A Summary of Site-Specific Lipid Nanoparticles for mRNA Delivery

What are Site-Specific Lipid Nanoparticles?

During the COVID-19 pandemic, the successful development of mRNA vaccines has greatly propelled the advancement of mRNA therapy. Site-specific lipid nanoparticles (LNP) are carriers used for mRNA delivery, designed to transport mRNA to specific cells, tissues, or organs to exert local or systemic therapeutic effects. These LNPs possess unique chemical structures or functionalities that enable precise targeted delivery in specific biological environments. Through the design of appropriate surface modifications or chemical alterations, site-specific LNPs can selectively interact with target cell surface receptors or other molecules, facilitating targeted delivery to specific tissues or cells. This targeted delivery helps enhance the efficiency of mRNA therapy, reduce the impact on non-target cells, thereby decreasing off-target side effects, and further optimizing therapeutic outcomes. The appeal of lipid nanoparticles (LNPs) lies in their ability to deliver various types of nucleic acids without altering their structure. These nucleic acids can include RNA, microRNA (miRNA), siRNA, and single-guide RNA (sgRNA). LNPs consist of various lipid compositions, making quality control easier as lipids are easier to purify compared to other types of carriers such as large molecules or viruses. Additionally, by altering the structure or composition of lipids, it's easy to develop new LNPs, thereby achieving their multifunctionality and site-specific design.

Site-specific lipid nanoparticles for mRNA delivery. (Xu, X.; Xia, T, 2023)

* Related services from BOC Sciences.

* Related lipid raw materials products from BOC Sciences.

Site-Specific Lipid Nanoparticles for Localized Administration

The route of administration is crucial for the delivery of mRNA loaded in LNP. Various routes of administration have been developed to achieve site-specific delivery of LNP, including oral administration, inhalation, and local injection (intramuscular, intratumoral, and intracerebral injection).

Oral Administration

Oral administration is a widely used, convenient, and effective drug delivery route, where drugs are ingested through the mouth and absorbed by the gastrointestinal system. However, the acidic environment and presence of enzymes in the gastrointestinal tract can potentially limit the effectiveness of drugs, especially for molecules susceptible to degradation by nucleases, such as mRNA. In response to these challenges, researchers are developing drug delivery systems that can be administered orally and directly interact with sites of gastrointestinal diseases. For example, loading mRNA encoding IL-22 into lipid nanoparticles (LNPs) aims to improve drug efficacy, particularly for difficult-to-treat conditions like inflammatory bowel disease (IBD).

Inhalation Administration

Inhalation therapy is a preferred route for drug delivery, particularly suitable for treating respiratory-related diseases. By inhaling drugs into the respiratory tract, they can quickly enter the bloodstream, enhancing their bioavailability. Despite the advantages of inhalation therapy, such as a large absorption area and rich pulmonary blood flow, challenges exist in dose control and airway clearance. Drugs administered through inhalation are typically delivered in the form of aerosols, undergoing clearance processes by mucociliary clearance or phagocytosis by macrophages. Especially when dealing with infectious diseases like COVID-19, scientists are striving to develop nebulized lipid nanoparticles (LNPs) suitable for inhalation to treat respiratory infections. However, while advanced nebulization techniques can assist drugs in entering the lungs, shear forces may damage the structure of nanoparticles, and physical barriers in the airways may limit drug delivery to the target site. To overcome these challenges, researchers are developing optimized LNP formulations to achieve more effective inhalation therapy, such as improving the efficiency of pulmonary delivery by adjusting the PEG lipid ratio.

Local Injection

Local injection administration refers to the delivery of drugs into specific areas of the body to achieve localized therapeutic effects, while also allowing the drug to spread or enter the bloodstream, exerting systemic therapeutic effects. Local injection of mRNA drugs based on lipid nanoparticles (LNPs) is an important therapeutic strategy. By injecting LNPs loaded with mRNA drugs into specific sites, such as muscle tissue or tumor sites, targeted therapy can be achieved while minimizing systemic side effects. This approach has been used in the treatment of various diseases, including Duchenne muscular dystrophy (DMD) and cancer. Through local injection of LNPs loaded with mRNA drugs, localized treatment of diseases can be achieved while reducing systemic side effects, offering promising avenues for gene editing, immunotherapy, and other fields.

Organ-Specific Lipid Nanoparticles via Intravenous Administration

Intravenous injection is another standard route of administration with a bioavailability of 100%. The biodistribution of LNPs after intravenous injection is crucial because off-target delivery of mRNA can lead to adverse reactions and significantly reduce therapeutic efficacy. In recent years, much research has focused on organ-specific LNPs.

Liver-Targeted LNPs

Using DMG-PEG2000 lipids and apolipoprotein E (ApoE) enables LNPs to target the liver after intravenous injection, aiding in the treatment of liver-related diseases. Onpattro siRNA is an example where the drug primarily accumulates in the liver, and this targeting mechanism can be applied to treat various liver-related diseases.

* Related products from BOC Sciences.

Spleen or lung-Targeted LNPs

Selective targeting of different organs such as the spleen or lungs can be achieved by adjusting the composition of LNPs. Modifying the components and composition of LNPs allows for selective targeting of organs like the spleen or lungs. Using different ratios of cationic or anionic lipids as the fifth lipid can regulate the distribution of LNPs in various organs. Specific ratios of cationic or anionic lipids contribute to the distribution of LNPs in the lungs, spleen, and liver.

Bone-Targeted LNPs

Lipids prepared with bisphosphonate (BP) headgroups can facilitate targeted delivery of LNPs to the bones. After intravenous injection, LNPs can persist in the bone microenvironment for an extended period and exhibit high expression in bone tissue, offering potential for treating bone-related diseases.

