Patent Description:
The risk for cancers intrinsically increases with aging, and also varies or increases with hereditary factors, unmethodical life style, etc..

An increased number of cancer patients in an aging society causes a serious problem, in that it imposes burdens on the relevant patients and their families. As a result, medical expenses increase from a social aspect. Thus, establishment of means for preventing onset of cancer and an appropriate treatment method therefore remain critical issues.

In particular, determination of a hereditary factor therefor enables appropriate provision of preventive treatments such as early-stage lifestyle guidance. Therefore, such determination has been more and more important in recent years.

<CIT> relates to eukaryotic initiation factor 5A and the use of polynucleotides encoding the same to inhibit cancer cell growth and inhibit metastases.

Currently, a part of digestive system cancer such as esophageal cancer and colon cancer exhibit high prevalence, as compared with other cancers. Thus, there is demand for a gene marker having excellent diagnostic performance in order to thoroughly perform genetic tests for detecting digestive system cancer.

Under such circumstances, the present inventors have surprisingly found that a "deoxyhypusine synthase gene," which was previously reported to correlate with prostate cancer and cervical cancer, is highly responsive to digestive system cancer, whereby the gene can be used as a desired cancer marker.

Accordingly, the present invention provides a method for determining cancer, which method comprises detecting the level of anti-deoxyhypusine synthase (hereinafter may be abbreviated as DHPS) autoantibody in a blood specimen obtained from a human, and determining digestive system cancer on the basis of an increase in the level of anti-deoxyhypusine synthase autoantibody in said blood specimen compared to a standard anti-deoxyhypusine synthase autoantibody level of a digestive system cancer-free subject as an index in said human. Hereinafter, the method may be referred to also as the "cancer determination method of the present invention. " The test sample employed in the cancer determination method of the present invention is a blood specimen. The cancer determination method of the present invention may be defined as a data acquisition method which is characterized by comprising acquiring data regarding expression of a DHPS gene in a test sample and, when an increase in the gene expression is observed, using the data as data showing the presence of digestive system cancer.

The cancer determination method of the present disclosure is generally categorized into the following three modes (i.e., cancer determination methods <NUM> to <NUM>). These methods may be carried out by means of a kit.

In the cancer determination method, expression of a DHPS gene (i.e., a target gene) may be confirmed by detecting the entirety or a part of a DHPS protein encoded by the gene, as a target polypeptide. Particularly, the entirety or a part of a DHPS protein is preferably detected by use of an antibody which specifically binds to the protein, preferably a monoclonal antibody.

In the cancer determination method of the present invention, expression of the DHPS gene (a target gene) may be confirmed by detecting an antibody (an autoantibody) against DHPS present in a test sample (hereinafter, "antibody against DHPS" and "autoantibody against DHPS" may also be referred to as "DHPS antibody" or "anti-DHPS antibody" and "DHPS autoantibody" or "anti-DHPS autoantibody," respectively). The autoantibody may be detected by, for example, bringing the test sample into contact with an immobilized polypeptide including the entirety or a part of DHPS, and detecting, as a signal, a bond between the antibody (autoantibody) against DHPS present in the test sample and the immobilized polypeptide. The number of amino acid units of the polypeptide which is a part of DHPS included in the immobilized polypeptide may be <NUM>/<NUM> or more the number of amino acid units of the polypeptide which is the entirety of DHPS, specifically, <NUM> amino acid units or more, and is preferably <NUM> or more, more preferably <NUM> or more. On the premise that the antigenicity of the polypeptide is ensured, a polypeptide having a shorter length has a tendency to exhibit high peptide stability, and to lead higher sensitivity since the number of the immobilized polypeptides per a unit amount of a polypeptide-immobilized product may be increased.

In the cancer determination method, expression of the DHPS gene (a target gene) may be confirmed by detecting, as a target nucleic acid (hereinafter, the expression "nucleic acid" encompasses a fragment thereof), the entirety or a part of the DHPS gene, or a nucleic acid complementary to the entirety or a part of the DHPS gene, present in the test sample. The target nucleic acid may be detected by, for example, hybridizing a nucleic acid probe including a nucleic acid having a sequence complementary to the nucleotide sequence of the target nucleic acid with the immobilized or non-immobilized target nucleic acid, and detecting the signal attributed to the hybridization. In this case, the entirety or a part of the DHPS gene or a nucleic acid complementary to the entirety or a part of the gene may be amplified through a gene amplification method such as PCR, and the gene amplification product may be detected as a target nucleic acid.

The cancer determination method of the present invention may be carried out by means of a cancer detection kit having elements which enables the determination.

The present invention also provides a method for using a polypeptide-immobilized plate, the method comprising the following steps (a) to (d). The polypeptide-immobilized plate is used as "an immobilized polypeptide including the entirety or a part of DHPS" in the above cancer determination method <NUM>. The steps are:.

