The impact of pharmacogenetics of metabolic enzymes and transporters on the pharmacokinetics of telmisartan in healthy volunteers

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.

Identification of selective inhibitors of uridine 5'-diphospho-glucuronosyltransferase (UGT) 1A3 and UGT1A8 and their application in UGT reaction phenotyping studies in human liver and intestinal microsomes

Uridine 5'-diphospho-glucuronosyltransferase (UGT) reaction phenotyping studies have posed significant challenges due to the limited availability of isoform-selective inhibitors. This recognized gap in reagent availability impedes the accurate determination of the contribution of specific UGT isoforms to the metabolism of UGT substrates. To address this challenge, 9 antibiotics were evaluated for their potential inhibitory effects on UGT isoforms. We identified 2 macrolide antibiotics, troleandomycin and erythromycin, as potent and selective inhibitors of UGT1A3 and UGT1A8, respectively. The mechanism of UGT inhibition by troleandomycin and erythromycin was investigated using recombinant UGT1A3 (mefenamic acid as probe substrate) and UGT1A8 (7-hydroxy-4-(trifluoromethyl)coumarin and apigenin as probe substrates). The results revealed a mixed-type inhibition mechanism, where troleandomycin and erythromycin allosterically inhibit UGT1A3 and UGT1A8, respectively. A slight positive cooperativity between erythromycin and substrate binding to UGT1A8 and a slight negative cooperativity between troleandomycin and substrate binding to UGT1A3 was observed. At saturating inhibitor concentrations, greater than 90% inhibition of glucuronidation catalyzed by UGT1A3 and UGT1A8 was observed. To validate these findings in human liver microsomes and human intestinal microsomes, telmisartan, a selective substrate of UGT1A3 and UGT1A8, was utilized. Similar to the results in expressed UGT isoforms, troleandomycin selectively inhibited UGT1A3 in human liver microsomes and erythromycin selectively inhibited UGT1A8 in human intestinal microsomes. The identification of these UGT isoform-selective inhibitors provides researchers with important new tools expanding the utility of in vitro UGT reaction phenotyping studies. SIGNIFICANCE STATEMENT: Identification of uridine 5'-diphospho-glucuronosyltransferase (UGT)1A3 (troleandomycin) and UGT1A8 (erythromycin) selective inhibitors addresses an important and heretofore unmet need for in vitro reaction phenotyping studies by facilitating the determination of the contribution of these enzymes to drug glucuronidation in humans.

Insight into the structure, oligomerization, and the role in drug resistance of human UDP-glucuronosyltransferases

Human UDP-glucuronosyltransferases (UGTs) are pivotal phase II metabolic enzymes facilitating the transfer of glucuronic acid from UDP-glucuronic acid (UDPGA) to various substrates. UGTs are classic type I transmembrane glycoproteins, mainly localized in the endoplasmic reticulum (ER) membrane. This review comprehensively explores UGTs, encompassing gene expression, functional characteristics, substrate specificity, and metabolic mechanisms. A recent analysis of C-terminal structures, compared with original data, underscores the pivotal role of α3, α4, and β4 functional domains in selectively recognizing diverse glycosyl donors. Accumulating evidence suggests that UGTs function as homo- and heterodimers, with oligomers likely stabilizing UGTs and modulating their activity. The review sheds light on the implications of UGT oligomerization on substrate glucuronidation and the interplay between protein-protein interaction and glucuronidation activity. UGT-mediated drug resistance, often underestimated, emerges as a clinically relevant form of chemical resistance, with delineated outcomes in tumors and other diseases. This review provides a multifaceted exploration of the physiological significance of UGTs, spanning genetics, proteins, oligomerization, drug resistance, and more, offering insights into their metabolic mechanisms. Understanding interactions between UGT isoforms is crucial for predicting drug-drug interactions, preventing drug toxicity, and enabling precision treatment.

Elucidating nonlinear pharmacokinetics of telmisartan: Integration of target-mediated drug disposition and OATP1B3-mediated hepatic uptake in a physiologically based model

Telmisartan, a selective inhibitor of angiotensin II receptor type 1 (AT1), demonstrates nonlinear pharmacokinetics (PK) when orally administered in ascending doses to healthy volunteers, but the underlying mechanisms remain unclear. This study presents a physiologically based pharmacokinetic model integrated with target-mediated drug disposition (TMDD-PBPK model) to explore the mechanism of its nonlinear PK. We employed the Cluster-Gauss Newton method for top-down analysis, estimating the in vivo Km,OATP1B3 (Michaelis-Menten constant for telmisartan hepatic uptake via Organic Anion Transporting Polypeptide 1B3) to be 2.0-5.7 nM. This range is significantly lower than the reported in vitro value of 810 nM, obtained in 0.3% human serum albumin (HSA) conditions. Further validation was achieved through in vitro assessment in plated human hepatocytes with 4.5% HSA, showing a Km of 4.5 nM. These results underscore the importance of albumin-mediated uptake effect for the hepatic uptake of telmisartan. Our TMDD-PBPK model, developed through a "middle-out" approach, underwent sensitivity analysis to identify key factors in the nonlinear PK of telmisartan. We found that the nonlinearity in the area under the concentration-time curve (AUC) and/or maximum concentration (Cmax) of telmisartan is sensitive to Km,OATP1B3 across all dosages. Additionally, the dissociation constant (Kd) for telmisartan binding to the AT1 receptor, along with its receptor abundance, notably influences PK at lower doses (below 20 mg). In conclusion, the nonlinear PK of telmisartan appears primarily driven by hepatic uptake saturation across all dose ranges and by AT1-receptor binding saturation, notably at lower doses.

