Nanoparticle-based delivery strategies of multifaceted immunomodulatory RNA for cancer immunotherapy

Although cancer immunotherapy has emerged as a novel cancer treatment modality, it still suffers from low therapeutic efficacy in clinics due to the presence of a low number of activated immune cells and immunosuppressive factors in the tumor microenvironment (TME). Immunomodulatory ribonucleic acids (RNAs) have been developed to improve the therapeutic efficacy of cancer immunotherapy through either regulating target cell functions [i.e., messenger RNA (mRNA) or small interfering RNA (siRNA)] or stimulating immune cells [i.e., toll-like receptors (TLRs) or cytosolic retinoic acid-inducible gene I (RIG-I) agonist]. However, RNA-based therapeutics face many biological barriers, including ineffective delivery to target cells, degradation by ribonucleases (RNases), and difficulties in passing through the cellular membranes. In this review, we discuss nanoparticle-based delivery strategies that can overcome these hurdles to enhance RNA-based immunomodulation in cancer immunotherapy. Various nanoparticle-based delivery has been reported to increase the delivery efficacy of RNAs, by improving cellular uptake, RNA stability, and accumulation at the desired sites (target cells and intracellular compartments). The nanoparticle-based delivery of multifaceted immunomodulatory RNAs could enhance cancer immunotherapy through the regulating functions of immune cells, tumor cells, and immunosuppressive factors as well as stimulating the immune cells by recognition of endosomal TLRs and cytosolic RIG-I. Nanotechnology-assisted RNA-based therapeutics are expected to offer tremendous potential and advances for treating cancer, viral infections, and other diseases.