Abstract:
The present invention relates to an aptamer comprising a nucleic acid comprising, or consisting of: the sequence ACUGU CCCAG UAUGA CGCGA CUGCU UAGGU GGGAU GUUUC CCAUG CCUCG (SEQ ID NO: 1), or a sequence comprising, or consisting of, at least 25 consecutive nucleotides in a sequence having at least 80% identity with SEQ ID NO: 1, with the proviso that a nucleic acid consisting of this sequence binds to the LAR protein.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an LAR protein-specific ligand, and also to the diagnostic and therapeutic use thereof, or the use thereof for the in vitro detection of the LAR protein in a biological sample. 
       TECHNICAL BACKGROUND 
       [0002]    Leukocyte common Antigen-Related Protein Tyrosine Phosphatase, PTP-LAR, or LAR protein, also known as protein tyrosine phosphatase, receptor type, F, PTPRF, plays an important role in mammary gland development (Schaapveld et al. (1997)  Dev. Biol.  188: 134-146) and in breast cancer tumorigenesis (Freiss et al. (2004)  Critical Reviews in Oncology/Hematology.  52: 9-17). It has been demonstrated, inter alia, that the expression of the LAR protein is increased in breast cancer cells, in particular breast cancer cells transformed with the ErbB-2 oncogene (Yang et al. (1999)  Mol. Carcinog.  25: 139-149; LeVea et al. (2000)  Breast Cancer Research and Treatment  64: 221-228). Furthermore, it would appear that the LAR protein is important for regulating the activity of several tyrosine kinase receptors (Kulas et al. (1996)  J Biol Chem  271: 748-754). The LAR protein can also serve as a biomarker for predicting the response to anti-EGFR treatments for breast cancer (WO 2009/021684). 
         [0003]    In addition, this protein is a known inhibitor of insulin activation pathways and an increased level of expression of this protein has been found in the insulin-sensitive tissues of obese individuals and insulin-resistant individuals (Ahmad et al. (1995)  J Clin Invest  95: 2806-2812). Thus, it has been demonstrated that the LAR protein can contribute to pathological conditions associated with insulin resistance, such as coronary artery disease in patients suffering from type 2 diabetes (Menzaghi et al. (2008)  J Intern Med  263: 653-654). 
         [0004]    The LAR protein ligands identified to date, essentially of immunoglobulin type, have limitations, in particular in terms of synthesis cost, immunogenicity or affinity for their target. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention follows from the unexpected demonstration, by the inventors, of an aptamer, of nucleotide nature, which specifically recognizes the LAR protein at the surface of cells, with a nanomolar dissociation constant. 
         [0006]    Thus, the present invention relates to an aptamer comprising a nucleic acid capable of specifically recognizing the LAR protein at the surface of a cell. 
         [0007]    More particularly, the invention relates to an aptamer comprising, or consisting of, a nucleic acid comprising, or consisting of:
       the sequence ACUGUCCCAGUAUGACGCGACUGCUUAGGUGGGAUGUUUCCCAUGCCUCG (SEQ ID NO: 1), or   a sequence comprising, or consisting of, at least 15 consecutive nucleotides of a polynucleotide having at least 60% identity with SEQ ID NO: 1, with the proviso that a nucleic acid consisting of this sequence binds to the LAR protein.       
 
         [0010]    In one particular embodiment, the invention relates to the aptamer according to the invention, for use thereof as a medicament or a diagnostic agent. 
         [0011]    The present invention also relates to a pharmaceutical or diagnostic composition comprising, as active substance, at least one aptamer according to the invention, in association with at least one pharmaceutically acceptable vehicle. 
         [0012]    In this respect, the invention also relates to an in vitro method for diagnosis of a cancer in an individual, comprising the following steps:
       bringing the biological sample into contact with an aptamer according to the invention;   determining the amount of aptamer bound in the sample;   optionally, comparing the amount of aptamer bound in the sample with at least one predetermined value;   deducing therefrom whether the individual is suffering from a cancer.       
 
         [0017]    The present invention also relates to a method for diagnosis of a cancer in an individual, comprising the following steps:
       administering an aptamer according to the invention to the individual;   detecting, quantifying and/or localizing the aptamer in the individual or a part of the individual;   deducing therefrom whether the individual is suffering from a cancer.       
 
         [0021]    The present invention also relates to the in vitro use of an aptamer according to the invention, for detecting the presence of LAR protein, or determining the amount of LAR protein, present in a biological sample. 
         [0022]    The present invention also relates to an in vitro method for detecting or determining the amount of LAR protein in a biological sample, comprising the following steps:
       bringing the biological sample into contact with an aptamer according to the invention;   quantifying or detecting the presence or absence of aptamer bound in the sample;   deducing therefrom the amount or the presence or absence of LAR protein in the sample.       
 
         [0026]    The present invention also relates to a method for detecting, quantifying or localizing LAR protein, in an individual or a part of an individual, comprising the following steps:
       administering an aptamer or a diagnostic composition as defined above to the individual;   detecting, quantifying and/or localizing the aptamer in the individual or a part of the individual;   deducing therefrom the presence or absence, the amount and/or the localization of LAR protein in the individual or the part of the individual.       
 
