title: The role of hydrophobic amino acid grafts in the enhancement of membrane-disruptive activity of pH-responsive pseudo-peptides.
abstract: pH-responsive polymers have been synthesised by grafting l-valine (PV-75), l-leucine (PL-75) and l-phenylalanine (PP-75) onto the pendant carboxylic acid moieties of a pseudo-peptide, poly(l-lysine iso-phthalamide), at a stoichiometric degree of substitution of 75 mol%. The effect of such modification on the pH-, concentration- and time-dependent cell membrane-disruptive activity of the grafted polymers has been investigated using a haemolysis model. At 0.025 mg mL(-1), the grafted polymers were almost non-haemolytic at pH 7.4, but mediated considerable membrane lysis after 60 min in the pH range characteristic of early endosomes, which ranked in the order: PP-75 > PL-75 > PV-75 > poly(l-lysine iso-phthalamide). PP-75 was 35-fold more lytic on a molar basis than the membrane-lytic peptide melittin. With increasing concentration, the grafted polymers showed an increased ability to lyse cell membranes and caused noticeable membrane disruption at physiological pH. The mechanism of the polymer-mediated membrane destabilisation has been investigated. The in-vitro cytotoxicity of the grafted polymers has been assessed using a propidium iodide fluorescence assay. It has been demonstrated by confocal microscopy that the grafted polymers can induce a significant release of endocytosed materials into the cytoplasm of HeLa cells, which is a feature critical for drug delivery applications.
authors.affiliation: Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2RA, UK.
authors.forename: Rongjun
authors.initials: R
authors.lastname: Chen
authors.forename: Sariah
authors.initials: S
authors.lastname: Khormaee
authors.forename: Mark E
authors.initials: ME
authors.lastname: Eccleston
authors.forename: Nigel K H
authors.initials: NK
authors.lastname: Slater
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002462:Cell Membrane / Q000187:drug effects*; D016503:Drug Delivery Systems; D004912:Erythrocytes / Q000187:drug effects; D006367:HeLa Cells; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D018613:Microscopy, Confocal; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology*; D010795:Phthalic Acids / Q000737:chemistry / Q000494:pharmacology*; D011107:Polylysine / Q000737:chemistry / Q000494:pharmacology*; D011108:Polymers / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000596:Amino Acids; D010455:Peptides; D010795:Phthalic Acids; D011108:Polymers; C507264:poly(L-lysine iso-phthalamide); D011107:Polylysine