The Effect of Famotidine, a MATE1-Selective Inhibitor, on the Pharmacokinetics and Pharmacodynamics of Metformin

Predicting OCT2/MATEs-Mediated Drug Interactions in Healthy Volunteers and Patients with Chronic Kidney Disease: Insights from Extended Clearance Concept, Endogenous Biomarkers, and In Vitro Inhibition Studies (Perspectives from the International Transporter Consortium)

Organic cation transporter (OCT) 2 and multidrug and toxin extrusion (MATE) transporters play significant roles in the renal secretion of organic cations and drug-drug interactions (DDIs). Recent in vitro studies indicate that the Ki values for OCT2 exhibit substrate dependency and increase in potency with pre-incubation. However, consensus is lacking on whether these factors should be considered in predicting in vivo inhibition. Physiologically based pharmacokinetic models, combined with the extended clearance concept, have been used and are discussed here for OCT2/MATEs probes. In addition to modeling, early clinical studies use endogenous biomarkers to evaluate transporter-mediated DDI risk, with the aim of avoiding unnecessary clinical DDI studies. Identified biomarkers for OCT2/MATEs, such as creatinine, N1-methylnicotinamide, and N1-methyladenosine, have proven useful in confirming clinically relevant OCT2/MATEs-mediated DDIs when renal clearance (CLr) is used as an endpoint; their application is discussed further. From a clinical perspective, the intact nephron hypothesis (INH), which postulates that the decrease in CLr in chronic kidney disease (CKD) is proportional to that in nephron numbers, has been proposed. However, reports suggest that the secretion clearance of creatinine and substrates of organic anion transporters (OATs) does not follow this proportionality in patients with CKD. This state-of-the-art review highlights key developments in predicting OCT2/MATEs-mediated DDIs in healthy volunteers and explores the prediction of clinical OCT2/MATEs DDI risk in patients with CKD by comparing substrate-dependent changes in secretion clearance for substrates of OCT2/MATEs and OATs. Recommendations for the prediction of OCT2/MATEs-mediated DDI risk, together with the current knowledge gaps and future directions, are discussed.

The role of the circadian timing system on drug metabolism and detoxification: an update

INTRODUCTION

The 24-hour variations in drug absorption, distribution, metabolism, and elimination, collectively known as pharmacokinetics, are fundamentally influenced by rhythmic physiological processes regulated by the molecular clock. Recent advances have elucidated the intricacies of the circadian timing system and the molecular interplay between biological clocks, enzymes and transporters in preclinical level.

AREA COVERED

Circadian rhythm of the drug metabolizing enzymes and carrier efflux functions possess a major role for drug metabolism and detoxification. The efflux and metabolism function of intestines and liver seems important. The investigations revealed that the ABC and SLC transporter families, along with cytochrome p-450 systems in the intestine, liver, and kidney, play a dominant role in the circadian detoxification of drugs. Additionally, the circadian control of efflux by the blood-brain barrier is also discussed.

EXPERT OPINION

The influence of the circadian timing system on drug pharmacokinetics significantly impacts the efficacy, adverse effects, and toxicity profiles of various drugs. Moreover, the emergence of sex-related circadian changes in the metabolism and detoxification processes has underscored the importance of considering gender-specific differences in drug tolerability and pharmacology. A better understanding of coupling between central clock and circadian metabolism/transport contributes to the development of more rational drug utilization and the implementation of chronotherapy applications.

Evaluation of OCT2-mediated drug-drug interactions between ulotaront and metformin in subjects with schizophrenia

Ulotaront (SEP-363856) is a TAAR1 agonist, with 5-HT1A agonist activity, currently in clinical development for the treatment of schizophrenia. In vitro studies indicate ulotaront is an OCT2-specific inhibitor with IC50 of 1.27 μM. The primary objective of this study is to determine if a single dose of ulotaront affects the PK of metformin, an index substrate of OCT2, in subjects with schizophrenia. In a randomized, single-blind, 2-period crossover study, 25 adults with schizophrenia received a single dose of metformin-HCl 850 mg (approximately 663 mg metformin) with and without coadministration of 100 mg ulotaront. The plasma samples were analyzed by fully validated LC-MS/MS methods. The primary PK endpoints for metformin were AUCinf, AUClast, Cmax, and tmax. The highest-anticipated clinical dose of ulotaront (100 mg) had no statistically significant effect on the PK of a single dose of metformin based on Cmax and AUCinf. Geometric least squares mean ratios were 89.98% and 110.63%, respectively, with the 90% confidential interval (CI) for each parameter contained within 80%-125%. Median tmax was comparable across the treatments. Ulotaront does not act as a perpetrator of OCT2-mediated DDI against metformin. Co-administration of ulotaront is not expected to require dose adjustment of metformin or other drugs cleared by OCT2.

Membrane transporters in drug development and as determinants of precision medicine

The effect of membrane transporters on drug disposition, efficacy and safety is now well recognized. Since the initial publication from the International Transporter Consortium, significant progress has been made in understanding the roles and functions of transporters, as well as in the development of tools and models to assess and predict transporter-mediated activity, toxicity and drug-drug interactions (DDIs). Notable advances include an increased understanding of the effects of intrinsic and extrinsic factors on transporter activity, the application of physiologically based pharmacokinetic modelling in predicting transporter-mediated drug disposition, the identification of endogenous biomarkers to assess transporter-mediated DDIs and the determination of the cryogenic electron microscopy structures of SLC and ABC transporters. This article provides an overview of these key developments, highlighting unanswered questions, regulatory considerations and future directions.

Use of a Double-Transfected System to Predict hOCT2/hMATE1-Mediated Renal Drug-Drug Interactions

