Effect of CYP3A5 Expression on the Inhibition of CYP3A-Catalyzed Drug Metabolism: Impact on Modeling CYP3A-Mediated Drug-Drug Interactions

Abstract

The purpose of this study was to determine the impact of CYP3A5 expression on inhibitory potency (K i or IC 50 values) of CYP3A inhibitors, using recombinant CYP3A4 and CYP3A5 (rCYP3A4 and rCYP3A5) and CYP3A5 genotyped human liver microsomes (HLMs). IC 50 ratios between rCYP3A4 and rCYP3A5 (rCYP3A5/rCYP3A4) of ketoconazole (KTZ) and itraconazole (ITZ) were 8.5 and 8.8 for midazolam (MDZ), 4.7 and 9.1 for testosterone (TST), 1.3 and 2.8 for terfenadine, and 0.6 and 1.7 for vincristine, respectively, suggesting substrate-and inhibitor-dependent selectivity of the two azoles. Due to the difference in the IC 50 values for CYP3A4 and CYP3A5, nonconcordant expression of CYP3A4 and CYP3A5 protein can significantly affect the observed magnitude of CYP3A-mediated drug-drug interactions in humans. Indeed, the IC 50 values of KTZ and ITZ for CYP3A-catalyzed MDZ and TST metabolism were significantly higher in HLMs with CYP3A5*1/*1 and CYP3A5*1/*3 genotypes than in HLMs with the CYP3A5*3/*3 genotype, showing CYP3A5 expression-dependent IC 50 values. Moreover, when IC 50 values of KTZ and ITZ for different HLMs were kinetically simulated based on CYP3A5 expression level and enzyme-specific IC 50 values, a good correlation between the simulated and the experimentally measured IC 50 values was observed. Further simulation analysis revealed that both the K i ratio (for inhibitors) and V max /K m ratio (for substrates) between CYP3A4 and CYP3A5 were major factors for CYP3A5 expression-dependent IC 50 values. In conclusion, the present study demonstrates that CYP3A5 genotype and expression level have a significant impact on inhibitory potency for CYP3A-catalyzed drug metabolism, but that the magnitude of its effect is inhibitor-substrate pair specific.

Relative Contributions of Cytochrome CYP3A4 Versus CYP3A5 for CYP3A-Cleared Drugs Assessed In Vitro Using a CYP3A4-Selective Inactivator (CYP3cide)

“…It had been previously suggested that midazolam 19-hydroxylase was potentially a better reaction for CYP3A5 than for CYP3A4 (Gibbs et al, 1999). This work used inferences from the enzyme kinetics of the reaction in HLMs and recombinant heterologously expressed systems as well as different inhibitory potencies for ketoconazole (Shirasaka et al, 2013). However, it is still Enzyme kinetics for cytochrome P450 CYP3A catalyzed reactions in recombinant human CYP3A4 and CYP3A5 clear from that work that both enzymes contributed and ascribing a particular percentage to each enzyme was not readily attainable.…”

“…However, for testosterone 6b-hydroxylase, the CYP3A4 contribution is dominant. As these two reactions are frequently used as marker reactions to test compounds as inhibitors of CYP3A, it becomes a possibility that a compound that inhibits one 3A enzyme and not the other could show different effects on different substrates (Shirasaka et al, 2013). It has been proposed that when testing new agents for inhibition of CYP3A, more than one probe reaction be used (Bjornsson et al, 2003).…”

Nuclear Receptors in Drug Metabolism, Drug Response and Drug Interactions

“…Dietary ingredients (e.g., furanocoumarins in grapefruit juice) or phytochemicals in medicinal herbs (e.g., hyperforin in St John’s Wort) can modulate a drug’s efficacy and engender potentially fatal drug-food and drug-herb interactions. CYP3A4/3A5 and CYP2D6 are most frequent participants in DDI [18, 110]. …”

CYP3A5 FNx01 3 genetic polymorphism is associated with childhood acute lymphoblastic leukemia risk: A meta-analysis

“…Therefore, CYP3A5 may be an important genetic contributor to inter-individual and inter-racial differences in CYP3A-mediated metabolism. [8,12] The most important functional single nucleotide polymorphism (SNP) in CYP3A5 gene is CYP3A5 * 3 6986A > G (rs776746). [13] CYP3A5 * 3 confers low CYP3A5 expression because of alternative mRNA splicing.…”