Ethnic variability in the plasma exposures of OATP1B1 substrates such as HMG-CoA reductase inhibitors: a kinetic consideration of its mechanism

Elucidating Contributions of Drug Transporters/Enzyme to Nonlinear Pharmacokinetics of Grazoprevir by PBPK Modeling With a Cluster Gauss-Newton Method

Grazoprevir (GZR), a direct-acting agent for hepatitis C virus, is recognized as a substrate for organic anion transporting polypeptide 1B (OATP1B), cytochrome P450 3A (CYP3A), and P-glycoprotein (P-gp). The objective of the present study was to elucidate the contribution of these molecules to the nonlinear pharmacokinetics of GZR using a physiologically based pharmacokinetic (PBPK) model. Utilizing plasma concentration-time profiles of GZR derived from reported dose-escalation (50-800 mg) clinical studies and cumulative excretion data, around 10 parameters, including Michaelis constants (Km) for OATP1B, CYP3A, and P-gp, were estimated via a cluster Gauss-Newton method (CGNM). Parameter combinations that could reproduce the clinical data of GZR were obtained; however, discrepancies were noted between the in vivo estimated Km and the corresponding in vitro Km. Next, by incorporating the in vitro Km values into our PBPK-CGNM analyses utilizing a penalized parameter method, newly obtained parameter combinations appropriately reflected both the in vivo and in vitro observations. Particularly regarding OATP1B, while saturation of uptake was not clearly observed in the in vitro experiments without human serum albumin (HSA), Km values capable of explaining in vivo saturation were obtained under physiological HSA concentrations. By estimating the extent of saturation for each molecule in the liver and intestine and conducting sensitivity analyses of the Km values, it was inferred that OATP1B3 contributed the most to the nonlinearity of plasma GZR concentrations, followed by P-gp. In conclusion, the PBPK-CGNM, supplemented by penalized in vitro parameters, was shown to be effective for analyzing complex pharmacokinetics involving drug transporters and enzymes.

The effect of organic solvents on the in vitro transport activity of three OATP isoforms

PURPOSE

In vitro studies of transporter activity often require the addition of organic solvents such as dimethyl sulfoxide (DMSO), methanol, and ethanol, to dissolve substrates and/or inhibitors. Although this may attenuate the transport activity, the influence of different types of organic solvents on transporter activity has not been elucidated. This study aimed to quantitatively assess the impact of organic solvents on the transport activity of organic anion transporting polypeptide (OATP) 1B1, 1A2, and 2B1.

METHODS

The concentration-dependent influence of DMSO, methanol, and ethanol on the uptake of [3H]estrone 3-sulfate mediated by OATP1A2, OATP2B1 or 2',7'-dichlorofluorescein (DCF) mediated by OATP1B1 was assessed using HEK293 cells expressed the respective OATP protein and the concentration that reduced the uptake by 20 % (IC20) was calculated.

RESULTS AND DISCUSSION

The uptake activities of OATPs were reduced by methanol and ethanol in a concentration-dependent manner, with IC20 values of 2.4-3.4 % and 0.51-3.8 % respectively. In contrast, DMSO did not affect the OATP2B1-mediated uptake at the maximum concentration (10 %) of DMSO whereas it exhibited concentration-dependent inhibition for OATP1B1 and 1A2 with IC20 values of approximately 3 % and 0.7 %, respectively. This study provides useful information regarding experimental conditions for evaluating OATPs activity in vitro.

Tutorial on model selection and validation of model input into precision dosing software for model-informed precision dosing

There has been rising interest in using model-informed precision dosing to provide personalized medicine to patients at the bedside. This methodology utilizes population pharmacokinetic models, measured drug concentrations from individual patients, pharmacodynamic biomarkers, and Bayesian estimation to estimate pharmacokinetic parameters and predict concentration-time profiles in individual patients. Using these individualized parameter estimates and simulated drug exposure, dosing recommendations can be generated to maximize target attainment to improve beneficial effect and minimize toxicity. However, the accuracy of the output from this evaluation is highly dependent on the population pharmacokinetic model selected. This tutorial provides a comprehensive approach to evaluating, selecting, and validating a model for input and implementation into a model-informed precision dosing program. A step-by-step outline to validate successful implementation into a precision dosing tool is described using the clinical software platforms Edsim++ and MwPharm++ as examples.

Model-based meta-analysis of ethnic differences and their variabilities in clearance of oral drugs classified by clearance mechanism

In this study, the ethnic ratios (ERs) of oral clearance between Japanese and Western populations were subjected to model-based meta-analysis (MBMA) for 81 drugs evaluated in 673 clinical studies. The drugs were classified into eight groups according to the clearance mechanism, and the ER for each group was inferred together with interindividual variability (IIV), interstudy variability (ISV), and inter-drug variability within a group (IDV) using the Markov chain Monte Carlo (MCMC) method. The ER, IIV, ISV, and IDV were dependent on the clearance mechanism, and, except for particular groups such as drugs metabolized by polymorphic enzymes or their clearance mechanism is not confirmative, the ethnic difference was found to be generally small. The IIV was well-matched across ethnicities, and the ISV was approximately half of the IIV as the coefficient of variation. To adequately assess ethnic differences in oral clearance without false detections, phase I studies should be designed with full consideration of the mechanism of clearance. This study suggests that the methodology of classifying drugs based on the mechanism that causes ethnic differences and performing MBMA with statistical techniques such as MCMC analysis is helpful for a rational understanding of ethnic differences and for strategic drug development.

The premise of capsid assembly modulators towards eliminating HBV persistence

INTRODUCTION

The burden of chronic hepatitis B virus (HBV) results in almost a million deaths per year. The most common treatment for chronic hepatitis B infection is long-term nucleoside analogs (NUC) or one-year interferon-alpha (pegylated or non-pegylated) therapy before or after NUC therapy. Unfortunately, these therapies rarely result in HBV functional cure because they do not eradicate HBV from the nucleus of the hepatocytes, where the covalently closed circular DNA (cccDNA) is formed and/or where the integrated HBV DNA persists in the host genome. Hence, the search continues for novel antiviral therapies that target different steps of the HBV replication cycle to cure chronically infected HBV individuals and eliminate HBV from the liver reservoirs.

AREAS COVERED

The authors focus on capsid assembly modulators (CAMs). These molecules are unique because they impact not only one but several steps of HBV viral replication, including capsid assembly, capsid trafficking into the nucleus, reverse transcription, pre-genomic RNA (pgRNA), and polymerase protein co-packaging.

EXPERT OPINION

Mono- or combination therapy, including CAMs with other HBV drugs, may potentially eliminate hepatitis B infections. Nevertheless, more data on their potential effect on HBV elimination is needed, especially when used daily for 6-12 months.

Ethnicity based differences in statin use and hypercholesterolemia control among patients with premature coronary artery disease-results of I-PAD study

Background

Statins use is the most important treatment for high LDL cholesterol in patients with premature coronary artery disease (CAD). Previous reports have shown racial and gender differences in statin use in the general population, but this wasn't studied in premature CAD based on different ethnicities.

Methods and results

Our study includes 1917 men and women with confirmed diagnosis of premature CAD. Logistic regression model was used to evaluate the high LDL cholesterol control in the groups and the OR with 95% confidence interval (CI) was reported as the effect size. After adjustment for confounders, the odds of controlling LDL in women taking Lovastatin, Rosuvastatin, and Simvastatin were 0.27 (0.03, 0.45) lower in comparison with men. Also, in participant who took 3 types of statins, the odds of controlling LDL were significantly different between Lor and Arab compared with Fars ethnicity. After adjustment to all confounders (full model), the odds of controlling LDL were lower for Gilak in Lovastatin, Rosuvastatin, and Simvastatin by 0.64 (0.47, 0.75); 0.61 (0.43, 0.73); 0.63 (0.46, 0.74) respectively and higher for Arab in Lovastatin, Rosuvastatin, and Simvastatin by 4.63 (18.28, 0.73); 4.67 (17.47, 0.74); 4.55 (17.03, 0.71) respectively compared to Fars.

