A VERSATILE VECTOR FOR GENE AND OLIGONUCLEOTIDE TRANSFER INTO CELLS IN CULTURE AND IN-VIVO - POLYETHYLENIMINE

Several polycations possessing substantial buffering capacity below ph ysiological pH, such as lipopolyamines and polyamidoamine polymers, ar e efficient transfection agents per se-i.e., without the addition of c ell targeting or membrane-disruption agents. This observation led us t o test the cationic polymer polyethylenimine (PEI) for its gene-delive ry potential. Indeed, every third atom of PEI is a protonable amino ni trogen atom, which makes the polymeric network an effective ''proton s ponge'' at virtually any pH. Luciferase reporter gene transfer with th is polycation into a variety of cell lines and primary cells gave resu lts comparable to, or even better than, lipopolyamines. Cytotoxicity w as low and seen only at concentrations well above those required for o ptimal transfection. Delivery of oligonucleotides into embryonic neuro ns was followed by using a fluorescent probe. Virtually all neurons sh owed nuclear labeling, with no toxic effects. The optimal PEI cation/a nion balance for in vitro transfection is only slightly on the cationi c side, which is advantageous for in vivo delivery. Indeed, intracereb ral luciferase gene transfer into newborn mice gave results comparable (for a given amount of DNA) to the in vitro transfection of primary r at brain endothelial cells or chicken embryonic neurons. Together, the se properties make PEI a promising vector for gene therapy and an outs tanding core for the design of more sophisticated devices, Our hypothe sis is that its efficiency relies on extensive lysosome buffering that protects DNA from nuclease degradation, and consequent lysosomal swel ling and rupture that provide an escape mechanism for the PEI/DNA part icles.