The therapeutic landscape for COVID-19 and post-COVID-19 medications from genetic profiling of the Vietnamese population and a predictive model of drug-drug interaction for comorbid COVID-19 patients

Despite the raised awareness of the role of pharmacogenomic (PGx) in personalized medicines for COVID-19, data for COVID-19 drugs is extremely scarce and not even a publication on this topic for post-COVID-19 medications to date. In the current study, we investigated the genetic variations associated with COVID-19 and post-COVID-19 therapies by using whole genome sequencing data of the 1000 Vietnamese Genomes Project (1KVG) in comparison with other populations retrieved from the 1000 Genomes Project Phase 3 (1KGP3) and the Genome Aggregation Database (gnomAD). Moreover, we also evaluated the risk of drug interactions in comorbid COVID-19 and post-COVID-19 patients based on pharmacogenomic profiles of drugs using a computational approach. For COVID-19 therapies, variants related to the response of two causal treatment agents (tolicizumab and ritonavir) and antithrombotic drugs are common in the Vietnamese cohort. Regarding post-COVID-19, drugs for mental manipulations possess the highest number of clinical annotated variants carried by Vietnamese individuals. Among the superpopulations, East Asian populations shared the most similar genetic structure with the Vietnamese population, whereas the African population showed the most difference. Comorbid patients are at an increased drug-drug interaction (DDI) risk when suffering from COVID-19 and after recovering as well due to a large number of potential DDIs which have been identified. Our results presented the population-specific understanding of the pharmacogenomic aspect of COVID-19 and post-COVID-19 therapy to optimize therapeutic outcomes and promote personalized medicine strategy. We also partly clarified the higher risk in COVID-19 patients with underlying conditions by assessing the potential drug interactions.

Effects of telmisartan on metabolic syndrome components: a comprehensive review

Telmisartan is an antagonist of the angiotensin II receptor used in the management of hypertension (alone or in combination with other antihypertensive agents. It belongs to the drug class of angiotensin II receptor blockers (ARBs). Among drugs of this class, telmisartan shows particular pharmacologic properties, including a longer half-life than any other angiotensin II receptor blockers that bring higher and persistent antihypertensive activity. In hypertensive patients, telmisartan has superior efficacy than other antihypertensive drugs (losartan, valsartan, ramipril, atenolol, and perindopril) in controlling blood pressure, especially towards the end of the dosing interval. Telmisartan has a partial PPARγ-agonistic effect whilst does not have the safety concerns of full agonists of PPARγ receptors (thiazolidinediones). Moreover, telmisartan has an agonist activity on PPARα and PPARδ receptors and modulates the adipokine levels. Thus, telmisartan could be considered as a suitable alternative option, with multi-benefit for all components of metabolic syndrome including hypertension, diabetes mellitus, obesity, and hyperlipidemia. This review will highlight the role of telmisartan in metabolic syndrome and the main mechanisms of action of telmisartan are discussed and summarized. Many studies have demonstrated the useful properties of telmisartan in the prevention and improving of metabolic syndrome and this well-tolerated drug can be greatly proposed in the treatment of different components of metabolic syndrome. However, larger and long-duration studies are needed to confirm these findings in long-term observational studies and prospective trials and to determine the optimum dose of telmisartan in metabolic syndrome.

Exploration and application of a liver-on-a-chip device in combination with modelling and simulation for quantitative drug metabolism studies

Microphysiological systems (MPS) are complex and more physiologically realistic cellular in vitro tools that aim to provide more relevant human in vitro data for quantitative prediction of clinical pharmacokinetics while also reducing the need for animal testing. The PhysioMimix liver-on-a-chip integrates medium flow with hepatocyte culture and has the potential to be adopted for in vitro studies investigating the hepatic disposition characteristics of drug candidates. The current study focusses on liver-on-a-chip system exploration for multiple drug metabolism applications. Characterization of cytochrome P450 (CYP), UDP-glucuronosyl transferase (UGT) and aldehyde oxidase (AO) activities was performed using 15 drugs and in vitro to in vivo extrapolation (IVIVE) was assessed for 12 of them. Next, the utility of the liver-on-a-chip for estimation of the fraction metabolized (f_m) via specific biotransformation pathways of quinidine and diclofenac was established. Finally, the metabolite identification opportunities were also explored using efavirenz as an example drug with complex primary and secondary metabolism involving a combination of CYP, UGT and sulfotransferase enzymes. A key aspect of these investigations was the application of mathematical modelling for improved parameter calculation. Such approaches will be required for quantitative assessment of metabolism and/or transporter processes in systems where medium flow and system compartments result in non-homogeneous drug concentrations. In particular, modelling was used to explore the effect of evaporation from the medium and it was found that the intrinsic clearance (CL_int) might be underestimated by up to 40% for low clearance compounds if evaporation is not accounted for. Modelling of liver-on-a-chip in vitro data also enhanced the approach to f_m estimation allowing objective assessment of metabolism models of different complexity. The resultant diclofenac f_m,UGT of 0.64 was highly comparable with values reported previously in the literature. The current study demonstrates the integration of mathematical modelling with experimental liver-on-a-chip studies and illustrates how this approach supports generation of high quality of data from complex in vitro cellular systems.

Pharmacokinetic Interaction Between Telmisartan and Rosuvastatin/Ezetimibe After Multiple Oral Administration in Healthy Subjects

INTRODUCTION

Telmisartan, rosuvastatin and ezetimibe are commonly recommended as combination therapies. However, the pharmacokinetic (PK) interaction among these therapeutic drugs has not been clearly reported. The objective of this study was to investigate possible interactions between telmisartan monotherapy and a fixed-dose combination (FDC) of rosuvastatin/ezetimibe.

METHODS

A randomized, open-label, multiple oral dose, three-treatment, three-period, six-sequence crossover study was conducted in healthy male volunteers. Monotherapy and cotherapy with telmisartan (80 mg) or a FDC of rosuvastatin and ezetimibe (20/10 mg) were compared after once-daily treatment for 7 days. The PK profiles for telmisartan, rosuvastatin, total ezetimibe (ezetimibe + exetimibe glucuronide) and ezetimibe were evaluated up to 48 h after the last dose. There was a 14-day washout period between each treatment.

