ANTI-CLAUDIN 18.2 ANTIBODY AND ANTIBODY-DRUG CONJUGATE THEREOF

Abstract

Provided are an antibody targeting Claudin 18.2, an antibody-drug conjugate, and use thereof in treatment of cancer. Also provided are a nucleotide encoding the Claudin 18.2 antibody, a polynucleotide combination, an expression vector, an expression vector combination, a pharmaceutical composition comprising the Caudill 18.2 antibody and the antibody-drug conjugate, and an application thereof in preparation of a medication for treatment or prevention of cancer.

Claims

1. An anti-Claudin 18.2 antibody or antigen-binding fragment thereof, comprising a heavy chain variable region and a light chain variable region, and the heavy chain variable region and/or the light chain variable region has a CDR sequence identical to that of an antibody defined by the following sequences or obtained by 1-2 amino acid substitutions of the CDR of the antibody defined by the following sequences: (1) an amino acid sequence of a heavy chain variable region as shown in SEQ ID NO: 1; and/or (2) an amino acid sequence of a light chain variable region as shown in SEQ ID NO: 2.

2. The antibody or antigen-binding fragment thereof according to claim 1, and: (1) for the heavy chain variable region, CDR1 has an amino acid sequence as shown in SEQ ID NO: 3, 4, 5, 6 or 7 or obtained by 1 or 2 amino acid substitutions of SEQ ID NO: 3, 4, 5, 6 or 7; CDR2 has an amino acid sequence as shown in SEQ ID NO: 8, 9, 10, 11 or 12, or obtained by 1 or 2 amino acid substitutions of SEQ ID NO: 8, 9, 10, 11 or 12; CDR3 has an amino acid sequence as shown in SEQ ID NO: 13, 14, 15, 16 or 17, or obtained by 1 or 2 amino acid substitutions of SEQ ID NO: 13, 14, 15, 16 or 17; (2) for the light chain variable region, CDR1 has an amino acid sequence as shown in SEQ ID NO: 18, 19, 20, 21 or 22 or obtained by 1 or 2 amino acid substitutions of SEQ ID NO: 18, 19, 20, 21 or 22; CDR2 has an amino acid sequence as shown in SEQ ID NO: 23, 24, 25, 26 or 27, or obtained by 1 or 2 amino acid substitutions of SEQ ID NO: 23, 24, 25, 26 or 27; CDR3 has an amino acid sequence as shown in SEQ ID NO: 28, 29, 30, 31 or 32, or obtained by 1 or 2 amino acid substitutions of SEQ ID NO: 28, 29, 30, 31 or 32.

3. The antibody or antigen-binding fragment thereof according to claim 2, and, (1) CDRs 1-3 of the heavy chain variable region have amino acid sequences of SEQ ID NOs: 3, 8 and 13 or obtained by 1 or 2 amino acid substitutions of SEQ ID NOs: 3, 8 and 13, and/or the CDRs 1-3 of the light chain variable region have amino acid sequences of SEQ ID NOs: 18, 23 and 28 or obtained by 1 or 2 amino acid substitutions of SEQ ID NOs: 18, 23 and 28; (2) CDRs 1-3 of the heavy chain variable region have amino acid sequences of SEQ ID NOs: 4, 9 and 14 or obtained by 1 or 2 amino acid substitutions of SEQ ID NOs: 4, 9 and 14, and/or the CDRs 1-3 of the light chain variable region have amino acid sequences of SEQ ID NOs: 19, 24 and 29 or obtained by 1 or 2 amino acid substitutions of SEQ ID NOs: 19, 24 and 29; (3) CDRs 1-3 of the heavy chain variable region have amino acid sequences of SEQ ID NOs: 5, 10 and 15 or obtained by 1 or 2 amino acid substitutions of SEQ ID NOs: 5, 10 and 15, and/or the CDRs 1-3 of the light chain variable region have amino acid sequences of SEQ ID NOs: 20, 25 and 30 or obtained by 1 or 2 amino acid substitutions of SEQ ID NOs: 20, 25 and 30; (4) CDRs 1-3 of the heavy chain variable region have amino acid sequences of SEQ ID NOs: 6, 11 and 16 or obtained by 1 or 2 amino acid substitutions of SEQ ID NOs: 6, 11 and 16, and/or the CDRs 1-3 of the light chain variable region have amino acid sequences of SEQ ID NOs: 21, 26 and 31 or obtained by 1 or 2 amino acid substitutions of SEQ ID NOs: 21, 26 and 31; (5) CDRs 1-3 of the heavy chain variable region have amino acid sequences of SEQ ID NOs: 7, 12 and 17 or obtained by 1 or 2 amino acid substitutions of SEQ ID NOs: 7, 12 and 17, and/or the CDRs 1-3 of the light chain variable region have amino acid sequences of SEQ ID NOs: 22, 27 and 32 or obtained by 1 or 2 amino acid substitutions of SEQ ID NOs: 22, 27 and 32.

