Bleomycin but not its derivatives inhibits the in vivo shedding of a rat tumor-associated antigen.

Rat fibrosarcoma (KMT-17) cells and their in vitro clone, 10% FCS A3 cells, shed a tumor-associated antigen (TAA), CE7, from the cell surface under growth-promoting conditions. We treated cells with the antitumor agent bleomycin (BLM) and its analogs peplomycin and liblomycin in vitro and in vivo in an attempt to increase expression of this antigen and induce an antitumor response. Although all three agents enhance antigen expression in vitro, proportionate to their direct antiproliferative effects, only BLM enhances antigen expression in vivo. The in vivo regulation of CE7 expression appears not to be related to the direct cytotoxic effects of the antitumor agents but rather to the immuno-augmenting effects of BLM.