Modified internucleoside linkages for nuclease-resistant oligonucleotides.

In the past few years, several drugs derived from nucleic acids have been approved for commercialization and many more are in clinical trials. The sensitivity of these molecules to nuclease digestion in vivo implies the need to exploit resistant non-natural nucleotides. Among all the possible modifications, the one concerning the internucleoside linkage is of particular interest. Indeed minor changes to the natural phosphodiester may result in major modifications of the physico-chemical properties of nucleic acids. As this linkage is a key element of nucleic acids' chemical structures, its alteration can strongly modulate the plasma stability, binding properties, solubility, cell penetration and ultimately biological activity of nucleic acids. Over the past few decades, many research groups have provided knowledge about non-natural internucleoside linkage properties and participated in building biologically active nucleic acid derivatives. The recent renewing interest in nucleic acids as drugs, demonstrated by the emergence of new antisense, siRNA, aptamer and cyclic dinucleotide molecules, justifies the review of all these studies in order to provide new perspectives in this field. Thus, in this review we aim at providing the reader insights into modified internucleoside linkages that have been described over the years whose impact on annealing properties and resistance to nucleases have been evaluated in order to assess their potential for biological applications. The syntheses of modified nucleotides as well as the protocols developed for their incorporation within oligonucleotides are described. Given the intended biological applications, the modifications described in the literature that have not been tested for their resistance to nucleases are not reported.

RNA-directed off/on switch of RNase H activity using boronic ester formation.

RNase H is a non-specific endonuclease which degrades selectively the RNA strand in DNA/RNA duplexes. We demonstrate in the present study that 5'-boronic acid modified oligonucleotides hybridized to a RNA target sequence converts RNase H to an inactivated enzyme complex. The dynamic formation of a boronate ester upon addition of a diol moiety disrupts the enzyme-inhibitor complex and reactivates RNase H. Moreover, we show that reactivation of RNase H function can also be engineered through short RNA trimers inputs that fashion RNase H from a non-specific DNA-guided enzyme into an informational and programmable RNA-guided one. Examples of programmable RNA recognition and cleavage illustrate the potential of this new stimuli-responsive system.

Nuclease stability of boron-modified nucleic acids: application to label-free mismatch detection.

5'-End boronic acid-modified oligonucleotides were evaluated against various nucleases at single and double stranded levels. The results show that these modifications induce a high resistance to degradation by calf-spleen and snake venom phosphodiesterases. More importantly, this eventually led to the development of a new label-free enzyme-assisted fluorescence-based method for single mismatch detection.