Mulberry Component Kuwanon C Exerts Potent Therapeutic Efficacy In Vitro against COVID-19 by Blocking the SARS-CoV-2 Spike S1 RBD:ACE2 Receptor Interaction

Abstract

There has been an immense effort by global pharmaceutical companies to develop anti-COVID-19 drugs, including small molecule-based RNA replication inhibitors via drug repositioning and antibody-based spike protein blockers related to cell entry by SARS-CoV-2. However, several limitations to their clinical use have emerged in addition to a lack of progress in the development of small molecule-based cell entry inhibitors from natural products. In this study, we tested the effectiveness of kuwanon C (KC), which has mainly been researched using in silico docking simulation and can serve as an effective building block for developing anti-COVID-19 drugs, in blocking the spike S1 RBD:ACE2 receptor interaction. KC is a natural product derived from Morus alba L., commonly known as mulberry, which has known antiviral efficacy. Molecular interaction studies using competitive ELISA and the BLItz system revealed that KC targets both the spike S1 RBD and the ACE2 receptor, successfully disrupting their interaction, as supported by the in silico docking simulation. Furthermore, we established a mechanism of action by observing how KC prevents the infection of SARS-CoV-2 spike pseudotyped virus in ACE2/TPRSS2-overexpressing HEK293T cells. Finally, we demonstrated that KC inhibits clinical isolates of SARS-CoV-2 in Vero cells. Future combinations of small molecule-based cell entry inhibitors, such as KC, with the currently prescribed RNA replication inhibitors are anticipated to significantly enhance the efficacy of COVID-19 therapies.

Analysis and Identification of Bioactive Compounds of Cannabinoids in Silico for Inhibition of SARS-CoV-2 and SARS-CoV

“…We discovered that CBNA interacted with Tyr449 and Gln498, producing three conventional H and three pi-alkyl bonds with Tyr453, Tyr495 and Tyr505, and one Alkyl bond with Arg403, respectively ( Figure 1 B). Similarly, Kuwanon C (KC) was identified that could interact with Gln498 of spike S1 RBD [ 45 ]. CBGVA formed two conventional H bonds with Gly496 and Asn501, as well as four pi-alkyl bonds with Tyr453, Tyr495, and Tyr505, which was identical to the KC interaction with ACE2 [ 45 ], and one Pi-Pi bond with Tyr505 ( Figure 1 C).…”

“…Similarly, Kuwanon C (KC) was identified that could interact with Gln498 of spike S1 RBD [ 45 ]. CBGVA formed two conventional H bonds with Gly496 and Asn501, as well as four pi-alkyl bonds with Tyr453, Tyr495, and Tyr505, which was identical to the KC interaction with ACE2 [ 45 ], and one Pi-Pi bond with Tyr505 ( Figure 1 C). The previous study showed that CBD and CBN formed two and one H bonds, respectively, at the Glu166 and Met165 sites [ 18 ].…”

“…The binding energy of luteolin with M pro and ACE2 was −8.2 and −10.1 kcal/mol, respectively [ 14 ]. Although KC has the ability to block RBD-ACE2 receptor interaction, the binding energy was −7.1 kcal/mol [ 45 ]. This suggests that different cannabis target proteins are different on SARS-CoV-2.…”

Importance, Applications and Features of Assays Measuring SARS-CoV-2 Neutralizing Antibodies

“…Third, the half-life of soluble ACE2 is very low, which means that it requires multiple administrations and makes treatment difficult and cumbersome. The latter two considerations may also apply for other low molecular weight compounds [ 123 , 124 ]. Alternatively, one may therefore consider topical administration or approaches blocking cell-bound ACE2 with compounds to prevent RBD–ACE2 interaction.…”

A Comprehensive Update of Various Attempts by Medicinal Chemists to Combat COVID-19 through Natural Products

“…In vitro studies showed that this natural compound inhibited the SARS-CoV-2 infection by interacting with both the viral spike proteins and the host ACE2 receptor cells with an IC 50 value of 91.4 μM at a concentration range of 25 μM to 100 μM. Furthermore, in silico studies demonstrated the more stable binding interactions of ligands with spike proteins compared to ACE2 receptors [ 53 ]. Some naturally occurring flavonoids (myricetin, quercetin, kaempferol, flavanone, and licoflavone C) were found to inhibit the enzymatic activities of SARS-CoV-2 by selectively antagonizing the action of NSP13 at nanomolar and micromolar concentrations.…”