In Vitro Metabolism of Oprozomib, an Oral Proteasome Inhibitor: Role of Epoxide Hydrolases and Cytochrome P450s

Abstract

Oprozomib is an oral proteasome inhibitor currently under investigation in patients with hematologic malignancies or solid tumors. Oprozomib elicits potent pharmacological actions by forming a covalent bond with the active site -terminal threonine of the 20S proteasome. Oprozomib has a short half-life across preclinical species and in patients due to systemic clearance via metabolism. Potential for drug-drug interactions (DDIs) could alter the exposure of this potent therapeutic; therefore, a thorough investigation of pathways responsible for metabolism is required. In the present study, the major drug-metabolizing enzyme responsible for oprozomib metabolism was identified in vitro. A diol of oprozomib was found to be the predominant metabolite in human hepatocytes, which formed via direct epoxide hydrolysis. Using recombinant epoxide hydrolases (EHs) and selective EH inhibitors in liver microsomes, microsomal EH (mEH) but not soluble EH (sEH) was found to be responsible for oprozomib diol formation. Coincubation with 2-nonylsulfanyl-propionamide, a selective mEH inhibitor, resulted in a significant decrease in oprozomib disappearance (>80%) with concurrent complete blockage of diol formation in human hepatocytes. On the contrary, a selective sEH inhibitor did not affect oprozomib metabolism. Pretreatment of hepatocytes with the -cytochrome P450 (P450) inhibitor 1-aminobenzotriazole resulted in a modest reduction (∼20%) of oprozomib metabolism. These findings indicated that mEH plays a predominant role in oprozomib metabolism. Further studies may be warranted to determine whether drugs that are mEH inhibitors cause clinically significant DDIs with oprozomib. On the other hand, pharmacokinetics of oprozomib is unlikely to be affected by coadministered P450 and sEH inhibitors and/or inducers.

Clinical pharmacokinetics of oral drugs in the treatment of multiple myeloma

“…The metabolism involves primarily the hydrolysis of oprozomib epoxide via microsomal (mEH) and not soluble epoxide hydrolases. Peptidases, CYP450, and gluthathion‐tranferases play a minor role in oprozomib metabolism . The variability in oprozomib pharmacokinetics might result from the prominent role of mEH that have a large and ubiquitous tissue expression attributable to environmental factors as well as polymorphism …”

Physiologically‐based pharmacokinetic modelling to predict oprozomib CYP3A drug–drug interaction potential in patients with advanced malignancies

“…inhibitory constant [K i ]) . With HLMs, oprozomib was shown to be a weak time‐dependent inhibitor of CYP3A4 (IC 50 > 30 μM for reversible inhibition; IC 50 reduced to 5.3 and 12 μM, respectively, with testosterone and midazolam as the CYP3A4 substrate and a 30‐min oprozomib pre‐incubation with HLMs in the presence of nicotinamide adenine dinucleotide phosphate [NADPH]) . The TDI of oprozomib on CYP3A4/5 observed in HLMs was NADPH‐dependent, suggesting it is likely due to CYP‐mediated metabolite(s).…”

“…The TDI of oprozomib on CYP3A4/5 observed in HLMs was NADPH‐dependent, suggesting it is likely due to CYP‐mediated metabolite(s). However, in vitro and in vivo studies on oprozomib have shown that in humans it is primarily metabolized by epoxide hydrolases rather than CYP‐mediated metabolism . Incubation in HLMs may overestimate CYP‐mediated oprozomib metabolism and results may not translate to humans in vivo .…”

“…Oprozomib is primarily metabolized by epoxide hydrolases and peptidases; cytochrome P450 (CYP) enzymes play a minor role in its metabolism and elimination . In an in vitro study using human liver microsomes (HLMs), oprozomib showed time‐dependent inhibition (TDI) of human CYP3A4 , and suppressed CYP3A mRNA expression, which is not commonly seen for small molecule drugs. The question remains regarding the optimal approach to predict the potential for drug–drug interaction (DDI) between oprozomib and CYP3A4 substrates.…”

1-Aminobenzotriazole: A Mechanism-Based Cytochrome P450 Inhibitor and Probe of Cytochrome P450 Biology

“…In these studies, 1-ABT administered to the rats before the lung study was shown to suppress P450 activities completely without any effect on the metabolism of the drug. A comparison of the effects of 1-ABT and inhibitors of epoxide hydrolases on the metabolism of oprozomib, an oral proteasome inhibitor, confirmed that the major metabolic pathway was epoxide hydrolysis rather than P450-catalyzed oxidation [ 122 ].…”