatography include protein A column and protein G column. Examples of the column using protein A column include Hyper D, POROS and Sepharose F. F. (Pharmacia). Also, an antibody can be purified using a carrier having an antigen immobilized thereon and taking advantage of binding ability to the antigen. 
     The antibody of the present invention is further characterized in that its recognition property to the antibody-drug conjugate according to the present invention is substantially independent of any difference in the average number of units of the drug-linker conjugated per antibody molecule (DAR) in the antibody-drug conjugate. The fact that the antibody has such a characteristic can be confirmed, for example, based on the fact that a calibration curve to the antibody-drug conjugate having a high DAR (DAR8) does not substantially differ from a calibration curve to the antibody-drug conjugate having a low DAR (DAR4). 
     As the antibody of the present invention obtained as described above, for example, mouse antibody 1A3, can be exemplified. The amino acid sequence of a heavy chain variable region of mouse antibody 1A3 is the amino acid sequence consisting of amino acid residues 20 to 141 of SEQ ID NO: 15, and the nucleotide sequence encoding the amino acid sequence is the nucleotide sequence consisting of nucleotide residues 58 to 423 of SEQ ID NO: 17. The amino acid sequence of a light chain variable region of mouse antibody 1A3 is the amino acid sequence consisting of amino acid residues 21 to 127 of SEQ ID NO: 16; and the nucleotide sequence encoding the amino acid sequence is the nucleotide sequence consisting of nucleotide residues 61 to 381 of SEQ ID NO: 18. 
     The antibody of the present invention is satisfactory if it is an antibody having all 6 CDR sequences derived from mouse antibody 1A3, and specifically recognizes the drug moiety of the antibody-drug conjugate according to the present invention. Several methods are known for use in determining a CDR sequence. For example, the Abm definition, Chothia definition, Kabat definition and Imgt (registered trademark) (The International ImMunoGeneTics information system (registered trademark)) are exemplified. The CDR sequences of the antibody of the present invention may be defined by any one of the methods. 
     According to the Abm definition, the heavy chain variable region of the antibody of the present invention has CDRH1 (GFTFSDYGMV) consisting of the amino acid sequence represented by SEQ ID NO: 1, CDRH2 (YISSGSSAIY) consisting of the amino acid sequence represented by SEQ ID NO: 2, and CDRH3 (PPRYDVYSAWFAY) consisting of the amino acid sequence represented by SEQ ID NO: 3; and the light chain variable region of the antibody of the present invention has CDRL1 (KASQDVGSAVV) consisting of the amino acid sequence represented by SEQ ID NO: 4, CDRL2 (WASTRHT) consisting of the amino acid sequence represented by SEQ ID NO: 5, and CDRL3 (QQYSSYPVT) consisting of the amino acid sequence represented by SEQ ID NO: 6. 
     According to the Chothia definition, the heavy chain variable region of the antibody of the present invention has CDRH1 (GFTFSDY) consisting of the amino acid sequence represented by SEQ ID NO: 7, CDRH2 (SSGSSA) consisting of the amino acid sequence represented by SEQ ID NO: 8, and CDRH3 (PPRYDVYSAWFAY) consisting of the amino acid sequence represented by SEQ ID NO: 3; and the light chain variable region of the antibody of the present invention has CDRL1 (KASQDVGSAVV) consisting of the amino acid sequence represented by SEQ ID NO: 4, CDRL2 (WASTRHT) consisting of the amino acid sequence represented by SEQ ID NO: 5, and CDRL3 (QQYSSYPVT) consisting of the amino acid sequence represented by SEQ ID NO: 6. 
     According to the Kabat definition, the heavy chain variable region of the antibody of the present invention has CDRH1 (DYGMV) consisting of the amino acid sequence represented by SEQ ID NO: 9, CDRH2 (YISSGSSAIYYADTVKG) consisting of the amino acid sequence represented by SEQ ID NO: 10, and CDRH3 (PPRYDVYSAWFAY) consisting of the amino acid sequence represented by SEQ ID NO: 3; and the light chain variable region of the antibody of the present invention has CDRL1 (KASQDVGSAVV) consisting of the amino acid sequence represented by SEQ ID NO: 4, CDRL2 (WASTRHT) consisting of the amino acid sequence represented by SEQ ID NO: 5, and CDRL3 (QQYSSYPVT) consisting of the amino acid sequence represented by SEQ ID NO: 6. 
     According to Imgt (registered trademark) definition, the heavy chain variable region of the antibody of the present invention has CDRH1 (GFTFSDYG) consisting of the amino acid sequence represented by SEQ ID NO: 11, CDRH2 (ISSGSSAI) consisting of the amino acid sequence represented by SEQ ID NO: 12, and CDRH3 (ARPPRYDVYSAWFAY) consisting of the amino acid sequence represented by SEQ ID NO: 13; and the light chain variable region of the antibody of the present invention has CDRL1 (QDVGSA) consisting of the amino acid sequence represented by SEQ ID NO: 14, CDRL2 consisting of a tripeptide represented by WAS (tryptophan-alanine-serine), and CDRL3 (QQYSSYPVT) consisting of the amino acid sequence represented by SEQ ID NO: 6. 
     The antibody of the present invention includes not only monoclonal antibodies mentioned above but also a gene-recombinant antibody, which is obtained by adding artificial modification for decreasing heterologous antigenicity, such as a chimeric antibody, a humanized antibody, a rabbit type antibody or a mouse type antibody. These antibodies can be produced using a known method. 
     As the chimeric antibody, an antibody in which antibody variable and constant regions are derived from different species, for example, a chimeric antibody in which a mouse- or rat-derived antibody variable region is connected to a human-derived antibody constant region, can be exemplified (Proc. Natl. Acad. Sci. USA, 81, 6851-6855, (1984)). As another example, a chimeric antibody in which a mouse- or rat-derived antibody variable region is connected to a rabbit-derived antibody constant region, can be exemplified. 
     As a specific example of the rabbit chimeric antibody, an antibody (rabbit chimeric antibody 1A3) comprising a heavy chain comprising mouse antibody 1A3-derived heavy chain variable region and a rabbit antibody-derived heavy chain constant region, and a light chain comprising mouse antibody 1A3-derived light chain variable region and a rabbit antibody-derived light chain constant region, can be exemplified. The heavy chain of the rabbit chimeric antibody 1A3 consists of the amino acid sequence consisting of amino acid residues 20 to 464 of SEQ ID NO: 19; whereas, the light chain of the rabbit chimeric antibody 1A3 consists of the amino acid sequence consisting of amino acid residues 21 to 233 of SEQ ID NO: 20. 
     As a non-clinical animal model for cancer research, mice are frequently used. If a mouse antibody is used, in order to avoid competition with an endogenous mouse IgG, the method that can be used is limited. Then, a rabbit chimeric antibody is used because it is possible to compare a mouse-derived sample and a human derived sample in a same platform and useful for translational research. 
     As the humanized antibody, an antibody obtained by integrating the complementarity determining region (CDR) alone into a human-derived antibody (Nature (1986) 321, pp. 522-525), and an antibody obtained by grafting a part of the amino acid residues of a framework as well as the CDR sequence to a human antibody (WO 90/07861), can be exemplified. As the rabbit type antibody, an antibody obtained by integrating the complementarity determining region (CDR) alone into a rabbit-derived antibody and an antibody obtained by grafting a part of the amino acid residues of a framework as well as the CDR sequence to a rabbit antibody, can be exemplified. 
     It is known that, in an antibody produced by culturing mammalian cells, a lysine residue at the carboxyl terminus of the heavy chain is deleted (Journal of Chromatography A, 705: 129-134 (1995)). It is also known that two amino acid residues (glycine and lysine) are deleted from the heavy chain carboxyl terminus and a proline residue positioned at the carboxyl terminus is newly amidated (Analytical Biochemistry, 360: 75-83 (2007)). However, such deletion and modification of the heavy chain sequence do not affect the antigen-binding affinity and the effector function (the activation of complement, antibody-dependent cellular cytotoxicity, etc.) of the antibody. Therefore, in the present invention, antibodies subjected to such modification are included, and deletion variants in which one or two amino acids have been deleted at the carboxyl terminus of the heavy chain, variants obtained by amidation of deletion variants (for example, a heavy chain in which the carboxyl terminus proline residue has been amidated), and the like can be exemplified. The type of deletion variant having a deletion at the carboxyl terminus of the heavy chain of the antibody according to the present invention is not limited to the above types of variants as long as the antigen-binding affinity and the effector function are conserved. The two heavy chains constituting the antibody according to the present invention may be any one of heavy chains selected from the group consisting of a full-length heavy chain and the above-described deletion variants or a combination of any two of these. The ratio of the amount of each deletion variant may sometimes be affected by the type of cultured mammalian cells which produce the antibody according to the present invention and the culture conditions; however, the case where one amino acid residue at the carboxyl terminus has been deleted in both of the two heavy chains can be exemplified as a main component of the antibody according to the present invention. 
     The antibody of the present invention may be an antibody consisting of amino acid sequence having an identity of at least 95% (preferably, at least 99%) with the amino acid sequence of mouse antibody 1A3 or rabbit chimeric antibody 1A3 as long as the characteristics of the antibody of the present invention are maintained. 
     The identity between two types of amino acid sequences can be determined by use of default parameter of Blast (Nucl. Acids Res., 25, p. 3389-3402 (1997)). Blast can be used by accessing the internet www.ncbi.nlm.nih.gov/blast. 
     The antibody of the present invention may be an antibody competing with mouse antibody 1A3 or rabbit chimeric antibody 1A3 for the recognition property to a drug moiety of the antibody-drug conjugate according to the present invention. 
     The antibodies obtained by the method as mentioned above are evaluated on the recognition property to a drug moiety of the antibody-drug conjugate according to the present invention. In this manner, a suitable antibody can be selected. As another index for comparing characteristics of antibodies, stability of an antibody can be exemplified. Differential scanning calorimetry (DSC) is a method quickly and accurately measuring the transition midpoint temperature (Tm) serving as a good index for relative stability of a protein structure. Difference in thermal stability can be compared by measuring Tm values by DSC and comparing them. It is known that the storage stability of an antibody shows correlation with the thermal stability of the antibody to some extent (Lori Burton, et. al., Pharmaceutical Development and Technology (2007) 12, p. 265-273). A suitable antibody can be selected based on the thermal stability as an index. Another index for selecting an antibody, high yield in an appropriate host cell and low cohesiveness in an aqueous solution can be exemplified. Since the antibody most highly produced does not always have high thermal stability, it is necessary to select the most suitable antibody by comprehensive judgment based on the aforementioned indicators. 
     A method for obtaining a single chain immunoglobulin by connecting the full length sequences of a heavy chain and a light chain of an antibody by use of an appropriate linker is known (Lee, H-S, et al., Molecular Immunology (1999) 36, p. 61-71, Shirrmann, T. et al., mAbs (2010), 2, (1) p. 1-4). If such a single-strand immunoglobulin is dimerized, an analogous structure and activity to those of an antibody, which is basically a tetramer, can be obtained. The antibody of the present invention may be an antibody having a single heavy chain variable region and no light chain sequence. Such an antibody, which is called as a single domain antibody (sdAb) or a nanobody, is actually found in camels or llamas and reported to have an antigen binding ability (Muyldemans S. et al., Protein Eng. (1994) 7 (9), 1129-35, Hamers-Casterman C. et al., Nature (1993) 363 (6428) 446-8). The above antibody can be interpreted as an antigen binding fragment of the antibody of the present invention. 
     If an antibody is produced by once isolating an antibody gene and then, introducing it in an appropriate host, an appropriate combination of a host and an expression vector can be used. As an example of the antibody gene, an antibody gene having a gene encoding a heavy chain sequence of an antibody described in the specification and a gene encoding a light chain sequence in combination can be exemplified. If a host cell is transformed, the gene having a heavy chain sequence and the gene having a light chain sequence can be inserted in the same expression vector or in different expression vectors. If a eukaryotic cell is used as a host, animal cells, plant cells and eukaryotic microbes can be used. Examples of the animal cells include (1) mammalian cells, for example, monkey cells such as COS cells (Gluzman, Y. Cell (1981) 23, p. 175-182, ATCC CRL-1650), mouse fibroblasts NIH3T3 (ATCC No. CRL-1658) and Chinese hamster ovary cells (CHO cell, ATCC CCL-61) dihydrofolate reductase deficient strain (Urlaub, G. and Chasin, L. A. Proc. Natl. Acad. Sci. U.S.A. (1980) 77, p. 4126-4220). If a prokaryotic cell is used, for example,  E. coli  and  Bacillus subtilis  can be exemplified. An antibody is obtained by introducing a desired antibody gene into these cells through transformation and culturing a transformant in vitro. In the following culture method, the yield differs depending on the sequence of the antibody. An antibody easily produced as a medicine can be selected based on the yield as an index from antibodies having equivalent binding activity. 
     Isotypes of the antibody of the present invention are not limited, for example, IgG (IgG1, IgG2, IgG3, IgG4), IgM, IgA (IgA1, IgA2), IgD or IgE can be exemplified. Preferably, IgG or IgM, further preferably, IgG1 or IgG2 can be exemplified. 
     The antibody of the present invention may be an antigen binding fragment of the antibody having an antigen binding site of the antibody or a modified fragment thereof. The fragment of an antibody can be obtained by treating the antibody with a protease such as papain or pepsin or modifying an antibody gene by a genetic engineering method and expressing the modified gene in appropriate culture cells. Of these antibody fragments, a fragment having all or part of function of the full-length antibody molecule can be referred to as an antigen binding fragment of the antibody. 
