Inhibition of SARS-CoV-2 by Highly Potent Broad-Spectrum Anti-Coronaviral Tylophorine-Based Derivatives

Abstract

Tylophorine-based compounds and natural cardiotonic steroids (cardenolides and bufadienolides) are two classes of transmissible gastroenteritis coronavirus inhibitors, targeting viral RNA and host cell factors, respectively. We tested both types of compounds against two types of coronaviruses, to compare and contrast their antiviral properties, and with view to their further therapeutic development. Examples of both types of compounds potently inhibited the replication of both feline infectious peritonitis virus and human coronavirus OC43 with EC50 values of up to 8 and 16 nM, respectively. Strikingly, the tylophorine-based compounds tested inhibited viral yields of HCoV-OC43 to a much greater extent (7–8 log magnitudes of p.f.u./ml) than the cardiotonic steroids (about 2–3 log magnitudes of p.f.u./ml), as determined by end point assays. Based on these results, three tylophorine-based compounds were further examined for their anti-viral activities on two other human coronaviruses, HCoV-229E and SARS-CoV-2. These three tylophorine-based compounds inhibited HCoV-229E with EC50 values of up to 6.5 nM, inhibited viral yields of HCoV-229E by 6–7 log magnitudes of p.f.u./ml, and were also found to inhibit SARS-CoV-2 with EC50 values of up to 2.5–14 nM. In conclusion, tylophorine-based compounds are potent, broad-spectrum inhibitors of coronaviruses including SARS-CoV-2, and could be used for the treatment of COVID-19.

Remdesivir and Cyclosporine Synergistically Inhibit the Human Coronaviruses OC43 and SARS-CoV-2

“…Cells were pretreated with serial dilutions of remdesivir and cyclosporine at the indicated concentrations for 0.5 h prior to HCoV-OC43 infection at an MOI of 0.05. At 30 h.p.i., the resulting adherent cells were then fixed with 4% formaldehyde, permeabilized with 100% methanol, and subsequently subjected to IFA analyses with an antibody against HCoV-OC43 N protein (Mab9013) and FITC-conjugated anti-mouse immunoglobulin (#55499) (green), and the EC 50 values determined as described ( Yang et al, 2020 ). CC 50 values were determined by staining nuclei blue with Hoechst dye and then determining relative cell viability using the number of nuclei in the vehicle control as 100%.…”

“…For IFA used in the SARS-CoV-2 study, Vero E6 cells (BCRC number: 60476; derived from ATCC CRL-1586) were passaged within 6 months of receipt and the 4th–15th passages used. Cells were pretreated with each compound at the indicated concentration for 1 h at 37°C and then adsorbed with SARS-CoV-2 (TCDC#4) (sequence available on the GISAID website) at 100 PFU (MOI = 0.01) for 1 h at 37°C as described ( Yang et al, 2020 ). The virus-containing supernatants were removed and then fresh medium containing each compound at the indicated concentrations added to the cells.…”

“…Plaque assays for SARS-CoV-2 were performed as described ( Yang et al, 2020 ). Briefly, Vero E6 cells were seeded 1 day before infection with SARS-CoV-2 for 1 h at 37°C.…”

Phytochemicals for the treatment of COVID-19

“…Treatment with topotecan, an analog of the plant-derived alkaloid camptothecin, reduced morbidity and mortality rates in mice infected with SARS-CoV-2, with indications of reduced inflammatory responses (Ho et al, 2021). Derivatives of tylophorine, a naturally occurring alkaloids, have also demonstrated the ability to inhibit SARS-CoV-2 infection in vitro (Yang et al, 2020).…”

Phytochemical Moieties From Indian Traditional Medicine for Targeting Dual Hotspots on SARS-CoV-2 Spike Protein: An Integrative in-silico Approach

“…Some previous studies have shown that Tylophora alkaloids can inhibit viral protease and suppresses viral RNA replication by blocking the JAK2 mediated NF-κB activation (49). While tylophorine derivatives have inhibitory effects on mouse hepatitis virus (MHV), transmissible gastroenteritis virus (TGEV), and SARS-CoV (50)(51)(52). A recent report revealed that Tylophora alkaloids could inhibit the CoV-infected cells of swine (53).…”