Similar to the case of the above cancer determination method <NUM>, the number of amino acid units of the polypeptide which is a part of DHPS immobilized on the plate is preferably <NUM>/<NUM> or more the number of amino acid units of the polypeptide which is the entirety of DHPS.

Examples of the plate (substrate) onto which the entirety or a part of DHPS is immobilized include a glass slide, a porous gel, and a micro-titer plate. The entirety or a part of DHPS may be immobilized onto the substrate through a known technique. Examples of the technique include antibody-binding techniques such as physical adsorption, covalent binding, ionic binding, and biochemically specific binding. Also, a substrate suited for the immobilization technique to be used may be employed. For example, a substrate having an amino-group-modified surface may be used in order to promote binding of protein on the substrate. In one specific mode, glutaraldehyde is bound to the amino groups on the substrate, and terminal amino groups or the like of the entirety or a part of DHPS is bound to the glutaraldehyde. In another mode, the entirety or a part of DHPS is immobilized onto the amino groups on the substrate through electrostatic interaction. Alternatively, a variety of commercially available substrates suited for immobilizing protein may also be employed.

The "deoxyhypusine synthase (DHPS)," which is a target component of the cancer determination method of the present invention, is a known enzyme protein which is known to be related to prostate cancer or cervical cancer (see Patent Document <NUM> and Non-Patent Document <NUM>) and to apoptosis (see Patent Document <NUM>). The amino acid sequence of a human DHPS is known to be represented by SEQ ID NO: <NUM> (Patent Document <NUM>), and the nucleotide sequence of the DHPS gene coding therefor is known to be represented by, for example, SEQ ID NO: <NUM>. Furthermore, antibodies (a monoclonal antibody and a polyclonal antibody) against DHPS are also known and may be produced through a conventional method. Commercial products thereof are available. The DHPS (also called DHPS protein) is a protein having an amino acid sequence represented by SEQ ID NO: <NUM>, or a protein having an amino acid sequence equivalent to SEQ ID NO: <NUM>, except that one or several amino acids are substituted, deleted, inserted, or added, and having substantially the same biological activity as that of the protein having an amino acid sequence represented by SEQ ID NO: <NUM>. The DHPS gene has a nucleotide sequence encoding the above DHPS.

As disclosed in Patent Document <NUM>, DHPS is an enzyme which activates eIF5A (eukaryotic translation Initiation Factor 5A) in the presence of spermidine, to form hypusine. The steric structure of DHPS includes an enzyme active site (i.e., a main structure), a chain structure, and a spherical structure, wherein the enzyme active site and the spherical structure are linked via the chain structure. Through a stearic structure analysis or the like, the enzyme active site and the spherical structure have been found to have a certain interaction, and the spherical structure is presumed to serve as a pseudo-substrate of the enzyme active site. Formation of hypusine is known to be an essential step in cytofunctions including cell proliferation. In other words, hypusine formation is a post-translation modification step intrinsic to eIF5A; i.e., NAD-dependent transformation of a butylamine moiety of spermidine into a ε-amino group of a specific lysine residue and subsequent hydroxylation. Thus, hypusine formation is essentially observed in the growth of a variety of living things ranging from yeasts to humans.

As described above, possible applications of DHPS particularly as a prostate cancer marker and a cervical cancer marker are known in the art. However, use of DHPS as a digestive system cancer marker has not been disclosed or suggested.

Examples of the digestive system cancer include esophageal cancer, stomach cancer, duodenum cancer, colorectal cancers (including rectal cancer and colon cancer), small intestine cancer, gallbladder cancer, pancreatic cancer, and liver cancer. Particularly, DHPS is a useful marker as esophageal cancer or a colorectal cancer.

According to the present disclosure, there can be provided digestive system cancer determination means, based on the expression of a deoxyhypusine synthase (DHPS) gene in a test sample.

As described above, the presence of DHPS is known in humans and other animals. The amino acid sequence of DPHS (SEQ ID NO: <NUM>, in the case of human) and the nucleotide sequence (e.g., SEQ ID NO: <NUM>) coding therefor are known.

Thus, a recombinant DHPS can be produced through a known method based on the known sequences. In one specific procedure, a nucleic acid-amplification primer for amplifying a double-strand DNA having the entirety or a part of the above nucleotide sequence is designed, for example, on the basis of the above nucleotide sequence, and a gene amplification product is yielded as the entirety or a part of the DHPS gene through PCR or a similar technique by use of the nucleic acid-amplification primer. The gene amplification product is inserted into an appropriate vector, and the vector is incorporated into an appropriate host. The transformant in which the vector is incorporated is selected and subjected to cloning. Through expressing the DHPS gene by use of the transformant, the entirety or a part of a recombinant DHPS is yielded. Alternatively, a DHPS gene obtained from the transformant is incorporated into a vector suitable for gene expression, and the resultant vector is incorporated into a host, to thereby produce a transformant. The DHPS gene is expressed in the thus-produced transformant, to thereby yield a recombinant DHPS. DHPS gene cloning may also be carried out via fabrication of a gene library, without employing a gene amplification technique such as PCR as described above. The amino acid sequence of the recombinant DHPS may optionally be changed from the natural type by subjecting the nucleic acid encoding for a target DHPS to a genetic modification technique such as point mutation introduction, random mutation introduction, or stepwise deleted gene production.

