Thermodynamics, in vitro release and cytotoxity studies on doxorubicin–toluidine blue O combination drugs co-loaded in aptamer-tethered DNA nanostructures

Abstract DNA nanostructures-based chemotherapy-phototherapy (CTPT) combination therapy can achieve targeted release and effectively overcome multidrug resistance (MDR). The therapeutic effect of CTPT combination drugs loaded in DNA nanostructures is related to the interactions among them. Herein, based on our previous research on AS1411NTrs loading with a single drug of DOX, the interactions between a single drug (toluidine blue O, TBO) or combination drugs (doxorubicin and toluidine blue O, DOX + TBO) and AS1411 aptamer-tethered DNA nanotrains (AS1411NTrs) were investigated. By fluorescence spectroscopy and isothermal titration calorimetry technique, the corresponding thermodynamic parameters were obtained, including the number of binding sites, binding constant, enthalpy change and entropy change. By combining with the differential scanning calorimetry and ferrocyanide ion quenching analysis, the binding mode-thermodynamic parameters were correlated. In addition, the effect of the binding affinity of DOX and TBO to AS1411NTrs on the drugs release rate was studied. Finally, the in vitro cytotoxicity and confocal laser scanning microscopy imaging of AS1411NTrs + TBO + DOX was investigated. The results showed that this drug delivery system could increase its in vitro cytotoxicity and overcome drug resistance in DOX-resistant human breast cancer cells (MCF-7/ADR). The work would provide important information for the combination therapy of DOX and TBO to overcome MDR effectively.