The National Institute of Neurological Disorders and Stroke (NINDS) Epilepsy Therapy Screening Program (ETSP).

For over 40 years, the National Institute of Neurological Disorders and Stroke/National Institutes of Health-funded Anticonvulsant Screening Program has provided a preclinical screening service for participants world-wide that helped identify/characterize new antiseizure compounds, a number of which advanced to the market for the treatment of epilepsy. The newly-renamed Epilepsy Therapy Screening Program (ETSP) has a refocused mission to identify novel agents which will help address the considerable remaining unmet medical needs in epilepsy. These include identifying antiseizure agents for treatment-resistant epilepsy, as well as anti-epileptogenic agents that will prevent the development of epilepsy or disease-modifying agents that will ameliorate or even cure established epilepsy and its comorbidities. This manuscript provides an overview of the ETSP's efforts aimed at identifying the next generation of therapeutic agents to further reduce the suffering from and burden of epilepsy.

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

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.