The long-range goal of the proposed research is to develop potential treatment medications for nicotine addiction. Our first strategy is to develop partial agonists and antagonists that act at the orthosteric site of nicotinic receptors. Our second strategy is to develop negative allosteric modulators for nicotinic receptors that may provide a pharmacological profile different from that of orthosteric ligands. Our discovery that ligands for the PCP (non-NMDA) second site acted as negative allosteric modulators at nicotinic receptors served as the basis for proposing a synthetic and evaluation program for hexahydroindeno[1,2]- pyrrole, tetrahydro-2,5-methano-2H-benzazepine, and tetrahydro-2,5-methano-1H-2-benzazepine analogs. This project's hypothesis is that a successful smoking cessation pharmacotherapy would at least include partial activating or blocking action (direct or indirect) at a4b2 nAChR subtypes. The orthosteric synthetic pro- gram's goal is to develop analogs with a wide range of efficacies to include partial agonists to pure antagonists. Our general approach will be to synthesize and evaluate epibatidine analogs for their ability to compete with [3H]epibatidine (a4b2* like-nAChR) and [125I]iodo-MLA binding (a7 like-nAChR) in rat brain. Analogs meeting criteria will be evaluated in vivo in a mouse, and those exhibiting specific criteria will be evaluated further in physical withdrawal and reward models (conditioned place preference and self-administration). Selected analogs will be evaluated in rat self-administration models. Interesting analogs will be evaluated in oocytes for receptor efficacy and selectivity at various nAChRs. A slightly modified approach will be required for allosteric modulators since they will not compete directly with [3H]epibatidine and [125I]iodo-MLA binding. Rather, they will be evaluated initially for their ability to alter ACh effects in oocytes containing a4b2, a3b4, and a7 nAChRs. Competitive Revision: It has not been possible to explain the pharmacological results from the various in vivo tests with the results obtained from the in vitro nAChR binding and efficacy assay results of many previously studied compounds. This supplement is to increase the scope of our studies by developing an a6b2* nAChR dopamine release efficacy assay and evaluating a number of previously prepared compounds and all new target compounds in this a6b2* assay. The results will allow us to better explain some of the in vivo results from previously studied compounds and to better prioritize new compounds for in vivo studies in the future. If this increase in the scope of our studies leads to potent and selective a6b2* nAChR ligands, these new ligands will be a valuable pharmacological tool not only for our research but that of other investigators studying the nAChRs as well.
In 2004, an estimated 46 million Americans were cigarette smokers. Even though most smokers want to quit, only about 3% can do so without the use of other intervention. Since smoking is associated with cancer, cardiovascular disease, cerebral vascular disease, chronic obstructive airway disease, and pregnancy complications, development of new and better pharmacotherapies to treat smokers would be tremendously beneficial to society. This application addresses this problem by proposing studies to develop competitive antagonists and partial agonists as well as allosteric modulators of nicotinic acetylcholine receptors as new pharmacotherapies to treat smokers.
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