Effects of Amiloride on Tumor Growth and Intracellular Element Content of Tumor Cells in Vivo¹

The effects of amiloride, a reported inhibitor of serum-stimulated sodium influx, were tested on tumor growth, tumor cell proliferation, and intracellular element content of cancer cells in vivo. We have shown previously that cancer cells have high intranuclear levels of sodium compared to those of their normal counterpart cells and have postulated that such a high level of sodium may be involved in the cancer state. We now report that amiloride, when given in a series of injections, inhibited both H6 hepatoma and DMA/J mammary adenocarcinoma growth in vivo in a dose-dependent fashion and that 3 injections of amiloride at a dose of 1.0 µg/g body weight into mice bearing H6 hepatomas resulted in a significant decrease in the intranuclear content of sodium but not the content of magnesium, phosphorus, sulfur, chlorine, or potassium as measured by electron probe X-ray microanalysis in the H6 hepatoma cells. Amiloride at dosages as low as 1.0 µg/g body weight per injection also inhibited tumor cell proliferation as measured by the tritated thymidine autoradiography labeling index. Amiloride caused no changes in the mean profile diameters of metaphase or interphase H6 hepatoma or DMA/J mammary adenocarcinoma cells, suggesting that the action of amiloride on tumor growth was not due to cell volume changes. These data show that amiloride both inhibited tumor growth and decreased the proliferation of the tumor cells in the H6 hepatomas which was correlated with a decreased intranuclear sodium content.