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  • Title: Relative importance of bacterial and mammalian nitroreductases for niridazole mutagenesis.
    Author: Blumer JL, Friedman A, Meyer LW, Fairchild E, Webster LT, Speck WT.
    Journal: Cancer Res; 1980 Dec; 40(12):4599-605. PubMed ID: 6893679.
    Abstract:
    Niridazole is a nitrothiazole anthelmintic agent used to treat schistosomiasis. Its antibacterial activity was found to require the presence of the nitro group; a synthetic desnitro analog was completely inactive. Niridazole was mutagenic for Salmonella tester strains TA1538, TA98, and TA100, suggesting that it was both a frame-shift- and a base substitution-type mutagen. It was effective under both aerobic and anaerobic conditions, while similar testing of the desnitro niridazole produced consistently negative results. Addition of rat liver S-9 fraction under either aerobic or anaerobic conditions did not enhance mutagenicity. However, since bacterial killing limited the dose of niridazole to 0.33 microgram/plate in standard tester strains (1/20 Km for the mammalian liver enzymes), further studies were performed using niridazole-resistant, histidine-dependent mutants derived from strains TA98 and TA100. These mutants were found to be nitroreductase deficient and to resist the mutagenic effects of niridazole, in the presence or absence of S-9, up to concentrations of 10 microgram/plate. In addition, even at niridazole concentrations of up to 100 microgram/plate, rat liver S-9 was ineffective in enhancing the mutagenicity of niridazole. These results suggest that the mutagenicity of niridazole is dependent on its aromatic nitro group and a specific bacterial nitroreductase.
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