Reversal of Bortezomib-Induced Neurotoxicity by Suvecaltamide, a Selective T-Type Ca-Channel Modulator, in Preclinical Models

This study evaluated suvecaltamide, a selective T-type calcium channel modulator, on chemotherapy-induced peripheral neurotoxicity (CIPN) and anti-cancer activity associated with bortezomib (BTZ). Rats received BTZ (0.2 mg/kg thrice weekly) for 4 weeks, then BTZ alone (n = 8) or BTZ+suvecaltamide (3, 10, or 30 mg/kg once daily; each n = 12) for 4 weeks. Nerve conduction velocity (NCV), mechanical threshold, β-tubulin polymerization, and intraepidermal nerve fiber (IENF) density were assessed. Proteasome inhibition was evaluated in peripheral blood mononuclear cells. Cytotoxicity was assessed in human multiple myeloma cell lines (MCLs) exposed to BTZ alone (IC50 concentration), BTZ+suvecaltamide (10, 30, 100, 300, or 1000 nM), suvecaltamide alone, or vehicle. Tumor volume was estimated in athymic nude mice bearing MCL xenografts receiving vehicle, BTZ alone (1 mg/kg twice weekly), or BTZ+suvecaltamide (30 mg/kg once daily) for 28 days, or no treatment (each n = 8). After 4 weeks, suvecaltamide 10 or 30 mg/kg reversed BTZ-induced reduction in NCV, and suvecaltamide 30 mg/kg reversed BTZ-induced reduction in IENF density. Proteasome inhibition and cytotoxicity were similar between BTZ alone and BTZ+suvecaltamide. BTZ alone and BTZ+suvecaltamide reduced tumor volume versus the control (day 18), and BTZ+suvecaltamide reduced tumor volume versus BTZ alone (day 28). Suvecaltamide reversed CIPN without affecting BTZ anti-cancer activity in preclinical models.

Regulation of auditory fear discrimination by the novel Kv3 voltage-gated potassium channel modulator AUT00206

Psychiatric diseases like anxiety-related disorders and schizophrenia are characterized by impaired cognition and emotional regulation linked to corticolimbic disinhibition. Restoring the balance between excitation and inhibition in corticolimbic circuits may therefore ameliorate certain features of these disorders, such as inappropriately attributing affective salience to innocuous cues. Corticolimbic activity is tightly controlled by parvalbumin-expressing GABAergic interneurons, which also regulate fear discrimination. The voltage-gated potassium channels Kv3.1 and Kv3.2 are highly expressed in these neurons, therefore Kv3.1/3.2 modulation may have potential for treating disorders associated with cognitive and emotional dysregulation. We determined the effects of the novel Kv3.1/3.2 positive modulator AUT00206 on fear discrimination. Female rats underwent limited or extended auditory fear discrimination training that we previously showed leads to discrimination or generalization, respectively, based on passive fear responding (i.e. freezing). We also assessed darting as an active fear response. We found that limited training resulted in discrimination based on freezing, which was unaffected by AUT00206. In contrast, we found that extended training resulted in generalization based on freezing and the emergence of discrimination based on darting. Importantly, AUT00206 had dissociable effects on fear discrimination and expression with extended training. While AUT00206 mitigated generalization without affecting expression based on freezing, it reduced expression without affecting discrimination based on darting. Our results indicate that Kv3.1/3.2 modulation regulates the attribution of affective significance to threat- and safety-related cues in a response-specific manner. This suggests that targeting Kv3.1 and Kv3.2 channels may provide a promising avenue for treating cognitive and emotional dysregulation in psychiatric disease.

K2P channel C-type gating involves asymmetric selectivity filter order-disorder transitions

K2P potassium channels regulate cellular excitability using their selectivity filter (C-type) gate. C-type gating mechanisms, best characterized in homotetrameric potassium channels, remain controversial and are attributed to selectivity filter pinching, dilation, or subtle structural changes. The extent to which such mechanisms control C-type gating of innately heterodimeric K2Ps is unknown. Here, combining K2P2.1 (TREK-1) x-ray crystallography in different potassium concentrations, potassium anomalous scattering, molecular dynamics, and electrophysiology, we uncover unprecedented, asymmetric, potassium-dependent conformational changes that underlie K2P C-type gating. These asymmetric order-disorder transitions, enabled by the K2P heterodimeric architecture, encompass pinching and dilation, disrupt the S1 and S2 ion binding sites, require the uniquely long K2P SF2-M4 loop and conserved “M3 glutamate network,” and are suppressed by the K2P C-type gate activator ML335. These findings demonstrate that two distinct C-type gating mechanisms can operate in one channel and underscore the SF2-M4 loop as a target for K2P channel modulator development.

Characterisation of δ-Conotoxin TxVIA as a Mammalian T-Type Calcium Channel Modulator

The 27-amino acid (aa)-long δ-conotoxin TxVIA, originally isolated from the mollusc-hunting cone snail Conus textile, slows voltage-gated sodium (NaV) channel inactivation in molluscan neurons, but its mammalian ion channel targets remain undetermined. In this study, we confirmed that TxVIA was inactive on mammalian NaV1.2 and NaV1.7 even at high concentrations (10 µM). Given the fact that invertebrate NaV channel and T-type calcium channels (CaV3.x) are evolutionarily related, we examined the possibility that TxVIA may act on CaV3.x. Electrophysiological characterisation of the native TxVIA on CaV3.1, 3.2 and 3.3 revealed that TxVIA preferentially inhibits CaV3.2 current (IC50 = 0.24 μM) and enhances CaV3.1 current at higher concentrations. In fish bioassays TxVIA showed little effect on zebrafish behaviours when injected intramuscular at 250 ng/100 mg fish. The binding sites for TxVIA at NaV1.7 and CaV3.1 revealed that their channel binding sites contained a common epitope.