         [0030]    The present invention also relates to the use of an aptamer as defined above, for screening for LAR protein ligands. 
         [0031]    The present invention also relates to a method for screening for LAR protein ligands comprising the following steps:
       bringing together LAR protein and, concomitantly or successively, a ligand to be screened and an aptamer as defined above;   determining the amount of aptamer bound to the LAR protein;   deducing therefrom whether the ligand is an LAR protein ligand.       
 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    As is intended herein, an “aptamer” denotes a compound, comprising at least one nucleic acid, capable of binding specifically to a target, in particular of a protein nature, by means of the nucleic acid. An aptamer is said to bind specifically to a target when it exhibits essentially no affinity for a compound which is structurally unrelated to the target. Preferably, in the case of a protein target, a protein compound is said to be structurally unrelated to the target according to the invention when the sequence identity between the target and the compound is less than 60%, preferably less than 70% and more preferably less than 80%. Preferably, according to the invention, an aptamer is said to exhibit essentially no affinity for a compound according to the invention, in particular when the dissociation constant of the aptamer with respect to the compound is greater than 10 −6  mol/l and preferably greater than 10 −7  mol/l. The dissociation constant can in particular be determined, under standard conditions, using the Scatchard and Lineweaver Burk representations well known to those skilled in the art. 
         [0036]    Advantageously, the aptamer according to the invention is specific for the LAR protein, in particular for the human LAR protein, especially when the LAR protein is expressed at the surface of a cell. The LAR protein, or leucocyte common antigen-related protein tyrosine phosphatase, PTP-LAR, also known as protein tyrosine phosphatase, receptor type, F, PTPRF, is well known to those skilled in the art. The human LAR protein is in particular described under reference P10586 in the GenBank database. By way of example, the human LAR protein is represented by the sequence SEQ ID NO: 3. 
         [0037]    The aptamer according to the invention can also comprise at least one additional group in addition to the nucleic acid. Thus, the nucleic acid according to the invention can be bonded to at least one additional group. However, preferentially, the aptamer according to the invention consists of the nucleic acid according to the invention and of at least one additional group according to the invention. 
         [0038]    The additional group according to the invention can be of any type and of any nature. The additional group according to the invention can thus be a radioisotope, an organic molecule comprising at most 100 carbon atoms, a nanoparticle, in particular a micelle, a protein, in particular a glycoprotein, a carbohydrate, a lipid, or else a polynucleotide. According to the invention, it is, however, preferred for the additional group according to the invention to be selected from the group consisting of a detectable label, a pharmacological compound, and a compound capable of modifying the pharmacokinetic characteristics of a nucleic acid to which it is bonded, such as polyethylene glycol (PEG). 
         [0039]    The detectable label according to the invention can be of any type; it can in particular be a fluorophore, for example fluorescein or luciferase; a radioisotope, in particular suitable for scintigraphy, for example  99m Tc; an antibody-recognizable tag, for example the c-Myc protein; an affinity tag, for example biotin; or an enzyme, for example horseradish peroxidase. 
         [0040]    The pharmacological compound according to the invention can also be of any type; it is in particular an anticancer chemotherapy agent, such as a cytostatic or cytolytic agent. The pharmacological compound according to the invention can also be of any nature; it can in particular be a platinum derivative, an organic molecule comprising less than 100 carbon atoms, a peptide, a nucleotide analog, a toxin, an interfering RNA or an antisense oligonucleotide. 
         [0041]    Preferably, the nucleic acid according to the invention is RNA. As will become clearly apparent to those skilled in the art, it is quite particularly preferable for the nucleic acid according to the invention to be single-stranded. It is also quite particularly preferable for the nucleic acid according to the invention to have a three-dimensional structure which allows it to bind specifically to the LAR protein. Moreover, the backbone or the ribose of the nucleic acid according to the invention can be totally or partially modified, especially so as to make it resistant to hydrolytic degradation, in particular due to the action of nuclease, especially when the nucleic acid is RNA. Such modifications are well known to those skilled in the art and cover, in particular, modifications of the OH function on the carbon in the 2′ position of the ribose by methylation, or the substitution of this OH function with an amino group or with a halogen, in particular with fluorine, and also recourse to a phosphorothioate backbone, or to structures of locked nucleic acid (LNA) or peptide nucleic acid (PNA) type. Thus, preferably, the nucleic acid according to the invention is an RNA in which the riboses of the pyrimidine nucleotides bear a fluorine atom on the carbon in the 2′ position, it being possible for the riboses of the purine nucleotides to be unchanged. 
         [0042]    A sequence having at least 60% nucleotide identity with SEQ ID NO: 1 according to the invention differs in particular from SEQ ID NO: 1 by virtue of the insertion, the deletion or the substitution of at least one nucleotide. As it is intended herein, the percentage identity between two sequences is defined as the number of positions for which the bases are identical when the sequences are optimally aligned, divided by the total number of bases of the larger of the two sequences. Two sequences are said to be optimally aligned when the percentage identity is at a maximum. Moreover, as will become clearly apparent to those skilled in the art, it may be necessary to call upon additions of gaps so as to obtain an optimal alignment between the two sequences. 
         [0043]    A nucleic acid is said to bind to the LAR protein if the dissociation constant of the nucleic acid with respect to the LAR protein, in particular the human LAR protein, preferably expressed by a cell, in particular a cell of the MCF-7, A-431, MDA-MB-231, HEK293, HEK293-KDR, 4T1 or EMT6 cell line, as is illustrated in the examples, is less than 10 −6  mol/l, preferably less than 10 −7  mol/l and more preferably less than 10 −8  mol/l. 
         [0044]    As will be clearly apparent to those skilled in the art, when the aptamer according to the invention comprises a nucleic acid according to the invention, it can also comprise other nucleic acids. On the other hand, when the aptamer according to the invention consists of the nucleic acid according to the invention it does not comprise other nucleic acids. Similarly, when the nucleic acid according to the invention comprises a sequence, it can also comprise additional sequences extending from the 5′ and/or 3′ side of the sequence in question. On the other hand, when the nucleic acid according to the invention consists of a sequence, it does not comprise additional sequences in addition to the sequence in question. 
         [0045]    A sequence comprising SEQ ID NO: 1 according to the invention can in particular comprise sequences on the 5′ and/or 3′ side aimed at structuring the nucleic acid. It is thus preferred for the nucleic acid according to the invention to comprise, or to consist of, SEQ ID NO: 2. In this context, the invention then also relates, in particular, to a nucleic acid comprising, or consisting of, at least 15 consecutive nucleotides of a sequence having at least 60% identity with SEQ ID NO: 2, with the proviso that a nucleic acid consisting of this sequences binds to the LAR protein. 
         [0046]    Preferably, the sequence comprising, or consisting of, at least 15 consecutive nucleotides of a sequence having at least 60% identity with SEQ ID NO: 1 or 2 according to the invention comprises or consists of at least 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44 or 45 consecutive nucleotides, or all the consecutive nucleotides, of a sequence having at least 60% identity with SEQ ID NO: 1 or 2. 
         [0047]    Likewise preferably, the sequence comprising, or consisting of, at least 15 consecutive nucleotides of a sequence having at least 60% identity with SEQ ID NO: 1 or 2 according to the invention comprises or consists of at least 15 consecutive nucleotides of a sequence having at least 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% identity with SEQ ID NO: 1 or 2 according to the invention. 
         [0048]    More preferably, the sequence comprising, or consisting of, at least 15 consecutive nucleotides of a sequence having at least 60% identity with SEQ ID NO: 1 or 2 according to the invention comprises or consists of at least 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44 or 45 consecutive nucleotides, or all the consecutive nucleotides, of a sequence having at least 80% identity with SEQ ID NO: 1 or 2. 
         [0049]    Preferably still, the sequence comprising, or consisting of, at least 15 consecutive nucleotides of a sequence having at least 60% identity with SEQ ID NO: 1 or 2 according to the invention comprises or consists of at least 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44 or 45 consecutive nucleotides, or all the consecutive nucleotides, of a sequence having at least 85% identity with SEQ ID NO: 1 or 2. 
         [0050]    Even more preferably, the sequence comprising, or consisting of, at least 15 consecutive nucleotides of a sequence having at least 60% identity with SEQ ID NO: 1 or 2 according to the invention comprises or consists of at least 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44 or 45 consecutive nucleotides, or all the consecutive nucleotides, of a sequence having at least 90% identity with SEQ ID NO: 1 or 2. 
         [0051]    Particularly preferably, the sequence comprising, or consisting of, at least 15 consecutive nucleotides of a sequence having at least 60% identity with SEQ ID NO: 1 or 2 according to the invention comprises or consists of at least 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44 or 45 consecutive nucleotides, or all the consecutive nucleotides, of a sequence having at least 95% identity with SEQ ID NO: 1 or 2. 
         [0052]    Moreover, alternatively, the sequence comprising, or consisting of, at least 15 consecutive nucleotides of a sequence having at least 60% identity with SEQ ID NO: 1 or 2 according to the invention can consist of a sequence of 95 nucleotides having at least 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95% identity with SEQ ID NO: 2, and a nucleic acid consisting of this sequence is capable of adopting the structure of formula (I) below: 
         [0000]    
       
