title: Modulation of nonspecific binding in ultrafiltration protein binding studies.
abstract: OBJECTIVE
  The aim of this study was to reduce or prevent nonspecific binding (NSB) of compounds to ultrafiltration (UF) protein binding (PB) testing units.
  
  
  METHODS
  UF units (regenerated cellulose, MWCO 10K) were used for PB and NSB measurements with or without pretreatment with 5% tween 80 (TW 80) or 5% benzalkonium chloride (BAK) on the filter membrane. Dosing solutions (10 microM) in human serum and pH 7.4 phosphate-buffered saline were centrifuged at 3,000 g and room temperature after 1-h incubation in UF testing units. In parallel, a 96-well equilibrium dialyzer was used for PB and NSB measurements in equilibrium dialysis (ED) at 37 degrees C for 4 h. Samples of UF and ED were analyzed by LC/MS or LSC.
  
  
  RESULTS
  Severe NSB was observed for etoposide, hydrocortisone, propranolol, and vinblastine in UF. In contrast, TW 80 or BAK pre-treatment on the filter membrane decreased the NSB from 87-95% to 13-64% without causing a significant change in membrane integrity. When NSB was below 50% as a result of pretreating agents, PB data of marker compounds were comparable to those of ED.
  
  
  CONCLUSIONS
  The pretreated membrane with TW 80 or BAK showed significantly less NSB for compounds that had a tendency toward high membrane binding. A modified UF method with pretreatment improved the performance of UF and was able to produce comparable PB results to ED.
authors.affiliation: DMPK, Lion Bioscience, San Diego, California 92121, USA.
authors.forename: Kyoung-Jin
authors.initials: KJ
authors.lastname: Lee
authors.forename: Rachel
authors.initials: R
authors.lastname: Mower
authors.forename: Tom
authors.initials: T
authors.lastname: Hollenbeck
authors.forename: Jesus
authors.initials: J
authors.lastname: Castelo
authors.forename: Nikole
authors.initials: N
authors.lastname: Johnson
authors.forename: Perry
authors.initials: P
authors.lastname: Gordon
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Sinko
authors.forename: Kevin
authors.initials: K
authors.lastname: Holme
authors.forename: Yong-Hee
authors.initials: YH
authors.lastname: Lee
mesh_terms: D001798:Blood Proteins / Q000378:metabolism*; D006801:Humans; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D014462:Ultrafiltration / Q000379:methods
chemical_list: D001798:Blood Proteins; D004364:Pharmaceutical Preparations