Conclusions

Major differences in different gender and ethnicities may have had led to disparities in statin use and LDL control. Awareness of the statins impact on high LDL cholesterol based on different ethnicities can help health decision-makers to close the observed gaps in statin use and control LDL to prevent CAD problems.

Asia-Inclusive Clinical Research and Development Enabled by Translational Science and Quantitative Clinical Pharmacology: Toward a Culture That Challenges the Status Quo

Access lag to innovative therapies in Asian populations continues to present a challenge to global health. Recent progressive changes in the global regulatory landscape, including newer guidelines, are enabling simultaneous global drug development and near-simultaneous global drug registration. The International Conference on Harmonization (ICH) E17 guideline outlines general principles for the design and analysis of multiregional clinical trials (MRCTs). We posit that translational research and quantitative clinical pharmacology tools are core enablers for Asia-inclusive global drug development aligned with ICH E17 principles. Assessment of ethnic sensitivity should be initiated early in the development lifecycle to inform the need for, and extent of, Asian phase I ethno-bridging data. Relevant ethno-bridging data may be generated as standalone Asian phase I trials, as part of Western First-In-Human trials, or under accelerated development settings as a lead-in phase in an MRCT. Quantitative understanding of human clearance mechanisms and pharmacogenetic factors is vital to forecasting ethnic sensitivity in drug exposure using physiologically-based pharmacokinetic models. Stratification factors to control heterogeneity in MRCTs can be identified by reverse translational research incorporating pharmacometric disease models and model-based meta-analyses. Because epidemiological variations can extend to the molecular level, quantitative systems pharmacology models may be useful in forecasting how molecular variation in therapeutic targets or pathway proteins across populations might impact treatment outcomes. Through prospective evaluation of conservation in drug- and disease-related intrinsic and extrinsic factors, a pooled East Asian region can be implemented in Asia-inclusive MRCTs to maximize efficiency in substantiating evidence of benefit-risk for the region at-large with a Totality of Evidence approach.

Pharmacokinetics, Safety, and Tolerability of Letermovir Following Single- and Multiple-Dose Administration in Healthy Japanese Subjects

Letermovir is a human cytomegalovirus terminase inhibitor for the prophylaxis of cytomegalovirus infection and disease in allogeneic hematopoietic stem cell transplant recipients. The pharmacokinetics, safety, and tolerability of letermovir were assessed in healthy Japanese subjects in 2 phase 1 trials: trial 1-single ascending oral doses (240, 480, and 720 mg) and intravenous (IV) doses (240, 480, and 960 mg), and trial 2-multiple oral doses (240 and 480 mg once daily for 7 days). Following administration of oral single and multiple doses, letermovir was absorbed with a median time to maximum plasma concentration of 2 to 4 hours, and concentrations declined in a biphasic manner with a terminal half-life of ≈10 to 13 hours. The post absorption plasma concentration-time profile of letermovir following oral administration was similar to the profile observed with IV dosing. There was minimal accumulation with multiple-dose administration. Letermovir exposure in healthy Japanese subjects was ≈1.5- to 2.5-fold higher than that observed in non-Japanese subjects. Based on the population pharmacokinetic analysis, weight differences primarily accounted for the higher exposures observed in Asians. Letermovir was generally well tolerated following oral and IV administration to healthy Japanese subjects.

Evaluation of the safety, tolerability, and pharmacokinetics of RO7049389 in healthy Chinese volunteers

The objectives of this phase I study are to assess the safety, tolerability, and pharmacokinetics (PKs) of RO7049389 in healthy Chinese volunteers (HVs) and evaluate potential ethnic differences in the safety and PKs using data from this study and the first‐in‐human study (in which most of the HVs were non‐Asian). HVs randomly received a single dose of 200–600 mg of RO7049389 or a placebo in a single ascending dose (n = 28) or multiple doses of 200–400 mg of RO7049389 or a placebo in multiple ascending doses (n = 24). Safety and tolerability were monitored throughout the study. Serial blood samples were collected for PK analysis. RO7049389 was safe and well‐tolerated in the HVs. The time to maximum concentration ranged from 1.5 to 3.0 h, and terminal half‐life ranged from 3.66 to 14.6 h. A single dose of 200–600 mg and multiple doses of 200–400 mg exhibited nonlinear PKs. In general, the safety profiles were comparable between non‐Asian and Asian HVs, but the plasma exposure of RO7049389 in Chinese HVs was higher than that in non‐Asian HVs. The data generated from this study will provide guidance for future clinical studies on RO7049389 in Chinese/Asian patients with hepatitis B virus.

Quantitative prediction of breast cancer resistant protein mediated drug-drug interactions using physiologically-based pharmacokinetic modeling

Quantitative assessment of drug‐drug interactions (DDIs) involving breast cancer resistance protein (BCRP) inhibition is challenged by overlapping substrate/inhibitor specificity. This study used physiologically‐based pharmacokinetic (PBPK) modeling to delineate the effects of inhibitor drugs on BCRP‐ and organic anion transporting polypeptide (OATP)1B‐mediated disposition of rosuvastatin, which is a recommended BCRP clinical probe. Initial static model analysis using in vitro inhibition data suggested BCRP/OATP1B DDI risk while considering regulatory cutoff criteria for a majority of inhibitors assessed (25 of 27), which increased rosuvastatin plasma exposure to varying degree (~ 0–600%). However, rosuvastatin area under plasma concentration‐time curve (AUC) was minimally impacted by BCRP inhibitors with calculated G‐value (= gut concentration/inhibition potency) below 100. A comprehensive PBPK model accounting for intestinal (OATP2B1 and BCRP), hepatic (OATP1B, BCRP, and MRP4), and renal (OAT3) transport mechanisms was developed for rosuvastatin. Adopting in vitro inhibition data, rosuvastatin plasma AUC changes were predicted within 25% error for 9 of 12 inhibitors evaluated via PBPK modeling. This study illustrates the adequacy and utility of a mechanistic model‐informed approach in quantitatively assessing BCRP‐mediated DDIs.

Efficacy and safety of statins in ethnic differences: a lesson for application in Indigenous Australian patient care

Although statins are effective in treating high cholesterol, adverse effects do occur with their use. Efficacy and tolerability vary among statins in different ethnic groups. Indigenous Australians have a high risk for cardiovascular and kidney diseases. Prescribing statins to Indigenous Australians with multi-morbidity requires different strategies to increase efficacy and reduce their toxicity. Previous studies have reported that Indigenous Australians are more susceptible to severe statin-induced myopathies. However, there is a lack of evidence in the underlying genetic factors in this population. This review aims to identify: inter-ethnic differences in the efficacy and safety of statins; major contributing factors accounting for any identified differences; and provide an overview of statin-induced adverse effects in Indigenous Australians.

Caspofungin pharmacokinetics and probability of target attainment in ICU patients in China

OBJECTIVES

Effective antifungal therapy is important to reduce mortality in patients with invasive fungal infections (IFIs). Numerous factors affect pharmacokinetic/pharmacodynamic (PK/PD) parameters in critically-ill patients. To guide individualised administration in critically-ill patients, it is of great significance to determine the population pharmacokinetics of caspofungin.

METHODS

A prospective study in 42 ICU patients with IFIs was conducted in China. A population pharmacokinetic model of caspofungin was established using a non-linear mixed-effects model, which was utilised to investigate the effects of demographic indices, liver function and kidney function on pharmacokinetics. Additionally, appropriate dosages of caspofungin under various scenarios were determined based on MICs and probability of target attainment (PTA) at specific dosages.

