Metabolism and transporter-mediated drug-drug interactions of the endothelin-A receptor antagonist CI-1034

Chem Biol Interact. 2006 Feb 1;159(2):156-68. doi: 10.1016/j.cbi.2005.11.001. Epub 2005 Dec 13.


CI-1034, an endothelin-A receptor antagonist was being developed for pulmonary hypertension. Drug-drug interaction studies using human hepatic microsomes were conducted to assess CYP1A2, CYP2C9, CYP2C19, CYP3A4 and CYP2D6 inhibition potential; CYP3A4 induction potential was evaluated using primary human hepatocytes. CI-1034 moderately inhibited CYP2C9 (IC(50) 39.6 microM) and CYP3A4 activity (IC(50) 21.6 microM); CYP3A4 inhibition was metabolism-dependent. In human hepatocytes, no increase in CYP3A4 activity was observed in vitro, while mRNA was induced 15-fold, similar to rifampin, indicating that CI-1034 is both an inhibitor and inducer of CYP3A4. A 2-week clinical study was conducted to assess pharmacokinetics, pharmacodynamics and safety. No significant changes were observed in [formula: see text] between days 1 and 14. However, reversible elevations of serum liver enzymes were observed with a 50mg BID dose and the program was terminated. To further understand the interactions of CI-1034 in the liver and possible mechanisms of the observed hepatotoxicity, we evaluated the effect of CI-1034 on bile acid transport and previously reported that CI-1034 inhibited biliary efflux of taurocholate by 60%, in vitro. This indicated that inhibition of major hepatic transporters could be involved in the observed hepatotoxicity. We next evaluated the in vitro inhibition potential of CI-1034 with the major hepatic transporters OATP1B1, OATP1B3, OATP2B1, MDR1, MRP2 and OCT. CI-1034 inhibited OATP1B1 (K(i) 2 microM), OATP1B3 (K(i) 1.8 microM) and OATP2B1 activity (K(i) 3.3 microM) but not OCT, MDR1 or MRP2 mediated transport. Our data indicates that CI-1034 is an inhibitor of major hepatic transporters and inhibition of bile efflux may have contributed to the observed clinical hepatotoxicity. We recommend that in vitro drug-drug interaction panels include inhibition and induction studies with transporters and drug metabolizing enzymes, to more completely assess potential in vivo interactions or toxicity.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Blotting, Western
  • Cells, Cultured
  • Cytochrome P-450 Enzyme Inhibitors
  • Cytochrome P-450 Enzyme System / genetics
  • Double-Blind Method
  • Drug Interactions
  • Endothelin A Receptor Antagonists*
  • Enzyme Inhibitors / pharmacology
  • Hepatocytes / drug effects
  • Hepatocytes / metabolism
  • Humans
  • Microsomes, Liver / metabolism
  • Organic Anion Transporters / metabolism
  • Placebos
  • RNA, Messenger / genetics
  • Thiazines / metabolism
  • Thiazines / pharmacokinetics
  • Thiazines / pharmacology*


  • Cytochrome P-450 Enzyme Inhibitors
  • Endothelin A Receptor Antagonists
  • Enzyme Inhibitors
  • Organic Anion Transporters
  • PD 180988
  • Placebos
  • RNA, Messenger
  • Thiazines
  • Cytochrome P-450 Enzyme System