Regulation of osmolality for cancer treatment

Abstract

Disseminated metastasis is associated with a poor prognosis, and its management in the peritoneal or pleural cavity is crucial in the treatment of cancer. Recent studies show that ion and water transporters play important roles in fundamental cellular functions, including the regulation of cell volume that would be involved in the cancer process. Here, we review the evidence for hypotonic treatments of cancer and evaluate the potential of the cellular physiological approach in clinical management. The regulation of extracellular osmolality is a promising method, with several studies demonstrating the cytocidal effects of hypotonic solution on cancer cells. Peritoneal lavage with distilled water (DW) during surgery is reported to improve the survival rate of patients with spontaneously ruptured hepatocellular carcinoma. The in vitro studies included in this review also indicate the cytocidal effects of hypotonic shock on esophageal, gastric, colonic, pancreatic, and liver cancer cells with several unique methods and apparatuses, such as a differential interference contrast microscope connected to a digital video camera, a high-resolution flow cytometer and re-incubation analysis. The in vivo studies demonstrate the safeness of a peritoneal injection of DW into mice and indicate that the development of dissemination nodules can be prevented by the pre-incubation of cancer cells with DW or the peritoneal injection of DW. We also demonstrate that the blockade of Cl^- channels/transporters enhances the cytocidal effects of hypotonic shock by inhibiting regulatory volume decrease in various cancer cells. A deeper understanding of molecular mechanisms may lead to the discovery of these cellular physiological approaches as a novel therapeutic strategy for disseminated metastasis.

Keywords: Cancer; Cl− channel; Disseminated metastasis; Hypotonic treatment; Regulatory volume decrease.

Fig. 1

Changes in hepatocellular carcinoma (HCC) cells after exposure to hypotonic stress induced by distilled water (DW). Video recordings were made using a differential interference contrast microscope connected to a digital video camera. HCC cells (Alexander cells) started to swell as soon as they had been exposed to the DW and then continued to swell until they ruptured. Bar: 10.0 μm

Fig. 2

Cell volume changes in esophageal cancer cells (line KYSE170) after hypotonic shock. The cell volume and the cell counts were simultaneously measured at 1, 5, 10 and 20 min after hypotonic shock at various osmolarities using a high-resolution flow cytometer (Cell Lab Quanta). When the cells were exposed to mild hypotonicity (×1/2 NaCl, i.e., the isotonic NaCl buffer was diluted twofold with DW), the cell volume initially increased and then decreased gradually to the pre-hypotonic shock level, suggesting that mild hypotonicity could induce regulatory volume decrease. When the cells were exposed to DW, the overall cell volume was smaller than the pre-hypotonic shock volume, suggesting that almost all of the cells had broken into fragments. Exposure to isotonic NaCl buffer did not cause any significant changes in cell volume within 20 min (data not shown)

Fig. 3

Mechanism of cell volume regulation under hypotonic shock. Regulatory volume decrease (RVD) occurs after hypotonicity-caused cell swelling and has been attributed to the activation of ion channels and transporters, which in turn cause Cl⁻, K⁺ and H₂O effluxes, ultimately leading to cell shrinkage

Fig. 4

Blockade of Cl⁻ channel enhances the cytocidal effect of hypotonic solution via the inhibition of regulatory volume decrease (RVD) in cancer cells. 5-Nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) is a broad spectrum Cl⁻ channel blocker