ABSTRACT
Background: Zotatifin (eFT226) is a potent and selective inhibitor of eukaryotic initiation factor 4A (eIF4A), a host RNA helicase required for SARS-CoV-2 replication. Zotatifin selectively inhibits translation of ribonucleic acids (RNAs) containing specific short polypurine motifs in their 5-prime (5') regions. Two such highly conserved motifs are found in the SARS-CoV-2 genome. Zotatifin is currently being evaluated in a Phase 1b dose escalation study in 36 patients with mild to moderate COVID disease. In this in vitro study, we evaluated the selectivity of zotatifin's inhibition of SARS-CoV-2 translation, the antiviral activity of zotatifin alone against different human coronaviruses and the antiviral activity of zotatifin in combination with other antivirals against SARSCoV-2. Method(s): The selectivity of zotatifin for viral translation was evaluated in a cell-based reporter assay wherein luciferase translation was driven by 5'-sequences from SARS-CoV-2 or tubulin, a housekeeping gene. The antiviral activity of zotatifin was evaluated against SARS-CoV-1, SARS-CoV-2 variants (Wash/1/2020 (ancestral), delta, omicron BA.2), MERS-CoV and HCoV-299E in primary or established cell lines using cytopathic effect or infectious virus as endpoints. The antiviral activity of zotatifin in combination with remdesivir, N-hydroxycytidine (NHC;active nucleoside analogue metabolite of molnupiravir), nirmatrelvir, baricitinib or sotrovimab was evaluated against SARS-CoV-2 and analyzed by the method of Pritchard and Shipman. Result(s): Zotatifin inhibited the translation of the SARS-CoV-2 luciferase reporter construct with a mean IC50 of 3 nM and was ~14-fold less potent in inhibiting the tubulin reporter construct. Zotatifin potently inhibited the replication of all human coronaviruses tested with 50% effective concentrations (EC50s) ranging from 0.016 to 37.3 nM. The 50% cytotoxic concentration (CC50) value for zotatifin was 250 to >100,000 nM, yielding selectivity indices of 7 to >6250. Zotatifin was ~20 to >100-fold more potent than remdesivir, nirmatrelvir or NHC (figure) and demonstrated additive interactions when combined with remdesivir, NHC, nirmatrelvir, baricitinib or sotrovimab in vitro. Conclusion(s): The potent broad-spectrum activity of zotatifin against a variety of human coronaviruses and additive activity when combined with different anti-SARS-CoV-2 antivirals highlight the advantages of eIF4A as a target and warrant further evaluation in human clinical trials.