RESULTS

The geometric mean ratios (GMRs) and 90% confidence intervals (CIs) for the peak plasma concentration at steady state (C_max,ss) and area under the plasma concentration-time curve during the dosing interval at steady state (AUC_τ,ss) were 1.258 (1.072-1.475) (P = 0.020) and 1.264 (1.167-1.370) (P < 0.001) for telmisartan, 0.796 (0.723-0.878) (P < 0.001) and 0.904 (0.842-0.970) (P = 0.021) for total ezetimibe and 1.237 (1.081-1.416) (P = 0.012) and 0.988 (0.899-1.086) (P = 0.832) for ezetimibe, respectively. With rosuvastatin, the GMR (90% CI) was 2.616 (2.287-2.992) (P < 0.001) for C_max,ss and 1.265 (1.168-1.369) (P < 0.001) for AUC_τ,ss. No serious adverse events or clinically significant results were reported.

CONCLUSIONS

The coadministration of multiple doses of telmisartan and rosuvastatin/ezetimibe led to a mild increase in systemic exposure with respect to telmisartan and rosuvastatin and a nonsignificant change in exposure to total ezetimibe and ezetimibe, which was not considered clinically significant without safety concerns. Furthermore, for the generalizability of the clinical effects, a large-scaled clinical study might be required in patients with hypertension and dyslipidemia.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov registry number: NCT03802526.

Human total clearance values and volumes of distribution of typical human cytochrome P450 2C9/19 substrates predicted by single-species allometric scaling using pharmacokinetic data sets from common marmosets genotyped for P450 2C19

Common marmosets (Callithrix jacchus) are small non-human primates that genetically lack cytochrome P450 2C9 (CYP2C9). Polymorphic marmoset CYP2C19 compensates by mediating oxidations of typical human CYP2C9/19 substrates.Twenty-four probe substrates were intravenously administered in combinations to marmosets assigned to extensive or poor metaboliser (PM) groups by CYP2C19 genotyping. Eliminations from plasma of cilomilast, phenytoin, repaglinide, tolbutamide, and S-warfarin in the CYP2C19 PM group were significantly slow; these drugs are known substrates of human CYP2C8/9/19.Human total clearance values and volumes of distribution of the 24 test compounds were extrapolated using single-species allometric scaling with experimental data from marmosets and found to be mostly comparable with the reported values.Human total clearance values and volumes of distribution of 15 of the 24 test compounds similarly extrapolated using reported data sets from cynomolgus or rhesus monkeys were comparable to the present predicted results, especially to those based on data from PM marmosets.These results suggest that single-species allometric scaling using marmosets, being small, has advantages over multiple-species-based allometry and could be applicable for pharmacokinetic predictions at the discovery stage of drug development.

Enzyme Kinetics of Uridine Diphosphate Glucuronosyltransferases (UGTs)

Glucuronidation, catalyzed by uridine diphosphate glucuronosyltransferases (UGTs), is an important process for the metabolism and clearance of many lipophilic chemicals, including drugs, environmental chemicals, and endogenous compounds. Glucuronidation is a bisubstrate reaction that requires the aglycone and the cofactor, UDP-GlcUA. Accumulating evidence suggests that the bisubstrate reaction follows a compulsory-order ternary mechanism. To simplify the kinetic modeling of glucuronidation reactions in vitro, UDP-GlcUA is usually added to incubations in large excess. Many factors have been shown to influence UGT activity and kinetics in vitro, and these must be accounted for during experimental design and data interpretation. While the assessment of drug-drug interactions resulting from UGT inhibition has been challenging in the past, the increasing availability of UGT enzyme-selective substrate and inhibitor "probes" provides the prospect for more reliable reaction phenotyping and assessment of drug-drug interaction potential. Although extrapolation of the in vitro intrinsic clearance of a glucuronidated drug often underpredicts in vivo clearance, careful selection of in vitro experimental conditions and inclusion of extrahepatic glucuronidation may improve the predictivity of in vitro-in vivo extrapolation. Physiologically based pharmacokinetic (PBPK) modeling has also shown to be of value for predicting PK of drugs eliminated by glucuronidation.

Evidence-based strategies for the characterisation of human drug and chemical glucuronidation in vitro and UDP-glucuronosyltransferase reaction phenotyping

Enzymes of the UDP-glucuronosyltransferase (UGT) superfamily contribute to the elimination of drugs from almost all therapeutic classes. Awareness of the importance of glucuronidation as a drug clearance mechanism along with increased knowledge of the enzymology of drug and chemical metabolism has stimulated interest in the development and application of approaches for the characterisation of human drug glucuronidation in vitro, in particular reaction phenotyping (the fractional contribution of the individual UGT enzymes responsible for the glucuronidation of a given drug), assessment of metabolic stability, and UGT enzyme inhibition by drugs and other xenobiotics. In turn, this has permitted the implementation of in vitro - in vivo extrapolation approaches for the prediction of drug metabolic clearance, intestinal availability, and drug-drug interaction liability, all of which are of considerable importance in pre-clinical drug development. Indeed, regulatory agencies (FDA and EMA) require UGT reaction phenotyping for new chemical entities if glucuronidation accounts for ≥25% of total metabolism. In vitro studies are most commonly performed with recombinant UGT enzymes and human liver microsomes (HLM) as the enzyme sources. Despite the widespread use of in vitro approaches for the characterisation of drug and chemical glucuronidation by HLM and recombinant enzymes, evidence-based guidelines relating to experimental approaches are lacking. Here we present evidence-based strategies for the characterisation of drug and chemical glucuronidation in vitro, and for UGT reaction phenotyping. We anticipate that the strategies will inform practice, encourage development of standardised experimental procedures where feasible, and guide ongoing research in the field.