The entirety or a part of DHPS may be produced through a known peptide chemical synthesis method. Examples of the peptide synthesis method include liquid phase peptide synthesis and solid phase peptide synthesis, which have been established as common techniques employed in the art. The solid phase peptide synthesis method may include Boc solid phase synthesis and Fmoc solid phase synthesis, which are generally acceptable as preferred chemical synthesis techniques. Particularly in the case of synthesis of a longchain peptide, ligation may be employed.

The above-produced DHPS gene may also be used in production of an antibody against DHPS through geneticimmunological technique. DHPS may be used as a nucleic acid probe employed in the cancer determination method of the present disclosure.

Furthermore, the above-produced DHPS gene may also be used as an immunogen in production of an antibody against DHPS; as an autoantibody-bonding field in carrying out the cancer determination method of the present invention through detection of an autoantibody; and as a standard substance in the cancer determination method of the present invention.

The antibody against DHPS may be produced through a conventional technique. In one specific mode, DHPS or a DHPS gene, serving as an immunogen, is administered to an immunization animal, whereby an antiserum is formed in the immunization animal. The antiserum can be used as a polyclonal antibody. A monoclonal antibody may be produced by collecting B cells from the immunization animal, producing a hybridoma from the B cells, administering the hybridoma to a host animal, and recovering a resultant target monoclonal antibody from the host animal.

If needed, the aforementioned DHPS gene, DHPS, and antibody against DHPS may optionally be subjected to an appropriate modification or treatment. Examples of the modification include addition of a label substance such as a fluorescent material, a dye, an enzyme, and a radioactive substance. Examples of the treatment include fragmentation of the antibody.

The aforementioned materials in relation to DHPS gene may be a commercially available product, including a readymade product and an order-made product.

A characteristic feature of the cancer detection method <NUM> resides in that the method comprises detecting expression of a DHPS gene in a test sample, and determining digestive system cancer of a test subject from which the test sample has been obtained, on the basis of an increase in the gene expression as an index, wherein expression of the DHPS gene (i.e., a target gene) is confirmed by detecting the entirety or a part of DHPS encoded by the gene, as a target polypeptide. Hereinafter, the entirety or a part of DHPS may be collectively referred to as DHPSes in the cancer determination method of the present invention.

Firstly, the DHPSes level of a test sample is determined. When the determined DHPSes level is greater than a standard DHPSes level of a subject exhibiting no digestive system cancer (hereinafter, the subject may be also be referred to as a digestive system cancer-free subject in the cancer determination method of the present invention), an increase in expression of the DHPS gene of a test subject from which the test sample has been obtained (hereinafter may be also referred to as test sample donor) is confirmed. On the basis of the increase as an index, digestive system cancer of the test sample donor can be determined. Examples of the test sample which may be used in the cancer determination method include blood specimens such as a serum specimen, a plasma specimen, and a whole blood specimen, and urine specimens. Of these, blood specimens are preferred. Also, such blood specimens may be subjected in advance to an appropriate treatment such as a treatment with heparin.

The standard DHPSes level of a test sample of a digestive system cancer-free subject (including a cut-off value) may be determined by making a sample group of subjects which have not been found to exhibit digestive system cancer in a general inspection; determining the DHPSes levels of samples obtained from the sample group; and subjecting the determined DHPSes levels to statistical processing, to thereby obtain the average, standard deviation, etc. thereof.

No particular limitation is imposed on the method of determining the DHPSes level of a test sample. Examples of the determination method include a quantification method employing an antibody (preferably a monoclonal antibody) which specifically binds to DHPSes. Specific examples include immunoprecipitation, western blotting, immunostaining, EIA, RIA, turbidimetry, nephelometry, latex agglutination turbidimetry, and CLEIA. Alternatively, the DHPSes level may be directly determined through TOF-MASS. Among EIA techniques, ELISA employing an immobilized antibody is particularly preferred. Any of these quantification methods may be carried out through a technique which is established for quantifying DHPSes in a test sample as a quantification target substance. Some of these quantification methods will next be described briefly.

In one mode of the quantification means based on ELISA, a test sample is brought into contact with DHPS antibody immobilized on a microplate, to thereby bind DHPSes present in the test sample to the immobilized antibody. The DHPSes bound to the immobilized antibody is detected with another DHPS-antibody labelled with an enzyme or the like, whereby the quantification can be performed. Alternatively, the DHPSes level of the test sample may be determined through simultaneous reaction of the immobilized antibody, the test sample, and the enzyme-labelled antibody.

