BEZ235 enhances the photodynamic antitumor efficacy of hypoxia-responsive BODIPY prodrug nanoparticles by inhibiting the PI3K/mTOR pathway and alleviating hypoxia

Hypoxia is a distinctive characteristic of solid tumors, limiting the efficiency of photodynamic therapy (PDT). In this study, transcriptomics was applied to analyze the changes in mRNA levels in mouse tumors treated with multiple photodynamic therapy sessions, revealing that 12 genes in the PI3K/mTOR pathway were significantly upregulated. In order to improve delivery efficiency and enhance the efficacy of PDT photosensitizers, a nitroreductase-responsive BODIPY prodrug (BNP) was designed and employed to encapsulate a PI3K/ mTOR dual inhibitor (BEZ235) to self-assemble into nanoparticles (BNP@BEZ NPs). The fluorescence level of BNP@BEZ NPs in hypoxic cells was 12.20-fold that in normoxic cells because of the responsiveness of nitrobenzyl groups to hypoxia. Such minimized off-target effects also resulted in preferential intratumoral activation of prodrugs. Meanwhile, BEZ co-loading alleviated tumor hypoxia and increased intracellular ROS levels to 155.26% compared to blank prodrug nanoparticles. BNP@BEZ NPs-mediated PI3K/mTOR inhibition and apoptosis of tumor cells exhibited sufficient antitumor efficacy with a tumor inhibition rate of 93.31%. In conclusion, this study confirms that the PI3K/mTOR pathway promotes tumor PDT resistance by enhancing mitochondrial respiration. The hypoxic -responsive photodynamic properties of BNP, combined with BEZ's oxygen consumption-inhibiting capacity, can enhance tumor suppression rates. This strategy of nanomedicine development by capitalizing on the synergistic effect between active ingredients will avoid the low efficacy and adverse effects of monotherapies.