Accurate predictions of renal drug-drug interactions (DDIs) mediated by the human organic cation transporter 2 (hOCT2) and multidrug and toxin extrusion proteins (hMATEs) remain challenging. Current DDI evaluation using plasma maximal unbound inhibitor concentrations (Imax,u) and IC50 values determined in single transporter-transfected cells frequently leads to false or overprediction especially for hMATE1. Emerging evidence suggests intracellular unbound inhibitor concentration may be more relevant for hMATE1 inhibition in vivo. However, determination of intrarenal inhibitor concentrations is impractical. Here, we explored the use of hOCT2/hMATE1 double-transfected Madin-Darby canine kidney (MDCK) cells as a new in vitro tool for DDI risk assessment. Our results showed that potent in vitro hMATE1 inhibitors (hydroxychloroquine, brigatinib, and famotidine) failed to inhibit metformin B-to-A flux in the double-transfected system. On the other side, the classic hOCT2/hMATE1 inhibitors, pyrimethamine and cimetidine, dose-dependently inhibited metformin apparent B-to-A permeability (Papp). The different behaviors of these hMATE1 inhibitors in the double-transfected system can be explained by their different ability to gain intracellular access either via passive diffusion or transporter-mediated uptake. A new parameter (IC50,flux) was proposed reflecting the inhibitor's potency on overall hOCT2/hMATE1-mediated tubular secretion. The IC50,flux values significantly differ from the IC50 values determined in single transporter-transfected cells. Importantly, the IC50,flux accurately predicted in vivo DDIs (within 2-fold) when used in a static model. Our data demonstrated that the IC50,flux approach circumvents the need to measure intracellular inhibitor concentrations and more accurately predicted hOCT2/hMATE1-mediated renal DDIs. This system represents a new approach that could be used for improved DDI assessment during drug development. SIGNIFICANCE STATEMENT: This study demonstrated that flux studies in double-transfected MDCK cells and the IC50,flux represents a better approach to assess in vivo DDI potential for the renal organic cation secretion system. This study highlights the importance of inhibitor intracellular accessibility for accurate prediction of hMATE1-mediated renal DDIs. This approach has the potential to identify in vitro hMATE1 inhibitors that are unlikely to result in in vivo DDIs, thus reducing the burden of unnecessary and costly clinical DDI investigations.

Metformin-Cimetidine Drug Interaction and Risk of Lactic Acidosis in Renal Failure: A Pharmacovigilance-Pharmacokinetic Appraisal

OBJECTIVE

This study aimed to evaluate lactic acidosis (LA) risk when using metformin combined with histamine H2 receptor inhibitors (H2RI) in patients with renal failure (RF).

RESEARCH DESIGN AND METHODS

This study analyzed FDA Adverse Event Reporting System data (2012Q4 to 2022Q4) to characterize reports of LA associated with metformin alone or combined with H2RI. Using a disproportionality approach, LA risk signal in the overall population and in patients with RF was assessed. A physiologically based pharmacokinetic (PBPK) model was developed to predict metformin and cimetidine pharmacokinetic changes following conventional doses of the combinations in patients with various degrees of RF. To explore its correlation with LA risk, a peak plasma metformin concentration of 3 mg/L was considered the threshold.

RESULTS

Following the 2016 U.S. Food and Drug Administration metformin approval for mild-to-moderate RF, the percentage of patients with RF reporting LA associated with metformin combined with H2RI increased. Disproportionality analysis showed reported LA risk signal associated with metformin and cimetidine in the overall population within the study timeframe only. Furthermore, with PBPK simulations, for metformin (1,000 mg b.i.d.) with cimetidine (300 mg q.i.d. or 400 mg b.i.d.) in stage 1 of chronic kidney disease, metformin (1,000 mg b.i.d.) with cimetidine (300 mg q.i.d. or 400 mg b.i.d. or 800 mg q.d.) in stage 2, and most combinations in stage 3, the peak plasma metformin concentrations exceeded the 3 mg/L threshold.

CONCLUSIONS

Metformin combined with cimetidine at conventional doses may cause LA in patients with mild-to-moderate RF.

Targeting the multidrug and toxin extrusion 1 gene (SLC47A1) sensitizes glioma stem cells to temozolomide

Glioblastoma multiforme (GBM) is the most aggressive type of brain tumor, with an extremely poor prognosis due to resistance to standard-of-care treatments. Strong evidence suggests that the small population of glioma stem cells (GSCs) contributes to the aggressiveness of GBM. One of the mechanisms that promote GSC progression is the dysregulation of membrane transporters, which mediate the influx and efflux of substances to maintain cellular homeostasis. Here, we investigated the role of multidrug and toxin extrusion transporter gene SLC47A1 in GSCs. Results show that SLC47A1 is highly expressed in GSCs compared to non-stem cell glioma cells, and non-tumor cells. Additionally, in-silico analysis of public datasets showed that high SLC47A1 expression is linked to malignancy and a poor prognosis in glioma patients. Further, SLC47A1 expression is correlated with important biological processes and signaling pathways that support tumor growth. Meanwhile, silencing SLC47A1 by short-hairpin RNA (shRNA) influenced cell viability and self-renewal activity in GSCs. Interestingly, SLC47A1 shRNA knockdown or pharmacological inhibition potentiates the effect of temozolomide (TMZ) in GSC cells. The findings suggest that SLC47A1 could serve as a useful therapeutic target for gliomas.

Quantitative Consideration of Clinical Increases in Serum Creatinine Caused by Renal Transporter Inhibition

Creatinine is a common biomarker of renal function and is secreted in the renal tubular cells via drug transporters, such as organic cation transporter 2 and multidrug and toxin extrusion (MATE) 1/2-K. To differentiate between drug-induced acute kidney injury (AKI) and drug interactions through the renal transporter, it has been examined whether these transporter inhibitions quantitatively explained increases in serum creatinine (SCr) at their clinically relevant concentrations using drugs without any changes in renal function. For such renal transporter inhibitors and recently approved tyrosine kinase inhibitors (TKIs), this mini-review describes clinical increases in SCr and inhibitory potentials against the renal transporters. Most cases of SCr elevations can be explained by considering the renal transporter inhibitions based on unbound maximum plasma concentrations, except for drugs associated with obvious changes in renal function. SCr increases for cobicistat, dolutegravir, and dronedarone, and some TKIs were significantly underestimated, and these underestimations were suggested to be associated with low plasma unbound fractions. Sensitivity analysis of SCr elevations regarding inhibitory potentials of MATE1/2-K demonstrated that typical inhibitors such as cimetidine, DX-619, pyrimethamine, and trimethoprim could give false interpretations of AKI according to the criteria based on relative or absolute levels of SCr elevations. Recent progress and current challenges of physiologically-based pharmacokinetics modeling for creatinine disposition were also summarized. Although it should be noted for the potential impact of in vitro assay designs on clinical translatability of transporter inhibitions data, mechanistic approaches could support decision-making in clinical development to differentiate between AKI and creatinine-drug interactions. SIGNIFICANCE STATEMENT: Serum creatinine (SCr) is widely used as an indicator of kidney function, but it increases due to inhibitions of renal transporters, such as multidrug and toxin extrusion protein 1/2-K despite no functional changes in the kidney. Such SCr elevations were quantitatively explained by renal transporter inhibitions except for some drugs with high protein binding. The present analysis demonstrated that clinically relevant inhibitors of the renal transporters could cause SCr elevations above levels corresponding to acute kidney injury criteria.

