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Intramolecular catalytic hairpin assembly (intraCHA) has recently been developed. However, non-nucleic acid-initiated intraCHA is rarely explored. The only protein-initiated intraCHA depends on the unwarrantable binding affinity between protein and its aptamer, which generally results in limited initiation efficiency. Herein, a "repaired and initiated" intraCHA (RI-intraCHA) nanosystem was designed and its operation was reported for amplified imaging of DNA repair enzyme activity in live cells. 8-oxoguanine (8-OG) DNA glycosylase was selected as the model DNA repair enzyme. The RI-intraCHA nanosystem was constructed by linking a dsDNA (containing 8-OG sites and trigger strand), two hairpins to different vertexes of DNA tetrahedron. The nanosystem could independently enter into live cells in virtue of cell permeability of DNA tetrahedron. Upon repair action of endogenous 8-OG DNA glycosylase, intraCHA reaction in the nanosystem was initiated efficiently, generating amplified fluorescence signal. The nanosystem provided a detection limit of 0.2443 U/mL for 8-OG DNA glycosylase, which was lower than that of the reported imaging approaches. Furthermore, the nanosystem exhibited satisfactory biosafety and biostability, achieving amplified imaging of intracellular 8-OG DNA glycosylase activity. The designed RI-intraCHA nanosystem provided a promising tool for the research of basic biology of intracellular DNA repair enzymes as well as their clinic correlations. Schematic representation of the "repaired and initiated" intramolecular catalytic hairpin assembly (RI-intraCHA) nanosystem for amplified imaging the activity of intracellular 8-oxoguanine (8-OG) DNA glycosylase (a model DNA repair enzyme). [Display omitted] • "Repaired and initiated" intramolecular catalytic hairpin assembly system was showed. • The system depended on the repair action of 8-oxoguanine DNA glycosylase. • High efficient initiation of intramolecular catalytic hairpin assembly was achieved. • The system entered cells independently with satisfactory biosafety and biostability. • Amplified imaging intracellular 8-oxoguanine DNA glycosylase activity was realized. [ABSTRACT FROM AUTHOR]

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. Unlabelled Image • Doxorubicin (DOX) and toluidine blue O (TBO) were intercalated into DNA nanotrains. • The binding affinity of DOX with DNA nanotrains was stronger than that of TBO. • The addition order of DOX and TBO could affect the stability of DNA nanotrains. • Due to the stronger binding to DNA nanotrains, DOX released more slowly than TBO. • DOX + TBO combination drugs loaded in DNA nanotrains could overcome drug resistance. [ABSTRACT FROM AUTHOR]

• AS1411-DNA nanotrains (AS1411NTrs) were constructed by hybridization chain reaction (HCR). • DOX, EPI and DAU interacted with AS1411NTrs through the intercalative binding mode. • The constructed AS1411NTrs had high drug payload capacity. • The drug release from AS1411NTrs followed first-order release model. • The drug-loaded AS1411NTrs could target to specific cancer cells. As one of the most promising drug delivery carriers, self-assembled DNA nanostructures are characterized of well-defined sizes, excellent biocompatibility, high drug loading and ability to control drug release. Studying the interactions between anticancer drugs and DNA nanostructures can help to associate microstructure-drug loading-release rate-therapeutic effect. Herein AS1411 aptamer-tethered DNA nanotrains (AS1411NTrs) were constructed and used as anthracyclines carrier with high payload for targeted delivery. The bindings of doxorubicin (DOX), epirubicin (EPI), and daunorubicin (DAU) to AS1411NTrs were investigated by isothermal titration calorimetry and fluorescence spectroscopy, and thermodynamic parameters were obtained. The high drug payload capacity of AS1411NTrs was verified by the large number of binding sites (~20). The binding mode was determined by differential scanning calorimetry and potassium iodide (KI) quenching experiments. The release experiment data showed that DNase I facilitated drug release and the release followed the first-order kinetic model. MTT cell viability assay demonstrated that the drug-loaded AS1411NTrs had significantly higher cytotoxicity against target HeLa cells than normal human liver L02 cells. These findings revealed that AS1411NTrs had high payload and targeted release capacity for DOX, EPI, and DAU. This result can provide a theoretical basis for constructing reasonable DNA nanostructures based on drug carriers. Image, graphical abstract [ABSTRACT FROM AUTHOR]