Efficacy of the 4-Florouridine nucleoside analog against Nipah virus in the Syrian hamster model. Henipavirus nipahense strain:Bangladesh

Nipah virus (NiV) is a zoonotic paramyxovirus with pandemic potential, for which currently no licensed vaccines and therapeutics for human use are available. Nucleoside analogs such as remdesivir and favipiravir have previously shown promise as antiviral therapeutics for NiV infection through termination of viral replication and transcription. The nucleoside analog 4-fluorouridine (4-FlU, EIDD-2749) has broad activity against RNA viruses and has shown efficacy in vitro against NiV-M (Malaysia) and NiV-B (Bangladesh). Here, we assessed the pharmacokinetic parameters of orally available 4-FlU in the Syrian Golden hamster model and investigated its protective efficacy against NiV-B. The bioactive form (4-FlU-TP) crossed the blood-brain barrier and repetitive daily treatment at 10mg/kg showed high levels in sera. While a seven-day treatment regimen post-NiV infection only delayed time to death, extending treatment to 28 days reduced viremia, incidence of lung disease, lung lesion severity, inflammation, and mortality rate. However, lesions, virus antigen, and viral RNA could be detected in some survivors, suggesting that further optimization is needed. Interestingly, nonsynonymous single-nucleotide variants were found in nucleocapsid (N, T191S), polymerase (L, T1341I) and phosphoprotein (P, I286V) genes after 21-28 days of therapy. These were solely found in brain tissues from 4-FlU-treated subjects, and the corresponding amino acid changes occurred either in a groove interacting with RNA for N, in an intrusion loop of the PRNTase domain for L, or in the N-terminal domain for P and could result from adaptation to treatment. Further studies assessing these mutations individually or in concert in escaping nucleoside analogs are warranted.