Altering bioelectricity on inhibition of human breast cancer cells.
BACKGROUND
Membrane depolarization is associated with breast cancer. Depolarization-activated voltage-gated ion channels are directly implicated in the initiation, proliferation, and metastasis of breast cancer.


METHODS
In this study, the role of voltage-gated potassium and calcium ion channel modulation was explored in two different invasive ductal human carcinoma cell lines, MDA-MB-231 (triple-negative) and MCF7 (estrogen-receptor-positive).


RESULTS
Resting membrane potential is more depolarized in MCF7 and MDA-MB-231 cells compared to normal human mammary epithelial cells. Increasing extracellular potassium concentration up to 50 mM depolarized membrane potential and greatly increased cell growth. Tetraethylammonium (TEA), a non-specific blocker of voltage-gated potassium channels, stimulated growth of MCF7 cells (control group grew by 201 %, 1 mM TEA group grew 376 %). Depolarization-induced calcium influx was hypothesized as a requirement for growth of human breast cancer. Removing calcium from culture medium stopped growth of MDA and MCF7 cells, leading to cell death after 1 week. Verapamil, a blocker of voltage-gated calcium channels clinically used in treating hypertension and coronary disease, inhibited growth of MDA cells at low concentration (10-20 μM) by 73 and 92 % after 1 and 2 days, respectively. At high concentration (100 μM), verapamil killed >90 % of MDA and MCF7 cells after 1 day. Immunoblotting experiments demonstrated that an increased expression of caspase-3, critical in apoptosis signaling, positively correlated with verapamil concentration in MDA cells. In MCF7, caspase-9 expression is increased in response to verapamil.


CONCLUSIONS
Our results support our hypotheses that membrane depolarization and depolarization-induced calcium influx stimulate proliferation of human breast cancer cells, independently of cancer subtypes. The underlying mechanism of verapamil-induced cell death involves different caspases in MCF7 and MDA-MB-231. These data suggest that voltage-gated potassium and calcium channels may be putative targets for pharmaceutical remediation in human invasive ductal carcinomas.
Department of Biology, West Virginia University, Morgantown, WV 26506 USA.
Seher
S
Berzingi
Department of Physiology & Pharmacology, West Virginia University, Morgantown, WV 26506 USA.
Mackenzie
M
Newman
Department of Physiology & Pharmacology, West Virginia University, Morgantown, WV 26506 USA.
Han-Gang
0000-0001-6838-8310
HG
Yu
Caspase-3; Caspase-9; Membrane potential; TEA; Verapamil; Voltage-gated calcium channels; Voltage-gated potassium channels
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