Hydrophobic Oxime Ethers: A Versatile Class of pDNA and siRNA Transfection Lipids

Abstract

The manipulation of cationic lipid structure to increase polynucleotide binding and delivery properties while also minimizing associated cytotoxicity has been a principal strategy for developing next-generation transfection agents. The polar (DNA-binding) and hydrophobic domains of transfection lipids have been extensively studied; however, the linking domain comprising the substructure used to tether the polar and hydrophobic domains has attracted considerably less attention as an optimization variable. Here, we examine the use of an oxime ether as the linking domain. Hydrophobic oxime ethers were readily assembled via click chemistry by oximation of hydrophobic aldehydes using an aminooxy salt. The facile ligation reaction delivered the title compounds with hydrophobic domain asymmetry. Using the MCF-7 breast cancer, H1792 lung cancer and PAR C10 salivary epithelial cell lines, our findings show that lipoplexes derived from the oxime ether lipids transfect in the presence of serum at higher levels than commonly used liposome formulations, based on both luciferase and GFP assays. Given the biological compatibility of oxime ethers and their ease of formation, this functional group should find much application as a linking domain in future designs of transfection vectors.

Aerosol Delivery of siRNA to the Lungs. Part 2: Nanocarrier-based Delivery Systems

“…Other groups have made lipoplexes composed of phospholipids and cholesterol with particle size of approximately 100 nm that have shown higher cellular internalization in lung cancer cells than with Lipofectamine2000, but had higher cytotoxicity. Oxime ether lipid nanoparticles with particle size of 150–220 nm transfected cells more efficiently with serum present than conventional liposomal formulations (Biswas S. et al, 2011). …”

siRNA Delivery to the lung: What's new?

“…Many of the studies, in which these reagents are used, are functional genomics studies in which novel targets for the treatment of lung cancer [54, 55, 57-62, 64] or other diseases [56, 63] are identified. Others made lipoplexes with phospholipids and cholesterol of about 100 nm in size that showed higher uptake in lung cancer cells than LF2000 but decreased cell viability [65], with oxime ether lipids that are 150-220 nm in size and transfect in the presence of serum at higher levels than commonly used liposome formulations [66], or with ethylphosphocholine of about 200 nm in size that were administered intratracheally. Shim et al administered 0.21 mg/kg myeloid cell leukemia sequence 1 (Mcl1)-specific siRNA using a microsprayer four times every other day starting 5 days after the i.v.…”

Aminooxy reagents in nanomedicine and bioanalysis.

“…Their high charge density encourages association with cell membranes and facilitates endocytosis. [141][142] This capacity has also been exploited in concert with NPs in the practice of magnetofection where cationic lipid-coated NPs have been explored as magnetic gene vectors. 141,[143][144] As the surface of SNPs, like iron oxide, is anionic, we envisioned constructing a CML that could auto-assemble by simple mixing of a custom quaternary ammonium-based lipid and SNPs.…”

“…By mixing an aminooxy headgroup with aldehyde tails of the desired chain lengths and unsaturation, a wide variety of oxime ether lipids can be prepared. 141,145 The panel of oxime ether-based cationic lipids we synthesized for loading onto SNPs were designed with quaternary ammonium headgroups as the permanent positive charge ensures that pH changes in the particle environment will not alter the electronic character of the lipid. Building on our work with hydroxylated QAOs and Fe3O4 NPs, we also added hydroxyl functionality to the lipid headgroups to encourage association with the hydrophilic surface of the SNPs.…”

“…Given the similar but distinct structures of the oxime ether lipids prepared for the CML study as compared to those that had previously proven 141 to be efficient transfection agents (Figure 4.12), we chose to examine these novel compounds for their potential for nucleic acid delivery. We were especially interested to see the effect that the 1,2 diol component of lipids 2 and 3 might have on transfection efficiency, as recent reviews of structure-activity relationships in cationic lipids had cited enhanced transfection for lipids with hydroxylated headgroups.…”