Biological Characterization of AB-343, a Novel and Potent SARS-CoV-2 Mpro Inhibitor with Pan-Coronavirus Activity.

Since the SARS-CoV-2 outbreak, there have been ongoing efforts to identify antiviral molecules with broad coronavirus activity to combat COVID-19. SARS-CoV-2's main protease (M^pro) is responsible for processing the viral polypeptide into non-structural proteins essential for replication. Here, we present the biological characterization of AB-343, a covalent small-molecule inhibitor of SARS-CoV-2 M^pro with potent activity in both cell-based (EC₅₀ = 0.018 μM) and enzymatic (K_i = 0.0028 μM) assays. AB-343 also demonstrated excellent inhibition of M^pro of other human coronaviruses, including those from the alpha (229E and NL63) and beta (SARS-CoV, MERS, OC43, and HKU1) families, suggesting the compound could be active against future coronaviruses. No change in AB-343 potency was observed against M^pro of SARS-CoV-2 variants of concern, including Omicron, suggesting that AB-343 could be developed as a treatment against currently circulating coronaviruses. AB-343 also remained active against several M^pro variants which confer significant resistance to nirmatrelvir and ensitrelvir, which are presently the only M^pro inhibitors authorized for the treatment of COVID-19, further supporting the evaluation of AB-343 as a novel and potent therapeutic for COVID-19 and other coronaviruses.