In one mode of the quantification means based on immunoprecipitation, a test sample is brought into contact with a DHPS antibody immobilized on beads, to thereby bind DHPSes in the test sample to the immobilized antibody, and the DHPSes bound to the immobilized antibody is separated. The DHPSes in the separated product is detected, whereby the quantification can be performed. The DHPSes quantification method based on immunoprecipitation may be carried out by subjecting the aforementioned separated product to electrophoresis, and causing a labelled DHPS antibody to react with a transferred electrophoresis pattern, to thereby detect bands attributed to DHPSes (i.e., western blotting).

The quantification may also be carried out through a method based on western blotting. In one specific mode, cells are removed from a test sample, and the cell-removed test sample is directly separated through electrophoresis. A labelled DHPS-antibody is caused to act on the transferred product thereof, and bands attributed to DHPSes are detected, to thereby quantify DHPSes in the test sample.

In one mode of the quantification means based on latex agglutination turbidimetry, a test sample is brought into contact with the DHPS-antibody bound to latex particles, to thereby form an aggregate of an immune complex through antigen-antibody reaction in the liquid phase, and the turbidity change is measured, whereby the quantification can be performed.

The cancer determination method <NUM> of the present invention is a method, characterized in that expression of the DHPS gene is confirmed in a test sample, and digestive system cancer of a test subject from which the test sample has been obtained is determined on the basis of an increase in the gene expression as an index, wherein expression of the DHPS gene (a target gene) is confirmed by detecting anti-DHPS-autoantibody present in the test sample.

That is, the DHPS autoantibody level of a test sample is determined. When the determined DHPS autoantibody level is greater than a standard DHPS autoantibody level of a digestive system cancer-free subject, an increase in expression of the DHPS gene of a test subject from which the test sample has been obtained is confirmed. On the basis of the increase as an index, digestive system cancer of the test sample donor can be determined. Examples of the test sample which may be used in the cancer determination method include blood specimens such as a serum specimen, a plasma specimen, and a whole blood specimen, and urine specimens. Of these, blood specimens are preferred. Also, such blood specimens may be subjected in advance to an appropriate treatment such as a treatment with heparin.

The standard DHPS autoantibody level of a test sample of a digestive system cancer-free subject (including a cut-off value) may be determined by making a sample group of subjects which have not been found to exhibit digestive system cancer in a general inspection; determining the DHPS autoantibody levels of test samples obtained from the sample group; and subjecting the determined DHPS autoantibody levels to statistical processing, to thereby obtain the average, standard deviation, etc. thereof.

The DHPS autoantibody level may be determined by, for example, bringing the test sample into contact with an immobilized polypeptide including DHPSes, and detecting, as a signal, a bond between the antibody (autoantibody) against DHPS present in the test sample and the immobilized polypeptide. Specific examples of the quantification method which may be employed in the invention include indirect immunofluorescence, ELISA, western blotting (immunoblotting), turbidimetry, nephelometry, latex agglutination turbidimetry, and CLEIA. Any of these quantification methods may be carried out through a technique which is established for quantifying DHPS autoantibody in a test sample as a quantification target substance. One mode of indirect immunofluorescence (FANA) includes bringing a test sample into contact with a DHPSes-immobilized protein array; binding the immobilized DHPSes to a DHPS antibody in the test sample, to thereby form an immobilized DHPSes-anti-DHPS antibody complex; and bringing the complex into contact with a fluorescent-labelled secondary antibody, to thereby quantify the DHPS autoantibody. In ELISA, quantification is carried out by using an enzyme label instead of the label of the secondary antibody employed in indirect immunofluorescence. A variety of labels may be chosen for the secondary antibody. One mode of western blotting include subjecting DHPSes to electrophoresis on SDS-polyacrylamide gel; transferring the electrophoresis results from the gel to a substrate (e.g., a nitrocellulose membrane); bringing a test sample into contact with the transfer substrate, to thereby form a complex between DHPSes on the transfer substrate and the DHPS antibody present in the test sample; and detecting the complex, whereby the quantification can be performed. In one mode of turbidimetry or nephelometry, a DHPSes-anti-DHPS antibody complex, formed via contact of a test sample with DHPSes, is detected by turbidity (turbidimetry) or a change in scattered light intensity (nephelometry), whereby the quantification can be performed. In one mode of latex agglutination turbidimetry, a test sample is brought into contact with DHPSes-bound latex particles, to thereby form an aggregate of latex particles via interaction between autoantibodies bound to latex particles, and the aggregate is detected, whereby the quantification can be performed. In one mode of CLEIA, a test sample is brought into contact with DHPSes-bound magnetic particles, to thereby form a DHPSes-anti-DHPS antibody complex on the magnetic particles, these particles are magnetically collected, unreacted matter is removed, and an appropriate fluorescent treatment or the like is carried out to detect the complex, whereby the quantification can be performed.

