SELF-ASSEMBLY OF POLYAMINE-POLY(ETHYLENE GLYCOL) COPOLYMERS WITH PHOSPHOROTHIOATE OLIGONUCLEOTIDES

The cationic copolymers for DNA delivery were synthesized by conjugati ng poly(ethylene glycol) (PEG) and polyamines: polyspermine(PSP) and p olyethyleneimine (PEI). These molecules spontaneously form electrostat ic complexes with a model 24-mer phoshorothioate oligonucleotide, T-24 (PS-ODN). The copolymer complexes are water soluble. This is a marked contrast with the complexes formed by nonmodified PSP and PEI, which immediately precipitate out of solution. The potentiometric titration study suggests that the amino groups of the copolymers form a cooperat ive system of salt bonds with the thiophosphate groups of the PS-ODN. The PEG-PEI complexes are stable at physiological pH and ionic strengt hs. The PEG-PSP complexes are less stable in the presence of the low m olecular mass electrolytes compared to the PEG-PEI complexes. The dyna mic light scattering and transmission electron microscopy demonstrate that the complex particles are small-ca. 12 nm for PEG-PSP and ca. 32 nm for PEG-PEI. They can be lyophilized and redissolved or stored in s olution for up to several months without changing size. The study sugg ests that as a result of formulation with the PEG-PEI the interactions of PS-ODNs with serum proteins (using the example of bovine serum alb umin) are decreased and PS-ODN is protected against nuclease degradati on. The simplicity of preparation and long shelf life make these syste ms attractive as potential pharmaceutical formulations for oligonucleo tides.