LAVR-289, a broad-spectrum antiviral, protects immunosuppressed Syrian hamsters against lethal adenovirus challenge

LAVR-289, a newly described acyclic nucleoside phosphonate prodrug, has previously shown in vitro efficacy against adenovirus (HAdV) species B, C, D, E, and F with EC₅₀ values of 100 nM to 1.2 μM. The compound was efficacious prophylactically against systemic HAdV infection in immunosuppressed Syrian hamsters. Here, we present further, more detailed data on its efficacy against HAdV. We tested the two enantiomers at chiral phosphorus center (Sp and Rp) of LAVR-289 and found that both stereoisomers were equally efficacious against HAdV-C5 and -C6 infecting human foreskin fibroblast primary cells in vitro, indicating that the racemic mixture of the compound could be used as a drug. Following these favorable in vitro results, the antiviral activity of racemic LAVR-289 was evaluated in the immunosuppressed Syrian hamster model, in which the hamsters were challenged with the intravenous LD₉₀ dose of HAdV-C6. Prophylactic administration of LAVR-289 completely prevented mortality at doses of 24 mg/kg p.o. q.d. or higher. At the efficacious dose levels, it significantly inhibited virus replication in the liver and mitigated HAdV-C6-induced liver damage. As prophylactic administration may not be advisable in a clinical setting, we delayed the administration of LAVR-289 and showed that the compound prevented mortality and significantly reduced morbidity even when the drug was withheld for 3 days post challenge. Based on these results, we believe that these data demonstrate in vitro and in vivo potency of LAVR-289 against HAdVs and support its continued development.