     Examples of the antibody fragment include Fab, F(ab′)2, Fv, a single-chain Fv (scFv) obtained by linking Fv of a heavy chain and a light chain via an appropriate linker, a diabody (diabodies), a linear antibody and a polyspecific antibody formed of antibody fragments. Also, Fab′, which is a monovalent fragment of a variable region of an antibody obtained by treating F(ab′)2 under reducing conditions, is included in antibody fragments. 
     The antibody of the present invention may be a polyspecific antibody having specificity to at least two types of antigens. Usually, such a molecule binds to two types of antigens (that is, bispecific antibody). The polyspecific antibody of the present invention includes antibodies having a specificity to two types or more antigens (for example, 3 types). 
     The polyspecific antibody of the present invention may be a full-length antibody or a fragment of the antibody (for example, F(ab′)2 bispecific antibody). The bispecific antibody can be produced by connecting heavy chains and light chains (HL pairs) of two types of antibodies or fusing hybridomas cells producing different monoclonal antibodies to produce a bispecific antibody-producing fusion cell (Millstein et al., Nature (1983) 305, p. 537-539). 
     The antibody of the present invention may be a single-chain antibody (also referred to as scFv). The single-chain antibody is obtained by connecting a heavy chain variable region and a light chain variable region via a polypeptide linker (Pluckthun, The Pharmacology of Monoclonal Antibodies, 113 (edited by Rosenberg and Moore, Springer Verlag, New York, p. 269-315 (1994), Nature Biotechnology (2005), 23, p. 1126-1136). Alternatively, a BiscFv fragment produced by connecting two scFv via a polypeptide linker can be used as a bispecific antibody. 
     A method for producing a single-chain antibody is known in the technical field (see, for example, U.S. Pat. Nos. 4,946,778, 5,260,203, 5,091,513, 5,455,030). In the scFv, a heavy chain variable region and a light chain variable region are connected via a linker which will not form a conjugate, preferably, a polypeptide linker (Huston, J. S. et al., Proc. Natl. Acad. Sci. U.S.A. (1988), 85, p. 5879-5883). The heavy chain variable region and light chain variable region in an scFv may be derived from the same antibody or different antibodies. As the polypeptide linker connecting the variable regions, for example, a single-chain peptide consisting of 12 to 19 residues is used. 
     DNA encoding an scFv can be obtained as follows. Of DNA encoding a heavy chain or a heavy chain variable region of the antibody and DNA encoding a light chain or a light chain variable region, a DNA encoding a whole or a desired part of the amino acid sequence was selected. Using the DNA selected as a template, and a primer pair defining both ends thereof, PCR amplification is carried out. In addition, using DNA encoding a polypeptide linker portion in combination with a primer pair defining the both ends so as to be connected respectively to the heavy chain and light chain, amplification is carried out. 
     Once DNA encoding an scFv produced, an expression vector comprising DNA and a host transformed with the expression vector can be obtained in accordance with a customary method. Also, using the host, scFv can be obtained in accordance with a customary method. These antibody fragments can be produced in the same manner as above, that is, obtaining a gene and expressing the gene by use of a host. 
     The antibody of the present invention may be multimerized and enhanced in affinity to an antigen. The antibody to be multimerized may be a single type or a plurality of antibodies recognizing a plurality of epitopes of a same antigen. As a method for multimerizing an antibody, binding of an IgG CH3 domain and two scFvs, binding to streptavidin and introduction of a helix-turn-helix motif, etc., can be exemplified. 
     The antibody of the present invention may be polyclonal antibodies, which are a collection of a plurality of types of antibodies different in amino acid sequence. As polyclonal antibodies, for example, a collection of a plurality of types of antibodies different in CDR can be exemplified. As the polyclonal antibodies, a collection of cells producing different antibodies are cultured and antibodies purified from the culture can be used (see WO2004/061104). 
     For modifying an antibody, an antibody bound to various molecules such as polyethylene glycol (PEG) can be used. 
     The antibody of the present invention may be a conjugate (immunoconjugate) in which the antibody is conjugated to another drug. Examples of such an antibody include an antibody to be bound to a radioactive substance and a compound having a pharmacological action (Nature Biotechnology (2005) 23, p. 1137-1146). 
     4. Use of the Protein of the Present Invention 
     The protein of the present invention can be used in a detection method such as an ELISA (Enzyme-Linked ImmunoSorbent Assay) method, an ECL (Electrochemiluminescence) method, an RIA (Radio Immunoassay) method, an ELISPOT (Enzyme-Linked ImmunoSpot) method, a dot blot method, an octalony method, a CIE (Counterimmunoelectrophoresis) method, CLIA (Chemiluminescent immunoassay) and FCM (Flow Cytometry); and an immunohistochemistry (IHC) method, and preferably used in an ELISA method, an ECL method and an IHC method. 
     The ELISA and ECL methods may be used as a method for quantifying the concentration in plasma of an antibody-drug conjugate in a mammal (examples of the “mammal” in the present invention include, but are not limited to, a human, a mouse, a rat, a monkey and a rabbit) administered with the antibody-drug conjugate of the present invention. 
     More specifically, steps of: (1) contacting an antibody-drug conjugate contained in the plasma with a plate having the antigen of the antibody-drug conjugate immobilized thereon, to form a complex, (2) contacting the protein of the present invention labeled with a marker with the complex to form a further complex, and then, (3) detecting the marker, are included. 
     Also, the steps of:(1) contacting an antibody-drug conjugate contained in the plasma with a plate having the protein of the present invention immobilized thereon to form a complex, (2) contacting a second protein capable of recognizing an antibody moiety of the antibody-drug conjugate and labeled with a marker with the complex to form a further complex, and then, (3) detecting the marker can be included. 
     The ELISA and ECL methods can also be used as a method for quantifying the concentration in plasma of a drug (for example, compound (1), compound (2), compound (4) and compound (5)) released from the antibody-drug conjugate in a mammal administered with the antibody-drug conjugate of the present invention. 
     More specifically, the steps of: (1) contacting a drug released from an antibody-drug conjugate contained in the plasma with a plate having the protein of the present invention immobilized thereon, in the presence of a competitive drug labeled with a marker to form a complex and (2) detecting the marker are included. 
     The IHC method can be used as a method for determining the tissue distribution of the antibody-drug conjugate and/or a drug released from the antibody-drug conjugate, for example, in a mammal administered with the antibody-drug conjugate of the present invention. 
     More specifically, the steps of: (1) contacting the antibody-drug conjugate and/or a drug released from the antibody-drug conjugate in a tissue with the protein of the present invention to form a complex, (2) contacting a second protein capable of recognizing the protein of the present invention and labeled with a marker with the complex to form a further complex, and then, (3) detecting the marker are included. 
     Also, the steps of: (1) contacting the antibody-drug conjugate and/or a drug released from the antibody-drug conjugate in a tissue with the protein of the present invention labeled with a marker to form a complex, and then, (2) detecting the marker can be included. 
     In the present invention, the “marker” refers to a substance generating a detectable signal or a substance acting on another substance to generate a detectable signal. Examples of the marker include a fluorescent substance, an enzyme, an enzyme fragment, an enzyme substrate, an enzyme inhibitor, a coenzyme, a catalyst, a dye, a light-emitting material, a sensitizer and a radioactive substance. 
     In the present invention, the phrase “labeled with a marker” means that a marker is connected directly or with a partial structure (for example, a linker) interposed between them. Connection using interaction between a biotin and an avidin (or streptavidin) is included in labeling. 
     In order to label the protein of the present invention with a marker, for example, a reagent (having an active ester group) having a marker as a component is reacted with a lysine residue of the protein of the present invention to form an amide bond; however, the labeling method is not limited to this. 
     If the marker is a fluorescent substance, the marker can be detected by sensing fluorescence of the marker. 
     Examples of the fluorescent substance include DyLight (registered trademark) 350, DyLight (registered trademark) 405, DyLight (registered trademark) 488, DyLight (registered trademark) 550, DyLight (registered trademark) 594, DyLight (registered trademark) 633, DyLight (registered trademark) 650, DyLight (registered trademark) 680, DyLight (registered trademark) 747, DyLight (registered trademark) 755, DyLight (registered trademark) 800, Alexa Fluor (registered trademark) 350, Alexa Fluor (registered trademark) 405, Alexa Fluor (registered trademark) 488, Alexa Fluor (registered trademark) 532, Alexa Fluor (registered trademark) 546, Alexa Fluor (registered trademark) 555, Alexa Fluor (registered trademark) 568, Alexa Fluor (registered trademark) 594, Alexa Fluor (registered trademark) 647, Alexa Fluor (registered trademark) 680, Alexa Fluor (registered trademark) 750, BODIPY (registered trademark) FL, Coumarin, Cy (registered trademark) 3, Cy (registered trademark) 5, Cy (registered trademark), Fluorescein (FITC) Oregon Green (registered trademark), Pacific Blue, Pacific Green, Pacific Orange, Tetramethylrhodamine (TRITC) and Texas Red (registered trademark). 
     Also, nanocrystals such as Qdot (registered trademark) 525, Qdot (registered trademark) 565, Qdot (registered trademark) 605, Qdot (registered trademark) 655, Qdot (registered trademark) 705 and Qdot (registered trademark) 800 and fluorescent proteins such as Allophycocyanin (APC), R-Phycoerythrin (R-PE), Cyan Fluorescent Protein (CFP), Green Fluorescent Protein (GFP) and Red Fluorescent Protein (RFP) can be used as a fluorescent substance. 
     If the marker is an enzyme, the marker is detected by sensing light or color developed by a reaction between the enzyme and a substrate. 
     As the enzyme, for example, peroxidase (for example, horseradish peroxidase; HRP etc.,) can be exemplified. In this case, as a substrate of the enzyme, for example, TMB (3,3′,5,5′-tetramethylbenzidine), DAB (3,3′-diaminobenzidine tetrahydrochloride), OPD (o-phenylenediamine) and ABTS (3-ethylbenzothiazoline-6-sulfonic acid) can be exemplified. 
     As another enzyme, alkaline phosphatase can be exemplified. In this case, as a substrate for the enzyme, for example, BCIP (5-bromo-4-chloro-3-indolyl phosphate) and PNPP (ρ-nitrophenyl phosphate) can be exemplified. 
     As another enzyme, luciferase can be exemplified. In this case, as a substrate for the enzyme, for example, Luciferin and Coelenterazine can be exemplified. 
     As another enzyme, β-galactosidase can be exemplified. In this case, as a substrate for the enzyme, for example, o-nitrophenyl-β-D-galactopyranoside (ONPG) can be exemplified. 
     If the marker is a light-emitting material, the marker is detected by sensing luminescence from the marker based on an electrochemical reaction. 
     As the light-emitting material, for example, a ruthenium complex, preferably a ruthenium-pyridine complex, and more preferably, ruthenium (II) tris(bipyridyl) complex can be exemplified. 
     The electrochemical reaction can be carried out in the presence of, for example, tripropylamine (TPA). More specifically, a TPA cation radical and a trivalent ruthenium complex are produced by an electrode reaction. The TPA cation radical immediately loses a hydrogen ion into a TPA radical having a strong reduction action, which reacts with a trivalent ruthenium complex to emit light. 
     If the marker is a radioactive substance, the marker is detected by sensing radiation emitted from the marker. 
     Examples of the radioactive substance include tritium ( 3 H), carbon-14 ( 14C ), nitrogen-15 ( 15 N), sulfur-35 ( 35 S), yttrium-90 ( 90 Y), technetium-99 ( 99 Tc), indium-111 ( 111 In), iodine-125 ( 125 I) and iodine-131 ( 131 I) 
     The protein of the present invention may be used as a component of a composition (hereinafter referred to as “the composition of the present invention”) formed by adding a pH buffer, an osmotic pressure regulator, a salt, a stabilizer, a preservative, a developer, a sensitizer and an anticoagulant, etc. 
     The protein of the present invention (or the composition of the present invention) can be used as a component of a kit comprising materials and reagents for assay in combination (hereinafter referred to as “the kit of the present invention”). The reagents can be provided in a liquid or lyophilized state, in a same container or different containers depending on the degree of stability. The amounts and the ratio of the reagents provided in the kit of the present invention can be selected such that optimal results can be provided for the specific use. The kit of the present invention may contain, other than the protein of the present invention (or the composition of the present invention), for example, a reagent for attaching a marker, a substrate for an enzyme, a blocking reagent, a polymer reagent, an antigen activation solution, a calibrator, a dilution buffer, a washing buffer, an immobilization buffer, an immobilized antibody, a detection antibody and microtiter wells etc. In addition, instructions for using the kit of the present invention may be contained. Using the kit, the tissue distribution of the antibody-drug conjugate and/or a drug released from the antibody-drug conjugate can be confirmed and plasma-concentration, etc., can be quantified. 
     EXAMPLES 
     The present invention will be specifically described by way of the examples shown below. However, the present invention is not limited to these. These examples should not be interpreted as limiting the invention in any way. Note that, unless otherwise specified, individual operations regarding to gene manipulation in the following Examples were carried out in accordance with the methods described in “Molecular Cloning” (written by Sambrook, J., Fritsch, E. F. and Maniatis, T., published by Cold Spring Harbor Laboratory Press, in 1989) or in accordance with the instructions attached to commercially available reagents and kits if they were employed. In the specification, the reagents, solvents and starting materials not specified can be easily obtained from commercial sources. 
     [Example 1] Synthesis of compound 
     i) Synthesis of 8-[(2,5-dioxopyrrolidin-1-yl)oxy]-N-(4-{[(1S,9S)-9-ethyl-5-fluoro-9-hydroxy-4-methyl-10,13-dioxo-2,3,9,10,13,15-hexahydro-1H,12H-benzo[de]pyrano[3′,4′:6,7]indolizino[1,2-b]quinolin-1-yl]amino}-4-oxobutyl)-8-oxooctane Amide (Compound (6)) 
     
