P042

1:Universitat Autònoma de Barcelona

Mycobacterium bovis Bacillus Calmette-Guérin (BCG) is the standard treatment for high-risk nonmuscle-invasive bladder cancer (NMIBC). Despite to be the first therapy option for more than 40 years, the mechanism of action is unknown. The interaction between BCG and tumor cells is critical for investigating the antitumoral effects and new strategies for cancer treatment. Until now, only 2D in vitro cultures have been studied to understand mycobacteria-bladder cancer cell interaction. However, studies using 3D cultures such as spheroids has not been performed. Spheroids are cell aggregates composed of non-progenitor and differentiated cells. Three-dimensional structure enables the formation of oxygen, nutrient, and pH gradients. This gradient variability creates layer heterogeneity and makes spheroids mimic avascular solid tumors more effectively compared to 2D cultures. 

In the present study, we have optimized five types of bladder cancer spheroids derived from different cell lines. The interaction between BCG and Mycobacterium brumae, a nontuberculous immunomodulatory species safer than BCG, and spheroids has been analyzed. Our results showed that each spheroid type exhibited distinct size, morphology, and growth rate. When treated with mycobacteria, the data indicated that the differentiation grade of the cancer cell lines drives the interaction with mycobacteria modulating their antitumoral effects with corresponding variations in tumor cell proliferation inhibition and induction of cytokines’ release. Our work adds evidence of the relevance of culture conditions for unraveling the immunomodulatory and antitumor ability of mycobacteria.