RESULTS

In critically-ill Chinese patients, clearance (CL), volume of distribution (V) and area under the curve at steady-state (AUC_ss) of caspofungin were 0.32 L/h, 6.77 L and 135.47 mg•h/L, respectively. Blood albumin and total bilirubin levels were factors affecting CL, while body weight was the only factor affecting V among Chinese people with relatively low weight compared with other populations. A maintenance dose of 50 mg caspofungin achieved a high PTA for treating IFIs caused by Candida albicans (MIC ≤ 0.06 mg/L) and Candida glabrata (MIC ≤ 0.125 mg/L). The maintenance dose of caspofungin should be adjusted to 70-200 mg for IFIs caused by C. albicans (MIC, 0.06-0.125 mg/L). For IFIs caused by Candida parapsilosis, an MIC > 0.03 mg/L is associated with a very low PTA, but higher doses of caspofungin or alternative antifungals need to be further studied.

CONCLUSION

The population pharmacokinetic model established here described well the PK/PD characteristics of caspofungin in critically-ill Chinese patients. These results could guide the formulation of individualised caspofungin dosing regimens for critically-ill patients.

How Semiphysiological Population Pharmacokinetic Modeling Incorporating Active Hepatic Uptake Supports Phase II Dose Selection of RO7049389, A Novel Anti-Hepatitis B Virus Drug

The pharmacokinetics (PK) of RO7049389, a new hepatitis B virus (HBV) core protein allosteric modulator of class I, and of its active metabolite M5 were studied in fasted and fed conditions after single and multiple once‐a‐day and twice‐a‐day doses in healthy subjects and patients with HBV. The nonlinearity of the pharmacokinetics, the large variability, the small sample size per dose arms, the higher plasma exposure in Asians, and the heterogeneity in patient baseline characteristics seen in phase I studies made the ethnic sensitivity assessment and the selection of the recommended phase II dose difficult. A population PK model, simultaneously modeling RO7049389 and M5, was developed to characterize the complex PK, quantify ethnicity (i.e., Asian vs. non‐Asian) and gender effects on the PK of RO7049389 and M5, and infer the quantity of RO7049389 in liver relative to plasma. Exposures in the liver are of particular importance for dose selection since the liver is the site of action of the compound. The model described and reproduced the population PK profiles as well as the between‐subject variability of RO7049389 and its metabolite. It could show that the PK is similar between healthy subjects and in HBV patients, once the ethnicity and gender effects are accounted for. The model predicts that, despite a large difference in the plasma exposure of RO7049389 between Asians and non‐Asians, the exposure in the liver is comparable, allowing the use of the same dose to treat Asian and non‐Asian patients. This model provides a valuable basis to develop this new anti‐HBV drug and to define optimal dosing.

Personalized medicine in lipid-modifying therapy

The choice of lipid-modifying treatment is largely based on the absolute level of cardiovascular risk and baseline lipid profile. Statins are the first-line treatment for most patients requiring reduction of low-density-lipoprotein cholesterol (LDL-C) and ezetimibe and proprotein convertase subtilisin/kexin type 9 inhibitors can be added to reach LDL-C targets. Statins have some adverse effects that are somewhat predictable based on phenotypic and genetic factors. Fibrates or omega-3 fatty acids can be added if triglyceride levels remain elevated. The RNA-targeted therapeutics in development offer the possibility of selective liver targeting for specific lipoproteins such as lipoprotein(a) and long-term reduction of LDL-C with infrequent administration of a small-interfering RNA may help to overcome the problem of adherence to therapy.

Statin Therapy in Post-Operative Atrial Fibrillation: Focus on the Anti-Inflammatory Effects

BACKGROUND

Atrial fibrillation (AF) occurring after cardiac surgery, post-operative AF (POAF), is a serious and common complication of this treatment. POAF may be life-threatening and the available preventive strategies are insufficient or are associated with significantly increased risk of adverse effects, especially in long-term use. Therefore, more appropriate treatment strategies are needed.

METHODS

In this paper, the efficacy, safety, and other aspects of using statins in the prevention of POAF focusing on their anti-inflammatory effects are reviewed.

RESULTS

Recent studies have suggested that inflammation has a significant role in POAF, from the first AF episode to its serious complications including stroke and peripheral embolism. On the other hand, statins, the most widely used medications in cardiovascular patients, have pleiotropic effects, including anti-inflammatory properties. Therefore, they may potentially be effective in POAF prevention. Statins, especially atorvastatin, appear to be an effective option for primary prevention of POAF, especially in patients who had coronary artery bypass grafting (CABG), a cardiac surgery treatment associated with inflammation in the heart muscle. However, several large studies, particularly with rosuvastatin, did not confirm the beneficial effect of statins on POAF. One large clinical trial reported higher risk of acute kidney injury (AKI) following high-dose rosuvastatin in Chinese population. In this study, rosuvastatin reduced the level of C-reactive protein (CRP) but did not reduce the rate of POAF.

CONCLUSION

Further studies are required to find the most effective statin regimen for POAF prevention with the least safety concern and the highest health benefits.

PBPK Model of Coproporphyrin I: Evaluation of the Impact of SLCO1B1 Genotype, Ethnicity, and Sex on its Inter-Individual Variability

Coproporphyrin I (CPI) is an endogenous biomarker of OATP1B activity and associated drug-drug interactions. In this study, a minimal physiologically-based pharmacokinetic model was developed to investigate the impact of OATP1B1 genotype (c.521T>C), ethnicity, and sex on CPI pharmacokinetics and interindividual variability in its baseline. The model implemented mechanistic descriptions of CPI hepatic transport between liver blood and liver tissue and renal excretion. Key model parameters (e.g., endogenous CPI synthesis rate, and CPI hepatic uptake clearance) were estimated by fitting the model simultaneously to three independent CPI clinical datasets (plasma and urine data) obtained from white (n = 16, men and women) and Asian-Indian (n = 26, all men) subjects, with c.521 variants (TT, TC, and CC). The optimized CPI model successfully described the observed data using c.521T>C genotype, ethnicity, and sex as covariates. CPI hepatic active was 79% lower in 521CC relative to the wild type and 42% lower in Asian-Indians relative to white subjects, whereas CPI synthesis was 23% higher in male relative to female subjects. Parameter sensitivity analysis showed marginal impact of the assumption of CPI synthesis site (blood or liver), resulting in comparable recovery of plasma and urine CPI data. Lower magnitude of CPI-drug interaction was simulated in 521CC subjects, suggesting the risk of underestimation of CPI-drug interaction without prior OATP1B1 genotyping. The CPI model incorporates key covariates contributing to interindividual variability in its baseline and highlights the utility of the CPI modeling to facilitate the design of prospective clinical studies to maximize the sensitivity of this biomarker.

Pharmacogenetics of Statin-Induced Myotoxicity

Statins, a class of lipid-lowering medications, have been a keystone treatment in cardiovascular health. However, adverse effects associated with statin use impact patient adherence, leading to statin discontinuation. Statin-induced myotoxicity (SIM) is one of the most common adverse effects, prevalent across all ages, genders, and ethnicities. Although certain demographic cohorts carry a higher risk, the impaired quality of life attributed to SIM is significant. The pathogenesis of SIM remains to be fully elucidated, but it is clear that SIM is multifactorial. These factors include drug-drug interactions, renal or liver dysfunction, and genetics. Genetic-inferred risk for SIM was first reported by a landmark genome-wide association study, which reported a higher risk of SIM with a polymorphism in the SLCO1B1 gene. Since then, research associating genetic factors with SIM has expanded widely and has become one of the foci in the field of pharmacogenomics. This review provides an update on the genetic risk factors associated with SIM.

