The cannabinoid receptor subtype 2 (CB2), a class-A membrane-bound G-protein coupled receptor (GPCR) is a preferred therapeutic target for treating neuroinflammation, pain, arthritis and various other associated metabolic disorders due to its lack of CNS side effects relative to the CB1 receptor. Allosteric modulators (AMs) exhibit distinct therapeutic advantages over orthosteric modulators in terms of enhanced target specificity and reduced or null off-target side-effects. Only a few AMs of the CB2 receptor have been identified, possessing only micromolar activity at best, and there is not sufficient knowledge of the allosteric site(s) within the CB2 receptor to allow efficient targeting and aid the search for new, more potent AMs. Therefore, we identified and characterized the allosteric binding site(s) of known negative AMs (NAMs) of CB2, dihydrogambogic acid (DHGA) and trans-β-caryophyllene (TBC). We first mapped allosteric sites using a CB2 receptor model complexed with the well-known orthosteric ligand CP 55,940 within the orthosteric site and then performed Glide docking of multiple conformers of DHGA and TBC into the five predicted binding sites. Each of the two top-ranked protein-ligand complexes, for CB2–DHGA–CP 55,940 and CB2–TBC–CP 55,940, were then separately embedded into a hydrated lipid bilayer system and subjected to 200 ns molecular dynamics simulation using the NAMD program. The presence of an AM affected the CB2–CP 55,940 complex, causing a significant change to the CB2 receptor conformation, consisting of altering the relative positioning of the toggle switch residues, promoting a strong π-π interaction between Phe117 and Trp258, and reducing the binding free energy of CP 55,940. The insight gained from this study will be used to guide the design and synthesis of novel high affinity and selective NAMs for the CB2 receptor.

Negative allosteric modulators of the cannabinoid receptor 2: Protein modeling, binding site identification and molecular dynamics simulations in the presence of an orthosteric agonist

255th National Meeting (2018)

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