                 
         
             
             
         
       
       
                 
         
             
             
         
       
     
         [0000]    in which:
       A, C, G and U are the ribonucleotides adenosine, cytidine, guanosine and uridine;   each one of the X and of the Y, which may be identical or different, represents A, C, G or U;   each of the pairs X-Y or Y-X, which may be identical or different, represent A-U, U-A, G-C, C-G, G-U or U-G pairs.       
 
         [0056]    Those skilled in the art can easily determine the secondary structure capable of being adopted by a nucleic acid having a sequence according to the invention, for example by means of modeling algorithms or software well known to those skilled in the art, such as mfold (version 3.4) described in  Nucleic Acids Res . (2003) 31: 3406-15 and vsfold5 RNA Pseudoknot Prediction described in  PLoS One  (2007), 2:905. In this respect, the inventors have established, by means of such modeling tools, that the V8 aptamer of sequence SEQ ID NO: 2, which is described in the examples, adopts a structure of formula (I). 
         [0057]    When the aptamer according to the invention is used as a medicament or is included in a pharmaceutical composition, it is in particular useful for inhibiting angiogenesis, and also for the prevention or treatment, in particular by inhibiting angiogenesis, of cancers, and of diseases involving ocular neovascularization, such as age-related macular degeneration and diabetic retinopathy. Moreover, when it is used as a medicament or is included in a pharmaceutical composition, the aptamer according to the invention is also useful for the treatment of metabolic diseases, in particular insulin resistance, diabetes, especially type 2 diabetes, metabolic syndrome or cardiovascular diseases, such as coronary artery disease, in particular in patients suffering from type 2 diabetes. 
         [0058]    When the aptamer according to the invention is used as a diagnostic agent or is included in a diagnostic composition, it is in particular useful for the diagnosis of cancers or of metabolic diseases, such as insulin resistance. 
         [0059]    Preferably, in the methods for detection or diagnosis according to the invention, the detection of aptamer bound in the sample is carried out by performing a polymerase chain reaction (PCR) intended to amplify the aptamer, in particular an RT-PCR (PCR comprising a reverse transcription step). Preferably, when the nucleic acid according to the invention comprises SEQ ID NO: 2, the PCR is performed using the pair of primers of sequences CTTGTCATCAACCTGCCAGCCAGT (SEQ ID NO: 4) and GGGAGATGCTCTGTCAGACTACG (SEQ ID NO: 5) or the pair of primers having the sequences complementary to SEQ ID NO: 4 and SEQ ID NO: 5. Moreover, the invention also relates to a nucleic acid comprising or consisting of SEQ ID NO: 4 or SEQ ID NO: 5 or the sequences complementary to SEQ ID NO: 4 or SEQ ID NO: 5. 
         [0060]    Likewise preferably, in the methods for detection or diagnosis according to the invention, when the aptamer is administered to an individual, it is preferred for the aptamer to be detectable by means of in vivo imaging methods, which are in particular external, such as planar or three-dimensional (3D) fluorescent imaging, or internal, such as endoscopy, for example. 
         [0061]    Moreover, the present invention also relates to an LAR protein ligand for use thereof as an angiogenesis inhibitor, and also for the prevention or treatment, in particular by inhibiting angiogenesis, of cancers, and of diseases involving ocular neovascularization, such as age-related macular degeneration and diabetic retinopathy. The LAR protein ligand according to the invention can be of any type; it can in particular be an antibody or an antibody fragment comprising the antigen-binding part or paratope, a single-chain Fv (scFv) fragment, or else an aptamer, in particular, as has been indicated above, an aptamer according to the invention. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0062]      FIG. 1 : selection protocol diagram 
           [0063]      FIG. 1  represents the protocol for the selection of the aptamers used by the inventors in order to obtain the V8 aptamer. 
           [0064]      FIG. 2 : V8 aptamer structure prediction 
           [0065]      FIG. 2  represents the secondary structure of the V8 aptamer predicted using the mfold program (version 3.4, http://mfold.bioinfo.rpi.edu/cgi-bin/rna-form1.cgi). On this structure, the fixed sequences which enable a PCR amplification have been highlighted in gray. 
           [0066]      FIG. 3 : protocol for identifying the target of the V8 aptamer 
           [0067]      FIG. 3  represents the protocol for identifying the target of the V8 aptamer. Briefly, the biotinylated aptamer is incubated on MCF-7 cells in suspension. After several washes, streptavidin-coupled magnetic beads are added. Only the cells which have bound the biotinylated V8 aptamer will be retained on the beads. The cells are then lysed and the proteins retained by the V8 aptamer are eluted. The proteins are then loaded on an SDS-PAGE gel and the specific bands are analyzed by mass spectrometry. 
           [0068]      FIG. 4 : protein migration by SDS-PAGE electrophoresis 