Absorption and Disposition of Coproporphyrin I (CPI) in Cynomolgus Monkeys and Mice: Pharmacokinetic Evidence to Support the Use of CPI to Inform the Potential for Organic Anion-Transporting Polypeptide Inhibition

Despite a recent expansion in the recognition of the potential utility of coproporphyrin (CP) as an endogenous biomarker of organic anion-transporting polypeptide (OATP) 1B activity, there have been few detailed studies of CP's pharmacokinetic behavior and an overall poor understanding of its pharmacokinetic fate from tissues and excretion. Here, we describe the pharmacokinetics of octadeuterium-labeled coproporphyrin I (CPI-d8) in cynomolgus monkeys following oral and intravenous administration. CPI-d8 has a half-life and bioavailability of 7.6 hours and 3.2%, respectively. Cynomolgus monkeys received oral cyclosporin A (CsA) at 4, 20, and 100 mg/kg which yielded maximum blood concentrations (C max) and area under the plasma concentration-time curve (AUC) values of 0.19, 2.5, and 3.8 µM, and 2.7, 10.5, and 26.6 µM·h, respectively. The apparent CsA-dose dependent increase in the AUC ratio of CPI-d8 (1.8, 6.2, and 10.5), CPI (1.1, 1.4, and 4.4), and CPIII (1.1, 1.8, and 4.6) at 4, 20, and 100 mg, respectively. In contrast, the plasma concentrations of CPI and CPIII were generally not affected by intravenous administration of the renal organic anion and cation transporter inhibitors (probenecid and pyrimethamine, respectively). In addition, tritium-labeled coproporphyrin I ([3H]CPI) showed specific and rapid distribution to the liver, intestine, and kidney after an intravenous dose in mice using quantitative whole-body autoradiography. Rifampin markedly reduced the liver and intestinal uptake of [3H]CPI while increasing the kidney uptake. Taken together, these results suggest that hepatic OATP considerably affects the disposition of CPI in animal models, indicating CPI is a sensitive and selective endogenous biomarker of OATP inhibition. SIGNIFICANCE STATEMENT: This study demonstrated that coproporphyrin I (CPI) has favorable oral absorption, distribution, and elimination profiles in monkeys and mice as an endogenous biomarker. It also demonstrated its sensitivity and selectivity as a probe of organic anion-transporting polypeptide (OATP) 1B activity. The study reports, for the first time, in vivo pharmacokinetics, tissue distribution, sensitivity, and selectivity of CPI as an OATP1B endogenous biomarker in animals. The data provide preclinical support for exploration of its utility as a sensitive and selective circulating OATP biomarker in humans.

Practical Synthesis of [18F]Pitavastatin and Evaluation of Hepatobiliary Transport Activity in Rats by Positron Emission Tomography

We developed a practical synthetic method for fluorine-18 (¹⁸F)-labeled pitavastatin ([¹⁸F]PTV) as a positron emission tomography (PET) tracer to assess hepatobiliary transporter activity and conducted a PET scan as a preclinical study for proof-of-concept in rats. This method is a one-pot synthesis involving aromatic ¹⁸F-fluorination of an arylboronic acid ester followed by deprotection under acidic conditions, which can be reproduced in general clinical sites equipped with a standard radiolabeling system due to the simplified procedure. PET imaging confirmed that intravenously administered [¹⁸F]PTV was rapidly accumulated in the liver and gradually transferred into the intestinal lumen through the bile duct. Radiometabolite analysis showed that [¹⁸F]PTV was metabolically stable, and 80% of the injected dose was detected as the unchanged form in both blood and bile. We applied integration plot analysis to assess tissue uptake clearance (CL_{uptake, liver} and CL_{uptake, kidney}) and canalicular efflux clearance (CL_int, bile), and examined the effects of inhibitors on membrane transport. Treatment with rifampicin, an organic anion transporting polypeptide inhibitor, significantly reduced CL_{uptake, liver} and CL_{uptake, kidney} to 44% and 64% of control, respectively. In contrast, Ko143, a breast cancer resistance protein inhibitor, did not affect CL_{uptake, liver} but significantly reduced CL_int, bile to 39% of control without change in [¹⁸F]PTV blood concentration. In addition, we found decreased CL_{uptake, liver} and increased CL_int, bile in Eisai hyperbilirubinemic rats in response to altered expression levels of transporters. We expect that [¹⁸F]PTV can be translated into clinical application, as our synthetic method does not need special apparatus in the radiolabeling system and PET scan with [¹⁸F]PTV can quantitatively evaluate transporter activity in vivo.

Dose-Dependent Inhibition of OATP1B by Rifampicin in Healthy Volunteers: Comprehensive Evaluation of Candidate Biomarkers and OATP1B Probe Drugs

To address the most appropriate endogenous biomarker for drug–drug interaction risk assessment, eight healthy subjects received an organic anion transporting polypeptide 1B (OATP1B) inhibitor (rifampicin, 150, 300, and 600 mg), and a probe drug cocktail (atorvastatin, pitavastatin, rosuvastatin, and valsartan). In addition to coproporphyrin I, a widely studied OATP1B biomarker, we identified at least 4 out of 28 compounds (direct bilirubin, glycochenodeoxycholate‐3‐glucuronide, glycochenodeoxycholate‐3‐sulfate, and hexadecanedioate) that presented good sensitivity and dynamic range in terms of the rifampicin dose‐dependent change in area under the plasma concentration‐time curve ratio (AUCR). Their suitability as OATP1B biomarkers was also supported by the good correlation of AUC_0‐24h between the endogenous compounds and the probe drugs, and by nonlinear regression analysis (AUCR⁻¹ vs. rifampicin plasma C_max (maximum total concentration in plasma)) to yield an estimate of the inhibition constant of rifampicin. These endogenous substrates can complement existing OATP1B‐mediated drug–drug interaction risk assessment approaches based on agency guidelines in early clinical trials.

Physiologically-Based Pharmacokinetic Models for Evaluating Membrane Transporter Mediated Drug-Drug Interactions: Current Capabilities, Case Studies, Future Opportunities, and Recommendations

Physiologically-based pharmacokinetic (PBPK) modeling has been extensively used to quantitatively translate in vitro data and evaluate temporal effects from drug-drug interactions (DDIs), arising due to reversible enzyme and transporter inhibition, irreversible time-dependent inhibition, enzyme induction, and/or suppression. PBPK modeling has now gained reasonable acceptance with the regulatory authorities for the cytochrome-P450-mediated DDIs and is routinely used. However, the application of PBPK for transporter-mediated DDIs (tDDI) in drug development is relatively uncommon. Because the predictive performance of PBPK models for tDDI is not well established, here, we represent and discuss examples of PBPK analyses included in regulatory submission (the US Food and Drug Administration (FDA), the European Medicines Agency (EMA), and the Pharmaceuticals and Medical Devices Agency (PMDA)) across various tDDIs. The goal of this collaborative effort (involving scientists representing 17 pharmaceutical companies in the Consortium and from academia) is to reflect on the use of current databases and models to address tDDIs. This challenges the common perceptions on applications of PBPK for tDDIs and further delves into the requirements to improve such PBPK predictions. This review provides a reflection on the current trends in PBPK modeling for tDDIs and provides a framework to promote continuous use, verification, and improvement in industrialization of the transporter PBPK modeling.

Comparative and quantitative assessment on statin efficacy and safety: insights into inter-statin and inter-individual variability via dose- and exposure-response relationships

Introduction: Statins are prescribed widely for cholesterol-lowering therapy, but it is known that their efficacy and safety profiles vary, despite the shared pharmacophore and pharmacological target. The immense body of related clinical and preclinical data offers a unique opportunity to explore the possible factors underlying inter-statin and inter-individual variabilities.Area covered: Clinical and preclinical data from various statins were compiled with regard to the efficacy (cholesterol-lowering effect) and safety (muscle toxicity). Based on the compiled data, dose- and exposure-response relationships were explored to obtain mechanistic and quantitative insights into the variations in the efficacy and safety profiles of statins.Expert opinion: Our analyses indicated that the inter-statin variability in the cholesterol-lowering effect may be mainly attributable to variations in potency of inhibition of the pharmacological target, rather than variations in drug exposure at the site of drug action. However, the drug exposure at the sites of drug action (i.e., the liver for efficacy and the muscle for safety) may contribute to the differences in the efficacy and safety observed in individual patients.

