The discovery of RNA interference which leads to efficient silencing of specific genes by double-stranded RNA (siRNA) has opened up a revolutionary way of treating cancer-related diseases. Nonetheless, in order for it to be a viable and universal therapeutic option, a number of important issues must be first addressed. Of particular importance is the poor in vivo stability of siRNA due to the presence of degrading enzymes (RNAse and DNAse) within the blood plasma. Additionally, efficacy of cell transfection is often compromised due to poorly-designed carrier vehicles (or in the case of free siRNA, electrostatic repulsion from the cell membrane).
To overcome many of the difficulties described above, we aim to develop a wide reaching and broadly applicable platform technology for the effective delivery of siRNA and complementary chemotherapeutics to cell-specific tissues using charge-neutral hyperbranched polymers (HBPs). Due to large functional-group availability on hyperbranched molecules, it is possible to covalently integrate all the modalities required (therapeutic agents, targeting ligands, imaging moieties etc.) into a single molecule. A comprehensive structural analysis of our RAFT polymerised HBPs was investigated by a broad range of spectroscopic techniques (NMR, UV-Vis, FTIR). We have been also developing various strategies for attachment of siRNA and imaging modalities using various well-established ligation chemistries (such as thiol-disulfide exchange and DBCO-azide click reactions). This includes the synthesis of dual-fluorescent label RNA-HBP conjugates where the RNA and polymer are separately stained (Figure 1a). Optical imaging techniques were used to monitor the stability of these dual-label conjugates in vivo and also the RNA release in vitro (Figure 1b).