A characteristic feature of the cancer determination method <NUM> resides in that the method comprises detecting expression of a DHPS gene in a test sample, and determining digestive system cancer of a test subject from which the test sample has been obtained, on the basis of an increase in the gene expression as an index, wherein expression of the DHPS gene (i.e., a target gene) is confirmed by detecting, as a target nucleic acid, the entirety or a part of the DHPS gene, or a nucleic acid complementary to the entirety or a part of the DHPS gene, present in the test sample.

In one specific procedure, the level of mRNA encoding DHPSes in the test sample is determined. When the determined mRNA level is greater than a standard mRNA level of a digestive system cancer-free subject, an increase in expression of the DHPSes gene of a test subject from which the test sample has been obtained is confirmed. On the basis of the increase as an index, digestive system cancer of the test sample donor can be determined. Examples of the test sample which may be used in the cancer determination method include blood specimens such as a serum specimen, a plasma specimen, and a whole blood specimen, and urine specimens. Of these, blood specimens are preferred. Also, such blood specimens may be subjected in advance to an appropriate treatment such as a treatment with heparin.

The nucleic acid, serving as a basic material in the determination of the level of mRNA encoding DHPSes in the test sample, may be produced by extracting RNA from the test sample through a known technique and reversely transcribing the RNA to the corresponding DNA, to thereby yield a cDNA. The cDNA is subjected to gene amplification such as PCR employing a gene amplification primer for amplifying the DHPSes gene (RT-PCR). Through measuring the mRNA level equivalent (e.g., the copy number of the DHPSes gene in gene amplification at specific cycles, or an increasing rate of the DHPSes gene copy number) as a basic index, the expression level of the DHPSes gene in the test sample can be determined.

The target nucleic acid may be detected by hybridizing a nucleic acid probe including a nucleic acid fragment having a nucleotide sequence complementary to the nucleotide sequence of the target nucleic acid, with the target nucleic acid obtained as an immobilized or non-immobilized gene amplification product, and detecting the signal attributed to hybridization.

The signal may be detected through, for example, southern blotting. Alternatively, a series of steps of the cancer determination method <NUM> may be carried out through, for example, a real-time analysis employing RT-PCR.

As described above, the cancer detection kit used according to the present invention is a kit having elements for carrying out the cancer determination method of the present invention. The elements of the cancer detection kit vary in accordance with the mode and purpose of use of the cancer determination method of the present invention, the degree of kit design, and other factors.

In one mode of the use of the cancer detection kit for carrying out the cancer determination method <NUM>, the kit is employed for ELISA, which kit includes a plate on which a DHPS-antibody is immobilized as a primary antibody, a labelled secondary antibody, and an agent for developing the label of the secondary antibody. Alternatively, the kit is employed for latex agglutination turbidimetry, which kit contains latex particles onto which a DHPS-antibody is bound. Yet alternatively, the kit is employed for CLEIA, which kit includes magnetic particles onto which a DHPS-antibody is bound, a labelled secondary antibody, and an agent for developing the label of the secondary antibody. The above-mentioned elements of the kits are merely examples, and the present disclosure also encompasses kits for carrying out other aspects of the cancer determination method <NUM>. Furthermore, it is possible for a similar kit having fewer elements so as to shear with an outsourcing inspection and to self-procurement. Also, another possible embodiment of the kit to be used according to the invention is a cancer detection kit which has further elements such as a diluent and a tube for an agent, so as to be immediately used. Needless to say, the kit may further include an additional element suited for a specific inspection procedure.

In one mode of the use of the cancer detection kit for carrying out the cancer determination method <NUM> of the present invention, the kit is employed for FANA or ELISA, which kit includes a plate on which a DHPSes is immobilized, a labelled secondary antibody against the autoantibody, and an agent for developing the label of the secondary antibody. Alternatively, the kit is employed for latex agglutination turbidimetry, which kit contains latex particles onto which a DHPSes is bound. Yet alternatively, the kit is employed for CLEIA, which kit includes magnetic particles onto which a DHPSes is bound, a labelled secondary antibody against the autoantibody, and an agent for developing the label of the secondary antibody. The above-mentioned elements of the kits are merely examples, and the present invention also encompasses kits for carrying out other embodiments of the cancer determination method <NUM> of the present invention. Furthermore, it is possible for a similar kit having fewer elements so as to shear with an outsourcing inspection and to self-procurement. Also, another possible embodiment of the kit to be used according to the invention is a cancer detection kit which has further elements such as a diluent and a tube for an agent, so as to be immediately used. Needless to say, the kit may further include an additional element suited for a specific inspection procedure.

