Poly(lactide-co-glycolide) microspheres for the controlled release of oligonucleotide/polyethylenimine complexes

In this article, microspheres able to induce the controlled release of oligonucleotide/polyethylenimine complexes are proposed. A model oligonucleotide (the oligothymidilate pdT16) was encapsulated within poly(lactide-co-glycolide) microspheres alone or associated with polyethylenimine (PEI) at different nitrogen/phospate (N/P) ratios. Microspheres were prepared by the multiple emulsion-solvent evaporation technique and characterized for morphology, diameter, encapsulation efficiency, and release kinetics. The introduction of PEI in the internal aqueous phase resulted in the formation of a soluble complex with pdT16 and in a strong increase of the oligonucleotide encapsulation efficiency. PEI affected microsphere morphology inducing the formation of very porous particles yielding to an accelerated release of pdT16. When incubated with HeLa cells, microspheres encapsulating pdT16/PEI complexes allowed both a reduction of the complex toxicity and an improvement of the intracellular penetration of the released oligonucleotide. We conclude that biodegradable microspheres encapsulating oligonucleotides/PEI complexes have a great potential as controlled release system because they allow the sustained release of an oligonucleotide carrier that crosses biological membranes and locates in nucleus.