Reduction-sensitive lipopolyamines as a novel nonviral gene delivery system for modulated release of DNA with improved transgene expression

We have designed and synthesized original cationic lipids for modulated rel ease of DNA from cationic lipid/DNA complexes. Our rationale was that modul ated degradation of the lipids during or after penetration into the cell co uld improve the trafficking of DNA to the nucleus resulting in increased tr ansgene expression. The new reduction-sensitive lipopolyamines (RSL) harbor a disulfide bridge within different positions in the backbone of the lipid s as biosensitive function. A useful synthetic method was developed to obta in, with very good yields and reproducibility, unsymmetrical disulfide-brid ged molecules, starting from symmetrical disulfides and thiols. The new lip opolyamines are good candidates as carriers of therapeutic genes for in viv o gene delivery. To optimize the transfection efficiency in these novel ser ies, we have carried out structure-activity relationship studies by placing the disulfide bridge at different positions in the backbone of the cationi c lipid and by systematic variation of lipid chain length. Results indicate that the transfection level can be modulated as a function of the location of the disulfide bridge in the molecule. We suggest that an early release of DNA. during or after penetration into the cell, probably promoted by red uction of a disulfide bridge placed between the polyamine and the lipid, im plies a total loss of transfection efficiency. On the other hand, proper mo dulation of DNA release by inserting the disulfide bridge between one lipid chain and the rest of the molecule brings about increased transfection eff iciency as compared to previously described nondegradable lipopolyamine ana logues. Finally, preliminary physicochemical characterization of the comple xes demonstrates that DNA release from complexes can be modulated as a func tion of the surrounding reducing conditions of the complexes and of the loc alization of the disulfide bridge within the lipopolyamine. Our results sug gest that RSL is a promising new approach for gene delivery.