4-(4-NITROBENZYL)PYRIDINE TESTS FOR ALKYLATING-AGENTS FOLLOWING CHEMICAL OXIDATIVE ACTIVATION

A chemical activation system (CAS) designed to mimic the mammalian mixed-function oxidase enzymes was found to activate target compounds to reactive electrophiles. Activated compounds were assayed by reaction with 4-(4-nitrobenzyl)pyridine (NBP). A model nucleophile of 7-alkylguanine of nucleic acids, NBP produces a violet color following alkylation. Twenty compounds from several chemical classes were tested. The test generally gave positive and negative responses where expected. Two compounds, trichloroethylene and diethylnitrosamine, exhibited a linear Beer's law relationship in the concentration range tested. A high degree of linear correlation (r > 0.97) was obtained for these compounds. Other compounds showed varying degrees of linear correlation from high correlation (r = 0.94) to weak correlation (r = 0.44). The CAS-NBP assay results were compared to bacterial mutagenicity and animal carcinogenicity test results when information was available. A good correlation (r = 0.80) existed between direct alkylating activity and direct mutagenicity. Similar correlations existed between NBP alkylation following activation and mutagenicity following microsomal activation (r = 0.73). Also, different correlations were observed between carcinogenicity and NBP alkylation following activation (r = 0.69) and without activation (r = 0.38).