No abstract

The reversible switching of catalytic systems capable of performing complex DNA  computing operations using the temporal control of two orthogonal photoswitches is described. Two distinct photoresponsive molecules have been separately incorporated into a split horseradish peroxidase-mimicking DNAzyme. We show that its catalytic function can be turned on and off reversibly upon irradiation with specific wavelengths of light. The system responds orthogonally  to a  selection of irradiation wavelengths    and   durations of irradiation. Furthermore, the DNAzyme exhibits reversible switching and retains this ability throughout multiple switching cycles. We apply our system as a light-controlled 4:2 multiplexer. Orthogonally photoswitchable DNAzyme-based catalysts as introduced here have potential use for controlling complex logical operations and for future applications in DNA nanodevices.

Platforms for targeted drug-delivery must simultaneously exhibit serum stability, efficient directed cell internalization, and triggered drug release. Here, using lipid-mediated self-assembly of aptamers, we combine multiple structural motifs into a single nanoconstruct that targets hepatocyte growth factor receptor (cMet). The nanocarrier consists of lipidated versions of a cMet-binding aptamer and a separate lipidated GC-rich DNA hairpin motif loaded with intercalated doxorubicin. Multiple 2′,6′-dimethylazobenzene moieties are incorporated into the doxorubicin-binding motif to trigger the release of the chemotherapeutics by photoisomerization. The lipidated DNA scaffolds self-assemble into spherical hybrid-nanoconstructs that specifically bind cMet. The combined features of the nanocarriers increase serum nuclease resistance, favor their import into cells presumably mediated by endocytosis, and allow selective photo-release of the chemotherapeutic into the targeted cells. cMet-expressing H1838 tumor cells specifically internalize drug-loaded nanoconstructs, and subsequent UV exposure enhances cell mortality. This modular approach thus paves the way for novel classes of powerful aptamer-based therapeutics.

Photoregulation is among the most promising tools for development of dynamic DNA nanosystems, due to its high spatiotemporal precision, biocompatibility, and ease of use. So far, azobenzene and its derivatives have shown high potential in photocontrolling DNA duplex hybridization by light-dependent photoisomerization. Despite many recent advances, obtaining sufficiently high photoswitching efficiency under conditions more suitable for work with DNA nanostructures are challenging. Here we introduce a pair of arylazopyrazoles as new photoswitches for efficient and reversible control of DNA hybridization achieved even at room temperature with a low number of required modifications. Their photophysical properties in the native state and in DNA strands result in near-quantitative isomerization rates by irradiation with UV and orange light. To demonstrate the applicability of these photoswitches, we have successfully applied one of them to open and close a DNA hairpin by light at room temperature.

Targeted extrahepatic delivery of siRNA remains a challenging task in the field of nucleic acid therapeutics. An ideal delivery tool must internalize siRNA exclusively into the cells of interest without affecting the silencing activity of siRNA. Here, we report the use of anti-EGFR Nanobodies (trademark of Ablynx N.V.) as tools for targeted siRNA delivery. A straightforward procedure for site-specific conjugation of siRNA to an engineered C-terminal cysteine residue on the Nanobody (trademark of Ablynx N.V.) is described. We show that siRNA-conjugated Nanobodies (Nb−siRNA) retain their binding to EGFR and enter EGFR-positive cells via receptor-mediated endocytosis. The activity of Nb−siRNAs was assessed by measuring the knockdown of a housekeeping gene (AHSA1) in EGFR-positive and EGFR-negative cells. We demonstrate that Nb− siRNAs are active in vitro and induce mRNA cleavage in the targeted cell line. In addition, we discuss the silencing activity of siRNA conjugated to fused Nbs with various combinations of EGFR-binding building blocks. Finally, we compare the performance of Nb−siRNA joined by four different linkers and discuss the advantages and limitations of using cleavable and noncleavable linkers in the context of Nanobody-mediated siRNA delivery.