Special delivery: Transporters constructed on a sorbitol scaffold with eight guanidine residues show significant translocation across the cell membrane and the blood–brain barrier and high affinities toward mitochondria in HeLa and KG1a leukemia cells. The picture shows colocalisation of one such transporter (T) with MitoTracker red in KG1a cells (scale bars: 10 μm).

No abstract

The exact mechanisms by which cell-penetrating peptides such as oligo-arginines and penetratin cross biological membranes has yet to be elucidated, but this is required if they are to reach their full potential as cellular delivery vectors. In the present study, qualitative and quantitative analysis of the influence of temperature, peptide concentration and plasma membrane cholesterol on the uptake and subcellular distribution of the model cell-penetrating peptide octa-arginine was performed in a number of suspension and adherent cell lines. When experiments were performed on ice, the peptide at 2 microM extracellular concentration efficiently entered and uniformly labelled the cytoplasm of all the suspension cells studied, but a 10-fold higher concentration was required to observe similar results in adherent cells. At 37 degrees C and at higher peptide concentrations, time-lapse microscopy experiments showed that the peptide rapidly penetrated the entire plasma membrane of suspension cells, with no evidence of a requirement for nucleation zones to promote this effect. Cholesterol depletion with methyl-beta-cyclodextrin enhanced translocation of octa-arginine across the plasma membrane of suspension cells at 37 degrees C, but decreased overall peptide accumulation. Under the same conditions in adherent cells this agent had no effect on peptide uptake or distribution. Cholesterol depletion increased the overall accumulation of the peptide at 4 degrees C in KG1a cells, but this effect could be reversed by re-addition of cholesterol as methyl-beta-cyclodextrin-cholesterol complexes. The results highlight the relatively high porosity of the plasma membrane of suspension cells to this peptide, especially at low temperatures, suggesting that this feature could be exploited for delivering bioactive entities.

Spezialzustellung: Transporter, die auf einem Sorbitolgerüst mit acht Guanidinresten aufgebaut wurden, zeigen eine signifikante Translokation über die Zellmembran und die Blut‐Hirn‐Schranke sowie hohe Affinitäten gegenüber Mitochondrien in HeLa‐Zellen und KG1a‐Leukämiezellen. In den Bildern ist die Colokalisierung eines solchen Transporters (T) mit MitoTracker (rot) in KG1a‐Zellen gezeigt (Maßstab: 10 μm).

Delivering apoptosis inducing peptides to cells is an emerging area in cancer and molecular therapeutics. Here, we have identified an alternative mechanism of action for the proapoptotic chimeric peptide D-NuBCP-9-r8. Integral to D-NuBCP-9-r8 is the Nur-77-derived D-isoform sequence fsrslhsll that targets Bcl-2, and the cell-penetrating peptide (CPP) octaarginine (r8) that is required for intracellular delivery. We find that the N-terminal phenylalanine of fsrslhsll acts in synergy with the cell-penetrating moiety to enhance peptide uptake at low nontoxic levels and cause rapid membrane blebbing and cell necrosis at higher (IC(50)) concentrations. These effects were not observed when a single phenylalanine-alanine mutation was introduced at the N-terminus of D-NuBCP-9-r8. Using primary samples from chronic lymphocytic leukemia (CLL) patients and cancer cell lines, we show that NuBCP-9-r8 induced toxicity, via membrane disruption, is independent of Bcl-2 expression. Overall, this study demonstrates a new mechanism of action for this peptide and cautions its use as a highly specific entity for targeting Bcl-2. For delivery of therapeutic peptides the work emphasizes that key amino acids in cargo, located several residues away from the cell-penetrating sequence, can significantly influence their cellular uptake and mode of action.