Impact of Positively Charged Backbone Modifications on the Properties of Spherical Nucleic Acids.

Spherical nucleic acids (SNAs) are nanostructures consisting of densely packed, radially oriented oligonucleotides arranged on nanoparticle cores. They are highly relevant to nanomedicine due to their unique physicochemical and biological properties, including efficient uptake across a broad range of cell types (over 50). This uptake is mediated in part by interactions between the oligonucleotide shell and scavenger receptors, making the DNA charge and sequence critical factors governing cellular internalization pathways. Recent advances in deoxynucleic guanidines (DNGs), nucleic acid analogues featuring positively charged guanidinium backbones, provide an opportunity to systematically probe how DNA charge influences SNA uptake. In this work, we report the synthesis of SNAs incorporating DNG-DNA chimeras and evaluate how DNG incorporation alters SNA properties and cellular internalization. We find that cellular uptake increases with the number of DNG inserts, but only when these modifications are displayed on the outer surface of the SNA architecture. Furthermore, receptor blocking experiments indicate that uptake depends not only on scavenger receptor interactions but also on broader cell membrane composition. These findings demonstrate that both structural design and chemical composition can be tuned to control SNA uptake, underscoring the promise of structural nanomedicine for directing SNA-cell interactions and rationally designing next-generation nanotherapeutics.