A New Platform for Oligonucleotide Delivery Utilizing the PEG Prodrug Approach

The oligonucleotide (oligo, ODN), Genasense (GS), an ODN currently waiting for FDA approval, was chosen as a model and modified with a 5' or 3' aminohexyl functionality (1 and 4, respectively) using solid-state synthesis. These amino derivatives were reacted with different releasable PEGs (rPEGs). The in vitro results of the PEG-modified oligos (Table 1) clearly show a substantial increase in rat plasma half-life and enhanced stability against a variety of nucleases, especially the predominant nuclease (PEII) in mammals, which is the main source of oligo degradation in cells. The advantage of using a PEG prodrug approach was further demonstrated by the pharmacokinetic (PK) results, which exhibited much greater C(max), plasma half-life, and area under the curve (AUC) for 3 compared to unmodified GS. A key step in the synthesis of ODN prodrug conjugates with a dye label was also accomplished successfully by employing dihydropyran derivatives of alcohols and acids as orthogonal protecting groups during the synthesis.