Endogenously Activated Multiple DNAzyme-Encoded Nanoflowers for High-Contrast Imaging of Long Noncoding RNA and Cancer Therapy

Long noncoding RNAs (lncRNAs) are implicated in various physiological and pathological processes with the potential as diagnostic biomarkers and therapeutic targets. Watson-Crick base pairing-based DNA nanomaterials have been developed previously for diagnosis-guided therapy, but they are limited by undesired signal leakage and uncontrollable drug release due to nonspecific activation and nuclease susceptibility. Rolling circle amplification (RCA) products can noncanonically self-assemble into compact DNA nanoflowers with high loading performance and excellent nuclease resistance, but they are scarcely explored for intracellular analysis due to inefficient integration/release/activation of probes. Herein, we design endogenous acid-activatable ZnO-encapsulated RCA nanoflowers encoded by DNA-cleaving DNAzyme (D-DNAzyme) and RNA-cleaving DNAzyme (R-DNAzyme) for high-contrast imaging of lncRNA and controlled cancer therapy in living cells and mice. Upon the endocytosis of ZnO-RCA nanoflowers into the cells, the acidic microenvironment of tumor cells stimulates the decomposition of ZnO into Zn²⁺ that serves as DNAzyme cofactor and therapeutic reactive oxygen species producer. Zn²⁺-motivated D-DNAzyme-catalyzed detachment of RCA nanoflowers releases the deactivated R-DNAzyme. In the presence of lncRNA, the activity of R-DNAzyme is restored to cleave Cy5-labeled substrate probes on the AuNP surface with high turnover rate and specifically knocks down survivin gene, resulting in the generation of an enhanced fluorescence signal and R-DNAzyme-mediated gene silencing. Notably, the intrinsic resistance to nucleases and acid-stimulated detachment of RCA nanoflowers dramatically reduce the background signal leakage and improve the imaging contrast. This nanoplatform can accurately measure HOTAIR in living cells, real-time monitor HOTAIR in mice, and distinguish HOTAIR levels in healthy and cancerous breast tissues.