In one mode of the use of the cancer detection kit for carrying out the cancer determination method <NUM>, the kit may include a reverse transcriptase and a reverse transcription primer for reverse transcription of mRNA, a gene amplification primer for amplifying a cDNA encoding DHPSes, a nucleic acid probe for detecting the gene amplification product, and an agent for developing the signal of the nucleic acid probe. The above-mentioned elements of the kits are merely examples, and the present disclosure also encompasses kits for carrying out other aspects of the cancer determination method <NUM>. Furthermore, it is possible for a similar kit having fewer elements so as to shear with an outsourcing inspection and to self-procurement. Also, another possible embodiment of the kit to be used according to the invention is a cancer detection kit which has further elements such as a diluent and a tube for an agent, so as to be immediately used. Needless to say, the kit may further include an additional element suited for a specific inspection procedure.

The present invention will next be described by way of examples.

Firstly, an insert was produced through PCR. In a specific procedure, a primer having a restriction enzyme recognition site suited for gene recombination to an expression vector pET28 or pGEX-4T was produced in advance. Reverse transcription PCR was carried out by use of RNA extracted from osteosarcoma cell line U2-OS as a template, to thereby yield cDNA, and PCR was repeated, to thereby produce a full-length insert. The thus-produced insert and an expression vector were treated with restriction enzymes, and the insert was ligated with the expression vector by means of Ligation-Convenience Kit (product of Nippon Gene Co. ), to thereby produce a plasmid including the insert. coli competent cells BL21 (product of Nippon Gene Co. ) was transformed by use of the plasmid. The thus-obtained transformant was cultured in an LB medium containing an antibiotic. By use of IPTG, production of an insert DNA-originating protein via gene expression was induced. The thus-transformed E. coli cells were centrifuged, and the recovered product was further separated into soluble fractions and insoluble fractions. The insoluble fractions were solubilized with urea. The thus-obtained protein was purified with ProBond Resin (product of Invitrogen) and Glutathione-Sepharose (product of GE Healthcare).

Through the above procedure, a plurality of purified recombinant proteins were produced, and then injected to a <NUM>-well ELISA plate at <NUM>µg/mL. The well was maintained overnight at <NUM> so as to immobilize the proteins on the plate. Thus, a <NUM>-well ELISA plate for use in ELISA on which recombinant proteins were immobilized was produced.

In the ELISA procedure, the recombinant proteinimmobilized plate was washed with PBS and blocked with a solution containing <NUM>% sugar and <NUM>% synthetic polymer (product of NOF Corporation). Then, the immobilized proteins were reacted with a <NUM>-fold dilution of a serum sample of a patient or a control serum (a serum sample of a healthy subject). Subsequently, the plate was washed with PBS, and an HRP-labelled goat anti-human IgG antibody was added to the plate. Finally, an enzyme chromogenic substrate was added to the plate, and the absorbance (OD) of the developed color was measured by means of a plate reader at a wavelength of <NUM>.

As a result of the screening based on ELISA, about <NUM> members of the about <NUM> autoantibody (antigen protein) candidates were selected. The about <NUM> candidates included DHPS (i.e., subject matter of the present invention). Actually, autoantibodies against proteins other than DHPS were also studied. However, only the case of DHPS is disclosed herein.

Studies through ELISA were performed three times. (a) Studies on autoantibody through ELISA (<NUM>).

Serum specimens of acute cerebral infarction patients (<NUM> cases) and those of healthy subjects (<NUM> cases) obtained from a medical facility A were employed. <FIG> show the results. <FIG> is a graph showing DHPS autoantibody titers of serum specimen of acute cerebral infarction patients (patient group) and healthy subjects (normal group), with distribution profiles thereof. <FIG> is a graph showing ROC (receiver operation characteristic) curves regarding the distribution profiles.

Table <NUM> shows the statistical test results obtained from <FIG>. As shown in Table <NUM>, the cut-off value was found to be about <NUM>, represented by a dotted line in <FIG>.

The P value was smaller than <NUM> (<NUM>), indicating that "the serum antibody titer against DHPS is significantly greater in the arteriosclerosis patient group than that in the healthy subject group.

The percent positive at the above cut-off value was about <NUM>%.

Serum specimens of acute cerebral infarction patients (<NUM> cases) obtained from a medical facility B, and those of acute cerebral infarction patients (<NUM> cases) obtained from a medical facility C (the total no. of cases: <NUM>), and those of healthy subjects (<NUM> cases) obtained from the medical facility A were employed. <FIG> show the results. <FIG> is a graph showing DHPS autoantibody titers of serum specimen of acute cerebral infarction patients (patient group) and healthy subjects (normal group), with distribution profiles thereof. <FIG> is a graph showing ROC (receiver operation characteristic) curves regarding the distribution profiles.

The P value was considerably smaller than <NUM> (<NUM>), indicating that "the serum antibody titer against DHPS is significantly greater in the arteriosclerosis patient group than that in the healthy subject group.

