Digoxin enhances radiation response in radioresistant A549 cells by reducing protein phosphatase 2A

Abstract

Protein phosphatase 2A (PP2A) is a ubiquitous multifunctional enzyme usually known as a tumor suppressor. Recent studies have reported that although inhibition of PP2A leads to acceleration of cell growth, it also induces damaged cells to pass through the cell cycle and renders them sensitive to radiotherapy. Here, we investigated the radiosensitizing effects of digoxin as a PP2A inhibitor in two non-small-cell lung cancer (NSCLC) cell types (H460 and A549) with differential sensitivity to radiation. Digoxin inhibited the proliferation of H460 and A549 cells in a dose-dependent fashion and was especially effective on radioresistant A549 cells. Interestingly, the radiosensitizing effect of digoxin was only present in the radioresistant A549 cells and xenografts. The combination of digoxin and ionizing radiation (IR) significantly reduced clonogenic survival and xenograft tumor growth (PP<0.001). In conclusion, digoxin has a novel function as a PP2A inhibitor, and combined with IR produces a synergistic effect on radiosensitizing cells, thereby indicating a potentially promising therapeutic approach to radioresistant lung cancer treatment.