Explaining Ethnic Variability of Transporter Substrate Pharmacokinetics in Healthy Asian and Caucasian Subjects with Allele Frequencies of OATP1B1 and BCRP: A Mechanistic Modeling Analysis

Background

Ethnic variability in the pharmacokinetics of organic anion transporting polypeptide (OATP) 1B1 substrates has been observed, but its basis is unclear. A previous study hypothesizes that, without applying an intrinsic ethnic variability in transporter activity, allele frequencies of transporters cannot explain observed ethnic variability in pharmacokinetics. However, this hypothesis contradicts the data collected from compounds that are OATP1B1 substrates but not breast cancer resistance protein (BCRP) substrates.

Objective

The objective of this study is to evaluate a hypothesis that is physiologically reasonable and more consistent with clinical observations.

Methods

We evaluated if allele frequencies of two transporters (OATP1B1 and BCRP) are key contributors to ethnic variability. In this hypothesis, the same genotype leads to the same activity independent of ethnicity, in contrast to the previous hypothesis of intrinsic ethnic variability in OATP1B1 activity. As a validation, we perform mechanistic pharmacokinetic modeling for SLCO1B1 (encoding OATP1B1) and ABCG2 (encoding BCRP) genotyped pharmacokinetic data from 18 clinical studies with healthy Caucasian and/or Asian subjects.

Results

Simulations based on the current hypothesis reasonably describe SLCO1B1 and ABCG2 genotyped pharmacokinetic time course data for five transporter substrates (atorvastatin, pitavastatin, pravastatin, repaglinide, and rosuvastatin) in Caucasian and Asian populations.

Conclusion

This hypothesis covers the observations that can (e.g., ethnic differences in rosuvastatin pharmacokinetics) or cannot (e.g., lack of differences for pitavastatin pharmacokinetics) be explained by the previous hypothesis. It helps to characterize sources of ethnic variability and provides a foundation for predicting ethnic variability in transporter substrate pharmacokinetics.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-017-0568-7) contains supplementary material, which is available to authorized users.

Effects of Food and Gender on Pharmacokinetics of Rosuvastatin in a Chinese Population Based on 4 Bioequivalence Studies

The effects of food and gender on the pharmacokinetics of rosuvastatin in healthy Chinese subjects were investigated from 4 bioequivalence studies. These studies were designed as randomized, open-label, and 2-period crossover in both fasting and fed states. A total of 204 subjects were enrolled, 134 men and 70 women. These subjects received a single oral 10-mg dose of rosuvastatin with a 7-day washout between 2 periods. The plasma concentrations were determined using a validated liquid chromatography tandem mass spectrometry method, and pharmacokinetic parameters were calculated by noncompartmental methods. Compared with the fasting condition, administration after a high-fat and high-calorie meal resulted in an approximately 40% reduction of rosuvastatin exposure and a near 50% decrease in absorption rate. Moreover, the apparent clearance was significantly greater in the fed state than that in the fasting state. It was noted that the adverse events incidence is increased by approximately 30% in the fasting state; however, no serious adverse events were observed. Additionally, small differences in pharmacokinetic characteristics were found between male and female subjects. Food effect might be considered for optimal effectiveness and safety of rosuvastatin therapy.

Precision Medicine and Personalized Management of Lipoprotein and Lipid Disorders in Chronic and End-Stage Kidney Disease

Precision medicine is an emerging field that calls for individualization of treatment strategies based on characteristics unique to each patient. In lipid management, current guidelines are driven mainly by clinical trial results that presently indicate that patients with non-dialysis-dependent chronic kidney disease (CKD) should be treated with a β-hydroxy β-methylglutaryl-CoA reductase inhibitor, also known as statin therapy. For patients with end-stage kidney disease (ESKD) being treated with hemodialysis, statin therapy has not been shown to successfully reduce poor outcomes in trials and therefore is not recommended. The two major guidelines dissent on whether statin therapy should be of moderate or high intensity in non-dialysis-dependent CKD patients, but often leave the prescribing clinician to make that decision. These decisions often are complicated by the increased concerns for adverse events such as myopathies in patients with advanced kidney disease and ESKD. In the future, there may be an opportunity to further identify CKD and ESKD patients who are more likely to benefit from lipid-modifying therapy as opposed to those who likely will suffer from its side effects using precision medicine tools. For now, data from genetics studies and subgroup analyses may provide insight for future research directions in this field and we review some of the work that has been published in this regard.

Population Pharmacokinetic Analysis of Daclatasvir, Asunaprevir, and Beclabuvir Combination in HCV-Infected Subjects

A fixed-dose combination of daclatasvir (pangenotypic NS5A inhibitor), asunaprevir (NS3/4A protease inhibitor), and beclabuvir (nonnucleoside NS5B inhibitor) was approved for hepatitis C virus treatment in Japan. The objectives of the analyses were to develop the daclatasvir, asunaprevir, and beclabuvir population pharmacokinetic models for the combination regimen. First, an original population pharmacokinetic model was developed using the data in non-Japanese hepatitis C virus-infected subjects. The model was subsequently updated after a phase 3 study in Japanese hepatitis C virus-infected subjects was available. A total of 11,382, 11,300, and 10,728 pharmacokinetic records from 1,228 subjects were included for daclatasvir, asunaprevir, and beclabuvir in the updated model, respectively. Daclatasvir and beclabuvir pharmacokinetics (PK) were described by a 1-compartment model with linear elimination and asunaprevir PK was described by 2-compartment model with linear elimination. Cirrhosis, baseline, and time-varying ALT were significant covariates on asunaprevir apparent oral clearance. Asian subjects had greater asunaprevir and beclabuvir exposures than white subjects. The effects of all covariates on daclatasvir PK were modest and not considered clinically significant. With the exception of race on asunaprevir and beclabuvir PK, no other parameters for daclatasvir, asunaprevir and beclabuvir population PK models were meaningfully impacted during the refinement with Japanese subjects.

Pharmacokinetic drug evaluation of letermovir prophylaxis for cytomegalovirus in hematopoietic stem cell transplantation

INTRODUCTION

Letermovir is a new antiviral approved to prevent cytomegalovirus infection in hematopoietic stem cell transplant recipients. It has a distinct mechanism of action as it acts as a terminase complex inhibitor, and shows some advantages compared to the current treatment options for cytomegalovirus infection. Areas covered: This review focuses on the efficacy, safety, pharmacokinetics, pharmacodynamics, and drug-drug interactions of letermovir. Expert opinion: Letermovir is a new antiviral to prevent cytomegalovirus infection. Unlike the currently used polymerase inhibitors, it has a distinct mechanism of action with better safety, limited resistance, and no cross-resistance. Although a lot of research on pharmacokinetics and drug-drug interactions has already been performed, it might be useful to clarify the effect of letermovir on voriconazole exposure, the drug-drug interaction between caspofungine and letermovir and the effect of statins on letermovir exposure. Also, the lack of an exposure-response relationship should be confirmed in large real-life post-marketing studies in order to be able to lower the intravenous dose of letermovir.

Advancing Predictions of Tissue and Intracellular Drug Concentrations Using In Vitro, Imaging and Physiologically Based Pharmacokinetic Modeling Approaches

This white paper examines recent progress, applications, and challenges in predicting unbound and total tissue and intra/subcellular drug concentrations using in vitro and preclinical models, imaging techniques, and physiologically based pharmacokinetic (PBPK) modeling. Published examples, regulatory submissions, and case studies illustrate the application of different types of data in drug development to support modeling and decision making for compounds with transporter-mediated disposition, and likely disconnects between tissue and systemic drug exposure. The goals of this article are to illustrate current best practices and outline practical strategies for selecting appropriate in vitro and in vivo experimental methods to estimate or predict tissue and plasma concentrations, and to use these data in the application of PBPK modeling for human pharmacokinetic (PK), efficacy, and safety assessment in drug development.

