title: Design of a potent and selective inhibitor of the intermediate-conductance Ca2+-activated K+ channel, IKCa1: a potential immunosuppressant.
abstract: The antimycotic clotrimazole, a potent inhibitor of the intermediate-conductance calcium-activated K(+) channel, IKCa1, is in clinical trials for the treatment of sickle cell disease and diarrhea and is effective in ameliorating the symptoms of rheumatoid arthritis. However, inhibition of cytochrome P450 enzymes by clotrimazole limits its therapeutic value. We have used a rational design strategy to develop a clotrimazole analog that selectively inhibits IKCa1 without blocking cytochrome P450 enzymes. A screen of 83 triarylmethanes revealed the pharmacophore for channel block to be different from that required for cytochrome P450 inhibition. The "IKCa1-pharmacophore" consists of a (2-halogenophenyl)diphenylmethane moiety substituted by an unsubstituted polar pi-electron-rich heterocycle (pyrazole or tetrazole) or a -C≡N group, whereas cytochrome P450 inhibition absolutely requires the imidazole ring. A series of pyrazoles, acetonitriles, and tetrazoles were synthesized and found to selectively block IKCa1. TRAM-34 (1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole) inhibits the cloned and the native IKCa1 channel in human T lymphocytes with a K(d) of 20-25 nM and is 200- to 1,500-fold selective over other ion channels. Using TRAM-34, we show that blocking IKCa1 in human lymphocytes, in the absence of P450-inhibition, results in suppression of mitogen-stimulated [(3)H]thymidine incorporation of preactivated lymphocytes with EC(50)-values of 100 nM-1 microM depending on the donor. Combinations of TRAM-34 and cyclosporin A are more effective in suppressing lymphocyte mitogenesis than either compound alone. Our studies suggest that TRAM-34 and related compounds may hold therapeutic promise as immunosuppressants.
authors.affiliation: Department of Physiology and Biophysics, University of California, Irvine, CA 92697, USA. hwulff@uci.edu
authors.forename: H
authors.initials: H
authors.lastname: Wulff
authors.forename: M J
authors.initials: MJ
authors.lastname: Miller
authors.forename: W
authors.initials: W
authors.lastname: Hansel
authors.forename: S
authors.initials: S
authors.lastname: Grissmer
authors.forename: M D
authors.initials: MD
authors.lastname: Cahalan
authors.forename: K G
authors.initials: KG
authors.lastname: Chandy
mesh_terms: D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects*; D003022:Clotrimazole / Q000737:chemistry; D016572:Cyclosporine / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects; D015195:Drug Design; D004347:Drug Interactions; D004553:Electric Conductivity; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D015640:Ion Channel Gating; D015759:Ionomycin / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000187:drug effects; D015221:Potassium Channels; D011720:Pyrazoles / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D013601:T-Lymphocytes / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D007166:Immunosuppressive Agents; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496923:KCNN4 protein, human; D015221:Potassium Channels; D011720:Pyrazoles; C411671:TRAM 34; D015759:Ionomycin; D016572:Cyclosporine; D003577:Cytochrome P-450 Enzyme System; D003022:Clotrimazole; D013755:Tetradecanoylphorbol Acetate