The greatest barrier to the application of small interfering RNA (siRNA) for cancer therapy is a reliable method for site-specific siRNA delivery to the tumor site. Viral vectors have an unacceptable level of toxicity, and cationic liposomes and polymeric micelles suffer from rapid clearance from circulation and non-specific delivery. Thus, there remains a need for long- circulating non-viral carriers that can deliver siRNA efficiently and specifically to targeted cells. To fulfill these requirements, we propose a neutral ultrasound-triggerable nanoemulsion that can be administered systemically and deliver siRNA in a site-specific manner. The nanoemulsion consists of perfluorocarbon nanodroplets coated with a mixture of cationic lipophilic peptides, helper lipids, and PEGylated lipids and phospholipids. After siRNA complexation, an acetylating agent is added to neutralize the residual surface charge, which minimizes non- specific cellular uptake of the complex. The liquid perfluorocarbon core can be vaporized with focused ultrasound pulses, creating bubbles and releasing the siRNA. Additional acoustic pulses are used to drive cavitation (i.e. bubble oscilations), which temporarily increases the permeability of tumor cell through bubble/cell interactions and facilitates the delivery of siRNA.to cancer cells. Using this innovative approach, we bypass the endocytic pathway, which is the conventional pathway for siRNA to gain access to the cell cytoplasm. Furthermore, siRNA is delivered to cells only within the transducer focal zone, thus addressing the lack of specificity that plagues conventional non-viral siRNA delivery methods. In preliminary studies, we have confirmed that this approach can successfully deliver fluorescently-labeled siRNA to cultured cells, thus becoming the first group to combine pressure-sensitive nanoemulsions and ultrasound for localized siRNA delivery. The proposed delivery scheme has potential to resolve the limitations associated with current siRNA delivery techniques, thus allowing siRNA to reach its full potential as an agent for cancer therapy.
Cancer is the second leading cause of death in the United States. The research outlined in this proposal will develop technology and protocols for localized delivery of siRNA for the management of solid tumors.