Inhibition of human N‐ and T‐type calcium channels by an ortho‐phenoxyanilide derivative, MONIRO‐1

Jeffrey R McArthur, Leonid Motin, Ellen C Gleeson, Sandro Spiller, Richard J Lewis, Peter J Duggan, Kellie L Tuck, David J Adams

Voltage-gated calcium channels are involved in peripheral and central nervous system nociception. N-type (Cav 2.2) and T-type (Cav 3.1, Cav 3.2 and Cav 3.3) voltage-gated calcium channels are particularly important in studying and treating pain and epilepsy. In this study, whole-cell patch clamp electrophysiology was used to assess the potency and mechanism of action of a novel ortho-phenoxylanilide derivative, MONIRO-1, against a panel of voltage-gated calcium channels including Cav 1.2, Cav 1.3, Cav 2.1, Cav 2.2, Cav 2.3, Cav 3.1, Cav 3.2 and Cav 3.3. MONIRO-1 was 5-20-fold more potent at inhibiting human T-type calcium channels, hCav 3.1, hCav 3.2 and hCav 3.3 (IC50 : 3.3 ± 0.3 μM, 1.7 ± 0.1 μM, and 7.2 ± 0.3 μM, respectively) than N-type calcium channel, hCav 2.2 (IC50 : 34.0 ± 3.6 μM). It interacts with L-type calcium channels Cav 1.2 and Cav 1.3 with significantly lower potency (IC50 >100 μM), and does not inhibit hCav 2.1 or hCav 2.3 at concentrations as high as 100 μM. Interestingly, state- and use-dependent inhibition of hCav 2.2 was observed, whereas stronger inhibition occurred at high stimulation frequencies for hCav 3.1 suggesting a different mode of action between these two channels. Selectivity, potency, reversibility and multi-modal effects distinguish MONIRO-1 from other small molecule inhibitors acting on Cav channels involved in pain and/or epilepsy pathways. For both hCav 2.2 and hCav 3.1, high frequency firing increases the affinity for MONIRO-1 for both channels. Such Cav channel modulators have potential clinical use in the treatment of epilepsies, neuropathic pain and other nociceptive pathophysiologies.