In studies (c), the behavior of a DHPS autoantibody marker was investigated in known arteriosclerosis markerpositive and -negative groups, respectively. CRP was used as the known arteriosclerosis marker. CRP (C-reactive protein) is an acute-phase protein (acute phase reactant: APR) and was found by Tillet and other researchers in <NUM>, as a serum protein which causes sedimentation reaction with a C polysaccharide extracted from Diplococcus pneumoniae (Streptococcus pneumoniae). Some studies in recent years have revealed that, when an inflammation associated with arteriosclerosis occurs in the vascular tissue, CRP is produced in the liver by the action of an inflammatory cytokine secreted from inflammatory cells which infiltrate an arteriosclerosis site, thereby elevating the CRP level. The studies have also revealed that the CRP concentration correlates with the severity of the functional disorder of the vascular endothelium, and that an increase in CRP level is a risk factor for causing angina and myocardial infarction (<NPL>).

The specimens for CRP measurement which were employed in studies (c) were serum specimens of acute cerebral infarction patients (<NUM> cases) and those of healthy subjects (<NUM> cases) obtained from a medical facility A (the total number of the specimens: <NUM>). Each of the specimens was subjected to a CRP assay through latex agglutination turbidimetry by means of a C-reactive protein kit (Nanopia, product of Sekisui Medical Co. The results were categorized on the basis of a CRP cut-off value of <NUM>/dL. More specifically, when the CRP level of a specimen was higher than <NUM>/dL, the specimen was categorized into a "CRP arteriosclerosis risk group," whereas when the CRP level of a specimen was <NUM>/dL or lower, the specimen was categorized into a "CRP arteriosclerosis non-risk group. " Each CRP risk group was divided into the patient group and the healthy group, and the DHPS autoantibody titer of a serum specimen was determined through ELISA in each group. <FIG> shows the results. Also, <FIG> shows an ROC curve of the CRP arteriosclerosis non-risk group having a CRP level of <NUM>/dL or lower.

The P value was <NUM>, which is definitely smaller than <NUM> (<NUM>).

The percent positive was <NUM>%. Thus, even in the case of a group assessed to have a low risk of arteriosclerosis through CRP level, arteriosclerosis can be significantly detected through an arteriosclerosis test by use of DHPS.

No significance test was conducted for a "CRP arteriosclerosis risk group," since the number of the specimens of the normal group was insufficient. However, as is clear from <FIG>, determination of a DHPS autoantibody is also effective for detecting arteriosclerosis in the risk group.

An insert was produced through the procedure shown in Reference Example (<NUM>) above, and purified proteins were produced in the same manner. In a specific procedure, a primer having a restriction enzyme recognition site suited for gene recombination to an expression vector pET28 or pGEX-4T was produced in advance. Reverse transcription PCR was carried out by use of RNA extracted from osteosarcoma cell line U2-OS as a template, to thereby yield cDNA, and PCR was repeated, to thereby produce a full-length insert. The thus-produced insert and an expression vector were treated with restriction enzymes, and the insert was ligated with the expression vector by means of Ligation-Convenience Kit (product of Nippon Gene Co. ), to thereby produce a plasmid including the insert. coli competent cells BL21 (product of Nippon Gene Co. ) was transformed by use of the plasmid. The thus-obtained transformant was cultured in an LB medium containing an antibiotic. By use of IPTG, production of an insert DNA-originating protein via gene expression was induced. The thus-transformed E. coli cells were centrifuged, and the recovered product was further separated into soluble fractions and insoluble fractions. The insoluble fractions were solubilized with urea. The thus-obtained protein was purified with ProBond Resin (product of Invitrogen) and Glutathione-Sepharose (product of GE Healthcare).

Each purified protein produced through the above procedure was denatured with an SDS sample buffer, to thereby prepare a western blotting sample. The sample was subjected to electrophoresis on <NUM>% polyacrylamide gel, and the obtained protein pattern was transferred to a nitrocellulose membrane by means of a pattern-transfer apparatus. The transferred protein was blocked with <NUM>% skim milk, and <NUM>-fold diluted serum samples of patients (specimens <NUM> to <NUM>) were added as primary antibodies to the membrane, followed by overnight incubation. Thereafter, the membrane was washed with PBST, and a <NUM>,<NUM>-fold diluted HRP-labeled goat anti-human IgG antibody (ab98633, product of Abcam) was added to the membrane. After reaction for <NUM> minutes, the membrane was washed with PBST, and a luminescent reagent (Immobilon Western, product of MILLIPORE) was added thereto. A photographic film was exposed to the resultant luminescence and then developed.