Famotidine Enhances Rifampicin Activity against Acinetobacter baumannii by Affecting OmpA

The development of novel antibiotic adjuvants is imminent because of the frequent emergence of resistance in Gram-negative bacteria, which severely restricts the efficiency and longevity of commonly used clinical antibiotics. It is reported that famotidine, a clinical inhibitor of gastric acid secretion, enhances the antibacterial activity of rifamycin antibiotics, especially rifampicin, against Gram-negative bacteria and reverses drug resistance. Studies have shown that famotidine disrupts the cell membrane of Acinetobacter baumannii and inhibits the expression of the outer membrane protein ompA gene, while causing a dissipation of the plasma membrane potential, compensatively upregulating the pH gradient and ultimately increasing the accumulation of reactive oxygen species by leading to increased bacterial mortality. In addition, famotidine also inhibited the efflux pump activity and the biofilm formation of A. baumannii. In the Galleria mellonella and mouse infection models, the combination of famotidine and rifampicin increased the survival rate of infected animals and decreased the bacterial load in mouse organs. In conclusion, famotidine has the potential to be a novel rifampicin adjuvant, providing a new option for the treatment of clinical Gram-negative bacterial infections. IMPORTANCE In this study, famotidine was discovered for the first time to have potential as an antibiotic adjuvant, enhancing the antibacterial activity of rifamycin antibiotics against A. baumannii and overcoming the limitations of drug therapy. With the discovery of novel applications for the guanidine-containing medication famotidine, the viability of screening prospective antibiotic adjuvants from guanidine-based molecules was further explored. In addition, famotidine exerts activity by affecting the OmpA protein of the cell membrane, indicating that this protein might be used as a therapeutic drug target to treat A. baumannii infections.

The development and benefits of metformin in various diseases

Metformin has been used for the treatment of type II diabetes mellitus for decades due to its safety, low cost, and outstanding hypoglycemic effect clinically. The mechanisms underlying these benefits are complex and still not fully understood. Inhibition of mitochondrial respiratory-chain complex I is the most described downstream mechanism of metformin, leading to reduced ATP production and activation of AMP-activated protein kinase (AMPK). Meanwhile, many novel targets of metformin have been gradually discovered. In recent years, multiple pre-clinical and clinical studies are committed to extend the indications of metformin in addition to diabetes. Herein, we summarized the benefits of metformin in four types of diseases, including metabolic associated diseases, cancer, aging and age-related diseases, neurological disorders. We comprehensively discussed the pharmacokinetic properties and the mechanisms of action, treatment strategies, the clinical application, the potential risk of metformin in various diseases. This review provides a brief summary of the benefits and concerns of metformin, aiming to interest scientists to consider and explore the common and specific mechanisms and guiding for the further research. Although there have been countless studies of metformin, longitudinal research in each field is still much warranted.

Identification and Characterization of ACP-5862, the Major Circulating Active Metabolite of Acalabrutinib: Both Are Potent and Selective Covalent Bruton Tyrosine Kinase Inhibitors

Acalabrutinib is a covalent Bruton tyrosine kinase (BTK) inhibitor approved for relapsed/refractory mantle cell lymphoma and chronic lymphocytic leukemia/small lymphocytic lymphoma. A major metabolite of acalabrutinib (M27, ACP-5862) was observed in human plasma circulation. Subsequently, the metabolite was purified from an in vitro biosynthetic reaction and shown by nuclear magnetic resonance spectroscopy to be a pyrrolidine ring-opened ketone/amide. Synthesis confirmed its structure, and covalent inhibition of wild-type BTK was observed in a biochemical kinase assay. A twofold lower potency than acalabrutinib was observed but with similar high kinase selectivity. Like acalabrutinib, ACP-5862 was the most selective toward BTK relative to ibrutinib and zanubrutinib. Because of the potency, ACP-5862 covalent binding properties, and potential contribution to clinical efficacy of acalabrutinib, factors influencing acalabrutinib clearance and ACP-5862 formation and clearance were assessed. rCYP (recombinant cytochrome P450) reaction phenotyping indicated that CYP3A4 was responsible for ACP-5862 formation and metabolism. ACP-5862 formation Km (Michaelis constant) and Vmax were 2.78 μM and 4.13 pmol/pmol CYP3A/min, respectively. ACP-5862 intrinsic clearance was 23.6 μL/min per mg. Acalabrutinib weakly inhibited CYP2C8, CYP2C9, and CYP3A4, and ACP-5862 weakly inhibited CYP2C9 and CYP2C19; other cytochrome P450s, UGTs (uridine 5'-diphospho-glucuronosyltransferases), and aldehyde oxidase were not inhibited. Neither parent nor ACP-5862 strongly induced CYP1A2, CYP2B6, or CYP3A4 mRNA. Acalabrutinib and ACP-5862 were substrates of multidrug resistance protein 1 and breast cancer resistance protein but not OATP1B1 or OATP1B3. Our work indicates that ACP-5862 may contribute to clinical efficacy in acalabrutinib-treated patients and illustrates how proactive metabolite characterization allows timely assessment of drug-drug interactions and potential contributions of metabolites to pharmacological activity. SIGNIFICANCE STATEMENT: This work characterized the major metabolite of acalabrutinib, ACP-5862. Its contribution to the pharmacological activity of acalabrutinib was assessed based on covalent Bruton tyrosine kinase binding kinetics, kinase selectivity, and potency in cellular assays. The metabolic clearance and in vitro drug-drug interaction potential were also evaluated for both acalabrutinib and ACP-5862. The current data suggest that ACP-5862 may contribute to the clinical efficacy observed in acalabrutinib-treated patients and demonstrates the value of proactive metabolite identification and pharmacological characterization.

In Vitro ADME and Preclinical Pharmacokinetics of Ulotaront, a TAAR1/5-HT1A Receptor Agonist for the Treatment of Schizophrenia

Purpose

Ulotaront (SEP-363856) is a TAAR1 agonist with 5-HT_1A agonist activity currently in clinical development for the treatment of schizophrenia. The objectives of the current study were to characterize the in vitro ADME properties, preclinical PK, and to evaluate the DDI potential of ulotaront and its major metabolite SEP-383103.

Methods

Solubility, permeability, plasma protein binding, CYP inhibition and induction, transporter inhibition and uptake studies were conducted in vitro. Phenotyping studies were conducted using recombinant human CYPs and FMOs, human liver microsomes and human liver homogenates. Preclinical plasma and brain pharmacokinetics were determined after a single intraperitoneal, intravenous, and oral administration of ulotaront.

