The neuronal calcium ion channel activity of constrained analogues of MONIRO-1.

Structural modifications of the neuronal calcium channel blocker MONIRO-1, including constraining the phenoxyaniline portion of the molecule and replacing the guanidinium functionality with tertiary amines, led to compounds with significantly improved affinities for the endogenously expressed CaV2.2 channel in the SH-SY5Y neuroblastoma cell line. These analogues also showed promising activity towards the CaV3.2 channel, recombinantly expressed in HEK293T cells. Both of these ion channels have received attention as likely targets for the treatment of neuropathic pain. The dibenzoazepine and dihydrobenzodiazepine derivatives prepared in this study show an encouraging combination of neuronal calcium ion channel inhibitory potency, plasma stability and potential to cross the blood-brain-barrier.

N-Sulfonylphenoxazines as neuronal calcium ion channel blockers.

Neuropathic pain is a type of chronic pain, usually caused by nerve damage, that responds poorly to traditional pain therapies. The N-type calcium channel (CaV2.2) is a well-validated pharmacological target to treat this condition. In order to further improve the inhibition of the N-type calcium channel relative to previously described inhibitors, and also address their problematic instability in blood plasma, the development of N-sulfonylphenoxazines as new calcium channel inhibitors was pursued. A series of N-sulfonylphenoxazines bearing ammonium side chains were synthesised and tested for their ability to inhibit both CaV2.2 and CaV3.2 (T-type) neuronal ion channels. Compounds with low micromolar activity in CaV2.2 were identified, equivalent to the most effective reported for this class of bioactive, and calculations based on their physical and chemical characteristics suggest that the best performing compounds have a high likelihood of being able to penetrate the blood-brain barrier. Representative N-sulfonylphenoxazines were tested for their stability in rat plasma and were found to be much more resilient than the previously reported N-acyl analogues. These compounds were also found to be relatively stable in an in vitro liver microsome metabolism model, the first time that this has been investigated for this class of compound. Finally, molecular modelling of the CaV2.2 channel was used to gain an understanding of the mode of action of these inhibitors at a molecular level. They appear to bind in a part of the channel, in and above its selectivity filter, in a way that hinders its ability to undergo the conformational changes required to open and allow calcium ions to pass through.

Inhibition of N-type calcium ion channels by tricyclic antidepressants - experimental and theoretical justification for their use for neuropathic pain.

A number of tricyclic antidepressants (TCAs) are commonly prescribed off-label for the treatment of neuropathic pain. The blockade of neuronal calcium ion channels is often invoked to partially explain the analgesic activity of TCAs, but there has been very limited experimental or theoretical evidence reported to support this assertion. The N-type calcium ion channel (CaV2.2) is a well-established target for the treatment of neuropathic pain and in this study a series of eleven TCAs and two closely related drugs were shown to be moderately effective inhibitors of this channel when endogenously expressed in the SH-SY5Y neuroblastoma cell line. A homology model of the channel, which matches closely a recently reported Cryo-EM structure, was used to investigate via docking and molecular dynamics experiments the possible mode of inhibition of CaV2.2 channels by TCAs. Two closely related binding modes, that occur in the channel cavity that exists between the selectivity filter and the internal gate, were identified. The TCAs are predicted to position themselves such that their ammonium side chains interfere with the selectivity filter, with some, such as amitriptyline, also appearing to hinder the channel's ability to open. This study provides the most comprehensive evidence to date that supports the notion that the blockade of neuronal calcium ion channels by TCAs is at least partially responsible for their analgesic effect.