       
         
         
             
             
         
       
     
     To a N,N-dimethylformamide (0.5 mL) solution of 4-amino-N-[(1S,9S)-9-ethyl-5-fluoro-9-hydroxy-4-methyl-10,13-dioxo-2,3,9,10,13,15-hexahydro-1H,12H-benzo[de]pyrano[3′,4′:6,7]indolizino[1,2-b]quinolin-1-yl]butanamide (0.032 g, 0.050 mmoL) (compound obtained in Step 2 of Example 1 described in International Publication No. WO 2014/057687), triethylamine (7 μL, 0.050 mmoL) and di(N-succinimidyl) suberate (20.4 mg, 0.055 mmoL) were added. The reaction solution was stirred for 20 minutes at room temperature. The solvent was evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography [chloroform-chloroform: methanol=9:1 (v/v)] to obtain the title compound (16.0 mg, 41%) as a light yellow solid. 
       1 H-NMR (400 MHz, DMSO-d 6 ) δ: 0.87 (3H, t, J=7.6 Hz), 1.18-1.37 (4H, m), 1.40-1.50 (2H, m), 1.54-1.64 (2H, m), 1.65-1.74 (2H, m), 1.78-1.93 (2H, m), 2.02 (2H, t, J=7.6 Hz), 2.09-2.20 (4H, m), 2.40 (3H, s), 2.60-2.68 (2H, m), 2.80 (4H, s), 3.00-3.08 (2H, m), 3.13-3.21 (2H, m), 5.19 (2H, dd, J=32.0, 18.0 Hz), 5.37-5.47 (2H, m), 5.53-5.60 (1H, m), 6.52 (1H, s), 7.30 (1H, s), 7.74-7.82 (2H, m), 8.44 (1H, d, J=8.5 Hz). 
     MS (APCI) m/z: 774 (M+H) +   
     ii) Synthesis of 4-amino-N-[(1S,9S)-9-ethyl-5-fluoro-9,10-dihydroxy-4-methyl-13-oxo-2,3,9,10,13,15-hexahydro-1H,12H-benzo[de]pyrano[3′,4′:6,7]indolizino[1,2-b]quinolin-1-yl] butanamide Trifluoroacetate (Compound (7)) 
     
       
         
         
             
             
         
       
     
     Step 1: 
     First, tert-butyl(4-{[(1S,9S)-9-ethyl-5-fluoro-9-hydroxy-4-methyl-10,13-dioxo-2,3,9,10,13,15-hexahydro-1H,12H-benzo[de]pyrano[3′,4′:6,7]indolizino[1,2-b]quinolin-1-yl]amino}-4-oxobutyl) carbamate (0.092 g, 0.148 mmoL) (compound obtained in Step 1 of Example 1 described in International Publication No. WO 2014/057687) was dissolved in methanol (1.6 mL) and cooled on ice. To this, sodium borohydride (0.028 g, 0.740 mmoL) was added and the reaction solution was stirred for 20 minutes under ice cooling. The solution was diluted with methanol (10 mL) and chloroform (50 mL) and a 10% aqueous citric acid solution was added thereto, and then, extracted with chloroform. The obtained organic layer was washed with a 10% aqueous citric acid solution followed by a saturated saline solution, dried over sodium sulfate and filtered. The solvent was evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography-[chloroform: methanol=100: 0-95:5 (v/v)] to obtain tert-butyl(4-{[(1S,9S)-9-ethyl-5-fluoro-9-hydroxy-4-methyl-13-oxo-2,3,9,10,13,15-hexahydro-1H,12H-benzo[de]pyrano[3′,4′:6,7]indolizino[1,2-b]quinolin-1-yl]amino}-4-oxobutyl) carbamate (0.078 g, 85%) as a light yellow solid. 
       1 H-NMR (400 MHz, DMSO-d 6 ) δ: 0.89 (3H, t, J=7.4 Hz), 1.31 (9H, s), 1.62-1.73 (4H, m), 2.08-2.18 (4H, m), 2.39 (3H, s), 2.91 (2H, q, J=6.5 Hz), 3.12-3.20 (2H, m), 4.49 (1H, d, J=17.2 Hz), 4.61 (1H, d, J=17.2 Hz), 4.97 (1H, s), 4.99 (1H, d, J=4.7 Hz), 5.10 (2H, d, J=18.8 Hz), 5.21 (2H, d, J=18.8 Hz), 5.54-5.58 (1H, m), 6.74-6.82 (2H, m), 7.33 (1H, s), 7.78 (1H, d, J=11.0 Hz), 8.40 (1H, d, J=8.6 Hz). 
     Step 2: 
     The compound (0.078 g, 0.125 mmoL) obtained in Step 1 above was added to dichloromethane (2 mL). The reaction solution was cooled on ice and trifluoro acetate (2 mL) was added. The reaction solution was stirred for 40 minutes. The solvent was evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography [chloroform-organic layer having a distribution ratio of chloroform: methanol: water=7:3:1 (v/v/v)]. The obtained solid was dissolved in methanol and ether was added. The resultant precipitation was filtered and dried under vacuum to obtain the title compound (0.045 g, 56%) as a yellow-solid. 
       1 H-NMR (400 MHz, DMSO-d 6 ) δ: 0.89 (3H, t, J=7.4 Hz), 1.71 (2H, q, J=7.4 Hz), 1.80-1.88 (2H, m), 2.09-2.19 (2H, m), 2.27 (2H, t, J=7.0 Hz), 2.40 (3H, s), 2.84 (2H, t, J=7.6 Hz), 3.13-3.20 (2H, m), 4.50 (1H, d, J=17.2 Hz), 4.62 (1H, d, J=17.2 Hz), 4.97-5.02 (2H, m), 5.09 (1H, d, J=18.8 Hz), 5.21 (1H, d, J=18.8 Hz), 5.55-5.59 (1H, m), 6.79 (1H, d, J=4.7 Hz), 7.34 (1H, s), 7.64-7.75 (3H, m), 7.79 (1H, d, J=11.3 Hz), 8.53 (1H, d, J=8.6 Hz). 
     MS (APCI) m/z: 523 (M+H) +   
     iii) Synthesis of 4-amino-N-cyclohexyl-butanamide Hydrochloride (Compound (8)) 
     
       
         
         
             
             
         
       
     
     Step 1: 
     First, 4-(tert-butoxycarbonylamino)butanoic acid (0.492 g, 2.42 mmoL) was dissolved in dichloromethane (15 mL) and N,N-dimethylformamide (2 mL), and then, N-hydroxysuccinimide (0.279 g, 2.42 mmoL) and EDCI (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride) (0.464 g, 2.42 mmoL) were added. The reaction solution was stirred at room temperature for 30 minutes. The reaction solution was added dropwise to a dichloromethane solution (2 mL) of cyclohexylamine (0.200 g, 2.02 mmoL) and stirred at room temperature for 20 minutes. The reaction solution was diluted with dichloromethane and a 10% aqueous citric acid solution was added, and then, extracted with dichloromethane. The obtained organic layer was washed with a saturated sodium bicarbonate solution, dried over sodium sulfate and filtered. The solvent was evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography-[hexane: ethyl acetate=50: 50-25:75 (v/v)] to obtain tert-butyl N-[4-(cyclohexylamino)-4-oxo-butyl]carbamate (0.308 g, 54%) as a colorless-oil. 
       1 H-NMR (400 MHz, CDCl 3 ) δ: 1.08-1.23 (4H, m), 1.29-1.42 (2H, m), 1.44 (9H, s), 1.66-1.75 (2H, m), 1.77-1.83 (2H, m), 1.86-1.95 (2H, m), 2.17 (2H, t, J=7.0 Hz), 3.11-3.21 (2H, m), 3.69-3.82 (1H, m), 4.75 (1H, brs), 5.89 (1H, brs). 
     Step 2: 
     The compound (0.200 g, 0.703 mmoL) obtained in Step 1 above was dissolved in ethyl acetate (50 mL) and dioxane (10 mL). A 4N dioxane hydrochloride (10 mL) was added and the mixture was stirred for two hours. The precipitation generated was filtered, dried under vacuum to obtain the title compound (0.098 g, 63%) as a colorless solid. 
       1 H-NMR (400 MHz, DMSO-d 6 ) δ: 1.06-1.30 (5H, m), 1.50-1.58 (1H, m), 1.62-1.82 (6H, m), 2.16 (2H, t, J=7.2 Hz), 2.69-2.79 (2H, m), 3.45-3.58 (1H, m), 4.73 (1H, brs), 7.89 (1H, d, J=7.8 Hz), 7.96-8.10 (2H, m). 
     MS (APCI) m/z: 185 (M+H) +   
     [Example 2] Production of Antibody-Drug Conjugate 
     i) Production (1) of Anti-B7-H3 Antibody-Drug Conjugate 
     In accordance with the production method described in International Publication No. WO 2014/057687 and using an anti-B7-H3 antibody (antibody comprising a heavy chain consisting of the amino acid sequence consisting of amino acid residues 20 to 471 of SEQ ID NO: 27 and a light chain consisting of the amino acid sequence consisting of amino acid residues 21 to 233 of SEQ ID NO: 28), an anti-B7-H3 antibody-drug conjugate, in which a drug-linker represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein A represents a connecting position to the antibody,
 
is conjugated to the anti-B7-H3 antibody via a thioether bond (referred to as “B7-H3-ADC (I)” in the present invention), was produced.
 
