Fibroin particle-supported cationic lipid layers for highly efficient intracellular protein delivery

Directly delivering therapeutic proteins into cells has promise as an intervention without side effects for protein deficiencies caused by genetic defects. However, as negatively charged macromolecules, proteins require carriers for achieving cellular uptake and maintaining their activity in the cytoplasm. The biodegradable natural polymer silk fibroin has demonstrated outstanding advantages as a protein drug scaffold in vitro and in vivo, but its usage has been limited in the extracellular space because of its negatively charged character. Here, we present an intracellular protein delivery system based on fibroin particles coated with cationic lipid layers, denoted as Fibroplex, the surface charge of which can be modulated. Fibroplex showed higher delivery efficiency than conventional delivery methods as well as long-term cargo release in the cytoplasm without toxicity. Furthermore, in vivo experiments showed that Fibroplex efficiently delivered tyrosinase and horseradish peroxidase, which led to hyper-pigmentation and tumor regression, respectively, suggesting its potential for therapeutic protein applications in hereditary diseases or cancer.