Synthetic θ-Defensin Antibacterial Peptide as a Highly Efficient Nonviral Vector for Redox-Responsive miRNA Delivery

Synthetic cationic vectors have shown great promise for nonviral gene delivery. However, their cytotoxicity and low efficiency impose great restrictions on clinic applications. To push through this limitation, humanized peptides or proteins with cationic biocompatibility as well as biodegradation would be an excellent candidate. Herein, for the first time, we describe how an arginine-rich humanized antimicrobial cyclopeptide, theta-defensin, can be used as a synthetic cationic vector to load and deliver miRNA into bone mesenchymal stem cells with high efficiency and ultralow cytotoxicity, surpassing the efficiency of the commercial polyethylenimine (25 kD) and Lipofectamine 3000. To note, theta-defensin can redox-responsively release the loaded miRNA through a structural change: in extracellular oxidative environment, theta-defensin has large beta-sheet structures stabilized by three disulfide linkages, and this special structure enables highly efficient delivery of miRNA by passing through cell membranes; in intracellular environment, redox-responsive disulfide linkages are broken and the tight beta-sheet structures are destroyed, so that the miRNA can be released. Our results suggest that synthetic theta-defensin peptides are a new class of nonviral gene vectors and this study may also provide a promising strategy to design smart-responsive gene vectors with high efficiency and minimal toxicity.