title: The bumetanide prodrug BUM5, but not bumetanide, potentiates the antiseizure effect of phenobarbital in adult epileptic mice.
abstract: The loop diuretic bumetanide has been reported to potentiate the antiseizure activity of phenobarbital in rodent models of neonatal seizures, most likely as a result of inhibition of the chloride importer Na-K-Cl cotransporter isoform 1 (NKCC1) in the brain. In view of the intractability of neonatal seizures, the preclinical findings prompted a clinical trial in neonates on bumetanide as an add-on to phenobarbital, which, however, had to be terminated because of ototoxicity and lack of efficacy. We have recently shown that bumetanide penetrates only poorly into the brain, so that we developed lipophilic prodrugs such as BUM5, the N,N-dimethylaminoethylester of bumetanide, which penetrate more easily into the brain and are converted to bumetanide.
  
  
  
  In the present study, we used a new strategy to test whether BUM5 is more potent than bumetanide in potentiating the antiseizure effect of phenobarbital. Adult mice were made epileptic by pilocarpine, and the antiseizure effects of bumetanide, BUM5, and phenobarbital alone or in combination were determined by the maximal electroshock seizure threshold test.
  
  
  
  In nonepileptic mice, only phenobarbital exerted seizure threshold-increasing activity, and this was not potentiated by the NKCC1 inhibitors. In contrast, a marked potentiation of phenobarbital by BUM5, but not bumetanide, was determined in epileptic mice.
  
  
  
  Thus, bumetanide is not capable of potentiating phenobarbital's antiseizure effect in an adult mouse model, which, however, can be overcome by using the prodrug BUM5. These data substantiate that BUM5 is a promising tool compound for target validation and proof-of-concept studies on the role of NKCC1 in brain diseases.
authors.affiliation: Department of Medicinal Chemistry, University of Vienna, Vienna, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Erker
authors.affiliation: Department of Pharmacology, Toxicology and Pharmacy, University of Veterinary Medicine Hannover, Hannover, Germany.|Center for Systems Neuroscience, Hannover, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Brandt
authors.affiliation: Department of Pharmacology, Toxicology and Pharmacy, University of Veterinary Medicine Hannover, Hannover, Germany.|Center for Systems Neuroscience, Hannover, Germany.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Töllner
authors.affiliation: Department of Medicinal Chemistry, University of Vienna, Vienna, Austria.
authors.forename: Philipp
authors.initials: P
authors.lastname: Schreppel
authors.affiliation: Department of Pharmacology, Toxicology and Pharmacy, University of Veterinary Medicine Hannover, Hannover, Germany.|Center for Systems Neuroscience, Hannover, Germany.
authors.forename: Friederike
authors.initials: F
authors.lastname: Twele
authors.affiliation: Department of Pharmacology, Toxicology and Pharmacy, University of Veterinary Medicine Hannover, Hannover, Germany.|Center for Systems Neuroscience, Hannover, Germany.
authors.forename: Alina
authors.initials: A
authors.lastname: Schidlitzki
authors.affiliation: Department of Pharmacology, Toxicology and Pharmacy, University of Veterinary Medicine Hannover, Hannover, Germany.|Center for Systems Neuroscience, Hannover, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Löscher
mesh_terms: D000818:Animals; D000927:Anticonvulsants / Q000627:therapeutic use*; D002034:Bumetanide / Q000627:therapeutic use*; D003292:Convulsants / Q000633:toxicity; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004569:Electroencephalography / Q000187:drug effects; D004597:Electroshock / Q000009:adverse effects; D004833:Epilepsy, Temporal Lobe / Q000188:drug therapy* / Q000209:etiology; D051379:Mice; D010433:Pentylenetetrazole / Q000633:toxicity; D010634:Phenobarbital / Q000627:therapeutic use*; D010862:Pilocarpine / Q000633:toxicity; D011355:Prodrugs / Q000627:therapeutic use*
chemical_list: D000927:Anticonvulsants; D003292:Convulsants; D011355:Prodrugs; D010862:Pilocarpine; D002034:Bumetanide; D010433:Pentylenetetrazole; D010634:Phenobarbital
keywords: Chloride; GABA; Maximal electroshock seizures; NKCC1; Pilocarpine