Torcetrapib
A workaround measures two acyl-glucuronide metabolites of torcetrapib in monkey urine without ever having reference standards for them (Biomed Chromatogr 2010)
Original title: Challenges in the indirect quantitation of acyl-glucuronide metabolites of a cardiovascular drug from complex biological mixtures in the absence of reference standards
This paper describes quantifying acyl-glucuronide metabolites M26 and M5 of torcetrapib in monkey urine without reference standards for those specific metabolites. Because reference standards were available for M1 and M4, the aglycone forms of M26 and M5, in vivo samples were treated with sodium hydroxide to hydrolyze the acyl-glucuronides to their aglycones, and the difference in M1 and M4 concentrations before and after hydrolysis estimated the urinary levels of M26 and M5. During method optimization, a prolonged rise in M4 over time was observed that was inconsistent with the expected rapid base-hydrolysis of an acyl-glucuronide, prompting an investigation of possible interference from M9, an ether-glucuronide metabolite isobaric to M4, using chromatographic and wet-chemistry approaches. The resulting LC/MS/MS assay was established as reliable, and metabolite exposure was correlated with toxicological observations to gain initial insight into the physiological role of these torcetrapib metabolites.
Original abstract
This paper describes the quantitation of acyl-glucuronide metabolites (M26 and M5) of a cardiovascular-drug (torcetrapib) from monkey urine, in the absence of their reference standards. LC/MS/MS assays for M1 and M4 (aglycones of M26 and M5, respectively) were characterized from normal and base-treated urine, as their respective reference standards were available. The in vivo study samples containing M26 and M5 were treated with 1 n sodium hydroxide to hydrolyze them to their respective aglycones. The study samples were assayed for M1 and M4 before and after alkaline hydrolysis and the difference in the concentrations provided an estimate of the urinary levels of M26 and M5. Prior to the main sample analysis, conditions for alkaline hydrolysis of the glucuronides were optimized by incubating pooled study samples. During incubations, a prolonged increase in M4 levels over time was observed, which is inconsistent with the base-hydrolysis of an acyl-glucuronide (expected to hydrolyze rapidly). Possible interference of the metabolite M9 (an ether-glucuronide metabolite isobaric to M4) was investigated to explain this observation using chromatographic and wet-chemistry approaches. The strategies adopted herein established that the LC/MS/MS assay and our approach were reliable. The metabolite exposure was then correlated to toxicological observations to gain initial insights into the physiological role of these metabolites.
Summary written by cetpinhibition.org from the published abstract; figures as published. Page updated 18 August 2026. Methods.