Human variability in isoform-specific UDP-glucuronosyltransferases: markers of acute and chronic exposure, polymorphisms and uncertainty factors

UDP-glucuronosyltransferases (UGTs) are involved in phase II conjugation reactions of xenobiotics and differences in their isoform activities result in interindividual kinetic differences of UGT probe substrates. Here, extensive literature searches were performed to identify probe substrates (14) for various UGT isoforms (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B7 and UGT2B15) and frequencies of human polymorphisms. Chemical-specific pharmacokinetic data were collected in a database to quantify interindividual differences in markers of acute (Cmax) and chronic (area under the curve, clearance) exposure. Using this database, UGT-related uncertainty factors were derived and compared to the default factor (i.e. 3.16) allowing for interindividual differences in kinetics. Overall, results show that pharmacokinetic data are predominantly available for Caucasian populations and scarce for other populations of different geographical ancestry. Furthermore, the relationships between UGT polymorphisms and pharmacokinetic parameters are rarely addressed in the included studies. The data show that UGT-related uncertainty factors were mostly below the default toxicokinetic uncertainty factor of 3.16, with the exception of five probe substrates (1-OH-midazolam, ezetimibe, raltegravir, SN38 and trifluoperazine), with three of these substrates being metabolised by the polymorphic isoform 1A1. Data gaps and future work to integrate UGT-related variability distributions with in vitro data to develop quantitative in vitro-in vivo extrapolations in chemical risk assessment are discussed.

Effects of UGT1A1 Polymorphism, Gender and Triglyceride on the Pharmacokinetics of Telmisartan in Chinese Patients with Hypertension: A Population Pharmacokinetic Analysis

BACKGROUND AND OBJECTIVE

Telmisartan is an angiotensin receptor blocker used for the treatment of hypertension. The effects of gender and uridine diphosphate-glycosytransferase 1A1 (UGT1A1) genetic polymorphisms (rs4124874, rs4148323, and rs6742078) on telmisartan plasma concentration and blood pressure in Chinese patients with hypertension have been reported previously. In this study, we aimed to develop a population pharmacokinetic (PopPK) model to quantify the effects of gender and UGT1A1 polymorphisms on the pharmacokinetics of telmisartan.

METHODS

Population pharmacokinetic analyses were performed using data collected prospectively from 58 Chinese patients with mild to moderate essential hypertension (aged 45-72 years; 36 men, 22 women) receiving 80 mg/day telmisartan orally for 4 weeks. Blood samples were collected in heparinized tubes at 0, 0.5, 1, and 6 h on day 28 after telmisartan administration. The plasma concentrations and UGT1A1 genetic variants were determined by high-performance liquid chromatography-mass spectrometry and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, respectively.

RESULTS

A two-compartment pharmacokinetic structural model with first-order elimination and absorption best described the pharmacokinetic characteristics of telmisartan. Gender and triglyceride influenced the apparent oral clearance (CL) of telmisartan. UGT1A1 (rs4124874) affected the bioavailability (F1) of telmisartan. Lower CL and bioavailability resulted in higher plasma concentrations being observed in female subjects with UGT1A1 CC or CA genotype and high triglyceride.

CONCLUSION

A PopPK model of telmisartan was established to confirm that UGT1A1 genotype, gender and triglyceride can affect the pharmacokinetics of telmisartan in Chinese patients with hypertension. Our findings can provide relevant pharmacokinetic parameters for further study of telmisartan.

Emerging Roles of Aryl Hydrocarbon Receptors in the Altered Clearance of Drugs during Chronic Kidney Disease

Chronic kidney disease (CKD) is a major public health problem, since 300,000,000 people in the world display a glomerular filtration rate (GFR) below 60 mL/min/1.73m². Patients with CKD have high rates of complications and comorbidities. Thus, they require the prescription of numerous medications, making the management of patients very complex. The prescription of numerous drugs associated with an altered renal- and non-renal clearance makes dose adjustment challenging in these patients, with frequent drug-related adverse events. However, the mechanisms involved in this abnormal drug clearance during CKD are not still well identified. We propose here that the transcription factor, aryl hydrocarbon receptor, which is the cellular receptor for indolic uremic toxins, could worsen the metabolism and the excretion of drugs in CKD patients.

Quantitative Prediction of Human Hepatic Clearance for P450 and Non-P450 Substrates from In Vivo Monkey Pharmacokinetics Study and In Vitro Metabolic Stability Tests Using Hepatocytes

Accurate prediction of human pharmacokinetics for drugs remains challenging, especially for non-cytochrome P450 (P450) substrates. Hepatocytes might be suitable for predicting hepatic intrinsic clearance (CL_int) of new chemical entities, because they can be applied to various compounds regardless of the metabolic enzymes. However, it was reported that hepatic CL_int is underestimated in hepatocytes. The purpose of the present study was to confirm the predictability of human hepatic clearance for P450 and non-P450 substrates in hepatocytes and the utility of animal scaling factors for the prediction using hepatocytes. CL_int values for 30 substrates of P450, UDP-glucuronosyltransferase, flavin-containing monooxygenase, esterases, reductases, and aldehyde oxidase in human microsomes, human S9 and human, rat, and monkey hepatocytes were estimated. Hepatocytes were incubated in serum of each species. Furthermore, CL_int values in human hepatocytes were corrected with empirical, monkey, and rat scaling factors. CL_int values in hepatocytes for most compounds were underestimated compared to observed values regardless of the metabolic enzyme, and the predictability was improved by using the scaling factors. The prediction using human hepatocytes corrected with monkey scaling factor showed the highest predictability for both P450 and non-P450 substrates among the predictions using liver microsomes, liver S9, and hepatocytes with or without scaling factors. CL_int values by this method for 80% and 90% of all compounds were within 2- and 3-fold of observed values, respectively. This method is accurate and useful for estimating new chemical entities, with no need to care about cofactors, localization of metabolic enzymes, or protein binding in plasma and incubation mixture.