4. The antibody or antigen-binding fragment thereof according to claim 1, and: (1) the heavy chain variable region has an amino acid sequence as shown in SEQ ID NO: 1, or comprises the same CDRs 1-3 as in SEQ ID NO: 1 and more than 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to SEQ ID NO: 1; and/or (2) the light chain variable region has an amino acid sequence as shown in SEQ ID NO: 2, or comprises the same CDRs 1-3 as in SEQ ID NO: 2 and more than 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to SEQ ID NO: 2; (1) the heavy chain has an amino acid sequence as shown in SEQ ID NO: 33; and/or (2) the light chain has an amino acid sequence as shown in SEQ ID NO: 34.

5. (canceled)

6. The antibody or antigen-binding fragment thereof according to claim 1, wherein the antibody or antigen-binding fragment thereof includes a monoclonal antibody, Fab, Fab′, Fab′-SH, F(ab′)2, Fv, single chain Fv (scFv), bispecific antibody, multispecific antibody, chimeric antibody, humanized antibody or fusion protein comprising an antigen-binding fragment of an antibody; the antibody is a humanized monoclonal antibody.

7. The antibody or antigen-binding fragment thereof according to claim 1, further comprising a human or murine constant region; the constant region is selected from the group consisting of IgG1, IgG2, IgG3, and IgG4.

8. An antibody-drug conjugate comprising the antibody or antigen-binding fragment thereof according to claim 1.

9. The antibody-drug conjugate according to claim 8, wherein the antibody-drug conjugate has a structure represented by formula (I):
Ab-L-D  (I) wherein: Ab is the antibody or antigen-binding fragment thereof according to claim 1; D is an active drug unit; L is any linking group, which is covalently linked to the antibody or antigen-binding fragment thereof Ab and the active drug unit D, respectively; wherein, Ab is linked to one or more active drug units D through one or more linking groups L.

10. The antibody-drug conjugate according to claim 9, wherein L is covalently linked to an amino residue or a thiol residue of the antibody Ab; may be L is covalently linked to a thiol residue of the antibody Ab; may be, L is covalently linked to a thiol residue formed by breaking an interchain disulfide bond of the antibody Ab.

11. The antibody-drug conjugate according to claim 9, wherein L includes a cleavable linker and a non-cleavable linker; the cleavable linker includes a peptide unit comprising 2 to 20 amino acids, the peptide linker is selected from the group consisting of -valine-citrulline- (-Val-Cit-), -glycine-glycine-phenylalanine-glycine- (-Gly-Gly-Phe-Gly-), -valine-alanine- (-Val-Ala-), -valine-lysine- (-Val-Lys-), -valine-arginine- (-Val-Arg-), -phenylalanine-citrulline- (-Phe-Cit-), -phenylalanine-lysine- (-Phe-Lys-), -phenylalanine-arginine- (-Phe-Arg-) and a combination thereof.

12. (canceled)

13. The antibody-drug conjugate according to claim 9, wherein L comprises a structure selected from the group consisting of: ##STR00017## ##STR00018## ##STR00019## ##STR00020## ##STR00021## ##STR00022## ##STR00023##

14. The antibody-drug conjugate according to claim 9, wherein the active drug unit D is selected from the group consisting of a cytotoxic molecule, cell differentiation factor, stem cell trophic factor, steroid drug, drug for the treatment of autoimmune diseases, anti-inflammatory drug, and drug for the treatment of infectious diseases; the cytotoxic molecule includes but is not limited to a tubulin inhibitor or a DNA damaging agent; the tubulin inhibitor includes but is not limited to a cytotoxic molecule of dolastatins and auristatins, a cytotoxic molecule of maytansines; the DNA damaging agent includes but is not limited to calicheamicins, duocarmycins, anthramycin derivative pyrrolobenzodiazepine (PBD), camptothecins and a derivative thereof, and SN-38; more the cytokine molecule of auristatins includes but is not limited to MMAE, MMAF, or a derivative thereof; and the cytotoxic molecule of maytansines includes but is not limited to DM1, DM4, or a derivative thereof.

15. The antibody-drug conjugate according to claim 9, wherein the active drug unit D has a structure selected from the group consisting of: ##STR00024## ##STR00025## ##STR00026## ##STR00027##

16. The antibody-drug conjugate according to claim 9, wherein the antibody-drug conjugate has a structure selected from the group consisting of: ##STR00028## wherein, p is an integer selected from 1, 2, 3, 4, 5, 6, 7, and 8, and q is an integer selected from 1, 2, 3, and 4.

17. An isolated polynucleotide or combination thereof, encoding the antibody or antigen-binding fragment thereof according to claim 1.

18. A nucleic acid construct comprising the polynucleotide according to claim 17, wherein the nucleic acid construct is a vector.

19. (canceled)

20. A host cell comprising the nucleic acid construct according to claim 18, wherein the cell is selected from the group consisting of a prokaryotic cell, eukaryotic cell, yeast cell, mammalian cell, E. coli cell or CHO cell, NS0 cell, Sp2/0 cell, and BHK cell.

