Drug transporters in drug disposition - the year 2022 in review

On behalf of all the authors, I am pleased to share our third annual review on drug transporter science with an emphasis on articles published and deemed influential in signifying drug transporters' role in drug disposition in the year 2022. As the drug transporter field is rapidly evolving several key findings were noted including promising endogenous biomarkers, rhythmic activity, IVIVE approaches in transporter-mediated clearance, new modality interaction, and transporter effect on gut microbiome. As identified previously (Chothe et Cal. 2021, 2022) the goal of this review is to highlight key findings without a comprehensive overview of each article and to this end, each coauthor independently selected 1-3 peer-reviewed articles published or available online in the year 2022 (Table 1). Each article is summarized in synopsis and commentary with unbiased viewpoints by each coauthor. We strongly encourage readers to consult original articles for specifics of the study. Finally, I would like to thank all coauthors for their continued support in writing this annual review on drug transporters and invite anyone interested in contributing to future versions of this review.

Novel Insights in Drug Transporter Sciences: the Year 2021 in Review

On behalf of the team I am pleased to present the second annual 'novel insights into drug transporter sciences review' focused on peer-reviewed articles that were published in the year 2021. In compiling the articles for inclusion, preprints available in 2021 but officially published in 2022 were considered to be in scope. To support this review the contributing authors independently selected one or two articles that were thought to be impactful and of interest to the broader research community. A similar approach as published last year was adopted whereby key observations, methods and analysis of each paper is concisely summarized in the synopsis followed by a commentary highlighting the impact of the paper in understanding of drug transporters' role in drug disposition.As the goal of this review is not to provide a comprehensive overview of each paper but rather highlight important findings that are well supported by the data, the reader is encouraged to consult the original articles for additional information. Further, and keeping in line with the goals of this review, it should be noted that all authors actively contributed by writing synopsis and commentary for individual papers and no attempt was made to standardize language or writing styles. In this way, the review article is reflective of not only the diversity of the articles but also that of the contributors. I extend my thanks to the authors for their continued support and also welcome Diane Ramsden and Pallabi Mitra as contributing authors for this issue.

Recent Advances in Drug Transporter Sciences: Highlights From the Year 2020

Drug Metabolism Reviews has an impressive track record of providing scientific reviews in the area of xenobiotic biotransformation over 47 years. It has consistently proved to be resourceful to many scientists from pharmaceutical industry, academia, regulatory agencies working in diverse areas including enzymology, pharmacology, pharmacokinetics and toxicology. Over the last 5 years Drug metabolism Reviews has annually published an industry commentary aimed to highlight novel insights and approaches that have made significant impacts on the field of biotransformation (led by Cyrus Khojasteh). We hope to continue this tradition by providing an overview of advances made in the field of drug transporters during 2020. The field of drug transporters is rapidly evolving as they play an essential role in drug absorption, distribution, clearance and elimination. In this review we have selected outstanding drug transporter articles that have significantly contributed to moving forward the field of transporter science with respect to translation and improved understanding of diverse aspects including uptake clearance, clinical biomarkers, induction, proteomics, emerging transporters and tissue targeting.The theme of this review consists of synopsis that summarizes each article followed by our commentary. The objective of this work is not to provide a comprehensive review but rather exemplify novel insights and state-of-the-art highlights of recent research that have advanced our understanding of drug transporters in drug disposition. We are hopeful that this effort will prove useful to the scientific community and as such request feedback, and further extend an invitation to anyone interested in contributing to future reviews.

Cyclic Penta- and Hexaleucine Peptides without N-Methylation Are Orally Absorbed

Development of peptide-based drugs has been severely limited by lack of oral bioavailability with less than a handful of peptides being truly orally bioavailable, mainly cyclic peptides with N-methyl amino acids and few hydrogen bond donors. Here we report that cyclic penta- and hexa-leucine peptides, with no N-methylation and five or six amide NH protons, exhibit some degree of oral bioavailability (4-17%) approaching that of the heavily N-methylated drug cyclosporine (22%) under the same conditions. These simple cyclic peptides demonstrate that oral bioavailability is achievable for peptides that fall outside of rule-of-five guidelines without the need for N-methylation or modified amino acids.

