Abstract 4902: Low dose Ganetespib (STA-9090) enhances radiotherapy effects on lung cancer cells by synergistically altering levels of cell cycle progression proteins

Abstract

Abstract Radiotherapy is an important component for the curative management of locally advanced non-small cell lung cancer (LA-NSCLC); however radioresistance can hamper the efficacy of treatment. Biological innovations by combining molecular targeted therapy with radiation could potentially enhance radiotherapy efficacy. Hsp90 (heat shock protein 90) is a chaperone protein that assists other proteins in folding, stability and degradation. Since Hsp90 stabilizes a variety of client proteins required for survival of cancer cells, Hsp90 inhibitors are currently studied for their therapeutic benefit in the treatment of various types of malignancies. One drug in particular is Ganetespib, a potent second generation HSP90 inhibitor with minimal ocular and hepatic toxicities, has proven improved efficacy in Stage IV NSCLC in combination with docetaxel, and is now in phase III clinical testing (GALAXY-II). The purpose of our study is to determine if low dose (25 nM) Ganetespib in combination with irradiation can enhance the radiotherapeutic effects on human lung cancer cells. The experiments were conducted using Kras mutant H460 and A549 cells, and Kras wild type H1650 cells with p53 mutation. Cell survival was measured by clonogenic survival assay (CSA). Cell cycle distribution was analyzed by flow cytometry. Expression and activity of radiosensitivity related proteins was investigated by RPPA and western blotting. Our results demonstrated that Ganetespib reduced radiation clonogenic survival on lung cancer cells, and greatly attenuated DNA damage repair with irradiation as assessed by P53BP1 foci formation. Cell cycle analysis showed that Ganetespib dramatically increased G2/M arrest between 24-48 hours, which placed cells in the radiosensitive part of the cell cycle, thereby promoting subsequent apoptosis after 48 hours. On RPPA, while higher doses of Ganetespib (50-100 nM) completely attenuated the expression of important client growth factor and survival promoting proteins such as EGFR, Her-2, AKT, and mTOR, and enhanced expressed of apoptotic pathways proteins, radiation dose-dependently acted in concert with low dose Ganetespib to upregulate p21 and downregulate pRb levels that were not apparent with either drug or radiation alone. These results suggest that low dose Ganetespib can act as a potent radiosensitizer in the treatment of NSCLC by altering levels of cell cycle progression proteins. Ganetespib in combination with radiotherapy should be explored clinically in LA-NSCLC. Citation Format: Hui Liu, Adam Potter, Jingya Wang, Uma Giri, Steven H. Lin. Low dose Ganetespib (STA-9090) enhances radiotherapy effects on lung cancer cells by synergistically altering levels of cell cycle progression proteins. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4902. doi:10.1158/1538-7445.AM2014-4902