RT Journal Article SR Electronic T1 Structural Characterization of Anti-HIV Drug Candidate PA-457 [3-O-(3′,3′-Dimethylsuccinyl)-betulinic acid] and Its Acyl Glucuronides in Rat Bile and Evaluation of in Vitro Stability in Human and Animal Liver Microsomes and Plasma JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 1436 OP 1442 DO 10.1124/dmd.106.009233 VO 34 IS 9 A1 Zhiming Wen A1 Stephan T. Stern A1 David E. Martin A1 Kuo-Hsiung Lee A1 Philip C. Smith YR 2006 UL http://dmd.aspetjournals.org/content/34/9/1436.abstract AB PA-457 [3-O-(3′,3′-dimethylsuccinyl)-betulinic acid] represents a new class of anti-HIV drug candidates termed maturation inhibitors. After oral administration to rats, PA-457 was metabolized to several glucuronide conjugates and mainly eliminated into rat bile. Liquid chromatography-electrospray ionization-mass spectrometry analysis showed that the glucuronidation products of PA-457 were acyl glucuronides including one di-glucuronide, di-PA-457G, and two mono-glucuronides, referred to as mono-PA-457G (I) and mono-PA-457G (II), respectively. In-source fragmentation of MS spectra supported the conclusion that mono-PA-457G (I) was glucuronidated at the C-28 carboxyl of PA-457, whereas mono-PA-457G (II) was conjugated at the dimethylsuccinic acid side chain of the C-3 position. Quantification demonstrated that the predominant glucuronide of PA-457 in rat bile was mono-PA-457G (I) with lower amounts of mono-PA-457G (II) and di-PA-457G. In vitro stability indicated that the mono-acyl glucuronides of PA-457 were not degraded after incubation with 0.1 M phosphate buffer (pH 4, 7.4 and 9), plasma (human, rat, and mouse), and UDP-glucuronosyltransferase reaction media (without uridine 5′-diphosphoglucuronic acid) with microsomes (human, rat, and mouse liver microsomes), respectively, whereas the minor diglucuronide was unstable in rodent liver microsomes. All glucuronides of PA-457 could be hydrolyzed both by β-glucuronidase and alkaline (1 M NaOH). Minor putative acyl migration products were slowly formed at pH 9, suggesting that the acyl glucuronides of PA-457 have relatively high in vitro stability. The American Society for Pharmacology and Experimental Therapeutics