NNC 55-0396 [(1S,2S)-2-(2-(N-[(3-benzimidazol-2-yl)propyl]-N-methylamino)ethyl)-6-fluoro-1,2,3,4-tetrahydro-1-isopropyl-2-naphtyl cyclopropanecarboxylate dihydrochloride]: a new selective inhibitor of T-type calcium channels.
Mibefradil is a Ca2+ channel antagonist that inhibits both T-type and high-voltage-activated Ca2+ channels. We previously showed that block of high-voltage-activated channels by mibefradil occurs through the production of an active metabolite by intracellular hydrolysis. In the present study, we modified the structure of mibefradil to develop a nonhydrolyzable analog, (1S, 2S)-2-(2-(N-[(3-benzimidazol-2-yl)propyl]-N-methylamino)ethyl)-6-fluoro-1,2,3,4-tetrahydro-1-isopropyl-2-naphtyl cyclopropanecarboxylate dihydrochloride (NNC 55-0396), that exerts a selective inhibitory effect on T-type channels. The acute IC(50) of NNC 55-0396 to block recombinant alpha(1)G T-type channels in human embryonic kidney 293 cells was approximately 7 microM, whereas 100 microM NNC 55-0396 had no detectable effect on high-voltage-activated channels in INS-1 cells. NNC 55-0396 did not affect the voltage-dependent activation of T-type Ca2+ currents but changed the slope of the steady-state inactivation curve. Block of T-type Ca2+ current was partially relieved by membrane hyperpolarization and enhanced at a 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. After incubating cells from an insulin-secreting cell line (INS-1) with NNC 55-0396 for 20 min, mass spectrometry did not detect the mibefradil metabolite that causes L-type Ca2+ channel inhibition. We conclude that NNC 55-0396, by virtue of its modified structure, does not produce the metabolite that causes inhibition of L-type Ca2+ channels, thus rendering it more selective to T-type Ca2+ channels.
Huang
Luping
L
Department of Pharmacology SL-83, Tulane University Health Sciences Center, 1430 Tulane Avenue, New Orleans, LA 70112, USA.
Keyser
Brian M
BM
Tagmose
Tina M
TM
Hansen
J Bondo
JB
Taylor
James T
JT
Zhuang
Hean
H
Zhang
Min
M
Ragsdale
David S
DS
Li
Ming
M
D000818:Animals; D001562:Benzimidazoles / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D020747:Calcium Channels, T-Type / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D002460:Cell Line; D002478:Cells, Cultured; D003521:Cyclopropanes / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D004594:Electrophysiology; D006801:Humans; D013058:Mass Spectrometry; D020748:Mibefradil / Q000737:chemistry / Q000494:pharmacology; D009281:Naphthalenes / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D051381:Rats
D001562:Benzimidazoles; D002121:Calcium Channel Blockers; D020747:Calcium Channels, T-Type; D003521:Cyclopropanes; D009281:Naphthalenes; C484287:NNC 55-0396; D020748:Mibefradil