Voltage-gated sodium channel blockers as antimyotonic and antiarrhythmic agentsAuthor(s): Alessia Carocci
Voltage-gated sodium channel blockers are clinically used in several disorders of membrane excitability including cardiac arrhythmias, epileptic seizures, pain and myotonia. The safety of these drugs relies on their ability to block sodium channels in a frequency-dependent manner, allowing a selective inhibition of over excited cells while sparing the healthy organs. Among them mexiletine is an antiarrhythmic drug belonging to class IB. Besides its well-known antiarrhythmic activity, its usefulness in the treatment of skeletal muscle channelopathy, as myotonia, which are rare human genetic diseases, is now widely recognized. Mexiletine has been recently appointed as an orphan-drug in myotonic-syndromes. Nevertheless, it has been discontinued in many countries because of its side effects. Consequently, numerous attempts have been made in recent years to develop an alternative to mexiletine, including the design of new analogues that offer the same pharmacological effect but without the unwanted side effects. In the past decade, my research group has been focusing on the development of mexiletine and its relative, tocainide, analogues that helped to clarify the structural requirements for ameliorating the therapeutic profile, in terms of potency and use-dependent block of myofiber sodium currents. As these identified compounds were more potent channel blockers than the parent compounds, they have been proposed as mexiletine alternatives for the treatment of myotonia. Furthermore, compounds with a dual action as voltage-gated sodium channel blockers and anti-oxidants have been identified, that may have an interesting therapeutic action in degenerating myopathies in which the alteration of excitation-contraction coupling is accompanied by chronic inflammatory state and unbalanced oxidative stress. Some of these compounds showed also a better antiarrhythmic activity along with the same or less cardiovascular effects than mexiletine, thus presenting a higher selectivity of action and reduced side effects. Herein the results of this study will be presented.