RNA nanotechnology provides molecules that have the simplicity in design with the characteristics of DNA and can be used in therapies. However, a major problem in RNA nanotechnology is that RNA molecules are relatively unstable such as their degradation in vivo and dissociation at ultra-low concentration after administration. Intravitreal injection is the most common method to deliver macromolecular therapeutic agents to the posterior segment of the eye for the treatments of diseases. Repeated intravitreal injection can cause severe adverse effects to the eye. For small drug molecules, systemic administration can be used but this route of administration is complicated by systemic toxicity. There is an unmet need of a more effective drug delivery method in the treatment of posterior eye diseases. We have recently studied RNA nanoparticles derived from the three-way junction (3WJ) of the packaging RNA (pRNA) of bacteriophage phi29 DNA packaging motor for ocular drug delivery. These nanoparticles are thermodynamically and chemically stable both in vitro and in vivo and can harbor multiple modules with different functionalities such as RNA aptamer, reporter moiety, and therapeutic siRNA, miRNA, or other chemical drugs or ligands as subunits all in the same nanoparticles. Our preliminary studies have shown that the pRNA nanoparticles (pRNA nano) were internalized in the cells in the cornea, retinal pigment epithelium, and retina in the eye after subconjunctival injection in mice in vivo. This suggests the potential of subconjunctival injection of pRNA nano as an efficient drug delivery system of RNA-based therapeutic agents to the cells in the posterior segment of the eye: pRNA nano can overcome both the RNA molecule stability and posterior eye delivery problems. The preliminary studies have also suggested that the delivery and retention of pRNA nano are particle size dependent and the existence of an optimal size range for their effective delivery to the cells in the eye. The objectives of the present project are to (a) determine the optimal pRNA nano for ocular drug delivery, (b) demonstrate the ability of pRNA nano to deliver therapeutic agents to treat posterior eye disease, and (c) develop an episcleral implant system for prolonged delivery of these nanoparticles. pRNA nano of different sizes and module subunits will be constructed and evaluated for effective intraocular delivery and therapeutic effects after subconjunctival injection in animal models. The episcleral implant is refillable and is placed on the sclera in the subconjunctival or sub-Tenon pocket to provide sustained delivery of the nanoparticles. The ultimate goal is to develop a platform of ocular drug delivery using the pRNA technology for nucleotide-based therapies via the periocular route (a less invasive approach than intravitreal injection). The present project will examine the feasibility of the combined pRNA nano and episcleral implant approach for the proof of concept of this new technology.
Posterior eye diseases affect more than a million people in the United States each year. The present project will develop an ocular drug delivery system based on RNA technology to deliver nucleotide-based drugs into the eye to treat posterior eye diseases. It will be a great benefit to the public if an effective drug delivery system can replace repeated intravitreal injections and allow effective nucleotide-based drug delivery for the treatments of these diseases.
