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Lung Cancer-associated Monoclonal Antibody 15 That Recognizes Cell Growth-related Membrane Antigens gp85/45 and Its Growth-inhibitory Effect on Human Lung Cancer Cells in Vitro¹

Department of Pathology, Institute of Basic Medical Sciences [H. K., H. H., T. I., T. O.], and Department of Surgery, Institute of Clinical Medicine [K. E.], University of Tsukuba, Tsukuba-shi, Ibaraki-ken 305, Japan

In order to find lung cancer-specific markers, monoclonal antibody 15 (MAb15) was produced against a variant-type cell of small cell lung carcinoma. Its gp85/45 antigens were demonstrated in 70% of lung cancers, and particularly in the proliferating zone of cancer cell nests, but they are scarcely detected in noncancerous tissues. Immunoelectron microscopy revealed that gp85/45 antigens were expressed alternatively on the cell membrane of living cancer cells according to their biological states. MAb15 added to the culture medium inhibited the proliferation of lung cancer cells, depending on its concentration, but cell death rate did not increase. The growth inhibition by MAb15 was reevaluated by a colonogenic assay. On DNA histogram, MAb15 decreased the number of DNA-synthesizing cells in the S phase with an elevation of the G₁ peak, indicating a G₁-S boundary block in the cell cycle. gp85/45 detected by this lung cancer-associated monoclonal antibody could be a functional membrane unit, such as a growth factor receptor, which is related to the cell proliferation of lung cancer. The growth inhibition by MAb15 may be caused by the blocking of a growth factor receptor which is specific to lung cancer.

¹ This study was supported in part by grants from the University of Tsukuba Project Research.

² To whom requests for reprints should be addressed.

Received 2/21/89. Revised 6/12/89. Accepted 6/15/89.