Molecular Mechanisms of Irinotecan Induced Fatty Liver Disease and Drug-Drug Interaction

Chemotherapy drugs due to their inherent cytotoxicity, inevitably causes negative consequences. Liver being the primary site of metabolism for many chemotherapy drugs, hepatotoxicity is collateral and occurs frequently in an unpredictable or idiosyncratic fashion. Despite significant advances in our understanding of the mechanisms of action and pharmacodynamics, the underlying etiology of hepatic toxicity for various chemotherapy drugs remains unexplained. With knowledge about interrelationships between the liver and chemotherapy, many potential side effects and serious damage can be avoided. Furthermore, understanding the mechanisms involved in chemotherapy-associated hepatotoxicity will help lay out dose modification guidelines and platform for interventions to reduce the hepatotoxicity without compromising their efficacy. Irinotecan is a very potent neoadjuvant chemotherapy for colorectal liver metastases but its treatment is associated with non-alcoholic fatty liver disease (NAFLD or FLD) that increases risk for post-operative morbidity and mortality. Drug-induced hepatotoxic reactions are mostly idiosyncratic (i.e not typically dose-dependent and unpredictable) and immunologic mechanisms or variations in host metabolic response play major role. Furthermore, altered expression and activities of drug metabolizing enzymes (DMEs) and transporters have been associated with drug-induced hepatotoxicity, leading to potential drug-drug interactions (DDIs). Our overall goal is thus to determine molecular mechanisms of irinotecan induced hepatotoxicity and DDIs. Hepatotoxicity can reproduce virtually any known pattern of liver injury, including all stages of FLD. Pathogenesis of FLD is not yet fully understood, however “multiple hit theory” has been suggested in recent years including insulin resistance, disturbed fat homeostasis and inflammation. Compelling evidences suggests critical role of “gut–liver axis” through involvement of liposaccharide (LPS)/Toll-like receptor 4 (TLR4) signaling pathway in FLD onset and progression. The cause and mechanism of FLD induced by irinotecan therapy is still not known and need to be explored. Recent study indicates role of MyD88, common adaptor of TLR4 signaling, in augmenting irinotecan-induced intestinal damage. Further, DDI was observed for combination chemotherapy of irinotecan and co-administered anticancer drug, taxol, which is a TLR4 agonist. Irinotecan is metabolized in the liver to active and toxic metabolite, SN-38. The levels of SN-38 are determined by involvement of multiple DMEs, which includes, CYP3A, carboxylesterases (CES) and uridine diphosphate-glucuronosyltransferase (UGT1A1). We have previously shown that activation of TLR4 by LPS suppress DMEs and transporters genes (Ghose et al., 2009)leading to altered PK/PD of drug. Our central hypothesis is that TLR signaling-mediated alteration in DMEs and transporters results in accumulation of SN-38 which is associated with irinotecan-induced FLD and DDI with drug taxol that can activate TLR4. We propose to achieve our goals by pursuing the following specific aims: Aim 1: To determine molecular mechanisms of irinotecan-induced FLD. We hypothesis that irinotecan-induced FLD is mediated by MyD88 signaling. We developed a reproducible, reliable, simple mouse model with irinotecan in C57BL/6 mice and our results demonstrate an essential role of MyD88 signaling in promoting irinotecan-induced hepatic steatosis that involved increased serum levels of toxic metabolite SN-38 and disturbed fat homeostasis. Aim 2: To determine potential dietary component(s) as strategic intervention to ameliorate irinotecan-induced FLD. We hypothesize that diets with lard as fat source will have increased severity in irinotecan-induce FLD compared to diets with plant based fat source. We found that plant derived diet, chow diet and herbal compound rich in isoflavonoids have a protective effect against irinotecan-induced FLD. Aim 3: To determine mechanism of irinotecan DDI. We hypothesize that pharmacokinetics (PK) of irinotecan and SN-38 will be altered by another drug (taxol) through activation of TLR4. We find that taxol alters the PK of irinotecan in TLR4-dependent pathway that parallels with TLR4-mediated alteration in DME genes by taxol. Thus, our finding proposes a novel mechanism of the regulation of DDIs by TLR4 and indicates two possible unwanted effects because of TLR4 involvement in regulation of DMEs, (i) decreased SN-38 levels may result in population with TLR4 polymorphism, thus loss of efficacy with irinotecan treatment; and (ii) TLR4 agonists pose potential for DDIs when given as combination therapy or lead to own PK variations and an increased propensity for hepatotoxicity.Pharmacological and Pharmaceutical Sciences, Department o