Carboxylesterase 2 and Intestine Transporters Contribute to the Low Bioavailability of Allisartan, a Prodrug of Exp3174 for Hypertension Treatment in Humans

Abstract

Exp3174 is an active metabolite of losartan for the treatment of hypertension. Allisartan (ALS3) is a marketed ester prodrug of Exp3174 to reduce bioavailability variation of losartan in China. However, ALS3 exhibited a lower oral absorption than losartan in humans. In this study, the enzymes and transporters involved in ALS3 and Exp3174 disposition were investigated to clarify the mechanisms. ALS3 underwent extensive hydrolysis to Exp3174 in S9 of Caco-2 cells, human intestine microsomes (HIM), recombinant carboxylesterase (rCES) 1, and rCES2. ALS3 exhibited similar affinity in HIM and rCES2 with K m values of 6.92 and 6.77 mM, respectively, indicating that ALS3 is mainly hydrolyzed to Exp3174 in human intestine by CES2. Transport assays of ALS3 and Exp3174 suggested that ALS3 and Exp3174 are substrates of P-glycoprotein, breast cancer resistance protein, and multidrug resistance protein 2 with poor permeability. Organic anion-transporting polypeptide 2B1 showed higher affinity and clearance toward ALS3 (K m 0.75 mM and intrinsic clearance 215 ml/min/mg) than those of Exp3174 (K m 7.85 mM and intrinsic clearance 16.1 ml/min/mg), indicating that ALS3 is preferred to be uptaken into intestinal epithelia. Hydrolysis of ALS3 was increased from approximately 30% to 55% in CES2-transfected human embryonic kidney 293-OATP2B1 cells, indicating the possible interplay between OATP2B1 and CES2. The influx and efflux of ALS3 across Caco-2 cells increased the potential of ALS3 hydrolysis to Exp3174, and the produced Exp3174 was rapidly pumped out, which led to undetectable ALS3 and Exp3174 in basolateral (receiver) side in Caco-2 cells. Overall, our study provided supportive evidences that the interplay between CES2 and transporters in intestine contributes to the low bioavailability of ALS3 in humans.

Comparison of Cellular Monolayers and an Artificial Membrane as Absorptive Membranes in the in vitro Lipolysis-permeation Assay

“…These differences can be explained by limited esterase expression in the kidney cell line. Fenofibrate is a substrate of the hepatic carboxylesterase CES1, which, has been reported to be expressed in MDCK II cells in other labs, 37 but not in the MDCK cells used in our lab. 32 Conversely, expression of CES1 in the colonic cell line is a well-known phenomenon, 38 and confirmed as highly expressed in the Caco-2 cells used in the previous study.…”

Pharmacokinetics and Safety of a Single Dose and Multiple Doses of Allisartan Isoproxil, an Angiotensin II Receptor Blocker, in Healthy Chinese People

“…Animal studies have indicated that AI can significantly decrease BP, improve baroreflex sensitivity, protect organs, and show low toxicity. 8 AI at a dose from 20 to 400 mg has been shown to be safe and tolerable in a phase 1 trial among healthy volunteers (unpublished data). Moreover, a phase 2 trial of AI (240 mg) versus placebo was conducted in hypertensive patients at low to medium risk in China.…”

“…6,7 Losartan was the first orally available selective antagonist of AT1R and is used widely in hypertensive patients. 8 Cytochrome P450 (CYP) 2C9 and CYP3A4 can catalyze losartan into many metabolites, including the carboxylic acid derivative EXP3174. 9 The latter has a more potent effect for blocking AT1Rs than losartan and has a half-life (t 1/2 ) that is 15-fold greater than that of losartan in vivo.…”

Differential Tissue Abundance of Membrane-Bound Drug Metabolizing Enzymes and Transporter Proteins by Global Proteomics

“…The predominant intestinal expression of CES2 is critical for the activation of dabigatran etexilate (double prodrug) to its intermediate metabolite, BIBR0951 (mono-prodrug) in the intestine, which is further converted into dabigatran (BIBR953) by CES1 in the liver (Ishiguro et al, 2014). CES2, P-gp, MRP2, and BCRP in the intestine collectively contribute to the low bioavailability of allisartan, a prodrug of Exp3174 for hypertension treatment in humans (Li et al, 2019). Similarly, if these pathways are important in the activation or inactivation of a toxic drug, the tissue-specific abundance of DMET proteins can lead to local toxicity without affecting plasma levels.…”