AN INTERCALATION INHIBITOR ALTERING THE TARGET SELECTIVITY OF DNA-DAMAGING AGENTS - SYNTHESIS OF SITE-SPECIFIC AFLATOXIN B-1 ADDUCTS IN A P53 MUTATIONAL HOTSPOT

Aflatoxin B-1 (AFB(1)) is a potent human carcinogen implicated in the etiology of hepatocellular carcinoma, Upon metabolic activation to the reactive epoxide, AFB(1) forms DNA adducts primarily at the N7 positi on of guanines. To elucidate more fully the molecular mechanism of AFB (1)-induced mutagenesis, an intercalation inhibitor was designed to pr obe the effects of intercalation by AFB(1) epoxide on its reaction wit h DNA, DNA duplexes were prepared consisting of a target strand contai ning multiple potentially reactive guanines and a nontarget strand con taining a cis-syn thymidine-benzofuran photoproduct, Because the coval ently linked benzofuran moiety physically occupies an intercalation si te, we reasoned that such a site would be rendered inaccessible to AFB (1) epoxide, By strategic positioning of this intercalation inhibitor in the intercalation site 5' to a specific guanine, the adduct yield a t that site was greatly diminished, indicating that intercalation by A FB(1) epoxide contributes favorably to adduct formation, Using this ap proach it has been possible to simplify the production of site-specifi cally modified oligonucleotides containing AFB(1) adducts in the seque nce context of a p53 mutational hotspot. Moreover, we report herein is olation of site-specifically AFB(1)-modified oligonucleotides in seque nces containing multiple guanines, Use of intercalation inhibitors wil l facilitate bath investigation of the ability of other carcinogens to intercalate into DNA and the synthesis of specific carcinogen-DNA add ucts.