The Discovery and Characterization of ML218: A Novel, Centrally Active T-Type Calcium Channel Inhibitor with Robust Effects in STN Neurons and in a Rodent Model of Parkinson’s Disease

Abstract

T-type Ca2+ channel inhibitors hold tremendous therapeutic potential for the treatment of pain, epilepsy, sleep disorders, essential tremor and other neurological disorders; however, a lack of truly selective tools has hindered basic research, and selective tools from the pharmaceutical industry are potentially burdened with intellectual property (IP) constraints. Thus, an MLPCN high-throughput screen (HTS) was conducted to identify novel T-type Ca2+ channel inhibitors free from IP constraints, and freely available through the MLPCN, for use by the biomedical community to study T-type Ca2+ channels. While the HTS provided numerous hits, these compounds could not be optimized to the required level of potency to be appropriate tool compounds. Therefore, a scaffold hopping approach, guided by SurflexSim, ultimately afforded ML218 (CID 45115620) a selective T-Type Ca2+ (Cav3.1, Cav3.2, Cav3.3) inhibitor (Cav3.2, IC50 = 150 nM in Ca2+ flux; Cav3.2 IC50 = 310 nM and Cav3.3 IC50 = 270 nM, respectively in patch clamp electrophysiology) with good DMPK properties, acceptable in vivo rat PK and excellent brain levels. Electrophysiology studies in subthalamic nucleus (STN) neurons demonstrated robust effects of ML218 on the inhibition of T-Type calcium current, inhibition of low threshold spike and rebound burst activity. Based on the basal ganglia circuitry in Parkinson’s disease (PD), the effects of ML218 in STN neurons suggest a therapeutic role for T-type Ca2+ channel inhibitors, and ML218 was found to be orally efficacious in haloperidol-induced catalepsy, a preclinical PD model, with comparable efficacy to an A2A antagonist, a clinically validated PD target. ML218 proves to be a powerful new probe to study T-Type Ca2+ function in vitro and in vivo, and freely available.

Anatomical localization of Cav3.1 calcium channels and electrophysiological effects of T-type calcium channel blockade in the motor thalamus of MPTP-treated monkeys

“…Not surprisingly, local ML218 injections reduced the burst surprise values, the incidence of LTS-like bursts, and the proportion of spikes in rebound and LTS-like bursts. These results confirm previous findings about the effects of this drug on bursting activity in the rat STN (Tai et al 2011;Xiang et al 2011). As expected, ML218 did not strongly affect non-rebound bursting, suggesting that mechanisms other than T-type calcium channel activation may drive non-rebound bursting.…”

“…The attainment of a high drug concentration at the recording site is very important, because experiments in rodent-slice preparations and computer-modeling studies have suggested that robust LTS bursting can still be present when a large proportion (up to 70%) of T-type calcium channels is blocked (Broicher et al 2007;Dreyfus et al 2010). However, the concentration of ML218 used in our study (2.5 mM) was high compared with its effective concentrations at Ca v 3.3 and Ca v 3.2 channels found in in vitro electrophysiology [IC 50 of 270 and 310 nM, respectively (Xiang et al 2011)], making us confident that a very large proportion of the T-type calcium channels were, in fact, blocked in our experiments. Further confirmation comes from the fact that we saw, as expected, a reversal of many Parkinsonism-associated changes in parameters describing burst behaviors.…”

“…ML218 is a specific blocker of T-type calcium channels (Xiang et al 2011). Not surprisingly, local ML218 injections reduced the burst surprise values, the incidence of LTS-like bursts, and the proportion of spikes in rebound and LTS-like bursts.…”

“…Recently, a family of highly specific T-type calcium channel blockers has become available Xiang et al 2011;Yang et al 2008). The primary agent in this group, ML218, which blocks the three subtypes of T-type calcium channels, robustly inhibits low-threshold spike (LTS)-driven bursting and has anticataleptic properties in haloperidol-treated rats (Xiang et al 2011).…”

Inhibition of SOCE disrupts cytokinesis in zebrafish embryos via inhibition of cleavage furrow deepening

“…4C a-e), which also might be linked to an inhibition of SOCE. As SKF 96365 is also reported to block T-type Ca 2+ channels (Bomben and Sontheimer, 2008), we also tested the effect of a specific T-type Ca 2+ channel inhibitor, ML 218 (Xiang et al, 2011), and showed that cytokinesis progressed normally. The possible role of the two pore channel (TPC) in regulating cytokinesis via Ca 2+ release from lysosomes was also tested via the introduction of the specific TPC inhibitor, trans- Ned-19 (Naylor et al, 2009), and again we showed that cytokinesis was normal (Fig.…”