These studies demonstrate that by adjusting the composition and components of LNPs, selective targeted delivery to different organs can be achieved, providing new possibilities for treating relevant diseases.

Cell-Specific Lipid Nanoparticles for Systemic Administration

In order to achieve a more specific mRNA delivery system, cell-targeting LNPs have been developed, designed to be absorbed by specific cells to induce protein expression within those cells. Typically, this cell-specific uptake is mediated by ligand-receptor interactions, and recent research has found that this interaction can also be achieved by altering the lipid structure within LNPs.

Leukocyte-Targeting LNPs

To achieve cell-specific mRNA therapy for inflammatory bowel disease (IBD), research has reported and prepared an antibody-modified LNP for targeted delivery of IL-10 mRNA to Ly6c+ inflammatory leukocytes. Ly6c+ cells serve as targets for treating IBD. The immune-suppressive cytokine IL-10 can inhibit IBD. To induce long-term IL-10 production, IL-10 mRNA-loaded LNPs were prepared first, followed by incubation with anchored secondary scFv enabling targeting (ASSET) micelles at 4°C for 48 hours, and then incubated with anti-Ly6c monoclonal antibodies for 30 minutes. ASSET is an original modular targeting platform created to bridge LNPs and specific antibodies under mild conditions. Following intravenous injection into mice with dextran sodium sulfate-induced colitis, these surface-modified LNPs actively targeted Ly6c+ leukocytes and induced IL-10 production, significantly inhibiting inflammation in the colon.

T cell-Targeting LNPs

Cardiac fibrosis is caused by excessive production of extracellular matrix by cardiac fibroblasts. Limiting fibrosis progression through anti-fibrotic therapy is unsatisfactory for treating cardiac fibrosis. A reshaping fibrosis CAR-T therapy has been reported, which delivers mRNA targeting to T cells intracellularly. Fibroblast activation protein CAR (FAP-CAR) is encoded into mRNA, which is then loaded into LNP modified with anti-CD5 antibodies to achieve specific targeting to CD5+ T cells. FAP-CAR is expressed on the surface of T cells, specifically recognizing FAP-positive cells and inducing cell death, thus alleviating cardiac fibrosis. Systemic administration of CD5-targeting LNPs loaded with FAP-CAR mRNA significantly reduces fibrosis and improves cardiac function. This represents a significant success of mRNA-loaded LNPs in treating heart diseases.

Kupffer cell and liver sinusoidal endothelial cell (LSEC)-Targeting LNPs

Kupffer cells play a crucial role in liver inflammation and immune tolerance by clearing particles through phagocytosis. Increasing the size of LNPs and surface modification with hydrophobic molecules enhances the cellular uptake by Kupffer cells and promotes immune regulation. LSECs are located within the liver sinusoid and are responsible for blood filtration, metabolic regulation, antigen presentation, and lipid metabolism. To achieve cell-specific mRNA delivery to Kupffer cells or LSECs, it has been reported that different types of cholesterol were applied in the formulation of LNPs, revealing a significant influence of cholesterol structure on LNP targeting ability. Using the fast identification of nanoparticle delivery (FIND) system for screening LNPs formulated with various oxidized cholesterol, it was concluded that LNPs containing oxidized cholesterol deliver mRNA to cells within the liver microenvironment, including Kupffer cells and LSECs, unlike traditional LNPs primarily targeting hepatocytes. Considering the crucial roles of Kupffer cells and LSECs in antigen presentation and anti-inflammatory functions, these LNPs can further be utilized in immunotherapy. Additionally, the targeting ability of LNPs to different liver cells is also influenced by the PEG-lipid ratio. As the PEG-lipid ratio increases from 1.0% to 3.0%, more LNPs are delivered to hepatocytes, while delivery to Kupffer cells and LSECs decreases. Moreover, if PEG-lipid is replaced with glucose-modified lipid, LNPs specifically target LSECs, indicating that cell-specific mRNA delivery can be achieved by altering the ratio and structure of PEG-lipid.

Prospects of Site-Specific Lipid Nanoparticles for mRNA Delivery

mRNA therapy based on LNPs is a promising nucleic acid therapy that can target many diseases that are difficult to target with small molecules. With the development of delivery technologies, mRNA can be used to treat various diseases including infections, cancers, and genetic disorders. Meanwhile, the size, shape, and surface properties of LNPs are largely influenced by the lipid structure and composition, and these physical properties will affect the efficacy, safety, and drug distribution of LNPs. There are also challenges regarding mRNA and nanoparticles themselves. On one hand, since protein expression from mRNA is transient, repeated injections of mRNA-loaded LNPs are required. However, repeated injections may induce immune responses, such as neutralizing antibodies against PEG, which in turn could reduce drug efficacy. Therefore, finding disease-specific mRNA is crucial for enhancing drug efficacy, reducing injection frequency, and minimizing associated immunogenicity. On the other hand, intravenous administration of nanoparticles can lead to hypersensitivity reactions, which are pseudoallergic reactions that can be explained by inadvertent complement activation. Further development of LNPs should aim to eliminate or reduce the chance of such allergic reactions.

Despite challenges in developing site-specific mRNA therapies, advancements in chemical synthesis and nanotechnology will lead to the development of increasingly effective treatment methods.

Reference

1. Xu, X.; Xia, T. Recent Advances in Site-Specific Lipid Nanoparticles for mRNA Delivery. ACS Nanoscience Au. 2023, 3(3): 192-203.