The ability to design nanostructured materials that deliver DNA to specific populations of cells at desired times, or to sub-populations of cells within a larger colony or tissue, would be broadly useful in a variety of contexts both in vitro (e.g., basic biological and biomedical research or tissue engineering) and in vivo (e.g., development of new gene-based therapies). Although a range of nanoscopic assemblies, including those formed from cationic lipids and polymers, have been reported to form complexes with DNA and enable the delivery of DNA to cells, the majority of these complexes are active from the time of their formation (and, thus, they do not readily permit control over the ‘activation’ or ‘inactivation’ in ways that provide methods for spatial and temporal control over delivery and/or internalization). In this presentation, we will report an advance in the design of nano-scale complexes of DNA and ferrocene-containing lipids that are stable in physiologically-relevant concentrations of serum and provide the basis of methods for redox-based control over the activation or inactivation of lipid/DNA assemblies in extracellular environments.
Past studies have established that the oxidation state of the ferrocene groups of the redox-active lipid bis(11-ferrocenylundecyl)dimethylammonium bromide (BFDMA) strongly influences the efficiency with which lipoplexes formed by BFDMA and DNA transfect cells. In this presentation, we will describe key findings that have emerged from an investigation of lipoplexes formed from mixtures of BFDMA, DNA, and dioleylphosphatidylethanolamine (DOPE, a zwitterionic lipid commonly used as a ‘helper’-lipid for lipid-mediated DNA delivery). Whereas lipoplexes prepared from BFDMA and DNA exhibit low transfection efficiencies in the presence of serum, we have found that lipoplexes containing mixtures of BFDMA and DOPE expand the range of media compositions over which BFDMA can be used to control transfection efficiencies (e.g., from serum-free medium to media that contain physiologically-relevant concentrations of serum). Importantly, we also find the strong influence of the oxidation state of BFDMA on transfection efficiency observed for BFDMA/DNA lipoplexes in serum-free media to be maintained when this mixed lipid system is used in media containing up to 80% serum. Specifically, lipoplexes containing reduced BFDMA and DOPE promote high levels of cell transfection in vitro in serum-containing media, whereas lipoplexes formed using DOPE and oxidized BFDMA do not.
To provide fundamental insights into the influence of DOPE on the properties of lipoplexes formed from BFDMA and DOPE, we have also performed small angle X-ray scattering and small angle neutron scattering measurements. These measurements have revealed that incorporation of DOPE into lipoplexes containing reduced BFDMA leads to a change in the nanostructure of the lipoplex from multilamellar, Lαc (BFDMA only), to inverse hexagonal, HIIc (BFDMA and DOPE). Because lipoplexes with HIIc nanostructures have been reported to fuse with cell membranes whereas Lαc lipoplexes generally do not, we hypothesize that the change in nanostructure from Lαc to HIIc may underlie the high cell transfection efficiency of the BFDMA-DOPE/DNA lipoplexes that we have measured in the presence of serum. Overall, the results presented in this study suggest that lipoplexes formed from BFDMA and DOPE may offer the basis of approaches that permit active and external control of transfection of cells in the presence of serum via manipulation of the oxidation state of BFDMA.