Towards Selective Antagonists of T-Type Calcium Channels: Design, Characterization and Potential Applications of NNC 55-0396

Abstract

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.

Comparative Effects of Azelnidipine and Amlodipine on Myocardial Function and Mortality After Ischemia/Reperfusion in Dogs

“…Koike et al (17) have reported that azelnidipine not only has an affinity for the L-type Ca 2+ channels (high-voltage activated), but also for the T-type Ca 2+ channels (low-voltage activated). Li et al (18) have reported that the low voltage-dependent activation/inactivation and slow deactivation of T-type Ca 2+ channels may play a physiological role in carrying the depolarizing current at low membrane potentials. They have speculated that these channels may play a crucial role in triggering high voltage-activated channels (pacemaker function) by modulating the rate of repetitive firing (low-threshold spikes).…”

Calcium signaling and T-type calcium channels in cancer cell cycling

“…More recently, the antiproliferative effect of the T-type calcium channel inhibitor NNC 55-0396 [56] has been examined in cell lines derived from breast epithelial tissue, MCF-7, MDA-MB-231(ER-α), and an adriamycin resistant cell line ADR. All three of these cell types express α 1G and α 1H Ca 2+ channel mRNA and their proliferation was suppressed by NNC 55-0396, with IC 50 of about 1-2 μmol/L [32,33] .…”

The Mibefradil Derivative NNC55-0396, a Specific T-Type Calcium Channel Antagonist, Exhibits Less CYP3A4 Inhibition than Mibefradil

“…Thus, L-type activity is a nonspecific feature of mibefradil administration (Li et al, 2005) and may account for other adverse effects associated with mibefradil. Recently, several analogs of mibefradil have been synthesized and tested for effects against T-type and L-type Ca 2ϩ channels (Huang et al, 2004;Li et al, 2005). These analogs were designed to achieve more selectivity toward T-type Ca 2ϩ channels.…”

“…NNC55-0396 was developed to be resistant to hydrolysis by substituting the methoxyacetyl side chain of mibefradil with cyclopropanecarboxylate ( Fig. 1) (Huang et al, 2004;Li et al, 2005). This compound is not able to generate the hydrolyzed L-type Ca 2ϩ channel blocker metabolite, Ro 40-5966, thus rendering NNC55-0396 selective to T-type Ca 2ϩ channels (Huang et al, 2004;Li et al, 2005).…”