Modulation of cell membrane disruption by pH-responsive pseudo-peptides through grafting with hydrophilic side chains.

Department of Chemical Engineering, University of Cambridge, Pembroke Street, Cambridge, CB2 3RA, UK.
Journal of Controlled Release (Impact Factor: 7.26). 12/2005; 108(1):63-72. DOI: 10.1016/j.jconrel.2005.07.011
Source: PubMed

ABSTRACT The effect of grafting an amphiphilic pseudo-peptide, poly (L-lysine iso-phthalamide), with poly (ethylene glycol) or a hydrophilic poly (ethylene glycol) analogue, Jeffamine M-1000, on the pH-dependent erythrolytic activity and in vitro cytotoxicity have been studied together with the concentration-dependent haemolysis of the polymers with different degrees of grafting. PEGylated polymers showed pH-dependent membrane-disruptive ability similar to the parent poly (L-lysine iso-phthalamide). The polymers showed a better ability to haemolyse the erythrocyte membrane at mildly acidic pHs with increasing degree of PEGylation (up to 17.0 wt.%). Further increasing the degree of PEGylation resulted in a decrease in haemolytic ability. Grafting poly (L-lysine iso-phthalamide) with the lower molecular weight Jeffamine M-1000 had little effect on the haemolytic ability. Finally, the in vitro cytotoxicity of the grafted polymers was assessed by MTT assay, LDH assay and viable cell counts. At pH 7.4, these polymers were well tolerated by a range of mammalian cell lines and grafting reduced the cytotoxicity of polymers. However, at pH 5.5, relative to poly (L-lysine iso-phthalamide), the grafted polymers displayed a better ability to rupture the outer membranes of these cells.

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    ABSTRACT: The neutralization reaction between the meso-tetrakis(4-carboxyphenyl)porphyrin (TPPC) and O-(2-aminopropyl)-O‘-(2-methoxyethyl)poly(propylene glycol) (Jeffamine M-600) in 1:4 stoichiometric ratio affords a stable supramolecular adduct (TPPC@Jeffamine). This species has been characterized in aqueous and chloroform solution through a series of spectroscopic techniques, including 1H and 13C NMR spectroscopy, UV/vis absorption, steady-state and time-resolved fluorescence emission, time-resolved fluorescence anisotropy, and resonance light scattering. All the experimental findings point to a different structural arrangement of the porphyrin chromophores within the supramolecular adduct depending on the quality of the solvent. In aqueous solution, the TPPC@Jeffamine contains mainly monomeric porphyrins while the flexible polymeric chains are folded and entangled to give larger aggregates. An insight into the structure of the basic building unit is given by SAXS measurements which, assuming a core−shell model, afford an internal core radius R1 = 15.3 Å and an external radius R2 = 21.8 Å, in line with the expected dimension of the single unit, based on a single porphyrin surrounded by four Jeffamine chains. In chloroform, the adduct rearranges and porphyrins oligomers are stabilized by ion-pairing with Jeffamine, which, due to its hydrophobic nature, swells in this solvent.
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Dec 8, 2014