ProTides for Antiviral Activity Beyond Liver Cells

Prodrugs of nucleotides with aminoacidyl esters as one of the two masking groups of the phosphate are successful molecular constructs for making nucleosidic antivirals bioavailable. Still, some of those '"ProTide" prodrugs have a strong bias to exert their antiviral activity in liver cells, with little activity in nonhepatic tissues. Here, we show that the alcohol residue of the alaninyl esters of two established antivirals has a strong effect on the activity against RNA viruses with pandemic potential. This was first shown for remdesivir (REM), for which a cycloheptyl residue gave 50% inhibition against four different viruses at ≤110 nM concentration. With the cyclobutyl derivative of bemnifosbuvir (BEM), nanomolar EC₅₀ values against dengue virus were measured in a range of cell lines, including cells with much lower metabolic activity than hepatocytes, without significant cytotoxicity up to 50 µM. These findings show how easily activity can be improved and broadened across different tissues through seemingly minor changes in ProTide structure. Our results may instruct the design of new antivirals with broad activity against RNA viruses to increase pandemic preparedness.