Milk exosomes - Natural nanoparticles for siRNA delivery

Gene-silencing with targeted siRNAs has great potential as a therapeutic approach for various diseases including cancer. However, intracellular delivery of siRNA is challenging. We used bovine milk exosomes as a novel system for siRNA delivery. First, we demonstrated that exosomes can deliver endogenous RNA payloads into recipient cells. Next, we loaded siRNA against specific genes including VEGF, EGFR, AKT, MAPK, and KRAS. We utilized 5'^-32P-labeled siKRAS as a tracer and found exosome loading with siRNA could be variable. We demonstrated that the siRNA of loaded exosomes is stable and resist degradation. Our results indicated that siRNAs against target genes ranged from 2 to 10-fold knockdown in expression levels in various cancers. Since mutated KRAS has been implicated in the development of various cancers including lung cancer, we tested a mutant-allele specific siRNA against KRAS^G12S, in A549 cells. We observed a dose-dependent anti-proliferative activity against A549 cells treated with exosomes carrying siKRAS^G12S. We observed significant inhibition of A549 tumor xenografts in animals treated with folic acid-functionalized exosomes carrying siKRAS. In summary, milk-derived exosomes represent a viable natural nano-carrier for the delivery of siRNA for therapeutic application against cancer.