MiR-195/-16 Family Enhances Radiotherapy via T Cell Activation in the Tumor Microenvironment by Blocking the PD-L1 Immune Checkpoint

Background/Aims: Radiotherapy is the standard treatment option for advanced prostate cancer. Unfortunately, despite significant advances in radiation delivery, prostate cancer radioresistance occurs in a large proportion of patients undergoing radiotherapy. As a way to enhance radiotherapy effectiveness, research advances into the mechanisms regulating the immune response have revived interest in combination radiation and immune-based therapies. Methods: miR-195/-16 family and PD-L1 levels were analyzed in samples from a GSE21032 data set. Kaplan-Meier analysis was used to evaluate the difference in biochemical recurrence-free survival associated with miR-195 and miR-16 expression. qRT-PCR and western blot were used to evaluate the miR-195, miR-16 and PD-L1 expression. Then, we used bioinformatics analysis and luciferase reporter assay to predict and confirm the miR-195 and miR-16 target gene. Finally, we elucidate the miR-195 and miR-16 function on immune evasion in the DU145/T cell co-culture model and syngeneic mouse model treated with radiotion through qRT-PCR, western blot, Flow cytometry and ELISA. Results: High levels of miR-195 and miR-16 were positively correlated with the biochemical recurrence-free survival of prostate cancer patients. miR-195 and miR-16 were inversely correlated with PD-L1, PD-1, CD80 and CTLA-4 expression. Further mechanistic investigations revealed that miR-195 and miR-16 inhibited PD-L1 expression. Additionally, restoration of miR-195 and miR-16 expression enhanced radiotherapy via T cell activation in the tumor microenvironment by blocking PD-L1 expression. This synergistic effect of immunotherapy and radiotherapy was associated with the proliferation of functional cytotoxic CD8+ T cells and inhibition of myeloid-derived suppressor cells and regulatory T cells. Conclusions: Our data revealbiological and functional interactions between immunotherapy and radiotherapy through the miR-195/-16 family regulatory cascade.