RNA molecules can be designed and manipulated as easily as DNA. They also display versatility in structure and diversity in function (including enzymatic activity) similar to that of proteins. These properties make RNA suitable candidates to act as building blocks for applications in nanotechnology and nanomedicine.
“RNA can fold into well-defined tertiary structures with specialized functions,” said Peixuan Guo, Ph.D., who holds the William Farish Endowed Chair of Nanobiotechnology at the University of Kentucky’s Markey Cancer Center, and who also serves as a professor at the university’s College of Pharmacy. “We use this information to rationally design building blocks that self-assemble into RNA nanoparticles.”
Dr. Guo, a pioneer of RNA nanotechnology, published a paper in 1998 that described how a virus known as bacteriophage phi29 uses six RNAs strung together in the shape of a hexagon to create a kind of molecular motor. He has since used phi29 packaging RNA (pRNA) for siRNA or drug delivery to specific cells and single-molecule imaging. He has also incorporated the phi29 motor channel into a lipid membrane for single-molecule sensing and developed a new system with the potential for high-throughput dsDNA sequencing.
Although a number of techniques are available to design RNA nanoparticles, Dr. Guo’s group is focusing on three. “We focus on using RNA designs involving interlocking loops for hand-in-hand interactions, palindrome sequences for foot-to-foot interactions, and an RNA three-way junction for branch extensions,” said Dr. Guo. These techniques are used in Dr Guo’s lab to make toolkits to construct RNA architectures with diverse shapes and angles.
“Because of its many useful structural features, [phi29 pRNA] is often used as a backbone for the assembly of RNA nanoparticles,” said Dr. Guo. “We have developed our toolkits using pRNA as a delivery platform. After they incorporate the desired functionalities (such as siRNAs, miRNA, ribozymes, or ligands), the RNA nanoparticles are thermodynamically and chemically stable.”
Dr. Guo sees many applications for the technology. His group is initially focusing on cancers such as colon, lung, etc. According to Dr Guo, the size of pRNA-based nanoparticles is ideal for passively delivering them into tumors.
“Research over the last decade has demonstrated that the size of nanoparticles is a critical determinant of their in vivo behavior,” said Dr. Guo. “If nanoparticles are smaller than 10 nanometers, the result is nonspecific diffusion into tissue, while if they are larger than 100 nanometers, nanoparticles are less likely to gain access to cells. Our RNA nanoparticles are 20–50 nanometers. Their size allows enhanced permeability and retention effects that minimize off-target effects or toxicity.”
According to Dr. Guo, active delivery of RNA nanoparticles can be achieved by adding specific targeting moieties to the complex. “These functionalized RNA nanoparticles, with the combination of detection molecules, targeting groups, and therapeutic payload, are useful for the diagnosis of and therapy for cancer and viral disease.”