Identification of dual role of piperazine-linked phenyl cyclopropyl methanone as positive allosteric modulator of 5-HT 2C and negative allosteric modulator of 5-HT 2B receptors.

Allosteric modulators of G-protein-coupled receptors have lately gained significant traction in drug discovery. Recent studies have shown that allosteric modulation of serotonin 2C receptor (5-HT _2C ) as a viable strategy for the treatment of various central nervous system (CNS) disorders. Considering the critical role of 5-HT _2C in the modulation of appetite, a selective positive allosteric modulator (PAM) of 5-HT _2C offers a new opportunity for anti-obesity therapeutic development. In this study, phenyl cyclopropyl-linked N-heterocycles were synthesized and evaluated at 5-HT _2C for agonist and PAM activity. Our study shows that imidazole linked phenyl cyclopropyl methanones has PAM activity on both 5-HT _2C and serotonin 2B receptor (5-HT _2B ). Interestingly, piperazine linked phenyl cyclopropyl methanones (58) was active as PAM of 5-HT _2C (increased the E _max of 5-HT to 139%), and as negative allosteric modulator (NAM) of 5-HT _2B (decreases EC ₅₀ of 5-HT 10 times without affecting E _max ). Similar effect of compound 58 was observed with synthetic orthosteric agonist lorcaserin on 5-HT _2B . Molecular docking study revealed that all active compounds were binding to the predicted allosteric site on 5-HT _2C and shared a common interacting residues. Finally, compound 58 suppressed food intake in Sprague Dawley (SD) rats similar to lorcaserin after i.c.v. administration. Therefore, these results suggest that piperazine moiety is essential for dual activity (PAM & NAM) of compounds 58, and supports the hypothesis of 5-HT _2C PAM for the treatment of obesity similar to the full agonist.
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