Abstract 277: Radioprotection of lung tissue involves modulation of radiation-induced macrophage activation by soy isoflavones

Radiation therapy for lung cancer is limited by radiation toxicity to lung tissue that results from a chronic inflammatory response, leading to pneumonitis and fibrosis. We have reported in preclinical mouse models that treatment with soy isoflavones mitigates inflammatory cytokines and fibrosis, but the cellular mediators of radioprotection remain unclear. Macrophages possess the plasticity to respond to environmental stressors in tissues that functionally may range from proinflammatory to immunosuppressive phenotypes. We hypothesize that soy isoflavones mediate radioprotection of normal lung tissue by modifying macrophage phenotype and function in irradiated lungs. In this study, we investigate the role of lung macrophage subsets in radioprotection of lung tissue by soy. BALB/c mice received a single 10 Gy dose of thoracic irradiation with soy isoflavones given orally at 1 mg per day, prior-to and continuously after radiation for up to 18 weeks. Bronchoalveolar lavage (BAL) fluid and lungs were harvested at early and late time points post-radiation. Differential cell counts on BAL fluid cytospins were performed and ratios of enlarged, foamy macrophages and smaller macrophages were calculated. At 4 weeks, lungs were dissociated into single cell suspensions and cells were stained with anti-CD45, anti-F4/80, and anti-CD11c fluorescent antibodies to analyze interstitial (F4/80+CD11c-) and alveolar (F4/80+CD11c+) lung tissue macrophages by flow cytometry. In situ M1 macrophages were detected by immunohistochemical staining in lung tissue sections for the pan-macrophage marker F4/80 and the M1 macrophage activation marker NOS2. At 18 weeks after radiation, there was a significant increase in the percentage of enlarged, foamy macrophages in BAL fluid to 79.0±6.7% compared with 14.6±5.3% in control (p = 0.0003). Soy significantly inhibited this radiation-induced increase to 33.1±8.3% compared with radiation alone (p = 0.0091). In situ staining of F4/80 and NOS2 in lung tissue sections revealed an increase of activated M1 macrophages caused by radiation in contrast to relatively low NOS2 levels in lungs of mice treated with radiation and soy or control. Soy significantly reduced the percentage of F4/80+CD11c- interstitial macrophage (p = 0.0313) in lung tissue post-radiation. F4/80+CD11c+ alveolar macrophages in lungs are significantly decreased (p = 0.0074) after radiation, however soy did not have a significant effect (p = 0.7160). These data indicate that radiation-induced proinflammatory M1 macrophage activation is inhibited by soy. Further studies are ongoing to clarify the role of interstitial and alveolar macrophages in radiation-induced lung inflammation and its regulation by soy. These findings suggest that soy modulation of the macrophage subset functions in response to radiation may play a critical role in soy-mediated radioprotective effects in lungs. Citation Format: Lisa M. Abernathy, Matthew D. Fountain, John M. David, Christopher K. Yunker, Michael C. Joiner, Gilda G. Hillman. Radioprotection of lung tissue involves modulation of radiation-induced macrophage activation by soy isoflavones. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 277. doi:10.1158/1538-7445.AM2015-277