           [0069]      FIG. 4  is a photograph of an SDS-PAGE gel on which the eluates originating from beads brought directly into contact with the cells (beads), a control oligonucleotide (control sequence) or the V8 aptamer are migrated. The main band corresponding to the eluate originating from the aptamer is indicated. The band corresponding to bovine serum albumin (BSA), used as a nonspecific competitor, is also represented. Briefly, the proteins are loaded onto an SDS 10%-PAGE gel. The gel is then stained using the proteosilver silver stain kit (Sigma). The interesting bands are cut out, destained with the same kit and analyzed by mass spectrometry. 
           [0070]      FIG. 5 : UV-bridging of the V1, V8 and V10 aptamers 
           [0071]      FIG. 5  is an autoradiograph of an SDS 10%-PAGE gel on which are migrated cell lysates of HEK293-KDR cells placed in the presence of the V1, V8 and V10 aptamers or the naïve library (NL) radiolabeled and bridged by UV irradiation. The aptamer alone, for its part, migrates at around 37 kDa (Apta lane). The arrow indicates the main protein bridged by the V8 aptamer, the size of which corresponds to that of the LAR protein. Briefly, the aptamers and the naïve library were incubated on the cells at a concentration of 25 nM. After 15 minutes of incubation at 37° C., the sequences not associated with the cells were eliminated. The UV-bridging was carried out with an irradiation energy of 800 000 μJ/cm 2 , and the cells were then lysed and the proteins were loaded on a 10% gel. 
           [0072]      FIG. 6 : effect of the overexpression of the LAR protein on the binding of the V8 aptamer 
           [0073]      FIG. 6  represents the amount of V8 aptamers bound per well (y-axis, pmol) containing untransfected HEK293 cells (O), untransfected HEK293 cells placed in the presence of lipofectamine (0(+lipo)), or HEK293 cells transfected with 0.25 μg, 0.5 μg, 0.75 μg or 1 μg of plasmid expressing the LAR protein (x-axis). The radiolabeled aptamer is incubated at a concentration of 10 nM for 15 minutes. After several washes, the radioactivity bound to the cells is counted and the amount of aptamers bound is determined (in pmol/well). 
           [0074]      FIG. 7 : effect of the overexpression of the LAR protein on the binding of the V8 aptamer 
           [0075]      FIG. 7  represents the amount of V8 aptamers bound per well (y-axis, pmol) containing untransfected HEK293 cells (0), untransfected HEK293 cells placed in the presence of lipofectamine (0) (+lipo)), or HEK293 cells transfected with a plasmid expressing the LAR protein, in the presence of 5 nM, 10 nM and 50 nM of V8 aptamer (x-axis). The radiolabeled aptamers are incubated for 15 minutes. After several washes, the radioactivity bound to the cells is counted and the amount of aptamers bound is determined (in pmol/well). 
           [0076]      FIGS. 8A and 8B : study of the binding of the V8 aptamer to MCF-7 and U87-MG cells by flow cytometry 
           [0077]      FIGS. 8A and 8B  represent the amount of MCF-7 cells ( FIG. 8A ) and U87-MG cells ( FIG. 8B ) sorted by flow cytometry (y-axis, as percentage of maximum fluorescence) as a function of the fluorescence emitted by the V8 aptamer (black curve), the control sequence (dark gray curve) and the cells alone (light gray curve) (x-axis, arbitrary units). The cells were incubated with the aptamers at a concentration of 5 nM for 30 minutes, washed and analyzed by FACS. 100 000 events were counted for each condition. 
           [0078]      FIG. 9 : biodistribution of the V8 aptamer and of a control sequence in “nude” mice having developed tumors after a xenograft of MCF-7 cells 
           [0079]      FIG. 9  represents images, acquired on a Tomofluo 3D instrument, of “nude” mice having developed tumors after a xenograft of MCF-7 cells, which were injected intravenously with 1.4 nmol of V8 aptamer (upper part of the figure, V8) or of control sequence (lower part of the figure, Ctrl) labeled with Alexa Fluor 680. The images were acquired between 5 and 180 minutes after injection. The tumor and the reference zone which makes it possible to measure the ratio of signal in the tumor/internal reference are indicated. 
           [0080]      FIG. 10 : percentage of the injected dose of V8 aptamer and of a control sequence present in tumors after xenograft of MCF-7 cells 
           [0081]    The V8 aptamer or a control sequence, which were labeled with Alexa Fluor 680, were injected into mice developing tumors following a subcutaneous injection of MCF-7 cells. Three hours post-injection, the fluorescent signal in the tumor was measured by fluorescent tomography using a TomoFluo 3D instrument.  FIG. 10  represents the amount of fluorescence determined in triplicate as a percentage of the dose injected (% DI, y-axis) in the tumor for the V8 aptamer and a control sequence. 
           [0082]      FIG. 11 : effect of the V8 aptamer on the formation of endothelial tubes by HUVECs 
           [0083]    HUVEC cells were cultured in the presence or absence of 5 μM V8 aptamer or of control sequence. After 16 hours of incubation at 37° C. and 5% CO 2 , the tube formation was evaluated by phase contrast microscopy. The ratio between the number of tubes and the number of nodes visualized per field of view was calculated.  FIG. 11  represents the number of tubes per node of cells on four randomly chosen fields of view (y-axis), in the absence of oligonucleotide (control), in the presence of a control sequence, and in the presence of the V8 aptamer (x-axis). 
       
