The Current Status and Future Perspectives of Studies of Cannabinoid Receptor 1 Antagonists as Anti-Obesity Agents

Since the discovery of rimonabant (Acomplia: 1), a large effort has been directed at the discovery of new, potent and selective CB1R antagonists that serve as anti obesity drugs. As a result, a number of compounds reached various stages of clinical trials by late 2008. However, the announcement by Sanofi-Aventis that they were discontinuing all ongoing trials with rimonabant, as a result of the finding that risks associated with depression and anxiety outweighed its benefits, had a major impact on this area. A wave of terminations of programs targeting the development of CB1R blockers for treatment of obesity ensued. However, abandoning this CB1R therapeutic target for anti-obesity drug development seems to be premature, since there are a number of potential approaches have been uncovered to circumvent the problems of the current agents. In this review, we summarize advances that have been made and the status of studies of a diverse array of CB1R antagonists that have been identified mainly based on modifications of the first-in-class CB1R antagonist, rimonabant. Various approaches have been employed to design these analogs, such as bioisosteric replacement, introduction of conformational constraints, scaffold hopping and ligand-based molecular modeling. In addition, current approaches that have been uncovered to avoid psychiatric side effects of CB1R antagonists are summarized. Finally, the design of non-brain penetrating and peripherally acting CB1R antagonists, allosteric modulators of CB1R, and neutral antagonists for CB1R is also discussed in this review.