Lack of UGT polymorphism association with idasanutlin pharmacokinetics in solid tumor patients

Purpose

Idasanutlin is a selective small-molecule MDM2 antagonist. It activates the tumor suppressor TP53 and is in phase 3 clinical trial for acute myeloid leukemia. Nonclinical studies have shown that glucuronidation is the major metabolizing mechanism for idasanutlin and UGT1A3 is the major metabolizing enzyme. There are reported examples of UGT polymorphisms associated with drug metabolism or response. Thus, the aim of this analysis is to investigate if UGT polymorphism is associated with idasanutlin pharmacokinetics.

Method

Idasanutlin clearance was derived and normalized from two phase I studies. Its clearance level was compared between patients with different genotypes at 44 non-monomorphic UGT SNPs. Several single-locus and multi-locus association analysis, including haplotype association analysis and pairwise SNP interaction (epistasis) analyses were performed to investigate if there is any association between UGT genotypes and idasanutlin clearance.

Results and conclusion

A total of 69 patients who have both idasanutlin pharmacokinetic data and UGT genotyping data were analyzed for association. The major clearance enzyme for idasanutlin, UGT1A3, has no association with idasanutlin clearance. Further single-locus and multi-locus association analyses also suggest that no significant UGT polymorphism association with idasanutlin clearance can be detected with the current datasets. However, the possibility of association with rare allele(s) of UGT family genes cannot be excluded due to the limited sample size of the current phase I studies.

Polymorphisms of the Multidrug Pump ABCG2: A Systematic Review of Their Effect on Protein Expression, Function, and Drug Pharmacokinetics

The widespread expression and polyspecificity of the multidrug ABCG2 efflux transporter make it an important determinant of the pharmacokinetics of a variety of substrate drugs. Null ABCG2 expression has been linked to the Junior blood group. Polymorphisms affecting the expression or function of ABCG2 may have clinically important roles in drug disposition and efficacy. The most well-studied single nucleotide polymorphism (SNP), Q141K (421C>A), is shown to decrease ABCG2 expression and activity, resulting in increased total drug exposure and decreased resistance to various substrates. The effect of Q141K can be rationalized by inspection of the ABCG2 structure, and the effects of this SNP on protein processing may make it a target for pharmacological intervention. The V12M SNP (34G>A) appears to improve outcomes in cancer patients treated with tyrosine kinase inhibitors, but the reasons for this are yet to be established, and this residue's role in the mechanism of the protein is unexplored by current biochemical and structural approaches. Research into the less-common polymorphisms is confined to in vitro studies, with several polymorphisms shown to decrease resistance to anticancer agents such as SN-38 and mitoxantrone. In this review, we present a systematic analysis of the effects of ABCG2 polymorphisms on ABCG2 function and drug pharmacokinetics. Where possible, we use recent structural advances to present a molecular interpretation of the effects of SNPs and indicate where we need further in vitro experiments to fully resolve how SNPs impact ABCG2 function.

Chemical Probes for Human UDP-Glucuronosyltransferases: A Comprehensive Review

UGTs play crucial roles in the metabolism and detoxification of both endogenous and xenobiotic compounds. The key roles of UGTs in human health have garnered great interest in the design and development of specific probes for human UGTs. However, in contrast to other human enzymes, the probe substrates for human UGTs are rarely reported, owing to the highly overlapping substrate specificities of UGTs and the lack of the integrated crystal structures of UGTs. Over the past decades, many efforts are made to develop specific probe substrates for UGTs and use them in both basic research and drug discovery. This review focuses on recent progress in the development of probe substrates for UGTs and their biomedical applications. A long list of chemical probes for UGTs, including non-fluorescent and fluorescent probes along with their structural information and kinetic parameters, are prepared and analyzed. Additionally, challenges and future directions in this field are highlighted in the final section. All information and knowledge presented in this review provide practical tools/methods for measuring UGT activities in complex biological samples, which will be very helpful for rapid screening and characterization of UGT modulators, and for exploring the relevance of UGT enzymes to human diseases.

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.

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).

Comparative pharmacokinetics of a fixed-dose combination vs concomitant administration of telmisartan and S-amlodipine in healthy adult volunteers

Objective

This study compared the pharmacokinetic (PK) and safety profiles of a fixed-dose combination (FDC) formulation of telmisartan and S-amlodipine with those of concomitant administration of the two drugs.

Materials and methods

This was an open-label, randomized, crossover study in healthy male Koreans. All subjects were administered an FDC tablet containing 40 mg telmisartan and 5 mg S-amlodipine and were also coadministered the same dose of both drugs given separately. The crossover study design included a 14-day washout period between the two treatments. Blood samples were collected up to 168 h following drug administration. The plasma concentrations of telmisartan and S-amlodipine were determined by liquid chromatography tandem mass spectrometry. PK parameters and plasma concentration–time curves were compared. Safety was assessed by measuring vital signs, clinical laboratory tests, physical examinations, and patient interviews.

Results

The geometric mean ratios and 90% CIs for the maximum plasma concentration (C_max) and area under the curve from time zero to the last sampling time (AUC_t) were 0.8782 (0.8167–0.9444) and 0.9662 (0.9210–1.0136) for telmisartan and 1.0069 (0.9723–1.0427) and 1.0324 (0.9969–1.0690) for S-amlodipine, respectively. A total of 36 adverse events (AEs) were reported by 23 subjects, but no statistical differences were observed between the two treatments. The most frequently reported AE was a mild-to-moderate headache that was generally self-limiting.

Conclusion

For both telmisartan and S-amlodipine, the C_max and AUC_t 90% CIs were between ln (0.8) and ln (1.25). These results suggest that the FDC formulation is pharmacokinetically bioequivalent and has a similar safety profile to the coadministration of these drugs.

