Entropy and Enthalpy in RNA Nanoparticle Assembly and Thermodynamic Stability for Medical Application Using RNA Nanotechnology

Abstract

The field of RNA nanotechnology has developed from proof-of-concept to a contender in revolutionizing the therapeutic industry. With the large role of RNA in the human body, RNA is poised as the third milestone in pharmaceutics following small molecule and protein drugs. Bottom-up construction of RNA nanoparticles is analogous Lego building blocks. In vivo application of RNA nanotechnology requires assembly efficiency and stability of the building blocks in harsh conditions and ultra-low concentrations within the body. RNA nanoparticles self-assemble, governed by thermodynamics and related energy levels, that is, Gibbs free energy controlled by enthalpy and entropy. Thermostability of RNA nanoparticles are crucial to particle stability, module dissociation, strand breathing, and drug loading capacity, which hinges on thermodynamic parameters and kinetics to spontaneously bring together multiple strands. This review focuses on the assembly of RNA nanoparticles using the pRNA three-way junction (3WJ) from the bacteriophage phi29 DNA packaging motor as example. The pRNA-3WJ is well studied and used to develop stable nanoparticles for the treatment of cancer. In depth thermodynamic and kinetic studies demonstrated the pRNA-3WJ, composed of three short RNA strand, folds rapidly and remains highly stable. Enthalpy and entropy play critical roles as the change from unstable single strands to the 3WJ is an energy releasing step; and the structure flexibility and diversity of the 3WJ allows for higher entropy over double-stranded RNA. The strong thermostability allows for this 3WJ to serve as a central motif and building block to many complex RNA nanoparticles such as dendrimers, prisms, and polygon shapes that are used as therapeutic delivery platforms for specific treatment of cancers. Methods for the assembly of RNA nanoparticles using 3WJ and their application in cancer therapy are also reviewed.