Further Studies to Support the Use of Coproporphyrin I and III as Novel Clinical Biomarkers for Evaluating the Potential for Organic Anion Transporting Polypeptide 1B1 and OATP1B3 Inhibition

In a recent study, limited to South Asian Indian subjects (n = 12), coproporphyrin (CP) I and CPIII demonstrated properties appropriate for an organic anion-transporting polypeptide (OATP) 1B endogenous probe. The current studies were conducted in healthy volunteers of mixed ethnicities, including black, white, and Hispanic subjects, to better understand the utility of these biomarkers in broader populations. After oral administration with 600 mg rifampin, AUC(0-24h) values were 2.8-, 3.7-, and 3.6-fold higher than predose levels for CPI and 2.6-, 3.1-, and 2.4-fold higher for CPIII, for the three populations, respectively. These changes in response to rifampin were consistent with previous results. The sensitivity toward OATP1B inhibition was also investigated by evaluating changes of plasma CP levels in the presence of diltiazem and itraconazole [administered as part of an unrelated drug-drug interaction (DDI) investigation], two compounds that were predicted to have minimal inhibitory effect on OATP1B. Administration of diltiazem and itraconazole did not increase plasma CPI and CPIII concentrations relative to prestudy levels, in agreement with predictions from in vitro parameters. Additionally, the basal CP concentrations in subjects with SLCO1B1 c.521TT genotype were comparable to those with SLCO1B1 c.521TC genotype, similar to studies with probe substrates. However, subjects with SLCO1B1 c.388AG and c.388GG genotypes (i.e., increased OATP1B1 transport activity for certain substrates) had lower concentrations of CPI than those with SLCO1B1 c.388AA. Collectively, these findings provide further evidence supporting the translational value of CPI and CPIII as suitable endogenous clinical probes to gauge OATP1B activity and potential for OATP1B-mediated DDIs.

Influence of Transporter Polymorphisms on Drug Disposition and Response: A Perspective From the International Transporter Consortium

Advances in genomic technologies have led to a wealth of information identifying genetic polymorphisms in membrane transporters, specifically how these polymorphisms affect drug disposition and response. This review describes the current perspective of the International Transporter Consortium (ITC) on clinically important polymorphisms in membrane transporters. ITC suggests that, in addition to previously recommended polymorphisms in ABCG2 (BCRP) and SLCO1B1 (OATP1B1), polymorphisms in the emerging transporter, SLC22A1 (OCT1), be considered during drug development. Collectively, polymorphisms in these transporters are important determinants of interindividual differences in the levels, toxicities, and response to many drugs.

Comparative Study of the Dose-Dependence of OATP1B Inhibition by Rifampicin Using Probe Drugs and Endogenous Substrates in Healthy Volunteers

PURPOSE

To evaluate association of the dose-dependent effect of rifampicin, an OATP1B inhibitor, on the plasma concentration-time profiles among OATP1B substrates drugs and endogenous substrates.

METHODS

Eight healthy volunteers received atorvastatin (1 mg), pitavastatin (0.2 mg), rosuvastatin (0.5 mg), and fluvastatin (2 mg) alone or with rifampicin (300 or 600 mg) in a crossover fashion. The plasma concentrations of these OATP1B probe drugs, total and direct bilirubin, glycochenodeoxycholate-3-sulfate (GCDCA-S), and coproporphyrin I, were determined.

RESULTS

The most striking effect of 600 mg rifampicin was on atorvastatin (6.0-times increase) and GCDCA-S (10-times increase). The AUC_0-24h of atorvastatin was reasonably correlated with that of pitavastatin (r² = 0.73) and with the AUC_0-4h of fluvastatin (r² = 0.62) and sufficiently with the AUC_0-24h of rosuvastatin (r² = 0.32). The AUC_0-24h of GCDCA-S was reasonably correlated with those of direct bilirubin (r² = 0.74) and coproporphyrin I (r² = 0.78), and sufficiently with that of total bilirubin (r² = 0.30). The AUC_0-24h of GCDCA-S, direct bilirubin, and coproporphyrin I were reasonably correlated with that of atorvastatin (r² = 0.48-0.70) [corrected].

CONCLUSION

These results suggest that direct bilirubin, GCDCA-S, and coproporphyrin I are promising surrogate probes for the quantitative assessment of potential OATP1B-mediated DDI.

Evaluation of Alteration in Hepatic and Intestinal BCRP Function In Vivo from ABCG2 c.421C>A Polymorphism Based on PBPK Analysis of Rosuvastatin

Polymorphism c.421C>A in the ABCG2 gene is thought to reduce the activity of breast cancer resistance protein (BCRP), a xenobiotic transporter, although it is not clear which organ(s) contributes to the polymorphism-associated pharmacokinetic change. The aim of the present study was to estimate quantitatively the influence of c.421C>A on intestinal and hepatic BCRP activity using a physiologically based pharmacokinetic (PBPK) model of rosuvastatin developed from clinical data and several in vitro studies. Simultaneous fitting of clinical data for orally and intravenously administered rosuvastatin, obtained in human subjects without genotype information, was first performed with the PBPK model to estimate intrinsic clearance for hepatic elementary process. The fraction of BCRP activity in 421CA and 421AA (fca and faa values, respectively) with respect to that in 421CC subjects was then estimated based on extended clearance concepts and simultaneous fitting to oral administration data for the three genotypes (421CC, 421CA, and 421AA). On the assumption that c.421C>A affects both intestinal and hepatic BCRP, clinical data in each genotype were well reproduced by the model, and the estimated terminal half-life was compatible with the observed values. The assumption that c.421C>A affects only either intestinal or hepatic BCRP gave poorer agreement with observed values. The faa values obtained on the former assumption were 0.48-0.54. Thus, PBPK model analysis enabled quantitative evaluation of alteration in BCRP activity owing to c.421C>A, and BCRP activity in 421AA was estimated as half that in 421CC.

Gadoxetic acid-enhanced magnetic resonance imaging to predict paritaprevir-induced hyperbilirubinemia during treatment of hepatitis C

Background

Paritaprevir inhibits organic anion–transporting polypeptide (OATP)1B1 and OATP1B3, which transport bilirubin. Hyperbilirubinemia is an adverse event reported during hepatitis C treatment. Gadoxetic acid is also transported by OATP1B1/1B3. We evaluated whether the enhancement effect in gadoxetic acid–enhanced magnetic resonance (MR) imaging could predict the plasma concentration of paritaprevir and might anticipate the development of hyperbilirubinemia.

Methods

This prospective study evaluated 27 patients with hepatitis C who underwent gadoxetic acid–enhanced MR imaging prior to treatment with ombitasvir, paritaprevir, and ritonavir. The contrast enhancement index (CEI), a measure of liver enhancement during the hepatobiliary phase, was assessed. Plasma trough concentrations, and concentrations at 2, 4, and 6 h after dosing were determined 7 d after the start of treatment.

Results

Seven patients (26%) developed hyperbilirubinemia (≥ 1.6 mg/dl). Paritaprevir trough concentration (C_trough) was significantly higher in patients with hyperbilirubinemia than in those without (p = 0.022). We found an inverse relationship between CEI and C_trough (r = 0.612, p = 0.001), while there was not a significantly weak inverse relationship between AUC_{0–6 h} and CEI (r = −0.338, p = 0.085). The partial correlation coefficient between CEI and C_trough was −0.425 (p = 0.034), while excluding the effects of albumin and the FIB-4 index. Receiver operating characteristic (ROC) curve analysis showed that the CEI was relatively accurate in predicting hyperbilirubinemia, with area under the ROC of 0.882. Multivariate analysis showed that the CEI < 1.61 was the only independent predictor related to the development of hyperbilirubinemia, with an odds ratio of 9.08 (95% confidence interval 1.05–78.86, p = 0.046).

Conclusions

Hepatic enhancement with gadoxetic acid was independently related to paritaprevir concentration and was an independent pretreatment factor in predicting hyperbilirubinemia. Gadoxetic acid–enhanced MR imaging can therefore be useful in determining the risk of paritaprevir-induced hyperbilirubinemia.

