Hedgehog Inhibition and Radiation Therapy in Non-Small Cell Lung Cancer.

7065 Background: Radiation concurrent with cytotoxic chemotherapy remains the standard of care for the management of locally advanced NSCLC. Despite this treatment paradigm, local control remains a problem with local recurrence in 50-75% of patients, and may be an important contributor to metastatic spread. The hedgehog signaling pathway is aberrantly activated in adult malignancies, including NSCLC. We seek to investigate the effect of Hh pathway inhibition on radiation response in preclinical modals of NSCLC. Methods: Utilizing in vitro and in vivo models, we studied hedgehog inhibitor (HhI) cytotoxicity and radiosensitization in NSCLC. In vitro we examined the effect of HhI with and without radiation on cell death, clonogenic survival, cell cycle distribution, and GLI1 expression. Using a hind-flank xenograft model, we looked at tumor growth delay and Ki-67 staining. In a novel inducible transgenic mouse model of KrasG12D/Twist-induced autochthonous lung adenocarcinoma, tumor responses to lung radiation with or without HhI were assessed serially with weekly microCT. Results: HhI sensitized A549 cells to ionizing radiation as shown by colony formation assays (enhancement ratio 1.3). Increased cell death was a result of increased apoptosis as shown by annexin-V expression. A549 had high GLI1 expression via Western, but did not show cell cycle changes upon treatment with HhI. Hind-flank xenograft experiments demonstrate HhI and radiation delay tumor growth in vivo (one-way ANOVA p<0.001). Ki-67 immunofluorescence showed decreased cellular proliferation in tumors treated with HhI. In transgenic mice with autochthonous lung tumors, weekly micro-CT revealed improved tumor shrinkage with the addition of HhI to lung radiation. At 1-week post-radiation, HhI and radiation induced 45% tumor shrinkage, whereas radiation alone was 17% and HhI alone was 12% (p<0.01 by two-tailed t-test). Conclusions: Our data show that selectively targeting the hedgehog pathway increases the effectiveness of radiation in in-vitro and in-vivo systems of NSCLC. This data provides a framework for clinical translation of HhI with concurrent chemoradiotherapy in locally advanced NSCLC.