Targeted RNA delivery using ribonucleoprotein

ABSTRACT Silencing RNA (siRNA) is of considerable current interest in medicine because it can elicit potent, target specific knockdown of virtually any mRNA, creating a useful and proven genetic surrogate tool. Three siRNA- based therapies have been FDA-approved, while another seven candidates are in phase 3 trials. A key obstacle limiting the scope of siRNA clinical uses, however, is in vivo targeted delivery, a `chronic' problem that has plagued the development of virtually all antisense therapies. Recent advances in nanotechnology have produced many nanocarriers such as cationic lipids, polymers, inorganic nanoparticles, and peptides. Although the cationic charge is important for siRNA condensation and endosomal escape, it interferes with specific targeting by non-specifically binding to most proteins and cells. To address this fundamental and chronic problem, here we propose to further develop a one-of-its-kind RNA nanocarrier for delivery of siRNA cocktails building on a recent breakthrough we made on human RNA-binding proteins (Corey & Gao Nature BME, PCT filed, US phase granted). Optimized through millions of years of evolution, these proteins are neutral or slightly negatively charged yet still binding to cargo RNA tightly and with a very high payload. The absence of excessive cationic charges is in direct contrast to conventional delivery technologies. Through orientation controlled self-assembly with siRNA-targeting ligand chimeras, the complex simultaneously achieves all the desired properties for efficient siRNA delivery and cancer treatment.