Synergism of endogenous inhibitors, exogenous cytostatic agents and hormones in arrest of proliferation.

The synergism between endogenous regulators of proliferation (protors), alkylating agents and hormones in vitro was studied. The effects were monitored by the incorporation of 3H-TdR into human and rat short term bone marrow cultures and by the formation of mouse granulocyte-macrophage colonies in semisolid agar capillaries. An additive and/or slight potentiating synergism was demonstrated between different types of inhibitory protors (GI-3S2, GI-3S3 and GI-3B), between GI-3 and hydrocortisone, and between GI-3 and the alkylating agents (adriamycin, dianhydrogalactitol) examined. The results offer a real possibility of strengthening the inhibition of neoplastic proliferation without increasing cytotoxicity of the drugs used.