Results

Ulotaront is a compound of high solubility, high permeability, and low binding to plasma proteins. Ulotaront metabolism is mediated via both NADPH-dependent and NADPH-independent pathways, with CYP2D6 as the major metabolizing enzyme. Ulotaront is an inducer of CYP2B6, and an inhibitor of CYP2D6, OCT1 and OCT2, while SEP-383103 is neither a CYP inducer nor a potent inhibitor of CYPs and human transporters. Ulotaront exhibits rapid absorption, greater than 70% bioavailability, approximately 3.5 L/kg volume of distribution, 1.5-4 h half-life, 12-43 ml/min/kg clearance, and good penetration across the blood–brain barrier in preclinical species.

Conclusions

Ulotaront has been designated as a BCS1 compound by US FDA. The ability of ulotaront to penetrate the blood–brain barrier for CNS targeting has been demonstrated in mice and rats. The potential for ulotaront and SEP-383103 to act as perpetrators of CYP and transporter-mediated DDIs is predicted to be remote.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11095-022-03267-1.

Advancing Estimation of Hepatobiliary Clearances in Physiologically Based Pharmacokinetic Models of Rosuvastatin Using Human Hepatic Concentrations

PURPOSE

To estimate hepatobiliary clearances of rosuvastatin via simultaneously fitting to reported human positron emission tomography (PET) data in the liver and gallbladder.

METHODS

A hepatobiliary model incorporating five intrinsic hepatobiliary clearances (active uptake clearance at the sinusoidal membrane, efflux clearance by passive diffusion through the sinusoidal membrane, influx clearance by passive diffusion through sinusoidal membrane, clearance of biliary excretion at the canalicular membrane, and intercompartment clearance from the intrahepatic bile duct to the gallbladder) and three compartments (liver, intrahepatic bile duct, and gallbladder) was developed to simultaneously fit rosuvastatin liver and gallbladder data from a representative subject reported by Billington et al. (1). Two liver blood supply input functions, arterial input function and dual input function (using peripheral venous as an alternative to portal vein), were assessed. Additionally, the predictive performance between the established model and four reported models trained with only systemic exposure data, was evaluated by comparing simulated liver and gallbladder profiles with observations.

RESULTS

The established hepatobiliary model well captured the kinetic profiles of rosuvastatin in the liver and gallbladder during the PET scans. Application of dual input function led to a marked underestimation of liver concentrations at the initial stage after i.v. dosing which cannot be offset by altering model parameter values. The simulated hepatobiliary profiles from three of the reported models demonstrated substantial deviation from the observed data.

CONCLUSIONS

The present study highlights the necessity of using hepatobiliary data to verify and improve the predictive performance of hepatic disposition of rosuvastatin.

Genomic editing of metformin efficacy-associated genetic variants in SLC47A1 does not alter SLC47A1 expression

Several pharmacogenetics studies have identified an association between a greater metformin-dependent reduction in HbA1c levels and the minor A allele at rs2289669 in intron 10 of SLC47A1, encoding multidrug and toxin extrusion 1 (MATE1), a presumed metformin transporter. It is currently unknown if the rs2289669 locus is a cis-eQTL, which would validate its role as predictor of metformin efficacy. We looked at association between common genetic variants in the SLC47A1 gene region and HbA1c reduction after metformin treatment using locus-wise meta-analysis from the MetGen consortium. CRISPR-Cas9 was applied to perform allele editing of, or genomic deletion around, rs2289669 and of the closely linked rs8065082 in HepG2 cells. The genome-edited cells were evaluated for SLC47A1 expression and splicing. None of the common variants including rs2289669 showed significant association with metformin response. Genomic editing of either rs2289669 or rs8065082 did not alter SLC47A1 expression or splicing. Experimental and in silico analyses show that the rs2289669-containing haploblock does not appear to carry genetic variants that could explain its previously reported association with metformin efficacy.

Impact of fedratinib on the pharmacokinetics of transporter probe substrates using a cocktail approach

INTRODUCTION

Fedratinib, an oral, selective Janus kinase 2 inhibitor, has been shown to inhibit P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), organic anion transporting polypeptide (OATP) 1B1, OATP1B3, organic cation transporter (OCT) 2, and multidrug and toxin extrusion (MATE) 1 and MATE2-K in vitro. The objective of this study was to evaluate the influence of fedratinib on the pharmacokinetics (PK) of digoxin (P-gp substrate), rosuvastatin (OATP1B1/1B3 and BCRP substrate), and metformin (OCT2 and MATE1/2-K substrate).

METHODS

In this nonrandomized, fixed-sequence, open-label study, 24 healthy adult participants received single oral doses of digoxin 0.25 mg, rosuvastatin 10 mg, and metformin 1000 mg administered as a drug cocktail (day 1, period 1). After a 6-day washout, participants received oral fedratinib 600 mg 1 h before the cocktail on day 7 (period 2). An oral glucose tolerance test (OGTT) was performed to determine possible influences of fedratinib on the antihyperglycemic effect of metformin.

RESULTS

Plasma exposure to the three probe drugs was generally comparable in the presence or absence of fedratinib. Reduced metformin renal clearance by 36% and slightly higher plasma glucose levels after OGTT were observed in the presence of fedratinib. Single oral doses of the cocktail ± fedratinib were generally well tolerated.

CONCLUSIONS

These results suggest that fedratinib has minimal impact on the exposure of P-gp, BCRP, OATP1B1/1B3, OCT2, and MATE1/2-K substrates. Since renal clearance of metformin was decreased in the presence of fedratinib, caution should be exercised in using coadministered drugs that are renally excreted via OCT2 and MATEs.

TRIAL REGISTRATION

Clinicaltrials.gov NCT04231435 on January 18, 2020.

Transporter-mediated drug-drug interactions: advancement in models, analytical tools, and regulatory perspective

Drug-drug interactions mediated by transporters are a serious clinical concern hence a tremendous amount of work has been done on the characterization of the transporter-mediated proteins in humans and animals. The underlying mechanism for the transporter-mediated drug-drug interaction is the induction or inhibition of the transporter which is involved in the cellular uptake and efflux of drugs. Transporter of the brain, liver, kidney, and intestine are major determinants that alter the absorption, distribution, metabolism, excretion profile of drugs, and considerably influence the pharmacokinetic profile of drugs. As a consequence, transporter proteins may affect the therapeutic activity and safety of drugs. However, mounting evidence suggests that many drugs change the activity and/or expression of the transporter protein. Accordingly, evaluation of drug interaction during the drug development process is an integral part of risk assessment and regulatory requirements. Therefore, this review will highlight the clinical significance of the transporter, their role in disease, possible cause underlying the drug-drug interactions using analytical tools, and update on the regulatory requirement. The recent in-silico approaches which emphasize the advancement in the discovery of drug-drug interactions are also highlighted in this review. Besides, we discuss several endogenous biomarkers that have shown to act as substrates for many transporters, which could be potent determinants to find the drug-drug interactions mediated by transporters. Transporter-mediated drug-drug interactions are taken into consideration in the drug approval process therefore we also provided the extrapolated decision trees from in-vitro to in-vivo, which may trigger the follow-up to clinical studies.

