Passive, active and endogenous organ-targeted lipid and polymer nanoparticles for delivery of genetic drugs

Abstract

Genetic drugs based on nucleic acid biomolecules are a rapidly emerging class of medicines that directly reprogramme the central dogma of biology to prevent and treat disease. However, multiple biological barriers normally impede the intracellular delivery of nucleic acids, necessitating the use of a delivery system. Lipid and polymer nanoparticles represent leading approaches for the clinical translation of genetic drugs. These systems circumnavigate biological barriers and facilitate the intracellular delivery of nucleic acids in the correct cells of the target organ using passive, active and endogenous targeting mechanisms. In this Review, we highlight the constituent materials of these advanced nanoparticles, their nucleic acid cargoes and how they journey through the body. We discuss targeting principles for liver delivery, as it is the organ most successfully targeted by intravenously administered nanoparticles to date, followed by the expansion of these concepts to extrahepatic (non-liver) delivery. Ultimately, this Review connects emerging materials and biological insights playing key roles in targeting specific organs and cells in vivo.

Keywords: Biomedical engineering; Drug delivery.

Fig. 1. Self-assembled nanoparticles based on lipid and polymer materials are the state of the art for the delivery of genetic drugs.

Currently, lipid nanoparticles that incorporate an ionizable lipid are the most advanced delivery system for genetic drugs in the clinic. These materials feature a tertiary amine that can acquire charge at acidic pH to facilitate nucleic acid loading during formulation and promote endosomal escape following cellular uptake. Dilinoleylmethyl-4-dimethylaminobutyrate (DLin-MC3-DMA) is a component of the US Food and Drug Administration-approved drug Onpattro. LP-01 is a component of Intellia Therapeutics’ clinical candidates NTLA-2001 and NTLA-2002 for gene editing in the liver, and SM-102 and ALC-315 are the ionizable lipid components of the Moderna and Pfizer–BioNTech vaccines, respectively. Alternatively, certain polymers that incorporate ionizable amine groups can also be used to formulate nanoparticles, and the choice of monomers will impact nanoparticle delivery efficiency and tissue selectivity. For both ionizable lipids and polymers, supplementary components can be included to improve the stability, fusogenicity (the ability to facilitate fusion with cellular membranes) and selectivity of the formulated nanoparticle. Additionally, the surfaces of these nanoparticles can be further modified using synthetic or biological targeting ligands and stealth coatings to alter nanoparticle circulation time, biodistribution and cellular uptake. Nucleic acid biomolecules can be loaded into nanoparticles to reprogramme the central dogma of biology through gene silencing, expression and editing to correct the course of disease. 18:1 PA, 1,2-dioleoyl-sn-glycero-3-phosphatidic acid; CART, charge-altering releasable transporter; DOPE, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine; DOTAP, 1,2-dioleoyl-3-trimethylammonium-propane; DSPC, 1,2-distearoyl-sn-glycero-3-phosphocholine; PBAE, poly(beta-amino ester); PEI, polyethyleneimine; SORT, selective organ targeting.

Fig. 2. The journey of a nanoparticle through the human body following intravenous injection.

Upon contact with the blood, plasma proteins often adsorb to the nanoparticle surface to form an interfacial layer known as the protein corona. The composition of the protein corona is influenced by the surface properties and composition of the nanoparticle. To reach the target organ, nanoparticles must exit the vasculature (extravasation) by passing through gaps in the endothelium, a size-limited process, or by active transcytosis, involving interaction with specific receptors expressed on the endothelium. Following extravasation, nanoparticles must interact with and be internalized by target cells. They must then escape the endosome into the cytosol and release their genetic payload. Throughout this journey, nanoparticles can be cleared from the systemic circulation by the mononuclear phagocytic system (MPS), hepatobiliary elimination (by the faeces) or renal excretion (by urine). These processes limit how much of the injected nanoparticle dose reaches the desired target site; thus, steps must be taken to minimize their action.

Fig. 3. Lipid nanoparticles are a clinically mature technology for genetic drug delivery to the liver.

a, The liver microanatomy is composed of four distinct cell types. Nanoparticles in the blood can either be sequestered by Kupffer cells, taken up by liver sinusoidal endothelial cells, or extravasate through the wide fenestrations in liver endothelium into the Space of Disse. There, the nanoparticles can target hepatic stellate cells or hepatocytes. The hepatobiliary system can eliminate nanoparticles from the body via the bile duct. b, Endogenous targeting of liver cells is a clinically validated mechanism for small interfering RNA delivery to hepatocytes. For example, delivery of Onpattro lipid nanoparticles occurs by exchange of polyethylene glycol (PEG) lipid at the nanoparticle surface with apolipoprotein E (ApoE) in the blood. Adsorption of ApoE to the nanoparticle surface results in binding of the nanoparticle by low-density lipoprotein receptor (LDL-R), highly expressed by hepatocytes, and subsequent endocytosis. c, Active targeting of hepatocytes can also be achieved by functionalizing the nanoparticle surface with an N-acetylgalactosamine (GalNAc) ligand and reducing non-specific protein binding through extensive PEGylation. GalNAc binds asialoglycoprotein receptor 1 (ASGR1) to facilitate nanoparticle uptake by hepatocytes. Part a reprinted from ref. , Springer Nature Limited.