RAFT-DNA Polymers

The development of gene and protein therapeutics has the potential to revolutionise the way we treat infectious diseases and cancer.[1] Challenges that need to be overcome to realise the potential of these new therapies include the targeted delivery and efficacy of these new therapies.[1, 2] Polymers are being designed to incorporate short interfering RNA (siRNA) as the vehicle that can transport the siRNA to the disease of interest in a targeted approach.[2, 3]

Recently the CSIRO has reported designing block copolymers that have a positively charged core and a hydrophilic outer layer.[4] The negatively charged siRNA interacts electrostatically with the positive core and the hydrophilic outer layer prevents degradation of the siRNA by providing protection from the body’s defences.[4]  When the polymer particle enters the cell, the conditions inside the cell degrade the polymer, allowing delivery of the siRNA to the target cell.[4] Here at Flinders University my PhD, under the supervision of Professor Amanda Ellis, is also looking at fabricating polymer bio conjugates.

The idea is to use the CSIRO developed Reversible Addition Fragmentation chain Transfer (RAFT) process to synthesise these polymers. RAFT gives unprecedented control over the polymer architecture, meaning we can design polymers which are much better delivery vehicles for the siRNA.[5, 6] Our approach differs in that it involves a covalent attachment to the polymer and the release of the siRNA will involve a toe hold mediated release of the appropriate siRNA.  As a proof of concept we have been looking at conjugating single stranded oligonucleotides to a RAFT agent and then polymerising a hydrophilic monomer with the RAFT-Oligonucleotide agent.

Many different methods of characterising these polymers are used to identify these new materials, one of which is polyacrylamide gel electrophoresis (PAGE). PAGE is used to separate DNA based on its molecular weight. This gel image (Figure 1) shows the change in mobility of a synthesised RAFT-DNA-polymer, the DNA ladder on the left represents the mobility of a different numbers of bases for oligonucleotides; the original sequence (Figure 1, labelled DNA) was 23 bases long. The RAFT-DNA-Polymer over a few days showed a change in its mobility consistent with increasing molecular weight (MW). After four days of the polymerisation the MW is closer to 26 bases long equivalent to an increase in MW of approximately 900 mass units.

Further work needs to be done to characterise these RAFT-DNA-Polymers to see if they can be used as a vehicle delivery system for siRNA.



Figure 1: PAGE gel image of RAFT- DNA -Polymer after 4 days of polymerisation


Blog Entry written by Simon Bou, Supervisor Professor Amanda Ellis



[1]           White, P. J. “BARRIERS TO SUCCESSFUL DELIVERY OF SHORT INTERFERING RNA AFTER SYSTEMIC ADMINISTRATION,” Clinical and Experimental Pharmacology and Physiology, 35(11), 1371-1376 (2008).

[2]           Barrett, S. E., Abrams, M. T., Burke, R., Carr, B. A., Crocker, L. S., Garbaccio, R. M., Howell, B. J., Kemp, E. A., Kowtoniuk, R. A., Latham, A. H., Leander, K. R., Leone, A. M., Patel, M., Pechenov, S., Pudvah, N. T., Riley, S., Sepp-Lorenzino, L., Walsh, E. S., Williams, J. M. and Colletti, S. L. “An in vivo evaluation of amphiphilic, biodegradable peptide copolymers as siRNA delivery agents,” International Journal of Pharmaceutics, 466(1–2), 58-67 (2014).

[3]           Convertine, A. J., Benoit, D. S. W., Duvall, C. L., Hoffman, A. S. and Stayton, P. S. “Development of a novel endosomolytic diblock copolymer for siRNA delivery,” Journal of Controlled Release, 133(3), 221-229 (2009).

[4]           Lam, S. J., Sulistio, A., Ladewig, K., Wong, E. H. H., Blencowe, A. and Qiao, G. G. “Peptide-Based Star Polymers as Potential siRNA Carriers*,” Australian Journal of Chemistry, 67(4), 592-597 (2014).

[5]           Moad, G., Chong, Y. K., Postma, A., Rizzardo, E. and Thang, S. H. “Advances in RAFT polymerization: the synthesis of polymers with defined end-groups,” Polymer, 46(19), 8458-8468 (2005).

[6]           Gregory, A. and Stenzel, M. H. “Complex polymer architectures via RAFT polymerization: From fundamental process to extending the scope using click chemistry and nature’s building blocks,” Progress in Polymer Science, 37(1), 38-105 (2012).



Posted in

Leave a Reply