Lipid nanoparticles are a promising delivery system for gene therapy, but getting suitable lipids is challenging. Only a few facilities are outfitted to produce the effective ionizable cationic lipids used in LNP-mRNA formulations.
The companies that can supply these critical components are in high demand. For example, some contracted to provide lipid components for Pfizer-BioNTech’s COVID-19 vaccine.
How Lipid Nanoparticles Can Advance Gene Therapy
Lipid nanoparticles are currently the lead nonviral delivery system for enabling the clinical potential of generic drugs. They allow the safe and effective treatment of most diseases by silencing pathological genes or expressing therapeutic proteins, thereby correcting a defective gene or mutated protein. However, lipid-based gene delivery systems must overcome several obstacles to achieve their full therapeutic potential, including hepatic clearance and immunosuppression.
A new generation of lipid-based delivery systems has been developed to address these challenges. These systems incorporate lipids with functional groups that facilitate hepatic clearance, subvert pattern-recognition receptor signaling, and maximize the potency of encapsulated siRNA. They also exhibit superior cellular uptake, overcoming the limitations of existing liposomal systems. In addition, lipid-based gene delivery systems can be engineered for organ-specific targeting by modulating the lipid structures.
For example, lipids with various lengths of alkyl chains can target different cell types. Lipid-nanoparticle-mRNA formulations with longer alkyl chains preferentially accumulate in liver endothelial cells and Kupffer cells, while shorter lipids concentrate in the brain after administration.
Moreover, ionizable and cationic lipids can trigger immune activation by interacting with complement and Toll-like receptors. Depending on the dose and lipid properties, this interaction can result in cytotoxicity and inflammation.
Therefore, the design of lipid nanoparticle-mRNA formulations is critical to their success as a clinically effective treatment tool. The lipid-nanoparticle-mRNA complexes need to meet the specific requirements of each application, such as unique biodistribution profiles and the ability to induce efficient gene expression or antigen-specific cellular immunity. They must also be stable and have good manufacturing practices for successful clinical development. Moreover, the lipids used in these formulations should have multifunctional properties to enhance their efficacy, such as self-adjuvant lipids that boost vaccine efficacy and paclitaxel-derived lipids that can be combined with chemotherapies.
Lipid Nanoparticles For mRNA Vaccines
Lipid nanoparticles are the most clinically advanced nonviral gene delivery systems. They safely and effectively deliver nucleic acids and have opened the door to genetic medicine applications, including mRNA vaccines, RNA editing, and immuno-oncology. The first RNA interference drug (Patisiran) used LNPs to achieve therapeutic efficacy in patients.
LiNPs are stable in physiological fluids and deliver mRNA cargo to cells without stabilizing agents such as polyethylene glycol. Despite this stability, LNPs must be able to penetrate the cell membrane and accumulate at disease sites. This is accomplished through the lipid-mediated endosomal escape effect. The lipid composition of the LNP is critical to achieving this efficacy. In this regard, ionizable phospholipids are essential to lipid nanoparticles, determining mRNA cellular uptake and endosomal escape.
Ionizable phospholipids have a positive charge at low pH, enabling them to interact with the anionic membranes of blood cells. However, they remain neutral at physiological pH and improve the biocompatibility of lipid nanoparticles. This is particularly important for mRNAs, which are negatively charged.
Moreover, ionizable phospholipids increase the stability of lipid nanoparticles against proteases, reducing mRNA degradation and allowing for longer circulation times in the body. They also reduce the particle size, facilitating cellular uptake and ensuring targeted gene delivery to specific target cells.
Several lipid nanoparticle companies have used ionizable lipids to formulate lipid nanoparticle-mRNA vaccines and are currently conducting clinical trials. mRNA-based vaccination has demonstrated promising efficacy in preclinical models against viral infections, including human metapneumovirus, cytomegalovirus, respiratory syncytial, and rabies.
Furthermore, mRNA-based lipid nanoparticle vaccines have been developed to induce immune responses against parasitic infections, bacterial infections (e.g., multidrug-resistant bacterial sepsis), and even cancers. mRNA-based vaccines effectively generate antimicrobial antibodies, reduce tumor growth, and promote cellular death in cancer cells.
Lipid Nanoparticles For Gene Therapy
Lipid nanoparticles are currently the most clinically advanced nonviral gene delivery systems. They safely and effectively deliver nucleic acids overcoming a significant barrier to developing genetic medicine, such as fast vaccine development, immuno-oncology, and treatment of rare genetic and undruggable diseases.1
Lipids with a low pKa value can be combined with negatively charged oligonucleotides to form lipoplexes. These lipid-oligonucleotide complexes can pass the blood-brain barrier (BBB) and target cells inside the brain.
However, despite the success of lipoplexes in cancer therapy, there are limitations. For example, the lipid-pDNA ratio affects the kinetic properties of the resulting complexes, which impact how many oligonucleotides can be delivered to target cells. In addition, lipid-pDNA complexes exhibit a high level of liver toxicity and are cleared from the body by macrophages after cellular uptake.
To address these issues, lipid-mRNA nanoparticles (LNP) were developed. These lipid-mRNA nanoparticles are engineered to be highly polarized and soluble in water to promote BBB penetration and intracellular uptake. In addition, they are designed to be nontoxic and to have a prolonged circulation time in the body. The lipid-mRNA complexes formed by LNPs can target the brain, muscle, and other tissue for high levels of oligonucleotide expression while maintaining an increased cellular uptake efficiency.
A key challenge for mRNA-based therapeutics is ensuring that mRNA reaches targeted cells and produces sufficient amounts of the desired protein. This is challenging because mRNA must be transported from the cell surface into the cytoplasm and escape from the endosomal compartment. Lipid nanoparticles are a promising vehicle for mRNA-based therapeutics because they facilitate efficient endosomal escape. They can be augmented with zwitterionic ionizable lipids that activate the STING pathway in dendritic cells to enhance protein production.
The first mRNA-based therapeutic to reach the clinic was the lipid-mRNA-pDNA formulated SPLP, which exhibited desirable extended circulation properties and could target mouse tumor cells. SPLP demonstrated high gene expression in the target tissue with little toxicity in the liver and spleen. The mRNA-pDNA complexes formed by SPLP were also stable and retained their mRNA delivery efficacy for over three months in vivo. This was attributed to using a high sucrose concentration and including trehalose as cryoprotectants.