Combinatorial lipid-like materials for intracellular delivery of small RNAs that activate innate antiviral immune responses and adjuvant vaccines

Abstract

RNA-based therapy is an exciting new realm of experimental medicine due to the diverse roles of RNA in the human body. RNA function depends on sequence, structure, and cellular location. Whereas cytosolic short-interfering RNA (siRNA) can be used to turn off genes through RNA interference (RNAi), it was observed that the same siRNA can also activate an innate immune response. Recognition of RNA by specialized immune cells occurs through pattern recognition receptors, which have evolved to respond to RNA viruses, such as the Toll-like receptors (TLR) 7 and 8 located in the endosome of dendritic cells. Tailoring the multiple functions of RNA for a desired clinical application will require novel systems for intracellular delivery. A library of structurally-related cationic lipid-like materials, termed "lipidoids", was developed to facilitate uptake of small RNAs, and the role of drug delivery in controlling RNA function was investigated. In an experimental animal model of RNA interference of influenza virus, treatment with a lipidoid-siRNA nanoparticle efficiently activated a type I interferon response in a sequence-dependent manner suppressing lung viral titer over 97%. Specific chemical modifications to the siRNA prevented TLR7/8 engagement and also prevented antiviral responses, confirming an RNAi-independent mechanism of antiviral activity. Recognizing the therapeutic potential of immunostimulatory RNA (isRNA), a novel in vitro high- throughput assay was developed to screen the lipidoid library for delivery of isRNA.

(cont.) Over 800 combinations of lipidoid and isRNA were screened for the ability to form nanoparticles and deliver isRNA in vitro. Drawing upon structure-function relationships observed in the lipidoid library, 2nd generation lipidoids were synthesized. These lipidoids could efficiently deliver isRNA to TLR7/8 in vivo and activated systemic innate immune responses following subcutaneous administration. Further, the 2nd generation lipidoid-isRNA nanoparticles increased antibody responses to protein vaccination by many orders of magnitude and stimulated cell-mediated immunity. Taken together, the results of these studies demonstrates the role of drug delivery in controlling the function of small RNAs, and that activation of innate immune responses to immunostimulatory small RNAs has therapeutic potential.