TRANS-1,2-DIHYDRO-1,2-DIHYDROXY-6-AMINOCHRYSENE IS METABOLIZED TO FORM A MAJOR ADDUCT WITH DEOXYGUANOSINE AND PRODUCES MUTATIONS IN THE HPRT GENE OF CHINESE-HAMSTER OVARY CELLS AT G-C BASEPAIRS

6-Nitrochrysene can be activated to genotoxic derivatives by two major metabolic pathways: nitroreduction to N-hydroxy-6-aminochrysene, and a combination of ring-oxidation and nitroreduction that involves the intermediate formation of trans-1,2-dihydro-1,2-dihydroxy-6-aminochrysene (6-AC-1,2-dihydrodiol). The DNA adduct formed from this latter pathway was evaluated by reacting individual deoxynucleoside 5'-monophosphates with 6-AC-1,2-dihydrodiol in the presence of liver microsomal enzymes from 3-methylcholanthrene-pretreated rats. Binding was greatest to deoxyguanosine monophosphate and the major deoxyguanosine (dG) adduct co-chromatographed with the single major adduct formed from the microsome-catalyzed reaction of 6-AC-1,2-dihydrodiol with DNA. In order to characterize the mutational changes associated with the 6-AC-1,2-dihydrodiol pathway, we analyzed the mutational spectrum produced by 6-AC-1,2-dihydrodiol in the hypoxanthine-guanine phosphoribosyl-transferase (hprt) gene of CHO-K1 cells. cDNA was synthesized from the RNA of 28 6-thioguanine-resistant mutants, the hprt coding region amplified by the polymerase chain reaction, and the DNA products directly sequenced. Twenty independent primary mutations were found: 12 G:C --> T:A transversions, three G:C --> C:G transversions, one G:C --> A:T transition, one A:T --> T:A transversion, two -1 frameshift mutations in sequences containing consecutive guanines, and one 11 bp deletion. All G:C basepair substitutions had the mutated dG on the non-transcribed strand and 86% of the G:C basepair substitutions had one purine 3' to the mutated dG. The pattern of 6-AC-1,2-dihydrodiol-induced basepair substitutions was distinct from the pattern observed in solvent control mutants. These results are consistent with the formation of a promutagenic dG adduct from a metabolite of 6-AC-1,2-dihydrodiol.