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

BACKGROUND AND PURPOSE Voltage-gated calcium channels are involved in peripheral and central nervous system nociception. N-type (Cav2.2) and T-type (Cav3.1, Cav 3.2 and Cav 3.3) voltage-gated calcium channels are particularly important in studying and treating pain and epilepsy. EXPERIMENTAL APPROACH 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 Cav1.2, Cav1.3, Cav2.1, Cav2.2, Cav2.3, Cav3.1, Cav3.2 and Cav3.3. KEY RESULTS MONIRO-1 was 5-20-fold more potent at inhibiting human T-type calcium channels, hCav3.1, hCav3.2 and hCav3.3 (IC50: 3.3 ± 0.3 μM, 1.7 ± 0.1 μM, and 7.2 ± 0.3 μM, respectively) than N-type calcium channel, hCav2.2 (IC50: 34.0 ± 3.6 μM). It interacts with L-type calcium channels Cav1.2 and Cav1.3 with significantly lower potency (IC50 >100 μM), and does not inhibit hCav2.1 or hCav2.3 at concentrations as high as 100 μM. Interestingly, state- and use-dependent inhibition of hCav2.2 was observed, whereas stronger inhibition occurred at high stimulation frequencies for hCav3.1 suggesting a different mode of action between these two channels. CONCLUSIONS AND IMPLICATIONS 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 hCav2.2 and hCav3.1, 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.