Comparative Study of the Cellular Uptake and Intracellular Behavior of a Library of Cyclic Peptide–Polymer Nanotubes with Different Self-Assembling Properties

Particle shape has been described as a key factor in improving cell internalization and biodistribution among the different properties investigated for drug-delivery systems. In particular, tubular structures have been identified as promising candidates for improving drug delivery. Here, we investigate the influence of different design elements of cyclic peptide–polymer nanotubes (CPNTs) on cellular uptake including the nature and length of the polymer and the cyclic peptide building block. By varying the composition of these cyclic peptide–polymer conjugates, a library of CPNTs of lengths varying from a few to over a 150 nm were synthesized and characterized using scattering techniques (small-angle neutron scattering and static light scattering). In vitro studies with fluorescently labeled CPNTs have shown that nanotubes comprised of a single polymer arm with a size between 8 and 16 nm were the most efficiently taken up by three different mammalian cell lines. A mechanistic study on multicellular tumor spheroids has confirmed the ability of these compounds to penetrate to their core. Variations in the proportion of paracellular and transcellular uptake with the self-assembling potential of the CPNT were also observed, giving key insights about the behavior of CPNTs in cellular systems.