The synthesis of compounds derived from SR141716A, a potent antagonist of delta9-THC and cannabimimetics, may lead to the identification of unique antagonists, inverse agonists, as well as a new structural class of agonists. These efforts can also further our understanding of cannabinoid structure-activity relationships, facilitate our understanding of the cannabinoid neurochemical system and provide biochemical tools and potential medicinal agents relevant to drug abuse and to brain dysfunction.
The specific aims of the proposed research are based on results of studies conducted in our laboratory showing that analogs of SR141716A could be synthesized with unique characteristics: high affinity for cannabinoid receptors, and that are able to fully displace [3H]CP55940 and [3H]SR141716A with reasonable affinity, while simultaneously much less able, or unable, to displace [3H]WIN55212-2. In addition, we have evidence to suggest that because of this binding selectivity, these compounds possess a unique profile of pharmacological activity. These results suggest that it might be necessary to change current paradigms of cannabinoid ligand-receptor interaction, and this could lead to innovative approaches to investigating, and manipulating the pharmacology of cannabinoids. The diverse structures of compounds generated to date appear amenable to three dimensional structure-activity relationship analyses, which serves as a paradigm for the further design, synthesis and testing of the structural requirements of this class of compounds in an iterative fashion. Compounds intended for synthesis comprise a systematic structural modification of each substituent position of the pyrazole nucleus and also include alternative pyrazole, imidazoles and pyrazolo [l,5-f] phenanthridine ring systems where the substituents may or may not maintain the original spacial relationships in SR141716A. Bivalent ligands derived from SR141716A are also proposed, and we believe this represents the first synthesis of bivalent ligands to probe for CB1 oligomerization. Pharmacological assays to evaluate these analogs will continue to include a comparative receptor binding assay with [3H]SR141716A, [3H]CP55940 and [3H]WIN55212-2 in human and rat brain preparations and transfected cell lines expressing CB1 or CB2 receptors to establish each compounds affinity and selectivity. An accepted signal transduction assay using GTP-gamma-[35S] will be performed on selected compounds to characterize their efficacy and ability to antagonize other cannabimimetic ligands, particularly CP55940 and WIN55212-2. Analogs of highest interest will also be tested in isolated tissues (mouse vas deferens and guinea pig ileum) and in vivo in the mouse and rat to identify compounds with in situ and in vivo activity.
