Selective Integrin α5ß1 Targeting through Spatially Constrained Multivalent DNA-Based Nanoparticles.

Targeting cells specifically based on receptor expression levels remains an area of active research to date. Selective binding of receptors cannot be achieved by increasing the individual binding strength, as this does not account for differing distributions of receptor density across healthy and diseased cells. Engaging receptors above a threshold concentration would be desirable in devising selective diagnostics. Integrins are prime target candidates as they are readily available on the cell surface and have been reported to be overexpressed in diseases. Insights into their spatial organization would therefore be advantageous to design selective targeting agents. Here, we investigated the effect of activation method on integrin α5ß1 clustering by immunofluorescence and modeled the global neighbor distances with input from an immuno-staining assay and image processing of microscopy images. This data was used to engineer spatially-controlled DNA-scaffolded bivalent ligands, which we used to compare trends in spatial-selective binding observed across HUVEC, CHO and HeLa in resting versus activated conditions in confocal microscopy images. For HUVEC and CHO, the data demonstrated an improved selectivity and localisation of binding for smaller spacings ~7 nm and ~24 nm, in good agreement with the model. A deviation from the mode predictions for HeLa was observed, indicative of a clustered, instead of homogeneous, integrin organization. Our findings demonstrate how low-technology imaging methods can guide the design of spatially controlled ligands to selectively differentiate between cell type and integrin activation state.

Engineering a stable future for DNA-origami as a biomaterial.

DNA as a biomaterial has evoked great interest as a potential platform for therapeutics and diagnostics and as hydrogel scaffolds due to the relative ease of programming its robust and uniform shape, site-specific functionality and controlled responsive behavior. However, for a stable self-assembled product, a relatively high cation concentration is required to prevent denaturation. Physiological and cell-culture conditions do not match these concentrations and present additional nucleases that cause a serious threat to the integrity of DNA-based materials. For the translation of this promising technology towards bioengineering challenges, stability needs to be guaranteed. Over the past years, various methods have been developed addressing the stability-related weaknesses of DNA-origami. This mini-review explains the common stability issues and compares the stabilization strategies recently developed. We present a detailed overview of each method in order to ease the selection process on which method to use for future users of DNA-origami as a biomaterial.

Quantifying Guest-Host Dynamics in Supramolecular Assemblies to Analyze Their Robustness.

The most basic function of synthetic microenvironments for tissue engineering is to act as a physical substrate for cell attachment, migration, and proliferation, similar to the natural cell environment. Functionalization of supramolecular materials with guest compounds that display the same recognition moieties is a common strategy to introduce biofunctionality. However, besides a robust interaction with the material, a certain level of dynamics needs to be conserved for an adaptive interface toward the living environment. A balance between robust material functionalization and dynamic cell interaction needs to be met. The detailed analysis hereof using a ureido-pyrimidinone (UPy) poly(ethylene glycol) system in dilute and transient network regime is demonstrated. Monovalent and bivalent UPy-functionalized guest molecules are designed and their interaction with UPy-host fibers is evaluated. Analysis of guest interaction in the dilute state by microfluidics, and in the gel state, by fluorescence recovery after photobleaching and fluorescence resonance energy transfer is proven to be suitable to quantify the local and ensemble guest mobility. The results demonstrate that the interaction of bioactive moieties through supramolecular host-guest chemistry yields a dynamic system, which is stronger for divalent guests but risks unintended leakage in the case of functional monomeric units.