An injectable hydrogel co-loading with cyanobacteria and upconversion nanoparticles for enhanced photodynamic tumor therapy.

Photodynamic therapy (PDT) is an exceedingly promising cancer treatment. However, the hypoxic environment in tumor and the low penetration efficiency of short-wavelength light limit the effects of PDT. In this paper, an injectable red blood cell membrane doped hydrogel system (UCNPs/S7942/RB-RHY) containing upconversion nanoparticles (UCNPs), a photosensitizer (Rose Bengal) and a strain of cyanobacteria Synechococcus elongatus PCC 7942 (S. 7942) was developed to improve the PDT effects with a good biocompatibility and biosafety. In the system, S. 7942 was capable of inexhaustibly generating oxygen triggered by the 640 nm laser irradiation for alleviating hypoxic tumor microenvironment. In addition, UCNPs converted near-infrared light to visible light upon excitation by a 980 nm laser, which further activated the photosensitizer to release reactive singlet oxygen to eradicate tumors. In vivo experiments showed that the tumor volume in the UCNPs/S7942/RB-RHY combined 640 nm with 980 nm light group was 496.9 mm3, in compared with 955.5 mm3 of the tumor volume in the group without irradiation. The results demonstrated that UCNPs/S7942/RB-RHY was able to not only dramatically alleviate tumor hypoxia but also achieve a more efficient PDT treatment. The oxygen-generating system described here provides a new idea for hypoxia-resistant cancer therapy in the future.