The project focuses on a priori design of pH-sensitive non viral gene delivery system based on the hypothesis that 1,3-dialkyl cationic amphiphiles bearing saturated hydrophobic chains of increased interchain distance designed to have a cylindrical molecular geometry could provide lamellar assembly structures of increased fluidity and elasticity at physiological temperatures, relative to their corresponding 1,2-dialkyl derivatives and phospholipid analogues. The pH-dependent conformational changes of the polar headgroup bis-[2-dimethylamino-ethyl]-amine effectively modify the molecular geometry of the amphiphile to resemble a cone shape which in turn favors formation of nonbilayer phases at acidic pH. This design, aims to overcome the following barriers for a successful gene delivery: (1) adhesion of the delivery system onto cell surface (2) lipoplex cell internalization (3) fusion-mediated lysosome escape of therapeutic gene. Such a design eliminates the need for the presence of the helper lipid DOPE which is known to undergo chemical degradation and other peroxidation reactions that render lipoplex formulations therapeutically unsuitable.Moreover, a much simpler two-component formulation allows accurate assessment of physicochemical properties of lipoplexes that can effectively be correlated with transfection potency. Research design is composed of two parts, namely synthetic and biophysical. In the first part, a number of cationic lipids are synthesized. In the second part, the physicochemical properties of these lipids in isolation and in the presence of DNA will be determined and correlated with transfection activity. The results of the study will contribute to the long-term goals of the project, that is, (1) rationalize the design of cationic lipids for gene delivery (2) provide surrogate models for transfection activity and (3) delineate the structural requirements of double-chained surfactants for a pH controllable cohesive artificial bilayer with adjusted fluid characteristics at will. Relevance of this research to public health: The study focuses on the discovery of more potent and clinically safe cationic lipids that is desperately needed for gene therapy to become common therapeutics. ? ? ? ?