Update on drug-drug interaction at organic cation transporters: mechanisms, clinical impact, and proposal for advanced in vitro testing

Introduction: Organic cation transporters collectively called OCTs belong to three gene families (SLC22A1 OCT1, SLC22A2 OCT2, SLC22A3 OCT3, SLC22A4 OCTN1, SLC22A5 OCTN2, SLC29A4 PMAT, SLC47A1 MATE1, and SLC47A1 MATE2-K). OCTs transport structurally diverse drugs with overlapping selectivity. Some OCTs were shown to be critically involved in pharmacokinetics and therapeutic efficacy of cationic drugs. Drug-drug interactions at individual OCTs were shown to result in clinical effects. Procedures for in vitro testing of drugs for interaction with OCT1, OCT2, MATE1, and MATE2-K have been recommended.Areas covered: An overview of functional properties, cation selectivity, location, and clinical impact of OCTs is provided. In addition, clinically relevant drug-drug interactions in OCTs are compiled. Because it was observed that the half maximal concentration of drugs to inhibit transport by OCTs (IC₅₀) is dependent on the transported cation and its concentration, an advanced protocol for in vitro testing of drugs for interaction with OCTs is proposed. In addition, it is suggested to include OCT3 and PMAT for in vitro testing.Expert opinion: Research on clinical roles of OCTs should be reinforced including more transporters and drugs. An improvement of the in vitro testing protocol considering recent data is imperative for the benefit of patients.

A Whole-Body Physiologically Based Pharmacokinetic Model Characterizing Interplay of OCTs and MATEs in Intestine, Liver and Kidney to Predict Drug-Drug Interactions of Metformin with Perpetrators

Transmembrane transport of metformin is highly controlled by transporters including organic cation transporters (OCTs), plasma membrane monoamine transporter (PMAT), and multidrug/toxin extrusions (MATEs). Hepatic OCT1, intestinal OCT3, renal OCT2 on tubule basolateral membrane, and MATE1/2-K on tubule apical membrane coordinately work to control metformin disposition. Drug–drug interactions (DDIs) of metformin occur when co-administrated with perpetrators via inhibiting OCTs or MATEs. We aimed to develop a whole-body physiologically based pharmacokinetic (PBPK) model characterizing interplay of OCTs and MATEs in the intestine, liver, and kidney to predict metformin DDIs with cimetidine, pyrimethamine, trimethoprim, ondansetron, rabeprazole, and verapamil. Simulations showed that co-administration of perpetrators increased plasma exposures to metformin, which were consistent with clinic observations. Sensitivity analysis demonstrated that contributions of the tested factors to metformin DDI with cimetidine are gastrointestinal transit rate > inhibition of renal OCT2 ≈ inhibition of renal MATEs > inhibition of intestinal OCT3 > intestinal pH > inhibition of hepatic OCT1. Individual contributions of transporters to metformin disposition are renal OCT2 ≈ renal MATEs > intestinal OCT3 > hepatic OCT1 > intestinal PMAT. In conclusion, DDIs of metformin with perpetrators are attributed to integrated effects of inhibitions of these transporters.

Impact of Direction of Transport on the Evaluation of Inhibition Potencies of Multidrug and Toxin Extrusion Protein 1 Inhibitors

Multidrug and toxin extrusion (MATE) transporters are expressed on the luminal membrane of renal proximal tubule cells and extrude their substrates into the luminal side of the tubules. Inhibition of MATE1 can reduce renal secretory clearance of its substrate drugs and lead to drug-drug interactions (DDIs). To address whether IC50 values of MATE1 inhibitors with regard to their extracellular concentrations are affected by the direction of MATE1-mediated transport, we established an efflux assay of 1-methyl-4-phenylpyridinium (MPP+) and metformin using the human embryonic kidney 293 model transiently expressing human MATE1. The efflux rate was defined by reduction of the cellular amount of MPP+ and metformin for 0.25 minutes shortly after the removal of extracellular MPP+ and metformin. Inhibition potencies of 12 inhibitors toward MATE1-mediated transport were determined in both uptake and efflux assays. When MPP+ was used as a substrate, 8 out of 12 inhibitors showed comparable IC50 values between assays (<4-fold). IC50 values from the efflux assays were higher for cimetidine (9.9-fold), trimethoprim (10-fold), famotidine (6.4-fold), and cephalexin (>3.8-fold). When metformin was used as a substrate, IC50 values of the tested inhibitors when evaluated using uptake and efflux assays were within 4-fold of each other, with the exception of cephalexin (>4.7-fold). IC50 values obtained from the uptake assay using metformin showed smaller IC50 values than those from the efflux assay. Therefore, the uptake assay is recommended to determine IC50 values for the DDI predictions. SIGNIFICANCE STATEMENT: In this study, a new method to evaluate IC50 values of extracellular added inhibitors utilizing an efflux assay was established. IC50 values were not largely different between uptake and efflux directions but were smaller for uptake. This study supports the rationale for a commonly accepted uptake assay with metformin as an in vitro probe substrate for multidrug and toxin extrusion 1-mediated drug-drug interaction risk assessment in drug development.

Increased Glomerular Hydrostatic Pressure is Associated with Tubular Creatinine Reabsorption in Healthy Subjects

<b><i>Background:</i></b> Cr is secreted by the proximal tubules and thus Cr clearance (<i>C</i>_cr) can overestimate inulin clearance (<i>C</i>_in). However, in some cases, <i>C</i>_cr can even underestimate <i>C</i>_in. This suggests that Cr could be reabsorbed in the tubuli. We examined the clinical parameters that are associated with tubular Cr reabsorption. <b><i>Methods:</i></b> In 80 kidney donor candidates (53.9 ± 13.2 years, 29 males), <i>C</i>_in and para-aminohippuric acid clearance were measured simultaneously. Intrarenal hemodynamic parameters were calculated by Gomez’s formulae. To quantify the secretory component of <i>C</i>_cr (SF_cr), it was calculated as follows: SF_cr = (<i>C</i>_cr − <i>C</i>_in)/<i>C</i>_cr. <b><i>Results:</i></b> Twenty-five subjects (31.3%) showed SF_cr values &#x3c;0. SF_cr that correlated significantly and negatively with efferent arteriolar resistance (<i>R</i>_e) and glomerular hydrostatic pressure (<i>P</i>_glo) (<i>R</i>_e: <i>r</i> = −0.30, <i>p</i> = 0.008; <i>P</i>_glo: <i>r</i> = −0.28, <i>p</i> = 0.025). In multiple regression analyses, <i>R</i>_e and <i>P</i>_glo were significantly and negatively associated with SF_cr after adjustment for other confounders. <b><i>Conclusions:</i></b> These findings suggest that tubular reabsorption of Cr can occur in some cases. Intrarenal glomerular hemodynamic burden may be related to tubular creatinine reabsorption, which possibly leads to lower <i>C</i>_cr values.