21. (canceled)

22. A pharmaceutical composition comprising the antibody or antigen-binding fragment thereof according to claim 1, and a pharmaceutically acceptable carrier.

23. A method for producing an anti-Claudin 18.2 antibody, comprising culturing the host cell according to claim 20 under a condition suitable for expressing a vector encoding an anti-Claudin 18.2 antibody or an antigen-binding fragment thereof, and recovering the antibody or fragment.

24. A method for treating or preventing cancer, comprising administering the antibody or antigen-binding fragment thereof according to claim 1 to a subject in need thereof, the cancer is a solid tumor; further, the solid tumor includes gastric cancer and pancreatic cancer.

25. (canceled)

Description

BRIEF DESCRIPTION OF DRAWINGS

[0057] FIG. 1 is a graph showing the change in tumor volume of animals after administration of anti-Claudin 18.2 murine antibodies CLN-03-3A7, CLN-03-4E5 and CLN-03-6H2;

[0058] FIG. 2 is a graph showing the change in body weight of animals after administration of anti-Claudin 18.2 murine antibodies CLN-03-3A7, CLN-03-4E5 and CLN-03-6H2;

[0059] FIG. 3 is a graph showing the comparison of the detected affinity of chimeric antibodies CLN-03-4E5-01, CLN-03-6H2-01 and IMAB362;

[0060] FIG. 4A is a graph showing the comparison of the endocytosis efficiency of CLN-03-6H2-01 and IMAB362 in the gastric cancer model KATOIII;

[0061] FIG. 4B is a graph showing the comparison of the endocytosis efficiency of CLN-03-6H2-01 and IMAB362 in the pancreatic cancer model AsPC-1;

[0062] FIG. 4C is a graph showing the comparison of the endocytosis efficiency of CLN-03-6H2-01 and IMAB362 in the lung cancer model A549;

[0063] FIG. 5 is a graph showing the comparison of the endocytosis effect of RGCLN18.2, RGCLN18.2-PY-Val-Cit-PAB-MMAE, RGCLN18.2-MC-Val-Cit-PAB-MMAE, RGCLN18.2-D07-Val-Cit-PAB-MMAE and IMAB362-MC-Val-Cit-MMAE detected by flow cytometry;

[0064] FIG. 6 is a graph showing the change in body weight of animals after administration of RGCLN18.2-MC-Val-Cit-PAB-MMAE, IMAB362-MC-Val-Cit-PAB-MMAE and PBS;

[0065] FIG. 7 is a graph showing the change in tumor volume of animals after administration of RGCLN18.2-MC-Val-Cit-PAB-MMAE, IMAB362-MC-Val-Cit-PAB-MMAE and PBS.

DETAILED DESCRIPTION

Definition

[0066] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as understood in the art. With regard to the definitions and terms in the art, reference may be made to Current Protocols in Molecular Biology (Ausubel). The standard three- and/or one-letter code used for expressing one of 20 common L-amino acids in the art is adopted as the abbreviation of an amino acid residue.

[0067] In the present disclosure, a method for determining or numbering the complementarity determining region (CDR) of an antibody's variable domain includes IMGT, Kabat, Chothia, AbM and Contact, which are well known in the art.

[0068] For the purposes of the present disclosure, the “consistency”, “identity” or “similarity” between two nucleic acid or amino acid sequences refers to the percentage of identical nucleotides or identical amino acid residues between the two sequences to be compared after optimal alignment. The percentage is purely statistical and the differences between the two sequences are randomly distributed and cover their full length. Sequence comparison between two nucleic acid or amino acid sequences are usually performed by comparing these sequences after they have been optimally matched, and the comparison can be performed on a segment or on a “comparison window”. In addition to manual implementation, the optimal alignment for comparing sequences can also be performed by the local homology algorithm of Smith and Waterman (1981) [Ad. App. Math. 2: 482], the local homology algorithm of Neddleman and Wunsch (1970) [J. Mol. Biol. 48: 443], the similarity search method of Pearson and Lipman (1988) [Proc. Natl. Acad. Sci. USA 85: 2444), or a computer software using these algorithms (GAP, BESTFIT, FASTA and TFASTA in the Wisconsin Genetics Software Package, Genetics Computer Group, 575 Science Dr., Madison, Wis., or BLAST N or BLAST P comparison software).

