Effects of antineoplastic ether lipids on model and biological membranes.

Differential scanning calorimetry and electron spin resonance were utilized to measure the effects of di-ether glycerophospholipid analogs (EL) on the physical properties of model membranes and on the membrane fluidity of HL60 leukemic cells. 1-Octadecyl-2-methyl-rac-glycero-3-phosphocholine (ET-18-OMe) and 1-thiohexadecyl-2-ethyl-rac-glycero-3-phosphocholine (ET-16S-OEt) lower the transition temperature of dimyristoylphosphatidylcholine vesicles in a range of concentrations between 0.5 and 15 mol %. Studies conducted on the interaction of EL with a wide spectrum of different phospholipids, namely dipalmitoylphosphatidylcholine, 1-hexadecyl-2-palmitoylphosphatidylcholine, dipalmitoylphosphatidylethanolamine, and dielaidoylphosphatidylethanolamine confirmed the ability of EL to effect the physical properties of model membranes. Changes in calorimetric enthalpy were observed only with phosphatidylethanolamine-containing phospholipids. ET-18-OMe and ET-16S-OEt increased the membrane fluidity of HL60 leukemic cells labeled with the fatty acid spin label probe 5-nitroxystearate. These data demonstrate the ability of EL to partition into phospholipidic domains and to change their physical properties. Furthermore, they affect the membrane fluidity of whole cells. These effects indicate an interaction between EL and the plasma membrane which may be of importance in determining the cytotoxic activity against tumor cells exerted by EL.

Synthesis of quaternary amine ether lipids and evaluation of neoplastic cell growth inhibitory properties.

Novel quaternary amine ether lipids have been synthesized and tested for inhibition of neoplastic cell proliferation with the HL-60 promyelocytic leukemia cell line. These compounds contain a positively charged quaternary amine functional group attached either directly to the glycerol backbone or at the end of an alkoxy chain. The biological testing has identified several analogues with activity equivalent to or greater than that exhibited by the reference compound in this assay, ET-18-OMe (1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine). Among the most active analogues are compounds 11, [N,N,N-triethyl-3-(hexadecyloxy)-2-ethoxy-1-propylammonium bromide] and 22 [N-[4-[3-(hexadecyloxy)-2-ethoxypropoxy]-1-butyl]pyridinium bromide], which are approximately 3 times as active as the reference standard.

Membrane damage in leukemic cells induced by ether and ester lipids: an electron microscopic study.

This paper reports a scanning electron microscopy (SEM) study of different leukemic cell lines exposed to 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine (ET-18-OMe). This is an ether lipid analog of platelet activating factor (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) which inhibits neoplastic cell growth in vitro and in vivo and is believed to exert its action through an interaction with the plasma membrane. In this paper evidence of the morphological alteration of leukemic cell membranes due to the exposure to varying concentrations of ET-18-OMe in vitro and in vivo is presented. This membrane damage consists of formation of blebs and holes, and the severity of these two phenomena correlate with the degree of cell viability loss. These alterations were analyzed in comparison to those induced by the known and structurally related permeabilizing agent, lysophosphatidylcholine, an ester lipid.