title: Implications of plasma protein binding for pharmacokinetics and pharmacodynamics of the γ-secretase inhibitor RO4929097.
abstract: OBJECTIVE
  Understanding of plasma protein binding will provide mechanistic insights into drug interactions or unusual pharmacokinetic properties. This study investigated RO4929097 binding in plasma and its implications for the pharmacokinetics and pharmacodynamics of this compound.
  
  
  METHODS
  RO4929097 binding to plasma proteins was determined using a validated equilibrium dialysis method. Pharmacokinetics of total and unbound RO4929097 was evaluated in eight patients with breast cancer receiving RO4929097 alone and in combination with the Hedgehog inhibitor GDC-0449. The impact of protein binding on RO4929097 pharmacodynamics was assessed using an in vitro Notch cellular assay.
  
  
  RESULTS
  RO4929097 was extensively bound in human plasma, with the total binding constant of 1.0 × 10(6) and 1.8 × 10(4) L/mol for α1-acid glycoprotein (AAG) and albumin, respectively. GDC-0449 competitively inhibited RO4929097 binding to AAG. In patients, RO4929097 fraction unbound (Fu) exhibited large intra- and interindividual variability; GDC-0449 increased RO4929097 Fu by an average of 3.7-fold. Concomitant GDC-0449 significantly decreased total (but not unbound) RO4929097 exposure. RO4929097 Fu was strongly correlated with the total drug exposure. Binding to AAG abrogated RO4929097 in vitro Notch-inhibitory activity.
  
  
  CONCLUSIONS
  RO4929097 is highly bound in human plasma with high affinity to AAG. Changes in plasma protein binding caused by concomitant drug (e.g., GDC-0449) or disease states (e.g., ↑AAG level in cancer) can alter total (but not unbound) RO4929097 exposure. Unbound RO4929097 is pharmacologically active. Monitoring of unbound RO4929097 plasma concentration is recommended to avoid misleading conclusions on the basis of the total drug levels.
authors.affiliation: Karmanos Cancer Institute, Wayne State University, Detroit, MI 48201, USA.
authors.forename: Jianmei
authors.initials: J
authors.lastname: Wu
authors.forename: Patricia M
authors.initials: PM
authors.lastname: Lorusso
authors.forename: Larry H
authors.initials: LH
authors.lastname: Matherly
authors.forename: Jing
authors.initials: J
authors.lastname: Li
mesh_terms: D000465:Algorithms; D053829:Amyloid Precursor Protein Secretases / Q000037:antagonists & inhibitors*; D000813:Anilides / Q000378:metabolism / Q000493:pharmacokinetics; D000818:Animals; D019540:Area Under Curve; D001552:Benzazepines / Q000097:blood / Q000378:metabolism* / Q000493:pharmacokinetics*; D001667:Binding, Competitive; D001798:Blood Proteins / Q000378:metabolism*; D001943:Breast Neoplasms / Q000097:blood / Q000188:drug therapy / Q000378:metabolism; D004347:Drug Interactions; D005260:Female; D006801:Humans; D007700:Kinetics; D008657:Metabolic Clearance Rate; D008954:Models, Biological; D009961:Orosomucoid / Q000378:metabolism; D011485:Protein Binding; D011725:Pyridines / Q000378:metabolism / Q000493:pharmacokinetics; D005466:Fluorocarbons
chemical_list: D053829:Amyloid Precursor Protein Secretases; D000813:Anilides; D001552:Benzazepines; D001798:Blood Proteins; D009961:Orosomucoid; D011725:Pyridines; C538724:HhAntag691; C545185:2,2-dimethyl-N-(6-oxo-6,7-dihydro-5H-dibenzo(b,d)azepin-7-yl)-N'-(2,2,3,3,3-pentafluoropropyl)malonamide; D005466:Fluorocarbons