Selective lysis of breast carcinomas by simultaneous stimulation of sodium channels and blockade of sodium pumps

Abstract

Sodium influx through voltage-gated sodium channels (VGSCs) coupled with balanced removal of sodium ions via Na+, K+-ATPase is a major determinant of cellular homeostasis and intracellular ionic concentration. Interestingly, many metastatic carcinomas express high levels of these channels. We hypothesized that if excess VGSCs are activated and Na+, K+-ATPase is simultaneously blocked, the intracellular Na+ concentration should increase, resulting in water movement into the cell, causing swelling and lytic cell death. MDA-MB-231 breast cancer cells over-express VGSCs by 7-fold. To test our hypothesis, we treated these cells in vitro with the Na+, K+-ATPase blocker, ouabain, and then stimulated with a sublethal electric current. For in vivo histologic and survival studies, MDA-MB-231 xenografts were established in Nu/J mice. Mice injected with saline or ouabain were electrically stimulated with trains of 10 msec 10V DC pulses. Within seconds to minutes, the cells swelled and lysed. MCF-10a cells, which express normal VGSCs levels, were unaffected by this treatment. Cells from the weakly-malignant cell line, MCF-7, which express 3-fold greater VGSCs than MCF-10a cells, displayed an intermediate time-to-lysis. The rate of lysis correlated directly with the degree of sodium channel expression and malignancy. We also demonstrated efficacy in cell lines from prostate, colon and lung carcinomas. Treated MDA-MB-231 xenografts showed 60–80% cell death. In survival studies, TOL-treated mice showed significantly slower tumor growth vs. controls. These results are evidence that this ”targeted osmotic lysis” represents a novel method for selectively killing cancer cells and warrants further investigation as a potential treatment for advanced and end-stage breast cancer.

Targeted Osmotic Lysis of Highly Invasive Breast Carcinomas Using Pulsed Magnetic Field Stimulation of Voltage-Gated Sodium Channels and Pharmacological Blockade of Sodium Pumps

“…The results of the present study are in vitro and in vivo evidence that support our earlier observation that targeted osmotic lysis, the simultaneous stimulation of VGSCs and Na + , K + -ATPase blockade, is able to kill highly malignant MDA-MB-231 human and 4T1 mouse breast cancer cells while preserving similarly treated normal breast cells [17]. In the in vitro experiments, the lysis of the cancer cells was dependent upon the intensity of the PMF, with greater than 95% of the digoxin treated cancer cells lysing within 15 min, with as little as 80 mT PMF.…”

“…The cells of normal tissues have only a fraction of the number of VGSCs compared to highly malignant cancer cells. Consequently, less Na + and thus less water enters the cells, and they do not lyse [17].…”

“…Flow cytometry evaluation of the two cell populations revealed protein expression of VGSCs in 4T1 cells was similar to the expression in MDA-MB-231 cells (4.1 + 0.09 vs. 3.9 + 0.12 -fold greater than autofluorescence). The MDA-MB-231 cells had been previously shown to express VGSC protein about 7.5-fold greater than "normal" MCF-10a cells [17]. Therefore, 4T1 cells also over-express these channels.…”

“…When this "targeted osmotic lysis" (TOL) is administered to several lines of malignant cells in vitro using Na + , K + -ATPase-blocking cardiac glycosides in combination with electrical stimulation, we have been able to affect 100% lysis of the malignant cells. However, when TOL is similarly applied to ectopic xenografts of malignant breast cancer MDA-MB-231 cells in vivo, the response to treatment has been less complete [17].…”

Sodium homeostasis in the tumour microenvironment

“…However, viral delivery of Na + channels would need to be precisely targeted to neoplastic cells in order for this method to be of use. In a different study, targeted osmotic lysis of VGSC-expressing tumours in mice was demonstrated by systemic administration of the Na + /K + ATPase-inhibiting cardiac glycoside ouabain in conjunction with electrical pulses to open VGSCs, leading to cytotoxic influx of Na + into tumour cells (234). Blocking the Na + efflux activity of Na + /K + ATPase with cardiac glycosides has the added advantage of decreasing inflammation and increasing specific anti-tumour immunity (235).…”