Cyclic enhancement of hypoxic microenvironment via an intelligent nanoamplifier for activated NIR-II fluorescence/photoacoustic imaging-guided precise synergistic therapy.

Tumor microenvironment (TME)-activated theranostics is a promising strategy to effectively identify small lesions, improve antitumor efficacy, and reduce the risk of undesired side effects. Hypoxia, as a common characteristic of TME, can serve as a preferred site for stimulus-dependent activation; however, tumor-hypoxia levels in various developmental stages exhibit different characteristics, severely limiting the response sensitivity. Herein, a circulating self-reinforcing hypoxic nanoamplifier (CGH NAs) is developed that utilizes a dual-chain reaction process (internal regulation, internal regulation) to achieve precise activation of NIR-II FL/photoacoustic (PA) imaging-guided synergistic therapy. Inspired by the positive correlation of nitroreductase (NTR) with hypoxia, the CGH NAs encapsulate CQ4T and GOx into NTR-sensitive hyaluronic acid-nitroimidazole (HA-NI) shell via a self-assembly approach, enabling aggregation-caused NIR-II FL quenching and tumor-accurate delivery. When CGH NAs efficiently accumulated in the tumor region, the intensive local NTR reduced hydrophobic -NO to hydrophilic -NH, which lead to disassembly of CGH NAs. The released GOx could consume O (internal regulation) and glucose to cut off the energy supply, inducing tumor-starvation therapy; generate gluconic acid and HO (oxidative stress). Meanwhile, the released CQ4T promoted rapid recovery of NIR-II FL signals for imaging-guided PDT, which could simultaneously deplete intratumoral O (external stimulation). Remarkably, the strengthened tumor-hypoxia levels in turn accelerated the NTR-responsive degradation of the CGH NAs, thereby achieving high-efficiency theranostic.