Physiologically-based pharmacokinetic predictions of intestinal BCRP-mediated drug interactions of rosuvastatin in Koreans

It was recently reported that the C_max and AUC of rosuvastatin increases when it is coadministered with telmisartan and cyclosporine. Rosuvastatin is known to be a substrate of OATP1B1, OATP1B3, NTCP, and BCRP transporters. The aim of this study was to explore the mechanism of the interactions between rosuvastatin and two perpetrators, telmisartan and cyclosporine. Published (cyclosporine) or newly developed (telmisartan) PBPK models were used to this end. The rosuvastatin model in Simcyp (version 15)'s drug library was modified to reflect racial differences in rosuvastatin exposure. In the telmisartan–rosuvastatin case, simulated rosuvastatin C_maxI/C_max and AUC_I/AUC (with/without telmisartan) ratios were 1.92 and 1.14, respectively, and the T_max changed from 3.35 h to 1.40 h with coadministration of telmisartan, which were consistent with the aforementioned report (C_maxI/C_max: 2.01, AUC_I/AUC:1.18, T_max: 5 h → 0.75 h). In the next case of cyclosporine–rosuvastatin, the simulated rosuvastatin C_maxI/C_max and AUC_I/AUC (with/without cyclosporine) ratios were 3.29 and 1.30, respectively. The decrease in the CL_{int,BCRP,intestine} of rosuvastatin by telmisartan and cyclosporine in the PBPK model was pivotal to reproducing this finding in Simcyp. Our PBPK model demonstrated that the major causes of increase in rosuvastatin exposure are mediated by intestinal BCRP (rosuvastatin–telmisartan interaction) or by both of BCRP and OATP1B1/3 (rosuvastatin–cyclosporine interaction).

Elucidating the Plasma and Liver Pharmacokinetics of Simeprevir in Special Populations Using Physiologically Based Pharmacokinetic Modelling

The disposition of simeprevir (SMV) in humans is characterised by cytochrome P450 3A4 metabolism and hepatic uptake by organic anion transporting polypeptide 1B1/3 (OATP1B1/3). This study was designed to investigate SMV plasma and liver exposure upon oral administration in subjects infected with hepatitis C virus (HCV), in subjects of Japanese or Chinese origin, subjects with organ impairment and subjects with OATP genetic polymorphisms, using physiologically based pharmacokinetic modelling. Simulations showed that compared with healthy Caucasian subjects, SMV plasma exposure was 2.4-, 1.7-, 2.2- and 2.0-fold higher, respectively, in HCV-infected Caucasian subjects, in healthy Japanese, healthy Chinese and subjects with severe renal impairment. Further simulations showed that compared with HCV-infected Caucasian subjects, SMV plasma exposure was 1.6-fold higher in HCV-infected Japanese subjects. In subjects with OATP1B1 genetic polymorphisms, no noteworthy changes in SMV pharmacokinetics were observed. Simulations suggested that liver concentrations in Caucasians with HCV are 18 times higher than plasma concentrations.

A Pooled Analysis of Pharmacokinetic Variability Information for Common Probe Substrates Used in Drug-Drug Interaction Studies

Sample size estimates for drug-drug interaction (DDI) studies are often based on variability information from the literature or from historical studies, but small sample sizes in these sources may limit the precision of the estimates obtained. This project aimed to create an intra-subject variability library of the pharmacokinetic (PK) exposure parameters, area under the curve, and maximum plasma concentration, for probes commonly used in DDI studies. Data from 66 individual DDI studies in healthy subjects relating to 18 common probe substrates were pooled to increase the effective sample size for the identified probes by 1.5- to 9-fold, with corresponding improvements in precision of the intra-subject PK variability estimates in this library. These improved variability estimates will allow better assessment of the sample sizes needed for DDI studies in future.

Precision medicine: does ethnicity information complement genotype-based prescribing decisions?

Inter-ethnic differences in drug response are all too well known. These are underpinned by a number of factors, including pharmacogenetic differences across various ethnic populations. Precision medicine relies on genotype-based prescribing decisions with the aim of maximizing efficacy and mitigating the risks. When there is no access to genotyping tests, ethnicity is frequently regarded as a proxy of the patient's probable genotype on the basis of overall population-based frequency of genetic variations in the ethnic group the patient belongs to, with some variations being ethnicity-specific. However, ever-increasing transcontinental migration of populations and the resulting admixing of populations have undermined the utility of self-identified ethnicity in predicting the genetic ancestry, and therefore the genotype, of the patient. An example of the relevance of genetic ancestry of a patient is the inadequate performance of European-derived pharmacogenetic dosing algorithms of warfarin in African Americans, Brazilians and Caribbean Hispanics. Consequently, genotyping a patient potentially requires testing for all known clinically actionable variants that the patient may harbour, and new variants that are likely to be identified using state-of the art next-generation sequencing-based methods. Furthermore, self-identified ethnicity is associated with a number of ethnicity-related attributes and non-genetic factors that potentially influence the risk of phenoconversion (genotype-phenotype discordance), which may adversely impact the success of genotype-based prescribing decisions. Therefore, while genotype-based prescribing decisions are important in implementing precision medicine, ethnicity should not be disregarded.

Modelling of atorvastatin pharmacokinetics and the identification of the effect of a BCRP polymorphism in the Japanese population

AIM

Ethnicity plays a modulating role in atorvastatin pharmacokinetics (PK), with Asian patients reported to have higher exposure compared with Caucasians. Therefore, it is difficult to safely extrapolate atorvastatin PK data and models across ethnic groups. This work aims to develop a population PK model for atorvastatin and its pharmacologically active metabolites specifically for the Japanese population. Subsequently, it aimed to identify genetic polymorphisms affecting atorvastatin PK in this population.

METHODS

Atorvastatin acid (ATA) and ortho-hydroxy-atorvastatin acid (o-OH-ATA) plasma concentrations, clinical/demographic characteristics and genotypes for 18 (3, 3, 1, 1, 7, 2 and 1 in the ABCB1, ABCG2, CYP3A4, CYP3A5, SLCO1B1, SLCO2B1 and PPARA genes, respectively) genetic polymorphisms were collected from 27 Japanese individuals (taking 10 mg atorvastatin once daily) and analysed using a population PK modelling approach.

RESULTS

The population PK model developed (one-compartment for ATA linked through metabolite formation to an additional compartment describing the disposition of o-OH-ATA) accurately described the observed data and the associated population variability. Our analysis suggested that patients carrying one variant allele for the rs2622604 polymorphism (ABCG2) show a 55% (95% confidence interval: 16-131%) increase in atorvastatin oral bioavailability relative to the value in individuals without the variant allele.

CONCLUSION

The current work reports the identification in the Japanese population of a BCRP polymorphism, not previously associated with the PK of any statin, that markedly increases ATA and o-OH-ATA exposure. The model developed may be of clinical importance to guide dosing recommendations tailored specifically for the Japanese.

Rosuvastatin Pharmacokinetics in Asian and White Subjects Wild Type for Both OATP1B1 and BCRP Under Control and Inhibited Conditions

The Food and Drug Administration recommends rosuvastatin dosage reductions in Asian patients because pharmacokinetic studies have demonstrated an approximate 2-fold increase in median exposure to rosuvastatin in Asian subjects compared with Caucasian controls. Yet, no explanation for this ethnic difference has been confirmed. Here we show that rosuvastatin exposure in Asians and Whites does not differ significantly when all subjects are wild-type carriers for both solute carrier organic anion transporter 1B1 *1a and ATP-binding cassette subfamily G member 2 c.421 transporters in a 2-arm, randomized, cross-over rosuvastatin pharmacokinetics study in healthy white and Asian volunteers. For single rosuvastatin doses, AUC0-48 were 92.5 (±36.2) and 83.5 (±32.2) ng/mL × h and Cmax were 10.0 (±4.1) and 7.6 (±3.0) ng/mL for Asians and Whites, respectively. When transporters were inhibited by intravenous rifampin, rosuvastatin AUC0-48 and Cmax also showed no ethnic differences. Our study suggests that both SLCO1B1 and ABCG2 polymorphisms are better predictors of rosuvastatin exposure than ethnicity alone and could be considered in precision medicine dosing of rosuvastatin.

