A reliable and practical CYP3A induction assay with cryopreserved human hepatocytes in a 96-well format was developed. Various 96-well plates with different basement membrane were evaluated using prototypical inducers, rifampicin, phenytoin, and carbamazepine. Thin-layer (TL) Matrigel was found to yield the highest basal and induced levels of CYP3A activity as determined by testosterone 6β-hydroxylation. Concentration-dependent CYP3A induction of rifampicin was reproducible with the EC(50) values of 0.36 ± 0.28 μM from four batches of human hepatocytes using the 96-well plate with TL Matrigel. The rank order of induction potency for nine inducers or noninducers at a concentration of 10 μM were well comparable among the multiple donors, by expressing the results as percentage of change compared with the positive control, 10 μM rifampicin. Cotreatment of avasimibe or efavirenz with 10 μM rifampicin was found to reduce CYP3A activities induced by rifampicin at a lower rate than treatment with rifampicin alone, whereas treatment with phenobarbital and carbamazepine had no effect. From a comparison of induced CYP3A activities and gene expression levels, there were compounds that would cause induction of CYP3A4 mRNA but not activity, presumably due to their inhibitory effect on CYP3A activity. The cotreatment assay of test compound with rifampicin allows us to exclude the false-negative results caused by the cytotoxicity and/or the mechanism-based inactivation, when the drug candidate's ability for CYP3A induction is evaluating the enzyme activity. This 96-well plate assay, which is robust, reproducible, and convenient, has demonstrated the paramount applicability to the early drug discovery stage.
[Show abstract][Hide abstract] ABSTRACT: The induction of cytochrome P450 (P450) enzymes is one of the risk factors for drug-drug interactions (DDIs). To date, the human pregnane X receptor (PXR)-mediated CYP3A4 induction has been well studied. In addition to CYP3A4, the expression of CYP2C subfamily is also regulated by PXR, and the DDIs caused by the induction of CYP2C enzymes have been reported to have a major clinical impact. The purpose of the present study was to investigate whether chimeric mice with a humanized liver (PXB mice) can be a suitable animal model for investigating the PXR-mediated induction of CYP2C subfamily, together with CYP3A4. We evaluated the inductive effect of rifampicin (RIF), a typical human PXR ligand, on the plasma exposure to the four P450 substrate drugs (triazolam/CYP3A4, pioglitazone/CYP2C8, (S)-warfarin/CYP2C9, and (S)-(-)-mephenytoin/CYP2C19) by cassette dosing in PXB mice. The induction of several drug-metabolizing enzymes and transporters in the liver was also examined by measuring the enzyme activity and mRNA expression levels. Significant reductions in the exposure to triazolam, pioglitazone, and (S)-(-)-mephenytoin, but not to (S)-warfarin, were observed. In contrast to the in vivo results, all the four P450 isoforms, including CYP2C9, were elevated by RIF treatment. The discrepancy in the (S)-warfarin results between in vivo and in vitro studies may be attributed to the relatively small contribution of CYP2C9 to (S)-warfarin elimination in the PXB mice used in this study. In summary, PXB mice are a useful animal model to examine DDIs caused by PXR-mediated induction of CYP2C and CYP3A4.
Drug metabolism and disposition: the biological fate of chemicals 11/2011; 40(3):474-80. DOI:10.1124/dmd.111.042754 · 3.25 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rationale: The aim of the present study was to assess the stability of cryopreserved human hepatocytes over 5 years and to explore experimental condition-related variables such as seeding density, culture matrix and medium, start and duration of treatment that could potentially affect the quality of cultures and their response to cytochrome P450 (CYP) inducers. Results: 63/125 batches of cryopreserved human hepatocytes were plateable after thawing. Of those, 17 batches showed reproducible recovery, viability and plateability (less than 5% intra-batch variability) up to 5 years. When cultured in collagen home-coated 48-well plates at a seeding density allowing 70% confluence, cryopreserved human hepatocytes display activities equivalent to fresh counterparts. Their response to CYP inducers is maximal and equivalent to fresh counterpart for an incubation of 72 h starting at Day 2 or Day 3 after plating when cultured in modified Hepatocyte Maintenance Medium (HMM). The number of cryopreserved human hepatocytes can be further reduced by using a cocktail of CYP substrates for the assessment of their inducibility. Conclusions: Experimental condition-related variables, such as seeding density, culture matrix and medium, start and duration of treatment, affecting the response of plateable thawed cryopreserved human hepatocytes to cytochrome P450 inducers can be reduced by optimizing critical steps of the protocols.
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