Synthesis of two novel grafted polyethylenimines for enhanced delivery of biologically active agents to mammalian cells

Delivery of fragile, biologically active substances is of increasing interest in the treatment of various disease states. For three decades, drug delivery has focused on long-term cases (i.e. localized delivery to a tumor), or targeted delivery (i.e. a selected cell type). The next horizon falls into intracellular delivery (e.g. delivery of the drug to the appropriate intracellular compartment). For several years polyethylenimine (PEI) has been used as a non-viral means of delivering DNA to cells. Polymeric systems have many theoretical advantages compared with other non-viral delivery techniques (e.g. liposomes). PEI, however, has failed to produce high transfection levels as anticipated. We have developed two modified PEI complexes for the delivery of biologically active substances to cells. These modifications retain the attractive properties of native PEI, but address possible shortcomings discovered with DNA delivery observed by many groups. Our modifications consist of grafting low molecular weight, branched form PEI together into a large complex, wherein the linkages can be cleaved by intracellular machinery. Proteins can be linked to the novel PEI complexes through the establishment of a disulfide bond, thereby expanding the utility of PEI as a delivery system. Intracellular delivery is then accomplished by reducing agents within the cytosol of the cell, thus effecting protein delivery to cells. Using the novel grafted PEI molecules, we have successfully protected and delivered biologically active proteins and DNA to targeted cells.