Genetically engineered probiotics for an optical imaging-guided tumor photothermal therapy/immunotherapy

Bacteria-based cancer therapy (BCT) has been extensively investigated because of the tumor targeting and antitumor immunity activating abilities of bacteria over traditional nanodrugs, but their potential systemic toxicity poses a challenge. Therefore, it is important to visualize the precise localization and real-time distribution of bacteria in vivo to guide the treatment. Herein, biogenetically engineered Escherichia coli Nissle 1917 (EcN) were constructed to highly express tyrosinase to intracellularly generate cyanine 5-labeled melanin-like polymers (Cy5-Mel), thus endowing them with a bright fluorescence and an excellent photothermal performance upon NIR laser irradiation, thereby inducing the intense immunogenic death of tumor cells and release of tumor-associated antigens. Acting as adjuvants, bacteria can greatly stimulate the maturation of dendritic (DC) cells. The in vivo behaviors of these bacteria was monitored via noninvasive optical imaging when they were intravenously administrated to tumor-bearing mice. From this, NIR exposure on tumor sites was carried out at an appropriate time point to induce the damage to tumor cells and for the modulation of tumor immune microenvironments. Thus, via a simple bioengineering strategy, a promising bacteria-based theranostic platform was constructed for tumor treatment. It is important to visualize the precise localization and real-time distribution of bacteria in vivo to guide bacteria-based cancer therapy.