    
    
     EXAMPLES 
     Example 1 
     Obtaining the V8 Aptamer Specific for the LAR Protein 
       [0084]    1—Identification of the V8 Aptamer after 17 Rounds of Selection on HEK293-VEGFR2 Cells 
         [0085]    The inventors used the SELEX technique, in particular described in application WO 2005/093097, for the purpose of selecting aptamers against the VEGFR2 receptor (vascular endothelial growth factor receptor 2). For this, HEK293 cells overexpressing VEGFR2 and, for the counterselection, HEK293 cells not expressing VEGFR2, were used ( FIG. 1 ). 
         [0086]    During this SELEX, the inventors varied various parameters for the purpose of gradually increasing the selection pressure (table 1). Compared with the protocol described in application WO 2005/093097, the inventors introduced a few modifications: during a few rounds, the inventors changed cell type for the purpose of increasing the specificity. For these rounds, the inventors used porcine aortic endothelial (PAE) cells stably transfected so as to express VEGFR2 (PAE-VEGFR2) for the selection, and non-transfected porcine endothelial cells (PAE) for the counterselection (rounds 13 and 14). Furthermore, the inventors inverted the selection and counterselection step (rounds 16 and 17). Finally, throughout the selection process, VEGFR, which is the VEGFR2 receptor ligand, was added 10 minutes before the end of the incubation with the library, at each round of SELEX. This was for the purpose of selecting aptamers which are not detached by VEGF. The selection conditions are given in table 1 below: 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 evolution of the selection pressure during the SELEX 
               
             
          
           
               
                   
                   
                 CS: 
                 S: 
                   
                   
                   
                   
                   
                   
                   
               
               
                   
                   
                 Number 
                 Number 
                   
                   
                 [ ] of 
               
               
                   
                   
                 of 
                 of 
                   
                 Incubation 
                 2′F-Py 
                 Incubation 
                 Number 
                 Specific 
               
               
                   
                 Cell 
                 cells 
                 cells 
                 Inversion 
                 volume 
                 RNA 
                 time 
                 of 
                 washing 
               
               
                 Cycle 
                 type 
                 (million) 
                 (million) 
                 CS and S 
                 (ml) 
                 (μM) 
                 (min) 
                 washes 
                 condition 
                 tRNa 
               
               
                   
               
             
          
           
               
                 1 
                 HEK293 
                 10 
                 10 
                   
                 3 
                 1 
                 30 
                 3 
                   
                   
               
               
                 2 
                 HEK293 
                 10 
                 10 
                   
                 3 
                 1 
                 30 
                 3 
               
               
                 3 
                 HEK293 
                 10 + 10 
                 10 
                   
                 3 
                 1 
                 25 
                 3 
               
               
                 4 
                 HEK293 
                 5 + 5 
                 5 
                   
                 3 
                 1 
                 25 
                 4 
               
               
                 5 
                 HEK293 
                 5 + 5 
                 5 
                   
                 3 
                 1 
                 20 
                 4 
               
               
                 6 
                 HEK293 
                 5 + 5 
                 5 
                   
                 3 
                 1 
                 20 
                 5 
               
               
                 7 
                 HEK293 
                 5 + 5 
                 5 
                   
                 3 
                 1 
                 20 
                 5 
               
               
                 8 
                 HEK293 
                 5 + 5 
                 5 
                   
                 3 
                 1.5 
                 20 
                 5 
                 W5: 5 min 
               
