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

Radiotherapy is one of the most common cancer treatment approaches. Yet its therapeutic outcome has been significantly restricted by tumor hypoxia. Despite glucose oxidase (GOx) coupled with catalase (CAT) or CAT-like nanoenzymes can be used for tumor oxygenation for synergistic cancer starving-like/radiation therapies, direct intratumoral injection is restricted to solid tumors with known and accessible sites. Systemic delivery of GOx and CAT/CAT-like nanoenzymes cascade with tumor-targeting nanomaterials has the potential to enhance tumor oxygenation. Yet it faces the challenge of intermediate (H 2 O 2 ) escape from nanomaterials during systemic circulation if the enzyme pair is not strictly placed into close spatiotemporal proximity allowing complete H 2 O 2 conversion, which imposes deleterious oxidative stress on normal tissues. Moreover, of the materials reported to deliver GOx and CAT/CAT-like nanoenzymes, they are principally non-biodegradable and not tumor microenvironment (TME)-responsive. Therefore, in the present study, a multifunctional oxygen-generating nanocascade, termed n(GOx-CAT) C7A , which is constructed by strategically placing an enzymatic cascade (GOx and CAT) within a polymeric coating rich in pH-responsive (hexamethyleneimine) (C7A) moieties, is reported. During blood circulation, C7A remains predominantly non-protonated; therefore, n(GOx-CAT) C7A can achieve long blood circulation and effective tumor accumulation through passive targeting due to its neutral and zwitterionic low-fouling surface. As soon as n(GOx-CAT) C7A reaches the tumor site, the acidic tumor microenvironment will induce abrupt protonation of C7A moieties, resulting in a positively charged surface for enhanced tumor transcytosis and retention. Moreover, GOx and CAT are covalently conjugated into close spatial proximity (< 10 nm) for effective H 2 O 2 elimination and prevention of intermediate (H 2 O 2 ) escape. As demonstrated by the subsequent in vitro and in vivo studies, n(GOx-CAT) C7A achieved effective tumor retention and oxygenation, potent radiosensitization and antitumor effects, and low systemic toxicity. In addition, n(GOx-CAT) C7A is biodegradable in response to the intracellular glutathione because the chemical linkers between GOx and CAT, and among polymer chains are disulfate linkers. Such a multistage-responsive dual-enzyme nanocascade for smart O 2 delivery holds great potential for enhancing the current hypoxia-compromised cancer therapies. This article is protected by copyright. All rights reserved.