title: Complete reversal of Lambert-Eaton myasthenic syndrome synaptic impairment by the combined use of a K+ channel blocker and a Ca2+ channel agonist.
abstract: Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder in which a significant fraction of the presynaptic P/Q-type Ca(2+) channels critical to the triggering of neurotransmitter release at the neuromuscular junction (NMJ) are thought to be removed. There is no cure for LEMS, and the current most commonly used symptomatic treatment option is a potassium channel blocker [3,4-diaminopyridine (3,4-DAP)] that does not completely reverse symptoms and can have dose-limiting side-effects. We previously reported the development of a novel Ca(2+) channel agonist, GV-58, as a possible alternative treatment strategy for LEMS. In this study, we tested the hypothesis that the combination of GV-58 and 3,4-DAP will elicit a supra-additive increase in neurotransmitter release at LEMS model NMJs. First, we tested GV-58 in a cell survival assay to assess potential effects on cyclin-dependent kinases (Cdks) and showed that GV-58 did not affect cell survival at the relevant concentrations for Ca(2+) channel effects. Then, we examined the voltage dependence of GV-58 effects on Ca(2+) channels using patch clamp techniques; this showed the effects of GV-58 to be dependent upon Ca(2+) channel opening. Based on this mechanism, we predicted an interaction between 3,4-DAP and GV-58. We tested this hypothesis using a mouse passive transfer model of LEMS. Using intracellular electrophysiological ex vivo recordings, we demonstrated that a combined application of 3,4-DAP plus GV-58 had a supra-additive effect that completely reversed the deficit in neurotransmitter release magnitude at LEMS model NMJs. This reversal contrasts with the less significant improvement observed with either compound alone. Our data indicate that a combination of 3,4-DAP and GV-58 represents a promising treatment option for LEMS and potentially for other disorders of the NMJ.
authors.affiliation: Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA, USA Center for the Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: Tyler B
authors.initials: TB
authors.lastname: Tarr
authors.affiliation: Division of Neuromuscular Diseases, Department of Neurology, University of Pittsburgh, Pittsburgh, PA, USA Department of Pathology, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: David
authors.initials: D
authors.lastname: Lacomis
authors.affiliation: Department of Clinical Neurology, Concord Hospital, Sydney, NSW, Australia.
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Reddel
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, PA, USA Center for Chemical Methodologies and Library Development, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: Mary
authors.initials: M
authors.lastname: Liang
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, PA, USA Center for Chemical Methodologies and Library Development, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: Guillermo
authors.initials: G
authors.lastname: Valdomir
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, PA, USA Center for Chemical Methodologies and Library Development, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Frasso
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, PA, USA Center for Chemical Methodologies and Library Development, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Wipf
authors.affiliation: Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA, USA Center for the Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, PA, USA meriney@pitt.edu.
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Meriney
mesh_terms: D015761:4-Aminopyridine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000077770:Amifampridine; D000818:Animals; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D045744:Cell Line, Tumor; D004357:Drug Synergism; D005260:Female; D006801:Humans; D015624:Lambert-Eaton Myasthenic Syndrome / Q000378:metabolism* / Q000503:physiopathology; D051379:Mice; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000503:physiopathology; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D011687:Purines / Q000494:pharmacology* / Q000627:therapeutic use; D055366:Synaptic Potentials; D013876:Thiophenes / Q000494:pharmacology* / Q000627:therapeutic use
chemical_list: D002120:Calcium Channel Agonists; C583131:GV-58 compound; D026902:Potassium Channel Blockers; D011687:Purines; D013876:Thiophenes; D015761:4-Aminopyridine; D000077770:Amifampridine