Changes In Radiosensitivity Of PC3 Prostate Cancer Cells Induced By Alteration Of The Autophagy Process

Purpose:Treatment options vary depending on the age, stage and grade of the cancer. Current treatment for prostate cancer consists of extirpative, radiation or ablation based approaches for clinically for metastatic disease and androgen deprivation therapy for metastatic disease. Recent studies have indicated that autophagy may be one of the important pathways induced by ionizing radiation. In our study, changes in radiosensitivity of radioresistant human PC3 prostate cancer cells to radiotherapy by alteration of pathways related to autophagy were investigated.Methods and Materials:Activation of the autophagy pathway was analyzed using the GFP-LC3 assay and western blot to determine LC3-II expression. The radiosensitivity of PC3 cells was determined using the clonal survival assay and the Annexin V assay after exposure to gamma irradiation and/or various chemicals. The expression profiles of autophagy related genes were analyzed using a pathway specific real-time polymerase chain reaction array.Results:PC3 cells exhibited an induced autophagic response after exposure to gamma rays. Inhibition of the autophagic process using small interfering RNAs targeting Atg7 and/or Atg 12 significantly reduced radiosensitivity of PC3 cells. The lysosomotropic agent chloroquine did not significantly affect the colony formation of the irradiated PC3 cells, but did induce apoptosis in a fraction of irradiated cells (20%). Both autophagy activators RAD001 and Statin sensitized the cells to gamma irradiation, showing significantly reduced colony forming efficiency in response to 6 Gy of gamma irradiation. Statin treatment of pc3 cells for 24h increased expression of GFP-LC3-â…¡by more than 25% fold and keep expressing for more than 72h,whereas, apoptosis is not significantly induced within these moment. Analysis of autophagy and its regulatory gene profile showed that the expressions of 22 genes out of 84 genes assessed were significantly altered in the cells exposed to combined treatment with Statin and radiation, including nine genes encoding components of the autophagy machinery.Conclusions:The prostate cancer research on the cell level showed autophagy can be induced by gamma ray, and no matter combined with autophagy inducer/inhibitor or Atg specific siRNA to mediate activation of autophagy pathway, the cell survival status can be affected. The further experiment suggested that activate the cellular autophagy pathway can enhance the gamma ray radiosensitivity of PC3 cells. Therefore, combined treatment with radiation and autophagic inducers, such as Statin, may be synergistic in tumor cell killing and tumor control.