The role of HMGB1 in radio-resistance of bladder cancer.
Although radical cystectomy surgery is the standard of care for muscle-invasive bladder cancer, it entails complete removal of the bladder and surrounding organs which leads to substantial loss in patient quality of life. Radiation therapy, which spares the bladder, would be a more appropriate treatment modality if we can utilize molecular markers to select patients with better response to radiation. In this study we investigate a protein called HMGB1 (High Mobility Group Box protein 1) as a predictive marker for radiation therapy response in bladder cancer. Our in vitro results indicate a positive correlation between higher levels of HMGB1 protein and resistance to radiation in various cell lines. Upon HMGB1 protein knockdown highly significant (more than 1.5 fold) sensitization to radiation therapy was achieved. We saw that loss of HMGB1 was associated with atleast 2 times higher (P<0.001) DNA damage in cell lines post radiation. Our results also depicted that autophagy was inhibited more than 3 fold (P<0.001) upon HMGB1 knockdown implicating its role in autophagy as another cause of bladder cancer radioresistance. Further validation was done in vivo by conducting mice tumor xenograft experiments, where HMGB1 knockdown tumors showed a significantly better (P<0.001) response to radiation therapy and decreased autophagy (shown by P62 staining) as compared to controls. The cumulative findings of our in vitro and in vivo studies highlight the significance of HMGB1 as a radiation response marker as well as its utility in radio-sensitization of bladder cancer.