Generically mediated gene therapy and gene vaccines have also usher in a new kind of medicine involving delivery of DNA and RNA. Such treatments can be applied to all manner of conditions, from genetic conditions and cancer to viral infections. But it's still not easy to deliver these nucleic acids to the target cells. One of the many delivery systems in development, PEGylated cationic liposomes (especially those based on the cationic lipid DOTAP (1,2-dioleoyl-3-trimethylammonium-propane), is now a common nanocarrier for gene therapy and drug delivery. Such liposomes enhance cellular absorption, prevent nucleic acid degrading, and enhance total therapeutic activity, hence the reason they have been the focus of so much contemporary research. DOTAP (1,2-dioleoyl-3-trimethylammoniumpropane) is an artificial cationic phospholipid, whose identity is simply its quaternary ammonium head group which enables it to bind to nucleic acids and cell membranes. With DOTAP, you can make cationic liposomes as it is positively charged (NH4+ group) and is not as toxic as other cationic lipids. DOTAP is usually pre-sampled with neutral lipids such as DOPC (dioleoyl phosphatidylcholine) to make stable liposomes. In experiments, researchers found that DOTAP ratio effects liposome size and stability. If DOTAP is in 1:99 ratio with DOPC, for instance, liposomes of various charge densities and zeta potentials can be prepared. Moreover, pH and ionic strength are related to DOTAP liposome dispersibility and stability in media. DOTAP liposomes work well for gene transfection and drug delivery especially when paired with nucleic acid components like DNA or RNA. For instance, DOTAP can be used to captain nucleic acid molecules like DNA and RNA to make them easier to transfect.
Figure 1. Schematic representation of the preparation of the PEGylated DOTAP-DOPE liposomes and lipoplexes. (Pereira S, et al. 2021)
The special structure of DOTAP liposomes is ideal for the delivery of negatively charged nucleic acids. Because DOTAP is a cationic lipid, it reacts electrostatically with the anionic base of DNA and RNA molecules, so that they get packed in the liposome. This is a very stable, but also efficient interaction to load nucleic acids and also keep liposomes stable during storage and transportation. But getting the nucleic acids to their destination is difficult, since cell membranes are a huge impediment to large molecules entering. PEGylation solves these problems by bonding polyethylene glycol (PEG) chains to the surface of liposomes. This change makes the liposomes hydrophilic and hence creates a barrier that lessens the immune response by being detected and cleared. Hence, PEGylated liposomes can survive longer in the bloodstream and hence, are more likely to penetrate targeted tissues. The protection of PEG helps keep the liposomes from clumping and fusion together. Aggregated liposomes will result in less efficient delivery and unpredictable nucleic acid cargo. The addition of PEG not only stable the liposomal but also keeps its integrity until it gets to its intended cellular destination. Once in the cytoplasm, PEGylated cationic DOTAP liposomes induce endosomal escape, the next step in releasing nucleic acids into the cytoplasm. If scientists programme these liposomes to act on specific environmental conditions (such as pH changes or the presence of certain enzymes), then we can develop smart delivery systems that control the release of nucleic acids and optimize the efficacy of treatment.
The versatility of PEGylated cationic DOTAP liposomes also boosts their delivery capacity with nucleic acids. Scientists can adjust the liposomal structure, from the lipid ratios to the PEG chain lengths, to tailor the formulation to the requirements of specific therapeutic objectives. Variation in the quantity of cationic lipid, for example, can alter the charge of the liposomes, which will have an impact on their interactions with nucleic acids and cells. Shorter PEG chains increase circulation time and immunogenicity, and longer chains increase cellular absorption. Furthermore, the targeting ligands present on the liposomal surface can also give the delivery system much more specificity. When they put ligands attached to receptors on target cells, they can enable receptor-mediated endocytosis, increasing even more the uptake of nucleic acids by those cells. This personalization opens the door to tailored therapies that can improve treatment rigour, especially in oncology and personalized medicine. And PEGylated cationic DOTAP liposomes are not only used for basic delivery of nucleic acids, they are also being tested as a carrier for mRNA vaccines, a field that has been expanding in recent years. With the success of mRNA vaccines for infectious diseases like COVID-19, it's been imperative that we develop delivery mechanisms that are safe and efficient to get mRNA into cells. These are particularly useful with PEGylated cationic liposomes, which can hold mRNA in the membrane to ensure it does not get degraded, but will reach the cytoplasm for translation into proteins. The possibility of circulating mRNA makes it possible to develop and deliver vaccines more quickly, especially against new infectious diseases. PEGylated cationic DOTAP liposomes for the delivery of CRISPR/Cas9 elements, a concept that is transforming gene editing, are being tested in vaccines and gene therapies as well. CRISPR/Cas9 depends on getting guide RNA and the Cas9 protein into the editing cell. These components can be encapsulated by PEGylated cationic liposomes that can then be taken up and delivered to the nucleus where gene editing happens. This power could set these liposomes up as an engine for the next generation of gene-editing tools that would permit a more precise and controlled genome editing. Combining DOTAP's cationic and PEG's stealth-enhanced features is an attractive approach to design multifunctional liposomes. In the interest of future era, scientists increasingly seek to engineer hybrids that bring new functionality (for example, adding peptides or other small molecules to drive cellular uptake or provide therapeutic effects). Such hybrid systems can improve the total function of PEGylated cationic DOTAP liposomes and can result in higher delivery rates and therapeutic efficacy.
Alternate Names:
DOTAP Liposomes
DOTAP Cationic Liposomes
1,2-Dioleoyl-3-trimethylammonium-propane Liposomes
DOTAP/Cholesterol Liposomes
Cationic Lipid DOTAP Liposomes
DOTAP Nanoliposomes
Cationic Lipid Nanoparticles (DOTAP)
Cationic Vesicles (DOTAP)
DOTAP-Based Liposomes
DOTAP-Formulated Liposomes
References:
1. Pereira S, et al. Lipoplexes to Deliver Oligonucleotides in Gram-Positive and Gram-Negative Bacteria: Towards Treatment of Blood Infections. Pharmaceutics. 2021,13(7):989.
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