Bioisosteric Modification of To042: Synthesis and Evaluation of Promising Use‐Dependent Inhibitors of Voltage‐Gated Sodium Channels

Abstract

Three analogues of To042, a tocainide‐related lead compound recently reported for the treatment of myotonia, were synthesized and evaluated in vitro as skeletal muscle sodium channel blockers possibly endowed with enhanced use‐dependent behavior. Patch‐clamp experiments on hNav1.4 expressed in HEK293 cells showed that N‐[(naphthalen‐1‐yl)methyl]‐4‐[(2,6‐dimethyl)phenoxy]butan‐2‐amine, the aryloxyalkyl bioisostere of To042, exerted a higher use‐dependent block than To042 thus being able to preferentially block the channels in over‐excited membranes while preserving healthy tissue function. It also showed the lowest active transport across BBB according to the results of P‐glycoprotein (P‐gp) interacting activity evaluation and the highest cytoprotective effect on HeLa cells. Quantum mechanical calculations and dockings gave insights on the most probable conformation of the aryloxyalkyl bioisostere of To042 in solution and the target residues involved in the binding, respectively. Both approaches indicated the conformations that might be adopted in both the unbound and bound state of the ligand. Overall, N‐[(naphthalen‐1‐yl)methyl]‐4‐[(2,6‐dimethyl)phenoxy]butan‐2‐amine exhibits an interesting toxico‐pharmacological profile and deserves further investigation.

hERG stereoselective modulation by mexiletine‐derived ureas: Molecular docking study, synthesis, and biological evaluation

“…The cytotoxic effect was assessed by the 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT) test (Figure 7) on the human neuroblastoma (SH-SY5Y) cell line which was used to predict possible neural toxicity of our compounds being known that mexiletine clinical use is often associated with CNS toxicity. [16,19] Mexiletine was found to be nontoxic, showing an IC 50 value >100 μM, which is consistent with its current use as a drug. The IC 50 b Calculated from log concentration-response curves (Probit analysis according to Litchfield and Wilcoxon [50] with n = 6-8).…”

“…The cytotoxic effect was assessed by the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) test (Figure 7) on the human neuroblastoma (SH‐SY5Y) cell line which was used to predict possible neural toxicity of our compounds being known that mexiletine clinical use is often associated with CNS toxicity. [ 16,19 ]…”

“…[12,13] Therefore, they are potentially useful for the treatment of both congenital and druginduced forms of long QT syndrome (LQTS), [12] a cardiovascular disorder characterized by abnormal cardiac repolarization, leading to a prolonged QT interval and T-wave irregularities on the surface electrocardiogram (ECG), and responsible for a concomitant risk of Torsade de Pointes, a well-known potentially life-threatening arrhythmia. [14,15] Starting from the consideration that mexiletine-a wellknown voltage-gated sodium channel blocking agent clinically useful as class Ib antiarrhythmic and antimyotonic agent [16][17][18][19][20] -can reverse the action potential prolongation in patients with LQTS, [21][22][23][24][25][26] and in analogy with the urea-based hERG potassium channel activators, we recently described an asymmetric mexiletine urea [(R,R)-1,3-bis [1-(2,6-dimethylphenoxy)propan-2-yl]urea, MC450, Figure 1], which shared some structure and electrophysiological features with the "Type 2" activators of the hERG potassium channel. [27] It mainly acts on the inactivation mechanism of the channel unlike "Type 1" activators that slow the rate of channel deactivation.…”

Development of Riluzole Analogs with Improved Use-Dependent Inhibition of Skeletal Muscle Sodium Channels

“…The most interesting compound ( 14 ), while being slightly less potent than the reference compound ( 1 ), showed greater use-dependent Nav1.4 blocking activity; thus, it might be more useful than the parent compound in conditions involving pathological hyperexcitability, such as myotonic syndromes. Indeed, use-dependence in vivo allows a selective block of sodium channels in pathologic tissues, thus preserving healthy ones where channel block would instead cause undesired off-target effects . It was also evaluated in an in vitro model of myotonia, where it was only slightly less potent than riluzole in reducing action potential firing, thus confirming the results obtained in vitro.…”

“…Indeed, use-dependence in vivo allows a selective block of sodium channels in pathologic tissues, thus preserving healthy ones where channel block would instead cause undesired off-target effects. 31 It was also evaluated in an in vitro model of myotonia, where it was only slightly less potent than riluzole in reducing action potential firing, thus confirming the results obtained in vitro.…”