Poly(I:C) potentiates Bacillus Calmette-Guérin immunotherapy for bladder cancer.

ABSTRACT

Non-specific immunotherapy consisting of intravesical instillation of Bacillus Calmette-Guérin (BCG) is currently the best available treatment to prevent non-muscle-invasive bladder tumor recurrence and progression. This treatment however is suboptimal, and more effective immunotherapeutic approaches are needed. Toll-like receptors (TLRs) play a major role in the activation of the immune system in response to pathogens and danger signals but also in anti-tumor responses. We previously showed that human urothelial cells express functional TLRs and respond to TLR2 and TLR3 agonists. In this study, we analyzed the potential of polyinosinicpolycytidylic acid [poly(IC)], a TLR3 agonist, to replace or complement BCG in the treatment of non-muscle-invasive bladder cancer. We observed that poly(IC) had an anti-proliferative, cytotoxic, and apoptotic effect in vitro on two low-grade human bladder cancer cell lines, MGH-U3 and RT4. In MGH-U3 cells, poly(IC) induced growth arrest at the G1-S transition. Poly(IC) also increased the immunogenicity of MGH-U3 and RT4 cells, inducing the secretion of MHC class I molecules and of pro-inflammatory cytokines. By comparison, poly(IC) had less in vitro impact on two high-grade human bladder cancer cell lines, 5637 and T24, and on MBT-2 murine high-grade bladder cancer cells. The latter can be used as an immunocompetent model of bladder cancer. The combination poly(IC)/BCG was much more effective in reducing MBT-2 tumor growth in mice than either treatment alone. It completely cured 29% of mice and also induced an immunological memory response. In conclusion, our study suggests that adding poly(IC) to BCG may enhance the therapeutic effect of BCG.