ABT-737, a BH3 Mimetic, Enhances the Therapeutic Effects of Ionizing Radiation in K-ras Mutant Non-Small Cell Lung Cancer Preclinical Model

PURPOSE: Tumor radioresistance and dose-limiting toxicity restrict the curative potential of radiotherapy, requiring novel approaches to overcome the limitations and augment the efficacy. Here, we investigated the effects of signal transducer and activator of transcription 3 (STAT3) activation and autophagy induction by irradiation on antiapoptotic proteins and the effectiveness of the BH3 mimetic ABT-737 as a radiosensitizer using K-ras mutant non-small cell lung cancer (NSCLC) cells and a Kras(G12D):p53(fl/fl) mouse (KP mouse) model. MATERIALS AND METHODS: A549 and H460 cells were irradiated, and the expression of Bcl-2 family proteins, JAK/STAT transcriptional pathway, and autophagic pathway were evaluated by immunoblotting. The radiosensitizing effects of ABT-737 were evaluated using A549 and H460 cell lines with clonogenic assays and also by a KP mouse model with microcomputed tomography and immunohistochemistry. RESULTS: In A549 and H460 cells and mouse lung tissue, irradiation-induced overexpression of the antiapoptotic molecules Bcl-xL, Bcl-2, Bcl-w, and Mcl-1 through JAK/STAT transcriptional signaling induced dysfunction of the autophagic pathway. After treatment with ABT-737 and exposure to irradiation, the number of surviving clones in the cotreatment group was significantly lower than that in the group treated with radiation or ABT-737 alone. In the KP mouse lung cancer model, cotreatment with ABT-737 and radiation-induced significant tumor regression; however, body weight changes in the combination group were not significantly different, suggesting that combination treatment did not cause systemic toxicity. CONCLUSION: These findings supported the radiosensitizing activity of ABT-737 in preclinical models, and suggested that clinical trials using this strategy may be beneficial in K-ras mutant NSCLC.