Clinical Aspects of Transporter-Mediated Drug-Drug Interactions

Drug transporters play an essential role in disposition and effects of multiple drugs. Plasma concentrations of the victim drug can be modified by drug-drug interactions occurring in enterocytes (e.g., P-glycoprotein), hepatocytes (e.g., organic anion-transporting polypeptide 1B1 (OATP1B1)), and/or renal proximal tubular cells (e.g., organic cation transporter 2 (OCT2)/multidrug and toxin extrusion 1 and 2-K (MATE1/MATE2-K)). In addition, transporter-mediated drug-drug interactions can cause altered local tissue concentrations and possibly altered effects/toxicity (e.g., in liver and kidneys). During drug development, there is now an intensive in vitro screening of new molecular entities as transporter substrates and inhibitors, followed if necessary by drug-drug interaction studies in healthy volunteers. Nevertheless, there are still unresolved issues, which will also be discussed in this review article (e.g., the clinical significance of transporter-mediated drug-drug interactions of particular relevance to the elderly who are prescribed multiple drugs, with additional impaired liver or kidney function, and the extent to which medication safety in real life could be improved by a reduction of those interactions).

Estimation of changes in serum creatinine and creatinine clearance caused by renal transporter inhibition in healthy subjects

Creatinine is excreted into urine by glomerular filtration and renal tubular secretion through drug transporters such as organic anion transporter 2 (OAT2), organic cation transporter 2 (OCT2), OCT3, multidrug and toxin extrusion protein 1 (MATE1), and MATE2-K. We aimed to investigate whether our method for estimating percentage changes in serum creatinine concentration (SCr) and creatinine clearance (CL_cre) from the baseline is applicable for studying renal transporter inhibitors. We tested 14 compounds (cimetidine, cobicistat, dolutegravir, dronedarone, DX-619, famotidine, INCB039110, nizatidine, ondansetron, pyrimethamine, rabeprazole, ranolazine, trimethoprim, and vandetanib), which were reported to cause reversible changes in SCr and/or CL_cre in healthy subjects excluding elderly. Percentage changes were estimated from the relative contributions of the forementioned transporters to CL_cre and competitive inhibition by these compounds at their maximum plasma unbound concentrations. For 7 and 9 out of these compounds, changes in SCr and/or CL_cre were estimated within 2- and 3-fold of observed values, respectively. Less than 10% changes in SCr and/or CL_cre caused by cobicistat, dolutegravir, and rabeprazole were reproduced as such by our method. These findings suggest that our method can be used to estimate changes in SCr and CL_cre caused by competitive inhibitions of renal drug transporters.

No Effect of Plazomicin on the Pharmacokinetics of Metformin in Healthy Subjects

Plazomicin is an aminoglycoside that was engineered to overcome aminoglycoside-modifying enzymes, which are the most common aminoglycoside resistance mechanism in Enterobacteriaceae. Because plazomicin is predominantly eliminated via renal pathways, an in vitro study was conducted to determine whether plazomicin inhibits the organic cation transporter 2 (OCT2) and the multidrug and toxin extrusion (MATE1 and MATE2-K) transporters, using metformin as a probe substrate. Plazomicin inhibited OCT2, MATE1, and MATE2-K transporters with half-maximal inhibition of the transporter values of 5120, 1300, and 338 µg/mL, respectively. To determine whether this in vitro inhibition translates in vivo, an open-label, randomized, 2-period, 2-treatment crossover study (NCT03270553) was carried out in healthy subjects (N = 16), who received a single oral dose of metformin 850 mg alone and in combination with a single intravenous infusion of plazomicin 15 mg/kg. Geometric least-squares mean ratios of the test treatment (combination) vs the reference treatment (metformin alone) and 90% confidence intervals were within the equivalence interval of 80% to 125% (peak plasma concentration, 104.5 [95.1-114.9]; area under the plasma concentration-time curve from time zero to time of last quantifiable concentration, 103.7 [93.5-115.0]; area under the plasma concentration-time curve from time zero to infinity, 104.0 [94.2-114.8]). The results demonstrate that there is no clinically significant drug-drug interaction resulting from coadministration of single doses of intravenous plazomicin 15 mg/kg and oral metformin 850 mg in healthy subjects. Coadministration of plazomicin and metformin was well tolerated in healthy subjects.

Comprehensive Evaluation of the Utility of 20 Endogenous Molecules as Biomarkers of OATP1B Inhibition Compared with Rosuvastatin and Coproporphyrin I

Endogenous biomarkers can be clinically relevant tools for the assessment of transporter function in vivo and corresponding drug-drug interactions (DDIs). The aim of this study was to perform systematic evaluation of plasma data obtained for 20 endogenous molecules in the same healthy subjects (n = 8-12) in the absence and presence of organic anion transporting polypeptide (OATP) inhibitor rifampicin (600 mg, single dose). The extent of rifampicin DDI magnitude [the ratio of the plasma concentration-time area under the curve (AUCR)], estimated fraction transported (fT), and baseline variability was compared across the biomarkers and relative to rosuvastatin and coproporphyrin I (CPI). Out of the 20 biomarkers investigated tetradecanedioate (TDA), hexadecanedioate (HDA), glycocholic acid, glycodeoxycholic acid (GDCA), taurodeoxycholic acid (TDCA), and coproporphyrin III (CPIII) showed the high AUCR (2.1-8.5) and fT (0.5-0.76) values, indicative of substantial OATP1B-mediated transport. A significant positive correlation was observed between the individual GDCA and TDCA AUCRs and the magnitude of rosuvastatin-rifampicin interaction. The CPI and CPIII AUCRs were significantly correlated, but no clear trend was established with the rosuvastatin AUCR. Moderate interindividual variability (15%-62%) in baseline exposure and AUCR was observed for TDA, HDA, and CPIII. In contrast, bile acids demonstrated high interindividual variability (69%-113%) and significant decreases in baseline plasma concentrations during the first 4 hours. This comprehensive analysis in the same individuals confirms that none of the biomarkers supersede CPI in the evaluation of OATP1B-mediated DDI risk. Monitoring of CPI and GDCA/TDCA may be beneficial for dual OATP1B/sodium-taurocholate cotransporting polypeptide inhibitors with consideration of challenges associated with large inter- and intraindividual variability observed for bile acids. Benefit of monitoring combined biomarkers (CPI, one bile acid and one fatty acid) needs to be confirmed with larger data sets and against multiple OATP1B clinical probes and perpetrators.

