title: Increased sodium channel use-dependent inhibition by a new potent analogue of tocainide greatly enhances in vivo antimyotonic activity.
abstract: Although the sodium channel blocker, mexiletine, is the first choice drug in myotonia, some myotonic patients remain unsatisfied due to contraindications, lack of tolerability, or incomplete response. More therapeutic options are thus needed for myotonic patients, which require clinical trials based on solid preclinical data. In previous structure-activity relationship studies, we identified two newly-synthesized derivatives of tocainide, To040 and To042, with greatly enhanced potency and use-dependent behavior in inhibiting sodium currents in frog skeletal muscle fibers. The current study was performed to verify their potential as antimyotonic agents. Patch-clamp experiments show that both compounds, especially To042, are greatly more potent and use-dependent blockers of human skeletal muscle hNav1.4 channels compared to tocainide and mexiletine. Reduced effects on F1586C hNav1.4 mutant suggest that the compounds bind to the local anesthetic receptor, but that the increased hindrance and lipophilia of the N-substituent may further strengthen drug-receptor interaction and use-dependence. Compared to mexiletine, To042 was 120 times more potent to block hNav1.4 channels in a myotonia-like cellular condition and 100 times more potent to improve muscle stiffness in vivo in a previously-validated rat model of myotonia. To explore toxicological profile, To042 was tested on hERG potassium currents, motor coordination using rotarod, and C2C12 cell line for cytotoxicity. All these experiments suggest a satisfactory therapeutic index for To042. This study shows that, owing to a huge use-dependent block of sodium channels, To042 is a promising candidate drug for myotonia and possibly other membrane excitability disorders, warranting further preclinical and human studies.
authors.affiliation: Section of Pharmacology, Department of Pharmacy and Drug Sciences, University of Bari Aldo Moro, 70125, Bari, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: De Bellis
authors.affiliation: Section of Pharmacology, Department of Pharmacy and Drug Sciences, University of Bari Aldo Moro, 70125, Bari, Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: Carbonara
authors.affiliation: Section of Pharmacology, Department of Pharmacy and Drug Sciences, University of Bari Aldo Moro, 70125, Bari, Italy.
authors.forename: Julien
authors.initials: J
authors.lastname: Roussel
authors.affiliation: Section of Pharmacology, Department of Pharmacy and Drug Sciences, University of Bari Aldo Moro, 70125, Bari, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Farinato
authors.affiliation: Section of Pharmacology, Department of Pharmacy and Drug Sciences, University of Bari Aldo Moro, 70125, Bari, Italy.
authors.forename: Ada
authors.initials: A
authors.lastname: Massari
authors.affiliation: Section of Pharmacology, Department of Pharmacy and Drug Sciences, University of Bari Aldo Moro, 70125, Bari, Italy.
authors.forename: Sabata
authors.initials: S
authors.lastname: Pierno
authors.affiliation: Section of Medicinal Chemistry, Department of Pharmacy and Drug Sciences, University of Bari Aldo Moro, 70125, Bari, Italy.
authors.forename: Marilena
authors.initials: M
authors.lastname: Muraglia
authors.affiliation: Section of Medicinal Chemistry, Department of Pharmacy and Drug Sciences, University of Bari Aldo Moro, 70125, Bari, Italy.
authors.forename: Filomena
authors.initials: F
authors.lastname: Corbo
authors.affiliation: Section of Medicinal Chemistry, Department of Pharmacy and Drug Sciences, University of Bari Aldo Moro, 70125, Bari, Italy.
authors.forename: Carlo
authors.initials: C
authors.lastname: Franchini
authors.affiliation: Section of Pharmacology, Department of Biomedical Sciences and Human Oncology, University of Bari Aldo Moro, 70126 Bari, Italy.
authors.forename: Maria Rosaria
authors.initials: MR
authors.lastname: Carratù
authors.affiliation: Section of Pharmacology, Department of Pharmacy and Drug Sciences, University of Bari Aldo Moro, 70125, Bari, Italy.
authors.forename: Annamaria
authors.initials: A
authors.lastname: De Luca
authors.affiliation: Section of Pharmacology, Department of Pharmacy and Drug Sciences, University of Bari Aldo Moro, 70125, Bari, Italy.
authors.forename: Diana
authors.initials: D
authors.lastname: Conte Camerino
authors.affiliation: Section of Pharmacology, Department of Biomedical Sciences and Human Oncology, University of Bari Aldo Moro, 70126 Bari, Italy. Electronic address: jeanfrancois.desaphy@uniba.it.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Desaphy
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D051638:Ether-A-Go-Go Potassium Channels / Q000502:physiology; D006801:Humans; D008297:Male; D008801:Mexiletine / Q000494:pharmacology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology; D009222:Myotonia / Q000503:physiopathology / Q000517:prevention & control*; D062553:NAV1.4 Voltage-Gated Sodium Channel / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D057897:Reflex, Righting / Q000187:drug effects; D045442:Rotarod Performance Test; D016677:Tocainide / Q000009:adverse effects / Q000031:analogs & derivatives / Q000494:pharmacology* / Q000627:therapeutic use; D061567:Voltage-Gated Sodium Channel Blockers / Q000009:adverse effects / Q000494:pharmacology* / Q000627:therapeutic use
chemical_list: D051638:Ether-A-Go-Go Potassium Channels; D062553:NAV1.4 Voltage-Gated Sodium Channel; C106251:SCN4A protein, human; D061567:Voltage-Gated Sodium Channel Blockers; D008801:Mexiletine; D016677:Tocainide
keywords: Membrane hyperexcitability; Mexiletine; Myotonia; Sodium channel; Tocainide derivative; Use-dependence