<FIG> shows the results in an electrophoresis chart. As shown in <FIG>, specimens <NUM>, <NUM>, <NUM>, and <NUM> were serum specimens of acute cerebral infarction patients obtained from the medical facility A. ELISA measurements (autoantibody) in terms of protein His-DHPS (a. <NUM>-<NUM>) were <NUM> (specimen <NUM>), <NUM> (specimen <NUM>), <NUM> (specimen <NUM>), and <NUM> (specimen <NUM>). ELISA measurements (autoantibody) in terms of protein GST-DHPS (a. <NUM>-<NUM>) were <NUM> (specimen <NUM>), <NUM> (specimen <NUM>), <NUM> (specimen <NUM>), and <NUM> (specimen <NUM>).

The following Tables <NUM>-<NUM> to <NUM>-<NUM> show detected band intensities as relative values with respect to the band intensity of each membrane marker (<NUM> kDa) as "<NUM>. " Table <NUM>-<NUM> shows the results of specimen <NUM>, Table <NUM>-<NUM> shows the results of specimen <NUM>, Table <NUM>-<NUM> shows the results of specimen <NUM>, and Table <NUM>-<NUM> shows the results of specimen <NUM>. In the Tables, protein His-DHPS (a. <NUM>-<NUM>) is abbreviated as His-36C, and protein GST-DHPS (a. <NUM>-<NUM>) is abbreviated as GST-36C.

The above results have revealed that the autoantibodies present in the specimens <NUM>, <NUM>, <NUM>, and <NUM>--serum specimens of acute cerebral infarction patients--were found to exhibit strong reactivity to protein His-DHPS (a. <NUM>-<NUM>). As a result of the western blotting analysis, reaction between the target bands with the autoantibodies was confirmed. In addition, the obtained band intensities have revealed that specimens having a greater measurement in ELISA exhibited higher reactivity to protein His-DHPS (a. <NUM>-<NUM>).

Next, the presence of endogenous DHPS in each specimen was investigated through western blotting by use of an anti-DHPS-antibody. In a specific procedure, each of the His-DHPS (SEQ ID NO: <NUM>, a. <NUM>-<NUM>) protein (positive control) and the serum specimens of patients (specimens <NUM> to <NUM>) was denatured with an SDS sample buffer, to thereby prepare a western blotting sample. The sample was subjected to electrophoresis on <NUM>% polyacrylamide gel, and the obtained protein pattern was transferred to a nitrocellulose membrane by means of a pattern-transfer apparatus. The transferred protein was blocked with <NUM>% skim milk, and a <NUM>-fold diluted anti-DHPS-antibody (H00001725-B02P, product of Abnova) was added as a primary antibody to the membrane, followed by overnight incubation. Thereafter, the membrane was washed with PBST, and a <NUM>,<NUM>-fold diluted HRP-labeled sheep anti-mouse IgG antibody (NA931, product of GE Healthcare) was added to the membrane. After reaction for <NUM> minutes, the membrane was washed with PBST, and a luminescent reagent (Immobilon Western, product of MILLIPORE) was added thereto. A photographic film was exposed to the resultant luminescence and then developed.

The results are shown in an electrophoresis diagram of <FIG>. As is clear from <FIG>, the presence of a band suggesting the presence of endogenous DHPS was confirmed in all specimens. Thus, the results strongly suggested the presence of endogenous DHPS in blood.

Antigen proteins against a DHPS-autoantibody were produced as recombinant proteins through the following steps.

In the ELISA procedure, the recombinant proteinimmobilized plate was washed with PBS and blocked with <NUM>% fetal bovine serum PBS. Then, the immobilized proteins were reacted with a <NUM>,<NUM>-fold dilution of a serum sample of a patient or a control serum (a serum sample of a healthy subject). Subsequently, the plate was washed with PBS, and an HRP-labelled goat anti-human IgG antibody was added to the plate. Finally, an enzyme chromogenic substrate was added to the plate, and the absorbance (OD) of the developed color was measured by means of a plate reader at a wavelength of <NUM>.

Serum specimens of esophageal cancer patients (<NUM> cases) and colorectal cancer patients (<NUM> cases) (total n: <NUM>) obtained from a medical facility D, and those of healthy subjects (<NUM> cases) obtained from a medical facility A were employed. <FIG> show the results. <FIG> is a graph showing DHPS autoantibody titers of cancer patients (patient group) and healthy subjects (normal group), with distribution profiles thereof. <FIG> is a graph showing ROC (receiver operation characteristic) curves regarding the distribution profiles.

The P value was smaller than <NUM>, indicating that "the serum antibody titer against DHPS is significantly greater in the esophageal cancer and colorectal cancer patient group than that in the healthy subject group.

Claim 1:
A method for determining a cancer, comprising detecting the level of anti-deoxyhypusine synthase autoantibody in a blood specimen obtained from a human, and determining digestive system cancer on the basis of an increase in the level of anti-deoxyhypusine synthase autoantibody in said blood specimen compared to a standard anti-deoxyhypusine synthase autoantibody level of a digestive system cancer-free subject as an index in said human.