# Metal Nanozymes: New Horizons in Cellular Homeostasis Regulation
## 8 Metal Nanozymes in Cancer Treatment
Furthermore, they presented that metal/metal oxide nanomaterials with excellent dual enzyme-like activities can provide a new perspective for the design of nanomedicines and achieve the balanced combination of tumor catalytic therapy and PTT. [PERSON] et al. have focused on metal-oxidase nanozymes WO3/Pt nanoparticles, an NADPH oxidase biomimetic that uses NADPH to synthesize ROS. They prepared nanoparticles that can be excited by visible light using the photodeposition method. WO3 absorbed a visible light, and an electron was promoted from the valence band to the conduction band and accumulated at Pt sites. Next, it catalyzed the multielectron reduction of O2 to hydroxyl radicals. At the same time, in the semiconductor, a valence band hole appeared and migrated to the NPs surface, where it abstracted an electron from the environment  
Figure 8: Schematic illustration of the photo-enhanced tumor catalytic therapy for PtFe@Fe3O4 nanozyme. Reproduced from Reference [223] with permission from [PERSON] Wiley and Sons. (e.g., TME). The reaction at both the photocathode and photoanode led to target tumor cell damage. The authors developed WO\({}_{3}\)/Pt nanoparticles tailored for implementation and use in PDT. They have found that the chemical reactions of WO\({}_{3}\)/Pt nanoparticles mimic those of the NADPH oxidase and suggest that WO\({}_{3}\)/Pt nanoparticles can augment or replace this functional attribute of immune effector cells and, in consequence, to killing tumor cells. Furthermore, they suggested that these nanoparticles could be targeted to other sites or employed in other indications by using different ligands. The WO\({}_{3}\)/Pt nanoparticles developed by [PERSON] et al. have numerous therapeutic benefits such as producing large amounts of hydroxyl radicals, lowering cellular anti-oxidant defenses by utilizing NADPH while simultaneously producing hydroxyl radicals, minimal toxicity, remaining effective at low pH, and being resistant to photobleaching [224; 225; 226]. However, due to light's limited tissue penetration depth, PDT is commonly used to treat relatively small, superficial tumors [227]. Moreover, the drawback of PDT clinical application is serious skin phototoxicity after systemic administration of photosensizers. As an alternative to PDT, sonodynamic therapy (SDT) developed uses highly penetrating acoustic waves to activate a class of sound-responsive materials called sonosensitizers (organic sonosensitizers and inorganic sonosensitizers). Organic sonosensitizers are mostly porphyrin derivatives and other fat-soluble small molecules. However, they have some limitations concerning water solubility, poor stability during ultrasound (US), and fast body clearance, leading to low enrichment in tumor sites. By contrast, inorganic sonosensitizers have stable chemical properties, long blood circulation time, and can effectively reduce phototoxicity. They can also operate as carriers for delivering organic sonosensitizers, effectively overcoming their inherent shortcomings. Possible mechanisms of SDT could be summed up as a generation of ROS, mechanical effects, and thermal effects [228; 229]. The most recognized mechanism of SDT is the ROS, including singlet oxygen (\({}^{1}\)O\({}_{2}\)), hydroxyl radicals (\({}^{\bullet}\)OH), superoxide anion (O\({}_{2}\)\({}^{\bullet}\)\(-\)), or hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) after absorbing the energy from the ultrasound. As an example, [PERSON] et al. presented an ultrasmall oxygen-deficient bimetallic oxide MnWOX nanoparticle for multimodal imaging-guided enhanced SDT against cancer which, as PEGylated MnWOX nanoparticles, could be used for efficient ultrasound (US)-triggered cancer therapy [227]. Similar observations related to generating singlet oxygen and hydroxyl radicals for enhanced SDT efficiency were made by [PERSON] et al. [230], who applied for the experiments titanium oxide TiO\({}_{2}\) NPs NPs. However, [PERSON] et al.