[0069] As used herein, “antibody” is used in a broadest sense and encompasses various antibodies including, but not limited to, a monoclonal antibody and a multispecific antibody (e.g., a bispecific antibody). As used herein, “antigen-binding fragment” refers to an antibody fragment consisting of or including a partial sequence of a heavy or light variable chain of an antibody from which it is derived, and the partial sequence for retaining the same binding specificity as the antibody from which it is derived and a sufficient affinity, may be equal to at least 1/100, may be at least 1/10 of the affinity of the antibody from which it is derived. Such a functional fragment includes a minimum of 5 amino acids, and 10, 15, 25, 50 or 100 contiguous amino acids of the antibody sequence from which it is derived, including (particularly) Fab, F(ab′), F(ab′).sub.2, Fv, dAb, Fd, a complementarity determining region (CDR) fragment, a single chain antibody (scFv), and a bivalent single chain antibody, that contains at least an immunoglobulin fragment enough to allow a specific antigen to bind to the polypeptide. The above fragments can be prepared by a synthetic or enzymatic method, or by chemical cleavage of an intact immunoglobulin, or can be genetically engineered by recombinant DNA technology. The preparation methods thereof are well known in the art. A heavy chain contains a heavy chain variable region (abbreviated as VH) and a heavy chain constant region. The heavy chain constant region contains three domains, CH1, CH2 and CH3. A light chain contains a light chain variable region (abbreviated as VL) and a light chain constant region. The light chain constant region contains a domain, CL. VH and VL regions can be further subdivided into multiple regions with high variability, called as complementarity determining regions (CDRs), interspersed with more conservative regions called as framework regions (FRs). Each VH and VL is composed of three CDRs and four FRs, which are arranged from the amino terminal to the carboxy terminal in the following order: FR1, CDR1, FR2, CDR2, FR3, CDR3, FR4. These variable regions of the heavy and light chains contain a binding domain that interacts with an antigen. The constant region of an antibody can mediate binding of an immunoglobulin to a host tissue or factor, including various cells in the immune system (such as effector cells) and the first component of the classical complement system (Clq). Chimeric or humanized antibodies are also encompassed by the antibodies according to the present disclosure.

[0070] The term “humanized antibody” refers to an antibody that contains a CDR region derived from a non-human antibody, with the rest deriving from one (or several) human antibody. In one embodiment, in order to retain binding affinity, some residues at the backbone (called FR) segment can be modified (Document 8: Jones et al., Nature, 321: 522-525, 1986; Verhoeyen et al., Science, 239: 1534-1536, 1988; Riechmann et al., Nature, 332: 323-327, 1988.). Humanized antibodies or fragments thereof according to the present disclosure can be prepared by techniques known in the art (Document 9: Singer et al., J. Immun. 150: 2844-2857, 1992; Mountain et al., Biotechnol. Genet. Eng. Rev., 10: 1-142, 1992; or Bebbington et al., Bio/Technology, 10: 169-175, 1992.).

[0071] The term “chimeric antibody” refers to an antibody in which the variable region sequence is from one species while the constant region sequence is from another species, for example, an antibody in which the variable region sequence is from a mouse antibody while the constant region sequence is from a human antibody. A chimeric antibody or a fragment thereof according to the present disclosure can be prepared by using genetic recombination technology. For example, the chimeric antibody can be produced by cloning a recombinant DNA including a promoter and a sequence encoding a variable region of a non-human, especially a murine monoclonal antibody according to the present disclosure, and a sequence encoding a constant region of a human antibody. The chimeric antibody of the present disclosure encoded by such a recombinant gene will be, for example, a murine-human chimera whose specificity is determined by the variable region derived from murine DNA, and the isotype is determined by the constant region derived from human DNA. For methods for preparing a chimeric antibody, for example, reference can be made to the document Verhoeyn et al. (BioEssays, 8:74, 1988).

[0072] The term “monoclonal antibody” refers to a preparation of an antibody molecule consisting of a single molecule. Monoclonal antibody compositions display a single binding specificity and affinity for a particular epitope.

[0073] The term an “isolated” nucleic acid molecule refers to a nucleic acid molecule identified and separated from at least one contaminant nucleic acid molecules, and is generally associated with the contaminant nucleic acid molecule in the natural source of an antibody nucleic acid. An isolated nucleic acid molecule is different in form or environment from when it is found in nature, and therefore different from that existing in natural cells. However, an isolated nucleic acid molecule includes a nucleic acid molecule contained in cells where an antibody is usually expressed, and where for example, it is located on a different chromosomal position from that in a natural cell.

[0074] Generally, in order to prepare a monoclonal antibody or functional fragment thereof, especially a murine-derived monoclonal antibody or functional fragment thereof, reference can be made to the technology especially described in the manual “Antibodies” (Document 10: Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor N.Y., pp. 726, 1988) or the technique for preparation from hybridoma cells described by Kohler and Milstein (Nature, 256: 495-497, 1975).

EXAMPLE

[0075] The embodiments of the present disclosure will be described in detail below in conjunction with examples. However, it will be understood in the art that the following examples are only used to illustrate the present disclosure and should not be regarded as limiting the scope of the present disclosure.

Example 1 Screening and Affinity Detection of Anti-Claudin 18.2 Murine Antibody

[0076] Claudin 18.2-knockout mice (from Biocytogen (Beijing) Pharmaceutical Technology Co., Ltd.) were immunized with cells including a eukaryotic expression plasmid encoding the first extracellular domain of Claudin 18.2 as an immunogen.

