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Species difference in glucuronidation formation kinetics with a selective mTOR inhibitor

Loren M Berry1, Jingzhou Liu, Adria Colletti

  • 1Departments of Pharmacokinetics and Drug Metabolism (L.M.B., J.L., A.C., Z.Z., Y.T.) and Discovery Research (P.K.), Amgen, Inc., Cambridge, Massachusetts.

Drug Metabolism and Disposition: the Biological Fate of Chemicals
|January 16, 2014
PubMed

Insights

The study investigated the metabolism of an mTOR inhibitor (compound 1) in rats and across species. N-glucuronidation was a major metabolic pathway, showing species-specific differences that may impact drug development.

Area of Science:

  • Pharmacology
  • Drug Metabolism
  • Biochemistry

Background:

  • The mammalian target of rapamycin (mTOR) is a key protein kinase implicated in age-related diseases and cancer.
  • mTOR inhibitors are promising therapeutic agents, necessitating a thorough understanding of their metabolic profiles.
  • Compound 1, a potent ATP-competitive mTOR inhibitor, was selected for metabolic investigation.

Purpose of the Study:

  • To elucidate the metabolic elimination pathways of compound 1 in vivo using bile duct-cannulated rats.
  • To compare the in vitro metabolism of compound 1 in liver microsomes across various species, including rat, dog, human, and cynomolgus monkey.
  • To assess the species selectivity of N-glucuronidation and its potential implications for drug development and animal modeling.

Main Methods:

  • Bile duct-cannulation in rats to study in vivo drug elimination.
  • In vitro incubation of compound 1 with liver microsomes from rat, dog, human, and cynomolgus monkey.
  • Identification and quantification of N-glucuronide metabolites using analytical techniques.
  • Kinetic analysis of metabolite formation to determine reaction kinetics.

Main Results:

  • Compound 1 undergoes extensive N-glucuronidation in rats, forming metabolites on the pyrazole moiety (N1, N2) and the primary amine.
  • All three N-glucuronide metabolites were found in rat, dog, and human liver microsomes, but primary amine glucuronidation was absent in monkeys.
  • Species-selective N-glucuronidation was observed, with N2 favored in rat, dog, and human, and N1 favored in monkeys. Monkey N-glucuronidation exhibited sigmoidal kinetics, distinguishing it from other species.
  • These findings suggest that monkeys may not be ideal models for predicting human N-glucuronidation of UGT1A9 or UGT1A1 substrates.

Conclusions:

  • N-glucuronidation is a significant metabolic pathway for compound 1, with notable species-specific differences.
  • The observed metabolic profile, particularly in higher species like monkeys and humans, could lead to high clearance and impact systemic exposure.
  • Medicinal chemistry strategies may be beneficial to reduce the metabolic liability of compound 1, thereby improving its pharmacokinetic properties for in vivo studies.

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