Storable Polydopamine Nanoparticles Combined with Bacillus Calmette‐Guérin for Photothermal‐Immunotherapy of Colorectal Cancer

Photothermal immunotherapy emerges as a promising strategy for treating tumors. However, the majority of current photothermal immunotherapy approaches do not yet show significant potential for clinical translation. In this study, lyophilized polydopamine (PDA) nanoparticles combined with Bacillus Calmette–Guérin (BCG) are investigated for photothermal immunotherapy against colorectal cancer. By simply mixing with two lyophilized powders, PDA nanoparticles can covalently bond onto BCG to form BCG@PDA. This combination demonstrates a potent photothermal cytotoxic effect on tumor cells by utilizing PDA nanoparticles. In addition, a heightened immune response triggered by the BCG vaccine, as evidenced by the secretion of important pro‐inflammatory cytokines and the activation of antigen‐presenting cells, is observed. In vivo testing on a murine colon cancer model demonstrates that the combined treatment significantly inhibits tumor growth. Further, the lyophilized PDA nanoparticles can be stored at −20 °C for up to 1 year with stable photothermal properties. Therefore, this study not only presents a reliable method for storing the therapeutic PDA nanoparticles but also demonstrates the potential application of BCG@PDA in photothermal immunotherapy for colorectal cancer. A convenient photothermal‐immunotherapy using lyophilized PDA nanoparticles and BCG vaccine is reported for the treatment of colorectal cancer. PDA nanoparticles can be stable in storage for at least 1 year. Meanwhile, the method shows promise for colorectal cancer ablation as it effectively inhibits tumor growth and stimulates a potent immune response.