MUTATIONAL SPECIFICITIES OF THE FOUR STEREOISOMERS OF BENZO [c] PHENANTHRENE (3 ,4)DIHYDRODIOL(1 ,2)EPDXIDE IN A SHUTTLE VECTOR REPLICATING IN HUMAN CELLS

Abstract

A shuttle vector system was used to investigate the types and sites of mutations induced in human cells by the four stereoisomers of benzo[c]phenanthrene(3,4)dihydrodiol(1,2) epoxide (BcPhDE). These exhibit carcinogenic activities ranging from the most carcinogenic of the polycyclic aromatic hydrocarbon dihydrodiol epoxides tested thus far R-)BcPhDE-21 to non-carcinogenic [(-)BcPhDE-1]. pS189 shuttle vector containing the mutagenesis target gene supF coding for a tyrosine suppressor tRNA was treated in vitro with various doses of the test diol epoxide and transfected into adenovirus 5-transformed human embryonic kidney (Ad293) cells. Mutant vectors were selected and amplified in a bacterial system and the types and sequence specificities of the mutations were determined by sequencing the DNA. The frequency of supF mutants increased with BcPhDE dose in each case. More than 80% of the mutant vectors in each treatment group contained point mutations. At the highest dose, the frequencies of point mutants were 9.6 x 10⁻⁴ [(-)BcPhDE-2], 8.1 x 10⁻⁴ [( + )BcPhDE-2], 28.0 x 10⁻⁴ [(-)BcPhDE-1], and 21.5 x 10⁻⁴ [( + )BcPhDE-1]. These frequencies ranged from 31 to 108 times the spontaneous point mutant frequency (0.26 x 10⁻⁴), indicating that these mutations were induced by the compounds. The induced mutations were not randomly distributed within the supF gene, but occurred at mutagenic hotspots. Comparison with the mutational specificity of each diol epoxide revealed that each exhibits a unique mutational specificity.