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Cell-penetrating peptides (CPPs) comprised of basic amino residues are able to cross cytoplasmic membranes and are able to deliver biologically active molecules inside cells. However, CPP/cargo entrapment in endosome limits biomedical utility as cargoes are destroyed in the acidic environment. In this study, we demonstrate protein transduction of a novel CPP comprised of an INF7 fusion peptide and nona-arginine (designated IR9). IR9 noncovalently interacts with quantum dots (QDs) and DNAs to form stable IR9/QD and IR9/DNA complexes which are capable of entering human A549 cells. Zeta-potentials were a better predictor of transduction efficiency than gel shift analysis, emphasizing the importance of electrostatic interactions of CPP/cargo complexes with plasma membranes. Mechanistic studies revealed that IR9, IR9/QD and IR9/DNA complexes may enter cells by endocytosis. Further, IR9, IR9/QD and IR9/DNA complexes were not cytotoxic at concentrations below 30, 5 and 20.1 µM, respectively. Without labor intensive production of fusion proteins from prokaryotes, these results indicate that IR9 could be a safe carrier of genes and drugs in biomedical applications.

Cell-penetrating peptides (CPPs) are a group of short, membrane-permeable cationic peptides that represent a nonviral technology for delivering nanomaterials and macromolecules into live cells. In this study, two arginine-rich CPPs, HR9 and IR9, were found to be capable of entering rotifers. CPPs were able to efficiently deliver noncovalently associated with cargoes, including plasmid DNAs, red fluorescent proteins (RFPs), and semiconductor quantum dots, into rotifers. The functional reporter gene assay demonstrated that HR9-delivered plasmid DNAs containing the enhanced green fluorescent protein and RFP coding sequences could be actively expressed in rotifers. The 1-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan assay further confirmed that CPP-mediated cargo delivery was not toxic to rotifers. Thus, these two CPPs hold a great potential for the delivery of exogenous genes, proteins, and nanoparticles in rotifers.