Interaction of an Antitumor Peptide with Lipids of the Cancer Plasma Membrane - Formation of Membrane Domains and Influence of Cholesterol

Abstract

R-DIM-P-LF11-322, derived from the cationic human host defense peptide lactoferricin, exhibits selective antitumor activity against several human cancer cell types. We have shown that cancer cells expose the negatively charged phosphatidylserine (PS) on the outer leaflet of the plasma membrane (1), which in healthy cells only comprises neutral lipids as phosphatidylcholine (PC) or cholesterol. Therefore the membrane interaction of R-DIM-P-LF11-322 with membrane mimics composed of mixtures of PS, PC and cholesterol was studied. Lipid analysis of normal melanocytes and melanoma revealed a slight increase of PC and cholesterol in the cancer lipid extracts.Tryptophan fluorescence showed that the peptide penetrated only in the cancer mimics containing ratios of PS. Addition of cholesterol slightly reduced the affinity of the peptide.Calorimetric studies with peptide and mixed liposomes of PS and PC indicated complete perturbation of the PS fraction leaving PC unaffected. Interestingly upon addition of cholesterol the peptide induced separation into PC and PS enriched domains, but seemed to be slightly reduced in its effect.Studies using giant unilamellar vesicles showed that the peptide interacts on cancer model membranes slightly stronger in the absence of cholesterol by formation of extremely deformed and destroyed vesicles. In the presence of cholesterol the peptide however still induced shrinking of the vesicles and formation of many small PS domains.In summary the antitumor peptide strongly interacts only with its target PS on cancer cells. However, cholesterol seems to play a role in the modulation of membrane domain formation and reducing the membrane affinity, which may represent a mechanism for cancer cells to protect themselves against antitumor peptides.Acknowledgment: Austrian Science Foundation FWF (grant no: P24608)(1) Riedl et al. BBA 1808: 2638-2645, 2011.