Enantiomer Selective Glucuronidation of the Non‐Steroidal Pure Anti‐Androgen Bicalutamide by Human Liver and Kidney: Role of the Human UDP‐Glucuronosyltransferase (UGT)1A9 Enzyme

Abstract

Bicalutamide (Casodex â ) is a non-steroidal pure anti-androgen used in the treatment of localized prostate cancer. It is a racemate drug, and its activity resides in the (R)-enantiomer, with little in the (S)-enantiomer. A major metabolic pathway for bicalutamide is glucuronidation catalysed by UDP-glucuronosyltransferase (UGT) enzymes. While (S)bicalutamide is directly glucuronidated, (R)bicalutamide requires hydroxylation prior to glucuronidation. The contribution of human tissues and UGT isoforms in the metabolism of these enantiomers has not been extensively investigated. In this study, both (R) and/or (S) bicalutamide were converted into glucuronide (-G) derivatives after incubation of pure and racemic solutions with microsomal extracts from human liver and kidney. Intestinal microsomes exhibited only low reactivity with these substrates. Km values of liver and kidney samples for (S)bicalutamide glucuronidation were similar, and lower than values obtained with the (R)-enantiomer. Among the 16 human UGTs tested, UGT1A8 and UGT1A9 were able to form both (S) and (R)bicalutamide-G from pure or racemic substrates. UGT2B7 was also able to form (R)bicalutamide-G. Kinetic parameters of the recombinant UGT2B7, UGT1A8 and UGT1A9 enzymes support a predominant role of the UGT1A9 isoform in bicalutamide metabolism. Accordingly, (S)bicalutamide inhibited the ability of human liver and kidney microsomes to glucuronidate the UGT1A9 probe substrate, propofol. In conclusion, the present study provides the first comprehensive analysis of in vitro bicalutamide glucuronidation by human tissues and UGTs and identifies UGT1A9 as a major contributor for (R) and (S) glucuronidation in the human liver and kidney.Bicalutamide (Casodex â , fig. 1) is a non-steroidal pure antiandrogen used for the treatment of early localized or locally advanced non-metastatic prostate cancer (reviewed in [1]). The drug is given once daily at a dosage of 150 mg as monotherapy or of 50 mg in combination with chemical or surgical castration. This pure anti-androgen competes with the active hormone, 5a-dihydrotestosterone, for androgen receptor binding and activation and thus blocks the prostate tumour growth-stimulating effects of androgens [2]. The drug used in clinic corresponds to a racemate of (R) and (S) enantiomers ( fig. 1), and its anti-androgenic activity resides almost exclusively in the (R)-enantiomer, with little, if any activity in the (S)-enantiomer [1,2]. Bicalutamide is cleared almost exclusively by metabolism. In human beings, the drug is excreted to similar extents in urine and faeces [3]. Two polar metabolites found in urines were identified as the glucuronide (-G) conjugates of (S)bicalutamide and hydroxy(R)bicalutamide [3]. Urinary concentrations of (S)bicalutamide-G are maximal 24 hr after administration of a single dose and represent up to 76% of the urinary metabolites. However, this percentage decreases to 14%, 9 days after dosage [3]. Urinary levels of the hydroxy (R)bicalutamide-G follow an inverse variation, and its...

Efficient Test for Nonlinear Dependence of Two Continuous Variables

“…1 and Table 3), which other methods could not easily find. These three genes were also reported to be involved in the kidney cancer development process in the literature [32][33][34][35][36].…”

“…The MCM3 gene was found to be overexpressed in various human cancers, including kidney cancer [34]. The UGT1A9 gene was identified as a major contributor for glucuronidation in the human liver and kidney [35]. From Fig.…”

Characterization of oxycodone in vitro metabolism by human cytochromes P450 and UDP-glucuronosyltransferases

“…RPLC has been broadly used for glucuronides analyses [21][22][23][24] and particularly for highly lipophilic stationary phases such as octadecyl-bonded phases C 18 [25][26][27][28]. More recently, RPLC, hydrophilic interaction liquid chromatography (HILIC), aqueous normal phase chromatography (ANPC), and subcritical fluid chromatography (SFC) were compared for their abilities to analyze UGT substrates and their corresponding glucuroconjugates [15].…”

Structure- and isoform-specific glucuronidation of six curcumin analogs

“…In fact, UGT1A9 and UGT2B7 showed glucuronidation activities toward a broad range of compounds containing an alcoholic hydroxyl group. These compounds include 1 0 -hydroxyestragole (Iyer et al, 2003), 3 0 -azido-3 0 -deoxythymidine (Barbier et al, 2000), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (Ren et al, 2000), 4-hydroxyretinoic acid (Samokyszyn et al, 2000), almokalant (Gaiser et al, 2003), bicalutamide (Grosse et al, 2013), dihydroartemisinin (Ilett et al, 2002), ethanol (Al Saabi et al, 2013Schwab & Skopp, 2014), ornidazole (Du et al, 2013), propafenone (Xie and Zeng, 2010), propranolol (Yu et al, 2010) and R-oxazepam (Court et al, 2002). It should be noted that both hepatic and renal UGTs would contribute to the metabolism of these curcumin analogs, because UGT1A9 and UGT2B7 were abundantly expressed in human liver and kidney (Fallon et al, 2013a;Sato et al, 2014).…”