               
                 9 
                 HEK293 
                 5 + 5 
                 5 
                   
                 3 
                 1.5 
                 20 
                 5 
                 W5: 5 min 
               
               
                 10 
                 HEK293 
                 5 + 5 
                 5 
                   
                 3 
                 1 
                 20 
                 5 
                 W5: 5 min 
               
               
                 11 
                 HEK293 
                 5 + 5 
                 5 
                   
                 3 
                 1.5 
                 20 
                 5 
                 W5: 5 min 
                 + 
               
               
                 12 
                 HEK293 
                 5 + 5 
                 5 
                   
                 3 
                 1 
                 20 
                 5 
                 W5: 5 min 
                 + 
               
               
                 13 
                 PAE 
                 5 + 5 
                 5 
                   
                 3 
                 2 
                 20 
                 5 
                 W5: 5 min 
                 + 
               
               
                 14 
                 PAE 
                 5 + 5 
                 5 
                   
                 3 
                 0.5 
                 20 
                 5 
                 W5: 5 min 
                 + 
               
               
                 15 
                 HEK293 
                 5 + 5 
                 5 
                   
                 3 
                 2 
                 20 
                 5 
                 W5: 5 min 
                 + 
               
               
                 16 
                 HEK293 
                  5 
                 5 
                 + 
                 3 
                 2 
                 20 
                 5 
                 W5: 5 min 
                 + 
               
               
                 17 
                 HEK293 
                  5 
                 5 
                 + 
                 3 
                 1.5 
                 20 
                 5 
                 W5: 5 min 
                 + 
               
               
                   
               
               
                 S: Selection, 
               
               
                 CS: Counterselection, 
               
               
                 W: Wash 
               
             
          
         
       
     
         [0087]    The library resulting from round 17 was cloned and sequenced. The inventors tested the affinity of about thirty sequences for the HEK293-VEGFR2 cells at 25 nM. This allowed them to identify three particularly interesting aptamers with a strong affinity for these cells, V1, V8 and V10. However, these aptamers also bind to HEK293 cells, which do not express the target, indicating that the target of these aptamers is not VEGFR2. The inventors then chose to continue the characterization of the V8 aptamer, which has the strongest affinity for the cells (Kd ˜5.3 nM). 
       2. Sequence of the V8 Aptamer: 
       [0088]    The sequence of the V8 aptamer is the following: 
         [0000]    
       
         
               
             
           
               
                 (SEQ ID NO: 2) 
               
               
                 5′ GGGAGAUGCUCUGUCAGACUACGACUGUCCCAGUAUGACGCGACU 
               
               
                   
               
               
                 GCUUAGGUGGGAUGUUUCCCAUGCCUCGACUGGCUGGCAGGUUGAUGA 
               
               
                   
               
               
                 CAAG3′. 
               
             
          
         
       
     
         [0089]    It should be noted that, in order to improve the nuclease resistance of the V8 aptamer, the riboses of the pyrimidines bear a fluorine atom on the carbon in the 2′ position (the riboses of the purines bear, for their part, as is the case in natural RNA, a hydroxyl function (OH) on the carbon in the 2′ position). 
         [0090]      FIG. 2  represents a secondary structure prediction formed using the mfold software (version 3.4) ( Nucleic Acids Res.  (2003) 31: 3406-15). 
       3. Validation of the Use of the V8 Aptamer for Establishing a Profile of Expression at the Surface of Various Cell Lines 
       [0091]    The affinity and the Cmaxof the V8 aptamer were determined for various cancer cell lines (table 2). 
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 affinity and number of targets per cell 
               
               
                 of the V8 aptamer for various cell lines 
               
             
          
           
               
                   
                   
                   
                   
                 Number of 
               
               
                 Species 
                 Cell type 
                 Kd (nm) 
                 Cmax (pM) 
                 targets/cell 
               
               
                   
               
               
                 Human 
                 MCF-7 
                 1.6 ± 0.6 
                 251 ± 40 
                  138 100 ± 21 800 
               
               
                   
                 A-431 
                 5.6 ± 0.6 
                 455 ± 21 
                 134 300 ± 6100  
               
               
                   
                 MDA- 
                     3 ± 0.4 
                 131 ± 12 
                 77 800 ± 7200 
               
               
                   
                 MB-231 
               
               
                   
                 U87-MG 
                 — 
                 — 
                 — 
               
               
                   
                 HEK293 
                 3.8 ± 0.9 
                 264 ± 52 
                     80 000 ± 15 600 
               
               
                   
                 HEK293- 
                 5.3 ± 1.5 
                 119 ± 6  
                 46 000 ± 2200 
               
               
                   
                 KDR 
               
               
                 Mouse 
                 4T1 
                 2.9 ± 0.1 
                 167 ± 13 
                 65 200 ± 4900 
               
               
                   
                 EMT6 
                 2.8 ± 0.6 
                 129 ± 24 
                 42 400 ± 8000 
               
               
                 Rat 
                 PC12- 
                 34.9 ± 4.4  
                  764 ± 112 
                  141 400 ± 20 800 
               
               
                   
                 MEN-2A 
               
               
                   
               
               
                 The binding curves were obtained for each cell type. From the specific binding, and using the Scatchard representation, the Kd and the Cmax were calculated for each cell type. Knowing the Cmax and the number of cells during the binding, the inventors were able to deduce therefrom an approximate number of targets per cell. 
               
