Potentiating SLC transporter activity: Emerging drug discovery opportunities

Maintaining the integrity of cellular membranes is critical to protecting metabolic activities and genetic information from the environment. Regulation of transport across membranes of essential chemicals, including water, nutrients, hormones and many drugs, is therefore key to cellular homeostasis and physiological processes. The two main transporter superfamilies are ATP-binding cassette (ABC) transporters that primarily function as efflux transporters, and the solute carrier (SLC) transporters. SLC transporters encompass 52 gene families with almost 400 different human transporter genes. Although long under-explored, SLC transporters are an emerging drug target class and the molecular target of several approved inhibitor drugs, such as selective serotonin reuptake inhibitors (SSRIs) for depression and sodium/glucose co-transporter (SGLT2) inhibitors for diabetes. Interestingly though, although loss-of-function mutations in numerous human SLC transporters are linked to Mendelian diseases, few reports of SLC transporter activators have appeared, and only inhibitors have been advanced to clinical studies. In this commentary, we discuss several strategies for potentiating SLC transporter function, from direct acting potentiators to modulators of transcription, translation or trafficking. We review the progress made in recent years toward the understanding of the structural and molecular basis of SLC transporter function and the pathways and mechanisms that regulate SLC expression, and describe the opportunities these new insights present for discovery of SLC transporter potentiators. Finally, we highlight the challenges associated with the various approaches and provide some thoughts on future directions that might facilitate the search for SLC potentiators with therapeutic potential.