Redox Gene Therapy Protects Human IB-3 Lung Epithelial Cells Against Ionizing Radiation-Induced Apoptosis

Abstract

Toxicity to nontumor-derived tissue has proven to be a significant obstacle in achieving therapeutic levels of gamma irradiation in the treatment of cancer. The formation of reactive oxygen species (ROS) such as superoxide radicals (O₂¯) following irradiation is thought to be a major determinant of cellular damage. To this end, we describe the generation of two recombinant adenoviral vectors expressing the radical-scavenging enzymes MnSOD and CuZnSOD to test therapeutic strategies of radioprotection. Using a human lung epithelial cell line (IB-3), we have demonstrated that infections with both Ad.CMVMnSOD or Ad.CMVCuZnSOD significantly increase both the levels of SOD protein and enzymatic activity as compared to control cells. This increase in SOD expression reduced the level of apoptosis at 72 hr post-irradiation by 50% as compared to mock- or Ad.CMVLacZ-infected cells. Such studies provide the foundation for radioprotective gene therapies in the treatment of cancer. Adenovirus-mediated gene delivery of MnSOD and CuZnSOD to human lung epithelial cells (IB-3) resulted in efficient expression of the two free-radical scavenging enzymes. Recombinant MnSOD and CuZnSOD localized to their normal endogenous sites, which are the mitochondria and cytoplasm, respectively. It is thought that ionizing radiation leads to the generation of superoxide radicals, which, in return, can be involved in cellular damage and death. The expression of the two enzymes gave rise to reduced apoptosis following gamma irradiation. These studies implicate superoxide radicals in the signaling of gamma irradiation-induced apoptosis and set the stage for radioprotective gene therapies.