Abstract 5667: Identification of chemopreventive agents against dibenzo[a,l]pyrene-induced DNA adducts and potential mechanisms

Abstract

Abstract Intervention with compounds of natural origin with little or no known toxicity is considered an effective means to prevent cancer development. We describe here a microsomal activation system in combination with 32P-postlabeling adduct assay to identify efficacious phytochemicals against the potent lung and breast carcinogen, dibenzo[a,l]pyrene (DBP). Briefly, salmon testes (st)-DNA was incubated with test agents (150 µM), DBP (10 µM), β-naphthoflavone-induced rat liver microsomes, co-factors in Tris. HCl (50 mM, pH 7.4). After incubation for 60 min at 37°C, the reaction was terminated. Analysis of the purified DNA by 32P-postlabeling showed essentially the same spectra of multiple adducts in all samples. However, quantitative differences were observed. Of nine phytochemicals tested, several compounds almost completely abolished the DNA adduct formation, some showed modest inhibition, while others were ineffective: resveratrol (95% reduction), delphinidin (94%), tanshinone I, (84%) tanshinone IIA (78%), diindolylmethane (73%), indole-3-carbinol (49%) and cyanidin (46%) and withaferin A (33%); cucurbitacin B showed insignificant reduction. All adducts were found to be equally inhibited, suggesting that activity of both CYP1A1 and 1B1, the major cytochromes P450s involved in the metabolism of DBP, were similarly affected. Oltipraz included as positive control, as expected, showed over 80-90% inhibition. To determine if the adduct inhibition occurred due to scavenging of electrophilic metabolites of DBP, st-DNA was incubated with the most effective test agents in the presence of anti-dibenzo[a,l]pyrene diolepoxide (anti-DBPDE). Analysis of the resultant adducts showed that only delphinidin, cyanidin and resveratrol showed modest inhibition (30-45%); other compounds were ineffective. Ellagic acid, which is known to scavenge the DBP electrophilic metabolite, almost completely abolished the adduct formation. Together, our data suggest that resveratrol, delphinidin, tanshinones and diindolylmethane are potent inhibitors of microsomal DBP-DNA adduct formation. While, the adduct inhibition for delphinidin and resveratrol may occur, in part, due to scavenging of the electrophilic metabolite of DBP, both these agents, tanshinones and diindolylmethane may also elicit their activity by inhibiting the cytochromes P450 activity. In summary, resveratrol, delphinidin, tanshinones and diindolylmethane, all of which are consumed either in fruits and vegetables or via folklore medicine (tanshinones) may be useful in the prevention of DBP-mediated lung and mammary tumorigenesis (Supported from the USPHS grants CA-118114, ES-011564 and Agnes Brown Duggan Endowment). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5667.