More Power to OATP1B1: An Evaluation of Sample Size in Pharmacogenetic Studies Using a Rosuvastatin PBPK Model for Intestinal, Hepatic, and Renal Transporter-Mediated Clearances

Rosuvastatin is a substrate of choice in clinical studies of organic anion-transporting polypeptide (OATP)1B1- and OATP1B3-associated drug interactions; thus, understanding the effect of OATP1B1 polymorphisms on the pharmacokinetics of rosuvastatin is crucial. Here, physiologically based pharmacokinetic (PBPK) modeling was coupled with a power calculation algorithm to evaluate the influence of sample size on the ability to detect an effect (80% power) of OATP1B1 phenotype on pharmacokinetics of rosuvastatin. Intestinal, hepatic, and renal transporters were mechanistically incorporated into a rosuvastatin PBPK model using permeability-limited models for intestine, liver, and kidney, respectively, nested within a full PBPK model. Simulated plasma rosuvastatin concentrations in healthy volunteers were in agreement with previously reported clinical data. Power calculations were used to determine the influence of sample size on study power while accounting for OATP1B1 haplotype frequency and abundance in addition to its correlation with OATP1B3 abundance. It was determined that 10 poor-transporter and 45 intermediate-transporter individuals are required to achieve 80% power to discriminate the AUC0-48h of rosuvastatin from that of the extensive-transporter phenotype. This number was reduced to 7 poor-transporter and 40 intermediate-transporter individuals when the reported correlation between OATP1B1 and 1B3 abundance was taken into account. The current study represents the first example in which PBPK modeling in conjunction with power analysis has been used to investigate sample size in clinical studies of OATP1B1 polymorphisms. This approach highlights the influence of interindividual variability and correlation of transporter abundance on study power and should allow more informed decision making in pharmacogenomic study design.

Randomized, double-blind, placebo-controlled phase III study of ixazomib plus lenalidomide-dexamethasone in patients with relapsed/refractory multiple myeloma: China Continuation study

Background

The China Continuation study was a separate regional expansion of the global, double-blind, placebo-controlled, randomized phase III TOURMALINE-MM1 study of ixazomib plus lenalidomide–dexamethasone (Rd) in patients with relapsed/refractory multiple myeloma (RRMM) following one to three prior therapies.

Methods

Patients were randomized (1:1) to receive ixazomib 4.0 mg or placebo on days 1, 8, and 15, plus lenalidomide 25 mg on days 1–21 and dexamethasone 40 mg on days 1, 8, 15, and 22, in 28-day cycles. Randomization was stratified according to number of prior therapies, disease stage, and prior proteasome inhibitor exposure. The primary endpoint was progression-free survival (PFS). In total, 115 Chinese patients were randomized (57 ixazomib-Rd, 58 placebo-Rd).

Results

At the preplanned final analysis for PFS, after median PFS follow-up of 7.4 and 6.9 months, respectively, PFS was improved with ixazomib-Rd versus placebo-Rd (median 6.7 vs 4.0 months; HR 0.598; p = 0.035). At the preplanned final analysis of overall survival (OS), after median follow-up of 20.2 and 19.1 months, respectively, OS was improved with ixazomib-Rd versus placebo-Rd (median 25.8 vs 15.8 months; HR 0.419; p = 0.001). On the ixazomib-Rd and placebo-Rd arms, respectively, 38 (67%) and 43 (74%) patients reported grade ≥3 adverse events (AEs), 19 (33%) and 18 (31%) reported serious AEs, and 4 (7%) and 5 (9%) died on-study. The most frequent grade 3/4 AEs were thrombocytopenia (18%/7% vs 14%/5%), neutropenia (19%/5% vs 19%/2%), and anemia (12%/0 vs 26%/2%).

Conclusions

This study demonstrated that PFS and OS were significantly improved with ixazomib-Rd versus placebo-Rd, with limited additional toxicity, in patients with RRMM.

Trial registration

ClinicalTrials.gov, NCT01564537

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-017-0501-4) contains supplementary material, which is available to authorized users.

Retracted: Physiologically based pharmacokinetic predictions of intestinal BCRP-mediated effect of telmisartan on the pharmacokinetics of rosuvastatin in humans

'Physiologically based pharmacokinetic predictions of intestinal BCRP-mediated effect of telmisartan on the pharmacokinetics of rosuvastatin in humans' by Soo Hyeon Bae, Wan-Su Park, Seunghoon Han, Gab-jin Park, Jongtae Lee, Taegon Hong, Sangil Jeon and Dong-Seok Yim The above article, published online on 06 February 2017 in Wiley Online Library (wileyonlinelibrary.com), has been retracted by agreement between the authors, the journal Editor in Chief, K. Sandy Pang, and John Wiley & Sons, Ltd. The authors retracted the paper due to errors associated with use of log D vs. log P of telmisartan as inputs of the PBPK model. The authors concluded that there are too many changes in the article to be resolved by an Erratum, and had requested a retraction. Reference Bae, S. H., Park, W.-S., Han, S., Park, G., Lee, J., Hong, T., Jeon, S., and Yim, D.-S. (2016) Physiologically based pharmacokinetic predictions of intestinal BCRP-mediated effect of telmisartan on the pharmacokinetics of rosuvastatin in humans. Biopharm. Drug Dispos., doi: 10.1002/bdd.2060.

Understanding the Potential Interethnic Difference in Rosuvastatin Pharmacokinetics

Here we address the potential difference in rosuvastatin pharmacokinetics in Asians vs. whites. Our prospective study, reported in this issue, shows no ethnic difference when all subjects are wild-type for OATP1B1 and BCRP. We argue that although our study may be under powered to prove no ethnic difference, and that further confirmatory study is required, the virtual clinical study analysis, also reported in this issue, does not contradict the results of our prospective clinical study and that previous retrospective analysis of clinical studies does not include enough relevant subjects to conclude that wild-type OATP1B1 and BCRP do still demonstrate ethnic differences.

Comparison of exposure response relationship of atrasentan between North American and Asian populations

AIMS

The selective endothelin (ET) A receptor antagonist atrasentan has been shown to lower albuminuria in North American and Asian patients with type 2 diabetes and nephropathy. As drug responses to many drugs may differ between North American and Asian populations, we assessed the influence of geographical region on the albuminuria and fluid retention response to atrasentan.

MATERIALS AND METHODS

Two 12-week double-blind randomised controlled trials were performed with atrasentan 0.75 or 1.25 mg/d vs placebo in patients with type 2 diabetes and nephropathy. The efficacy endpoint was the percentage change in albuminuria. Bodyweight change, a proxy of fluid retention, was used as a safety endpoint. Pharmacodynamics were determined in Asians (N = 77) and North Americans (N = 134). Atrasentan plasma concentration was measured in 161 atrasentan-treated patients.

RESULTS

Mean albuminuria reduction in Asian, compared to North American, patients was, respectively, -34.4% vs -26.3% for 0.75 mg/d ( P  = .44) and -48.0% vs -28.9% for 1.25 mg/d ( P  = .035). Bodyweight gain did not differ between North American and Asian populations. Atrasentan plasma concentrations were higher in Asians compared to North Americans and correlated with albuminuria response (7.2% albuminuria reduction per doubling atrasentan concentration; P  = .024). Body surface area (β = -1.09 per m² ; P  < .001) and bilirubin, as a marker of hepatic organic anion transporter activity, (β = 0.69 per mg/dL increment; P  = .010) were independent determinants of atrasentan plasma concentration; correction by body surface area and bilirubin left no significant difference in plasma concentration between Asian and North American populations.

CONCLUSION

The higher exposure and albuminuria reduction of atrasentan in Asian patients is not associated with more fluid retention, suggesting that Asian patients are less sensitive to atrasentan-induced sodium retention.