Binding of the carcinogen 2-acetamidophenanthrene to rat liver nucleic acids: Lack of correlation with carcinogenic activity, and failure of the hydroxamic acid ester model for in vivo activation

Abstract

2-Acetamidophenanthrene (AAP) is a potent mammary carcinogen in the female rat and induces leukemia and tumors of the ear duct and small intestine in both males and females (J.A. Miller, et al., Cancer Res., 15 (1955) 188) but produced no tumors in the liver. Only small amounts of N-hydroxy derivative are excreted (E.C. Miller, et al., Cancer Res., 26 (1966) 2239) and N-hydroxy-AAP appears to be a poor substrate for rat liver sulfotransferase (J.R. DeBaun, et al., Cancer Res., 30 (1970) 577). Binding studies have been lacking, however. After injection (18 h) of [ ring- 3H]AAP into male Fischer rats, specific binding to liver DNA was somewhat higher than for the (ring-labeled) liver carcinogen 2-acetamidofluorene (AAF), whereas binding to RNA was less. Three days after injection, DNA binding was about 40% of the level at 24 h, while RNA binding had increased slightly. After 28 days, binding to DNA was 30% of the initial level, while RNA binding had diminished to less than 3% of the maximum level. Both DNA and RNA obtained at times from 1 day to 28 days after injection of AAP were digested with S 1 nuclease and acid phosphatase and chromatographed on Sephadex LH-20 with synthetic 8-( N-2-phenanthrylacetamido)deoxyguanosine and N 6-1-(2-acetamidophenanthryl)deoxyadenosine as markers. Both are found when DNA is treated with either the sulfate or acetate ester of N-hydroxy-AAP (J.D. Scribner and N.K. Naimy, Cancer Res., 35 (1975) 1416), but were not found in the rat liver AAP-DNA, nor were the corresponding nucleosides found in the RNA digests. At least six adducts were found in the DNA digests, of which four were rapidly excised ( t 1 2 ≈ 15 h ). Some peaks were lacking in the RNA digests, but none were obtained from RNA which were not obtained from DNA. Injection of [ acetyl- 3H]AAP yielded no label on either DNA or RNA, indicating that all adducts found lacked the acetyl group. It seems clear that the mechanism of activation of AAF for nucleic acid binding in rat liver does not apply to AAP. Further conclusions are probably premature, however.