Development of Cell-Penetration PG-Surfactants and Its Application in External Peptide Delivery to Cytosol

Structural Modifications to the Internal Oligoguanidinium Transporter Uncover Two Potent Analogues that Effectively Deliver the Proapoptotic Peptide in Multiple Cancer Cell Lines

Efficient cytosolic delivery with serum-independent kinetics and low toxicity are the ultimate challenges towards the transformation of an antisense oligonucleotide or a therapeutic peptide to a suitable drug candidate for clinical trials. Most delivery vehicles falter on at least one of the above requirements, which hinders their potential in in vivo models as well. Our previous reports on internal guanidinium transporters (IGTs) have established the diversity of this particular class of molecule with the efficient delivery of antisense phosphorodiamidate morpholino oligonucleotides. In this paper, we report twenty IGTs with different types of evidence-backed structural modifications with different types of head-group linkage R, which significantly change the transfection, toxicity, and endosomal escape. Based on these three criteria, the analogues were sorted systematically to find the more promising IGTs, which were then further examined by LysoTracker studies. Finally, two analogues, with cholesteryl linkage (R = Chol) and pentafluorobenzyl linkage (R = PF Cbz), were selected for a proapoptotic peptide delivery as the final validation using a long-chain di-acid linker conjugation. Detailed mechanistic studies also revealed that the primary pathway of endocytosis is macropinocytosis, and that other pathways play different roles depending on the head group of the IGT. Since endocytosis pathways for entry depend on the nature of the cell line, we have shown the mechanistic variations in two cell lines for validation.

Protein Delivery: If Your GFP (or Other Small Protein) Is in the Cytosol, It Will Also Be in the Nucleus

Intracellular protein delivery is a transformative tool for biologics research and medicine. Delivery into the cytosol allows proteins to diffuse throughout the cell and access subcellular organelles. Inefficient delivery caused by endosomal entrapment is often misidentified as cytosolic delivery. This inaccuracy muddles what should be a key checkpoint in assessing delivery efficiency. Green fluorescent protein (GFP) is a robust cargo small enough to passively diffuse from the cytosol into the nucleus. Fluorescence of GFP in the nucleus is a direct readout for cytosolic access and effective delivery. Here, we highlight recent examples from the literature for the accurate assessment of cytosolic protein delivery using GFP fluorescence in the cytosol and nucleus.