"Clicking" Gene Therapeutics: A Successful Union of Chemistry and Biomedicine for New Solutions

Abstract

The use of nucleic acid, DNA and RNA, based strategies to disrupt gene expression as a therapeutic is quickly emerging. Indeed, synthetic oligonucleotides represent a major component of modern gene therapeutics. However, the efficiency and specificity of intracellular uptake for nonmodified oligonucleotides is rather poor. Utilizing RNA based oligonucleotides as therapeutics is even more challenging to deliver, due to extremely fast enzymatic degradation of the RNAs. RNAs get rapidly degraded in vivo and demonstrate large off-target binding events when they can reach and enter the desired target cells. One approach that holds much promise is the utilization of "click chemistry" to conjugate receptor or cell specific targeting molecules directly to the effector oligonucleotides. We discuss here the applications of the breakthrough technology of CuAAC click chemistry and the immense potential in utilizing "click chemistry" in the development of new age targeted oligonucleotide therapeutics.

Keywords: click chemistry; noncoding RNA; protein conjugates; siRNA.

Figure 1

Main principles of click chemistry (A), applications of “clicked” diagnostic tools, therapeutics and nanomaterials (B). FG1-2 = functional groups that are specific for bioconjugation and unreactive with other biological groups. L = linker.

Figure 2

Chemical structures of PNA (1), morpholino (2); Diels Alder (a), reverse electron-demand Diels-Alder (b) and SPAAC (c) for oligonucleotide-peptide conjugation.

Figure 3

Oligonucleotide nanomaterials as gene therapeutics. Functionalization of DNA-Polymer (A) microcapsules; and (B) Liposomes functionalized with CD44 Aptamer.

Figure 4

Specific recognition of BRAF RNA by internally clicked peptide-oligonucleotide conjugates (POCs)

Figure 5

Approaches of “clicked” therapeutic RNA. siRNA conjugate with lipophilic molecule on a solid CPG support A); Biotinylated siRNA conjugated with streptavidin activated monoclonal antibody B); Thiol-reactive siRNA conjugated with reduced Fab fragment C).