Summary COVID-19 (coronavirus disease 2019) is a contagious upper respiratory disease caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) infection, which features high morbidity and is rapidly spreading worldwide. The need to develop therapeutics against COVID-19 is urgent, and one route to shorten the time to an effective medicine is repurposing existing antiviral drugs or utilizing those in the pipeline. Three therapeutics that have shown initial promise in either pre-clinical or clinical settings are nucleoside-analog antivirals remdesivir, NHC (beta-D-N4-hydroxycytidine), and galidesivir. Currently, NHC and galidesivir are in clinical trials and remdesivir is approved for emergency use in U.S. The commonality between these drugs is that they are nucleoside analogs that target the SARS-CoV-2 RNA-dependent RNA polymerase. Because nucleosides are hydrophilic, specialized membrane transport proteins are required for their cellular uptake. In humans, two protein families mediate the selective membrane permeation of nucleosides: concentrative nucleoside transporters (CNTs) and equilibrative nucleoside transporters (ENTs). It is well established these nucleoside transporters control drug efficacies of many nucleoside-analog antiviral and anticancer therapeutics in a clinically relevant manner. Therefore, we reason that the cellular uptake of the aforementioned candidate COVID-19 therapeutics by human nucleoside transporters would prove critical to their antiviral efficacies. We aim to study the role of these transporters in the cellular uptake of these nucleoside antivirals by performing antiviral efficacy assays, structural studies of drug-transporter interactions, and in vitro transport assays. Structural and mechanistic studies of the interactions between potential COVID-19 antiviral drugs and human cellular transport proteins would uncover the molecular basis of antiviral drug cellular transport in humans. Such information would pave the way for the rational design of therapeutics with improved efficacies via enhanced drug disposition properties, and for personalized anti-COVID-19 treatments via drug-transporter pharmacogenomics.

Relevance The recent emergence of COVID-19 (novel coronavirus disease 2019) has proven catastrophic to global public health and has greatly disrupted the global economy. Nucleoside-analog RNA-dependent polymerase inhibitors that exhibit broad-spectrum antiviral properties have shown great promise as COVID-19 therapeutics, with some antivirals proving efficacious in reducing COVID-19 symptoms and shortening hospitalization time in severe disease. Our proposal is focused on characterizing nucleoside-analog antiviral drug interaction with human nucleoside membrane transport proteins, which will significantly inform the rational improvement of drug bioavailability and cell permeability, thus significantly improving their pharmacological properties.