Anti-COVID-19 Potential of Withaferin-A and Caffeic Acid Phenethyl Ester.

BACKGROUND: The recent COVID-19 (coronavirus disease 2019) pandemic triggered research on the development of new vaccines/drugs, repurposing of clinically approved drugs, and assessment of natural anti-COVID-19 compounds. Based on the gender difference in the severity of the disease, such as a higher number of men hospitalized and in intense care units, variations in sex hormones have been predicted to play a role in disease susceptibility. Cell surface receptors (Angiotensin-Converting Enzyme 2; ACE2 and a connected transmembrane protease serine 2- TMPSS2) are upregulated by androgens. Conversely, androgen antagonists have also been shown to lower ACE2 levels, implying their usefulness in COVID-19 management. OBJECTIVES: In this study, we performed computational and cell-based assays to investigate the anti- COVID-19 potential of Withaferin-A and Caffeic acid phenethyl ester, natural compounds from Withania somnifera and honeybee propolis, respectively. METHODS: Structure-based computational approach was adopted to predict binding stability, interactions, and dynamics of the two test compounds to three target proteins (androgen receptor, ACE2, and TMPRSS2). Further, in vitro, cell-based experimental approaches were used to investigate the effect of compounds on target protein expression and SARS-CoV-2 replication. RESULTS: Computation and experimental analyses revealed that (i) CAPE, but not Wi-A, can act as androgen antagonist and hence inhibit the transcriptional activation function of androgen receptor, (ii) while both Wi-A and CAPE could interact with ACE2 and TMPRSS2, Wi-A showed higher binding affinity, and (iii) combination of Wi-A and CAPE (Wi-ACAPE) caused strong downregulation of ACE2 and TMPRSS2 expression and inhibition of virus infection. CONCLUSION: Wi-A and CAPE possess multimodal anti-COVID-19 potential, and their combination (Wi-ACAPE) is expected to provide better activity and hence warrant further attention in the laboratory and clinic.

Molecular insights to the anti-COVID-19 potential of α-, ß- and γ-cyclodextrins.

SARS-CoV-2 viral infection is regulated by the host cell receptors ACE2 and TMPRSS2, and therefore the effect of various natural and synthetic compounds on these receptors has recently been the subject of investigations. Cyclodextrins, naturally occurring polysaccharides derived from starch, are soluble in water and have a hydrophobic cavity at their center enabling them to accommodate small molecules and utilize them as carriers in the food, supplements, and pharmaceutical industries to improve the solubility, stability, and bioavailability of target compounds. In the current study, computational molecular simulations were used to investigate the ability of α-, ß- and γ-Cyclodextrins on human cell surface receptors. Cell-based experimental approaches, including expression analyses at mRNA and protein levels and virus replication, were used to assess the effect on receptor expression and virus infection, respectively. We found that none of the three CDs could dock effectively to human cell surface receptor ACE2 and viral protease Mpro (essential for virus replication). On the other hand, α- and ß-CD showed strong and stable interactions with TMPRSS2, and the expression of both ACE2 and TMPRSS2 was downregulated at the mRNA and protein levels in cyclodextrin (CD)-treated cells. A cell-based virus replication assay showed ∼20% inhibition by ß- and γ-CD. Taken together, the study suggested that (i) downregulation of expression of host cell receptors may not be sufficient to inhibit virus infection (ii) activity of the receptors and virus protein Mpro may play a critical and clinically relevant role, and hence (iii) newly emerging anti-Covid-19 compounds warrant multimodal functional analyses.Communicated by Ramaswamy H. Sarma.

Identification of a novel inhibitor of SARS-CoV-2 main protease: an in silico, biochemical, and cell-based approach.

The recurrent nature of coronavirus outbreaks, severity of the COVID-19 pandemic, rapid emergence of novel variants, and concerns over the effectiveness of existing vaccines against novel variants have highlighted the need to develop therapeutic interventions. Targeted efforts to identify inhibitors of crucial viral proteins are the preferred strategy. In this study, we screened FDA-approved and natural product libraries using in silico approach for potential hits against the SARS-CoV-2 main protease (Mpro) and experimentally validated their potency using in vitro biochemical and cell-based assays. Seven potential hits were identified through in silico screening and were subsequently evaluated in SARS-CoV-2-based cell-free assays, followed by testing in the HCoV-229E-based culture system. Of the tested compounds, 4-(3,4-dihydroxyphenyl)-6,7-dihydroxy-1-isopropyl-1H-benzofuro[3,2-b]pyrazolo[4,3-e]pyridin-3(2H)-one (PubChem CID:71755304, hereafter referred to as STL522228) exhibited significant antiviral activity. Subsequently, its potential as a novel COVID therapeutic molecule was validated in the SARS-CoV-2-culture system, where STL522228 demonstrated superior antiviral activity (EC50 = 0.44 µm) compared to Remdesivir (EC50 = 0.62 µm). Based on these findings, we report the strong anti-coronavirus activity of STL522228, and propose that it as a promising pan-coronavirus Mpro inhibitor for further experimental and preclinical validation.