Structures from lysine-based dendrons and dendrimers: monolayers, dendriplexes, dendrisomes, nanoparticles and micellar aggregates

Supramolecular Self-Associations of Amphiphilic Dendrons and Their Properties

This review presents precisely defined amphiphilic dendrons, their self‐association properties, and their different uses. Dendrons, also named dendritic wedges, are composed of a core having two different types of functions, of which one type is used for growing or grafting branched arms, generally multiplied by 2 at each layer by using 1→2 branching motifs. A large diversity of structures has been already synthesized. In practically all cases, their synthesis is based on the synthesis of known dendrimers, such as poly(aryl ether), poly(amidoamine) (in particular PAMAM), poly(amide) (in particular poly(L‐lysine)), 1→3 branching motifs (instead of 1→2), poly(alkyl ether) (poly(glycerol) and poly(ethylene glycol)), poly(ester), and those containing main group elements (poly(carbosilane) and poly(phosphorhydrazone)). In most cases, the hydrophilic functions are on the surface of the dendrons, whereas one or two hydrophobic tails are linked to the core. Depending on the structure of the dendrons, and on the experimental conditions used, the amphiphilic dendrons can self‐associate at the air‐water interface, or form micelles (eventually tubular, but most generally spherical), or form vesicles. These associated dendrons are suitable for the encapsulation of low‐molecular or macromolecular bioactive entities to be delivered in cells. This review is organized depending on the nature of the internal structure of the amphiphilic dendrons (aryl ether, amidoamine, amide, quaternary carbon atom, alkyl ether, ester, main group element). The properties issued from their self‐associations are described all along the review.

Nonviral gene delivery with dendritic self-assembling architectures

In this review, we outline the concept and applicability of self-assembling dendrimers for gene-delivery applications. Low-molecular-weight, well-defined cationic dendritic arrays which have been modified with hydrophobic domains can form self-organized multivalent systems that have significant advantages over nonassembling, high-molecular-weight/polymeric gene vectors. Particular structural variations have been highlighted with respect to the individual components of the displayed dendritic amphiphiles, namely, the employed amine termini, the hydrophobic segment, the size of the dendritic array, and the integration of special features such as targeting ability and cleavability/degradability, which can all have a crucial effect on gene-transfection efficiencies. Accordingly, the scientific efforts to create new synthetic gene-delivery vectors to act as promising in vivo transfection agents in the future will be presented and discussed here.

Hydrophobically modified dendrons: developing structure-activity relationships for DNA binding and gene transfection

This paper develops a structure-activity relationship understanding of the way in which surfactant-like dendrons with hydrophilic spermine surface groups and a variety of lipophilic units at their focal points can self-assemble and subsequently bind to DNA with high affinity. The choice of functional group at the focal point of the dendron and the high tunability of the molecular structure have a very significant impact on DNA binding. Mesoscale modeling of the mode of dendron self-assembly provides a direct insight into how the mode of self-assembly exerts its effect on the DNA binding process. In particular, the hydrophobic unit controls the number of dendrons in the self-assembled micellar structures, and hence their diameters and surface charge density. The DNA binding affinity correlates with the surface charge density of the dendron aggregates. Furthermore, these structure-activity effects can also be extended to cellular gene delivery, as surface charge density plays a role in controlling the extent of endosomal escape. It is reported that higher generation dendrons, although binding DNA less strongly than the self-assembling lower generation dendrons, are more effective for transfection. The impact of the lipophilic group at the focal point is less significant for the DNA binding ability of these larger dendrons, which is predominantly controlled by the spermine surface groups, but it does modify the levels of gene transfection. Significant synergistic effects on gene delivery were observed when employing combinations of the dendrons and polyethyleneimine (PEI, 25 kDa), with transfection becoming possible at low loading levels where the two components would not transfect individually, giving practically useful levels of gene delivery.