An Acidic‐Microenvironment‐Driven DNA Nanomachine Enables Specific ATP Imaging in the Extracellular Milieu of Tumor

Extracellular ATP is an emerging target for cancer treatment because it is a key messenger for shaping the tumor microenvironment (TME) and regulating tumor progression. However, it remains a great challenge to design biochemical probes for targeted imaging of extracellular ATP in the TME. A TME‐driven DNA nanomachine (Apt‐LIP) that permits spatially controlled imaging of ATP in the extracellular milieu of tumors with ultrahigh signal‐to‐background ratio is reported. It operates in response to the mild acidity in the TME with the pH (low) insertion peptide (pHLIP) module, thus allowing the specific anchoring of the structure‐switching signaling aptamer unit to the membrane of tumor cells for “off–on” fluorescence imaging of the extracellular ATP. Apt‐LIP allows for acidity driven visualization of different extracellular concentrations of exogenous ATP, as well as the monitoring of endogenous ATP release from cells. Furthermore, it is demonstrated that Apt‐LIP represents a promising platform for the specific imaging of the extracellular ATP in both primary and metastatic tumors. Ultimately, since diverse aptamers are obtained through in vitro selection, this design strategy can be further applied for precise detection of various extracellular targets in the TME.     

DNA‐Au Nanomachine Equipped with i‐Motif and G‐Quadruplex for Triple Combinatorial Anti‐Tumor Therapy

In the present study, the design, construction, and operation of a functional DNA‐decorated dynamic gold (Au) nanomachine as a therapeutic agent for triple combinatorial anti‐cancer therapy are revealed. Taking advantage of the intrinsic optical properties of Au nanoparticles, which depend on their size, a cytosine rich i‐motif sequence is employed for intracellular pH‐sensitive duplex dissociation and subsequent aggregation of the DNA‐Au nanomachine, enabling anticancer drug release and photothermal ablation upon irradiation with infrared light. Moreover, another functional DNA sequence, a G‐quadruplex, is exploited for the stable loading and intracellular delivery of a photosensitizer to achieve effective photodynamic therapy under red light illumination. The G‐quadruplex‐assisted enhanced reactive oxygen species generation, pH‐responsive dynamic aggregation behavior, consequent drug release, and the photothermal effect are investigated. Furthermore, the combinatorial chemo, photodynamic, and photothermal therapeutic effects of the functional DNA‐decorated Au nanomachines are evaluated in vitro and in vivo using a triple negative breast cancer model.     

The Three S's for Aptamer‐Mediated Control of DNA Nanostructure Dynamics: Shape,Self‐Complementarity,and Spatial Flexibility

DNA aptamers are ideal tools to enable modular control of the dynamics of DNA nanostructures. For molecular recognition, they have a particular advantage over antibodies in that they can be integrated into DNA nanostructures in a bespoke manner by base pairing or nucleotide extension without any complex bioconjugation strategy. Such simplicity will be critical upon considering advanced therapeutic and diagnostic applications of DNA nanostructures. However, optimizing DNA aptamers for functional control of the dynamics of DNA nanostructure can be challenging. Herein, we present three considerations—shape, self‐complementarity, and spatial flexibility—that should be paramount upon optimizing aptamer functionality. These lessons, learnt from the growing number of aptamer–nanostructure reports thus far, will be helpful for future studies in which aptamers are used to control the dynamics of nucleic acid nanostructures.     

Thermal Modulation of Nanomotor Movement

Motion control is essential for various applications of man‐made nanomachines. The ability to control and regulate the movement of catalytic nanowire motors is illustrated by applying short heat pulses that allow the motors to be accelerated or slowed down. The accelerated motion observed during the heat pulses is attributed primarily to the thermal activation of the redox reactions of the H₂O₂ fuel at the Pt and Au segments and to the decreased viscosity of the aqueous medium at elevated temperatures. The thermally modulated motion during repetitive temperature on/off cycles is highly reversible and fast, with speeds of 14 and 45 µm s^?1 at 25 and 65 °C, respectively. A wide range of speeds can be generated by tailoring the temperature to yield a linear speed–temperature dependence. Through the use of nickel‐containing nanomotors, the ability to combine the thermally regulated motion of catalytic nanomotors with magnetic guidance is also demonstrated. Such on‐demand control of the movement of nanowire motors holds great promise for complex operations of future manmade nanomachines and for creating more sophisticated nanomotors.     

Fuel‐Free Synthetic Micro‐/Nanomachines

Inspired by the swimming of natural microorganisms, synthetic micro‐/nanomachines, which convert energy into movement, are able to mimic the function of these amazing natural systems and help humanity by completing environmental and biological tasks. While offering autonomous propulsion, conventional micro‐/nanomachines usually rely on the decomposition of external chemical fuels (e.g., H₂O₂), which greatly hinders their applications in biologically relevant media. Recent developments have resulted in various micro‐/nanomotors that can be powered by biocompatible fuels. Fuel‐free synthetic micro‐/nanomotors, which can move without external chemical fuels, represent another attractive solution for practical applications owing to their biocompatibility and sustainability. Here, recent developments on fuel‐free micro‐/nanomotors (powered by various external stimuli such as light, magnetic, electric, or ultrasonic fields) are summarized, ranging from fabrication to propulsion mechanisms. The applications of these fuel‐free micro‐/nanomotors are also discussed, including nanopatterning, targeted drug/gene delivery, cell manipulation, and precision nanosurgery. With continuous innovation, future autonomous, intelligent and multifunctional fuel‐free micro‐/nanomachines are expected to have a profound impact upon diverse biomedical applications, providing unlimited opportunities beyond one's imagination.     

Deoxyribozyme-Based DNA Machines for Cancer Therapy

Soon after their discovery, RNA-cleaving deoxyribozymes (RCDZ) were explored as anticancer gene therapy agents. Despite low toxicity found in clinical trials, there is no clinically significant anticancer RCDZ-based therapy. Some of the reported disadvantages of RCDZ agents include poor accessibility to folded nucleic acids, low catalytic efficiency inside cells, and problems of intracellular delivery. On the other hand, structural DNA nanotechnology provides an opportunity to build multifunctional nano-associations that can address some of these problems. Herein we discuss the possibility of building RCDZ-based multifunctional DNA nanomachines equipped with RNA unwinding, cancer marker recognition, and RCDZ-based RNA-cleavage functions. An important advantage of such “nanomachines” is the possibility to cleave a housekeeping gene mRNA in a cancer-cell-specific manner. The proposed design could become a starting point for building sophisticated DNA-based nanodevices for cancer treatment.