[0077] A total of 22 murine antibodies were screened: CLN-40-3C8, CLN-07-4C3, CLN-39-8D11, CLN-39-1E1, CLN-03-6H2, CLN-03-4E5, CLN-03-1A8, CLN-03-4A11, CLN-07-5B10, CLN-07-5G11, CLN-03-3A7, CLN-03-4C11, CLN-38-4H3, CLN-03-4G7, CLN-39-1B6, CLN-39-3E7, CLN-03-1F5, CLN-38-8A1, CLN-39-7H7, CLN-03-6G10, CLN-40-6C9 and CLN-07-5D9.

[0078] The binding activity of the obtained 22 murine antibodies to Claudin 18.2 was detected by FACS. The samples were diluted to the final concentration of 10 μg/mL, 1 μg/mL, 0.1 μg/mL, 0.01 μg/mL, and 0.001 μg/mL, and reacted with CHO-Claudin 18.2 cells at 4° C. for 30 min, respectively. After centrifugation and removal of the supernatant, each well was added with 200 μL of PBS, centrifuged at 2000 rpm for 5 min, and washed twice. Then, each well was added with 50 μL of 1:100 diluted anti-mouse IgGFc-FITC antibody (Abeam, Cat. No. ab97264) at 4° C. for 30 min of reaction, then washed once by repeating the washing step, and finally added with 200 μL of PBS to resuspend for the detection by the machine. The detection results are shown in Table 3, indicating that multiple antibodies showed good binding activity.

TABLE-US-00003 TABLE 3 Detection results of affinity of anti-Claudin 18.2 murine antibody Cell binding activity EC.sub.50 Clone No. μg/mL nM CLN-40-3C8 0.5022 0.335 CLN-07-4C3 0.703 0.469 CLN-39-8D11 0.8661 0.557 CLN-39-1E1 0.8726 0.582 CLN-03-6H2 1.168 0.779 CLN-03-4E5 1.281 0.854 CLN-03-1A8 1.367 0.911 CLN-03-4A11 1.373 0.915 CLN-07-5B10 1.511 1.007 CLN-07-5G11 1.601 1.067 CLN-03-3A7 2.386 1.59 CLN-03-4C11 2.655 1.77 CLN-38-4H3 2.792 1.86 CLN-03-4G7 3.337 2.22 CLN-39-1B6 3.635 2.43 CLN-39-3E7 3.676 2.42 CLN-03-1F5 4.259 2.83 CLN-38-8A1 4.806 3.2 CLN-39-7H7 5.154 3.43 CLN-03-6G10 6.054 4.03 CLN-40-6C9 7.185 4.78 CLN-07-5D9 9.093 6.06

Example 2 In Vivo Efficacy Evaluation of Anti-Claudin 18.2 Murine Antibody

[0079] 11 anti-Claudin 18.2 murine antibodies with good affinity (CLN-40-3C8, CLN-07-4C3, CLN-39-8D11, CLN-39-1E1, CLN-03-6H2, CLN-03-4E5, CLN-03-1A8, CLN-03-4A11, CLN-07-5B10, CLN-07-5G11 and CLN-03-3A7) were selected. Through gastric cancer PDX model, CLN-03-3A7, CLN-03-4E5 and CLN-03-6H2 were determined with therapeutic potential, and thus the above three antibodies were subjected to the subsequent in vivo efficacy evaluation.

[0080] B-NDG mice (this mouse model was provided by Biocytogen Jiangsu Gene Biotechnology Co., Ltd.) were subcutaneously inoculated with gastric cancer tumor, and divided into groups when the tumor volume reached 150 mm.sup.3, with 5 mice in each experimental group. After grouping, the murine antibodies CLN-03-3A7, CLN-03-4E5 and CLN-03-6H2 with good endocytosis and binding performance were injected into the abdominal cavity of mice at a dose of 10 mg/kg twice a week. The tumor growth of the mice was monitored twice a week (tumor volume=0.5*long diameter*short diameter2). The specific results are shown in FIG. 1 and FIG. 2. The experimental results show that the Claudin 18.2 murine antibody had a significant inhibitory effect on tumors and had a good safety, with the body weight of the mice not changing significantly, and the anti-tumor activity of the three murine antibodies was as follows: CLN-03-6H2>CLN-03-4E5>CLN-03-3A7.

Example 3 Preparation and Affinity Detection of Chimeric Antibody

[0081] Two murine antibodies CLN-03-4E5 and CLN-03-6H2 were subjected to chimeric antibody modification to obtain chimeric antibodies CLN-03-4E5-01 and CLN-03-6H2-01, respectively. The affinities of CLN-03-4E5-01, CLN-03-6H2-01 and IMAB362 (human-murine chimeric monoclonal antibody, claudiximab) were compared. It can be seen from the results (as shown in Table 4 and FIG. 3) that CLN-03-4E5-01, CLN-03-6H2-01 and IMAB362 all showed good affinity activities, and both of the two chimeric antibodies CLN-03-4E5-01 and CLN-03-6H2-01 provided by the present disclosure had a better binding activity than IMAB362.

