Organ-specific carboxylesterase profiling identifies the small intestine and kidney as major contributors of activation of the anticancer prodrug CPT-11

Abstract

The activation of the anticancer prodrug CPT-11, to its active metabolite SN-38, is primarily mediated by carboxylesterases (CE). In humans, three CEs have been identified, of which human liver CE (hCE1; CES1) and human intestinal CE (hiCE; CES2) demonstrate significant ability to hydrolyze the drug. However, while the kinetic parameters of CPT-11 hydrolysis have been measured, the actual contribution of each enzyme to activate the drug in biological samples has not been addressed. Hence, we have used a combination of specific CE inhibition and conventional chromatographic techniques to determine the amounts, and hydrolytic activity, of CEs present within human liver, kidney, intestinal and lung specimens. These studies confirm that hiCE demonstrates the most efficient kinetic parameters for CPT-11 activation, however, due to the high levels of hCE1 that are expressed in liver, the latter enzyme can contribute up to 50% of the total of drug hydrolysis in this tissue. Conversely, in human duodenum, jejunum, ileum and kidney, where hCE1 expression is very low, greater than 99% of the conversion of CPT-11 to SN-38 was mediated by hiCE. Furthermore, analysis of lung microsomal extracts indicated that CPT-11 activation was more proficient in samples obtained from smokers. Overall, our studies demonstrate that hCE1 plays a significant role in CPT-11 hydrolysis even though it is up to 100-fold less efficient at drug activation than hiCE, and that drug activation in the intestine and kidney are likely major contributors to SN-38 production in vivo.

P-Glycoprotein, CYP3A, and Plasma Carboxylesterase Determine Brain and Blood Disposition of the mTOR Inhibitor Everolimus (Afinitor) in Mice

“…Upon oral everolimus administration, local concentrations of everolimus might be high especially in the intestine, and possibly surpass the K i of approximately 20 mmol/L toward CES2. CES2 is for instance thought to be a main enzyme responsible for the conversion of irinotecan to SN-38 in humans (38), and for hydrolysis of a prodrug of gemcitabine (39). Coadministration of everolimus with ester (pro-) drugs affected by carboxylesterases, including the 5-FU anticancer prodrug capecitabine (40), should thus be assessed very carefully.…”

Intestinal glucuronidation protects against chemotherapy-induced toxicity by irinotecan (CPT-11)

“…Consistent with these studies, the importance of intestinal enzymes in CPT-11 toxicity has also been suggested in tissue-specific profiling studies of CES. Human intestinal CES2 exhibits a higher affinity and velocity than human hepatic CES1, demonstrating the significant ability to hydrolyze CPT-11 (10,26,27). Intestinal selective CES inhibitors have been suggested as a new clinical target to minimize CPT-11-induced late diarrhea (35,36).…”

“…However, its efficacy and safety are compromised because of severe late diarrhea, the side-effect resulting from CPT-11 bioactivation and subsequent metabolism, generally occurring more than 24 h after the administration of irinotecan (6)(7)(8)(9). CPT-11 is a prodrug that is hydrolyzed by carboxylesterase (CES) activity to the active topoisomerase 1 inhibitor, SN-38 (10,11). Inactivation and detoxification occur primarily by hepatic UDP-glucuronosyltransferase 1A1 (UGT1A1)-catalyzed glucuronidation to form the SN-38 glucuronide (SN-38G), which subsequently undergoes biliary excretion.…”

“…However, the intestinal tissue from both humans and rodents is also rich in these enzymes (10,11,(23)(24)(25). The direct conversion of CPT-11 to SN-38 in the intestine is considered to be one of the mechanisms leading to intestinal toxicity (10,26,27). Alternatively, intestinal microflora-derived β-glucuronidase is capable of catalyzing SN-38G to generate free SN-38 through enterohepatic circulation (18).…”

Carboxylesterases: General detoxifying enzymes

“…This includes the epithelia of the lung and gut, liver, kidney and skin [12, 13]. An example of CE expression in vivo is demonstrated in Figure 4 in a zebrafish model.…”