Abstract LB-358: Soy improves radiotherapy for lung tumors and mitigates radiation-induced injury to lung tissue.

Abstract

Abstract Radiotherapy of locally-advanced non-small cell lung cancer (NSCLC) is limited by pneumonitis and fibrosis caused by radiation-induced injury to normal lung tissue. We have investigated the effect of a high thoracic dose of radiation combined with soy isoflavones in a pre-clinical model of orthotopic A549 human lung carcinoma xenografts in nude mice. Mice bearing established lung tumors (>300µm) were pretreated with soy for 3 days starting day 15 after A549 cell injection, and then received 10 Gy irradiation administered to the whole lung. Soy treatment, given orally at 1mg/day (50mg/kg) was continued for 5 days per week for 4 more weeks, then lungs were perfused with formalin and processed for histology. The effect of the therapy on the tumor cells, the surrounding tumor microenvironment and lung tissue structures was further analyzed using novel immunostaining and quantitative techniques. Compared to large invasive lung tumor nodules (up to 1-2 x 106 µm2) in untreated mice, the combined therapy caused a significant inhibition of tumor progression in lungs resulting in few residual small tumor nodules (0.02-0.07 x 106 µm2, p<0.05) with a low index of proliferation (mean of 16 positive nuclei for Ki-67 compared to 147 in control tumors, p<0.001). Pneumonitis was evaluated by morphometric measurements of the thickness of alveolar septa on H&E stained lung tissue sections. Soy isoflavones reduced the extent of pneumonitis induced by radiation resulting in 30% of the lung tissue with thickened septa compared to 45% observed in lungs treated with radiation only. Fibrosis staining using Masson's Trichrome revealed that radiation caused a dramatic increase in collagen fibers supporting the vessel and bronchiole walls and this effect was mitigated by soy isoflavones. Triple immunofluorescent staining of lung vessel walls was performed on lung tissue sections using antibodies specific to endothelial cells (anti-CD31), pericytes (anti-SMA) and collagen (anti-collagen IV). This technique revealed that soy isoflavones combined with radiation decreased the fraction of vessels with damaged basement membrane to 25% down from 42% in radiation-alone treated lungs. Thus, these studies demonstrate a differential effect of soy isoflavones on augmenting tumor destruction induced by radiation while acting as radioprotectors for the surrounding lung tissue. Soy isoflavones reduced pneumonitis and fibrosis, and preserved the integrity of lung structures including alveolar septa, bronchioles and vessels, probably by mitigation of the inflammatory response induced by radiation. Complementing cancer radiotherapy with soy isoflavones has the potential to improve its effectiveness on the tumor target and reduce dose-limiting radiotoxicity to the normal lung and could be applied in the treatment of advanced stage NSCLC. Citation Format: Gilda Gali Hillman, Vinita Singh-Gupta, David J. Hoogstra, Lisa Abernathy, Joseph Rakowski, Christopher Yunker, Fazlul H. Sarkar, Andre A. Konski, Fulvio Lonardo, Michael C. Joiner. Soy improves radiotherapy for lung tumors and mitigates radiation-induced injury to lung tissue. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-358. doi:10.1158/1538-7445.AM2013-LB-358