Hsp90 Inhibitors NVP-AUY922 and NVP-BEP800 May Exert a Significant Radiosensitization on Tumor Cells along with a Cell Type-Specific Cytotoxicity

Targeting heat shock protein 90 (Hsp90) provides a promising therapeutic approach to enhance the sensitivity of tumor cells to ionizing radiation (IR). To explore the impact of scheduling drug-IR administration, in the present study, we analyzed the response of lung carcinoma A549 and glioblastoma SNB19 cells to simultaneous drug-IR treatment followed by a long-term drug administration. Cellular response was evaluated at different time intervals after IR-alone, drug-alone, or combined drug-IR treatments by colony counts and expression profiles of Hsp90 and its clients, along with several apoptotic markers and cell cycle-related proteins, as well as by IR-drug-induced cell cycle arrest, DNA damage, and repair. A short 30-minute exposure to either Hsp90 inhibitor did not affect the radiosensitivity of both tumor cell lines. Increasing the duration of post-IR-drug treatment progressively enhanced the sensitivity of SNB19 cells to IR. In contrast, the response of A549 cells to drug-IR combination was largely determined by the cytotoxic effects of both drugs without radiosensitization. Combined drug-IR treatment induced more severe DNA damage in both tumor cell lines than each treatment alone and also protracted the kinetics of DNA damage repair in SNB19 cells. In addition to large cell cycle disturbances, drug-IR treatment also caused depletion of the antiapoptotic proteins Akt and Raf-1 in both cell lines, along with a decrease of survivin in A549 cells in case of NVP-AUY922. The data show that simultaneous Hsp90 inhibition and irradiation may induce cell type-specific radiosensitization as well as cytotoxicity against tumor cells.