Abstract
There are, besides remdesivir, no approved antivirals for the treatment of SARS-CoV-2 infections. To aid in the search for antivirals against this virus, we explored the use of human tracheal airway epithelial cells (HtAEC) and human small airway epithelial cells (HsAEC) grown at the air-liquid interface (ALI). These cultures were infected at the apical side with one of two different SARS-CoV-2 isolates. Each virus was shown to replicate to high titers for extended periods of time (at least 8 days) and, in particular an isolate with the D614G in the spike (S) protein did so more efficiently at 35 °C than 37 °C. The effect of a selected panel of reference drugs that were added to the culture medium at the basolateral side of the system was explored. Remdesivir, GS-441524 (the parent nucleoside of remdesivir), EIDD-1931 (the parent nucleoside of molnupiravir) and IFN (β1 and λ1) all resulted in dose-dependent inhibition of viral RNA and infectious virus titers collected at the apical side. However, AT-511 (the free base form of AT-527 currently in clinical testing) failed to inhibit viral replication in these in vitro primary cell models. Together, these results provide a reference for further studies aimed at selecting SARS-CoV-2 inhibitors for further preclinical and clinical development.
Highlights
Remdesivir is currently the only approved antiviral for the treatment of COVID-19 (Beigel et al, 2020)
AT-511 was entirely devoid of antiviral activity (Table 1)
GS-441524 showed similar EC50 values when tested in human airway epithelial cells (HAEC) cultures in comparison with VeroE6 and Huh7 cells (Table 1)
Summary
Remdesivir is currently the only approved antiviral for the treatment of COVID-19 (Beigel et al, 2020). Major efforts are ongoing to develop novel antiviral drugs for effective COVID-19 treatment. To aid in their development, physiologically-relevant in vitro models are needed. Immortalized cell lines originating from non-respiratory (and often non-human) tissues are frequently used in early preclinical studies for antiviral assessment. VeroE6, a widely used cell line in SARS-CoV-2 studies, is defective in the expression of main SARS-CoV-2 receptors (angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2)). Screening campaigns often result in the discovery of antiviral agents that regulate autophagy pathways and endosomal-lysosomal maturation, which may not be pertinent or translatable as SARS-CoV-2 therapies (Murgolo et al, 2021)
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