361. Radiation-Induced Lung Apoptosis Is Mediated by TNF-alpha Action

Lung damage by radiation limits the efficacy of radiotherapy for lung cancer. This damage correlates with lung apoptosis that can be initiated by various cytokines. In this study, we investigated the role of TNF-alpha in radiation-induced lung apoptosis and the potential protective effect of inhibiting TNF-alpha action by using antisense oligonucleotide (ASO) gene therapy. We demonstrated that regional ionizing radiation induced lung apoptosis in mice in a time-and dose-dependent manner. TUNEL staining and caspase-3 activation in lung were increased maximally at 3 h after 15 Gy of radiation by approximately 5-and 3-fold. These inductions were correlated with the increases in TNF-alpha production (|[sim]|2-fold) and gene transcripts (|[sim]|30%), and moderate induction of TNFR1 mRNA levels (|[sim]|20%) in irradiated lung. Pre-treatment of mice using specific ASO significantly inhibited TNFR1 gene transcription by 50% in lung but had no effect on the induction of TNF-alpha transcription by radiation. The reduction of TNFR1 by ASO pre-treatment, and thus, the inhibition of TNF-alpha action, prevented lung from radiation-induced apoptosis. Moreover, we demonstrated that radiation stimulated TNF-alpha production in cultured lung macrophages (|[sim]|2-fold) but not microvascular endothelial cells, although increased caspase-3 activation was observed in both cell types after radiation treatment. Radiation-induced caspase-3 activation in co-cultured cells was diminished in the presence of TNF-alpha antibody, suggesting that radiation-induced TNF-alpha secretion mediated cell apoptosis. These findings support the idea that radiation induces lung apoptosis through upregulation of TNF-alpha, providing us the rationale for TNF-alpha targeted strategies for lung protection.