Comparison of patient-derived high and low phosphatidylserine-exposing colorectal carcinoma cells in their interaction with anti-cancer peptides.

Current cancer treatment is frequently compromised by severe adverse effects on healthy cells and tissues as well as by the increasing burden of (multi-)drug resistances. Some representatives of small, amphipathic peptides known as host defense peptides possess the potential to overcome these limitations and to evolve as future anti-cancer therapeutics. Peptide NK-2, derived from porcine NK-lysin, was originally discovered due to its broad-spectrum antimicrobial activities. Today, also potent anti-cancer activity is proven and accompanied by low toxicity towards normal human cells. The molecular basis underlying this target selectivity remains rather elusive. Nevertheless, it is presumptive that preferential peptide interactions with surface factors non-abundant on healthy human cells play a key role. Here, we investigated the cytotoxicity of peptide NK-2 and structurally improved anti-cancer variants thereof against two patient-derived colorectal cancer cell lines, exposing high and low levels of phosphatidylserine on their cell surfaces, respectively. Concluding from a range of in vitro tests involving cellular as well as lipid vesicle-based methods, it is proposed that the magnitude of the accessible membrane surface charge is not a primarily decisive factor for selective peptide interactions. Instead, it is suggested that the level of membrane surface-exposed phosphatidylserine is of crucial importance for the activity of peptide NK-2 and enhanced variants thereof in terms of their cancer cell selectivity, the overall efficacy, as well as the underlying mode of action and kinetics. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.