Preincubation with cyclosporin A (CsA), a potent inhibitor of organic anion transporting polypeptide 1B1 (OATP1B1) and OATP1B3, enhanced its inhibitory effects on these transporters in vitro. A ...similar effect was observed upon preincubation with some other inhibitors. Removing these from the incubation media did not readily reverse the inhibition on OATP1B1 and OATP1B3. This preincubation-dependent long-lasting inhibition appeared to be related to CsA concentration in the cells in addition to that in the incubation media. Thus, we hypothesized that CsA inhibits OATP1B1 and OATP1B3 from inside (trans-inhibition) as well as outside (cis-inhibition) the cells and constructed the cis- and trans-inhibition model. The enhanced inhibitory effect of CsA on OATP1B1 observed after preincubation was quantitatively described using K
and K
as inhibition constants for cis- and trans-inhibitions, respectively. In addition, a long-lasting inhibition was also described by this model. Additional factors taken into consideration when simulating in vivo pharmacokinetic alterations by CsA are potential inhibition by AM1, a major metabolite of CsA, which has been reported to inhibit OATP1B1 and OATP1B3. Based on the physiologically based pharmacokinetic model incorporating trans- and cis-inhibition of OATP1B1 by CsA, the simulation showed that OATP1B1-mediated drug-drug interaction with CsA was suggested to be time-dependent also in vivo although further clinical studies are required for confirmation.
Phase 0 approaches - which include microdosing - evaluate subtherapeutic exposures of new drugs in first-in-human studies known as exploratory clinical trials. Recent progress extends phase 0 ...benefits beyond assessment of pharmacokinetics to include understanding of mechanism of action and pharmacodynamics. Phase 0 approaches have the potential to improve preclinical candidate selection and enable safer, cheaper, quicker and more informed developmental decisions. Here, we discuss phase 0 methods and applications, highlight their advantages over traditional strategies and address concerns related to extrapolation and developmental timelines. Although challenges remain, we propose that phase 0 approaches be at least considered for application in most drug development scenarios.
3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) are widely used for the treatment of hypercholesterolemia. Their efficacy in preventing cardiovascular events has been ...shown by a large number of clinical trials. However, myotoxic side effects, sometimes severe, including myopathy or rhabdomyolysis, are associated with the use of statins. In some cases, such toxicity is associated with pharmacokinetic alterations. In this review, the pharmacokinetic aspects and physicochemical properties of statins are reviewed in order to understand the mechanism governing their pharmacokinetic alterations. Among the statins, simvastatin, lovastatin and atorvastatin are metabolized by cytochrome P450 3A4 (CYP3A4) while fluvastatin is metabolized by CYP2C9. Cerivastatin is subjected to 2 metabolic pathways mediated by CYP2C8 and 3A4. Pravastatin, rosuvastatin and pitavastatin undergo little metabolism. Their plasma clearances are governed by the transporters involved in the hepatic uptake and biliary excretion. Also for other statins, which are orally administered as open acid forms (i.e. fluvastatin, cerivastatin and atorvastatin), hepatic uptake transporter(s) play important roles in their clearances. Based on such information, pharmacokinetic alterations of statins can be predicted following coadministration of other drugs or in patients with lowered activities in drug metabolism and/or transport. We also present a quantitative analysis of the effect of some factors on the pharmacokinetics of statins based on a physiologically based pharmacokinetic model. To avoid a pharmacokinetic alteration, we need to have information about the metabolizing enzyme(s) and transporter(s) involved in the pharmacokinetics of statins and, along with such information, model-based prediction is also useful.
Transporter govern drug movement into and out of tissues, thereby playing an important role in drug disposition in plasma and to the site of action. The molecular cloning of such transporters has ...clarified the importance of members of the solute carrier family, such as OATP/SLCO, OCT/SLC22, OAT/SLC22, and MATE/SLC47, and the ATP-binding cassette transporters, such as P-glycoprotein/ABCB1, MRPs/ABCC, and BCRP/ABCG2. Elucidation of molecular characteristics of transporters has allowed the identification of transporters as mechanisms for drug-drug interactions, and of interindividual differences in drug dispositions and responses. Cumulative studies have highlighted the cooperative roles of uptake transporters and metabolic enzymes/efflux transporters. In this way, the concept of a rate-limiting process in hepatic/renal elimination across epithelial cells has developed. This review illustrates the concept of the rate-limiting step in the hepatic elimination mediated by transporters, and describes the prediction of the in vivo pharmacokinetics of drugs whose disposition is determined by transporters, based on in vitro experiments using pravastatin as an example. This review also illustrates the transporters regulating the peripheral drug concentrations.
Rosuvastatin is an HMG-CoA reductase inhibitor and one of the most hydrophilic among the commercially available statins. It is efficiently accumulated in the liver and excreted into the bile in an ...unchanged form in rats, suggesting that hepatic transporters play a major role in its clearance. Therefore, we investigated the transporters responsible for the hepatic uptake and biliary excretion of rosuvastatin. Uptake studies revealed that human organic anion transporting polypeptide (OATP) 1B1, OATP1B3, and OATP2B1 accept rosuvastatin as a substrate. Among the OATP family transporters, OATP1B1 contributes predominantly to the hepatic uptake of rosuvastatin, as estimated with the previously published relative activity factor method, and OATP1B3 is also partly involved. Significant vectorial basal-to-apical transport was observed in OATP1B1/multidrug resistance-associated protein 2 (MRP2), OATP1B1/multidrug resistance protein 1 (MDR1), and OATP1B1/breast cancer resistance protein (BCRP) double transfectants compared with that in an OATP1B1 single transfectant or in vector-transfected control cells. The ATP-dependent uptake of rosuvastatin by human BCRP-expressing membrane vesicles was significantly higher than the uptake by green fluorescent protein-expressing control vesicles, suggesting that MRP2, MDR1, and BCRP can transport rosuvastatin. Under in vivo conditions, the biliary excretion clearances based on the intrahepatic concentration of the parent rosuvastatin in Eisai hyperbilirubinemic rats and Bcrp1 knockout mice were reduced to 53% and 12% of those in the control Sprague-Dawley rats and FVB mice, respectively, indicating that rat Mrp2 and mouse Bcrp1 are both partly involved in the biliary excretion of rosuvastatin. These results suggest that multiple transporters are involved in the hepatic uptake and efflux of rosuvastatin.
The organic anion transporters (OATs) and organic anion–transporting polypeptides (OATPs) belong to the solute carrier (SLC) transporter superfamily and play important roles in handling various ...endogenous and exogenous compounds of anionic charge. The OATs and OATPs are often implicated in drug therapy by impacting the pharmacokinetics of clinically important drugs and, thereby, drug exposure in the target organs or cells. Various mechanisms (e.g. genetic, environmental, and disease-related factors, drug-drug interactions, and food-drug interactions) can lead to variations in the expression and activity of the anion drug-transporting proteins of OATs and OATPs, possibly impacting the therapeutic outcomes. Previous investigations mainly focused on the regulation at the transcriptional level and drug-drug interactions as competing substrates or inhibitors. Recently, evidence has accumulated that cellular trafficking, post-translational modification, and degradation mechanisms serve as another important layer for the mechanisms underlying the variations in the OATs and OATPs. This review will provide a brief overview of the major OATs and OATPs implicated in drug therapy and summarize recent progress in our understanding of the post-translational modifications, in particular ubiquitination and degradation pathways of the individual OATs and OATPs implicated in drug therapy.
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