IN-VIVO CISPLATIN-EXPOSED MACROPHAGES INCREASE IMMUNOSTIMULANT-INDUCED NITRIC-OXIDE SYNTHESIS FOR TUMOR-CELL KILLING

Mice pre-exposed to cisplatin increased their production of nitric oxi de (NO) when treated with lipopolysaccharide (LPS). Peritoneal macroph ages, isolated from mice 11 days after cisplatin treatment and culture d with LPS plus IFN-gamma, increased NO production, whereas the macrop hages isolated 2 days after cisplatin treatment decreased it. In both eases, NO was not produced without immunostimulant(s). Northern and We stern Blot analysis showed that macrophages exposed to cisplatin for 1 1 days increased production of mRNA and protein expression of inducibl e nitric oxide synthase (iNOS). This result indicated that macrophages became more sensitive to LPS and IFN-gamma when they were exposed to cisplatin in vivo. Peritoneal macrophages, when activated with LPS plu s IFN-gamma acid then cocultured with several tumor cells, exhibited c ytotoxic activity against both cisplatin-sensitive and cisplatin-resis tant tumor cells. There was no difference in cytotoxicity between the paired cells. Under the same experimental condition, macrophages that were exposed to cisplatin for 11 days had significantly increased thei r cytotoxicity to the tumor cells. This cytotoxic activity was inhibit ed by the NOS inhibitor N-G-monomethyl-L-arginine, indicating that NO is a major effector for macrophage-mediated tumor cell killing. Treatm ent of tumor cells with S-nitroso-N-acetylpenicillamine, a NO-generati ng compound, showed the similar tumoricidal effect. These data demonst rated that injection of cisplatin into the mice can enhance the sensit ivity of macrophages to the subsequent treatment of immunostimulant(s) for effective tumor cell killing through enhanced NO production.