OCT3 promoter haplotype is associated with metformin pharmacokinetics in Koreans

Organic cation transporter 3 (OCT3) is expressed in various organs in humans and plays an important role in the transport of organic cations and drugs including metformin. In this study, we identified genetic variations of the OCT3 promoter and functionally characterized each variant by in vitro assays. Next, the association between the functional haplotype of the OCT3 promoter and pharmacokinetics of metformin was evaluated. In our study population, 7 variations and 2 major haplotypes were identified, of which H2 haplotype yielded a significantly higher luciferase activity than did the wild type. Two variants of H2, c.-1603G > A and c.-1547T > G, yielded significantly lower luciferase activities, whereas the luciferase activity of another variant, c.-29G > A, was significantly higher. Two transcription factors, Sp1 and USF1, were involved in the regulation of OCT3 transcription. Analysis of clinical data revealed that 25 subjects, either homozygous or heterozygous for H2, showed increased AUC_inf and C_max by 17.2% and 15.9%, respectively [P = 0.016 and 0.031, GMR (90% CI) = 1.17 (1.06–1.29) and 1.17 (1.04–1.31), respectively], compared to the 20 subjects in the control group. Our study suggests that an OCT3 promoter haplotype affects the pharmacokinetics of metformin in Koreans as well as the OCT3 transcription rate.

Metformin transporter pharmacogenomics: insights into drug disposition-where are we now?

INTRODUCTION

Metformin is recommended as first-line treatment for type 2 diabetes (T2D) by all major diabetes guidelines. With appropriate usage it is safe and effective overall, but its efficacy and tolerability show considerable variation between individuals. It is a substrate for several drug transporters and polymorphisms in these transporter genes have shown effects on metformin pharmacokinetics and pharmacodynamics. Areas covered: This article provides a review of the current status of the influence of transporter pharmacogenomics on metformin efficacy and tolerability. The transporter variants identified to have an important influence on the absorption, distribution, and elimination of metformin, particularly those in organic cation transporter 1 (OCT1, gene SLC22A1), are reviewed. Expert opinion: Candidate gene studies have shown that genetic variations in SLC22A1 and other drug transporters influence the pharmacokinetics, glycemic responses, and gastrointestinal intolerance to metformin, although results are somewhat discordant. Conversely, genome-wide association studies of metformin response have identified signals in the pharmacodynamic pathways rather than the transporters involved in metformin disposition. Currently, pharmacogenomic testing to predict metformin response and tolerability may not have a clinical role, but with additional data from larger studies and availability of safe and effective alternative antidiabetic agents, this is likely to change.

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.

Transporters in Drug Development: 2018 ITC Recommendations for Transporters of Emerging Clinical Importance

This white paper provides updated International Transporter Consortium (ITC) recommendations on transporters that are important in drug development following the 3^rd ITC workshop. New additions include prospective evaluation of organic cation transporter 1 (OCT1) and retrospective evaluation of organic anion transporting polypeptide (OATP)2B1 because of their important roles in drug absorption, disposition, and effects. For the first time, the ITC underscores the importance of transporters involved in drug-induced vitamin deficiency (THTR2) and those involved in the disposition of biomarkers of organ function (OAT2 and bile acid transporters).

ITC Commentary on Metformin Clinical Drug-Drug Interaction Study Design That Enables an Efficacy- and Safety-Based Dose Adjustment Decision

Metformin drug-drug interaction (DDI) studies are conducted during development of drugs that inhibit organic cation transporters and/or multidrug and toxin extrusion proteins (OCTs/MATEs). Monitoring solely changes in systemic exposure, the typical DDI study endpoint appears inadequate for metformin, which is metabolically stable, has poor passive membrane permeability, and undergoes transporter-mediated tissue distribution and clearance. Evaluation of renal clearance, antihyperglycemic effects, and potentially lactate as an exploratory safety marker, can support rational metformin dose adjustment. The proposed DDI study design aims to adequately inform metformin dosing during comedication.

Indinavir Alters the Pharmacokinetics of Lamivudine Partially via Inhibition of Multidrug and Toxin Extrusion Protein 1 (MATE1)

PURPOSE

Lamivudine, a characterized substrate for human multidrug and toxin extrusion protein 1 (hMATE1) in vitro, was commonly used with indinavir as a therapy against human immunodeficiency virus (HIV). We aimed to investigate whether mouse MATE1 is involved in the disposition of lamivudine in vivo, and whether there is any transporter-mediated interaction between indinavir and lamivudine.

METHODS

The role of MATE1 in the disposition of lamivudine was determined using Mate1 wild type (+/+) and knockout (-/-) mice. The inhibitory potencies of indinavir on lamivudine uptake mediated by OCT2 and MATE1 were determined in human embryonic kidney 293 (HEK 293) cells stably expressing these transporters. The role of MATE1 in the interaction between indinavir and lamivudine in vivo was determined using Mate1 (+/+) and Mate1 (-/-) mice.

RESULTS

The plasma concentrations and tissue accumulation of lamivudine were markedly elevated in Mate1 (-/-) mice as compared to those in Mate1 (+/+) mice. Indinavir significantly increased the pharmacokinetic exposure of lamivudine in mice; however, the effect by indinavir was significantly less pronounced in Mate1 (-/-) mice as compared to Mate1(+/+) mice.

CONCLUSION

MATE1 played an important role in lamivudine pharmacokinetics. Indinavir could cause drug-drug interaction with lamivudine in vivo via inhibition of MATE1 and additional mechanism.

