Nucleic Acid Responsive DNA-based Micelle Drug Delivery System And The Bio-recognition

Nucleic acids are best known as biological information storage and transfer materials, but increasingly their potential as structural materials is being realized as chemists and physicists exploit new DNA and RNA sequences for functions not previously seen in nature. For diagnostic and therapeutic delivery applications, materials are needed that can switch their properties dependent on biological environment or stimulus. A particularly important aim of a switching operation is the need to keep a recognition ligand on a polymer or particle hidden/dormant but to expose the specific functionality in response to a biological trigger. In this study, single-stranded DNA(ssDNA) was conjugated with poly(ethylene glycol)(PEG) through a zero-length crosslinker and then hybridized with cholesterol/biotin-modified ssDNA to form a lipid-DNA-polymer amphiphile. The bioconjugate reactions were analysed and purified by RP-HPLC and the conversion was around 50 % ~ 70 %. The final products were characterized using Polyacrylamide gel electrophoresis(PAGE) and MALDI-TOF MS. Such designed structure could self-assemble into micellar architectures that hide a recognition signal, but also to contain toe-hold sequences which allow selective unveiling of the ligand on addition of a competing conjugate strand; thereby realizing its nucleic acid responsive property. Assembly of the conjugates into supramolecular structures was achieved by a simple mixing process and the critical micelle concentration(CMC) was calculated to be 19.62 nM. Size distribution and the morphology of the micelles were characterized by dynamic light scattering(DLS), transmission electron microscopy(TEM) and atom force microscopy(AFM), which gave a average diameters of approximately 20 nm. In addition, F?rster Resonance Energy Transfer(FRET) signaling and PAGE demonstrated that ‘bar-coding’ of base-pair sequences in the structure ensured that the micelles can only be opened by a specific competitive strand and at last, the biotin-avidin capture assay suggested that the percentage of ligand-receptor binding showed a dose-dependent manner.In conclusion, the DNA based micelle can be unpacked in a pre-programmable manner, thereby revealing the previously shielded ligands which are then available to act as targeting moieties. Such a “smart” property of dynamic switching in DNA materials design suggests that materials of this type could be useful as both diagnostics and therapeutics.