The polycyclic aromatic hydrocarbons dibenzo(a,i)pyrene and dibenzo(a,h)pyrene, each of which possesses two bay regions, and their bay-region difluorinated derivatives were tested for mutagenicity for ouabain and 6-thioguanine resistance in Chinese hamster V79 cells. Since V79 cells do not metabolize polycyclic aromatic hydrocarbons, mutagenesis was tested in both the presence and the absence of golden hamster embryo cells capable of metabolizing polycyclic aromatic hydrocarbons. Neither of the dibenzopyrenes nor their fluorinated derivatives were mutagenic in the absence of the golden hamster embryo cells. In the presence of these cells (cell-mediated assay), both dibenzopyrenes were mutagenic, whereas the difluorinated derivatives, 2,10-difluorodibenzo-(a,i)pyrene and 3,10-difluorodibenzo(a,h)pyrene, either were inactive or exhibited (on a dose basis) a week response. However, the mutagenicity of the dibenzopyrenes was eliminated when they were coincubated with 7,8-benzoflavone, a mixed-function oxidase inhibitor. The results suggest that metabolic oxidation of these polycyclic aromatic hydrocarbons at the bay region (presumably to diol-epoxides) is required for a mutagenic response in the cell-mediated assay.

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Research sponsored by the National Cancer Institute under Interagency Agreement 40-636-77; by the Environmental Protection Agency under Interagency Agreement 79-D-XO533 with the United States Department of Energy, under Contract W-7405-eng-26 with the Union Carbide Corporation; and by National Cancer Institute Grant CA 23454.

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