Cannabinoids Block Cellular Entry of SARS-CoV‑2 and the Emerging Variants
Richard B. van Breemen, Ruth N. Muchiri, Timothy A. Bates, Jules B. Weinstein, Hans C. Leier, Scotland Farley, and Fikadu G. Tafesse
Journal of Natural Products, 2022, 85, 176−184.
Doi : 10.1021/acs.jnatprod.1c00946
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 long6 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
Ligands with high affinity to the receptor binding domain on the S1 protein have the potential to function as entry inhibitors and prevent infection of human cells by SARS-CoV-2.13 For example, small peptides derived from the heptad repeat regions of SARS-CoV-1 spike S2 subunit have been shown to inhibit SARS-CoV infection by the interference of fusion with target cells.14,15 The approach of utilizing compounds that block virus−receptor interaction has also been useful for other viruses, including HIV-1 and hepatitis C virus.16,17
Natural products are the most successful source of drugs and drug leads in the history of pharmacology.18,19 Although combinatorial chemistry currently receives more emphasis for lead discovery by the pharmaceutical industry,20 nature continues to be a source of unique chemical structural diversity for new drug discovery.21 Approximately two-thirds of new small-molecule drugs since 1981 have been natural products, derivatives of natural products, natural product pharmacophores, or mimics of natural products.18,22 Less than 10% of the world’s biodiversity has been evaluated for potential biological activity, so that many more useful natural lead compounds await discovery.18 As an example of a natural product with anti-SARS-CoV-2 activity, panduratin from the medicinal plant Boesenbergia rotunda was reported recently to be active against SARS-CoV-2 at both pre-entry and postinfection phases.23
Although bioassay-guided fractionation is widely used for natural products drug discovery, affinity selection−mass spectrometry (AS-MS) provides a more efficient alternative.24 AS-MS involves incubating a therapeutically important receptor like the SARS-CoV-2 spike protein with a mixture of possible ligands such as a botanical extract. The ligand− receptor complexes are separated from nonbinding molecules using one of several methods such as ultrafiltration,25 size exclusion,26 or magnetic microbeads,27 and then ultra-highpressure liquid chromatography−mass spectrometry (UHPLCMS) is used to characterize the affinity-extracted ligands. In this investigation, we used the AS MS approach of magnetic microbead affinity selection screening (MagMASS).28,29
Hemp (Cannabis sativa L., Cannabaceae) is used for fiber, food, and animal feed, and various hemp extracts and compounds have become popular additions to cosmetics, body lotions, dietary supplements, and food. Over 170 secondary metabolites including some unique compounds are produced by hemp30,31 including flavonoids, diterpenes, triterpenes, lignans, and cannabinoids. Orally bioavailable,32 there are at least 70 cannabinoids including cannabidiols, Δ9-tetrahydrocannabinols, Δ8-tetrahydrocannabinols, cannabigerols, cannabinols, cannabichromenes, and cannabitriols, and in 2018, the U.S. FDA approved a cannabidiol isolate (Epidiolex), for the treatment of seizures associated with certain types of epileptic seizures.33
Using MagMASS to screen hemp extracts for ligands to the SARS-CoV-2 spike protein, several cannabinoid ligands were identified and ranked by affinity to the spike protein. Two cannabinoids with the highest affinities for the spike protein, cannabidiolic acid (CBDA) and cannabigerolic acid (CBGA), were confirmed to block infection of human epithelial cells by a pseudovirus expressing the spike protein. More importantly, both CBDA and CBGA block infection of the original live SARS-CoV-2 virus and variants of concern, including the B.1.1.7 and B.1.351.