Severe mammarenaviral disease in guinea pigs effectively treated by an orally bioavailable fusion inhibitor, alone or in combination with favipiravir.

Infections by pathogenic New World mammarenaviruses (NWM)s, including Junín virus (JUNV), can result in a severe life-threatening viral hemorrhagic fever syndrome. In the absence of FDA-licensed vaccines or antivirals, these viruses are considered high priority pathogens. The mammarenavirus envelope glycoprotein complex (GPC) mediates pH-dependent fusion between viral and cellular membranes, which is essential to viral entry and may be vulnerable to small-molecule inhibitors that disrupt this process. ARN-75039 is a potent fusion inhibitor of a broad spectrum of pseudotyped and native mammarenaviruses in cell culture and Tacaribe virus infection in mice. In the present study, we evaluated ARN-75039 against pathogenic JUNV in the rigorous guinea pig infection model. The compound was well-tolerated and had favorable pharmacokinetics supporting once-per-day oral dosing in guinea pigs. Importantly, significant protection against JUNV challenge was observed even when ARN-75039 was withheld until 6 days after the viral challenge when clinical signs of disease are starting to develop. We also show that ARN-75039 combination treatment with favipiravir, a viral polymerase inhibitor, results in synergistic activity in vitro and improves survival outcomes in JUNV-challenged guinea pigs. Our findings support the continued development of ARN-75039 as an attractive therapeutic candidate for treating mammarenaviral hemorrhagic fevers, including those associated with NWM infection.

Potent inhibition of arenavirus infection by a novel fusion inhibitor.

Several arenaviruses, including Lassa and Lujo viruses in Africa and five New World arenavirus (NWA) species in the Americas, cause life-threatening viral hemorrhagic fevers. In the absence of licensed antiviral therapies, these viruses pose a significant public health risk. The envelope glycoprotein complex (GPC) mediates arenavirus entry through a pH-dependent fusion of the viral and host endosomal membranes. It thus is recognized as a viable target for small-molecule fusion inhibitors. Here, we report on the antiviral activity and pre-clinical development of the novel broad-spectrum arenavirus fusion inhibitors, ARN-75039 and ARN-75041. In Tacaribe virus (TCRV) pseudotyped and native virus assays, the ARN compounds were active in the low to sub-nanomolar range with selectivity indices exceeding 1000. Pharmacokinetic analysis of the orally administered compounds revealed an extended half-life in mice supporting once-daily dosing, and the compounds were well tolerated at the highest tested dose of 100 mg/kg. In a proof-of-concept prophylactic efficacy study, doses of 10 and 35 mg/kg of either compound dramatically improved survival outcome and potently inhibited TCRV replication in serum and various tissues. Additionally, in contrast to surviving mice that received ribavirin or placebo, animals treated with ARN-75039 or ARN-75041 were cured of TCRV infection. In a follow-up study with ARN-75039, impressive therapeutic efficacy was demonstrated under conditions where treatment was withheld until after the onset of disease. Taken together, the data strongly support the continued development of ARN-75039 as a candidate therapeutic for the treatment of severe arenaviral diseases.