AV5080

Clade 2.3.4.4b highly pathogenic avian influenza (HPAI) A(H5N1) viruses that are responsible for devastating outbreaks in birds and mammals pose a potential threat to public health. Here, we evaluated their susceptibility to influenza antivirals. Of 1,015 sequences of HPAI A(H5N1) viruses collected in the United States during 2022, eight viruses (∼0.8%) had a molecular marker of drug resistance to an FDA-approved antiviral: three adamantane-resistant (M2-V27A), four oseltamivir-resistant (NA-H275Y), and one baloxavir-resistant (PA-I38T). Additionally, 31 viruses contained mutations that may reduce susceptibility to inhibitors of neuraminidase (NA) (n = 20) or cap-dependent endonuclease (CEN) (n = 11). A panel of 22 representative viruses was tested phenotypically. Overall, clade 2.3.4.4b A(H5N1) viruses lacking recognized resistance mutations were susceptible to FDA-approved antivirals. Oseltamivir was least potent at inhibiting NA activity, while the investigational NA inhibitor AV5080 was most potent, including against NA mutants. A novel NA substitution T438N conferred 12-fold reduced inhibition by zanamivir, and in combination with the known marker N295S, synergistically affected susceptibility to all five NA inhibitors. In cell culture-based assays HINT and IRINA, the PA-I38T virus displayed 75- to 108-fold and 37- to 78-fold reduced susceptibility to CEN inhibitors, baloxavir and the investigational AV5116, respectively. Viruses with PA-I38M or PA-A37T showed 5- to 10-fold reduced susceptibilities. As HPAI A(H5N1) viruses continue to circulate and evolve, close monitoring of drug susceptibility is needed for risk assessment and to inform decisions regarding antiviral stockpiling.

Development of a novel drug candidate with improved potency against influenza virus neuraminidase compared with currently available therapeutics, and high activity against oseltamivir-resistant viruses.

A number of synthetic compounds were evaluated for antiviral properties in vitro and in vivo. Three-dimensional molecular docking, assisted by a pharmacophore model, was applied to classify compounds within the series by their inhibitory potency. Compound stability in blood and in animal models was determined. Pharmacokinetic studies in dogs and rats after oral or intravenous administration were performed.

A novel highly potent drug candidate [(3R,4R,5S)-5-[(diaminomethylene)amino]-3-(1-ethylpropoxy)-4-[(fluoroacetyl)amino]cyclohex-1-ene-1-carboxylic acid; AV5080] was synthesized and tested. AV5080 exhibited high activity against influenza virus neuraminidase in vitro, with IC(50) values of 0.03 nM and 0.07 nM against the neuraminidase of A/Duck/Minnesota/1525/1981/H5N1 and A/Perth/265/2009/H1N1 (wild-type), respectively. Notably, AV5080 was highly active against oseltamivir-resistant influenza viruses.

Based on the results presented in this study, AV5080 is a promising novel oral drug candidate for the treatment of influenza, including oseltamivir-resistant types. Further pre-clinical development of AV5080 is warranted.