     ii) Production (2) of Anti-B7-H3 Antibody-Drug Conjugate 
     In accordance with the production method described in International Publication No. WO 2014/057687, and using an anti-B7-H3 antibody (antibody comprising a heavy chain consisting of the amino acid sequence consisting of amino acid residues 20 to 471 of SEQ ID NO: 27 and a light chain consisting of the amino acid sequence consisting of amino acid residues 21 to 233 of SEQ ID NO: 28), an anti-B7-H3 antibody-drug conjugate, in which a drug-linker represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein A represents a connecting position to the antibody,
 
is conjugated to the anti-B7-H3 antibody via a thioether bond (referred to as “B7-H3-ADC (II)” in the present invention), was produced.
 
     iii) Production (3) of Anti-B7-H3 Antibody-Drug Conjugate 
     In accordance with the production method described in International Publication No. WO 2014/057687, and using an anti-B7-H3 antibody (antibody comprising a heavy chain consisting of the amino acid sequence consisting of amino acid residues 20 to 471 of SEQ ID NO: 27 and a light chain consisting of the amino acid sequence consisting of amino acid residues 21 to 233 of SEQ ID NO: 28), an anti-B7-H3 antibody-drug conjugate, in which a drug-linker represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein A represents a connecting position to the antibody,
 
is conjugated to the anti-B7-H3 antibody via a thioether bond (referred to as “B7-H3-ADC (III)” in the present invention), was produced.
 
     iv) Production (1) of Anti-HER2 Antibody-Drug Conjugate 
     In accordance with the production method described in International Publication No. WO 2015/115091 and using an anti-HER2 antibody (antibody comprising a heavy chain consisting of the amino acid sequence consisting of amino acid residues 1 to 449 of SEQ ID NO: 21 and a light chain consisting of the amino acid sequence consisting of amino acid residues 1 to 214 of SEQ ID NO: 22), an anti-HER2 antibody-drug conjugate, in which a drug-linker represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein A represents a connecting position to the antibody,
 
is conjugated to the anti-HER2 antibody via a thioether bond (referred to as “HER2-ADC (I)” in the present invention), was produced.
 
     v) Production (1) of Anti-HER3 Antibody-Drug Conjugate 
     In accordance with the production method described in International Publication No. WO 2015/155998, and using an anti-HER3 antibody (antibody comprising a heavy chain consisting of the amino acid sequence represented by SEQ ID NO: 23 and a light chain consisting of the amino acid sequence represented by SEQ ID NO: 24), an anti-HER3 antibody-drug conjugate, in which a drug-linker represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein A represents a connecting position to the antibody,
 
is conjugated to the anti-HER3 antibody via a thioether bond (referred to as “HER3-ADC (I)” in the present invention), was produced.
 
     vi) Production (1) of Anti-TROP2 Antibody-Drug Conjugate 
     In accordance with the production method described in International Publication No. WO 2015/098099, and using an anti-TROP2 antibody (antibody comprising a heavy chain consisting of the amino acid sequence consisting of amino acid residues 20 to 470 of SEQ ID NO: 25 and a light chain consisting of the amino acid sequence consisting of amino acid residues 21 to 234 of SEQ ID NO: 26), an anti-HER3 antibody-drug conjugate, in which a drug-linker represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein A represents a connecting position to the antibody,
 
is conjugated to the anti-TROP2 antibody via a thioether bond (referred to as “TROP2-ADC (I)” in the present invention), was produced.
 
     [Example 3] Production of Monoclonal Antibody 
     i) Preparation of Antigen Protein 
     As the antigen protein, an antigen protein (hereinafter referred to as “antigen protein (1)”) prepared by adding bovine thyroglobulin serving as a carrier protein to compound (6) and an antigen protein (hereinafter referred to as “antigen protein (2)”) prepared by adding BSA to compound (6), were used. 
     ii) Immunization 
     In immunization, BALB/cAnNCrlCrlj (BALB/c) mice (4 individuals) and B6D2F1/Crlj (BDF1) female mice (4 individuals) (Charles River Laboratories Japan Inc.) were used. At the initial immunization, a mixture of the antigen protein (1) and Freund&#39;s Complete Adjuvant (manufactured by Wako Pure Chemical Industries Ltd.) was subcutaneously and intradermally administered. On and after the second immunization, a mixture of the antigen protein (1) and Freund&#39;s Incomplete Adjuvant (manufactured by Wako Pure Chemical Industries Ltd.) was subcutaneously and intradermally administered. Administration was carried out at the intervals of 7 days, 4 times in total. 
     iii) Evaluation of Antibody Titer of Antiserum 
     Before immunization and after immunization through four administrations, the sera of BALB/c mice (4 individuals) and BDF1 mice (4 individuals) were each diluted up to 200 to 204800 fold. The antibody titers of the dilutions were checked using the antigen protein (2) and B7-H3-ADC (II) as positive controls and BSA as a negative control. The antigen protein (2), B7-H3-ADC (II) and BSA were immobilized to ELISA immunoplates. Diluted mouse sera before immunization and after immunization through four administrations were allowed to react with the immunoplates at 37° C. for 30 minutes. After washing, horseradish peroxidase-conjugated anti-mouse IgG (anti-mouse IgG-HRP) was allowed to react at 37° C. for 30 minutes. After washing, an o-phenylenediamine dihydrochloride (OPD) solution was added. After termination of color development, the absorbance at 490 nm was measured. It was confirmed that antibody titer to a positive control increases in all individuals. 
     iv) Inhibition ELISA 
     To the sera of BALB/c mice (4 individuals) and BDF1 mice (4 individuals) after immunization through four administrations, compound (6), compound (7) and compound (1) as positive controls and compound (8) as a negative control were added and the unabsorption rate to antigen protein (2) was calculated. The mouse sera diluted to 50000 fold and compound (6), compound (8), compound (7) and compound (1), which were prepared to have a concentration of 12.5, 25, 50 and 100 μg/mL, were mixed and allowed to react at 4° C. overnight, and then, added to ELISA immunoplates having the antigen protein (2) immobilized thereon and allowed to react at 37° C. for 30 minutes. After washing, anti-mouse IgG-HRP was allowed to react at 37° C. for 30 minutes. After washing, an OPD solution was added. After termination of color development, absorbance at 490 nm was measured. The unabsorption rate was calculated in accordance with the following expression: 
       Unabsorption rate(%)=( a/b )×100
 
     a: Absorbance of positive control or negative control at an addition concentration of 12.5 μg/mL 
     b: Absorbance of a sample not containing positive control or a sample not containing a negative control 
     In any one of mouse sera, it was found that compound (6) and compound (1) as positive controls, and compound (7) in some individuals have a high inhibition effect. However, in none of the plasmas, a high inhibition effect on compound (8) as a negative control was found. From each of the BALB/c mice and BDF1 mice having sera exhibiting a high inhibition effect on compound (7) and no high inhibition effect on compound (8), an individual was selected. The lymph node and spleen were taken from each of the individuals and used for production of hybridomas. 
     v) Production of Hybridoma 
     Lymph node cells and spleen cells taken from individuals selected in iv) and mouse myeloma cells were fused by the PEG method. Using the culture supernatant of the emergent hybridoma cells, antibody-producing hybridoma cells were screened. 
     vi) Evaluation of Specific Binding to Antigen Protein (2) 
     The antigen protein (2) was immobilized to an ELISA immunoplate and the supernatant of antibody-producing hybridoma cells cultured was diluted double and allowed to react at 37° C. for 120 minutes. After washing, anti-mouse IgG-HRP was allowed to react at 37° C. for 30 minute. After washing, an OPD solution was added. After termination of color development, absorbance at 490 nm was measured. Eleven hybridoma strains producing a culture supernatant showing an OD value of 0.2 or more were elected as a positive. 
     vii) Cross Check 
     The 11 strains selected as a positive in vi) were subjected to inhibition ELISA using compound (6), compound (1), B7-H3-ADC (II), B7-H3-ADC (I) and B7-H3-ADC (III) as a positive control, and compound (8) and compound (7) as a compound for confirming whether a reaction proceeds or not. The culture supernatants of 11 strains selected as a positive and obtained in vi) were diluted double. To each of the culture supernatants, a positive control as mentioned above and the compound for confirming whether a reaction proceeds or not were added so as to obtain a final concentration of 25 μg/m. After a reaction was carried out at 4° C. overnight, the reaction solution was added to an ELISA immunoplate having the antigen protein (2) immobilized thereon and allowed to react at 37° C. for 30 minutes. After washing, anti-mouse IgG-HRP was allowed to react at 37° C. for 30 minutes. After washing, an OPD solution was added. After termination of color development, the absorbance at 490 nm was measured. Eight strains exhibiting high reactivity to the antigen protein (2) and confirmed to have an inhibition effect by the positive control were selected and subjected to primary cloning. 
     viii) Primary Cloning, Primary Screening 
     Eight strains selected in vii) were cloned by limiting dilution. Hybridomas were seeded so as to satisfy a rate of 60 cells/96 well plate and mouse thymocytes were added so as to satisfy a rate of 5×10 6  cells/well. Culture was carried out using a 10% FBS containing TIL (Immuno-Biological Laboratories Co., Ltd.). Inhibition ELISA was carried out in the same manner as in vii). Eight strains x 6 subclones, which were confirmed to have specificity, were selected. 
     ix) Primary Cross Check 
     Eight strains x 6 subclones selected in viii) were checked for reactivity to B7-H3-ADC (II) and B7-H3-ADC (I). B7-H3 Cl domain LotB7_OmJ1 was diluted with an immobilization buffer up to 1 μg/mL, added to Maxi-Sorp plates in a ratio of 100 μL per plate and allowed to immobilize at 4° C. overnight. The following day, the medium was removed from the plates and a 5% BSA-containing PBS was added in a ratio of 180 μL per plate. The plates were allowed to stand still at room temperature for 3 hours. After washing twice with 0.05% Tween20-containing PBS, B7-H3-ADC (II) and B7-H3-ADC (I), which were prepared to have a concentration of 0.1 μg/mL, were added in a ratio of 100 μL and allowed to stand still at room temperature for about one hour. After washing twice with 0.05% Tween20-containing PBS, 50 μL of the hybridoma supernatant serially diluted 7 times from 900 μg/mL at a common ratio of 3, was added per plate. The plates were allowed to stand still at room temperature for one hour. After washing twice with 0.05% Tween20-containing PBS, 100 μL of Peroxidase AffiniPure Goat Anti-Mouse IgG, Fcγ Fragment Specific (Jackson Immuno Research LABORATORIES, INC.) diluted 5000 fold, was added per plate. The plates were allowed to stand still at room temperature for one hour. After washing three times with 0.05% Tween20-containing PBS, 100 μL of a HRP substrate (OPD tablet) was added per plate and a color reaction was carried out. After the color reaction was terminated by adding 100 μL of 1M HCl per plate, absorbance at 450 nm was measured by ARVO (PerkinElmer). In all of 8 strains x 6 subclones, reactivity to B7-H3-ADC (II) and B7-H3-ADC (I) was confirmed. Of them, 4 strains×6 subclones which were highly reactive were subjected to confirmation by the primary calibration curve. 
     x) Confirmation by Primary Calibration Curve 
     Four strains x 6 subclones selected in ix) were checked for reactivity to B7-H3-ADC (I) (DAR7) and B7-H3-ADC (I) (DAR5) by ELISA. AffiniPure Goat Anti-Mouse IgG, Fcγ fragment specific (Jackson Immuno Research Inc.) was diluted with Coating Buffer up to 1 μg/mL and added to Maxi-Sorp plates in a ratio of 100 μL per plate, and then, allowed to immobilize at 4° C. overnight. The following day, the medium was removed from the plates. After washing with PBS, a 10% BSA-containing PBS was added in a ratio of 100 μL per plate. The plates were allowed to stand still at 37° C. for 2.5 hours. The medium was removed from the plates, hybridoma 4 strains x 6 subclones were diluted with 2% BSA and 0.2% Polysorbate20 (hereinafter referred to as “PS20”) containing PBS up to 10, 25 and 100 ng/mL. Each of the dilutions was added to the plates in a ratio of 100 μL per plate. The plates were allowed to stand still at 37° C. for one hour. After washing four times with 0.05% PS20-containing PBS, B7-H3-ADC (I) (DAR7) and B7-H3-ADC (I) (DAR5) were diluted with 2% BSA, 0.2% Tween20-containing PBS up to 1, 2.5, 10, 25, 100 and 250 ng/mL. Each of the dilutions was added in a ratio of 100 μL per plate. The plates were allowed to stand still at 37° C. for one hour. After washing four times with a 0.05% PS20-containing PBS, Goat Anti-Human kappa-HRP (Southern Biotechnology Associates, Inc.) diluted with 2% BSA, 0.2% PS20-containing PBS up to 7500 fold was added in a ratio of 100 μL per plate. The plates were allowed to stand still at room temperature for one hour. After washing four times with a 0.05% PS20-containing PBS, TMB soluble reagent (ScyTek Laboratories) was added in a ratio of 100 μL/well and a color reaction was carried out. After the color reaction was terminated by adding TMB stop buffer (ScyTek Laboratories) in a ratio of 100 μL/well and absorbance (reference 650 nm) at 450 nm was measured by VersaMax (manufactured by Molecular Devices). Relative errors were calculated in accordance with the following expression and clones having small values were selected 
       Relative error(%)={(measurement value DAR7)/(measurement value of DAR5)−1}×100
 
