Cellular Internalization of Water‐Soluble Helical Aromatic Amide Foldamers

Abstract

The intracellular transport of drugs and therapeutics represents one of the most exciting and challenging areas at the interface of chemistry, biology, and medicine. Most of the effort in this field so far has been devoted to the development of peptide-based delivery systems that can translocate therapeutic agents into their intracellular targets. More recently, the use of bioinspired non-natural foldamers has resulted in the successful delivery of cargo molecules, which possess a wide range of sizes and physicochemical properties across the cell membrane. We report herein the synthesis of aromatic amide foldamers and their biological evaluation as cell-penetrating agents. By using a well-established synthetic route, a series of fluorescein-labeled cationic aryl amide conjugates has been constructed, and their cellular uptake into various human cell lines has been analyzed by flow cytometry and fluorescence microscopy. The assays revealed that longer oligomers achieve greater cellular translocation, with octamer Q8 proving to be a remarkable vehicle for all three cell lines. Biological studies have also indicated that these helices are biocompatible, thus showing promise in their application as cell-penetrating agents and as vehicles to deliver biologically active molecules into cells.

An overview of peptide and peptoid foldamers in medicinal chemistry

“…It emerged that a minimum chain length and number of basic side-chains are necessary for efficient cell internalization. The oligomer with octameric chain length exhibited excellent penetration abilities in the HeLa, Huh-7 and Jurkat cell-lines too [81]. Importantly, these oligomers were nontoxic even in high concentrations.…”

“…Importantly, these oligomers were nontoxic even in high concentrations. Lowtemperature experiments suggested that the uptake is an endocytosis-dependent process [81]. All the oligomers formed stable helical structures, which is important from the aspect of the biological function.…”

Large-scale and chromatography-free synthesis of an octameric quinoline-based aromatic amide helical foldamer

“…Second, the same procedures serve, after some adjustments, to produce variants having other side chains than isobutoxy groups, including water-solubilizing side chains (see Experimental design). For example, a variant of the helical octamer bearing ornithine-like ammonium side chains shows promise for several biological applications [27][28][29][30] , and a variant bearing oligoethylene oxide side chains was recently prepared to be endowed with solubility in a broad range of media 32 . Anionic, aspartate-like side chains have been introduced as well 30,33 .…”

“…Thus, amphipathic aryl amide oligomers have been fine-tuned to show selective antimicrobial activity 23 or to interfere with heparin function 24 . Linear aryl amides have been used as α-helix mimetics designed to disrupt protein-protein interactions 25,26 , and helical oligomers bearing cationic side chains feature cell-penetrating properties 27,28 and selective binding to G-quadruplex DNA 29,30 .…”

Solid Phase Synthesis of Helically Folded Aromatic Oligoamides

“…Another advantage is that their helical shape is extremely predictable, and since monomer side-chains may be positioned away from the backbone amide motifs, folding is essentially independent of R-group functionality. This allows the display of arrays of side-chains to be tuned in order to optimize interactions with a specific biomolecule, affording foldamers with cell-penetrating properties (Gillies et al, 2007;Iriondo-Alberdi, Laxmi-Reddy, Bouguerne, Staedel & Huc, 2010), high affinity for G-quadruplex DNA (Delaurière, Dong, Laxmi-Reddy, Godde, Toulmé & Huc, 2012;Müller, Laxmi-Reddy, Jena, Baptiste, Dong, Godde et al 2014), or the potential to interact with protein surfaces. (Buratto, Colombo, Stupfel, Dawson, Dolain, Langlois d'Estaintot et al 2014).…”