Intratumoral hypoxia significantly constrains the susceptibility of solid tumors to oxygen-dependent photodynamic therapy (PDT), and effort to reverse such hypoxia has achieved limited success to date. Herein, we developed a novel engineered bacterial system capable of targeting hypoxic tumor tissues and efficiently mediating the photodynamic treatment of these tumors. For this system, we genetically engineered Escherichia coli to express catalase, after which we explored an electrostatic adsorption approach to link black phosphorus quantum dots (BPQDs) to the surface of these bacteria, thereby generating an engineered E. coli/BPQDs (EB) system. Following intravenous injection, EB was able to target hypoxic tumor tissues. Subsequent 660 nm laser irradiation drove EB to generate reactive oxygen species (ROS) and destroy the membranes of these bacteria, leading to the release of catalase that subsequently degrades hydrogen peroxide to yield oxygen. Increased oxygen levels alleviate intratumoral hypoxia, thereby enhancing BPQD-mediated photodynamic therapy. This system was able to efficiently kill tumor cells in vivo, exhibiting good therapeutic efficacy. In summary, this study is the first to report the utilization of engineered bacteria to facilitate PDT, and our results highlight new avenues for BPQD-mediated cancer treatment.
Keywords: black phosphorus quantum dots; engineered probiotic; photodynamic therapy; tumor hypoxia microenvironment; tumor targeting.