Enzyme/inorganic nanoparticle dual-loaded animal protein/plant protein composite nanospheres and their synergistic effect in cancer therapy.

It is a viable strategy to develop a safer and tumor-specific method by considering the tumor microenvironment to optimize the curative effect and reduce the side effects in cancer treatment. In this study, glucose oxidase (GOx) and FeO nanoparticles were successfully loaded inside regenerated silk fibroin/zein (RSF/zein) nanospheres to obtain dual-loaded FeO/GOx@RSF/zein nanospheres. The unique structure of the RSF/zein nanospheres reported in our previous work was favorable to loading sufficient amounts of GOx and FeO nanoparticles in the nanospheres. For FeO/GOx@RSF/zein nanospheres, GOx depletes endogenous glucose an enzyme-catalyzed bioreaction, simultaneously generating plenty of HO. It was further catalyzed through a FeO-mediated Fenton reaction to form highly toxic hydroxyl free radicals (˙OH) in the acidic tumor microenvironment. These two successive reactions made up the combination of starvation therapy and chemodynamic therapy during cancer treatment. The catalytic activity of GOx loaded in the RSF/zein nanospheres is similar to that of the pristine enzyme. It was maintained for more than one month due to the protection of the RSF/zein nanospheres. The methylene blue degradation results confirmed the sequential reaction by GOx and FeO from FeO/GOx@RSF/zein nanospheres. The experiments demonstrated that the FeO/GOx@RSF/zein nanospheres entered MCF-7 cells and generated ˙OH free radicals. Therefore, these FeO/GOx@RSF/zein nanospheres exhibited a considerable synergistic therapeutic effect. They showed more efficient suppression in cancer cell growth than either single-loaded GOx@RSF/zein or FeO@RSF/zein nanospheres, achieving the design goal for the nanospheres. Therefore, the FeO/GOx@RSF/zein nanospheres cut off the nutrient supply due to the strong glucose dependence of tumor cells and generated highly toxic ˙OH free radicals in tumor cells, effectively enhancing the anticancer effect and minimizing side effects. Therefore, in future clinical applications, the FeO/GOx@RSF/zein nanospheres developed in this study have significant potential for combining starvation and chemodynamic therapy.