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This article reports self-assembling dendrons which bind DNA in a multivalent manner. The molecular design directly impacts on self-assembly which subsequently controls the way these multivalent nanostructures bind DNA--this can be simulated by multiscale modelling. Incorporation of an S-S linkage between the multivalent hydrophilic dendron and the hydrophobic units responsible for self-assembly allows these structures to undergo triggered reductive cleavage, with dithiothreitol (DTT) inducing controlled breakdown, enabling the release of bound DNA. As such, the high-affinity self-assembled multivalent binding is temporary. Furthermore, because the multivalent dendrons are constructed from esters, a second slow degradation step causes further breakdown of these structures. This two-step double-degradation mechanism converts a large self-assembling unit with high affinity for DNA into small units with no measurable binding affinity--demonstrating the advantage of self-assembled multivalency (SAMul) in achieving highly responsive nanoscale binding of biological targets.

The ability of self-assembling multivalent DNA-binding dendrons to interact with biological targets is modified by co-assembly with two novel low-molecular-weight cholesterol-functionalised PEG units, one based on triethylene glycol (Chol-PEG-3) and one on an octaethylene glycol (Chol-PEG-8). The addition of either PEG lipid affected the co-assembled nanostructure surface charge and size in different ways depending on the structure of the self-assembling DNA-binding dendron. Co-assembly with Chol-PEG-8 enhanced DNA binding, while Chol-PEG-3 inhibited it. Insertion of Chol-PEG-8 into the aggregates modified their ability to cross a model mucus layer, the details of which can be understood in terms of a balance between the mucoadhesivity due to the surface charge of the nanoscale aggregates and that due to the PEG groups. This study demonstrates that the interaction of nanoscale assemblies with biological systems depends on a number of different factors in a sometimes unpredictable way. Given how simply multiple building blocks can be combined by self-assembly, we conclude that self-assembled multivalent systems have great potential for optimisation to maximise their biological and clinical activity.

This paper uses a combined experimental and theoretical approach to gain unique insight into gene delivery. We report the synthesis and investigation of a new family of second-generation dendrons with four triamine surface ligands capable of binding to DNA, degradable aliphatic-ester dendritic scaffolds, and hydrophobic units at their focal points. Dendron self-assembly significantly enhances DNA binding as monitored by a range of experimental methods and confirmed by multiscale modeling. Cellular uptake studies indicate that some of these dendrons are highly effective at transporting DNA into cells (ca. 10 times better than poly(ethyleneimine), PEI). However, levels of transgene expression are relatively low (ca. 10% of PEI). This indicates that these dendrons cannot navigate all of the intracellular barriers to gene delivery. The addition of chloroquine indicates that endosomal escape is not the limiting factor in this case, and it is shown, both experimentally and theoretically, that gene delivery can be correlated with the ability of the dendron assemblies to release DNA. Mass spectrometric assays demonstrate that the dendrons, as intended, do degrade under biologically relevant conditions over a period of hours. Multiscale modeling of degraded dendron structures suggests that complete dendron degradation would be required for DNA release. Importantly, in the presence of the lower pH associated with endosomes, or when bound to DNA, complete degradation of these dendrons becomes ineffective on the transfection time scale—we propose this explains the poor transfection performance of these dendrons. As such, this paper demonstrates that taking this kind of multidisciplinary approach can yield a fundamental insight into the way in which dendrons can navigate barriers to cellular uptake. Lessons learned from this work will inform future dendron design for enhanced gene delivery. [ABSTRACT FROM AUTHOR]