A crucial step in the arenavirus life cycle is the biosynthesis of the viral envelope
glycoprotein (GP) responsible for virus attachment and entry. Processing of the GP precursor (GPC) by the cellular
proprotein convertase site 1
protease (S1P), also known as
subtilisin-kexin-
isozyme 1 (SKI-1), is crucial for cell-to-cell propagation of
infection and production of infectious virus. Here, we sought to evaluate arenavirus GPC processing by S1P as a target for
antiviral therapy using a recently developed
peptide-based S1P inhibitor, decanoyl (dec)-RRLL-chloromethylketone (CMK), and the prototypic arenavirus lymphocytic choriomeningitis virus (LCMV). To control for off-target effects of dec-RRLL-CMK, we employed arenavirus reverse genetics to introduce a
furin recognition site into the GPC of LCMV. The rescued mutant virus grew to normal titers, and the processing of its GPC critically depended on cellular
furin, but not S1P. Treatment with the S1P inhibitor dec-RRLL-CMK resulted in specific blocking of viral spread and virus production of LCMV. Combination of the
protease inhibitor with
ribavirin, currently used clinically for treatment of human
arenavirus infections, resulted in additive
drug effects. In cells deficient in S1P, the
furin-dependent LCMV variant established
persistent infection, whereas wild-type LCMV underwent extinction without the emergence of S1P-independent escape variants. Together, the potent
antiviral activity of an inhibitor of S1P-dependent GPC cleavage, the additive
antiviral effect with
ribavirin, and the low probability of emergence of S1P-independent viral escape variants make S1P-mediated GPC processing by
peptide-derived inhibitors a promising strategy for the development of novel antiarenaviral drugs.