ABSTRACT
Background: SARS-CoV-2 enters host cells via an interaction between viral spike protein and cellular ACE2. However, in common with other enveloped viruses, apoptotic mimicry may also assist cell entry: phosphatidylserine (PS) exposed on the viral envelope interacts with cellular PS receptors leading to efferocytosis. The PS receptor, GAS6 bound to AXL, has also been shown to suppress type I interferon (IFN) responses. AXL is the predominant cellular PS receptor expressed on airway-derived cell lines. We hypothesized that the clinical-stage, AXL kinase-specific inhibitor, bemcentinib, inhibits SARS-CoV-2 infection and represents a potential therapy for COVID-19. Methods: Viral infection and host transcriptional responses to infection with SARS-CoV-2 or a VSV pseudovirion bearing SARS-CoV-2 spike were measured in human airway epithelial cell lines, engineered hACE2-expressing A549 lung cancer cells, and Vero E6 cells treated with bemcentinib or protease inhibitors. Studies also measured the effect of bemcentinib on SARS-CoV-2 binding and internalization into cells. The in vivo effect of bemcentinib (50mg/ kg, orally, twice daily) was assessed in C57BL6/J mice infected with the murine coronavirus, mouse hepatitis virus (MHV, 500 or 5x104 infectious units intraperitoneally). Viral titers and loads in liver were evaluated at day 5 postinfection. Spleen and liver were harvested to evaluate type 1 IFN-related gene expression changes. Results: Bemcentinib prevented infection by SARS-CoV-2 as assessed by viral transcripts in RNAseq studies as well as viral load in qRT-PCR analysis of human lung epithelial, A549-hACE2 and Vero E6 cells. Bemcentinib reduced virus internalization without affecting virus binding. Further, bemcentinib inhibition correlated well with inhibitors that block endosomal acidification and cathepsin activity, consistent with AXL-mediated SARS-CoV-2 uptake into endosomes. In vivo, bemcentinib significantly inhibited murine MHV liver titers and virus load and significantly enhanced signatures of type I IFN response. Conclusion: The orally bioavailable AXL inhibitor bemcentinib demonstrated potent antiviral effects in pre-clinical SARS-CoV-2 and other coronavirus models. These data support two ongoing phase 2 studies (EudraCT 2020-001736-95 [UK] & CTRI/2020/10/028602 [India] and DOH-27-092020-6170 [South Africa]) of bemcentinib for the treatment of COVID-19 in hospitalized patients, including those requiring supplemental oxygen and/or non-invasive ventilation, but not intubation.