Pre-incubation with cyclosporine A potentiates its inhibitory effects on pitavastatin uptake mediated by recombinantly expressed cynomolgus monkey hepatic organic anion transporting polypeptide.

Cyclosporine A, an inhibitor of hepatic organic anion transporting polypeptides (OATPs), reportedly increased plasma concentrations of probe substrates, although its maximum unbound blood concentrations were lower than the experimental half-maximal inhibitory (IC50 ) concentrations. Pre-incubation with cyclosporine A in vitro before simultaneous incubation with probes has been reported to potentiate its inhibitory effects on recombinant human OATP-mediated probe uptake. In the present study, the effects of cyclosporine A and rifampicin on recombinant cynomolgus monkey OATP-mediated pitavastatin uptake were investigated in pre- and simultaneous incubation systems. Pre-incubation with cyclosporine A, but not with rifampicin, decreased the apparent IC50 values on recombinant cynomolgus monkey OATP1B1- and OATP1B3-mediated pitavastatin uptake. Application of the co-incubated IC50 values toward R values (1 + [unbound inhibitor]inlet to the liver, theoretically maximum /inhibition constant) in static models, 1.1 in monkeys and 1.3 in humans, for recombinant cynomolgus monkey and human OATP1B1-mediated pitavastatin uptake might result in the poor prediction of drug interaction magnitudes. In contrast, the lowered IC50 values after pre-incubation with cyclosporine A provided better prediction with R values of 3.9 for monkeys and 2.7 for humans when the estimated maximum cyclosporine A concentrations at the inlet to the liver were used. These results suggest that the enhanced inhibitory potential of perpetrator medicines by pre-incubation on cynomolgus monkey OATP-mediated pitavastatin uptake in vitro could be of value for the precise estimation of drug interaction magnitudes in silico, in accordance with the findings from pre-administration of inhibitors on pitavastatin pharmacokinetics validated in monkeys. Copyright © 2016 John Wiley & Sons, Ltd.

Pitavastatin as an in vivo probe for studying hepatic organic anion transporting polypeptide-mediated drug-drug interactions in cynomolgus monkeys.

Drug-drug interactions (DDIs) caused by the inhibition of hepatic uptake transporters such as organic anion transporting polypeptide (OATP) can affect therapeutic efficacy and cause adverse reactions. We investigated the potential utility of pitavastatin as an in vivo probe substrate for preclinically studying OATP-mediated DDIs using cynomolgus monkeys. Cyclosporine A (CsA) and rifampicin (RIF), typical OATP inhibitors, inhibited active uptake of pitavastatin into monkey hepatocytes with half-maximal inhibitory concentration values comparable with those in human hepatocytes. CsA and RIF increased the area under the plasma concentration-time curve (AUC) of intravenously administered pitavastatin in cynomolgus monkeys by 3.2- and 3.6-fold, respectively. In addition, there was no apparent prolongation of the elimination half-life of pitavastatin due to the decrease in both hepatic clearance and volume of distribution. These findings suggest that DDIs were caused by the inhibition of hepatic uptake of pitavastatin. CsA and RIF increased the AUC of orally administered pitavastatin by 10.6- and 14.8-fold, respectively, which was additionally caused by the effect of the CsA and RIF in the gastrointestinal tract. Hepatic contribution to the overall DDI for oral pitavastatin with CsA was calculated from the changes in hepatic availability and clearance, and it was shown that the magnitude of hepatic DDI was comparable between the present study and the clinical study. In conclusion, pharmacokinetic studies using pitavastatin as a probe in combination with drug candidates in cynomolgus monkeys are useful to support the assessment of potential clinical DDIs involving hepatic uptake transporters.

Impact of intestinal glucuronidation on the pharmacokinetics of raloxifene.

