Radiosensitization of histone deacetylases inhibitor panobinostat in prostate cancer cells

Objective: To study the radiosensitization of histone deacetylases inhibitor (HDACI) panobinistat in prostate cancer cells in vitro, as well as the possible mechanisms. Methods: IC20 of two prostate cancer cell lines (LNCaP and PC-3)was determined using MTT assay. Cells received a single dose irradiation of 0, 2, 4, 6, or 8 Gy using 6 MV X-ray for radiosensitivity experiment, but only 2 Gy for western blot and flow cytometry. Radiosensitization of panobinostat was investigated with clonogenic assay, and sensitizing enhancement ratio (SER) was calculated with single-hit multi-target model.Western blot was used to compare γH2AX expression. Flowcytometry was used to detect the cell cycle distribution. Results: IC20 of LNCaP and PC-3 was 2.5 and 10.0 μmol/L, respectively. SER of panobinostat at IC20 was 1.37 (D0 ratio) and 1.11 (Dq ratio) for LNCaP cells, and 1.78 (D0 ratio) and 1.17 (Dq ratio) for PC-3 cells. Expression of γH2AX gradually decreased in the 2 Gy irradiation-alone cells standing for the DSB repair, while γH2AX expression was persistent in the combination group. Irradiation triggered a G2/M arrest 6-12 hours after irradiation in LNCaP and PC-3 cells. G2/M arrest was observed when cells were treated with panobinostat for 24 hours, however, no significant change concerning cell cycle distribution was showed when cells received further irradiation. Conclusions: Panobinostat Call radiosensitize prostate cancer cells, which may be related with increased DNA DSB, inhibition of DSB repair and attenuation of cell cycle modulation after irradiation. (authors)