TY - JOUR T1 - <em>N</em>-(Piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1<em>H</em>-pyrazole-3-carboxamide (SR141716A) Interaction with LYS 3.28(192) Is Crucial for Its Inverse Agonism at the Cannabinoid CB1 Receptor JF - Molecular Pharmacology JO - Mol Pharmacol SP - 1274 LP - 1287 DO - 10.1124/mol.62.6.1274 VL - 62 IS - 6 AU - Dow P. Hurst AU - Diane L. Lynch AU - Judy Barnett-Norris AU - Stephen M. Hyatt AU - Herbert H. Seltzman AU - Miao Zhong AU - Zhao-Hui Song AU - Jingjiang Nie AU - Deborah Lewis AU - Patricia H. Reggio Y1 - 2002/12/01 UR - http://molpharm.aspetjournals.org/content/62/6/1274.abstract N2 - In superior cervical ganglion neurons,N-(piperidiny-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716A) competitively antagonizes the Ca2+ current effect of the cannabinoid (CB) agonist (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone (WIN55212-2), and behaves as an inverse agonist by producing opposite current effects when applied alone. In contrast, in neurons expressing CB1 with a K→A mutation at residue 3.28(192) (i.e., K3.28A), SR141716A competitively antagonizes the effects of WIN55212-2, but behaves as a neutral antagonist by producing no current effects itself. Receptor modeling studies suggested that in the CB1 inactive (R) state, SR1417A16A stabilizes transmembrane helix 6 in its inactive conformation via aromatic stacking with F3.36/W6.48. In this binding site, SR141716A would exhibit higher affinity for CB1 R due to a hydrogen bond between the SR141716A C3 substituent and K3.28(192), a residue available to SR141716A only in R. To test this hypothesis, a “mutant thermodynamic cycle” was constructed that combined the evaluation of SR141716A affinity at WT CB1 and K3.28A with an evaluation of the wild-type CB1 and K3.28A affinities of an SR141716A analog, 5-(4-chlorophenyl)-3-[(E)-2-cyclohexylethenyl]-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole (VCHSR), that lacks hydrogen bonding potential at C3. Binding affinities suggested that K3.28 is involved in a strong interaction with SR141716A in WT CB1, but does not interact with VCHSR. Thermodynamic cycle calculations indicated that a direct interaction occurs between the C3 substituent of SR141716A and K3.28 in WT CB1. Consistent with these results, VCHSR acted as a neutral antagonist at WT CB1. These results support the hypothesis that hydrogen bonding of the SR141716A C3 substituent with K3.28 is responsible for its higher affinity for the inactive R state, leading to its inverse agonism. ER -