Intestinal UDP-Glucuronosyltransferase 1A1 and Protection against Irinotecan-Induced Toxicity in a Novel UDP-Glucuronosyltransferase 1A1 Tissue-Specific Humanized Mouse Model

The human UDP-glucuronosyltransferases (UGTs) represent an important family of drug-metabolizing enzymes, with UGT1A1 targeting the conjugation and detoxification of many exogenous substances, including pharmaceutical drugs. In this study we generated humanized UGT1A1 mice expressing the human UGT1A1 gene in either liver (hUGT1A1^HEP ) or intestine (hUGT1A1^GI ), enabling experiments to examine tissue-specific properties of UGT1A1-specific glucuronidation. Hepatic and intestinal tissue-specific expression and function of UGT1A1 were demonstrated. Although the liver is considered a major organ for detoxification, intestinal UGT1A1 is an important contributor for drug clearance. Mice were challenged with irinotecan (CPT-11), a prodrug hydrolyzed by carboxylesterases to form the active metabolite 7-ethyl-10-hydroxycamptothecin (SN-38) and detoxified by UGT1A1. Humanized UGT1A1^HEP mice that have no intestinal UGT1A1 displayed a greater lethality rate when exposed to CPT-11 than hUGT1A1^GI mice. When exposed to a low dose of CPT-11 (10 mg/kg), hUGT1A1^HEP mice displayed greater intestinal inflammatory (IL-1β and IL-6) insult in addition to p53-triggered apoptotic responses. In vitro studies with intestinal crypt organoids exposed to CPT-11 confirmed the results observed in vivo and indicated that CPT-11 impacts stemness, apoptosis, and endoplasmic reticulum (ER) stress in organoids deficient in UGT1A1. When we examined the induction of ER stress in organoids with thapsigargin, an inhibitor of sarco/endoplasmic reticulum Ca²⁺ ATPase, apoptosis and the caspase surge that occurred in hUGT1A1^HEP mice were blocked in hUGT1A1^GI organoids. This study reveals the importance of intestinal UGT1A1 in preventing inflammation, apoptosis, and loss of stemness capacity upon systemic challenge with an important chemotherapeutic agent. SIGNIFICANCE STATEMENT: Hepatic and intestinal UGT1A1 play a key role in the metabolism and detoxification of endogenous and exogenous compounds. The use of tissue-specific humanized models expressing UGT1A1 in liver or intestine has confirmed the relevance of the intestinal tract in the detoxification of irinotecan. Mechanistic studies using intestinal organoids highlighted the importance of UGT1A1 in reducing inflammation, apoptosis, and loss of stemness. These new models provide valuable tools for studying tissue-specific glucuronidation of substances that are metabolized by human UGT1A1.