Enhancement of naturally occurring human spontaneous monocyte-mediated cytotoxicity by cis-diamminedichloroplatinum(II).

The effect of the antineoplastic agent cis-diamminedichloroplatinum(II) (cis-DDP) on spontaneous cytotoxicity of human mononuclear cells in vitro was assessed. cis-DDP enhanced spontaneous monocyte-mediated cytotoxicity 300% compared to control values. Further, this spontaneous monocyte killing developed earlier (3 to 4 days) than did that of untreated cells (5 to 7 days). Since monocyte cytotoxicity is under the control of lymphocyte suppressor cells, the effect of cis-DDP on separated populations of lymphocytes and monocytes was examined. Unlike X-irradiation which enhanced monocyte cytotoxicity through the indirect pathway of inactivation of lymphocyte suppressors, cis-DDP directly stimulated the monocyte population. Direct stimulation of killer monocytes may be an important mechanism of the antitumor effect of cis-DDP.