Efficient delivery of intact phosphodiester oligonucleotides by poly-beta-amino esters.

Due to their great instability, phosphodiester antisense oligonucleotides (PO-ODNs) are rapidly degraded in the intracellular environment, which limits their biological activity. The release of PO-ODNs during a prolonged period of time could however greatly enhance their antisense effect by creating a pool of intact PO-ODNs at any time point. Poly-beta-aminoesters are biodegradable cationic polymers which show potential for the controlled release of short DNA fragments like ODNs and small interfering RNA (siRNA). In this research we evaluated biodegradable poly-beta-aminoesters as carriers for PO-ODNs and compared the antisense activity with nuclease stable phosphothioate (PS) ODNs. PBAE1 polymers were not able to generate an antisense effect with PO- or PS-ODNs, most likely due to their poor cellular uptake. When complexed to PBAE2 polymers at N/P ratio 10, both PO- and PS-ODNs downregulated the targeted protein expression with 70%. By confocal imaging we observed a high concentration of released PO-ODNs that formed nuclear bodies in the nucleoplasm. The ODNs in these nuclear bodies were still intact as could be demonstrated by Fluorescence Resonance Energy Transfer (FRET) and acceptor photobleaching. This was in clear contrast to PO-ODNs delivery by cationic liposomes where the ODNs that accumulated in the nucleus were degraded and nuclear bodies were not observed. We conclude that PBAE2 shows potential for the delivery of nuclease sensitive PO-ODNs. This occurs however not through a time controlled release profile, but rather due to the rapid delivery of a high concentration of intact PO-ODNs that form nuclear bodies in the nuclei of the cells. These nuclear bodies can most likely act as a depot of intact PO-ODNs, resulting in efficient antisense activity.