Raloxifene is extensively glucuronidated in humans, effectively reducing its oral bioavailability (2%). It was also reported to be glucuronidated in preclinical animals, but its effects on the oral bioavailability have not been fully elucidated. In the present study, raloxifene and its glucuronides in the portal and systemic blood were monitored in Gunn rats deficient in UDP-glucuronosyltransferase (UGT) 1A, Eisai hyperbilirubinemic rats (EHBRs), which hereditarily lack multidrug resistance-associated protein (MRP) 2, and wild-type rats after oral administration. The in vitro-in vivo correlation (IVIVC) of four UGT substrates (raloxifene, biochanin A, gemfibrozil, and mycophenolic acid) in rats was also evaluated. In Gunn rats, the product of fraction absorbed and intestinal availability and hepatic availability of raloxifene were 0.63 and 0.43, respectively; these values were twice those observed in wild-type Wistar rats, indicating that raloxifene was glucuronidated in both the liver and intestine. The ratio of glucuronides to unchanged drug in systemic blood was substantially higher in EHBRs (129-fold) than in the wild-type Sprague-Dawley rats (10-fold), suggesting the excretion of raloxifene glucuronides caused by MRP2. The IVIVC of the other UGT substrates in rats displayed a good relationship, but the oral clearance values of raloxifene and biochanin A, which were extensively glucuronidated by rat intestinal microsomes, were higher than the predicted clearances using rat liver microsomes, suggesting that intestinal metabolism may be a great contributor to the first-pass effect. Therefore, evaluation of intestinal and hepatic glucuronidation for new chemical entities is important to improve their pharmacokinetic profiles.

Alprazolam as an in vivo probe for studying induction of CYP3A in cynomolgus monkeys.

Induction of the cytochrome P450 (P450) enzyme is a major concern in the drug discovery processes. To predict the clinical significance of enzyme induction, it is helpful to investigate pharmacokinetic alterations of a coadministered drug in a suitable animal model. In this study, we focus on the induction of CYP3A, which is involved in the metabolism of approximately 50% of marketed drugs and is inducible in both the liver and intestine. As a marker substrate for CYP3A activity, alprazolam (APZ) was selected and characterized using recombinant CYP3A enzymes expressed in Escherichia coli. Both human CYP3A4 and its cynomolgus P450 ortholog predominantly catalyzed APZ 4-hydroxylation with sigmoidal kinetics. When administered intravenously and orally to cynomolgus monkeys, APZ had moderate clearance; its first-pass extraction ratio after oral dosing was estimated to be 0.09 in the liver and 0.45 in the intestine. Pretreatment with multiple doses of rifampicin (20 mg/kg p.o. for 5 days), a known CYP3A inducer, significantly decreased plasma concentrations of APZ after intravenous and oral administrations (0.5 mg/kg), and first-pass extraction ratios were increased to 0.39 in the liver and 0.63 in the intestine. The results were comparable to those obtained in clinical drug-drug interaction (DDI) reports related to CYP3A induction, although the rate of recovery of CYP3A activity seemed to be slower than rates estimated in clinical studies. In conclusion, pharmacokinetic studies using APZ as a probe in monkeys may provide useful information regarding the prediction of clinical DDIs due to CYP3A induction.

Identification of a potent and orally active non-peptide C5a receptor antagonist.

The anaphylatoxin C5a is a potent chemotactic factor for neutrophils and other leukocytes, and functions as an important inflammatory mediator. Through a high capacity screening followed by chemical optimization, we identified a novel non-peptide C5a receptor antagonist, N-[(4-dimethylaminophenyl)methyl]-N-(4-isopropylphenyl)-7-methoxy-1,2,3,4-tetrahydronaphthalen-1- carboxamide hydrochloride (W-54011). W-54011 inhibited the binding of (125)I-labeled C5a to human neutrophils with a K(i) value of 2.2 nm. W-54011 also inhibited C5a-induced intracellular Ca(2+) mobilization, chemotaxis, and generation of reactive super oxide species in human neutrophils with IC(50) values of 3.1, 2.7, and 1.6 nm, respectively. In C5a-induced intracellular Ca(2+) mobilization assay with human neutrophils, W-54011 did not show agonistic activity at up to 10 microm and shifted rightward the concentration-response curves to C5a without depressing the maximal responses. Examination on the species specificity of W-54011 revealed that it was able to inhibit C5a-induced intracellular Ca(2+) mobilization in neutrophils of cynomolgus monkeys and gerbils but not mice, rats, guinea pigs, rabbits, and dogs. In gerbils, oral administration of W-54011 (3-30 mg/kg) inhibited C5a-induced neutropenia in a dose-dependent manner. The present report is the first description of an orally active non-peptide C5a receptor antagonist that could contribute to the treatment of inflammatory diseases mediated by C5a.