Suramin inhibits tumor cell cytotoxicity mediated through natural killer cells, lymphokine-activated killer cells, monocytes, and tumor necrosis factor.

Suramin, a polysulfonated naphthylurea, is an antitrypanosomal and antifilarial drug. Because of its anti-reverse transcriptase activity and antiproliferative activity, suramin is also used for the treatment of acquired immunodeficiency syndrome and cancer. In spite of these uses, very little is known about its effects on the immune system. In this report, we investigated the effects of suramin on peripheral blood mononuclear cells. We found that natural killer (NK) cell-mediated cytotoxicity against human erythroblastoid cell line K562 was completely inhibited by suramin in a dose-dependent manner. It also completely blocked lymphokine-activated killer (LAK) cell-mediated cytotoxicity against the human B lymphoblastoid cell lines Raji and Daudi. The cytotoxicity against the human melanoma tumor cell line A-375 mediated by unstimulated and stimulated monocytes was also suppressed by suramin. Maximum inhibition of monocyte-mediated cytotoxicity was observed when suramin was present during both the activation and the effector phases of cytotoxicity. Besides its effects on cell-mediated cytotoxicity, suramin also inhibited the cytotoxic effects of tumor necrosis factor (TNF) against different tumor cell lines. Furthermore, we found that suramin interferes with the binding of TNF with its receptor. Thus our results indicate that suramin overall downregulates the immune system by inhibiting cell-mediated and TNF-mediated cytotoxicity against different tumor cells.