Improving on nature: making a cyclic heptapeptide orally bioavailable

The use of peptides in medicine is limited by low membrane permeability, metabolic instability, high clearance, and negligible oral bioavailability. The prediction of oral bioavailability of drugs relies on physicochemical properties that favor passive permeability and oxidative metabolic stability, but these may not be useful for peptides. Here we investigate effects of heterocyclic constraints, intramolecular hydrogen bonds, and side chains on the oral bioavailability of cyclic heptapeptides. NMR-derived structures, amide H-D exchange rates, and temperature-dependent chemical shifts showed that the combination of rigidification, stronger hydrogen bonds, and solvent shielding by branched side chains enhances the oral bioavailability of cyclic heptapeptides in rats without the need for N-methylation.

Mechanism-based pharmacokinetic modeling to evaluate transporter-enzyme interplay in drug interactions and pharmacogenetics of glyburide

The purpose of this study is to characterize the involvement of hepato-biliary transport and cytochrome-P450 (CYP)-mediated metabolism in the disposition of glyburide and predict its pharmacokinetic variability due to drug interactions and genetic variations. Comprehensive in vitro studies suggested that glyburide is a highly permeable drug with substrate affinity to multiple efflux pumps and to organic anion transporting polypeptide (OATP)1B1 and OATP2B1. Active hepatic uptake was found to be significantly higher than the passive uptake clearance (15.8 versus 5.3 μL/min/10(6)-hepatocytes), using the sandwich-cultured hepatocyte model. In vitro, glyburide is metabolized (intrinsic clearance, 52.9 μL/min/mg-microsomal protein) by CYP3A4, CYP2C9, and CYP2C8 with fraction metabolism of 0.53, 0.36, and 0.11, respectively. Using these in vitro data, physiologically based pharmacokinetic models, assuming rapid-equilibrium between blood and liver compartments or permeability-limited hepatic disposition, were built to describe pharmacokinetics and evaluate drug interactions. Permeability-limited model successfully predicted glyburide interactions with rifampicin and other perpetrator drugs. Conversely, model assuming rapid-equilibrium mispredicted glyburide interactions, overall, suggesting hepatic uptake as the primary rate-determining process in the systemic clearance of glyburide. Further modeling and simulations indicated that the impairment of CYP2C9 function has a minimal effect on the systemic exposure, implying discrepancy in the contribution of CYP2C9 to glyburide clearance.

High specificity in response of the sodium-dependent multivitamin transporter to derivatives of pantothenic acid

Essential nutrients are attractive targets for the transport of biologically active agents across cell membranes, since many are substrates for active cellular importation pathways. The sodium-dependent multivitamin transporter (SMVT) is among the best characterized of these, and biotin derivatives have been its most popular targets. We have surveyed 45 derivatives of pantothenic acid, another substrate of SMVT, long known as a competitive inhibitor of biotin transport. Variations of the β-alanyl fragment of pantothenate were uniformly rejected by the transporter, including derivatives with very similar steric and acidic characteristics to the natural substrate. The secondary hydroxyl of the 2,2-dimethyl-1,3-propanediol (pantoyl) fragment was the only position at which potential linkers could be attached while retaining activity as an inhibitor of biotin uptake and a substrate for sodium-dependent transport. However, triazole conjugates to several drug-like cargo motifs were not accepted as substrates by human SMVT in cell culture. Two compounds were observed which did not inhibit biotin uptake but were themselves transported in a sodium-dependent fashion, suggesting more complex behavior than expected. These studies represent the most extensive examination to date of pantothenate as an anchor for SMVT-mediated drug delivery, showing that this route requires further investigation before being judged promising.

pH-Dependent solubility and permeability criteria for provisional biopharmaceutics classification (BCS and BDDCS) in early drug discovery

