The Effects of the 4-(4-Methylpiperazine) phenyl Group on Nucleosides and Oligonucleotides: Cellular Delivery, Detection, and Stability

Abstract

As drug candidates, one promising way to improve the cellular delivery efficacy of oligonucleotides is to introduce a cationic group. By introducing a cationic moiety into the oligonucleotide structure, they become capable of approaching the cell surface and also of crossing the cellular membrane. In an effort to develop cell-permeable oligonucleotides, we examined the piperazinephenyl-bearing 2'-deoxyuridine ((PP)U), which can be not only cationic but also fluorescent as a cationic monomer for cationic oligonucleotides. Several modified DNA oligonu-cleotides with different numbers of (PP)U building blocks were synthesized and evaluated for the effect on thermal stability and conformation by the introduction of (PP)U. The cellular delivery of modified oligonucleotides was different depending on the number of (PP)U building blocks. Furthermore, these (PP)U-modified oligonucleotides had sufficient fluorescence that we were able to identify the delivery results without the use of conventional fluorescent tags. They were predominantly localized in the cell cytoplasm. In addition, they were stable enough after 3 hours in the presence of nuclease. These results showed that a piperazinephenyl moiety that is conjugated with nucleobase is able to deliver and detect the oligonucleotides, which suggests that this concept of 'dual-function oligonucleotides' might be utilized in diagnostics, therapeutics, and as a convenient biological tool for probing the activity of oligonucleotides inside cells.