Silk Nanocarrier Size Optimization for Enhanced Tumor Cell Penetration and Cytotoxicity In Vitro

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 Fe₃O₄ nanoparticles were successfully loaded inside regenerated silk fibroin/zein (RSF/zein) nanospheres to obtain dual-loaded Fe₃O₄/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 Fe₃O₄ nanoparticles in the nanospheres. For Fe₃O₄/GOx@RSF/zein nanospheres, GOx depletes endogenous glucose via an enzyme-catalyzed bioreaction, simultaneously generating plenty of H₂O₂in situ. It was further catalyzed through a Fe₃O₄-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 Fe₃O₄ from Fe₃O₄/GOx@RSF/zein nanospheres. The in vitro experiments demonstrated that the Fe₃O₄/GOx@RSF/zein nanospheres entered MCF-7 cells and generated ˙OH free radicals. Therefore, these Fe₃O₄/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 Fe₃O₄@RSF/zein nanospheres, achieving the design goal for the nanospheres. Therefore, the Fe₃O₄/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 Fe₃O₄/GOx@RSF/zein nanospheres developed in this study have significant potential for combining starvation and chemodynamic therapy.

Silk Nanocarrier with Tunable Size to Improve Transdermal Capacity for Hydrophilic and Hydrophobic Drugs

Transdermal drug delivery is an attractive option for multiple disease therapies as it reduces adverse reactions and improves patient compliance. Water-dispersible β-sheet rich silk nanofiber carriers have hydrophobic properties that benefit transdermal delivery but still show inferior transdermal capacities. Thus, hydrophobic silk nanofibers were fabricated to fine-tune their size and endow them with desirable transdermal delivery capacities. Silk nanocarrier length was shortened from 2000 nm to approximately 40 nm after ultrasonic treatment. In vitro human skin and in vivo animal studies revealed different transdermal behaviors for silk nanocarriers at different nanosizes. Silk nanocarriers passed slowly through the corneum without destroying the corneum structure. Improved transdermal capacity was achieved for smaller size carriers. Both hydrophilic and hydrophobic drugs could be loaded onto silk nanocarriers, suggesting a promising future for different disease therapies. No cytotoxicity and skin irritation were identified for silk nanocarriers, which strengthened their superiority as transdermal carriers. Therefore, silk nanocarriers <100 nm may promote the percutaneous absorption of active cargos for disease therapy and cosmetic applications.

Progress in silk and silk fiber-inspired polymeric nanomaterials for drug delivery

The fields of drug and gene delivery have been revolutionized by the discovery and characterization of polymer-based materials. Polymeric nanomaterials have emerged as a strategy for targeted delivery because of features such as their impressive biocompatibility and improved availability. Use of naturally derived polymers in these nanomaterials is advantageous due to their biodegradability and bioresorption. Natural biopolymer-based particles composed of silk fibroins and other silk fiber-inspired proteins have been the focus of research in drug delivery systems due to their simple synthesis, tunable characteristics, and ability to respond to stimuli. Several silk and silk-inspired polymers contain a high proportion of reactive side groups, allowing for functionalization and addition of targeting moieties. In this review, we discuss the main classes of silk and silk-inspired polymers that are being used in the creation of nanomaterials. We also focus on the fabrication techniques used in generating a tunable design space of silk-based polymeric nanomaterials and detail how that translates into use for drug delivery to several distinct microenvironments.