Modulation of polymorphic properties of dielaidoylphosphatidylethanolamineby the antineoplastic ether lipid 1-O-octadecyl-2-O-methyl-glycero-3-phosphocholine

The capacity of the antineoplastic ether lipid 1-O-octadecyl-2-O-methyl-gly cero-3-phosphocholine (ET-18-OCH3) to modulate the polymorphic properties o f dielaidoylphosphatidylethanolamine has been studied using biophysical tec hniques. Differential scanning calorimetry showed that ET-18-OCH3 depresses the onset of the L-beta to L-alpha phase transition, decreasing also Delta H of the transition. At the same time, the onset of the transition from L- alpha to inverted hexagonal H-II phase was gradually increased as the ether lipid concentration was increased, totally disappearing at concentrations higher than 5 mol%. Small-angle X-ray diffraction and P-31-NMR confirmed th at ET-18-OCH3 induced that the appearance of the inverted hexagonal H-II ph ase was shifted towards higher temperatures completely disappearing at conc entrations higher than 5 mol%. These results were used to elaborate a parti al phase diagram and they were discussed as a function of the molecular act ion of ET-18-OCH3. (C) 1999 Elsevier Science B.V. All rights reserved.