DNA Nanotechnology Targeting Mitochondria: From Subcellular Molecular Imaging to Tailor-Made Therapeutics.

Mitochondria, one of the most important organelles, represent a crucial subcellular target for fundamental research and biomedical applications. Despite significant advances in the design of DNA nanotechnologies for a variety of bio-applications, the dearth of strategies that enable mitochondria targeting for subcellular molecular imaging and therapy remains an outstanding challenge in this field. In this Minireview, we summarize the recent progresses on the emerging design and application of DNA nanotechnology for mitochondria-targeted molecular imaging and tumor treatment. We first highlight the engineering of mitochondria-localized DNA nanosensors for in situ detection and imaging of diverse key molecules that are essential to maintain mitochondrial functions, including mitochondrial DNA and microRNA, enzymes, small molecules, and metal ions. Then, we compile the developments of DNA nanotechnologies for mitochondria-targeted anti-tumor therapy, including modularly designed DNA nanodevices for subcellular delivery of therapeutic agents, and programmed DNA assembly for mitochondrial interference. We will place an emphasis on clarification of the chemical principles of how DNA nanobiotechnology can be designed to target mitochondria for various biomedical applications. Finally, the remaining challenges and future directions in this emerging field will be discussed, hoping to inspire further development of advanced DNA toolkits for both academic and clinical research regarding mitochondria.

Enzyme Translocation-Mediated Signal Amplification for Spatially Selective Aptasensing of ATP in Inflammatory Cells.

Amplified ATP imaging in inflammatory cells is highly desirable. However, the spatial selectivity of current amplification methods is limited, that is, signal amplification is performed systemically and not in a disease site-specific manner. Here we present a versatile strategy, termed enzymatically triggerable, aptamer-based signal amplification (ETA-SA), that enables inflammatory cell-specific imaging of ATP through spatially-resolved signal amplification. The ETA-SA leverages a translocated enzyme in inflammatory cells to activate DNA aptamer probes and further drive cascade reactions through the consumption of hairpin fuels, which, however, exerts no ATP response activity in normal cells, leading to a significantly improved sensitivity and spatial specificity for the inflammation-specific ATP imaging in vivo. Benefiting from the improved spatial selectivity, enhanced signal-to-background ratios were achieved for ATP imaging during acute hepatitis.

A Remotely Controlled Nanosystem for Spatiotemporally Specific Gene Regulation and Combinational Tumor Therapy.

The dearth of technologies that allow gene modulation and therapy with high spatiotemporal precision remains a bottleneck in biomedical research and applications. Here we present a near-infrared (NIR) light-controlled nanosystem that allows spatiotemporally controlled regulation of gene expression and thus combinational tumor therapy. The nanosystem is built by engineering of an enzyme-activatable antisense oligonucleotide and further combination with an upconversion nanoparticle-based photodynamic system and a mitochondria localization signal. The system relies on photodynamic effect-induced translocation of a DNA repair enzyme from nucleus into mitochondria, which enables spatially selective gene regulation via enzymatic reactions. We demonstrate that the NIR light-induced mitochondrial photodamage and gene regulation enable enhanced antitumor effect. Our approach may enable the specific gene regulation and tumor treatment with high precision both spatially and temporally.

Spatially resolved in vivo imaging of inflammation-associated mRNA via enzymatic fluorescence amplification in a molecular beacon.

The in vivo optical imaging of RNA biomarkers of inflammation is hindered by low signal-to-background ratios, owing to non-specific signal amplification in healthy tissues. Here we report the design and in vivo applicability, for the imaging of inflammation-associated messenger RNAs (mRNAs), of a molecular beacon bearing apurinic/apyrimidinic sites, whose amplification of fluorescence is triggered by human apurinic/apyrimidinic endonuclease 1 on translocation from the nucleus into the cytoplasm specifically in inflammatory cells. We assessed the sensitivity and tissue specificity of an engineered molecular beacon targeting interleukin-6 (IL-6) mRNA in live mice, by detecting acute inflammation in their paws and drug-induced inflammation in their livers. This enzymatic-amplification strategy may enable the specific and sensitive imaging of other disease-relevant RNAs in vivo.