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Medicine, Research & Experimental
Targeted osmotic lysis (TOL) takes advantage of the interdependent, sodium channel/sodium pump alliance that is present in the cells of all animals and is essential for cell communication and survival because of its role in maintaining membrane potential and cellular homeostasis [38,39]. TOL technology is based on the observation that many epithelially-derived cancers over-express voltage-gated sodium channels (VGSCs) and Na+, K+-ATPase, a feature that confers an enhanced ability to invade normal tissue and to metastasize and is found to be exceedingly prominent in advanced disease, and that the expression of VGSCs in the cancer cells is directly related to the level of malignancy.
- cancer
- targeted therapies
- targeted osmotic lysis
- sodium channels
- sodium pumps
- Na+, K+-ATPase
1. An Alternate Approach for Targeting Therapy
In the absence of a preventive vaccine, we offer for consideration a novel and fundamentally different approach, both in principle and design, for treating advanced-stage carcinoma that exploits a basic biological mechanism for survival. The process, called “targeted osmotic lysis (TOL)”, takes advantage of the interdependent, sodium channel/sodium pump alliance that is present in the cells of all animals and is essential for cell communication and survival because of its role in maintaining membrane potential and cellular homeostasis [38,39]. TOL technology is based on the observation that many epithelially-derived cancers over-express voltage-gated sodium channels (VGSCs) and Na+, K+-ATPase, a feature that confers an enhanced ability to invade normal tissue and to metastasize and is found to be exceedingly prominent in advanced disease, and that the expression of VGSCs in the cancer cells is directly related to the level of malignancy [38,40,41,42]. Although blocking the expression or impeding the function of VGSCs by pharmacologic means has been shown to slow tumor growth and reduces metastasis, these agents leave the original tumor intact and are associated with variable adverse effects imposed on cells that normally express VGSCs [43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58]. Unlike most targeted technologies that selectively deliver lethal therapies to targeted cells by identifying cellular markers unique to the specific cancer cells, TOL enhances, rather than impedes, VGSC marker functionality, thereby greatly increasing the influx of sodium while simultaneously preventing extrusion of these ions by blocking the sodium pumping mechanism with a cardiac glycoside (Figure 1). Because water passively follows sodium by osmosis and possibly through aquaporins [59], the cells swell beyond their capacity to comply, resulting in cell lysis. Normal cells, even highly-expressing excitable cells (e.g., nerve and muscle) are spared from damage because sodium channel expression in normal tissues is significantly less than that found in most advanced carcinomas. Less sodium, and consequently less water, enters normal cells precluding significant cell swelling and lysis. Unlike destructive therapies that deliver irreversible, lethal agents that destroy all recognized cells, whether malignant or normal, TOL only lyses highly malignant cells that are set apart from normal by the up to 50× greater expression of VGSCs than normal cells [60]. Although TOL affects all cells during active treatment, the Na+, K+-ATPase blockade is reversible, thus allowing normal cells that do not take on enough water for lysis to return to normal when the cardiac glycoside is released from the receptor and metabolized without producing significant morbidity in the patient.
Figure 1. The diagram illustrates how advanced cancers that greatly over-express the conserved and ubiquitous sodium channel/sodium pump mechanism that is essential for cell function and survival, carry their own means of destruction and that by manipulating this mechanism, cancer cells can be eliminated without affecting normal cells. Panels A show that relative to normal cells, cancer cells greatly over express voltage-gated sodium channels (VGSCs; green rectangles) and Na+, K+-ATPase (yellow dots) more than even highly-expressing normal cells (e.g., nerve and muscle). Panels B show that the functional ratio of VGSCs to sodium pumps is maintained in cancer cells to ensure that the influx of sodium ions (inward oriented black arrows) that occurs down a concentration gradient when the membrane is depolarized and the channels are open can be rapidly reversed (outward oriented black arrows), thereby restoring normal resting membrane potential and intracellular sodium ion concentrations. Panels C show that when the sodium pumps are blocked (red dots) sodium ions enter the cells in direct relation to the number of VGSCs but cannot be returned to the extracellular space. Water enters the cells osmotically (blue arrows) to dilute the intracellular sodium concentrations, causing cell swelling. Panels D show that the amount of water that enters the cancer cells exceeds the cell membrane’s capacity to comply, resulting in cell lysis. In normal cells, the sodium pumps return to normal functioning when the blocking agent clears. The smaller amount of water follows the sodium ions back to the extracellular space, returning the cells to normal configuration and functioning.
2. Targeted Osmotic Lysis in Cancer Therapies
Several studies have been conducted to date to support the initial proof-of-concept for TOL as a potential broad-spectrum treatment for many advanced carcinomas. Initial studies in vitro using immunocytofluorescence were able to confirm the enhanced expression of VGSCs in immortalized breast cancer cell lines [41,42], and that the level of expression correlates directly with the level of malignancy. The TOL effect was demonstrated when treating cells from human breast, lung, prostate, and colon cancer [38,42] and murine triple-negative breast cancer cell lines [38]. It was further shown that time to lysis, using a pulsed electric current (1V DC, 15 pulses per second) delivered with electrodes placed in the vicinity of MDA-MB-231, triple-negative breast cancer cells incubated in ouabain or digoxin, correlates directly with VGSC expression and is dependent on the presence of sodium in the media [38]. Cell lysis was not observed when the electric current was applied to glycoside-treated cell lines derived from normal tissues or malignant cells that were untreated or treated with a drug or stimulation only.
