Direct cytosolic delivery of siRNA via cell membrane fusion using cholesterol-enriched exosomes.

Efficient cytosolic delivery is a significant hurdle when using short interfering RNA (siRNA) in therapeutic applications. Here we show that cholesterol-rich exosomes are prone to entering cancer cells through membrane fusion, achieving direct cytosolic delivery of siRNA. Molecular dynamics simulations suggest that deformation and increased contact with the target cell membrane facilitate membrane fusion. In vitro we show that cholesterol-enriched milk-derived exosomes (MEs) achieve a significantly higher gene silencing effect of siRNA, inducing superior cancer cell apoptosis compared with the native and cholesterol-depleted MEs, as well as conventional transfection agents. When administered orally or intravenously to mice bearing orthotopic or subcutaneous tumours, the cholesterol-enriched MEs/siRNA exhibit antitumour activity superior to that of lipid nanoparticles. Collectively, by modulating the cholesterol content of exosome membranes to facilitate cell entry via membrane fusion, we provide a promising approach for siRNA-based gene therapy, paving the way for effective, safe and simple gene therapy strategies.