             
          
         
       
     
         [0092]    The V8 aptamer has an affinity of approximately 3 nM for most of the cell lines, except for the PC12-MEN-2A cells for which it has an affinity of 35 nM and the U87-MG cells for which it has no affinity. Interestingly, the target of the V8 aptamer appears to be very abundant at the surface of the MCF-7 breast cancer line and at the surface of the A-431 epidermal cancer line overexpressing EGFR. 
       4. Identification of the Target of the V8 Aptamer 
       [0093]    a. Protocol for Purifying the Target of the Aptamer 
         [0094]    In order to identify the target of the V8 aptamer, a protocol derived from Berezovski et al. (2008)  J. Am. Chem. Soc., Aptamer - Facilitated Biomarker Discovery  (AptaBiD) was used, in which BSA was added as a competitor in order to prevent the nonspecific binding of proteins to the beads. The protocol is summarized in  FIG. 3 . 
         [0000]    b. SDS-PAGE Gel and Mass Spectrometry 
         [0095]    The proteins eluted at the end of the protocol summarized in  FIG. 3  were analyzed by electrophoresis ( FIG. 4 ). A V8 aptamer-specific band was identified. This band was cut out and analyzed by mass spectrometry. The peptides of about twenty proteins were detected in the gel fragment. Among them, one protein was identified as being liable to correspond to the target of the V8 aptamer. This protein was identified as being protein tyrosine phosphatase, receptor type, F (PTPRF) also known as leukocyte common antigen-related (LAR) protein. It is a membrane protein of 213 kDa. 
         [0000]    c. Validation of the Target of the V8 Aptamer 
         [0096]    In order to verify that the V8 aptamer interacts with the LAR protein, the inventors first of all carried out UV-bridging experiments. 
         [0097]    UV irradiation can induce the formation of covalent bonds at the level of points of contact that exist between a protein and a nucleic acid (Zhang et al. (2004)  Biochem Biophys Res Commun  322: 705-711). 
         [0098]    The V1, V8 and V10 aptamers, and also the naïve library, which were radiolabeled, were incubated for 15 minutes on the cells and then the cells were UV-irradiated. The proteins were then extracted and loaded on an SDS 10%-PAGE gel. Interestingly, the V8 aptamer was bridged to a protein of which the size corresponds to that of the LAR protein ( FIG. 5 ). 
         [0099]    A second validation was carried out using an expression plasmid for the longest isoform of the LAR protein. HEK293 cells were used to carry out the transfection by means of lipofectamine 2000 (Invitrogen). Several amounts of plasmid were transfected (0.25 μg-1 μg). 48 Hours later, 10 nM of radiolabeled V8 aptamer or of radiolabeled control sequence were incubated with the cells. After several washes, the radioactivity associated with the cells was counted. 
         [0100]    The V8 aptamer exhibits affinity for HEK293 cells (table 2 and  FIG. 6 ). However, the binding of the V8 aptamer is at least twice as great when these cells were transfected with the expression plasmid for the LAR protein. It is observed that the binding does not increase when the amount of plasmid transfected is increased, thereby indicating that 0.25 μg of plasmid is sufficient to have a maximum expression. 
         [0101]    When the cells were treated with lipofectamine without the addition of plasmid, the binding of the V8 aptamer is identical to that obtained with untreated cells, thereby indicating that the increase in the binding is indeed due to the expression of the plasmid and not due to the presence of the lipofectamine. 
         [0102]    In order to confirm this result, the experiment was reproduced, by transfecting 0.25 μg of plasmid and by testing various concentrations of V8 aptamer ( FIG. 7 ). 
         [0103]    As previously, an increase in the binding of the V8 aptamer is observed when the cells were transfected with the plasmid expressing the LAR protein. This increase in binding is visible regardless of the concentration of aptamer used. It is noted that, the higher the concentration of aptamers incubated, the greater the binding of the aptamer compared with the untransfected cells (5 times more binding at 50 nM compared with twice as much binding at 5 nM). 
         [0104]    All these results demonstrate that the target of the V8 aptamer must be the LAR protein. 
       Example 2 
     Use of the V8 Aptamer in FACS 
       [0105]    The V8 aptamer and the control sequence (SEQ ID NO: 6), labeled with AlexaFluor 647 (Invitrogen), were incubated with the MCF-7 cells and the U87-MG cells ( FIGS. 8A and 8B ). 
         [0106]    Whether on the MCF-7 cells or the U87-MG cells, it is observed that the control sequence does not bind to the cells since the fluorescence intensity is identical to that obtained for the cells alone. The V8 aptamer binds to the MCF-7 cells, but no increase in fluorescence is observed on the U87-MG cells. These results are in agreement with the binding experiments described above. 
       Example 3 
     Use of the V8 Aptamer in Imaging 
       [0107]    In order to evaluate whether the V8 aptamer can enable tumor targeting in vivo, the inventors carried out fluorescence imaging experiments in mice. For this, the inventors used an imaging instrument (TomoFluo3D, LETI, Grenoble, France). This instrument allows semi-quantitative measurements by planar imaging and quantitative measurements by tomography (Garofalakis et al. (2010)  Optics Letters  35: 3024-3026). These experiments were carried out with athymic “nude” mice. MCF-7 cells were used in order to carry out xenografts in these mice. From 2 weeks to 2 months after the subcutaneous injection of the cells at the top of the back, the xenografts obtained reach volumes of about one hundred mm 3 . Aptamer biodistribution experiments can then be carried out by optical imaging. 
         [0108]    The biodistribution of the V8 aptamer was compared with that of a control sequence in MCF-7 xenografts. For this, the sequences labeled with Alexa Fluor 680 (1.4 nmol) were injected into the mice in the caudal vein. The planar imaging was carried out between 1 minute and 3 hours after the injection and the three-dimensional imaging was carried out in the tumors at time 3 hours in order to be able to quantify the amount of aptamers having reached the tumor. 
       1. Planar Imaging 
       [0109]    Following the intravenous injection of the V8 aptamer or of the control sequence, images were taken at various times post-injection. For each sequence, 3 mice were injected.  FIG. 9  represents, respectively, the biodistributions of the V8 aptamer and of the control sequence in a mouse. 
         [0110]    As expected, the sequences are rapidly eliminated in the urine and by the hepatobiliary system. Moreover, using these images obtained, and for each of the mice, regions of interest (ROIs) were traced at the level of the tumor and at the level of the head between the two ears (reference zone) using the ImageJ software (MacBiophotonics). The mean fluorescence intensity was then calculated for each ROI. The background noise was subtracted (autofluorescence of the mouse, measured using a photograph taken before injection) and the ratio between the fluorescence in the tumor and the fluorescence in the head was calculated over time. The means of these ratios over time are indicated in table 3. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 ratio of the fluorescence intensity 
               
