This project serves as the ligand/drug development component of a comprehensive collaborative effort to study the structural and functional properties of CB1 and CB2, the two known cannabinoid receptors. During the current funding period we have developed high-affinity covalent and non-covalent CB1/CB2 ligands that have allowed us to probe the manner in which structurally diverse classes of ligands interact and activate or deactivate each of the two receptors. To study the """"""""foot-printing"""""""" of individual ligands on each receptor, we developed a Ligand Assisted Protein Structure (LAPS) approach which includes the use of covalent ligands capable of irreversibly attaching to the receptor active site(s) in conjunction with judiciously designed receptor mutants and detailed LC/MS/MS methods. To date, our results provide initial evidence that different classes of cannabinergic ligands interact and activate/deactivate the CB1 and CB2 receptors through distinct binding motifs. We have hypothesized that the individual binding motifs we have identified may be associated with distinct identifiable signaling pathway(s) leading to different ligand-dependent pharmacological profiles (functional selectivity/biased agonism). The project will provide the basis for the development of novel functionally selective CB1 and CB2 ligands and includes two complementary components. This project encompasses two components: 1) The first is a ligand development aspect which proposes the design and synthesis of novel high-affinity photoactivatable and electrophilic covalent ligands for CB1 and CB2 in which the reactive groups are strategically introduced in one (monofunctional) or two (bifunctional) sites within the parent ligand. Additionally, this component includes the design and synthesis of high-affinity reversible functionally distinct ligands and a lead optimization aspect for the design and synthesis of functionally selective CB2 agonists;2) In the second component strategically designed single and multiple site mutants of CB1 and CB2 (human and rodent) expressed in HEK293 cells will be used to test individual successful ligands for covalent attachment and for their functional properties using the cAMP assay as an initial screen (under the auspices of Core 2). Binding site characterization will be based on the complementary use of a) receptor mutants;and b) LC/MS/MS characterization of the specific amino acid residue(s) to which the ligand is attached using our LAPS methodology. The results and ligands produced under the auspices of this project will serve as a basis for the treatment of addiction and pain using novel medications with improved pharmacological profiles. This Project 1 will design and synthesize novel ligands to probe their interactions with the CB1 and CB2 cannabinoid receptors. The results can be used to develop improved medications for pain and addictive disorders.
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