Drug Interactions of Metformin Involving Drug Transporter Proteins

Metformin is a most widely used medication all around the world to treat Type 2 diabetes mellitus. It is also found to be effective against various conditions including, Prediabetes, Gestational diabetes mellitus (GDM), Polycystic Ovarian Syndrome (PCOS), Obesity, Cancer, etc. It is a cationic drug and it depends Organic Cation Transporters (OCTs) and Multidrug and Toxin Extruders (MATEs) mostly for its pharmacokinetics movement. The probability of drug interaction increases with the number of concomitant medications. This article focuses the drug interactions of metformin and most of them are linked to the inhibition of OCTs and MATEs leading to increased plasma metformin concentrations and subsequent elevation of risk of Metformin Associated Lactic Acidosis (MALA). By identifying the drugs inhibiting OCTs and MATEs, the healthcare professionals can predict the drug interactions of metformin.

Emerging Clinical Importance of Hepatic Organic Cation Transporter 1 (OCT1) in Drug Pharmacokinetics, Dynamics, Pharmacogenetic Variability, and Drug Interactions

Hepatic organic cation transporter 1 (OCT1) can be a determinant of drug clearance and distribution, which can impact drug exposure and response. OCT1 was shown recently to be the rate-determining step in the clearance of several drugs in humans, and thereby a mechanism of pharmacogenetic variability and drug-drug interactions (DDIs). OCT1 mediates metformin distribution to the liver (key biophase). As OCT1 modulation impacts metformin response, but not pharmacokinetics (PK), metformin DDI studies require pharmacodynamic endpoint(s) to inform rational metformin dose adjustment.

Beyond drug-drug interactions: effects of transporter inhibition on endobiotics, nutrients and toxins

INTRODUCTION

Membrane transport proteins play a central role in regulating the disposition of endobiotics, dietary nutrients and environmental toxins. The inhibition of transporters by drugs has potential physiologic consequences. The full extent of the effect of drugs on the function of transporters is poorly understood because only a small subset of the hundreds of transporters expressed in humans - primarily those mediating the rate-determining step in the elimination of specific drugs - are assessed during clinical development. Areas covered: We provide a comprehensive overview of literature reports implicating the inhibition of transporters as the mechanism for off-target effects of drugs. Expert opinion: Transporter inhibition, the mechanism of action of many marketed drugs, appears to play an underappreciated role in a number of side effects including vitamin deficiency, edema, dyslipidemia, cholestasis and gout. Cell systems more broadly expressing transporter networks and methods like unbiased metabolomics should be incorporated into the screening paradigm to expand our understanding of the impact of drugs on the physiologic function of transporters and to allow for these effects to be taken into account in drug discovery and clinical practice.

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.

Evaluation of transporters in drug development: Current status and contemporary issues

Transporters govern the access of molecules to cells or their exit from cells, thereby controlling the overall distribution of drugs to their intracellular site of action. Clinically relevant drug-drug interactions mediated by transporters are of increasing interest in drug development. Drug transporters, acting alone or in concert with drug metabolizing enzymes, can play an important role in modulating drug absorption, distribution, metabolism and excretion, thus affecting the pharmacokinetics and/or pharmacodynamics of a drug. The drug interaction guidance documents from regulatory agencies include various decision criteria that may be used to predict the need for in vivo assessment of transporter-mediated drug-drug interactions. Regulatory science research continues to assess the prediction performances of various criteria as well as to examine the strength and limitations of each prediction criterion to foster discussions related to harmonized decision criteria that may be used to facilitate global drug development. This review discusses the role of transporters in drug development with a focus on methodologies in assessing transporter-mediated drug-drug interactions, challenges in both in vitro and in vivo assessments of transporters, and emerging transporter research areas including biomarkers, assessment of tissue concentrations, and effect of diseases on transporters.

The Liver Circadian Clock Modulates Biochemical and Physiological Responses to Metformin

Metformin is widely used in the treatment of type 2 diabetes to lower blood glucose. Although metformin is a relatively safe and effective drug, its clinical efficacy is variable and under certain circumstances it may contribute to life-threatening lactic acidosis. Thus, additional understanding of metformin pharmacokinetics and pharmacodynamics could provide important information regarding therapeutic use of this widely prescribed drug. Here we report a significant effect of time of day on acute blood glucose reduction in response to metformin administration and on blood lactate levels in healthy mice. Furthermore, we demonstrate that while metformin transport into hepatocytes is unaltered by time of day, the kinetics of metformin-induced activation of AMP-activated protein kinase (AMPK) in the liver are remarkably altered with circadian time. Liver-specific ablation of Bmal1 expression alters metformin induction of AMPK and blood glucose response but does not completely abolish time of day differences. Together, these data demonstrate that circadian rhythms affect the biological responses to metformin in a complex manner.

Transporters Involved in Metformin Pharmacokinetics and Treatment Response

Metformin, widely used as first-line treatment for type 2 diabetes, exists primarily as a hydrophilic cation at physiological pHs. As such, membrane transporters play a substantial role in its absorption, tissues distribution, and renal elimination. Multiple organic cation transporters are determinants of the pharmacokinetics of metformin, and many of them are important in its pharmacological action, as mediators of metformin entry into target tissues. Furthermore, a recent genome-wide association study in a large multi-ethnic population implicated polymorphisms in SLC2A2, encoding the glucose transporter, GLUT2, as important determinants of response to metformin. Here, we describe the key transporters associated with metformin pharmacokinetics and response.

Physiologically Based Pharmacokinetic Modeling of Drug Transporters to Facilitate Individualized Dose Prediction

Physiologically based pharmacokinetic modeling is a commonly used strategy in the drug development and regulatory submissions. This commentary provides a critical overview of the current status of physiologically based pharmacokinetic methodologies to predict transporter-mediated pharmacokinetics, in addition to the impact of disease and genetics with respect to local and systemic concentration.

Metabolomic and Genome-wide Association Studies Reveal Potential Endogenous Biomarkers for OATP1B1

Transporter-mediated drug-drug interactions (DDIs) are a major cause of drug toxicities. Using published genome-wide association studies (GWAS) of the human metabolome, we identified 20 metabolites associated with genetic variants in organic anion transporter, OATP1B1 (P < 5 × 10-8 ). Of these, 12 metabolites were significantly higher in plasma samples from volunteers dosed with the OATP1B1 inhibitor, cyclosporine (CSA) vs. placebo (q-value < 0.2). Conjugated bile acids and fatty acid dicarboxylates were among the metabolites discovered using both GWAS and CSA administration. In vitro studies confirmed tetradecanedioate (TDA) and hexadecanedioate (HDA) were novel substrates of OATP1B1 as well as OAT1 and OAT3. This study highlights the use of multiple datasets for the discovery of endogenous metabolites that represent potential in vivo biomarkers for transporter-mediated DDIs. Future studies are needed to determine whether these metabolites can serve as qualified biomarkers for organic anion transporters. Quantitative relationships between metabolite levels and modulation of transporters should be established.