Comparative Evaluation of Dehydroepiandrosterone Sulfate Potential to Predict Hepatic Organic Anion Transporting Polypeptide Transporter-Based Drug-Drug Interactions

Contribution of Japanese scientists to drug metabolism and disposition

Japanese researchers have played a pivotal role in advancing the field of drug metabolism and disposition, as demonstrated by their substantial contributions to the journal Drug Metabolism and Disposition (DMD) over the past 5 decades. This review highlights the historical and ongoing impact of Japanese scientists on DMD, celebrating their achievements in elucidating drug metabolism, membrane transport, pharmacokinetics, and toxicology. From the discovery of cytochrome P450 by Tsuneo Omura and Ryo Sato in 1962 to subsequent advances in drug transport research, Japan has maintained a leading position in the field. A geographical analysis of DMD publications reveals a notable increase in contributions from Japan during the 1980s, ranking second globally and maintaining this position through the 2000s. However, recent years have seen a slight decline in output, likely influenced by the COVID-19 pandemic and increased online journals as well as structural changes within academia and industry. Importantly, this trend is not unique to Japan. To sustain excellence and innovation in this field, it is crucial to strengthen funding for absorption, distribution, metabolism, excretion, and toxicity research and promote collaborations between academia, industry, and regulatory agencies. By prioritizing the translation of fundamental discoveries into drug development and clinical applications, scientists in this area can further advance global efforts toward achieving optimal drug efficacy and safety. This review underscores the enduring contributions of Japanese researchers to DMD and calls for renewed efforts to drive innovation and progress in this vital area of science. SIGNIFICANCE STATEMENT: Over the past 5 decades, Japanese scientists have made significant contributions to Drug Metabolism and Disposition through groundbreaking discoveries and advancements in the study of drug-metabolizing enzymes, transporters, pharmacokinetics analysis, and related areas. These contributions continue to shape the field, offering a foundation for future innovation in this area. We hope that the next generation of Japanese scientists will further solidify their global leadership in this area to advance drug development and proper pharmacotherapy.

Neurosteroid Transport in the Brain: Role of ABC and SLC Transporters

Neurosteroids, comprising pregnane, androstane, and sulfated steroids can alter neuronal excitability through interaction with ligand-gated ion channels and other receptors and have therefore a therapeutic potential in several brain disorders. They can be formed in brain cells or are synthesized by an endocrine gland and reach the brain by penetrating the blood–brain barrier (BBB). Especially sulfated steroids such as pregnenolone sulfate (PregS) and dehydroepiandrosterone sulfate (DHEAS) depend on transporter proteins to cross membranes. In this review, we discuss the involvement of ATP-binding cassette (ABC)- and solute carrier (SLC)-type membrane proteins in the transport of these compounds at the BBB and in the choroid plexus (CP), but also in the secretion from neurons and glial cells. Among the ABC transporters, especially BCRP (ABCG2) and several MRP/ABCC subfamily members (MRP1, MRP4, MRP8) are expressed in the brain and known to efflux conjugated steroids. Furthermore, several SLC transporters have been shown to mediate cellular uptake of steroid sulfates. These include members of the OATP/SLCO subfamily, namely OATP1A2 and OATP2B1, as well as OAT3 (SLC22A3), which have been reported to be expressed at the BBB, in the CP and in part in neurons. Furthermore, a role of the organic solute transporter OSTα-OSTβ (SLC51A/B) in brain DHEAS/PregS homeostasis has been proposed. This transporter was reported to be localized especially in steroidogenic cells of the cerebellum and hippocampus. To date, the impact of transporters on neurosteroid homeostasis is still poorly understood. Further insights are desirable also with regard to the therapeutic potential of these compounds.

Biomarkers for In Vivo Assessment of Transporter Function

Drug-drug interactions are a major concern not only during clinical practice, but also in drug development. Due to limitations of in vitro-in vivo predictions of transporter-mediated drug-drug interactions, multiple clinical Phase I drug-drug interaction studies may become necessary for a new molecular entity to assess potential drug interaction liabilities. This is a resource-intensive process and exposes study participants, who frequently are healthy volunteers without benefit from study treatment, to the potential risks of a new drug in development. Therefore, there is currently a major interest in new approaches for better prediction of transporter-mediated drug-drug interactions. In particular, researchers in the field attempt to identify endogenous compounds as biomarkers for transporter function, such as hexadecanedioate, tetradecanedioate, coproporphyrins I and III, or glycochenodeoxycholate sulfate for hepatic uptake via organic anion transporting polypeptide 1B or N1-methylnicotinamide for multidrug and toxin extrusion protein-mediated renal secretion. We summarize in this review the currently proposed biomarkers and potential limitations of the substances identified to date. Moreover, we suggest criteria based on current experiences, which may be used to assess the suitability of a biomarker for transporter function. Finally, further alternatives and supplemental approaches to classic drug-drug interaction studies are discussed.