Identification of bis-benzylisoquinoline alkaloids as SARS-CoV-2 entry inhibitors from a library of natural products in vitro (preprint)

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a major public health issue. To screen for antiviral drugs for COVID-19 treatment, we constructed a SARS-CoV-2 spike (S) pseudovirus system using an HIV-1-based lentiviral vector with a luciferase reporter gene to screen 188 small potential antiviral compounds. Using this system, we identified nine compounds, specifically, bis-benzylisoquinoline alkaloids, that potently inhibited SARS-CoV-2 pseudovirus entry, with EC50 values of 0.1-10 M. Mechanistic studies showed that these compounds, reported as calcium channel blockers (CCBs), inhibited Ca2+-mediated membrane fusion and consequently suppressed coronavirus entry. These candidate drugs showed broad-spectrum efficacy against the entry of several coronavirus pseudotypes (SARS-CoV, MERS-CoV, SARS-CoV-2 [S-D614 and S-G614]) in different cell lines (293T, Calu-3, and A549). Antiviral tests using native SARS-CoV-2 in Vero E6 cells confirmed that four of the drugs (SC9/cepharanthine, SC161/hernandezine, SC171, and SC185/neferine) reduced cytopathic effect and supernatant viral RNA load. Among them, cepharanthine showed the strongest anti-SARS-CoV-2 activity. Collectively, this study offers new lead compounds for coronavirus antiviral drug discovery.

Stability of the COVID-19 virus under wet, dry and acidic conditions (preprint)

COVID-19 has become a pandemic and is spreading fast worldwide. The COVID-19 virus is transmitted mainly through respiratory droplets and close contact. However, the fecal-oral transmission of the virus has not been ruled out and it is important to ascertain how acidic condition in the stomach affects the infectivity of the virus. Besides, it is unclear how stable the COVID-19 virus is under dry and wet conditions. In the present study, we have shown that the COVID-19 virus is extremely infectious as manifested by the infection of Vero-E6 cells by one PFU (Plaque Forming Unit) of the virus. We then investigated the stability of the COVID-19 virus in wet, dry and acidic (pH2.2) environments at room temperature. Results showed that the COVID-19 virus could survive for three days in wet and dry environments, but the dry condition is less favorable for the survival of the virus. Our study also demonstrated that the COVID-19 virus at a relative high titer (1.2 x 103 PFU) exhibits a certain degree of tolerance to acidic environment at least for 60 minutes. When the virus titer was [≤]1.0 x 103 PFU, acid treatment (pH2.2) for 30 or 60 minute resulted in virus inactivation. It suggests that the virus at a high concentration may survive in the acidic environment of the stomach. The finding of the present study will contribute to the control of the spread of the COVID-19 virus.