Polynitrogen-containing compounds as multi-target sEH/FAAH inhibitors: Structure-activity relationship and pharmacological studies

Both soluble epoxide hydrolase (sEH) and fatty acid amide hydrolase (FAAH) are involved in degradation of anti-inflammatory and antinociceptive lipids, thus inhibition of these enzymatic pathways represents a novel strategy in the discovery of non-opioid drugs for treating inflammatory pain. We previously discovered several multi-targeted designed ligands and described a pharmacophore necessary for inhibition of both sEH and FAAH. The potential for optimization on the left side of the pharmacophore led us to exploration of different heterocyclic moieties with the hope to keep strong inhibition potencies, but to increase the metabolic stability and solubility of new analogs. Eighteen analogs containing various substituted and unsubstituted pyrimidinyl-, quinoxalinyl- and tetrazolyl- rings are synthesized and tested for inhibition potency in human FAAH, and human, rat and mouse sEH. The structure-activity relationship study revealed quinoxalinyl- analog 4 m, the most potent dual inhibitor reported to date, with IC₅₀ values of 2.9 nM in human FAAH and 0.7 nM, 39.1 nM and 0.3 nM in human, mouse and rat sEH, respectively. 4 m showed no binding to opioid and most serotonin receptors and was tested in the human, mouse and rat liver microsomes stability assays where it exhibited good and/or moderate clearance rates. Lastly, we evaluated 4 m in vivo in a wheel running assay to determine its effects on voluntary locomotor behavior. Both 4 m and the traditional opioid morphine exhibited significant depression of wheel running after intraperitoneal administration indicating that 4 m may produce undesirable behavioral effects, which will be the basis for future studies.