In vivo, high VGSC expression has also been observed using immunohistochemical analysis of tissues taken from ectopic murine and human triple-negative breast cancer xenografts or homografts in Nu/J immune-compromised and BALBc immune-competent mice. TOL has also been shown consistently to be effective in reducing tumor size by 35–45% from baseline (maximum 80–100% reduction in 3 mice), in decreasing the rate of growth, and increasing the survival of mice that serve as hosts to ectopic murine and human triple-negative breast cancer xenografts or homografts treated with digoxin and exposed to pulsed magnetic or electric fields compared to grafts treated with vehicle or a drug or stimulation alone [39]. Despite the effect of TOL on malignant cells, there has been no demonstrable change noted in normal renal, hepatic, dermal, neural and muscle tissues. TOL efficacy has also been observed in dogs and cats when treating a variety of advanced carcinoma, e.g., nasopharyngeal adenocarcinoma, bronchoalveolar carcinoma and metastatic anal gland carcinoma (preliminary observations). In addition to the comparable histopathologic effects on malignancies, 75–90% tumor necrosis extending beyond typical areas of central necrosis, and the lack of damage to normal tissues, it has been possible to note a lack of aversive behavioral signs during and immediately after treatment with TOL and consistent observable, albeit subjective, improvements in appetite, energy and interactive behavior.
Most recently, similar observations related to VGSC expression and response to treatment have been made in a human patient that was allowed a single round of treatment with TOL for late-stage squamous cell carcinoma of the cervix under an Emergency Use protocol [60]. Consistent with the anthropomorphic interpretation of animal responses to treatment, the patient expressed no pain or discomfort related to the administration of treatment and observed increased appetite and a subjective improvement in energy and activity levels and cognitive ability following treatment. The results of the immunohistochemical analysis of VGSC expression (Figure 2) and the imaging (Figure 3) results were similar to those observed in companion animals and consistent with the observations of increased survival in animals, the patient’s 9-week post-treatment survival following a single round of treatment exceeded expectations beyond the days to 2 weeks anticipated when the treatment was requested.
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Figure 2. Sodium channel labeling in biopsy samples obtained from a patient with stage IIB squamous cell carcinoma (SCCA) of the cervix (A) and a companion canine (B,C) before (A,B) and after (C) treatment with TOL. The photomicrographs depict the immunohistochemical labeling of VGSCs (green) in a biopsy of the cervical malignancy (A) and a canine nasopharyngeal adenocarcinoma (B), before (A,B) and after (C) treatment with TOL. Nuclei are counterstained with DRAQ5 (blue). Note that the number of cells in a post-treatment biopsy sample obtained after a single treatment of the canine adenocarcinoma with TOL (C) that highly express VGSCs is significantly reduced. The number of cells that had expressed fewer VGSCs and pumps pre-treatment were unaffected and comprised the remaining amount of tumor. Calibration bar in C = 50 µm.
Figure 3. The computer tomographic images of the Stage IIB SCCA of the cervix(A,B) obtained from the patient in Figure 2 and a carcinoma of the prostate obtained from a companion canine (C,D) before (A,C) and 3–5 days after (B,D) treatment with TOL. The images before and after treatment were chosen to depict the respective tumors at levels as closely similar as possible. White arrows indicate points on the surface of the respective mass. Note that the relative size of both types of carcinoma, in the human and the dog post-treatment appears similar if not slightly larger than prior to treatment. By contrast, areas of hypodensity observed within the tumor mass appear larger and much more prominent after treatment (black asterisks) compared to pretreatment (white asterisks) with the region of interest (ROI) measurements of Hounsfield unit densities decreasing from 70 to 56 HU by 3 days post-treatment. Additional region of ROI reference measurements were made for each scan over pelvic musculature revealing values of 127 HU (A,C) and 120 HU (B,D), respectively. Calibration bar in D = 5 cm.
Summary. We argue that TOL is an alternate approach to targeted therapy that may be able to provide a major step forward in improving the level of care for advanced stage carcinoma and warrants further investigation. We propose that TOL is worthy of consideration because (1) it will likely be able to mitigate many limitations associated with current treatment options [60], (2) because TOL seems to be most effective when VGSCs are most highly expressed [38], and VGSCs expression in the cancer cells is greatest in the most malignant and advanced forms of a carcinoma, TOL is likely to be most effective for treating advanced stage cancers that are responsible for most of the over 60,000 cancer deaths seen each year in the U.S. alone [35], (3) because of the conserved nature, the ubiquitous distribution and the consistent functional characteristics of the sodium channel/sodium pump mechanism throughout the animal kingdom, TOL technology has the potential to provide broad-reaching treatment for many forms of advanced carcinoma, and (4) because of the broad coverage, the cost of research and development of the technology and delivery of treatment can be shared by a significant portion of the population, making it likely that the cost of treatment with TOL will be more affordable than currently available therapies. The potential adverse effects associated with tumor lysis syndrome, a complication associated with the elimination of large tumor masses that should be anticipated, to date, have not been observed following administration of TOL. This adverse effect is, however, subject to prophylactic measures of fluid hydration and treatment with allopurinol or hemodialysis.
This entry is adapted from the peer-reviewed paper 10.3390/biomedicines10040838
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