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Bioactivation of GPR40 Agonist MK-8666: Formation of Protein Adducts in Vitro from Reactive Acyl Glucuronide and Acyl CoA Thioester
journal contribution
posted on 2019-10-14, 19:40 authored by Jackie Shang, Richard Tschirret-Guth, Mark Cancilla, Koppara Samuel, Qing Chen, Harry R. Chobanian, Ann Thomas, Wei Tong, Hubert Josien, Alexei V. Buevich, Kaushik MitraMK-8666, a selective
GPR40 agonist developed for the treatment
of type 2 diabetes mellitus, was discontinued in phase I clinical
trials due to liver safety concerns. To address whether chemically
reactive metabolites played a causative role in the observed drug
induced liver injury (DILI), we characterized the metabolism, covalent
binding to proteins, and amino acid targets of MK-8666 in rat and
human hepatocytes or cofactor-fortified liver microsomes. MK-8666
was primarily metabolized to an acyl glucuronide in hepatocytes of
both species and a taurine conjugate in rat hepatocytes. Similar levels
of covalent binding to proteins were observed in rat and human hepatocytes
following incubation with [3H]MK-8666. After protease digestion
of hepatocyte pellets, amino acid adducts A1, A2, and A3 were identified
as transacylated products with lysine, serine, and cysteine residues,
respectively. Amino acid adducts A4a–c were identified as glycation
adducts resulting from rearrangement of MK-8666–1-O-β-acyl
glucuronide to ring-opened aldehydes which further condensed with
lysine residues of proteins into imine adducts. Adducts A1–A3
and A4a–c were detected in rat and human liver microsomes fortified
with UDPGA. Adducts A1–A3 were detected in rat and human liver
microsomes fortified with CoA and ATP. Additionally, a trace amount
of CoA thioester metabolite of MK-8666 and its transacylated GSH adduct
were detected in human liver microsomes fortified with CoA, ATP, and
GSH. Higher levels of covalent binding to protein were observed when
[3H]MK-8666 was incubated in liver microsomes supplemented
with CoA and ATP compared to UDPGA. Addition of GSH attenuated levels
of CoA thioester-mediated covalent binding by 41–45%. Collectively,
these studies indicated that metabolism of the −COOH moiety
of MK-8666 can form a reactive acyl glucuronide and an acyl CoA thioester,
which covalently modifies proteins and may represent one causative
mechanism of the observed DILI.
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Keywords
covalent bindingAmino acid adductscofactor-fortified liver microsomestransacylated GSH adductliver safety concernsreactive acyl glucuronideacyl CoA thioesterCoA thioester metaboliteMK -8666COOHliver microsomesDILIATPGPR 40 agonisthepatocytetype 2 diabetes mellitusAdductReactive Acyl GlucuronideGSH attenuated levelsproteinCoA thioester-mediated covalent bindingUDPGA
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