Molecular therapies such as messenger RNA (mRNA) vaccines and gene and cell therapies are transforming modern medicine. These treatments work by delivering genetic instructions into a patient’s cells with special delivery systems.
To get the genetic material, such as mRNA, DNA or other types of nucleic acids, into the body, scientists typically use one of two delivery systems: viral vectors or tiny fat-based “bubbles” called lipid nanoparticles (LNPs). The former are modified viruses that have a natural ability to enter cells; however, they can generally be administered only once, and they may trigger unwanted immune responses. LNPs, by contrast, are generated in a lab and are considered safer.
Although LNPs may offer a safer way to deliver molecular cargo to cells, the US Food and Drug Administration has approved only five LNP-based products, compared with dozens of viral-vector-based molecular therapies already in the clinic.
The dominance of viral vectors reflects not only their biological advantages but also their much earlier entry into therapeutic development than LNPs (about thirty years compared to less than ten, respectively). Since the success of the COVID-19 mRNA vaccines in which the molecular payload was carried by LNPs, the technology has gained widespread acceptance, speeding the pace of research, yet much remains to be understood about how each of their components behaves within the body as well as how to optimize them for precise targeting and efficient entry into cells, making these therapies more effective and easier for patients to tolerate.
Understanding the building blocks of lipid nanoparticles
A team of scientists from the mRNA Center of Excellence of Sanofi in Waltham, MA, USA, has now examined the individual components in lab-made LNPs to better understand how they interact with cells.
Lipid nanoparticles are built with four major components: ionizable lipids that wrap a payload of nucleic acids, protecting them from degradation and helping the payload release once the LNP enters a cell; helper lipids that give the particle its basic structure and help it merge with the cell’s outer membrane; cholesterol molecules that strengthen and stabilize the LNP, helping it stay intact as it moves through the bloodstream, and; PEG-lipids which form a protective coating on the outside of the particle, preventing it from clumping together and helping it circulate longer in the body.
“We engineered an optimized LNP system for delivering messenger RNA specifically to the liver, resulting in efficient and sustained protein production in liver cells,” says Ashish Sarode, associate director of the Formulation and Delivery department at Sanofi and lead author of the study.
When LNPs enter the blood system following intravenous administration, they preferentially accumulate in the liver due mainly to hepatic uptake. When they approach the liver cells (hepatocytes), the LNPs bind to a membrane protein called the apolipoprotein E (ApoE) and enter the cells via a mechanism dependent on another protein, the low-density lipoprotein receptor (LDLR). Since much of this knowledge is empirical, the researchers sought to better understand which LNP components drive these processes.
They tested different ionizable lipids, helper lipids and PEG-lipids, and cholesterol analogs. Then they selected, in each step, the best combination: the one with the best dose responsiveness, the best sustained payload expression in the liver, and the one with the most favourable tolerability in preclinical models.
The biggest surprise came when they realized that changing the ionizable lipid made the LNP independent of the LDLR entry pathway, a process previously believed to depend on the helper lipid.
“This breakthrough allowed us to circumvent the saturation bottleneck of the traditional LDLR route, leading to the highly potent, liver-tropic formulation described in the study and significantly expanding the potential therapeutic applications,” says Sarode. The work enables the rational design of LNPs with specific desired properties. “This LNP platform approach has the potential to significantly accelerate the development of mRNA therapies for numerous rare and genetic diseases.”
Rational design for efficient and safer genetic treatments
Molecular therapies dependent on lipid nanoparticle delivery are especially relevant for genetic diseases in which a gene malfunctions and affects an individual’s health.
Sarode and the team used a lab model of ornithine transcarbamylase (OTC) deficiency, a rare, inherited disorder that affects the body’s ability to remove ammonia from the blood. When the scientists treated animals with mRNA encoding the human OTC protein using their LNP system, they observed targeted expression in the liver, resulting in efficient, sustained OTC protein production in hepatocytes.
Importantly, because this mechanism does not rely on the LDLR protein, it could be used in medical conditions where LDLR function is reduced or impaired, such as severe liver disease or genetic disorders like familial hypercholesterolemia. “An LDLR-independent LNP formulation ensures that these patients can still be effectively treated,” comments Sarode.
The team has successfully moved beyond the traditional empirical trial-and-error approach for lipid nanoparticle formulation. Shrirang Karve, global head of Delivery and Formulations and co-author of the study, says: “Our work is grounded in mechanistic understanding, specifically identifying how individual lipid components control cellular entry pathways in the liver.”
Since their LNPs demonstrate robust mRNA delivery and sustained OTC protein expression with minimal toxicity, Karve believes the same technology could be extrapolated to other diseases, i.e., formulating LNPs to carry different nucleic acid cargo to treat other genetic diseases.
“This knowledge has allowed us to create a rational design framework for developing highly targeted, next-generation delivery systems,” comments Karve. “By creating a predictable and highly efficient delivery system, we can transform the typical treatment timeline from potentially decades down to mere years.”
Reference: A. Sarode et. al., Potent Liver-Tropic mRNA Lipid Nanoparticles: ApoE-Mediated Delivery Through a Low-Density Lipoprotein Receptor Independent Uptake Mechanism, Advanced Materials (2025), DOI: 10.1002/adma.202517893
Featured Image: “The needle” by Dr Partha Sarathi Sahana via Flickr, CC BY 2.0