The Biopharmaceutics Classification System (BCS) is a scientific framework that provides a basis for predicting the oral absorption of drugs. These concepts have been extended in the Biopharmaceutics Drug Disposition Classification System (BDDCS) to explain the potential mechanism of drug clearance and understand the effects of uptake and efflux transporters on absorption, distribution, metabolism, and elimination. The objective of present work is to establish criteria for provisional biopharmaceutics classification using pH-dependent passive permeability and aqueous solubility data generated from high throughput screening methodologies in drug discovery settings. The apparent permeability across monolayers of clonal cell line of Madin-Darby canine kidney cells, selected for low endogenous efflux transporter expression, was measured for a set of 105 drugs, with known BCS and BDDCS class. The permeability at apical pH 6.5 for acidic drugs and at pH 7.4 for nonacidic drugs showed a good correlation with the fraction absorbed in human (Fa). Receiver operating characteristic (ROC) curve analysis was utilized to define the permeability class boundary. At permeability ≥ 5 × 10(-6) cm/s, the accuracy of predicting Fa of ≥ 0.90 was 87%. Also, this cutoff showed more than 80% sensitivity and specificity in predicting the literature permeability classes (BCS), and the metabolism classes (BDDCS). The equilibrium solubility of a subset of 49 drugs was measured in pH 1.2 medium, pH 6.5 phosphate buffer, and in FaSSIF medium (pH 6.5). Although dose was not considered, good concordance of the measured solubility with BCS and BDDCS solubility class was achieved, when solubility at pH 1.2 was used for acidic compounds and FaSSIF solubility was used for basic, neutral, and zwitterionic compounds. Using a cutoff of 200 μg/mL, the data set suggested a 93% sensitivity and 86% specificity in predicting both the BCS and BDDCS solubility classes. In conclusion, this study identified pH-dependent permeability and solubility criteria that can be used to assign provisional biopharmaceutics class at early stage of the drug discovery process. Additionally, such a classification system will enable discovery scientists to assess the potential limiting factors to oral absorption, as well as help predict the drug disposition mechanisms and potential drug-drug interactions.

Optimizing PK properties of cyclic peptides: the effect of side chain substitutions on permeability and clearance()

A series of cyclic peptides were designed and prepared to investigate the physicochemical properties that affect oral bioavailabilty of this chemotype in rats. In particular, the ionization state of the peptide was examined by the incorporation of naturally occurring amino acid residues that are charged in differing regions of the gut. In addition, data was generated in a variety of in vitro assays and the usefulness of this data in predicting the subsequent oral bioavailability observed in the rat is discussed.

pH-sensitive interaction of HMG-CoA reductase inhibitors (statins) with organic anion transporting polypeptide 2B1

The human organic anion transporting polypeptide 2B1 (OATP2B1, SLCO2B1) is ubiquitously expressed and may play an important role in the disposition of xenobiotics. The present study aimed to examine the role of OATP2B1 in the intestinal absorption and tissue uptake of 3-hydroxy-3-methylglutaryl-Coenzyme A (HMG-CoA) reductase inhibitors (statins). We first investigated the functional affinity of statins to the transporter as a function of extracellular pH, using OATP2B1-transfeced HEK293 cells. The results indicate that OATP2B1-mediated transport is significant for rosuvastatin, fluvastatin and atorvastatin, at neutral pH. However, OATP2B1 showed broader substrate specificity as well as enhanced transporter activity at acidic pH. Furthermore, uptake at acidic pH was diminished in the presence of proton ionophore, suggesting proton gradient as the driving force for OATP2B1 activity. Notably, passive transport rates are predominant or comparable to active transport rates for statins, except for rosuvastatin and fluvastatin. Second, we studied the effect of OATP modulators on statin uptake. At pH 6.0, OATP2B1-mediated transport of atorvastatin and cerivastatin was not inhibitable, while rosuvastatin transport was inhibited by E-3-S, rifamycin SV and cyclosporine with IC(50) values of 19.7 ± 3.3 μM, 0.53 ± 0.2 μM and 2.2 ± 0.4 μM, respectively. Rifamycin SV inhibited OATP2B1-mediated transport of E-3-S and rosuvastatin with similar IC(50) values at pH 6.0 and 7.4, suggesting that the inhibitor affinity is not pH-dependent. Finally, we noted that OATP2B1-mediated transport of E-3-S, but not rosuvastatin, is pH sensitive in intestinal epithelial (Caco-2) cells. However, uptake of E-3-S and rosuvastatin by Caco-2 cells was diminished in the presence of proton ionophore. The present results indicate that OATP2B1 may be involved in the tissue uptake of rosuvastatin and fluvastatin, while OATP2B1 may play a significant role in the intestinal absorption of several statins due to their transporter affinity at acidic pH.