State-dependent properties of a new T-type calcium channel blocker enhance CaV3.2 selectivity and support analgesic effects

Abstract

T-type calcium channels encoded by the Ca(V)3.2 isoform are expressed in nociceptive primary afferent neurons where they contribute to hyperalgesia and thus are considered as a potential therapeutic target to treat pathological pain. Here we report that the small organic state-dependent T-type channel antagonist TTA-A2 efficiently inhibits recombinant and native Ca(V)3.2 currents. Although TTA-A2 is a pan Ca(V)3 blocker, it demonstrates a higher potency for Ca(V)3.2 compared to Ca(V)3.1. TTA-A2 selectivity for T-type currents was demonstrated in sensory neurons where it lowered cell excitability uniquely on neurons expressing T-type channels. In vivo pharmacology in Ca(V)3.2 knockout and wild type mice reveal that TTA-A2-mediated antinociception critically depends on Ca(V)3.2 expression. The pathophysiology of irritable bowel syndrome (IBS) was recently demonstrated to involve Ca(V)3.2 in a rat model of this disease. Oral administration of TTA-A2 produced a dose-dependent reduction of hypersensitivity in an IBS model, demonstrating its therapeutic potential for the treatment of pathological pain. Overall, our results suggest that the high potency of TTA-A2 in the depolarized state strengthen its analgesic efficacy and selectivity toward pathological pain syndromes. This characteristic would be beneficial for the development of analgesics targeting T-type channels, in particular for the treatment of pain associated with IBS.

Cross-Modulation and Molecular Interaction at the Cav3.3 Protein between the Endogenous Lipids and the T-Type Calcium Channel Antagonist TTA-A2.

“…As observed with endogenous lipids, TTA-A2 inhibited the Ca v 3 current at physiologic HP but not at very negative potentials (i.e., 2110 mV) (Kraus et al, 2010;Francois et al, 2013). Furthermore, as observed with endogenous lipids, TTA-A2 induced a negative shift in the steadystate inactivation properties of Ca v 3 current and slowed their recovery from inactivation (Kraus et al, 2010;Francois et al, 2013). It should be noted that several other structurally unrelated T-channel inhibitors, including mibefradil, flunarizine, and pimozide, which also exhibit similar state-dependent inhibition of T-currents (Martin et al, 2000;Santi et al, 2002), were shown to interact with [ 3 H]TTA-A1 binding to membranes containing Ca v 3.3 (Uebele et al, 2009b).…”

“…Recently, TTA-A2, a potent and specific synthetic inhibitor of T-current, was described (Uebele et al, 2009a,b;Kraus et al, 2010;Reger et al, 2011). As observed with endogenous lipids, TTA-A2 inhibited the Ca v 3 current at physiologic HP but not at very negative potentials (i.e., 2110 mV) (Kraus et al, 2010;Francois et al, 2013). Furthermore, as observed with endogenous lipids, TTA-A2 induced a negative shift in the steadystate inactivation properties of Ca v 3 current and slowed their recovery from inactivation (Kraus et al, 2010;Francois et al, 2013).…”

“…In vivo studies have demonstrated that TTA-A2 reduces absence epilepsy seizures (Uebele et al, 2009b;Reger et al, 2011), pain perception (Francois et al, 2013), nicotine selfadministration (Uslaner et al, 2010), and weight gain (Uebele et al, 2009a), and it ameliorates the sleep quality (Uebele et al, 2009a;Kraus et al, 2010;Reger et al, 2011) and displays antipsychotic properties (Uslaner et al, 2012).…”

The Physiology, Pathology, and Pharmacology of Voltage-Gated Calcium Channels and Their Future Therapeutic Potential

“…A series of compounds that combine the carbazole core of NMP-7 and features of Z944 also mediate potent Ca V 3 channel inhibition without off-target effects on cannabinoid receptors and with efficacy in several in vivo models of pain (Bladen et al, 2015). Another series of compounds that incorporates features of Z944 includes TTA-A2 [(R)-2-(4-cyclopropylphenyl)-N-(1-(5-(2,2,2-trifluoroethoxy) pyridin-2-yl)ethyl) acetamide] and TTA-P2 [3,5-dichloro-N-[1-(2,2-dimethyl-tetrahydro-pyran-4-ylmethyl)-4-fluoro-piperidin-4-ylmethyl]-benzamide] (Choe et al, 2011;Francois et al, 2013), both of which mediate state-dependent inhibition of T-type currents with a preference for Ca V 3.2. TTA-A2 increased sleep and prevented high-fat diet-induced weight gain in mice (Uebele et al, 2009).…”

Paracetamol: Update on its Analgesic Mechanism of Action

“…Silencing of Cav3.2 using oligonucleotide antisense [33], knockout mice [34], or pharmacological tools [35] resulted in impairment of pain in several pain tests, thereby confirming the strong role of this calcium channel in nociception. Because AM404 is the arachidonicrelated metabolite of paracetamol, the role of Cav3.2 in paracetamol action was investigated [30].…”