title: In vitro-in vivo extrapolation of CYP2C8-catalyzed paclitaxel 6α-hydroxylation: effects of albumin on in vitro kinetic parameters and assessment of interindividual variability in predicted clearance.
abstract: OBJECTIVE
  This study aimed to characterize the effects of bovine serum albumin (BSA) on the kinetics of CYP2C8-catalyzed paclitaxel 6α-hydroxylation in vitro; determine whether the addition of BSA to incubations improves the prediction of paclitaxel hepatic clearance via this pathway in vivo; and assess interindividual variability in predicted clearance.
  
  
  METHODS
  The kinetics of paclitaxel 6α-hydroxlation by human liver microsomes (HLM) and recombinant CYP2C8 were characterized in incubations performed with and without BSA (2% w/v) supplementation, and the in vitro kinetic data were extrapolated to provide estimates of in vivo clearances. The Simcyp population-based ADME simulator was used to determine interindividual variability in the predicted clearances.
  
  
  RESULTS
  Supplementation of incubations of HLM with BSA resulted in a 3.6-fold increase in the microsomal intrinsic clearance for paclitaxel 6α-hydroxylation, due mainly to a reduction in K(m) (7.08 ± 2.50 to 2.26 ± 0.39 μM), while addition of BSA to incubations of recombinant CYP2C8 resulted in an approximate doubling of intrinsic clearance. Mean values of predicted in vivo hepatic clearance were in good agreement with clinical data when in vitro data obtained in the presence of BSA were used for IV-IVE. Simcyp predicted 20- to 30-fold interindividual variability in in vivo paclitaxel hepatic clearance via the 6α-hydroxylation pathway.
  
  
  CONCLUSIONS
  Human liver microsomal K(m) and intrinsic clearance values are over- and underpredicted, respectively, when incubations of the CYP2C8 substrate paclitaxel are performed without BSA supplementation. IV-IVE based on kinetic parameters generated in the presence of BSA improves the accuracy of predicted paclitaxel hepatic clearance.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
authors.forename: Nitsupa
authors.initials: N
authors.lastname: Wattanachai
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Polasek
authors.forename: Tahlia M
authors.initials: TM
authors.lastname: Heath
authors.forename: Verawan
authors.initials: V
authors.lastname: Uchaipichat
authors.forename: Wongwiwat
authors.initials: W
authors.lastname: Tassaneeyakul
authors.forename: Wichittra
authors.initials: W
authors.lastname: Tassaneeyakul
authors.forename: John O
authors.initials: JO
authors.lastname: Miners
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000972:Antineoplastic Agents, Phytogenic / Q000097:blood / Q000378:metabolism* / Q000493:pharmacokinetics; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics / Q000378:metabolism*; D003198:Computer Simulation; D065727:Cytochrome P-450 CYP2C8; D043371:Fatty Acids, Omega-6 / Q000378:metabolism; D005260:Female; D006801:Humans; D006900:Hydroxylation; D007202:Indicators and Reagents / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008657:Metabolic Clearance Rate; D008862:Microsomes, Liver / Q000378:metabolism*; D008875:Middle Aged; D008954:Models, Biological; D017239:Paclitaxel / Q000097:blood / Q000378:metabolism* / Q000493:pharmacokinetics; D011994:Recombinant Proteins / Q000378:metabolism; D015203:Reproducibility of Results; D012710:Serum Albumin, Bovine / Q000378:metabolism*; D012984:Software; D014015:Tissue Banks
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D043371:Fatty Acids, Omega-6; D007202:Indicators and Reagents; D011994:Recombinant Proteins; D012710:Serum Albumin, Bovine; D001189:Aryl Hydrocarbon Hydroxylases; C450259:CYP2C8 protein, human; D065727:Cytochrome P-450 CYP2C8; D017239:Paclitaxel