     Of them, 4 strains x 2 subclones were subjected to secondary cloning. 
     xi) Secondary Cloning, Screening 
     Four strains x 2 subclones selected in x) were subjected to secondary cloning. Three wells were selected from the positive wells per clone. In this way, 24 clones in total were selected. Antibody titer to the antigen protein (2) was checked in the same manner as in vi). Further, using compound (6), compound (1), B7-H3-ADC (II), B7-H3-ADC (I) and B7-H3-ADC (III) as a positive control, and compound (8) and compound (7) as a compound for confirming whether a reaction proceeds or not, inhibition ELISA was carried out in the same manner as in vii). 
     xii) Confirmation by Secondary Calibration Curve 
     Of the 24 clones selected in xi), 6 clones exhibiting particularly high reactivity to compound (7) compared to compound (1) were eliminated. The remaining 18 clones were subjected to confirmation of reactivity to HER2-ADC (I) (DAR8), HER2-ADC (I) (DAR4) and HER2-ADC (I) (DAR2) and formation of calibration curves carried out by Gyrolab xP workstation (GYROS PROTEIN Technologies). As a capture reagent, Biotin-SP-conjugated AffiniPure Goat Anti-Mouse IgG, Fcγ specific (Jackson Immuno Research LABORATORIES, INC.) was used and the concentration thereof was controlled to be 172.5 nM with 0.01% PS20-containing PBS. The concentration of the cell culture supernatant was controlled with Rexxip CCS (GYROS PROTEIN Technologies) to be 200 ng/mL. HER2-ADC (I) (DAR8), HER2-ADC (I) (DAR4) and HER2-ADC (I) (DAR2) were serially diluted 6 times with 0.01% PS20-containing PBS from 1000 ng/mL at a common ratio of 4. As a detection reagent, Goat Anti Human kappa (Southern Biotechnology Associates, Inc.) was labeled using Alexa Fluor (registered trademark) 647 labeling kit (Thermo Fisher Scientific Inc.) and the concentration thereof was controlled to be 10 nM with Rexxip F. The reagents prepared above, cell culture supernatant and samples for a calibration curve were added in 96-well PCR plates and set together with Gyrolab Bioaffy 200 in a Gyrolab xP workstation. Measurement was carried out by 4-Step (2×C)-A-D (wizard method). Regression of the calibration curve was carried out in accordance with the 4-parameter logistic model (weight: Response) using Gyrolab Evaluator Software. All of the 18 clones evaluated did not depend on DAR of HER2-ADC (I) and no difference in reactivity between strains was recognized. Thus, three clones (1A3, 8B2, 11B1), which were derived from the same strain and had a high IgG concentration, were selected and subjected to a small-quantity production. 
     xiii) Preparation of Antibody Purified with Protein a and Cross Check 
     Three clones (1A3, 8B2, 11B1) selected in xii) were each cultured in a serum-free medium (ASF104 (N)) in a roller bottle. After the culture supernatant was collected, filtration by a 0.45 μm filter and purification by Protein A column were carried out. To ELISA immunoplates having antigen protein (2) immobilized in a ratio of 50 ng/well/50 μL, solutions (50 μL) containing the three clones purified with Protein A and serially diluted 10 times from 5 μg/mL at a common ratio of 2, were added and allowed to react at 37° C. for 30 minutes. After washing, anti-mouse IgG-HRP was allowed to react at 37° C. for 30 minutes. After washing, an OPD solution was added. After termination of color development, absorbance at 490 nm was measured. All antibodies purified with Protein A showed satisfactory reactivity with antigen protein (2). 
     xiv) Confirmation of Calibration Curve of Antibody Purified with Protein a 
     Reactivity of three clones (1A3, 8B2, 11B1) purified with protein A in xiii) to HER2-ADC (I) (DAR8) and HER2-ADC (I) (DAR4) and, B7-H3-ADC (I) (DAR8) and B7-H3-ADC (I) (DAR4) was checked by use of Gyrolab xP workstation. 
     As a capture reagent, the three clones purified with Protein A and labeled with EZ-Link NHS-LC-Biotin (Thermo Fisher Scientific Inc.) were used and the concentrations thereof were controlled with 0.01% PS20-containing PBS to be 700 nM. HER2-ADC (I) (DAR8) and HER2-ADC (I) (DAR4) were each serially diluted 6 times with Rexxip HN from 1000 ng/mL at a common ratio of 4. As the detection reagent used herein, Goat Anti Human kappa (Southern Biotechnology Associates, Inc.) which was labeled by use of Alexa Fluor (registered trademark) 647 labeling kit was used and the concentration thereof was controlled with Rexxip F to be 10 nM. The reagents prepared and an antibody-drug conjugate (sample for calibration curve) were added in 96-well PCR plates and set together with Gyrolab Bioaffy 200 in Gyrolab xP workstation. Measurement was carried out by 200-3W-001-A (wizard method). The regression of the calibration curve was carried out using 4-parameter logistic model (weighting; Response) and Gyrolab Evaluator Software. The calibration curve of clone 1A3 is shown in  FIG. 15 , the calibration curve of clone 8B2 in  FIG. 16  and the calibration curve of clone 11B1 in  FIG. 17 . All clones showed reactivity to HER2-ADC (I) independently of DAR. 
     Further, as capture reagents, Human Her2/ErbB2 Protein (ACROBiosystems) labeled with EZ-Link NHS-LC-Biotin and B7-H3 Cl domain also labeled with the biotin were used. The concentrations of them were controlled with 0.01% PS20-containing PBS to be 700 nM. HER2-ADC (I) (DAR8) and HER2-ADC (I) (DAR4) and B7-H3-ADC (I) (DAR8) and B7-H3-ADC (I) (DAR4) were serially diluted 6 times with Rexxip HN from 1000 ng/mL in a common ratio of 4. As detection reagents, three clones (1A3, 8B2, 11B1) purified with Protein A and labeled using DyLight650 (registered trademark) labeling kit (Thermo Fisher Scientific Inc.) were used. The concentrations of them were controlled with Rexxip F to be 10 nM. The reagents prepared and samples for calibration curves of the antibody-drug conjugates were added in 96-well PCR plates, which were set together with Gyrolab Bioaffy 200 in Gyrolab xP workstation. Measurement was carried out by 200-3W-001-A (wizard method). Regression of the calibration curve was carried out in accordance with the 4-parameter logistic model (weighting; Response) by Gyrolab Evaluator Software. As to the reactivity to HER2-ADC (I), the calibration curve of clone 1A3 is shown in  FIG. 18 , the calibration curve of clone 8B2 in  FIG. 19  and the calibration curve of clone 11B1 in  FIG. 20 . As to the reactivity to B7-H3-ADC (I), the calibration curve of clone 1A3 is shown in  FIG. 21 , the calibration curve of clone 8B2 in  FIG. 22  and the calibration curve of clone 11B1 in  FIG. 23 . All clones showed reactivity to HER2-ADC (I) and B7-H3-ADC (I) independently of DAR. 
     From the results, it was confirmed that all clones have reactivity to an antibody-drug conjugate independently of difference in DAR and antibody moiety, and are used as both a capture reagent and a detection reagent. Of the clones, clone 1A3 exhibiting the largest signal value was selected and intended to use in detecting the antibody-drug conjugate according to the present invention. 
     xv) Determination of Isotype of Mouse Monoclonal Antibody 
     The isotype of a mouse monoclonal antibody (hereinafter referred to as “mouse antibody 1A3”) of clone 1A3 obtained in xiv) was determined by Mouse monoclonal isotyping test kit (manufactured by AbD Serotec). As a result, the isotype was confirmed to be IgG2b, κ chain. 
     xvi) Gene Cloning of Monoclonal Antibody and Sequencing Analysis of N Terminus Amino Acid 
     Total RNA was prepared from mouse antibody 1A3-producing hybridoma using TRIzol Reagent (LIFE TECHNOLOGIES). Sequencing analysis (Edman sequencing) of N terminus amino acid of purified mouse antibody 1A3 was carried out. Further, the nucleotide sequence of clone 1A3 was analyzed by antibody gene cloning. As a result of the antibody gene cloning, a single sequence of a heavy chain variable region and a single sequence of a light chain variable region were obtained. As the result of analysis, it was confirmed that the N terminus amino acid sequence of the purified mouse antibody 1A3 matches with the N terminus amino acid sequence of the nucleotide sequence of clone 1A3 obtained by antibody gene cloning. 
