Effect of calmidazolium analogs on calcium influx in HL-60 cells

The structure-activity relationships of calmidazolium analogs with respect to intracellular calcium levels were investigated in HL-60 cells. Quaternized derivatives of miconazole and clotrimazole, known inhibitors of store-operated calcium (SOC) channels, were synthesized. The quaternary N-methyl derivatives of miconazole (3) and clotrimazole (6) had no effect on intracellular calcium levels, alone or after elevation of calcium induced by ATP. Calmidazolium alone induced a large increase in intracellular calcium levels in HL-60 cells (EC(50) 3 microM). Similar effects were observed for miconazole derivatives 1 (EC(50) 15 microM) and 2 (EC(50) 10 microM), wherein the diphenylmethyl group in calmidazolium was replaced by a 3,5-difluorobenzyl or cyclohexylmethyl group, respectively. The analogous clotrimazole derivatives 4 and 5 had no effect on intracellular calcium levels. The elevation of calcium levels by calmidazolium, 1, and 2 appears to be comprised of a calcium release component from inositol trisphosphate (IP(3))-sensitive stores followed by a large calcium influx component. Calcium influx was greater than that normally observed due to depletion of IP(3)-sensitive calcium stores and activation of SOC channels. In addition, only a small component of the calmidazolium-elicited influx was inhibited by the SOC channel blocker miconazole. Thus, certain quaternized imidazoles substituted with large residues at both nitrogens of the imidazole ring caused both release and influx of calcium, the latter in part through SOC channels but mainly through an undefined cationic channel. Quaternized imidazoles, unlike the parent nonquaternary imidazole miconazole, did not block SOC channels. Inhibitory effects on calmodulin-activated phosphodiesterase did not correlate with effects on calcium release and influx.