The purpose of this study was to determine whether nitric oxide (NO) production by different mammary tumor cell lines correlated with their sensitivity to NO mediated injury. Three mammary tumor cell lines LM2, LM3 and LMM3 syngeneic to BALB/c mice were cultured in vitro with IFNgamma + LPS. Different levels of NO production among the three lines were detected in culture supernatants. The only tumor cell line which did not produce NO (LM2) showed the highest sensitivity to SNP-derived NO cytotoxicity (87%), while LM3 and LMM3 which both produced higher levels of NO than LM2, showed lower cytotoxicity by SNP (39% and 22% respectively). Spleen cells (SC) from M2 tumor bearing mice (TBM) were able to lyse LM2 cells by NO-dependent mechanisms. SC from M3-TBM exerted cytotoxicity against LM3 cells mainly by NO-independent mechanisms. Thus, we postulate an inverse correlation between NO production and NO mediated cytotoxicity in the three mammary tumor cell lines. It is possible that tumor cells producing NO develop mechanisms to resist NO injury.

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