pH-Promoted Release of a Novel Anti-Tumour Peptide by “Stealth” Liposomes: Effect of Nanocarriers on the Drug Activity in Cis-Platinum Resistant Cancer Cells

Purpose: To evaluate the potential effects of PEGylated pH-sensitive liposomes on the intracellular activity of a new peptide recently characterized as a novel inhibitor of the human thymidylate synthase (hTS) over-expressed in many drug-resistant human cancer cell lines. Methods: Peptide-loaded pH-sensitive PEGylated (PpHL) and non-PEGylated liposomes (nPpHL) were carefully characterized and delivered to cis-platinum resistant ovarian cancer C13* cells; the influence of the PpHL on the drug intracellular activity was investigated by the Western Blot analysis of proteins involved in the pathway affected by hTS inhibition. Results: Although PpHL and nPpHL showed different sizes, surface hydrophilicities and serum stabilities, both carriers entrapped the drug efficiently and stably demonstrating a pH dependent release; moreover, the different behavior against J774 macrophage cells confirmed the ability of PEGylation in protecting liposomes from the reticuloendothelial system. Comparable effects were instead observed against C13* cells and biochemical data by immunoblot analysis indicated that PEGylated pH-sensitive liposomes do not modify the proteomic profile of the cells, fully preserving the activity of the biomolecule. Conclusion: PpHL can be considered as efficient delivery systems for the new promising anti-cancer peptide.