MUTAGENICITY AND CYTOTOXICITY OF BENZO(A)PYRENE BENZO-RING EPOXIDES

Abstract

Four benzo ring epoxides of the environmental carcinogen benzo(a)pyrene (BP) were tested for mutagenic and cytotoxic activity in 3 strains of Salmonella typhimurium (TA1538, TA98 and TA100) and Chinese hamster V79 cells. Although very unstable in aqueous solution, 7.beta.,8.alpha.-dihydroxy-9.beta.,10.beta.-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (diol epoxide 1), with the 7-hydroxyl group on the same face of the molecule as the epoxide O was 1.5-4 times as mutagenic in the bacterial strains as its more stable stereoisomer 7.beta.,8.alpha.-dihydroxy-9.alpha.,10.beta.-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (diol epoxide 2). In V79 cells, diol epoxide 1 had 1/3 the mutagenic activity of diol epoxide 2 but was at least 10 times more labile than diol epoxide 2 in the tissue culture medium. The half-life of diol epoxide 1 in tissue culture medium was about 30 s, whereas the half-life of diol epoxide 2 was between 6 and 12 min. 9,10-Epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene, which is saturated in the benzo ring, is also very unstable and has mutagenic activity equal to or greater than diol epoxide 1 in the bacterial and mammalian cells, 7,8,-Epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene was more stable in aqueous solution than any of the 9,10-epoxides of BP but was less mutagenic in the bacterial and mammalian cells. In V79 cells, diol epoxides 1 and 2 and 9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene were more than 40 times more cytotoxic than 7,8-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene. The mutagenicity of the 2 tetrahydro epoxides toward strain TA98 of S. typhimurium was readily abolished by purified epoxide hydrase, whereas the mutagenic activity of the 2 diol epoxides was relatively unaffected by coincubation with the enzyme.