Biotransformation of sodium nitroprusside into dinitrosyl iron complexes in tissue of ascites tumors of mice.

We have found that treatment of various types of murine ascites tumors with sodium nitroprusside (SNP) both in vitro (1.5 mM) and in vivo (25 mg/kg; i.p.) results in formation of EPR-detectable dinitrosyl nonheme iron complexes (DNIC) with RS- groups of proteins (g perpendicular = 2,037; g parallel = 2,012). The DNIC were mainly localized in the ascitic extracellular fluid. The appearance of DNIC was unaffected by an inhibitor of nitric oxide synthase, N omega-nitro-L-arginine (1 mM), but abolished with a SH-blockator, p-chloromercuribenzoate (0.1 mM). No DNIC formation was observed when ascitic fluid (after tumor cells separation) was incubated with SNP alone, but with SNP and L-cysteine (10 mM). Thus, ascites tumor cells contribute to the transformation of SNP into DNIC and thiols are essential in this process.