Novel copy-number variations in pharmacogenes contribute to interindividual differences in drug pharmacokinetics

PurposeVariability in pharmacokinetics and drug response is shaped by single-nucleotide variants (SNVs) as well as copy-number variants (CNVs) in genes with importance for drug absorption, distribution, metabolism, and excretion (ADME). While SNVs have been extensively studied, a systematic assessment of the CNV landscape in ADME genes is lacking.MethodsWe integrated data from 2,504 whole genomes from the 1000 Genomes Project and 59,898 exomes from the Exome Aggregation Consortium to identify CNVs in 208 relevant pharmacogenes.ResultsWe describe novel exonic deletions and duplications in 201 (97%) of the pharmacogenes analyzed. The deletions are population-specific and frequencies range from singletons up to 1%, accounting for >5% of all loss-of-function alleles in up to 42% of the genes studied. We experimentally confirmed novel deletions in CYP2C19, CYP4F2, and SLCO1B3 by Sanger sequencing and validated their allelic frequencies in selected populations.ConclusionCNVs are an additional source of pharmacogenetic variability with important implications for drug response and personalized therapy. This, together with the important contribution of rare alleles to the variability of pharmacogenes, emphasizes the necessity of comprehensive next-generation sequencing-based genotype identification for an accurate prediction of the genetic variability of drug pharmacokinetics.

Renal Drug Transporters and Drug Interactions

Transporters in proximal renal tubules contribute to the disposition of numerous drugs. Furthermore, the molecular mechanisms of tubular secretion have been progressively elucidated during the past decades. Organic anions tend to be secreted by the transport proteins OAT1, OAT3 and OATP4C1 on the basolateral side of tubular cells, and multidrug resistance protein (MRP) 2, MRP4, OATP1A2 and breast cancer resistance protein (BCRP) on the apical side. Organic cations are secreted by organic cation transporter (OCT) 2 on the basolateral side, and multidrug and toxic compound extrusion (MATE) proteins MATE1, MATE2/2-K, P-glycoprotein, organic cation and carnitine transporter (OCTN) 1 and OCTN2 on the apical side. Significant drug-drug interactions (DDIs) may affect any of these transporters, altering the clearance and, consequently, the efficacy and/or toxicity of substrate drugs. Interactions at the level of basolateral transporters typically decrease the clearance of the victim drug, causing higher systemic exposure. Interactions at the apical level can also lower drug clearance, but may be associated with higher renal toxicity, due to intracellular accumulation. Whereas the importance of glomerular filtration in drug disposition is largely appreciated among clinicians, DDIs involving renal transporters are less well recognized. This review summarizes current knowledge on the roles, quantitative importance and clinical relevance of these transporters in drug therapy. It proposes an approach based on substrate-inhibitor associations for predicting potential tubular-based DDIs and preventing their adverse consequences. We provide a comprehensive list of known drug interactions with renally-expressed transporters. While many of these interactions have limited clinical consequences, some involving high-risk drugs (e.g. methotrexate) definitely deserve the attention of prescribers.

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.

Transport properties of valsartan, sacubitril and its active metabolite (LBQ657) as determinants of disposition

1. The potential for drug-drug interactions of LCZ696 (a novel, crystalline complex comprising sacubitril and valsartan) was investigated in vitro. 2. Sacubitril was shown to be a highly permeable P-glycoprotein (P-gp) substrate and was hydrolyzed to the active anionic metabolite LBQ657 by human carboxylesterase 1 (CES1b and 1c). The multidrug resistance-associated protein 2 (MRP2) was shown to be capable of LBQ657 and valsartan transport that contributes to the elimination of either compound. 3. LBQ657 and valsartan were transported by OAT1, OAT3, OATP1B1 and OATP1B3, whereas no OAT- or OATP-mediated sacubitril transport was observed. 4. The contribution of OATP1B3 to valsartan transport (73%) was appreciably higher than that by OATP1B1 (27%), Alternatively, OATP1B1 contribution to the hepatic uptake of LBQ657 (∼70%) was higher than that by OATP1B3 (∼30%). 5. None of the compounds inhibited OCT1/OCT2, MATE1/MATE2-K, P-gp, or BCRP. Sacubitril and LBQ657 inhibited OAT3 but not OAT1, and valsartan inhibited the activity of both OAT1 and OAT3. Sacubitril and valsartan inhibited OATP1B1 and OATP1B3, whereas LBQ657 weakly inhibited OATP1B1 but not OATP1B3. 6. Drug interactions due to the inhibition of transporters are unlikely due to the redundancy of the available transport pathways (LBQ657: OATP1B1/OAT1/3 and valsartan: OATP1B3/OAT1/3) and the low therapeutic concentration of the LCZ696 analytes.

Identification and characterization of human UDP-glucuronosyltransferases responsible for the in vitro glucuronidation of ursolic acid

This study aims to characterize the glucuronidation kinetics of ursolic acid (UA) in human liver microsomes (HLMs) and intestinal microsomes (HIMs) and identify the main UDP-glucuronosyltransferases (UGTs) involved. In our present study, only one type of UA glucuronide was observed after incubation with HLMs and HIMs respectively and was identified as a UA hydroxyl O-glucuronide. The glucuronidation of UA can be shown in HLMs and HIMs with Km values of 3.29 ± 0.16 and 3.74 ± 0.22 μM and Vmax values of 0.33 ± 0.03 and 0.42 ± 0.03 nmol/min/(mg protein). Among the 12 recombinant UGT enzymes investigated, UGT1A3 and UGT1A4 were identified as the major enzymes catalyzing the glucuronidation of UA [Km values of 2.58 ± 0.12 and 4.66 ± 0.60 μM, Vmax values of 0.72 ± 0.01 and 1.00 ± 0.06 nmol/min/(mg protein)]. The chemical inhibition study showed that the IC50 for hecogenin inhibition of UA glucuronidation was 51.79 ± 4.32 μM in HLMs. And chenodeoxycholic acid inhibited UA glucuronidation in HLMs with an IC50 of 28.26 ± 2.91 μM. In addition, UA glucuronidation in a panel of eight HLM was significantly correlated with telmisartan glucuronidation (r(2) = 0.7660, p < 0.01) and trifluoperazine glucuronidation (r(2) = 0.5866, p < 0.01) respectively. These findings collectively indicate that UGT1A3 and UGT1A4 were the main enzymes responsible for the glucuronidation of UA in human.

