Inhibition of Heme Oxygenase-1 Enhances the Radiosensitivity in Human Nonsmall Cell Lung Cancer A549 Cells

Overexpression of the heme oxygenase-1 (HO-1) gene in many solid tumors was believed to be one reason why cancer patients undergoing radiotherapy or chemotherapy failed to respond. The aim of this study was to evaluate whether Inhibitor of HO-1, zinc protoporphyrin IX (Znpp), enhances the radiosensitivity in human nonsmall cell lung cancer (NSCLC) A549 Cells. A549 cells were induced by Znpp and irradiated by X-rays. Then, expression of HO-1 was measured by real-time polymerase chain reaction. Cell survival was evaluated using the MTS assay and the clonogenic survival assay; apoptosis and cell cycle distribution were monitored by flow cytometry. First, overexpression of the HO-1 mRNA was found in treatment with irradiation alone in A549 cells, and expression of the HO-1 mRNA was reduced after combined treatments with 12 mu mol/L of Znpp and irradiation. Second, diminished cell viability percentage, decreased cell clonogenic survival fraction, enhanced cell apoptotic index, and increased percentage of cells in the G1 phase were found after combined treatments with 12 mu mol/L of Znpp and irradiation compared to either treatment alone (p < 0.05). Inhibitor of HO-1, Znpp, can increase the radiosensitivity of human NSCLC A549 cells.