title: Suitability of commonly used excipients for electrophysiological in-vitro safety pharmacology assessment of effects on hERG potassium current and on rabbit Purkinje fiber action potential.
abstract: BACKGROUND
  Regulatory guidelines require investigation of the liability for delayed ventricular repolarization by new chemical entities within a broad concentration range in-vitro. However, investigation can be limited by poor drug aqueous solubility, and by solvent physicochemical attributes that disrupt cell membrane integrity. Although excipients or solubilizing agents may aid to achieve the necessary high concentrations, no comprehensive overview on the suitability of solvents for in-vitro electrophysiological safety studies exists.
  
  
  METHODS
  Excipients were tested for potential interference with the hERG (human ether-a-go-go-related gene) K(+) current (whole-cell voltage-clamp, 23+/-2 degrees C), and the shape of rabbit Purkinje fiber action potentials (conventional glass microelectrode technique, 37+/-1 degrees C).
  
  
  CONCLUSIONS
  Water-soluble complexation builders/carriers had little effect on hERG K(+) current at up to 50 mg/ml (BSA, bovine serum albumin) and 11 mg/ml (HP-beta-CD, hydroxypropyl-beta-cyclodextrin; IC(20), concentration of 20% inhibition). Water-soluble organic (co)solvents inhibited hERG K(+) currents (IC(20), %/mM): 0.7/152, ethanol; 0.9/67, Transcutol; 1.2/154, DMSO (dimethylsulfoxide); 1.6/389, acetonitrile; 1.9/48, polyethylene glycol 400; 2.1/660, methanol. Part of their inhibitory effect is attributed to the osmolality of extracellular solutions, because hERG IC(20) and extrapolated osmolality at the hERG IC(20) strongly correlate. Water-soluble non-ionic solubilizers/surfactants are potent inhibitors of hERG K(+) current with IC(20) concentrations of 0.07% (Cremophor EL) or lower (Tween 20, Tween 80: approximately 0.001%). Part of this inhibitory effect is attributed to their interaction with lipid membranes, because hERG inhibition occurs close to critical micelle concentrations (Cremophor, approximately 0.009%; Tween 20, approximately 0.007%). Purkinje fiber action potentials are little affected by HP-beta-CD at up to 2 mg/ml, while DMSO tends to shorten the action potential duration at 1%.
  
  
  CONCLUSIONS
  When conducting electrophysiological in-vitro assessments of drug effects, solubilizers/surfactants (Cremophor EL, Tween 20, Tween 80) should be avoided. Instead, water-soluble organic (co)solvents (methanol, acetonitrile, DMSO) or complexation builders/carriers (HP-beta-CD, BSA) appear to be more favorable.
authors.affiliation: Global Drug Discovery-Toxicology, Clinical Pathology and Safety Studies, Bayer HealthCare AG, Aprather Weg 18a, D-42096 Wuppertal, Germany. herbert.himmel@bayerhealthcare.com
authors.forename: Herbert M
authors.initials: HM
authors.lastname: Himmel
mesh_terms: D000073738:2-Hydroxypropyl-beta-cyclodextrin; D000097:Acetonitriles / Q000737:chemistry / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D002460:Cell Line; D004121:Dimethyl Sulfoxide / Q000737:chemistry / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004329:Droperidol / Q000494:pharmacology; D004353:Drug Evaluation, Preclinical / Q000379:methods; D004594:Electrophysiology / Q000379:methods*; D051638:Ether-A-Go-Go Potassium Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D005026:Ethylene Glycols / Q000494:pharmacology; D005079:Excipients / Q000737:chemistry / Q000494:pharmacology*; D005260:Female; D006801:Humans; D000432:Methanol / Q000737:chemistry / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011092:Polyethylene Glycols / Q000494:pharmacology; D011690:Purkinje Fibers / Q000187:drug effects* / Q000502:physiology; D011725:Pyridines / Q000494:pharmacology; D011817:Rabbits; D013015:Sotalol / Q000494:pharmacology; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: D000097:Acetonitriles; D051638:Ether-A-Go-Go Potassium Channels; D005026:Ethylene Glycols; D005079:Excipients; D010880:Piperidines; D011725:Pyridines; D047392:beta-Cyclodextrins; C063968:E 4031; D000073738:2-Hydroxypropyl-beta-cyclodextrin; D011092:Polyethylene Glycols; C010111:carbitol; D013015:Sotalol; D004329:Droperidol; D000432:Methanol; D004121:Dimethyl Sulfoxide; C032159:acetonitrile