     The amino acid sequence of a heavy chain of mouse antibody 1A3 is represented by SEQ ID NO: 15. The amino acid sequence consisting of amino acid residues 1 to 19 of SEQ ID NO: 15 represents a signal sequence; the amino acid sequence consisting of amino acid residues 20 to 141 thereof represents a heavy chain variable region; and the amino acid sequence consisting of amino acid residues 142 to 477 thereof represents a heavy chain constant region. 
     The amino acid sequence of a light chain of mouse antibody 1A3 is represented by SEQ ID NO: 16. The amino acid sequence consisting of amino acid residues 1 to 20 of SEQ ID NO: 16 represents a signal sequence; the amino acid sequence consisting of amino acid residues 21 to 127 thereof represents a light chain variable region; and the amino acid sequence consisting of amino acid residues 128 to 234 thereof represents a light chain constant region. 
     The nucleotide sequence encoding the amino acid sequence of a heavy chain of mouse antibody 1A3 is represented by SEQ ID NO: 17. The nucleotide sequence consisting of nucleotide residues 1 to 57 of SEQ ID NO: 17 represents a signal sequence; and the nucleotide sequence consisting of nucleotide residues 58 to 423 thereof encodes the amino acid sequence of a heavy chain variable region. 
     The nucleotide sequence encoding the amino acid sequence of a light chain of mouse antibody 1A3 is represented by SEQ ID NO: 18. The nucleotide sequence consisting of nucleotide residues 1 to 60 of SEQ ID NO: 18 represents a signal sequence; and the nucleotide sequence of nucleotides 61 to 459 thereof encodes the amino acid sequence of a heavy chain variable region. 
     In addition, CDR was analyzed. 
     According to the definition of Abm, it was found that the heavy chain variable region of mouse antibody 1A3 has CDRH1 (GFTFSDYGMV) consisting of the amino acid sequence represented by SEQ ID NO: 1, CDRH2 (YISSGSSAIY) consisting of the amino acid sequence represented by SEQ ID NO: 2, and CDRH3 (PPRYDVYSAWFAY) consisting of the amino acid sequence represented by SEQ ID NO: 3; and that the light chain variable region of mouse antibody 1A3 has CDRL1 (KASQDVGSAVV) consisting of the amino acid sequence represented by SEQ ID NO: 4, CDRL2 (WASTRHT) consisting of the amino acid sequence represented by SEQ ID NO: 5, and CDRL3 (QQYSSYPVT) consisting of the amino acid sequence represented by SEQ ID NO: 6. 
     According to the definition of Chothia, it was found that the heavy chain variable region of mouse antibody 1A3 has CDRH1 (GFTFSDY) consisting of the amino acid sequence represented by SEQ ID NO: 7, CDRH2 (SSGSSA) consisting of the amino acid sequence represented by SEQ ID NO: 8, and CDRH3 (PPRYDVYSAWFAY) consisting of the amino acid sequence represented by SEQ ID NO: 3; and that the light chain variable region of mouse antibody 1A3 has CDRL1 (KASQDVGSAVV) consisting of the amino acid sequence represented by SEQ ID NO: 4 CDRL2 (WASTRHT) consisting of the amino acid sequence represented by SEQ ID NO: 5, and CDRL3 (QQYSSYPVT) consisting of the amino acid sequence represented by SEQ ID NO: 6. 
     According to the definition of Kabat, it was found that the heavy chain variable region of mouse antibody 1A3 has CDRH1 (DYGMV) consisting of the amino acid sequence represented by SEQ ID NO: 9, CDRH2 (YISSGSSAIYYADTVKG) consisting of the amino acid sequence represented by SEQ ID NO: 10, and CDRH3 (PPRYDVYSAWFAY) consisting of the amino acid sequence represented by SEQ ID NO: 3; and that the light chain variable region of mouse antibody 1A3 has CDRL1 (KASQDVGSAVV) consisting of the amino acid sequence represented by SEQ ID NO: 4, CDRL2 (WASTRHT) consisting of the amino acid sequence represented by SEQ ID NO: 5, and CDRL3 (QQYSSYPVT) consisting of the amino acid sequence represented by SEQ ID NO: 6. 
     According to the definition of Imgt (registered trademark), it was found that the heavy chain variable region of mouse antibody 1A3 has CDRH1 (GFTFSDYG) consisting of the amino acid sequence represented by SEQ ID NO: 11, CDRH2 (ISSGSSAI) consisting of the amino acid sequence represented by SEQ ID NO: 12, and CDRH3 (ARPPRYDVYSAWFAY) consisting of the amino acid sequence represented by SEQ ID NO: 13; and that the light chain variable region of mouse antibody 1A3 has CDRL1 (QDVGSA) consisting of the amino acid sequence represented by SEQ ID NO: 14, CDRL2 consisting of a tripeptide represented by WAS (tryptophan-alanine-serine), and CDRL3 (QQYSSYPVT) consisting of the amino acid sequence represented by SEQ ID NO: 6. 
     [Example 4] Measurement of Plasma-Concentration in Non-Clinical Study 
     Using mouse antibody 1A3 obtained in Example 2, a method for measuring the concentration in plasma of HER2-ADC (I) in a mouse and a method for measuring the concentration in plasma of HER3-ADC (I), TROP2-ADC (I) and B7-H3-ADC (I) in a monkey were developed. Mouse antibody 1A3 can be used by labelling it with DyLight650 (registered trademark) or Alexa Fluor (registered trademark) 647 serving as a detection reagent. The plasma-concentration of the antibody-drug conjugate according to the present invention can be measured even if either one of them is selected. Further, a calibration curve can be prepared independent of difference in DAR and antibody moiety and can be used in measurement of the concentration in plasma of the antibody-drug conjugate according to the present invention. 
     i) HER2-ADC (I) 
     The method for measuring the concentration in plasma of HER2-ADC (I) in a mouse was developed by Gyrolab xP workstation. As a capture reagent, Biotinylated Mouse Anti-(Anti-HER2 Ab) idiotype Ab (herein, “(Anti-HER2 Ab)”) refers to an antibody comprising a heavy chain consisting of the amino acid sequence consisting of amino acid residues 1 to 449 of SEQ ID NO: 21 and a light chain consisting of the amino acid sequence consisting of amino acid residues 1 to 214 of SEQ ID NO: 22) (13C1) (IBL). The concentration thereof was controlled with 0.1% PS20-containing PBS to be 350 nM. Samples for a calibration curve were prepared by controlling the concentration of HER2-ADC (I) to be 0, 0.150, 0.200, 0.600, 1.60, 4.00, 16.0, 40.0, 100, and 140 μg/mL with the mouse plasma diluted with Rexxip HN 100 fold. As a detection reagent, mouse antibody 1A3 labeled by DyLight650 (registered trademark) labeling kit was used and the concentration thereof was controlled with Rexxip F to be 10 nM. These reagents and samples for a calibration curve were added to 96-well PCR plates and set together with Gyrolab Bioaffy 200 in Gyrolab xP workstation. As the measurement wizard, 200-3W-002-A (PMT1) was used. The regression analysis was carried out in accordance with the 5-parameter logistic model using Gyrolab Evaluator 3.3.9.175. The calibration curve is shown in  FIG. 24 . 
     A method for measuring the concentration in plasma of Total antibody (anti-HER2 antibody and HER2-ADC (I)) in a mouse was developed by Gyrolab xP workstation. As a capture reagent, Biotinylated Mouse Anti-(Anti-HER2 Ab) idiotype Ab (13C1) (IBL) was used and the concentration thereof was controlled with 0.1% PS20-containing PBS to be 350 nM. Samples for a calibration curve were prepared by controlling the concentration of HER2-ADC (I) to be 0, 0.150, 0.200, 0.600, 1.60, 4.00, 16.0, 40.0, 100 and 140 μg/mL with the mouse plasma diluted with Rexxip HN 100 fold. As a detection reagent, Alexa Fluor (registered trademark) 647 anti-human IgG, Fcγ antibody (Jakckson Immno Research Laboratories, Inc.) was used and the concentration thereof was controlled with Rexxip F to be 10 nM. These reagents prepared and samples for a calibration curve were added to 96-well PCR plates and set together with Gyrolab Bioaffy 200 in Gyrolab xP workstation. As the measurement wizard, 200-3W-002-A (PMT1) was used. The regression analysis was carried out in accordance with the 5-parameter logistic model using Gyrolab Evaluator 3.3.9.175. 
     The measurement results of concentration is shown in Table 1. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                   
                 Mean Plasma Concentration (μg/mL) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Time (d) 
                 0.00347 
                 0.292 
                 1 
                 3 
                 7 
                 14 
                 21 
               
