Investigating the STING Pathway to Explain Mechanisms of BCG Failures in Non-Muscle Invasive Bladder Cancer: Prognostic and Therapeutic Implications

Abstract

Background: Intravesical Bacillus Calmette Guerin (BCG) has been the gold standard immunotherapy to treat high risk non-muscle invasive bladder cancer (NMIBC) for over 40 years. Attenuation of Mycobacterium bovis for clinical use as BCG results in loss of its ability to activate the 'Stimulator of Interferon Genes' (STING) pathway and potentially limits local anti-tumor immune activity and subsequent BCG responsiveness due to reduced induction of the immune cell recruiting chemokines primarily, CXCL10. We conducted the current study to determine the potential of STING pathway agonist in synergizing with BCG to enhance chemokine induction. Methods: The TICE strain of BCG (OncoTICE) was used in combination with STING agonist to determine STING pathway activation and CXCL10 production in THP-1 monocytic cell line, THP-1 defNLRP3, THP-1 dual STING knock out cells, RT112 bladder cancer cells and primary bladder epithelial cells. NanoString platform-based gene expression profiling and multiplex cytokine analysis were performed to determine induction of interferon associated genes and secreted cytokines. Results: Activation of cytosolic pattern recognition receptor and downstream IFN1 pathways demonstrated synergistic activation of STING pathway enhanced BCG induced inflammasome and STING pathway gene expression in monocytes and bladder cancer cells. The significant differences in CXCL10, CCL5, IL-8 and MIP-1a/1b amongst the knock-out cell lines confirm the convergence of these pathways following combination treatment with BCG and STING agonist. Conclusions: Findings from our study are the first evidence indicating that STING pathway activators are promising new innate immune modulators with a potential to synergize with BCG therapy in the treatment of NMIBC.