Unraveling antiviral efficacy of multifunctional immunomodulatory triterpenoids against SARS‐COV‐2 targeting main protease and papain‐like protease

Abstract

The coronavirus disease 2019 (COVID‐19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) may be over, but its variants continue to emerge, and patients with mild symptoms having long COVID is still under investigation. SARS‐CoV‐2 infection leading to elevated cytokine levels and suppressed immune responses set off cytokine storm, fatal systemic inflammation, tissue damage, and multi‐organ failure. Thus, drug molecules targeting the SARS‐CoV‐2 virus‐specific proteins or capable of suppressing the host inflammatory responses to viral infection would provide an effective antiviral therapy against emerging variants of concern. Evolutionarily conserved papain‐like protease (PLpro) and main protease (Mpro) play an indispensable role in the virus life cycle and immune evasion. Direct‐acting antivirals targeting both these viral proteases represent an attractive antiviral strategy that is also expected to reduce viral inflammation. The present study has evaluated the antiviral and anti‐inflammatory potential of natural triterpenoids: azadirachtin, withanolide_A, and isoginkgetin. These molecules inhibit the Mpro and PLpro proteolytic activities with half‐maximal inhibitory concentrations (IC50) values ranging from 1.42 to 32.7 μM. Isothermal titration calorimetry (ITC) analysis validated the binding of these compounds to Mpro and PLpro. As expected, the two compounds, withanolide_A and azadirachtin, exhibit potent anti‐SARS‐CoV‐2 activity in cell‐based assays, with half‐maximum effective concentration (EC50) values of 21.73 and 31.19 μM, respectively. The anti‐inflammatory roles of azadirachtin and withanolide_A when assessed using HEK293T cells, were found to significantly reduce the levels of CXCL10, TNFα, IL6, and IL8 cytokines, which are elevated in severe cases of COVID‐19. Interestingly, azadirachtin and withanolide_A were also found to rescue the decreased type‐I interferon response (IFN‐α1). The results of this study clearly highlight the role of triterpenoids as effective antiviral molecules that target SARS‐CoV‐2‐specific enzymes and also host immune pathways involved in virus‐mediated inflammation.

Structure-based virtual screening methods for the identification of novel phytochemical inhibitors targeting furin protease for the management of COVID-19

“…In another study conducted by Lopes et al (2022), the plant compound amentoflavone was examined for its ability to inhibit five key targets of SARS-CoV-2, including main protease (Mpro or 3CLPro), RNA-dependent protease, NSP15 endoribonuclease, S protein, and ACE2 receptor. Choudhary et al (2023) found that withanolide A exhibits dual action, including as an antiviral agent that targets viral proteases like Mpro and PLpro and as an antiinflammatory agent that regulates cytokine levels as well as enhancing the type-I interferon response. That evidenced that withanolide plays a crucial role in the management of SARS-CoV-2 infection (Choudhary et al, 2023).…”

“…Choudhary et al (2023) found that withanolide A exhibits dual action, including as an antiviral agent that targets viral proteases like Mpro and PLpro and as an antiinflammatory agent that regulates cytokine levels as well as enhancing the type-I interferon response. That evidenced that withanolide plays a crucial role in the management of SARS-CoV-2 infection (Choudhary et al, 2023). Withanolide, robustaflavone, and amentoflavone are potential inhibitors compared to other studies.…”