Repurposing old drugs as antiviral agents for coronaviruses

Abstract

Background: New therapeutic options to address the ongoing coronavirus disease 2019 (COVID-19) pandemic are urgently needed. One possible strategy is the repurposing of existing drugs approved for other indications as antiviral agents for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Due to the commercial unavailability of SARS-CoV-2 drugs for treating COVID-19, we screened approximately 250 existing drugs or pharmacologically active compounds for their inhibitory activities against feline infectious peritonitis coronavirus (FIPV) and human coronavirus OC43 (HCoV-OC43), a human coronavirus in the same genus (Betacoronavirus) as SARS-CoV-2.

Methods: FIPV was proliferated in feline Fcwf-4 cells and HCoV-OC43 in human HCT-8 cells. Viral proliferation was assayed by visualization of cytopathic effects on the infected Fcwf-4 cells and immunofluorescent assay for detection of the nucleocapsid proteins of HCoV-OC43 in the HCT-8 cells. The concentrations (EC₅₀) of each drug necessary to diminish viral activity to 50% of that for the untreated controls were determined. The viabilities of Fcwf-4 and HCT-8 cells were measured by crystal violet staining and MTS/PMS assay, respectively.

Results: Fifteen out of the 252 drugs or pharmacologically active compounds screened were found to be active against both FIPV and HCoV-OC43, with EC₅₀ values ranging from 11 nM to 75 μM. They are all old drugs as follows, anisomycin, antimycin A, atovaquone, chloroquine, conivaptan, emetine, gemcitabine, homoharringtonine, niclosamide, nitazoxanide, oligomycin, salinomycin, tilorone, valinomycin, and vismodegib.

Conclusion: All of the old drugs identified as having activity against FIPV and HCoV-OC43 have seen clinical use in their respective indications and are associated with known dosing schedules and adverse effect or toxicity profiles in humans. Those, when later confirmed to have an anti-viral effect on SARS-CoV-2, should be considered for immediate uses in COVID-19 patients.

Keywords: COVID-19; Coronavirus; Cytopathic effect; Drug repurpose; HCoV-OC43; SARS-CoV-2.

Fig. 1

The cytopathic effects of 15 drugs and GS-441524 against FIPV. Fcwf-4 cells infected with FIPV (NTU156) showed typical cytopathic effects by crystal violet staining compared to uninfected cells. FIPV infected cells were treated with a series of 7 concentrations at different dilution of the testing compounds. The cytotoxicity of the compounds being tested was also investigated. The 50% maximal effective concentration (EC₅₀) and cytotoxicity concentration (CC₅₀) of each compound were calculated by visual assays. Shown are means ± S.D. from three rounds of experiments, each in triplicate.

Fig. 2

Immunofluorescent assay of 15 drugs and GS-441524 against HCoV-OC43. Indirect immunofluorescent assay (IFAs) with the antibody against HCoV-OC43 nucleocapsid protein (in green) and Hoechst dye staining (in blue) for the DNA of the host live cells in HCoV-OC43 (0.05 MOI) infected HCT-8 cells at 72 h.p.i. were performed shown here are the representative images of the cells with mock infection (MOCK), the infected cells treated with vehicle (0.5% DMSO), and the infected cells treated with drugs as indicated from 3 independent experiments. Nuclei of live HCT-8 cells in blue were stained with Hoechst dye. The treated concentrations of each drug are labelled with the corresponding images (200×).