Towards selective antagonists of T-type calcium channels: design, characterization and potential applications of NNC 55-0396.
NNC 55-0396 is a structural analog of mibefradil (Ro 40-5967) that inhibits both T-type and high-voltage-activated (HVA) Ca2+ channels with a higher selectivity for T-type Ca2+ channels. The inhibitory effect of mibefradil on HVA Ca2+ channels can be attributed to a hydrolyzed metabolite of the drug: the methoxy acetate side chain of mibefradil is removed by intracellular enzymes, thus it forms (1S,2S)-2-(2-(N-[(3-benzoimidazol-2-yl)propyl]-N-methylamino)ethyl)-6-fluoro-1,2,3,4-tetrahydro-1-isopropyl-2-naphtyl hydroxy dihydrochloride (dm-mibefradil), which causes potent inhibition of HVA Ca2+ currents. By replacing the methoxy acetate chain of mibefradil with cyclopropanecarboxylate, a more stable analog was developed (NNC 55-0396). The acute IC50 of NNC 55-0396 to block recombinant Cav3.1 T-type channels expressed in HEK293 cells is approximately 7 muM, whereas 100 microM NNC 55-0396 has no detectable effect on high voltage-activated currents in INS-1 cells. Block of T-type Ca2+ current was partially reduced by membrane hyperpolarization and was enhanced at high stimulus frequency. Washing NNC 55-0396 out of the recording chamber did not reverse the T-type Ca2+ current activity, suggesting that the compound dissolves in or passes through the plasma membrane to exert its effect; however, intracellular perfusion of the compound did not block T-type Ca2+ currents, arguing against a cytoplasmic route of action. We conclude that NNC 55-0396, by virtue of its modified structure, does not produce the metabolite that causes inhibition of L-type Ca2+ channel channels, thus rendering it more selective to T-type Ca2+ channels.
Li
Ming
M
Department of Pharmacology SL-83, Tulane University Health Science Center, 1430 Tulane Avenue, New Orleans, LA 70112, USA. mli@tulane.edu
Hansen
J Bondo
JB
Huang
Luping
L
Keyser
Brian M
BM
Taylor
James T
JT
D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020747:Calcium Channels, T-Type / Q000378:metabolism*; D002460:Cell Line; D003521:Cyclopropanes / Q000494:pharmacology*; D015195:Drug Design; D006801:Humans; D020748:Mibefradil / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology*
D001562:Benzimidazoles; D002121:Calcium Channel Blockers; D020747:Calcium Channels, T-Type; D003521:Cyclopropanes; D009281:Naphthalenes; C484287:NNC 55-0396; D020748:Mibefradil