TY - JOUR T1 - Structure-activity Relationship of Fenamates as Slo2.1 Channel Activators JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.112.079194 SP - mol.112.079194 AU - Priyanka Garg AU - Michael C. Sanguinetti Y1 - 2012/07/31 UR - http://molpharm.aspetjournals.org/content/early/2012/07/31/mol.112.079194.abstract N2 - Niflumic acid, 2-{[3-(trifluoromethyl)phenyl]amino}pyridine-3-carboxylic acid (NFA), a nonsteroidal anti-inflammatory drug that blocks cyclooxygenase (COX), was previously shown to activate [Na+]i-regulated Slo2.1 channels. Here we report that other fenamates, including flufenamic acid, mefenamic acid, tolfenamic acid, meclofenamic acid and a phenyl acetic acid derivative, diclofenac are also low potency (EC50 = 80 μM to 2.1 mM), partial agonists of human Slo2.1 channels heterologously expressed in Xenopus oocytes. Substituent analysis determined that N-phenylanthranilic acid was the minimal pharmacophore for fenamate activation of Slo2.1 channels. The effects of fenamates were biphasic, with an initial rapid activation phase followed by a slow phase of current inhibition. Ibuprofen, a structurally dissimilar COX inhibitor, did not activate Slo2.1. Pre-incubation of oocytes with ibuprofen did not significantly alter the effects of NFA, suggesting that neither channel activation nor inhibition is associated with COX activity. A point mutation (A278R) in the pore-lining S6 segment of Slo2.1 increased the sensitivity to activation and reduced the inhibition induced by NFA. Together our results suggest that fenamates bind to two sites on Slo2.1 channels: an extracellular accessible site to activate, and a cytoplasmic accessible site in the pore to inhibit currents. ER -