Interaction Between Irinotecan and Dietary Flavonoids

Sri International, Menlo Park CA

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Abstract

DESCRIPTION (provided by applicant): Over 50% of cancer patients use alternative medicines regularly while undergoing chemotherapy. These products, though derived from natural sources, may contain active ingredients that may influence the disposition and/or therapeutic outcome of concomitantly administered chemotherapeutics. This application will address the issue of drug/botanical interaction between the anticancer agent irinotecan (used against colorectal cancer) and the popular dietary flavonoids from soy (genistein and daidzein) and fruits and vegetables (chrysin and quercetin). Irinotecan has complex dispositional characteristics, with sequential metabolic activation and inactivation steps, biliary and urinary excretion. The PI has studied some of these pathways extensively and has shown that the enzyme UGT1A1 glucuronidates its active metabolite, SN-38, and that the multidrug resistance transporter, p-glycoprotein (P-gp), plays a major role in irinotecan's biliary excretion. Flavonoids such as chrysin and quercetin are known inducers of UGT1A1. Our hypothesis are that (i) the selected dietary flavonoids will influence the disposition and toxicity of irinotecan via induction of the glucuronidation (by UGT1A1) of its active metabolite, SN-38; and (ii) induction of UGT1A1 by dietary flavonoids is influenced by genetic differences in the promoter region of the UGT1A1 gene. The specific aims are to (1) investigate the in vivo interaction of soy isoflavones, chrysin and quercetin with irinotecan in rats, (2) determine whether hepatic UGT1A1 induction by flavonoids is responsible for their interaction with irinotecan, and (3) investigate the influence of the TATA polymorphism in the promoter region of UGT1A1 on inducibility by these flavonoids. Aim 1 will involve in vivo pharmacokinetic, biliary, and urinary excretion studies with irinotecan after chronic pretreatment of rats with the selected dietary flavonoids. The potential induction of UGT1A1 will be studied in Aim 2 by measuring SN-38 glucuronidation in hepatocytes and liver microsomes from flavonoid treated rats, as well as by measuring UGT1A1 protein levels. In Aim 3, luciferase reporter assays will be performed to investigate UGT1A1 activity after pretreatment with flavonoids in Hep G2 cells transfected with known polymorphic forms (TA5,TA6,TA7,TA8) of the TATA sequence of UGT1A1. As irinotecan has a narrow therapeutic index, minor changes in its disposition can significantly modify the therapeutic outcome, so this investigation will have major potential benefits to cancer patients and oncologists. This pilot/developmental project will generate significant preliminary results to propose larger (R01) grants being planned by the PI and colleagues on the interaction between natural medications & dietary supplements and conventional chemotherapy, and its pharmacogenetic implications.