The role of glucuronidation in drug resistance

The final therapeutic effect of a drug candidate, which is directed to a specific molecular target strongly depends on its absorption, distribution, metabolism and excretion (ADME). The disruption of at least one element of ADME may result in serious drug resistance. In this work we described the role of one element of this resistance: phase II metabolism with UDP-glucuronosyltransferases (UGTs). UGT function is the transformation of their substrates into more polar metabolites, which are better substrates for the ABC transporters, MDR1, MRP and BCRP, than the native drug. UGT-mediated drug resistance can be associated with (i) inherent overexpression of the enzyme, named intrinsic drug resistance or (ii) induced expression of the enzyme, named acquired drug resistance observed when enzyme expression is induced by the drug or other factors, as food-derived compounds. Very often this induction occurs via ligand binding receptors including AhR (aryl hydrocarbon receptor) PXR (pregnane X receptor), or other transcription factors. The effect of UGT dependent resistance is strengthened by coordinate action and also a coordinate regulation of the expression of UGTs and ABC transporters. This coupling of UGT and multidrug resistance proteins has been intensively studied, particularly in the case of antitumor treatment, when this resistance is "improved" by differences in UGT expression between tumor and healthy tissue. Multidrug resistance coordinated with glucuronidation has also been described here for drugs used in the management of epilepsy, psychiatric diseases, HIV infections, hypertension and hypercholesterolemia. Proposals to reverse UGT-mediated drug resistance should consider the endogenous functions of UGT.

Physiologically based pharmacokinetic prediction of telmisartan in human

A previously developed physiologically based pharmacokinetic model for hepatic transporter substrates was extended to an organic anion transporting polypeptide substrate, telmisartan. Predictions used in vitro data from sandwich culture human hepatocyte and human liver microsome assays. We have developed a novel method to calibrate partition coefficients (Kps) between nonliver tissues and plasma on the basis of published human positron emission tomography (PET) data to decrease the uncertainty in tissue distribution introduced by in silico-predicted Kps. With in vitro data-predicted hepatic clearances, published empirical scaling factors, and PET-calibrated Kps, the model could accurately recapitulate telmisartan pharmacokinetic (PK) behavior before 2.5 hours. Reasonable predictions also depend on having a model structure that can adequately describe the drug disposition pathways. We showed that the elimination phase (2.5-12 hours) of telmisartan PK could be more accurately recapitulated when enterohepatic recirculation of parent compound derived from intestinal deconjugation of glucuronide metabolite was incorporated into the model. This study demonstrated the usefulness of the previously proposed physiologically based modeling approach for purely predictive intravenous PK simulation and identified additional biologic processes that can be important in prediction.

Role of the breast cancer resistance protein (BCRP/ABCG2) in drug transport--an update

The human breast cancer resistance protein (BCRP, gene symbol ABCG2) is an ATP-binding cassette (ABC) efflux transporter. It was so named because it was initially cloned from a multidrug-resistant breast cancer cell line where it was found to confer resistance to chemotherapeutic agents such as mitoxantrone and topotecan. Since its discovery in 1998, the substrates of BCRP have been rapidly expanding to include not only therapeutic agents but also physiological substances such as estrone-3-sulfate, 17β-estradiol 17-(β-D-glucuronide) and uric acid. Likewise, at least hundreds of BCRP inhibitors have been identified. Among normal human tissues, BCRP is highly expressed on the apical membranes of the placental syncytiotrophoblasts, the intestinal epithelium, the liver hepatocytes, the endothelial cells of brain microvessels, and the renal proximal tubular cells, contributing to the absorption, distribution, and elimination of drugs and endogenous compounds as well as tissue protection against xenobiotic exposure. As a result, BCRP has now been recognized by the FDA to be one of the key drug transporters involved in clinically relevant drug disposition. We published a highly-accessed review article on BCRP in 2005, and much progress has been made since then. In this review, we provide an update of current knowledge on basic biochemistry and pharmacological functions of BCRP as well as its relevance to drug resistance and drug disposition.

Kinetic Interpretation of the Importance of OATP1B3 and MRP2 in Docetaxel-Induced Hematopoietic Toxicity

Neutropenia is a lethal dose-limiting toxicity of docetaxel. Our previous report indicated that the prevalence of severe docetaxel-induced neutropenia is significantly associated with genetic polymorphisms in solute carrier organic anion transporter 1B3 (SLCO1B3) (encoding organic anion–transporting polypeptide 1B3 (OATP1B3)) and ATP-binding cassette subfamily C2 (ABCC2) (encoding multidrug-resistant–associated protein 2 (MRP2)). Therefore, we investigated their significance in docetaxel-induced neutropenia. In vitro experiments suggested their possible involvement in the hepatic uptake of docetaxel and its efflux from bone marrow cells. To further characterize a quantitative impact of OATP1B3 and MRP2 on neutropenia, we used an in silico simulation of the neutrophil count in docetaxel-treated subjects with functional changes in OATP1B3 and MRP2 in a pharmacokinetic/pharmacodynamic model. The clinically reported odds ratios for docetaxel-induced neutropenia risk were explained by the decreased function of OATP1B3 and MRP2 to 41 and 32%, respectively. These results suggest that reduced activities of OATP1B3 and MRP2 associated with systemic exposure and local accumulation in bone marrow cells, respectively, account for the docetaxel-induced neutropenia observed clinically.

