Abstract

RNA interference (RNAi) provides researchers with a versicle means to modulate target gene expression. The major forms of RNAi molecules, genome-derived microRNAs (miRNA) and exogenous small interfering RNAs (siRNA), converge into RNA-induced silencing complexes to achieve post-transcriptional gene regulation. RNAi has proven to be an adaptable and powerful therapeutic strategy where advancements in chemistry and pharmaceutics continue to bring RNAi-based drugs into the clinic. With four siRNA medications already approved by the United States Food and Drug Administration (FDA), several RNAi-based therapeutics continue to advance to clinical trials with functions that closely resemble their endogenous counterparts. Although intended to enhance stability and improve efficacy, chemical modifications may increase risk of off-target effects by altering RNA structure, folding, and biological activity away from their natural equivalents. Novel technologies in development today seek to utilize intact cells to yield true biological RNAi agents that better represent the structures, stabilities, activities, and safety profiles of natural RNA molecules. In this review, we provide an examination of the mechanisms of action of endogenous miRNAs and exogenous siRNAs, the physiological and pharmacokinetic barriers to therapeutic RNA delivery, and a summary of the chemical modifications and delivery platforms in use. We overview the pharmacology of the four FDA approved siRNA medications (patisiran, givosiran, lumasiran, and inclisiran), as well as five siRNAs and several miRNA-based therapeutics currently in clinical trials. Furthermore, we discuss the direct expression and stable carrier-based, in vivo production of novel biological RNAi agents for research and development.

Significance Statement In our review, we summarize the major concepts of RNA interreference (RNAi), molecular mechanisms, and current state and challenges of RNAi drug development. We focus our discussion on the pharmacology of FDA-approved RNAi medications and those siRNAs and miRNA-based therapeutics entered the clinical investigations. Novel approaches to producing new true biological RNAi molecules for research and development are highlighted.