A multifunctional DNA tetrahedron for imaging, gene therapy, and chemotherapy-phototherapy combination: Binding affinity and anticancer activity.

Imaging, silencing cancer-related microRNA, and chemotherapy-phototherapy (CTPT) combination therapy are crucial for cancer diagnosis and drug resistance overcoming. In this study, we designed a multifunctional DNA tetrahedron (MB-MUC1-TD) for the targeted delivery of combined daunorubicin (DAU) + toluidine blue O (TBO). The detection limit of miRNA-21 was determined to be 0.91 nM. The intercalation of DAU and TBO into MB-MUC1-TD was proved by spectroscopic and calorimetric methods. The thermodynamic parameters for the interactions of DAU and/or TBO with MB-MUC1-TD confirmed high drug loading. The first addition of TBO in the ternary system achieved a higher loading of both drugs and a more stable complex structure. Deoxyribonuclease I (DNase I) accelerated the release of DAU and/or TBO loaded in MB-MUC1-TD. Confocal laser scanning microscope demonstrated that MB-MUC1-TD exhibited good imaging ability for miRNA-21 to accurately identify cancer cells, and DAU/TBO was predominantly distributed within the nucleus of cancer cells. In vitro cytotoxicity showed better gene therapy efficacy of MB on MCF-7 cells, better biocompatibility of loaded DAU and TBO on LO2 cells, and stronger synergistic cytotoxicity of DAU + TBO on MCF-7/ADR cells. This study may establish a theoretical foundation for co-loading CTPT combination drugs based on multifunctional DNA nanostructures.