TABLE-US-00004 TABLE 4 Affinity EC.sub.50 value of chimeric antibody and IMAB362 Name EC.sub.50 value (μg/mL) CLN-03-4E5-01 0.4475 CLN-03-6H2-01 0.4103 IMAB362 0.475

Example 4 Endocytosis Efficiency Detection of Chimeric Antibody

[0082] The endocytosis efficiency of the chimeric antibody CLN-03-6H2-01 and IMAB362 (human-murine chimeric monoclonal antibody, claudiximab) was detected and compared. The purified chimeric antibody was labeled according to the instructions of promega PHAb antibody dye labeling kit (Promega G9841), and the concentration of the antibody before the labeling was 2 mg/mL. The labeled antibody was incubated with cells of gastric cancer model KATOIII (ATCC), pancreatic cancer model AsPC-1 (ATCC), and lung cancer model A549 (ATCC) according to a certain concentration gradient at 37° C. The time gradient was set as: 0 h, 2 h, 4 h, 6 h, 8 h, 12 h, and 24 h, and the concentration gradient was set as: 0.1 nM, 1 nM, and 10 nM. After sampling at each point, the fluorescence intensity was detected by a flow cytometer. The experimental results (see FIG. 4A, FIG. 4B and FIG. 4C) show that the chimeric antibody CLN-03-6H2-01 had a better endocytosis effect than IMAB362 in different tumor cell lines, where FIG. 4A shows the comparison of the endocytosis efficiency of CLN-03-6H2-01 and IMAB362 in the gastric cancer model KATOIII, FIG. 4B shows the comparison of the endocytosis efficiency of CLN-03-6H2-01 and IMAB362 in the pancreatic cancer model AsPC-1, and FIG. 4C shows the comparison of the endocytosis efficiency of CLN-03-6H2-01 and IMAB362 in the lung cancer model A549.

Example 5 Humanization of Chimeric Antibody CLN-03-6H2-01

[0083] The chimeric antibody CLN-03-6H2-01 was humanized by grafting CDRs of light or heavy chain into the framework region of light or heavy chain of immunoglobulin. The CDRs of the light chain and heavy chain of the chimeric antibody CLN-03-6H2-01 were determined using the Kabat system. The human IgG1 framework region was determined by alignment in a database of antibody variable regions. The light chain variable region sequences of different humanized Clandin 18.2 antibodies and the heavy chain variable region sequences of different humanized Clandin 18.2 antibodies were designed and synthesized. The light chain variable region of the humanized Clandin 18.2 antibody was fused with the human kappa constant region by PCR to obtain the light chain of the humanized Clandin 18.2 antibody in full length. The heavy chain variable region of the humanized Clandin 18.2 was fused with the IgG1 constant region by PCR to obtain the heavy chain of the humanized Clandin 18.2 antibody in full length. Different light and heavy chains were combined and expressed, and the affinities of multiple purified humanized antibodies were detected by flow cytometry (FACS) (see Table 5). The antibody H-1 having the best affinity (named as RGCLN18.2 antibody) was selected for sequencing.

TABLE-US-00005 TABLE 5 Comparison of affinity of humanized chimeric antibody CLN-03-6H2-01 Humanized antibody No. EC.sub.50 (μg/mL) H-l 0.1656 H-2 0.2443 H-3 0.3006 H-4 0.3120 H-5 0.3969 H-6 0.3971 H-7 0.4884 H-8 0.5953 H-9 0.8415 H-10 0.8469 H-ll 1.009 H-12 1.122 H-13 1.541 H-14 1.636 H-15 1.940 CLN-03-6H2-01 0.462

[0084] Table 6 shows the amino acid sequences of CDRs of light and heavy chains of RGCLN18.2 antibody (Kabat numbering).

TABLE-US-00006 TABLE 6 Amino acid sequences of CDRs of heavy and light chains of RGCLN18.2 antibody (Kabat numbering) Heavy CDR1 SEQ ID NO: 5 NYLIE chain CDR2 SEQ ID NO: 10 LINPGSGGTNYNEKFKG CDR3 SEQ ID NO: 15 GGYYGNSFAY Light CDR1 SEQ ID NO: 20 KSSQSLLNSGNQKNYLT chain CDR2 SEQ ID NO: 25 WASTRES CDR3 SEQ ID NO: 30 QNAYYYPYT

[0085] Amino acid sequence of the heavy chain variable region of RGCLN18.2 antibody (SEQ ID NO: 1):

TABLE-US-00007 QVQLVQSGAE VKKPGASVKV SCKASGYAFT NYLIEWVRQA PGQGLEWMGL INPGSGGTNY 60 NEKFKGRVTM TRDTSTSTVY MELSSLRSED TAVYYCARGG YYGNSFAYWG QGTLVTVSS 119

