Aminopeptidase N (APN/CD13) is involved in tumor cell invasion and tumor angiogenesis and is considered a promising therapeutic target in the treatment of cancer. To develop a novel monoclonal antibody-based cancer therapy targeting APN/CD13, we established a fully humanized anti-APN/CD13 monoclonal antibody, MT95-4. In vitro, MT95-4 inhibited APN/CD13 enzymatic activity on the tumor cell surface and blocked tumor cell invasion. B16 mouse melanoma cells stably expressing human APN/CD13 were also established and were inoculated s.c. or injected i.v. into nude mice. We found that expression of human APN/CD13 in murine melanoma cells increased the size of subcutaneous tumors, extent of lung metastasis and degree of angiogenesis in the subcutaneous tumors; these tumor-promoting and angiogenesis-promoting characteristics were reduced by the i.p. administration of MT95-4. To further verify the specificity of MT95-4 for neutralization of APN/CD13 activity, MT95-4 was administered into NOD/SCID mice inoculated s.c. with H1299 or PC14 cells, which exhibit high expression of APN/CD13, or with A549 cells, which exhibit weak expression of APN/CD13. MT95-4 reduced tumor growth and angiogenesis in mice bearing H1299-derived and PC14-derived tumors, but not in mice bearing A549-derived tumors. These results suggested that the antitumor and anti-angiogenic effects of MT95-4 were dependent on APN/CD13 expression in tumor cells. Given that MT95-4 is the first fully humanized monoclonal antibody against APN/CD13, MT95-4 should be recognized as a promising candidate for monoclonal antibody therapy against tumors expressing APN/CD13.
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