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ChemPhysChem 20(16), 2110 - 2121 (2019). doi:10.1002/cphc.201900480, The physicochemical properties and transfection efficacies of two samples of a cationic lipid have been investigated and compared in 2D (monolayers at the air/liquid interface) and 3D (aqueous bulk dispersions) model systems using different techniques. The samples differ only in their chain composition due to the purity of the oleylamine (chain precursor). Lipid 8 (using the oleylamine of technical grade for cost-efficient synthesis) shows lateral phase separation in the Langmuir layers. However, the amount of attached DNA, determined by IRRAS, is for both samples the same. In 3D systems, lipid 8 p forms cubic phases, which disappear after addition of DNA. At physiological temperatures, both lipids (alone and in mixture with cholesterol) assemble to lamellar aggregates and exhibit comparable DNA delivery efficiency. This study demonstrates that non-lamellar structures are not compulsory for high transfection rates. The results legitimate the utilization of oleyl chains of technical grade in the synthesis of cationic transfection lipids, Published by Wiley-VCH Verl., Weinheim

Formulations based on ionizable amino-lipids have been put into focus as nucleic acid delivery systems. Recently, the in vitro efficacy of the lipid formulation OH4:DOPE has been explored. However, in vitro performance of nanomedicines cannot correctly predict in vivo efficacy, thereby considerably limiting pre-clinical translation. This is further exacerbated by limited access to mammalian models. The present work proposes to close this gap by investigating in vivo nucleic acid delivery within simpler models, but which still offers physiologically complex environments and also adheres to the 3R guidelines (replace/reduce/refine) to improve animal experiments. The efficacy of OH4:DOPE as a delivery system for nucleic acids is demonstrated using in vivo approaches. It is shown that the formulation is able to transfect complex tissues using the chicken chorioallantoic membrane model. The efficacy of DNA and mRNA lipoplexes is tested extensively in the zebra fish (Danio rerio) embryo which allows the screening of biodistribution and transfection efficiency. Effective transfection of blood vessel endothelial cells is seen, especially in the endocardium. Both model systems allow an efficacy screening according to the 3R guidelines bypassing the in vitro-in vivo gap. Pilot studies in mice are performed to correlate the efficacy of in vivo transfection.

The aggregation behavior of various zwitterionic helper phospholipids, such as DOPE, DOPC, and DPPC, in combination with two new cationic lipids, namely TH4 and OH4 (second generation of malonic acid diamides) in different molar ratios was studied with regard to their physical–chemical properties. Additionally, lipoplexes prepared from these lipid mixtures were characterized with respect to the transfection efficacy using an EGFP-assay. The lipid mixtures with the fluid cationic lipid OH4 and DOPE have shown comparable transfection efficiency with Lipofectamine 2000®. Furthermore, this report demonstrates the huge influence of the helper lipid on the transfection efficiency. Thereby, alkyl chain fluidity, lipid miscibility and charge density have an important influence on an efficient gene transfer. Practical applications: Although lipofection is a topic of gene therapy since 1989, finding an effective lipid system with new cationic lipids is still a process of trial and error. There is much unknown about the process of lipoplex formation as well as the release of the genetic cargo. Aim of the presented work is to find physical–chemical parameters which are connected with an effective gene transfer. This report demonstrates the influence of the cationic and helper lipid on the transfection efficiency. Thereby, alkyl chain fluidity, lipid miscibility and charge density have an important influence on an efficient gene transfer.

The aggregation behavior of a cationic lipid, N-[6-amino-1-oxo-1-(N-tetradecylamino)hexan-(2S)-2-yl]-N'-{2-[N,N-bis(2-aminoethyl)amino]ethyl}-2,2-ditetradecylpropandiamide (DiTT4), is investigated in aqueous dispersions at different pH values (5, 7.3, and 10). An unusual aggregation behavior is observed whereby DiTT4 forms bilayer structures at pH 10 and 7.3. At pH 5, rod-like micelles are the dominant aggregate form. The thermotropic and lyotropic behavior is studied using differential scanning calorimetry, small-angle X-ray scattering, and FTIR spectroscopy. In addition, investigations at the air-water interface are performed by recording area-pressure-isotherms and infrared reflection-absorption (IRRA) spectra. Complementary dynamic light scattering experiments and transmission electron microscopy (TEM and cryoTEM) are also used. The ability of DiTT4 to complex plasmid DNA is investigated using fluorescence techniques and zeta potential measurements. Cell culture experiments demonstrate the ability of DiTT4 to enhance plasmid transfer in A549 cells.