PIMSR is among the first neutral antagonists for the CB1R and was demonstrated pharmacologically to bind to the CB1R, yet not alter calcium flux. It was further shown computationally to be able to stabilize both the active and inactive states of CB1R revealing the molecular interactions that mechanistically afford the property of neutral antagonism. PIMSR shows dramatic positive effects in reducing weight, food intake, and adiposity as well as in improving glycemic control and lipid homeostasis in high-fat diet-induced obese mice, but also shows increased ALT and liver weight as markers of liver injury with chronic administration. Further, in a separate study, 3-day administration of PIMSR in C57BL/6J mice, hepatic steatosis from an acute administration of high of ethanol was significantly reduced. Also, it partially prevented alcohol-induced increases in ALT, AST, and LDH. The differences in ALT levels in obese and nonobese mice under different test paradigms are unlikely to be due to neutral antagonism itself since other neutral antagonists (AM6545) do not exhibit liver injury. The brain levels of low micromolar would support significant brain CB1 receptor occupancy (re: Ki = 17nM), thus potentially including both CNS and peripheral influences on the observed weight loss. Overall, these studies suggest that marked improvements in aspects of metabolic disease and alcoholic steatosis can be realized with CB1R neutral antagonists and hence warrants the exploration of further members of this class of cannabinoid ligands.
Metabolic profiling of CB1 neutral antagonists
Seltzman, H. H., Maitra, R., Bortoff, K., Henson, J., Reggio, P. H., Wesley, D., & Tam, J. (2017). Metabolic profiling of CB1 neutral antagonists: (Chapter 9). In PH. Reggio (Ed.), Cannabinoids and their receptors (1 ed., pp. 199-215). Elsevier Inc./Academic Press. Methods in Enzymology Vol. 593 https://doi.org/10.1016/bs.mie.2017.06.025