Abstract
As a complement to vaccines, small-molecule therapeutic agents are needed to treat or prevent infections by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and its variants, which cause COVID-19. Affinity selection–mass spectrometry was used for the discovery of botanical ligands to the SARS-CoV-2 spike protein. Cannabinoid acids from hemp (Cannabis sativa) were found to be allosteric as well as orthosteric ligands with micromolar affinity for the spike protein. In follow-up virus neutralization assays, cannabigerolic acid and cannabidiolic acid prevented infection of human epithelial cells by a pseudovirus expressing the SARS-CoV-2 spike protein and prevented entry of live SARS-CoV-2 into cells. Importantly, cannabigerolic acid and cannabidiolic acid were equally effective against the SARS-CoV-2 alpha variant B.1.1.7 and the beta variant B.1.351. Orally bioavailable and with a long history of safe human use, these cannabinoids, isolated or in hemp extracts, have the potential to prevent as well as treat infection by SARS-CoV-2.
Caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the COVID-19 pandemic includes at least 272 million cases worldwide, 5.3 million deaths, and over 600 000 new cases daily as of December 2021. (1) Vaccines have been developed, but due to their limited availability and the rate of virus mutation, SARS-CoV-2 infections are likely to continue for many years. As the pandemic continues, several SARS-CoV-2 variants have emerged that are circulating globally, including the variant B.1.1.7 (alpha, first detected in the United Kingdom), variant B.1.351 (beta, first detected in South Africa), and variant B.1.617.2 (delta, first detected in India). (2) These variants of concern are reported to have the capacity to escape humoral immunity elicited by natural infection or the current vaccinations. Moreover, the variants are associated with increases in infections and hospitalizations, suggesting a competitive fitness advantage over the original strain. (3)
A member of the Coronaviridae family, SARS-CoV-2 is an enveloped, nonsegmented, positive sense RNA virus that is characterized by crown-like spikes on the outer surface. (4,5) SARS-CoV-2 contains RNA strands 29.9 kb long (6) that encode the four main structural proteins, spike, envelope, membrane, and nucleocapsid, 16 nonstructural proteins, and several accessory proteins. (7) Any step of the SARS-CoV-2 virus infection and replication cycle is a potential target for antiviral intervention including cell entry, genome replication, viral maturation, or viral release. However, binding of the viral spike protein of SARS-CoV-2 to the human cell surface receptor angiotensin converting enzyme-2 (ACE2) is a critical step during the infection of human cells. Therefore, cell entry inhibitors could be used to prevent SARS-CoV-2 infection as well as to shorten the course of COVID-19 infections by preventing virus particles from infecting human cells.
A transmembrane protein with a molecular mass of ∼150 kDa, the spike protein forms homotrimers protruding from the SARS-CoV-2 surface. Subunits of the SARS-CoV-2 spike protein trimer consist of an S1 subunit that binds to ACE2 of the host cell to initiate infection, an S2 subunit that mediates virus fusion with host cells, and a transmembrane domain (Figure 1A). The infection of host cells by SARS-CoV-2 begins with the attachment of the receptor-binding domain (RBD) of the S1 protein, (8) which has been identified as residues 331 to 524, (9) to the host cell receptor ACE2. An enzyme on the outer cell membrane of host cells, ACE2 is expressed abundantly on human endothelial cells in the lungs, arteries, heart, kidney, and intestines. (10) TMPRSS2 protease on the host cell membrane activates the spike protein by cleaving it at S1/S2 and S2 sites, (11) leading to conformational changes that allow the virus to fuse with the host membrane and enter the cytoplasm. The S1 subunit is primarily responsible for the determination of the host virus range and cellular tropism. (12)
Figure 1. Affinity selection–mass spectrometric (AS-MS) discovery of natural ligands to the SARS-CoV-2 spike protein. (A) The spike protein of SARS-CoV-2 consists of trimers of a protein containing an S1 subunit, an S2 subunit, and a transmembrane domain. The S1 subunit binds to human ACE2 to initiate cell entry. Recombinant S1 containing a His-tag was immobilized on magnetic microbeads for affinity selection of ligands. (B) AS-MS was used to isolate and identify natural ligands to the spike protein S1 subunit. A magnetic probe retained the microbeads containing the S1 subunit and bound ligands, while unbound compounds were washed away. Ligands were released using organic solvent and then analyzed using UHPLC-MS. (C) During AS-MS, the SBP-1 peptide bound to immobilized S1 (equivalent to 0.17 μM) (positive control) but not to immobilized denatured S1 (negative control). (D) MagMASS was used for the affinity selection and identification of cannabinoid acids (0.10 μM each in this confirmatory chromatogram) as ligands from hemp extracts. Negative controls using denatured S1 showed no significant binding of cannabinoid acids.
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Richard B. van Breemen*, Ruth N. Muchiri, Timothy A. Bates, Jules B. Weinstein, Hans C. Leier, Scotland Farley, and Fikadu G. Tafesse
Photo Credit: Illustrations from study by authors
Source : Journal of Natural Products
Link to original : Cannabinoids Block Cellular Entry of SARS-CoV-2 and the Emerging Variants
