Bemnifosbuvir and ruzasvir in combination exhibit potent synergistic antiviral activity in vitro while maintaining a favorable nonclinical safety profile in vivo.

Bemnifosbuvir (BEM), the orally available hemisulfate salt of the double prodrug of a guanosine nucleotide analog, is a potent, selective, and pan-genotypic inhibitor of HCV nonstructural protein 5B, an RNA-dependent RNA polymerase necessary for viral replication. Similarly, ruzasvir (RZR) is an orally available, highly potent, selective, and pan-genotypic inhibitor of HCV nonstructural protein 5A, an essential component of the viral replication complex. The antiviral effects of the combination of these two complementary direct-acting antivirals were determined in HCV GT1b Huh-7 replicon cells. Two independent in vitro evaluations suggested that BEM and RZR act synergistically to inhibit HCV replication without accompanying cytotoxicity. Additionally, the toxicity and toxicokinetic properties of BEM and RZR administered individually or in combination were investigated in rats given daily oral doses at 500 mg/kg of each drug for 13 weeks, with an interim analysis at 4 weeks. All doses were well tolerated with no test article-related adverse effects identified in either the separate or combined dose groups. Moreover, toxicokinetic analyses conducted on dose days 1, 28 and 84 indicated minimal pharmacokinetic interactions between the two drugs in rats, with AUC values for AT-511 (free base form of BEM), its major circulating metabolites, and RZR being similar, regardless of separate or co-administration.