An Intricate Relationship Between miR-155-5p Expression and Oxidative Stress in Bladder Cancer Patients Treated with Calmette-Guerin Immunotherapy

Treatment failure after intravesical instillation of Bacillus Calmette-Guerin immunotherapy (BCG) for non- muscle-invasive bladder cancer (BCa) occurs frequently. The exact effects of BCG on cellular redox status and gene expression remain unclear. We assessed oxidative stress biomarkers and changes in miR-155-5p expression in response to BCG. Twenty-seven patients with BCa were recruited for measuring tissue and serum malondialdehyde (MDA) and total antioxidant capacity (TAC) levels, and tissue expression of miR-155-5p at two-time points: pre and 6 weeks post BCG. Recurrence of BCa was observed after 20 months. R statistical software was used for paired comparisons of biomarkers, as well as the correlation between variables. Significant increases in TAC were observed after BCG (P= <0.001). Tissue MDA levels were significantly reduced (P= 0.003). miR-155-5p was slightly overexpressed after BCG (median fold change=1.3, P=0.25). At the 20-month follow-up, it was observed that improved MDA and TAC changes were significant only in patients without recurrence of BCa. In patients with recurrence, the pre-treatment expression ratio of miR-155-p5 was positively correlated with TAC (R=0.63, P= 0.032) and negatively correlated with MDA (R=-0.72, P=0.037). In patients with recurrence of BCa pre-treatment miR-155-5p showed negative correlation with its expression changes after BCG (R=-0.78, P=0.004). Conclusions: Treatment with BCG has some beneficial effects on the oxidative stress status, which is probably modulated by miR-155-5p. A well-controlled oxidative balance may enhance overall survival of BCa. Considering its high recurrence rate, our pilot experiment can open a window toward better management of patients with BCa.