Novel selective and metabolically stable inhibitors of anandamide cellular uptake

Novel aromatic analogues of N-oleoylethanolamine and N-arachidonoylethanolamine (anandamide, AEA) were synthesized and, based on the capability of similar compounds to interact with proteins of the endocannabinoid and endovanilloid signaling systems, were tested on: (i) cannabinoid CB(1) and CB(2) receptors; (ii) vanilloid VR1 receptors; (iii) anandamide cellular uptake (ACU); and (iv) the fatty acid amide hydrolase (FAAH). The (R)- and, particularly, the (S)-1'-(4-hydroxybenzyl) derivatives of N-oleoylethanolamine and AEA (OMDM-1, OMDM-2, OMDM-3, and OMDM-4) inhibited to a varied extent ACU in RBL-2H3 cells (K(i) ranging between 2.4 and 17.7 micro M), the oleoyl analogues (OMDM-1 and OMDM-2, K(i) 2.4 and 3.0 micro M, respectively) being 6- to 7-fold more potent than the arachidonoyl analogues (OMDM-3 and OMDM-4). These four compounds exhibited: (i) poor affinity for either CB(1) (K(i)> or = 5 micro M) or CB(2) (K(i)>10 micro M) receptors in rat brain and spleen membranes, respectively; (ii) almost no activity at vanilloid receptors in the intracellular calcium assay carried out with intact cells over-expressing the human VR1 (EC(50)> or = 10 micro M); and (iii) no activity as inhibitors of FAAH in N18TG2 cell membranes (K(i)>50 micro M). The oleoyl- and arachidonoyl-N'-(4-hydroxy-3-methoxybenzyl)hydrazines (OMDM-5 and OMDM-6), inhibited ACU (K(i) 4.8 and 7.0 micro M, respectively), and were more potent as VR1 agonists (EC(50) 75 and 50nM, respectively), weakly active as CB(1) receptor ligands (K(i) 4.9 and 3.2 micro M, respectively), and inactive as CB(2) ligands (K(i)>5 micro M) as well as on FAAH (K(i)> or = 40 micro M). In conclusion, we report two novel potent and selective inhibitors of ACU (OMDM-1 and OMDM-2) and one "hybrid" agonist of CB(1) and VR1 receptors (OMDM-6). Unlike other compounds of the same type, OMDM-1, OMDM-2, and OMDM-6 were very stable to enzymatic hydrolysis by rat brain homogenates.