Cationic Liposomes as Vectors for Nucleic Acid and Hydrophobic Drug Therapeutics

Abstract

Cationic liposomes (CLs) are effective carriers of a variety of therapeutics. Their applications as vectors of nucleic acids (NAs), from long DNA and mRNA to short interfering RNA (siRNA), have been pursued for decades to realize the promise of gene therapy, with approvals of the siRNA therapeutic patisiran and two mRNA vaccines against COVID-19 as recent milestones. The long-term goal of developing optimized CL-based NA carriers for a broad range of medical applications requires a comprehensive understanding of the structure of these vectors and their interactions with cell membranes and components that lead to the release and activity of the NAs within the cell. Structure–activity relationships of lipids for CL-based NA and drug delivery must take into account that these lipids act not individually but as components of an assembly of many molecules. This review summarizes our current understanding of how the choice of the constituting lipids governs the structure of their CL–NA self-assemblies, which constitute distinct liquid crystalline phases, and the relation of these structures to their efficacy for delivery. In addition, we review progress toward CL–NA nanoparticles for targeted NA delivery in vivo and close with an outlook on CL-based carriers of hydrophobic drugs, which may eventually lead to combination therapies with NAs and drugs for cancer and other diseases.

Curvature effects in charge-regulated lipid bilayers

“…The effects of electrostatic interactions [1,2] on properties of lipid bilayer membranes are significant, ubiquitous and biologically [3] and biomedically [4] relevant, since naturally occurring as well as technologically relevant lipids usually carry numerous dissociable or polar groups [5], and lipid membrane charge density has been identified as a universal parameter that quantifies the transfection efficiency of lamellar cationic lipid-DNA complexes [4]. The particular relevance of electrostatic interactions in lipidic systems very clearly transpired from the structural principles of the two vaccines approved against COVID-19 in December 2020 and based on the cationic lipid vesicle vector and the anionic mRNA payload developed by Pfizer/BioNTech [6] and Moderna [7].…”

“…Among the cationic lipids DOTAP (1,2-dioleoyl-3-trimethylammonium-propane) remains charged irrespective of pH, while the amine groups of other cationic lipids acquire their charge by protonation only below a certain pH [29]. As an extreme case one could mention the customsynthesized cationic lipid MVLBG2 with a headgroup that bears no less than 16 positive charges at full protonation [4]. In ionizable lipids the quaternary ammonium head of cationic lipids can be in addition substituted with a titratable molecular moiety with an engineered dissociation constant that would ensure the charge would be mouldable by the environmental pH [8].…”

Methods of Liposomes Preparation: Formation and Control Factors of Versatile Nanocarriers for Biomedical and Nanomedicine Application

“…Liposomes represent versatile nanoplatforms for the improved delivery of pharmaceutical drugs and active compounds in a large variety of biomedical and nanomedicine applications [ 1 , 2 ]. They are characterized by easily controllable properties such as lipid composition, size, structure and morphology, surface charge, and the possibility of functionalizing their surfaces with polymers or ligands [ 3 , 4 , 5 ]. Particularly interesting is the ability of liposomal systems to encapsulate both hydrophilic and lipophilic active compounds as well as various biomolecules, including carbohydrates [ 6 ], proteins and peptides [ 7 ], DNA [ 8 ], or imaging compounds [ 9 ].…”

Curvature effects in charge-regulated lipid bilayers

“…Among the cationic lipids DOTAP (1,2-dioleoyl-3trimethylammonium-propane) remains charged irrespective of pH, while the amine groups of other cationic lipids acquire their charge by protonation only below a certain pH 29 . As an extreme case one could mention the custom-synthesized cationic lipid MVLBG2 with a headgroup that bears no less than 16 positive charges at full protonation 4 . In ionizable lipids the quaternary ammonium head of cationic lipids can be in addition substituted with a titratable molecular moiety with an engineered dissociation constant that would ensure the charge would be mouldable by the environmental pH 8 .…”

“…The effects of electrostatic interactions 1,2 on properties of lipid bilayer membranes are significant, ubiquitous and biologically 3 and biomedically 4 relevant, since naturally occurring as well as technologically relevant lipids usually carry numerous dissociable or polar groups, 5 and lipid membrane charge density has been identified as a universal parameter that quantifies the transfection efficiency of lamellar cationic lipid–DNA complexes. 4 The particular relevance of electrostatic interactions in lipidic systems very clearly transpired from the structural principles of the two vaccines approved against COVID-19 in December 2020 and based on the cationic lipid vesicle vector and the anionic mRNA payload developed by Pfizer/BioNTech 6 and Moderna. 7 In general, charged lipids capable of modulating their charge depending on the bathing environmental conditions, have been recognized as a key component of ionizable lipid nanoparticles which are currently acknowledged as one of the most advanced non-viral vectors for the efficient delivery of nucleic acids.…”