Acidic pH and High-H₂O₂ Dual Tumor Microenvironment-Responsive Nanocatalytic Graphene Oxide for Cancer Selective...

It is well known that tumors have an acidic pH microenvironment and contain a high content of hydrogen peroxide (H₂O₂). These features of the tumor microenvironment may provide physiochemical conditions that are suitable for selective tumor therapy and recognition. Here, for the first time, we demonstrate that a type of graphene oxide nanoparticle (N-GO) can exhibit peroxidase-like activities (i.e., can increase the levels of reactive oxygen species (ROS)) under acidic conditions and catalyze the conversion of H₂O₂ to ROS-hydroxyl radicals (HO^·) in the acidic microenvironment in Hela tumors. The concentrated and highly toxic HO^· can then trigger necrosis of tumor cells. In the microenvironment of normal tissues, which has a neutral pH and low levels of H₂O₂, N-GOs exhibit catalase-like activity (scavenge ROS) that splits H₂O₂ into O₂ and water (H₂O), leaving normal cells unharmed. In the recognition of tumors, an inherent redox characteristic of dopamine is that it oxidizes to form dopamine-quinine under neutral (pH 7.4) conditions, quenching the fluorescence of N-GOs; however, this characteristic has no effect on the fluorescence of N-GOs in an acidic (pH 6.0) medium. This pH-controlled response provides an active targeting strategy for the diagnostic recognition of tumor cells. Our current work demonstrates that nanocatalytic N-GOs in an acidic and high-H₂O₂ tumor microenvironment can provide novel benefits that can reduce drug resistance, minimize side effects on normal tissues, improve antitumor efficacy, and offer good biocompatibility for tumor selective therapeutics and specific recognition.