(4-(Bis(4-Fluorophenyl)Methyl)Piperazin-1-yl)(Cyclohexyl)Methanone Hydrochloride (LDK1229): A New Cannabinoid CB1Receptor Inverse Agonist from the Class of Benzhydryl Piperazine Analogs

Some inverse agonists of cannabinoid receptor type 1 (CB₁) have been demonstrated to be anorectic antiobesity drug candidates. However, the first generation of CB₁ inverse agonists, represented by rimonabant (SR141716A), otenabant, and taranabant, are centrally active, with a high level of psychiatric side effects. Hence, the discovery of CB₁ inverse agonists with a chemical scaffold distinct from these holds promise for developing peripherally active CB₁ inverse agonists with fewer side effects. We generated a new CB₁ inverse agonist, (4-(bis(4-fluorophenyl)methyl)piperazin-1-yl)(cyclohexyl)methanone hydrochloride (LDK1229), from the class of benzhydryl piperazine analogs. This compound binds to CB₁ more selectively than cannabinoid receptor type 2, with a K_i value of 220 nM. Comparable CB₁ binding was also observed by analogs 1-[bis(4-fluorophenyl)methyl]-4-cinnamylpiperazine dihydrochloride (LDK1203) and 1-[bis(4-fluorophenyl)methyl]-4-tosylpiperazine hydrochloride (LDK1222), which differed by the substitution on the piperazine ring where the piperazine of LDK1203 and LDK1222 are substituted by an alkyl group and a tosyl group, respectively. LDK1229 exhibits efficacy comparable with SR141716A in antagonizing the basal G protein coupling activity of CB₁, as indicated by a reduction in guanosine 5′-O-(3-thio)triphosphate binding. Consistent with inverse agonist behavior, increased cell surface localization of CB₁ upon treatment with LDK1229 was also observed. Although docking and mutational analysis showed that LDK1229 forms similar interactions with the receptor as SR141716A does, the benzhydryl piperazine scaffold is structurally distinct from the first-generation CB₁ inverse agonists. It offers new opportunities for developing novel CB₁ inverse agonists through the optimization of molecular properties, such as the polar surface area and hydrophilicity, to reduce the central activity observed with SR141716A.