Modulation of Monoacylglycerol Lipase Using Isothiazolinone-Based Inhibitors

Δ⁹-tetrahydrocannabinol (THC) is the active ingredient in cannabis plant, from which the name of a class of lipid neurotransmitters, the endocannabinoids, was developed. Endocannabinoids are derived from phospholipids within the cell membrane. Two main endocannabinoids in the body, anandamide and 2-arachidonoyl-sn-glycerol (2-AG), bind to type-1 cannabinoid (CB₁) receptors on nerve cells, regulating emotion, pain, inflammation, memory and energy balance (DiPatrizio and Piomelli, 2012). Monoacylglycerol lipase (MGL) is a serine hydrolase that inactivates 2-AG through hydrolysis. Therefore, inhibitors of MGL increase 2-AG levels and promote CB₁ receptor activation, which might be therapeutically effective in pain and other conditions. A previous study in our laboratory discovered that an isothiazolinone-based compound, octhilinone, is a reversible inhibitor for MGL with nanomolar potency: IC₅₀= 88 ± 12 nM (King et al., 2009). Although very potent, octhilinone was not selective; therefore in this study, new benzisothiazolinone-based compounds were designed and screened for MGL inhibition in hopes of finding a more selective drug. To test the potency of the new compounds, an MGL activity assay was conducted in vitro using recombinant MGL from overexpressed Hela cell homogenates and 2-oleoyl-sn-glycerol (2-OG) as substrate. Lipid extracts were analyzed for the product of 2-OG hydrolysis, oleic acid, by high-performance liquid chromatography-mass spectrometry (LC-MS). Two new compounds were found to have nanomolar potency comparable to octhilinone. In the future, in vivo and structural activity relationship studies will be performed for drug characterization and understanding the mechanism of action.