Self-assembled DNA nanotrains for targeted delivery of mithramycin dimers coordinated by different metal ions: Effect of binding affinity on drug loading, release and cytotoxicity

Abstract Self-assembled DNA nanostructures, as a novel type of nano-biomaterials, are widely used for smart and targeted drug delivery due to their precise structures and versatile functions. The binding affinity of drugs to DNA nanostructures plays an important role in drug loading, release and efficacy. The interaction of mithramycin (MTR) with AS1411-tethered DNA nanotrains (AS1411NTrs) in the presence of different divalent metal ions (Mg2+, Zn2+, and Mn2+) was studied by fluorescence spectroscopy, differential scanning calorimetry and viscosity measurement. The binding mode between the MTR dimers and AS1411NTrs was determined by viscosity experiment and melting temperature measurement. The thermodynamic parameters of the binding process (binding stoichiometry, binding constant, enthalpy change, entropy change and Gibbs free energy change) were determined by fluorescence spectroscopy and differential scanning calorimetry, and the effect of different metal ions on the binding was compared. The release of the MTR dimers loaded by AS1411NTrs in the absence and presence of DNase I was analyzed. The in vitro cytotoxicity of the MTR dimers to HepG2 cancer cells and L02 normal cells and their intracellular uptake efficiency were evaluated. The binding parameters were correlated with the loading, release and cytotoxicity of the MTR dimers. These studies showed that AS1411NTrs had high drug loading and sustained release effect on (MTR)2Mg2+, (MTR)2Zn2+ and (MTR)2Mn2+. This drug loading system improved the lethality to cancer cells and reduced the side effects on normal cells. This study may provide a theoretical basis for the clinical application of MTR loaded by DNA nanostructures.