We have developed an innovative RNA nanotechnology platform to improve drug delivery strategies for cancer treatment. Our novel junction scaffolds overcome conventional limitations of cancer therapeutics to provide more specific in vitro and in vivo delivery of therapeutic siRNA, miRNA or chemical drugs with significantly reduced toxicity and side effects.
Multi-Way Junction 2’-Fluoro RNA is highly thermodynamically and enzymatically stable and remains intact at ultra-low concentrations in blood circulation. It is an ideal scaffold for drug delivery. RNA scaffolds are available of various shapes and sizes.
Nucleic acid-based aptamers and small chemical ligands can be conjugated to either termini of the scaffold to achieve specific targeting. The high thermodynamic stability of the junction scaffolds ensures correct folding and function of aptamers.
Small nucleic acid based therapeutic candidates, such as miRNA, anti-miRNA, siRNA, CpG DNA immune modulators, and chemical drugs can be easily conjugated to the junction scaffold, with authentic functionalities.
Fluorescent or radioactive molecules can be conjugated to the scaffold as an imaging module. Near infrared labeling of RNA nanoparticles allows real time monitoring of bio-distribution in vivo using IVIS imaging system.
The thermodynamically stable 4WJ is a core structure of a multifunctional RNA nanoparticle. The structure has a Tm higher than 80°C and remains undissociated at ultralow concentration after being diluted as in blood circulation in vivo. This structure has been patented and licensed by ExonanoRNA for future drug development.
The proof-of-Concept study for RNA Nanotehnology was led by Dr. Peixuan Guo in 1998 ( https://rnanano.osu.edu/Guo/peixuanguo.html), with the first evidence for constructing RNA Nanoparticles by bottom-up self-assembly of multiple reengineered natural RNA molecules. The original work, which illustrated the bottom-up self-assembly of RNA dimer, trimer and hexamer from reengineered RNA fragments of the pRNA of bacteriophage phi29 DNA packaging motor, was published by Peixuan Guo, Chunlin Zhang, Chaoping Chen, Kyle Garver, and Mark Trottier in Molecular Cell 1998, 2(1):149-155 and was featured in Cell. [link] In the past 20 years, the effort of researches in the RNA Nanotechnology field has addressed the following concerns and paved the way for its application as a new drug delivery system:
a. Chemical and enzymatic stability
c. Toxicity and immunogenicity
Thermodynamically stable RNA nanoparticles harboring targeting ligands and fluorescent dyes have shown specific targeting to (A) head and neck cancer, (B) gastric cancer, (C) colorectal cancer metastasis in the mice model. The platform has great potential in developing next generation targeted cancer therapies to overcome current limitations of traditional cancer therapies.
1) Negative charge disallows nonspecific permeation through negatively charged cell membranes
2) Controlled synthesis provides defined structure and stoichiometry
3) Multi-valency allows combination therapy and simultaneous targeting and detection
4) Targeted delivery allows receptor mediated endocytosis
5) Advantageous size (10 – 40 nm)
6) Extended in vivo half-life (5-12 hr compared to 15-45 min for siRNA)
7) Avoidance of antibody induction (protein-free) allows repeated treatment for chronic diseases
8) Favorable pharmacokinetic profiles in mice:
– Half life (T1/2) : 5-10 hr compared to 0.25-0.76 hr of siRNA
– Clearance (Cl): <0.13 l/kg/hr
– Volume of distribution (V(d)): 1.2 l/kg
– Does not induce interferon response or cytokine
– Repeated IV up to 30 mg/kg do not result in toxicity
9) RNA nanoparticles are classified as chemical drugs rather than biologics. This classification facilitates new drug approval