THE CARCINOGENICITY OF METHOXYL DERIVATIVES OF 4-AMINOAZOBENZENE - CORRELATION BETWEEN DNA-ADDUCTS AND GENOTOXICITY

To elucidate the cause of the difference in genotoxic activity between carcinogenic 3-methoxy-4-aminoazobenzene (3-MeO-AAB) and noncarcinoge nic 2-methoxy-4-aminoazobenzene (2-MeO-AAB), we analyzed DNA adducts i n the livers of rats exposed to either of these chemicals and studied the resulting biologic potential with the aid of in vitro modified M13 phage DNA. P-32-Postlabeling analysis revealed that the carcinogen 3- MeO-AAB produced 20-fold higher amounts of adducts than did 2-MeO-AAB. Five adducts were formed in the 3-MeO-AAB case whereas only one adduc t was apparent in 2-MeO-AAB-treated rat. Studies of in vitro DNA repli cation using N-hydroxy (N-OH)-aminoazo dye-modified M13 phage DNA as a template demonstrated inhibition by 3-MeO-AAB adducts to be substanti ally greater than in the 2-MeO-AAB-adducts. The specificity of mutagen esis induced in M13mp9 phage DNA by these chemicals also was analyzed after transfection into SOS-induced Escherichia coli JM103, mutation f requencies being higher with N-OH-3-MeO-AAB- than N-OH-2-MeO-AAB-modif ied DNA. The mutation spectra differed in each case. Our data suggest that the difference in hepatocarcinogenic activity between the two che micals depends not only on qualitative and quantitative variation in a dduct formation but also on conformation changes in modified DNA.