title: hERG potency estimates based upon dose solution analysis: What have we learned?
abstract: BACKGROUND
  Measurement of drug-induced inhibition of potassium current flow through the hERG channel is used to determine potency at the channel, which is used as an in vitro risk assessment for QTc interval prolongation in vivo. In the hERG assay, test solutions of varying strength are prepared to construct a concentration-response curve based upon the nominal drug concentration (NOM). Dose-solution analysis (DSA) is an analytical approach to confirm the test concentration achieved in an in vitro assay (Herron, Towers, & Templeton, 2004), and can be included as a component of hERG channel study to confirm drug concentration in the assay buffer to determine potency using the "actual" drug level in solution (ACT). Thus, DSA could be helpful in confirming test article concentrations. This study examined whether inclusion of DSA improved the accuracy of potency estimates based upon the ACT compared to the NOM concentration during hERG voltage clamp assays (non-GLP) for 99 diverse agents.
  
  
  METHODS
  We examined the correlation of hERG IC(50) derived from NOM with hERG IC(50) derived from ACT, and analyzed potential mechanisms of deviation between ACT and NOM potency values, including solubility, cLogP, PKa, and molecular weights.
  
  
  RESULTS
  Seventy-four (74) of 99 agents (73.7%) had NOM- and ACT-derived IC(50) values within 3-fold, 87 of 99 (87.8%) had an IC(50) ratio within 10-fold, and 12 (12.1%) had a >10-fold difference in their NOM IC(50) and ACT IC(50) values. On average, these 12 compounds had less soluble, more lipophilic (high cLogP values), and more basic characters (high pKa values).
  
  
  CONCLUSIONS
  Our investigation indicated that DSA did not alter hERG potency estimation for the majority of compounds in this dataset, i.e., DSA confirmed the NOM concentration within 3-fold. For poorly soluble agents or agents with high cLogP and pKa values, however, DSA did not clarify or improve hERG potency estimates.
authors: Department of Toxicology Sciences, Amgen Inc., Thousand Oaks, CA 91320, USA. yqu@amgen.com
authors: Yusheng
authors: Y
authors: Qu
authors: Paul
authors: P
authors: Schnier
authors: Roger
authors: R
authors: Zanon
authors: Hugo M
authors: HM
authors: Vargas
mesh_terms: D002461:Cell Line, Transformed; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical / Q000379:methods*; D000072237:ERG1 Potassium Channel; D004594:Electrophysiology / Q000379:methods; D051638:Ether-A-Go-Go Potassium Channels / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques / Q000379:methods; D026902:Potassium Channel Blockers / Q000494:pharmacology; D012995:Solubility; D012996:Solutions / Q000737:chemistry
chemical_list: D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D026902:Potassium Channel Blockers; D012996:Solutions