[0086] Amino acid sequence of the light chain variable region of RGCLN18.2 antibody (SEQ ID NO: 2):

TABLE-US-00008 DIVMTQSPLS LPVTPGEPAS ISCKSSQSLL NSGNQKNYLT WYLQKPGQSP QLLIYWASTR 60 ESGVPDRFSG SGSGTDFTLK ISRVEAEDVG VYYCQNAYYY PYTFGGGTKV EIK 113

[0087] Amino acid sequence of the heavy chain of RGCLN18.2 antibody (SEQ ID NO: 33):

TABLE-US-00009 QVQLVQSGAE VKKPGASVKV SCKASGYAFT NYLIEWVRQA PGQGLEWMGL INPGSGGTNY 60 NEKFKGRVTM TRDTSTSTVY MELSSLRSED TAVYYCARGG YYGNSFAYWG QGTLVTVSSA 120 STKGPSVFPL APSSKSTSGG TAALGCLVKD YFPEPVTVSW NSGALTSGVH TFPAVLQSSG 180 LYSLSSVVTV PSSSLGTQTY ICNVNHKPSN TKVDKKVEPK SCDKTHTCPP CPAPELLGGP 240 SVFLFPPKPK DTLMISRTPE VTCVVVDVSH EDPEVKFNWY VDGVEVHNAK TKPREEQYNS 300 TYRVVSVLTV LHQDWLNGKE YKCKVSNKAL PAPIEKTISK AKGQPREPQV YTLPPSREEM 360 TKNQVSLTCL VKGFYPSDIA VEWESNGQPE NNYKTTPPVL DSDGSFFLYS KLTVDKSRWQ 420 QGNVFSCSVM HEALHNHYTQ KSLSLSPGK 449

[0088] Amino acid sequence of the light chain of RGCLN18.2 antibody (SEQ ID NO: 34):

TABLE-US-00010 DIVMTQSPLS LPVTPGEPAS ISCKSSQSLL NSGNQKNYLT WYLQKPGQSP QLLIYWASTR 60 ESGVPDRFSG SGSGTDFTLK ISRVEAEDVG VYYCQNAYYY PYTFGGGTKV EIKRTVAAPS 120 VFIFPPSDEQ LKSGTASVVC LLNNFYPREA KVQWKVDNAL QSGNSQESVT EQDSKDSTYS 180 LSSTLTLSKA DYEKHKVYAC EVTHQGLSSP VTKSFNRGEC 220

Example 6 Preparation of Antibody-Drug Conjugate (ADC)

[0089] The antibody-drug conjugate (ADC) was prepared using a common coupling method: a reducing agent and a protecting agent were prepared with purified water using 1-20 mM TCEP (tris-2-carboxyethyl-phosphine) and 1-20 mM DTPA (diethylene triamine pentacetate acid) stock solution. The reducing agent was mixed, at an amount varying within a certain concentration range according to the required coupling rate, with a certain concentration (e.g., 5-30 mg/mL) of a monoclonal antibody at a certain volume ratio (1:1) with stirring at 25° C. for 1 h of reaction, with a molar ratio of the final concentration of TCEP to the antibody being 0.5-6.0:1. The TCEP-reduced antibody may be used directly for conjugation.

[0090] A linker-active drug unit compound was prepared at a certain concentration (5 mM), dissolved in 25% DMSO (dimethyl sulfoxide), and slowly added with drug at a molar ratio of drug to thiol of 0.3-2.8:1, and stirred at 25° C. for 1-4 h of reaction. After the reaction was completed, centrifugation and ultrafiltration was performed 3 times with PBS buffer for purification to remove residual unreacted drugs and free small molecules such as DMSO. The conjugation was detected using SDS-PAGE electrophoresis and hydrophobic interaction chromatography-high performance liquid chromatography (HIC-HPLC).

[0091] The linker-active drug unit compounds used in this example were MC-Val-Cit-PAB-MMAE, D07-Val-Cit-PAB-MMAE and Py-MAA-Val-Cit-PAB-MMAE, which have the following structural formulas, respectively (refer to patent applications CN108853514A (page 14 of the specification), CN111433188A (page 53 of the specification), and WO2019223579A1 (pages 25-27 of the specification) for the synthesis methods).

##STR00015##

[0092] The following ADCs were prepared by the above method (p is an integer selected from 1, 2, 3, 4, 5, 6, 7 and 8, q is an integer selected from 1, 2, 3 and 4, and Ab is the RGCLN18.2 antibody provided by the present disclosure), and the average DAR of these ADCs is 3.5-4.5.