               
                 in the tumor/reference zone over time 
               
             
          
           
               
                   
                 Time (min) 
                 Control 
                 V8 
               
               
                   
                   
               
             
          
           
               
                   
                 5 
                 1.10 ± 0.12 
                 1.29 ± 0.12 
                 ns 
               
               
                   
                 10 
                 1.17 ± 0.10 
                 1.39 ± 0.09 
                 ns 
               
               
                   
                 15 
                 1.18 ± 0.04 
                 1.51 ± 0.04 
                 * 
               
               
                   
                 30 
                 1.32 ± 0.08 
                 1.66 ± 0.07 
                 * 
               
               
                   
                 60 
                 1.42 ± 0.09 
                 1.73 ± 0.09 
                 ns 
               
               
                   
                 90 
                 1.43 ± 0.18 
                 1.77 ± 0.18 
                 * 
               
               
                   
                 120 
                 1.52 ± 0.11 
                 2.01 ± 0.11 
                 ns 
               
               
                   
                 150 
                 1.54 ± 0.15 
                 1.80 ± 0.15 
                 ns 
               
               
                   
                 180 
                 1.57 ± 0.17 
                 2.25 ± 0.17 
                 ns 
               
               
                   
                   
               
               
                   
                 The results represent the mean of the tumor/reference zone fluorescence ratios obtained at various times for 3 mice. 
               
               
                   
                 * corresponds to a significant difference in the ratio between the aptamer and the control sequence measured using a Student&#39;s test with P &lt; 0.05. 
               
               
                   
                 ns: not significant. 
               
             
          
         
       
     
         [0111]    Interestingly, the tumor/reference zone ratio increases more rapidly for the V8 aptamer than for the control sequence and this significant difference is observed as early as 15 minutes after injection (1.51±0.04 for the V8 aptamer and 1.18±0.04 for the control sequence). After 15 minutes, the ratio gradually increases in a similar manner for the aptamer and the control sequence, and the difference between the aptamer and the control sequence then remains constant over time. 
       2. Three-Dimensional Imaging 
       [0112]    Three hours after the injection, the amount of aptamers accumulated in the tumors was quantified by tomography. After reconstruction, the fluorescence intensity is visualized in three dimensions in the tumors. 
         [0113]    Three hours after injection, the zones corresponding to the tumors were scanned using the Tomofluo3D instrument. After reconstruction using the Imo3D software, the fluorescence intensity was visualized in three dimensions. 
         [0114]    It thus appears that the fluorescence intensity is greater in the tumors originating from the mice injected with the V8 aptamer, compared with the mice injected with the control sequence. The accumulation in the tumors 3 hours after injection is therefore greater for the V8 aptamer, suggesting that this accumulation is specific, originating from the binding of the aptamer to its target, the LAR protein. 
         [0115]    Using the calibration curves produced by a positron emission tomography (PET)/fluorescence diffuse optical tomography (fDOT) combination, it is possible to quantify a probe labeled with Alexa Fluor 680 present at concentrations between 3 nM and 1 μM (Garofalakis et al. (2010)  Optics Letters  35: 3024-3026). The percentage of the dose injected (% DI) present in the tumors three hours after injection could therefore be determined in this way ( FIG. 10 ). 
         [0116]    Three hours after injection, 0.97±1.1% DI of V8 aptamer is present in the tumor, compared with 0.07±0.11% DI for the control sequence. The accumulation of the aptamer is therefore approximately 10 times greater than that of the control aptamer. It should be noted that the difference observed in three-dimensional imaging is greater than in planar imaging. 
       Example 4 
     Use of the V8 Aptamer for Inhibiting Angiogenesis 
       [0117]    The inventors tested whether the V8 aptamer could disturb the angiogenesis process by using an in vitro endothelial tube formation test. No role of the LAR protein is known at the current time in angiogenesis; nevertheless, it has been demonstrated that the LAR protein may be involved in the regulation of epithelial cell-cell contacts, and also in the control of the beta-catenin signaling pathways. 
         [0118]    Human umbilical vein endothelial cells (HUVECs) were cultured on Matrigel™ in a medium with a low growth hormone content comprising 2% of fetal calf serum and recombinant basic fibroblast growth factor (bFGF at 3 ng/mL) (Invitrogen). Under these conditions, HUVECs form a network of endothelial tubes which can be observed by microscopy and represents an in vitro model of angiogenesis. The effect of the V8 aptamer on the formation of this network was evaluated ( FIG. 11 ). 
         [0119]    It is observed that, after 16 hours of incubation, a network of tubes has formed for the control condition with an average of two tubes formed per node. The V8 aptamer inhibits the formation of tubes with an average of 0.72 tubes per node, whereas the control sequence has no effect, with an average of two tubes per node as for the control condition.