Multistage-Responsive Dual-Enzyme Nanocascades for Synergistic Radiosensitization-Starvation Cancer Therapy.

Radiotherapy is a common cancer treatment approach in clinical practice, yet its efficacy has been restricted by tumor hypoxia. Nanomaterials-mediated systemic delivery of glucose oxidase (GOx) and catalase (CAT) or CAT-like nanoenzymes holds the potential to enhance tumor oxygenation. However, they face the challenge of intermediate (hydrogen peroxide [H 2 O 2 ]) escape during systemic circulation if the enzyme pair is not closely placed to largely decompose H 2 O 2 , leading to oxidative stress on normal tissues. In the present study, a oxygen-generating nanocascade, n(GOx-CAT) C7A , constructed by strategically placing an enzymatic cascade (GOx and CAT) within a polymeric coating rich in hexamethyleneimine (C7A) moieties, is reported. During blood circulation, C7A remains predominantly non-protonated , achieving prolonged blood circulation due to its low-fouling surface. Once n(GOx-CAT) C7A reaches the tumor site, the acidic tumor microenvironment (TME) induces protonation of C7A moieties, resulting in a positively charged surface for enhanced tumor transcytosis. Moreover, GOx and CAT are covalently conjugated into close spatial proximity (<10 nm) for effective H 2 O 2  elimination. As demonstrated by the in vivo results, n(GOx-CAT) C7A achieves effective tumor retention and oxygenation, potent radiosensitization and antitumor effects. Such a dual-enzyme nanocascade for smart O 2  delivery holds great potential for enhancing the hypoxia-compromised cancer therapies.