In recent years, messenger RNA (mRNA) has come into the spotlight as a versatile therapeutic with the potential to prevent and treat a staggering range of diseases. Billions of dollars have been invested in the commercial development of mRNA drugs, with ongoing clinical trials focused on vaccines (for example, influenza and Zika viruses) and cancer immunotherapy (for example, myeloma, leukaemia and glioblastoma). Although significant progress has been made in the design of in vitro-transcribed mRNA that retains potency while minimizing unwanted immune responses, the widespread use of mRNA drugs requires the development of safe and effective drug delivery vehicles. In this Review, we provide an overview of the field of mRNA therapeutics and describe recent advances in the development of synthetic materials that encapsulate and deliver mRNA payloads.

The potential of mRNA therapeutics will be realized only once safe and effective delivery systems are established. Unfortunately, delivery vehicle development is stymied by an inadequate understanding of how the molecular properties of a vehicle confer efficacy. Here, a small library of lipidoid materials is used to elucidate structure–function relationships and identify a previously unappreciated parameter—lipid nanoparticle surface ionization—that correlates with mRNA delivery efficacy. The two most potent materials of the library, 306O10 and 306Oi10, induce substantial luciferase expression in mice following a single 0.75 mg kg−1 mRNA dose. These lipidoids, which have ten‐carbon tails and identical molecular weights, vary only in that the 306O10 tail is straight and the 306Oi10 tail has a one‐carbon branch. Remarkably, this small difference in structure conferred a tenfold improvement in 306Oi10 efficacy. The enhanced potency of this branched‐tail lipidoid is attributed to its strong surface ionization at the late endosomal pH of 5.0. A secondary lipidoid library confirms that Oi10 materials ionize more strongly and deliver mRNA more potently than lipidoids containing linear tails. Together, these data highlight the exquisite control that lipid chemistry exerts on the mRNA delivery process and show that branched‐tail lipids facilitate protein expression in animals.

Although mRNA and siRNA have significant therapeutic potential, their simultaneous delivery has not been previously explored. To facilitate the treatment of diseases associated with aberrant gene upregulation and downregulation, we sought to co-formulate siRNA and mRNA in a single lipidoid nanoparticle (LNP) formulation. We accommodated the distinct molecular characteristics of mRNA and siRNA in a formulation consisting of an ionizable and biodegradable amine-containing lipidoid, cholesterol, DSPC, DOPE, and PEG-lipid. Surprisingly, the co-formulation of siRNA and mRNA in the same LNP enhanced the efficacy of both drugs in vitro and in vivo. Compared to LNPs encapsulating siRNA only, co-formulated LNPs improved Factor VII gene silencing in mice from 44 to 87% at an siRNA dose of 0.03 mg/kg. Co-formulation also improved mRNA delivery, as a 0.5 mg/kg dose of mRNA co-formulated with siRNA induced three times the luciferase protein expression compared to when siRNA was not included. As not all gene therapy applications require both RNA drugs, we sought to extend the benefit of co-formulated LNPs to formulations encapsulating only a single type of RNA. We accomplished this by substituting the "helper" RNA with a negatively charged polymer, polystyrenesulfonate (PSS). LNPs containing PSS mediated the same level of protein silencing or expression as standard LNPs using 2-3-fold less RNA. For example, LNPs formulated with and without PSS induced 50% Factor VII silencing at siRNA doses of 0.01 and 0.03 mg/kg, respectively. Together, these studies demonstrate potent co-delivery of siRNA and mRNA and show that inclusion of a negatively charged "helper polymer" enhances the efficacy of LNP delivery systems.

The clinical translation of messengerRNA (mRNA) drugs has been slowed by a shortage of delivery vehicles that potently and safely shuttle mRNA into target cells. Here, we describe the properties of a particularly potent branched-tail lipid nanoparticle that delivers mRNA to >80% of

No abstract