##STR00016##

Example 7 Endocytosis Experiment of Antibody-Drug Conjugate

[0093] The human gastric cancer cell line NCI-N87 cells were resuspended in the wells of a 6-well plate at approximately 1×10.sup.5 cells per well. RGCLN18.2, RGCLN18.2-PY-Val-Cit-PAB-MMAE, RGCLN18.2-MC-Val-Cit-PAB-MMAE, and RGCLN18.2-D07-Val-Cit-PAB-MMAE were conjugated with pHAb amine reactive dye respectively, and then diluted to 10 μg/mL with cell culture medium. The cells were added with 100 μL of the dye complexes of RGCLN18.2 or ADCs, and incubated at 37° C. at an indicated time (0 h, 1 h, 3 h, 5 h, 21 h and 24 h). The endocytosis effect of RGCLN18.2 and ADCs was measured by a flow cytometer, and the results are shown in FIG. 5. From the results of the endocytosis experiment, it was found that the ADCs RGCLN18.2-PY-Val-Cit-PAB-MMAE, RGCLN18.2-MC-Val-Cit-PAB-MMAE, and RGCLN18.2-D07-Val-Cit-PAB-MMAE all had an endocytosis rate of about 98% at 24 h. The results show that the ADCs of RGCLN18.2 had a very good endocytosis effect in the human gastric cancer cell NCI-N87.

Example 8 In Vitro Cell Evaluation of Antibody-Drug Conjugate

[0094] The suspension of human gastric cancer cell line NCI-N87 cells was added to the wells of a 96-well plate at a density of 100 μL/well and 5000 cells/well, and then cultured overnight in a 37° C. water-saturated CO.sub.2 incubator. The antibody-drug conjugates (RGCLN18.2-PY-Val-Cit-PAB-MMAE, RGCLN18.2-D07-Val-Cit-PAB-MMAE, RGCLN18.2-MC-Val-Cit-PAB-MMAE, IMAB362-MC-Val-Cit-MMAE) were serially diluted, added to the 96-well plate containing cells at 100 μL/well, and cultured for another 72 h in a 37° C. incubator. The OD value at 450 nm was read by a microplate reader, and the inhibition rate was calculated as IR %=(OD blank-OD drug)×100/OD blank. The IC.sub.50 value was calculated by the curve fitting software Softmax Pro7.0.3 Gxp, and the results are shown in Table 7. From the above experimental data of the in vitro efficacy test, it was found that the ADCs RGCLN18.2-PY-Val-Cit-PAB-MMAE, RGCLN18.2-MC-Val-Cit-PAB-MMAE, and RGCLN18.2-D07-Val-Cit-PAB-MMAE had a better inhibition effect on proliferation than IMAB362-MC-Val-Cit-MMAE.

TABLE-US-00011 TABLE 7 In vitro IC50 value and maximum inhibition rate of antibody-drug conjugate Inhibition IC.sub.50 rate ADC DAR (ng/mL) (%) RGCLN18 2-PY-Val-Cit-PAB-MMAE 4.1 10.51 54.5 RGCLN18.2-D07-Val-Cit-P AB-MMAE 3.84 4.94 54.3 RGCLN18.2-MC-Val-Cit-P AB-MMAE 4.03 6.23 53.08 IMAB362-MC-Val-Cit-P AB-MMAE 4.22 501 52.27

Example 9 PDX (Patient-Derived Xenograft) Model Experiment of Antibody-Drug Conjugate

[0095] The human pancreatic cancer tissue was washed, cut into small pieces, and inoculated on the right scapula of the back of nude mice with a trocar. When the tumor grew to 100-300 mm.sup.3, the animals were randomly divided into groups. The administration of the control group and the experimental group is as shown in Table 8.

TABLE-US-00012 Table 8 Administration of control group and experimental group in PDX experiment Test drug Number of dead animals PBS One died on Day 25 after administration IMAB362-MC-Val-Cit-P AB-MMAE One died each on Day 14, Day 18, and Day 53 RGCLN18.2-MC-Val-Cit-P AB-MMAE No death

[0096] The experimental results are shown in FIG. 6 and FIG. 7, where FIG. 6 shows the graph of changes in the body weight of animals in the control group and the experimental group, and FIG. 7 shows the graph of changes in the tumor volume of animals in the control group and the experimental group. The results show that RGCLN18.2-MC-Val-Cit-PAB-MMAE had stronger anti-tumor effect than IMAB362-MC-Val-Cit-PAB-MMAE in human pancreatic cancer PDX model.

[0097] The above description is only for some embodiments by way of example only and without limitation to the combination of features necessary for carrying the present disclosure into effect. The headings provided herein are not intended to limit the various embodiments of the present disclosure. Terms such as “including”, “comprising” and “containing” are not intended to be limiting. In addition, unless otherwise indicated, the singular form “a”, “an”, or “the” includes plural references, as well as “or” means “and/or”. Unless otherwise defined herein, all technical and scientific terms used herein have the same meaning as commonly understood in the art.

[0098] All publications and patents mentioned in the present application are incorporated herein by reference. Without departing from the scope and spirit of the present disclosure, various modifications and variations of the described method and composition of the present disclosure will be apparent. Although the present disclosure has been described by using embodiments, it should be understood that the disclosure should not be unduly limited to these embodiments.