Mechanism-based inactivation of cytochrome P450 2C9 by tienilic acid and (+/-)-suprofen: a comparison of kinetics and probe substrate selection

Drug Metab Dispos. 2009 Jan;37(1):59-65. doi: 10.1124/dmd.108.023358. Epub 2008 Oct 6.


In vitro experiments were conducted to compare k(inact), K(I) and inactivation efficiency (k(inact)/K(I)) of cytochrome P450 (P450) 2C9 by tienilic acid and (+/-)-suprofen using (S)-flurbiprofen, diclofenac, and (S)-warfarin as reporter substrates. Although the inactivation of P450 2C9 by tienilic acid when (S)-flurbiprofen and diclofenac were used as substrates was similar (efficiency of approximately 9 ml/min/micromol), the inactivation kinetics were characterized by a sigmoidal profile. (+/-)-Suprofen inactivation of (S)-flurbiprofen and diclofenac hydroxylation was also described by a sigmoidal profile, although inactivation was markedly less efficient (approximately 1 ml/min/micromol). In contrast, inactivation of P450 2C9-mediated (S)-warfarin 7-hydroxylation by tienilic acid and (+/-)-suprofen was best fit to a hyperbolic equation, where inactivation efficiency was moderately higher (10 ml/min/micromol) and approximately 3-fold higher (3 ml/min/micromol), respectively, relative to that of the other probe substrates, which argues for careful consideration of reporter substrate when mechanism-based inactivation of P450 2C9 is assessed in vitro. Further investigations into the increased inactivation seen with tienilic acid relative to that with (+/-)-suprofen revealed that tienilic acid is a higher affinity substrate with a spectral binding affinity constant (K(s)) of 2 microM and an in vitro half-life of 5 min compared with a K(s) of 21 microM and a 50 min in vitro half-life for (+/-)-suprofen. Lastly, a close analog of tienilic acid with the carboxylate functionality replaced by an oxirane ring was devoid of inactivation properties, which suggests that an ionic binding interaction with a positively charged residue in the P450 2C9 active site is critical for recognition and mechanism-based inactivation by these close structural analogs.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural

MeSH terms

  • Anti-Inflammatory Agents, Non-Steroidal / pharmacokinetics
  • Anti-Inflammatory Agents, Non-Steroidal / pharmacology*
  • Aryl Hydrocarbon Hydroxylases / antagonists & inhibitors*
  • Chromatography, Liquid
  • Cytochrome P-450 CYP2C9
  • Diuretics / pharmacokinetics
  • Diuretics / pharmacology*
  • Enzyme Inhibitors / pharmacokinetics
  • Enzyme Inhibitors / pharmacology*
  • Spectrophotometry, Ultraviolet
  • Substrate Specificity
  • Suprofen / pharmacokinetics
  • Suprofen / pharmacology*
  • Tandem Mass Spectrometry
  • Ticrynafen / pharmacokinetics
  • Ticrynafen / pharmacology*


  • Anti-Inflammatory Agents, Non-Steroidal
  • Diuretics
  • Enzyme Inhibitors
  • Suprofen
  • CYP2C9 protein, human
  • Cytochrome P-450 CYP2C9
  • Aryl Hydrocarbon Hydroxylases
  • Ticrynafen