Engineering tumor-specific catalytic nanosystem for NIR-II photothermal-augmented and synergistic...

As an emerging therapeutic modality, chemodynamic therapy (CDT), converting hydrogen peroxide (H₂O₂) into highly toxic reactive oxygen species (ROS), has been developed for tumor-specific therapy. However, the deficiency of endogenous H₂O₂ and high concentration of glutathione (GSH) in the tumor microenvironment (TME) weaken the CDT-based tumor-therapeutic efficacy. Herein, a photothermal-enhanced tumor-specific cascade catalytic nanosystem has been constructed on the basis of glucose oxidase (GOD)-functionalized molybdenum (Mo)-based polyoxometalate (POM) nanoclusters, termed as GOD@POMs.

GOD@POMs were synthesized by a facile one-pot procedure and covalently conjugation. Then, its structure was characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). In addition, ultraviolet-visible-near-infrared (UV-vis-NIR) absorption spectrum and infrared thermal camera were applied to evaluate the catalytic and photothermal performance, respectively. Moreover, to confirm the therapeutic effects in vitro, cell counting kit-8 (CCK-8) assay, live/dead staining and ROS staining were performed. Furthermore, the biosafety of GOD@POMs was investigated via blood routine, blood biochemistry and hematoxylin and eosin (H&E) staining in Kunming mice. Besides, the C6 glioma tumor-bearing mice were constructed to evaluate its anti-tumor effects in vivo and its photoacoustic (PA) imaging capability. Notably, RNA sequencing, H&E, TdT-mediated dUTP nick end labeling (TUNEL) and Ki-67 staining were also conducted to disclose its underlying anti-tumor mechanism.

In this multifunctional nanosystem, GOD can effectively catalyze the oxidation of intratumoral glucose into gluconic acid and H₂O₂, achieving the cancer starvation therapy. Meanwhile, the generated gluconic acid decreases the pH in TME resulting in POM aggregation, which enables PA imaging-guided tumor-specific photothermal therapy (PTT), especially in the second near-infrared (NIR-II) biological window. Importantly, the Mo (VI) sites on POM can be reduced to Mo (V) active sites in accompany with GSH depletion, and then the post-produced Mo (V) transforms in situ overproduced H₂O₂ into singlet oxygen (¹O₂) via Russell mechanism, achieving self-enhanced CDT. Moreover, the PTT-triggered local tumor temperature elevation augments the synergistic nanocatalytic-therapeutic efficacy.

Consequently, the integration of GOD-induced starvation therapy, H₂O₂ self-supply/GSH-depletion enhanced Mo-based CDT, and POM aggregation-mediated PTT endow the GOD@POMs with remarkable synergistic anticancer outcomes with neglectable adverse effects.