Relevance of UDP-glucuronosyltransferase polymorphisms for drug dosing: A quantitative systematic review

UDP-glucuronosyltransferases (UGT) catalyze the biotransformation of many endobiotics and xenobiotics, and are coded by polymorphic genes. However, knowledge about the effects of these polymorphisms is rarely used for the individualization of drug therapy. Here, we present a quantitative systematic review of clinical studies on the impact of UGT variants on drug metabolism to clarify the potential for genotype-adjusted therapy recommendations. Data on UGT polymorphisms and dose-related pharmacokinetic parameters in man were retrieved by a systematic search in public databases. Mean estimates of pharmacokinetic parameters were extracted for each group of carriers of UGT variants to assess their effect size. Pooled estimates and relative confidence bounds were computed with a random-effects meta-analytic approach whenever multiple studies on the same variant, ethnic group, and substrate were available. Information was retrieved on 30 polymorphic metabolic pathways involving 10 UGT enzymes. For irinotecan and mycophenolic acid a wealth of data was available for assessing the impact of genetic polymorphisms on pharmacokinetics under different dosages, between ethnicities, under comedication, and under toxicity. Evidence for effects of potential clinical relevance exists for 19 drugs, but the data are not sufficient to assess effect size with the precision required to issue dose recommendations. In conclusion, compared to other drug metabolizing enzymes much less systematic research has been conducted on the polymorphisms of UGT enzymes. However, there is evidence of the existence of large monogenetic functional polymorphisms affecting pharmacokinetics and suggesting a potential use of UGT polymorphisms for the individualization of drug therapy.

Clinical significance of organic anion transporting polypeptides (OATPs) in drug disposition: their roles in hepatic clearance and intestinal absorption

Organic anion transporting polypeptide (OATP) family transporters accept a number of drugs and are increasingly being recognized as important factors in governing drug and metabolite pharmacokinetics. OATP1B1 and OATP1B3 play an important role in hepatic drug uptake while OATP2B1 and OATP1A2 might be key players in intestinal absorption and transport across blood-brain barrier of drugs, respectively. To understand the importance of OATPs in the hepatic clearance of drugs, the rate-determining process for elimination should be considered; for some drugs, hepatic uptake clearance rather than metabolic intrinsic clearance is the more important determinant of hepatic clearances. The importance of the unbound concentration ratio (liver/blood), K(p,uu) , of drugs, which is partly governed by OATPs, is exemplified in interpreting the difference in the IC(50) of statins between the hepatocyte and microsome systems for the inhibition of HMG-CoA reductase activity. The intrinsic activity and/or expression level of OATPs are affected by genetic polymorphisms and drug-drug interactions. Their effects on the elimination rate or intestinal absorption rate of drugs may sometimes depend on the substrate drug. This is partly because of the different contribution of OATP isoforms to clearance or intestinal absorption. When the contribution of the OATP-mediated pathway is substantial, the pharmacokinetics of substrate drugs should be greatly affected. This review describes the estimation of the contribution of OATP1B1 to the total hepatic uptake of drugs from the data of fold-increases in the plasma concentration of substrate drugs by the genetic polymorphism of this transporter. To understand the importance of the OATP family transporters, modeling and simulation with a physiologically based pharmacokinetic model are helpful.

A systematic comparison of the properties of clinically used angiotensin II type 1 receptor antagonists

Angiotensin II type 1 receptor antagonists (ARBs) have become an important drug class in the treatment of hypertension and heart failure and the protection from diabetic nephropathy. Eight ARBs are clinically available [azilsartan, candesartan, eprosartan, irbesartan, losartan, olmesartan, telmisartan, valsartan]. Azilsartan (in some countries), candesartan, and olmesartan are orally administered as prodrugs, whereas the blocking action of some is mediated through active metabolites. On the basis of their chemical structures, ARBs use different binding pockets in the receptor, which are associated with differences in dissociation times and, in most cases, apparently insurmountable antagonism. The physicochemical differences between ARBs also manifest in different tissue penetration, including passage through the blood-brain barrier. Differences in binding mode and tissue penetration are also associated with differences in pharmacokinetic profile, particularly duration of action. Although generally highly specific for angiotensin II type 1 receptors, some ARBs, particularly telmisartan, are partial agonists at peroxisome proliferator-activated receptor-γ. All of these properties are comprehensively reviewed in this article. Although there is general consensus that a continuous receptor blockade over a 24-hour period is desirable, the clinical relevance of other pharmacological differences between individual ARBs remains to be assessed.

In vitro assessment of drug-drug interaction potential of boceprevir associated with drug metabolizing enzymes and transporters

The inhibitory effect of boceprevir (BOC), an inhibitor of hepatitis C virus nonstructural protein 3 protease was evaluated in vitro against a panel of drug-metabolizing enzymes and transporters. BOC, a known substrate for cytochrome P450 (P450) CYP3A and aldo-ketoreductases, was a reversible time-dependent inhibitor (k(inact) = 0.12 minute(-1), K(I) = 6.1 µM) of CYP3A4/5 but not an inhibitor of other major P450s, nor of UDP-glucuronosyltransferases 1A1 and 2B7. BOC showed weak to no inhibition of breast cancer resistance protein (BCRP), P-glycoprotein (Pgp), or multidrug resistance protein 2. It was a moderate inhibitor of organic anion transporting polypeptide (OATP) 1B1 and 1B3, with an IC(50) of 18 and 4.9 µM, respectively. In human hepatocytes, BOC inhibited CYP3A-mediated metabolism of midazolam, OATP1B-mediated hepatic uptake of pitavastatin, and both the uptake and metabolism of atorvastatin. The inhibitory potency of BOC was lower than known inhibitors of CYP3A (ketoconazole), OATP1B (rifampin), or both (telaprevir). BOC was a substrate for Pgp and BCRP but not for OATP1B1, OATP1B3, OATP2B1, organic cation transporter, or sodium/taurocholate cotransporting peptide. Overall, our data suggest that BOC has the potential to cause pharmacokinetic interactions via inhibition of CYP3A and CYP3A/OATP1B interplay, with the interaction magnitude lower than those observed with known potent inhibitors. Conversely, pharmacokinetic interactions of BOC, either as a perpetrator or victim, via other major P450s and transporters tested are less likely to be of clinical significance. The results from clinical drug-drug interaction studies conducted thus far are generally supportive of these conclusions.