title: Current issues of RNAi therapeutics delivery and development.
abstract: 12 years following the discovery of the RNAi mechanism in Man, a number of RNAi therapeutics development candidates have emerged with profiles suggesting that they could become drugs of significant medical importance for diseases like TTR amyloidosis, HBV, solid cancers, and hemophilia. Despite this robust progress, the perception of RNAi therapeutics has been on a roller-coaster ride driven not only by science, but also regulatory trends, the stock markets, and Big Pharma business development decisions [1]. This presentation provides an update on the current state of RNAi therapeutics development with a particular focus on what RNAi delivery can achieve today and key challenges to be overcome to expand therapeutic opportunities. The delivery of RNAi triggers to disease-relevant cell types clearly represents the rate-limiting factor in broadly expanding the applicability of RNAi therapeutics. Today, with at least 3 delivery options (lipid nanoparticles/LNPs, GalNAc-siRNA conjugates, Dynamic PolyConjugates/DPCs) for which profound gene knockdowns have been demonstrated in non-human primates and in the clinic, RNAi therapeutics should in principle be able to address most diseases related to gene expression in the liver. Given the central importance of the liver in systemic physiology, this already represents a significant therapeutic and commercial opportunity rivaling that of e.g. monoclonal antibodies. Beyond the liver, there is a reason to believe that current RNAi therapeutics technologies can address a number of solid tumors (e.g. LNPs), diseases of the eye (e.g. self-delivering RNAi triggers) as well as diseases involving the respiratory epithelium (e.g. aerosolized LNPs), certain phagocytic cells (LNPs), hematopoietic stem cells and their progeny (lentiviral DNA-directed RNAi), vascular endothelial cells (cationic lipoplexes), and certain cell types in the kidney (self-delivering RNAi triggers, DPCs; Table 1). Despite this success, there has been a sense that the applications of RNAi therapeutics are rather limited. This is largely based on the observation that the biodistribution of RNAi formulations is typically more limited compared to small molecules and oral administration is not possible with current technologies. Similarly, the utility of a given RNAi formulation is limited to a few cell types and tissues at most and a universal delivery strategy should remain elusive for the foreseeable future. Therefore, to further expand on the therapeutic utility and patient convenience of RNAi, it is important to overcome a number of delivery-related technical and scientific challenges which will be discussed in this presentation. For systemic applications, these include the necessity for extended blood circulation times, vascular escape (probably the most rewarding inquiry currently), tissue penetration, cellular uptake, and escape into the cytoplasm. In terms of safety, it is important that these formulations do not accumulate in the body, do not cause excessive off-targeting due to 'chemical stickiness' (often useful for purposes of biodistribution), and overcome the physical/biological barriers in a controlled manner. The time for realizing the therapeutic potential of RNAi has come. At the same time, it is important to lay the foundations for the next leg of value creation by overcoming the challenges of delivering RNAi to new cell types. Based on results from exploratory research, the renewed interest in RNAi therapeutics and capital infusion, there is a reason to be optimistic that this can be achieved.
authors.affiliation: Independent RNAi Therapeutics Analyst and Consultant, Rastatt, Germany. Electronic address: dirk.haussecker@gmail.com.
authors.forename: D
authors.initials: D
authors.lastname: Haussecker
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D035683:MicroRNAs / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000008:administration & dosage*
chemical_list: D035683:MicroRNAs; D034741:RNA, Small Interfering
keywords: Delivery; RNAi therapeutics; Synthetic RNAi triggers