linogliride and Breast-Neoplasms

Whole-cell recordings were used to identify in MCF-7 human breast cancer cells the ion current(s) required for progression through G1 phase of the cell cycle. Macroscopic current-voltage curves were fitted by the sum of three currents, including linear hyperpolarized, linear depolarized and outwardly rectifying currents. Both linear currents, but not the outwardly rectifying current, were increased by 1 microm intracellular Ca(2+) and blocked by 2 mm intracellular ATP. When tested at concentrations previously shown to inhibit proliferation by 50%, linogliride, glibenclamide and quinidine inhibited the linear hyperpolarized current, and quinidine and linogliride inhibited the linear depolarized current; none of these agents affected the outwardly rectifying current. In contrast, tetraethylammonium completely inhibited the outwardly rectifying current, but did not inhibit either linear current. Changing the bath solution to symmetric K(+) shifted the reversal potential of the linear hyperpolarized current from near the K(+) equilibrium potential (-84 mV) to -4 mV. Arrest of the cell cycle in early G1 by quinidine was associated with significantly smaller linear hyperpolarized currents, without a change in the linear depolarized or outwardly rectifying currents, but this reduction was not observed with arrest by lovastatin at a site approximately 6 hr later in G1. The linear hyperpolarized current was significantly larger in ras-transformed than in untransformed cells. We conclude that the linear hyperpolarized current is an ATP-sensitive K(+) current required for progression of MCF-7 cells through G1 phase.

Topics: Adenosine Triphosphate; Breast Neoplasms; Calcium; Female; G1 Phase; Gene Expression; Genes, ras; Glyburide; Humans; Intracellular Fluid; Ion Transport; Membrane Potentials; Potassium; Potassium Channel Blockers; Pyrrolidines; Quinidine; Tetraethylammonium; Tumor Cells, Cultured

The purpose of this study was to determine if potassium channel activity is required for the proliferation of MCF-7 human mammary carcinoma cells. We examined the sensitivities of proliferation and progress through the cell cycle to each of nine potassium channel antagonists. Five of the potassium channel antagonists produced a concentration-dependent inhibition of cell proliferation with no evidence of cytotoxicity following a 3-day or 5-day exposure to drug. The IC50 values for these five drugs, quinidine (25 microM), glibenclamide (50 microM), linogliride (770 microM), 4-aminopyridine (1.6 mM), and tetraethylammonium (5.8 mM) were estimated from their respective concentration-response curves. Four other potassium channel blockers were tested at supra-maximal channel blocking concentrations, including charybdotoxin (200 nM), iberiotoxin (100 nM), margatoxin (10 nM), and apamin (500 nM), and they had no effect on MCF-7 cell proliferation, viability, or cell cycle distribution. Of the five drugs that inhibited proliferation, only quinidine, glibenclamide, and linogliride also affected the cell cycle distribution. Cell populations exposed to each of these drugs for 3 days showed a statistically significant accumulation in G0/G1 phase and a significant proportional reduction in S phase and G2/M phase cells. The inhibition of cell proliferation correlated significantly with the extent of cell accumulation in G0/G1 phase and the threshold concentrations for inhibition of growth and G0/G1 arrest were similar. The G0/G1 arrest produced by quinidine and glibenclamide were reversed by removing the drug, and cells released from arrest entered S phase synchronously with a lag period of approximately 24 hours. Based on the differential sensitivity of cell proliferation and cell cycle progression to the nine potassium channel antagonists, we conclude that inhibition of ATP-sensitive potassium channels in these human mammary carcinoma cells, reversibly arrests the cells in the G0/G1 phase of the cell cycle, resulting in an inhibition of cell proliferation.

Topics: 4-Aminopyridine; Breast Neoplasms; Cell Cycle; Cell Division; Glyburide; Humans; Potassium Channel Blockers; Potassium Channels; Pyrrolidines; Quinidine; Tetraethylammonium; Tetraethylammonium Compounds; Tumor Cells, Cultured