A monoclonal antibody against rat calcitonin inhibits the growth of a rat medullary thyroid carcinoma cell line in vitro.
Medullary thyroid carcinoma (MTC) cells synthesize large amounts of calcitonin (CT), which serves clinically as a useful tumor marker. To examine the possibility of CT serving as a target in immunotherapy for MTC, we raised and characterized more than 40 monoclonal antibodies (mAbs) against rat CT (rCT). The affinity constants for the mAbs were between 2.8 x 10(9) and 1.8 x 10(11) M(-1). Some mAbs react preferentially with solid phase rat CT, but not with liquid phase 125I-labeled rCT. Thirty-nine mAbs cross-react with human CT. We evaluated the antitumor effect of the mAbs in vitro by analysis of [3H]thymidine incorporation into the rat MTC cell line CRL-1607. Some antibodies show an antiproliferative effect, but most are inactive. One mAb (2E5G5, IgG2b), which preferentially reacts with solid phase rCT, but not with liquid phase 125I-labeled rCT, exerts an antiproliferative activity on CRL-1607. At 6.25 x 10(-7) M, 2E5G5 killed all of the tumor cells independently of complement in a cytotoxicity assay. We explored the cytotoxic mechanisms by assays for cell cycle arrest and DNA fragmentation. The antitumor effect was manifested by apoptosis and cell cycle arrest. Hence, a secreted peptide may serve as a target in tumor immunotherapy. Therapeutically antibodies may exert antitumor activity by a variety of mechanisms. The antitumor effect of this mAb in a rat animal tumor model is being tested.
Zhang
R
R
Department of Medicine, University of Chicago, Illinois 60637, USA.
DeGroot
L J
LJ
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D000970:Antineoplastic Agents; D017209:Apoptosis; D002116:Calcitonin / Q000276:immunology*; D018276:Carcinoma, Medullary / Q000473:pathology*; D002453:Cell Cycle; D002455:Cell Division / Q000187:drug effects; D053938:DNA Fragmentation; D004587:Electrophoresis, Agar Gel; D005434:Flow Cytometry; D006801:Humans; D066298:In Vitro Techniques; D051381:Rats; D013964:Thyroid Neoplasms / Q000473:pathology*; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D000970:Antineoplastic Agents; D002116:Calcitonin