               
                   
               
               
                 Total Ab 
                 66.9 ± 4.9 
                 41.3 ± 1.4 
                 27.9 ± 1.4 
                 24.3 ± 2.3 
                 17.0 ± 1.2 
                 10.7 ± 0.5  
                 6.66 ± 1.19 
               
               
                 HER2-ADC (1) 
                 73.4 ± 6.6 
                 44.8 ± 6.0 
                 30.3 ± 1.2 
                 23.5 ± 1.7 
                 16.9 ± 0.4 
                 8.92 ± 0.91 
                 5.20 ± 0.98 
               
               
                   
               
            
           
         
       
     
     ii) HER3-ADC (I) 
     A method for measuring the concentration in plasma of HER3-ADC (I) in a monkey was developed by Gyrolab xP workstation. Validation was obtained. As a capture reagent, HER3 (Recombinant Human ErbB-3/HER3 Protein, ACRO biosystems) labeled with EZ-Link Sulfo-NHS-LC-Biotin (Thermo Fisher Scientific Inc.) was used and the concentration thereof was controlled to be 700 nM with 0.1% PS20-containing PBS. Samples for a calibration curve were prepared by controlling the concentration of HER3-ADC (I) to be 0, 0.0750, 0.100, 0.250, 0.750, 2.25, 6.75, 20.0, 38.0 and 48.0 μg/mL with the monkey plasma and further diluting them with Polysorbate 20-containing PBS and Rexxip AN (GYROS PROTEIN Technologies) 100 fold. As a detection reagent, mouse antibody 1A3 labeled using Alexa Fluor (registered trademark) 647 labeling kit was used and the concentration thereof was controlled with Rexxip F to be 10 nM. These reagents prepared and samples for a calibration curve were added to 96-well PCR plates and set in Gyrolab xP workstation. As the measurement wizard, 200-3W-002-A (PMT5) was used. The regression analysis was carried out in accordance with the 4-parameter logistic model (weight: Response) using Gyrolab Evaluator 3.3.7.171. The calibration curve is shown in  FIG. 25 . 
     iii) TROP2-ADC (I) 
     A method for measuring the concentration in plasma of TROP2-ADC (I) in a monkey was developed by Gyrolab xP workstation. Validation was obtained. As a capture reagent, new hTrop2 (Lot number V35, Daiichi Sankyo co., ltd.) labeled with EZ-Link Sulfo-NHS-LC-Biotin was used and the concentration thereof was controlled to be 350 nM with 0.1% PS20-containing PBS. Samples for a calibration curve used were those prepared by controlling the concentration of TROP2-ADC (I) to be 0, 0.00750, 0.0100, 0.0250, 0.0750, 0.250, 0.750, 2.50, 7.50 and 10.0 μg/mL with the monkey plasma and the samples were further diluted 10 fold with Rexxip HN (GYROS PROTEIN Technologies). As a detection reagent, mouse antibody 1A3 labeled using Alexa Fluor (registered trademark) 647 labeling kit was used and the concentration thereof was controlled to be 10 nM with Rexxip F. These reagents and samples for a calibration curve were added to 96-well PCR plates and set in Gyrolab xP workstation. As the measurement wizard, 200-3W-002-A (PMT1) was used. The regression analysis was carried out in accordance with the 4-parameter logistic model (weight: Response) using Gyrolab Evaluator 3.3.7.171. The calibration curve is shown in  FIG. 26 . 
     iv) B7-H3-ADC (I) 
     A method for measuring the concentration in plasma measurement of B7-H3-ADC (I) in a monkey was developed by Gyrolab xP workstation. Validation was obtained. As a capture reagent, B7-H3 Cl domain (Lot number B7 OmJ1, Daiichi Sankyo co., ltd.) labeled with EZ-Link Sulfo-NHS-LC-Biotin (Thermo Fisher Scientific Inc.)was used and the concentration thereof was controlled with 0.1% PS20-containing PBS to be 700 nM. Samples for a calibration curve were prepared by controlling the concentration of B7-H3-ADC (I) to be 0, 0.0750, 0.100, 0.250, 0.750, 2.25, 6.75, 20.0, 38.0 and 48.0 μg/mL with the mouse plasma and further diluting them with Polysorbate 20 containing PBS and Rexxip HN (GYROS PROTEIN Technologies) 50 fold. As a detection reagent, mouse antibody 1A3 labeled using Alexa Fluor (registered trademark) 647 labeling kit was used and the concentration thereof was controlled to be 10 nM with Rexxip F. These reagents and samples for a calibration curve were added to 96-well PCR plates and set in Gyrolab xP workstation. As the measurement wizard, 200-3W-001-A (PMT5) was used. The regression analysis was carried out in accordance with the 4-parameter logistic model (weight: Response) using Gyrolab Evaluator 3.3.7.171. The calibration curve is shown in  FIG. 27 . 
     [Example 5] Immunostaining Using Mouse Antibody 1A3 
     i) Confirmation of Stainability Using Subcutaneously Transplanted Human-Derived Tumor 
     To a highly immunodeficient mouse (NOG mouse), a human-derived tumor is subcutaneously transplanted. After the antibody-drug conjugate according to the present invention is administered, the tumor tissue is taken to prepare paraffin-embedded specimens. Then, stainability of a mouse antibody 1A3 is examined. The tumor tissue is taken from a NOG mouse to which the antibody-drug conjugate according to the present invention is not administered and used as a negative control. Deparaffinization and antigen activation are carried out using Autostainer Link pretreatment system (PT Link, manufactured by DAKO) and an antigen retrieval solution (Target Retrieval Solution Low pH, manufactured by DAKO). The following staining operation is carried out using an automatic staining device (Dako Autostainer Link 48: Manufactured by DAKO). After washing with EnVision FLEX WASH BUFFER (manufactured by DAKO), Peroxidase Block 3% H 2 O 2  (manufactured by DAKO) is add; incubation is carried out; and washing is carried out with EnVision FLEX WASH BUFFER. Protein Block serum free (manufactured by DAKO) is added; incubation s carried out; and liquid is removed by air blow. Mouse antibody 1A3 is diluted with REAL Antibody Diluent (manufactured by DAKO) and reacted. After washing with EnVision FLEX WASH BUFFER, EnVision+System-HRP Labelled Polymer Anti-Mouse #K4000 (manufactured by DAKO) is added; incubation is carried out; and then, washing with EnVision FLEX WASH BUFFER is carried out. 
     DAKO Liquid DAB+Substrate Chromogen System is add and incubation is carried out; and washing with EnVision FLEX WASH BUFFER is carried out. EnVision FLEX Hematoxylin is added and incubation is carried out; and washing with EnVision FLEX WASH BUFFER and ion exchange water is carried out. 
     It is confirmed that the NOG mouse administered with the antibody-drug conjugate according to the present invention can be satisfactorily stained with mouse antibody 1A3, and that the staining intensity increases with an increase of concentration of mouse antibody 1A3. In addition, it is confirmed that a NOG mouse not administered with the antibody-drug conjugate according to the present invention is not stained with mouse antibody 1A3. Note that, since the NOG mouse is defective in B cells, it is known that the background is not stained with mouse-derived endogenous IgG (Ito M, et al. Blood 100 (9): 3175-3182, 2002). 
     ii) Confirmation of Specificity of Mouse Antibody 1A3 
     After mouse antibody 1A3 is mixed with compound (2) or SN-38, the mixture is used for immunostaining. The blending ratio of antibody 1A3: compound (2): SN-38 is defined to be 0.1:0.04:0.03 based on the molecular weights. Staining was carried out in the same manner as in i). 
     It is confirmed that stainability of mouse antibody 1A3 disappears by mixing it with compound (2). It is also confirmed that stainability of mouse antibody 1A3 does not disappear by mixing it with SN-38. 
     [Example 6] Preparation of Rabbit Chimeric Antibody 
     i) Design of Rabbit Chimeric Antibody Derived from Mouse Antibody 1A3 
     A rabbit chimeric antibody derived from mouse antibody 1A3 (hereinafter referred to as “rabbit chimeric antibody 1A3”) was designed as follows. The sequence of the rabbit chimeric antibody was designed with reference to IMGT (registered trademark) by connecting the heavy chain constant region IGHG*02 and the light chain constant region IGKC2*01 of a rabbit to respective variable regions of both chains of clone 1A3. 
     The amino acid sequence of a heavy chain of rabbit chimeric antibody 1A3 is represented by SEQ ID NO: 19. The amino acid consisting of amino acid residues 1 to 19 of SEQ ID NO: 19 represents a signal sequence; the amino acid sequence consisting of amino acid residues 20 to 141 thereof represents a heavy chain variable region, and the amino acid sequence of amino acid residues 142 to 464 thereof represents a heavy chain constant region. 
     The amino acid sequence of a light chain of rabbit chimeric antibody 1A3 is represented by SEQ ID NO: 20. The amino acid sequence consisting of amino acid residues 1 to 20 of SEQ ID NO: 20 represents a signal sequence; the amino acid sequence consisting of amino acid residues 21 to 127 thereof represents a light chain variable region; and the amino acid sequence consisting of amino acid residues 128 to 233 thereof represents a light chain constant region. 
     ii) Construction of Antibody Expression Vector pCMA-LK 
     A fragment (about 5.4 kb) obtained by digesting plasmid pcDNA3.3-TOPO/LacZ (Invitrogen) with restriction enzyme XbaI and PmeI was ligated to a DNA fragment having a nucleotide sequence (SEQ ID NO: 29) encoding the amino acid sequences of a human light chain signal sequence and a human κ chain constant region by use of In-Fusion Advantage PCR cloning kit (CLONTECH) to obtain pcDNA3.3/LK. 
     pCMA-LK was constructed by removing a neomycin expression unit from pcDNA3.3/LK. 
     iii) Construction of Rabbit Chimeric Antibody 1A3 Heavy Chain Expression Vector 
     A DNA fragment having the nucleotide sequence (SEQ ID NO: 30) encoding the amino acid sequence (SEQ ID NO: 19) of a heavy chain of rabbit chimeric antibody 1A3 was synthesized (GENEART). The nucleotide sequence of nucleotide residues 26 to 82 of SEQ ID NO: 30 represents a signal sequence; the nucleotide sequence of nucleotide residues 83 to 448 encodes the amino acid sequence of a heavy chain variable region; and the nucleotide sequence of nucleotide residues 449 to 1417 encodes the amino acid sequence of the constant region. 
     The DNA fragment synthesized by use of In-Fusion HD PCR cloning kit (CLONTECH) was ligated to the DNA fragment, which was prepared by digesting pCMA-LK with XbaI and PmeI and removing the nucleotide sequence (SEQ ID NO: 29) encoding the amino acid sequences of a light chain signal sequence and a human κ chain constant region to construct a rabbit chimeric antibody 1A3 heavy chain expression vector. 
     iv) Construction of Rabbit Chimeric Antibody 1A3 Light Chain Expression Vector 
     A DNA fragment having the nucleotide sequence (SEQ ID NO: 31) encoding the amino acid sequence (SEQ ID NO: 20) of a light chain of rabbit chimeric antibody 1A3 was synthesized (GENEART). The nucleotide sequence of nucleotide residues 26 to 85 of SEQ ID NO: 31 represents a signal sequence; the nucleotide sequence of nucleotide residues 86 to 406 encodes the amino acid sequence of a light chain variable region; and the nucleotide sequence of nucleotide residues 407 to 724 encodes the amino acid sequence of the constant region. A rabbit chimeric antibody 1A3 light chain expression vector was constructed in the same manner as in iii). 
     v) Production of Rabbit Chimeric Antibody 1A3 
     FreeStyle 293F cells (Invitrogen) were subcultured in accordance with a manual. FreeStyle 293F cells (Invitrogen) (2.4×10 9 ) during the logarithmic growth phase were seeded in Optimum Growth 5L Flask (Thomson), diluted with FreeStyle293 expression medium (Invitrogen) to prepare 1.88×10 6  cells/mL. To Opti-Pro SFM culture medium (Invitrogen) (40 mL), 0.48 mg of the rabbit chimeric antibody 1A3 heavy chain expression vector, 0.72 mg of rabbit chimeric antibody 1A3 light chain expression vector and 3.6 mg of polyethyleneimine (Polyscience #24765) were added. The mixture was gently stirred, allowed to stand still for further 5 minutes, and then, added to FreeStyle 293F cells. The mixture was incubated at 37° C., in an 8% CO 2  incubator for 4 hours while shaking at a rate of 90 rpm. Thereafter, 1200 mL of EX-CELL VPRO culture medium (SAFC Biosciences), 18 mL of GlutaMAX I (GIBCO) and 60 mL of Yeastolate Ultrafiltrate (GIBCO) were added. The mixture was cultured at 37° C. in an 8% CO 2  incubator for 7 days while shaking at a rate of 90 rpm. The resultant culture supernatant was filtered by Disposable Capsule Filter (Advantec #CCS-045-E1H) to obtain a culture supernatant containing rabbit chimeric antibody 1A3. 
     vi) Purification of Rabbit Chimeric Antibody 1A3 
     The culture supernatant obtained in v) was purified by a single step of rProtein A affinity chromatography. The culture supernatant was applied to a column (manufactured by GE Healthcare Bioscience) charged with MabSelectSuRe equilibrated with PBS, and then, washed with PBS (in a volume double or more as large as the column volume). Subsequently, elution was made with a 2 M arginine hydrochloride solution (pH4.0) and fractions containing the antibody were collected. The fractions collected were dialyzed (Slide-A-Lyzer Dialysis Cassette, company: Thermo Scientific) to perform PBS buffer replacement. The antibody was concentrated by Centrifugal UF Filter Device VIVASPIN20 (cutoff molecular weight UF10K, company: Sartorius) and the concentration of IgG was controlled to be 2 mg/mL or more. Finally, filtration was made by Minisart-Plus filter (Sartorius) to obtain a sample of purified rabbit chimeric antibody 1A3. 
     [Example 7] Production of Antibody-Drug Conjugate 
     i) Production (1) of Anti-GPR20 Antibody-Drug Conjugate 
     In accordance with the production method described in International Publication No. WO 2018/135501 and using an anti-GPR20 antibody (antibody comprising a heavy chain consisting of the amino acid sequence consisting of amino acid residues 20 to 472 of SEQ ID NO: 32 and a light chain consisting of the amino acid sequence consisting of amino acid residues 21 to 234 of SEQ ID NO: 33), an anti-GPR20 antibody-drug conjugate, in which a drug-linker represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein A represents a connection position to the antibody)
 
is conjugated to the anti-GPR20 antibody via a thioether bond (referred to as “GPR20-ADC (I)” in the present invention), was produced.
 
     ii) Production (1) of Anti-CDH6 Antibody-Drug Conjugate 
     In accordance with the production method described in International Publication No. WO2018/212136 and using an anti-CDH6 antibody (antibody comprising a heavy chain consisting of the amino acid sequence consisting of amino acid residues 20 to 471 of SEQ ID NO: 34 and a light chain consisting of the amino acid sequence consisting of amino acid residues 21 to 233 of SEQ ID NO: 35), an anti-CDH6 antibody-drug conjugate, in which a drug-linker represented by the following formula: 
     
       
         
         
             
             
         
       
     
     wherein A represents a connection position to the antibody)
 
is conjugated to the anti-CDH6 antibody via a thioether bond (referred to as “CDH6-ADC (I)” in the present invention), was produced.
 
