Discovery of a High Affinity, Selective and β-arrestin Biased 5-HT7R Agonist - Project Summary/Abstract: The 5-hydroxytryptamine 7 receptor (5-HT7R) is a member of the G protein- coupled 5-HT receptor family. Numerous studies have indicated that 5-HT7R plays a significant role in various behavioral and psychophysiological functions such as mood stability, cognitive and motor functions, behavioral inhibition, addictive behaviors, pain tolerance, sleep patterns, appetite, hormonal changes and thermoregulation. Pre-clinical findings have established the role of 5-HT7R in autism spectrum disorders, Fragile X syndrome (FXS), epilepsy, sleep disorders, neuropathic pain and migraine. Thus, 5-HT7R is emerging as a potential target for the treatment of various psychiatric and other associated disorders. Meanwhile, several 5-HT7R agonists, including AS-19, E-55888, LP-12, LP-44, LP-211, AGH-192 and compound 1g have been reported and their potential use in various CNS conditions (pain, memory and cognition), neuropathic pain, sleep disorders, alcohol and drug abuse are being investigated. However, the beneficial effects of activation or blockade of the 5-HT7R in each of these conditions is not often clearly established, primarily due to the lack of selective 5- HT7R agents. Even more critical is the absence of biased ligands that could clarify several controversial observations that relate to the 5-HT7R. Thus, our goal to design, synthesize and pharmacologically evaluate new agents with biased signaling towards G-Protein or β-arrestin signaling pathways hold great promise in understanding the 5-HT7R and its application to the treatment of various CNS disorders. There are three specific aims proposed in this application. Specific aim 1 will focus on extending our studies on the lead compounds (44080, 55933 and 57544) for their drug-like properties including brain penetration, pharmacokinetic studies, metabolic profiling, bioavailability assessments and cardiovascular toxicity predictions (HERG, 5-HT2BR). Based on the metabolic evaluations of lead compound 55933 from our preliminary studies, the synthesis and screening of new compounds is proposed in specific aim 2. This specific aim will also focus on the optimization and design of new agents to address the metabolic stability issues such as aromatization and glucuronidation observed in the preliminary studies. For this reason, aromatization susceptible tetrahydroisoquinoline (THI) moiety will be replaced with isoindoline which could not undergo aromatization and the CH2OH group will be replaced with substituents such as -F, -CONH2 to restrict glucuronidation while maintaining good drug-like characteristics. In addition, bioisosteric replacement of indanone with dihydronaphthalenone (DNO) moiety will be carried out. Furthermore, exploring the electron donating/withdrawing (σ values) and hydrophilic/hydrophobic (pi values) space around the THI/isoindoline ring systems with substituents such as Cl, OMe, CN, SOCH3 and NMe2, will reveal any improvements in their drug-like characteristics. Simultaneously, docking studies will be carried out using homology models to identify interactions with the key amino acid residues involved in inducing conformations associated with β-arrestin recruitment to the 5-HT7R. Specific Aim 3 will cover functional selectivity studies of lead 5-HT7R ligands for their agonist/antagonist properties and G-Protein or β-arrestin signaling bias followed by evaluation of their effect on sleep architecture and NREM/REM sleep pattern under in vivo conditions. Finally, selected test compounds will be compared with SB269970 (5-HT7R antagonist) and compound 1g, a 5-HT7R partial agonist (as a positive control) for their effect on NREM/REM sleep pattern and correlation of β-arrestin biased activity using a mice model.