     [Example 8] Immunostaining Using Rabbit Chimeric Antibody 1A3 
     i) Confirmation of Stainability Using Subcutaneously Transplanted Human-Derived Tumor after Administration of TROP2-ADC (I) 
     To an immunodeficient mouse (nude mouse), human head and neck cancer cell line FaDu was subcutaneously transplanted. After TROP2-ADC (I) was administered, the tumor tissue was taken to prepare paraffin-embedded specimens. Then, stainability of rabbit chimeric antibody 1A3 was examined. The tumor tissue was taken from a nude mouse to which an anti-TROP2 antibody (an antibody comprising a heavy chain consisting of amino acid sequence of amino acid residues 20 to 470 of SEQ ID NO: 25 and a light chain consisting of amino acid sequence of amino acid residues 21 to 234 of SEQ ID NO: 26, hereinafter referred to as “Anti-TROP2 Ab”) and used as a negative control. Deparaffinization and antigen activation were carried out using Autostainer Link pretreatment system (PT Link, manufactured by DAKO) and an antigen retrieval solution (Target Retrieval Solution Low pH, manufactured by DAKO) at 97° C. for 40 minutes. The following staining operation was carried out using an automatic staining device (Dako Autostainer Link 48: manufactured by DAKO) at room temperature. After washing once with EnVision FLEX WASH BUFFER (manufactured by DAKO), REAL Peroxidase-Blocking Solution (manufactured by DAKO) was added; incubation was carried out for 5 minutes; and washing was carried out once with EnVision FLEX WASH BUFFER. Protein Block serum free (manufactured by DAKO) was added; incubation was carried out for 30 minutes; and liquid was removed by air blow. Rabbit chimeric antibody 1A3 was diluted with REAL Antibody Diluent (manufactured by DAKO) to 0.1 μg/mL and reaction was made for 30 minutes. After washing three times with EnVision FLEX WASH BUFFER, EnVision+System-HRP Labelled Polymer Anti-Rabbit (manufactured by DAKO) was added; incubation was carried out for 30 minutes; and then, washing twice with EnVision FLEX WASH BUFFER was carried. 
     DAKO Liquid DAB+Substrate Chromogen System was added and incubation was carried out for 10 minutes in total; and washing once with EnVision FLEX WASH BUFFER was carried out. EnVision FLEX Hematoxylin was added and incubation was carried out for 5 minutes; and washing with EnVision FLEX WASH BUFFER and ion exchange water was carried out three times in total. 
       FIG. 35  shows a typical stained image. Rabbit chimeric antibody 1A3 showed satisfactory stainability to the subcutaneous tumor tissue of an animal administered with TROP2-ADC (I); whereas, rabbit chimeric antibody 1A3 did not show stainability to the subcutaneous tumor tissue of an animal administered with an anti-TROP2 Ab. 
     ii) Confirmation of Stainability Using Subcutaneously Transplanted Human-Derived Tumor after Administration GPR20-ADC (I) 
     To an immunodeficient mouse (nude mouse), GPR20 overexpressing human gastrointestinal stromal tumor cell line GIST-T1/GPR20 was subcutaneously transplanted. After GPR20-ADC (I) was administered, the tumor tissue was taken to prepare paraffin-embedded specimens. Then, stainability of rabbit chimeric antibody 1A3 was examined. The tumor tissue was taken from a mouse not administered with GPR20-ADC (I) and used as a negative control. Staining was carried out in the same manner as in i). 
       FIG. 36  shows a typical stained image. Rabbit chimeric antibody 1A3 showed satisfactory stainability to the subcutaneous tumor tissue of an animal administered with GPR20-ADC (I); whereas, rabbit chimeric antibody 1A3 did not show stainability to the subcutaneous tumor tissue of an animal not administered with an GPR20-ADC (I). 
     [Example 9] Immunostaining Using Mouse Antibody 1A3 
     i) Confirmation of Stainability Using Subcutaneously Transplanted Human-Derived Tumor after Administration of CDH6-ADC (I) 
     To a highly immunodeficient mouse (NOG mouse), a human tumor taken from a patient with clear cell renal cell carcinoma was subcutaneously transplanted. After CDH6-ADC (I) was administered, the tumor tissue was taken to prepare paraffin-embedded specimens. Then, stainability of mouse antibody 1A3 was examined. The tumor tissue was taken from an NOG mouse to which CDH6-ADC (I) was not administered and used as a negative control. Deparaffinization and antigen activation were carried out using Autostainer Link pretreatment system (PT Link, manufactured by DAKO) and an antigen retrieval solution (Target Retrieval Solution Low pH, manufactured by DAKO) at 97° C. for 40 minutes. The following staining operation was carried out using an automatic staining device (Dako Autostainer Link 48: manufactured by DAKO) at room temperature. After washing once with EnVision FLEX WASH BUFFER (manufactured by DAKO), Peroxidase Block 3% H 2 O 2  (manufactured by DAKO) was added; incubation was carried out for 5 minutes; and washing was carried out once with EnVision FLEX WASH BUFFER. Protein Block serum free (manufactured by DAKO) was added; incubation was carried out for 30 minutes; and liquid was removed by air blow. Mouse antibody 1A3 was diluted with REAL Antibody Diluent (manufactured by DAKO) to fall in the range of 0.03 μg/mL to 0.3 μg/mL and reaction was made for 60 minutes. After washing three times with EnVision FLEX WASH BUFFER, EnVision+System-HRP Labelled Polymer Anti-Mouse #K4000 (manufactured by DAKO) was added; incubation was carried out for 30 minutes; and then, washing with EnVision FLEX WASH BUFFER was carried out twice. 
     DAKO Liquid DAB+Substrate Chromogen System was added and incubation was carried out for 10 minutes in total; and washing once with EnVision FLEX WASH BUFFER was carried out. EnVision FLEX Hematoxylin was added and incubation was carried out for 5 minutes; and washing with EnVision FLEX WASH BUFFER and ion exchange water was carried out three times in total. 
       FIG. 37  shows a typical stained image. Mouse antibody 1A3 showed satisfactory stainability to an animal administered with CDH6-ADC (I) and staining intensity increased with an increase of the concentration of mouse antibody 1A3. In contrast, mouse antibody 1A3 did not show stainability to the animal administered with CDH6-ADC (I). Note that, since the NOG mouse is defective in B cells, it is known that the background staining is not observed with mouse-derived endogenous IgG (Ito M, et al. Blood 100 (9): 3175-3182, 2002). 
     ii) Confirmation of Specificity of Mouse Antibody 1A3 
     After mouse antibody 1A3 was mixed with compound (2) or SN-38, the mixture was used for immunostaining. 
     Note that the compound (2) is a compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     SN-38 is a compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     The blending ratio of mouse antibody 1A3: compound (2): SN-38 was defined to be 0.1:0.04:0.03 based on the molecular weights. Staining was carried out in the same manner as in i). 
       FIG. 38  shows a typical stained image. The staining ability of mouse antibody 1A3 disappeared by mixing with the compound (2) but did not disappear by mixing with SN-38. From this, it was demonstrated that mouse antibody 1A3 specifically recognizes the compound (2) in the tissue. 
     [Example 10] Measurement of Concentration in Plasma in Non-Clinical Study 
     The method for measuring the concentration in plasma of GPR20-ADC (I) in a mouse was developed by Gyrolab xP workstation (GYROS PROTEIN Technologies). As a capture reagent, mouse antibody 1A3 was labeled with biotin by use of a labeling kit (ChromaLink Biotin Protein Labeling Kit, Solulink) was used and the concentration thereof was controlled to be 700 nM with a 0.1% PS20-containing PBS. Samples for a calibration curve were prepared by controlling the concentration of GPR20-ADC (I) to be 0, 5, 10, 20, 50, 100, 200, 500, 1000, 2000, 5000, 10000 ng/mL with the mouse plasma and diluted with Rexxip AN (GYROS PROTEIN Technologies) up to 10 fold. As a detection reagent, Mouse Anti-(Anti-GPR20 Ab) (herein, “(Anti-GPR20 Ab)” represents an antibody comprising a heavy chain consisting of amino acid sequence consisting of amino acid residues 20 to 472 of SEQ ID NO: 32 and a light chain consisting of amino acid sequence consisting of amino acid residues 21 to 234 of SEQ ID NO: 33) idiotype Ab (71C1) (IBL) was labeled by DyLight650 (registered trademark) labeling kit and put in use, and the concentration thereof was controlled with Rexxip F (GYROS PROTEIN Technologies) to be 10 nM. These reagents and samples for a calibration curve were added to 96-well PCR plates and set at Gyrolab xP workstation. Using Bioaffy200, wizard was measured by 200-3W-002-A (PMT1). Regression analysis was carried out by use of Gyrolab Evaluator 3.3.9.175 in 4-parametric logistic model (weight: Response). The calibration curve is shown in  FIG. 39 . 
     [Example 11] Measurement of Plasma-Concentration in Non-Clinical Study 
     The method for measuring the concentration in plasma of HER2-ADC (I) in a human was developed by using ECL. A High Bind plate (Meso Scale Diagnostics, LLC: MSD) was coated with mouse antibody 1A3 and then washed. After blocking was made with a blocking buffer (BSA and PS20-contining PBS), HER2-ADC (I) was controlled in concentration to be 0, 200, 400, 800, 1600, 3200, 6400, 12800, 20000 and 25600 ng/mL, diluted 1000 fold with an assay diluent and used as samples for a calibration curve. The Biotinylated Mouse Anti-(Anti-HER2) idiotype Ab (13C1) (IBL) labeled with biotin by EZ-Link Sulfo-NHS-LC-LC Biotin (Thermo Fisher Scientific Inc.) and sulfo-tag streptavidin (MSD) were pre-incubated to prepare a detection solution. To the plate, to which the samples for a calibration curve were added, incubated and washed, the detection solution was added, to form a complex. Then, 4×Read Buffer T (MSD) was diluted double with purified water and added to the plate washed. Measurement was made by MSD SECTOR Imager 6000 (control software: MSD Discovery Workbench Version 3.0.18). The regression analysis was made by 4-parametric logistic model (weight: 1/Response 2 ). The calibration curve is shown in  FIG. 40 . 
     [Example 12] Confirmation of Chemical Structure to be Recognized by Mouse Antibody 1A3 
     The chemical structure to be recognized by mouse antibody 1A3 was checked by competitive inhibition with HER2-ADC (I) using Gyrolab xP workstation (GYROS PROTEIN Technologies). As the compound for use in competitive inhibition, compound (1), compound (2), compound (7), compound (8), compound (9), compound (10), compound (11), Topotecan and Rubitecan were selected. 
     Note that, the compound (1) is a compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     The compound (2) is a compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     The compound (7) is a compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     The compound (8) is a compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     The compound (9) is a compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     (Sugimori M. et al., J Med. Chem. 1994, 3033-3039). 
     The compound (10) is a compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     (U.S. Pat. No. 5,834,476). 
     The compound (11) is a compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     (Atsumi R. et al., Arzneimittel-Forschung 2001, 253-257). 
     Topotecan is a compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     Rubitecan is a compound represented by the following formula: 
     
       
         
         
             
             
         
       
     
     As the capture reagent, mouse antibody 1A3 labeled with biotin by a labeling kit (ChromaLink Biotin Protein LABELING Kit, Solulink) was used. The concentration thereof was controlled to be 700 nM with 0.1% PS20-containing PBS. The compounds for use in competitive inhibition, compound (1), compound (2), compound (7), compound (8), compound (9), compound (10), compound (11), Topotecan and Rubitecan were separately dissolved in DMSO. The solutions each was diluted with 10% or 20% DMSO in Rexxip HN (GYROS PROTEIN Technologies) to prepare 0, 1 and 100 μg/mL dilution solutions. To each of them, the 700 nM mouse antibody 1A3 solution was added in an equal amount. The mixture was stirred and allowed to react at room temperature in a dark place for one hour or more. The concentration of HER2-ADC (I) was controlled with Rexxip HN to be 0, 0.244, 0.977, 3.91, 15.6, 62.5, 250 and 1000 ng/mL. As the detection reagent, Mouse Anti-(Anti-HER2 Ab) idiotype Ab (13C1) (IBL) was labeled by DyLight650 (registered trademark) labeling kit and put in use. The concentration thereof was controlled with Rexxip F (GYROS PROTEIN Technologies) to be 10 nM. The above solution was set at Gyrolab xP workstation and measurement was carried out by use of Gyrolab Bioaffy 200 at 200-3W-002-A (PMT5). The regression analysis was carried out by use of Gyrolab Evaluator 3.4.0.24 in 4-parametric logistic model (weight: Response). The calibration curve of HER2-ADC (I) was prepared per concentration of the competitive inhibition compound. The inhibition rate (%) was calculated by comparing the response at an HER2-ADC (I) concentration of 250 ng/mL to that of the case where no compound was added (concentration 0 ng/mL). 
     The graph showing the inhibition rate is shown in  FIG. 41 . Compound (1), compound (2), compound (7) and compound (9) exhibited strong competitive inhibition. In contrast, compound (8), compound (10), compound (11), Topotecan, and Rubitecan did not exhibit competitive inhibition. From the result, it was demonstrated that mouse antibody 1A3 specifically recognizes a chemical structure having the basic skeleton of the compound (1) and a methyl group at position 4. 
     [Sequence Listing Free Text] 
     SEQ ID NO: 1—CDRH1 
     SEQ ID NO: 2—CDRH2 
     SEQ ID NO: 3—CDRH3 
     SEQ ID NO: 4—CDRL1 
     SEQ ID NO: 5—CDRL2 
     SEQ ID NO: 6—CDRL3 
     SEQ ID NO: 7—CDRH1 
     SEQ ID NO: 8—CDRH2 
     SEQ ID NO: 9—CDRH1 
     SEQ ID NO: 10—CDRH2 
     SEQ ID NO: 11—CDRH1 
     SEQ ID NO: 12—CDRH2 
     SEQ ID NO: 13—CDRH3 
     SEQ ID NO: 14—CDRL1 
     SEQ ID NO: 15—Amino acid sequence of a heavy chain of mouse antibody 1A3 
     SEQ ID NO: 16—Amino acid sequence of a light chain of mouse antibody 1A3 
     SEQ ID NO: 17—Nucleotide sequence encoding the amino acid sequence of a heavy chain variable region of mouse antibody 1A3. 
     SEQ ID NO: 18—Nucleotide sequence encoding the amino acid sequence of a light chain variable region of mouse antibody 1A3 
     SEQ ID NO: 19—Amino acid sequence of a heavy chain of rabbit chimeric antibody 1A3 
     SEQ ID NO: 20—Amino acid sequence of a light chain of rabbit chimeric antibody 1A3 
     SEQ ID NO: 21—Amino acid sequence of a heavy chain of the anti-HER2 antibody 
     SEQ ID NO: 22—Amino acid sequence of a light chain of the anti-HER2 antibody 
     SEQ ID NO: 23—Amino acid sequence of a heavy chain of the anti-HER3 antibody 
     SEQ ID NO: 24—Amino acid sequence of a light chain of the anti-HER3 antibody 
     SEQ ID NO: 25—Amino acid sequence of a heavy chain of the anti-TROP2 antibody 
     SEQ ID NO: 26—Amino acid sequence of a light chain of the anti-TROP2 antibody 
     SEQ ID NO: 27—Amino acid sequence of a heavy chain of the anti-B7-H3 antibody 
     SEQ ID NO: 28—Amino acid sequence of a light chain of the Anti-B7-H3 antibody 
     SEQ ID NO: 29—Nucleotide sequence encoding the amino acid sequences of a human light chain signal sequence and a human κ chain constant region. 
     SEQ ID NO: 30—Nucleotide sequence encoding the amino acid sequence of a heavy chain of rabbit chimeric antibody 1A3. 
     SEQ ID NO: 31—Nucleotide sequence encoding the amino acid sequence of a light chain of rabbit chimeric antibody 1A3. 
     SEQ ID NO: 32—Amino acid sequence of a heavy chain of the anti-GPR20 antibody 
     SEQ ID NO: 33—Amino acid sequence of a light chain of the anti-GPR20 antibody 
     SEQ ID NO: 34—Amino acid sequence of a heavy chain of the anti-CDH6 antibody 
     SEQ ID NO: 35—Amino acid sequence of a light chain of the anti-CDH6 antibody