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The effect of a serum-free medium (TNB-100), compared to RPMI 1640 containing 10% fetal bovine serum (FBS), on the lipid composition of HL60 and K562 leukemic cells was investigated. The 10% FBS RPMI medium contained approximately three times more phospholipids (PL), about three times more protein and eight times more cholesterol (CHOL) than did the TNB-100 medium. Cells cultured in TNB-100 medium, referred to as HL60-TNB and K562-TNB cells, were significantly lower in PL and CHOL than 10% FBS RPMI cells, with about a threefold higher PL-to-CHOL ratio; however, these cells were significantly higher in protein content. Cells grown in TNB-100 were also significantly more fluid than 10% FBS RPMI cells and were more sensitive to the fluidizing action of the ether lipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine. The 50% inhibitory dose of the drug was about 50% lower in TNB-grown cells than in 10% FBS RPMI cells.

Ether-linked glycerophospholipids (ether lipids, EL) are membrane-interactive drugs selectively cytotoxic toward neoplastic cells compared with normal cells. No conclusive explanation has yet been provided for this selectivity. We now present data indicating that the drug 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine (ET-18-OMe) induces apoptosis, or programmed cell death, in human leukemic cells. Apoptotic death is induced selectively by ET-18-OMe in HL60 cells, which are sensitive to the drug's cytotoxic action, but not in the resistant K562 cell line. Enrichment of HL60 cells with cholesterol (HL60-CHOL cells) significantly protects the cells from the cytotoxic effect and from the induction of apoptosis by ET-18-OMe; the percentage of fragmented DNA is only 17% for HL60-CHOL, compared with 50% in native HL60 cells after exposure to 20 microns ET-18-OMe for 24 hr. Our study provides a possible explanation for differences in sensitivity to EL among different cell types and illustrates an indirect interaction of EL with cellular DNA.

Ether-linked glycerophospholipids (ether lipids, EL) are selectively toxic and anti-proliferative agents against cancer cells in vitro. The reason for such selectivity is not completely clear. Their mechanism of action is mediated through an interaction with the plasma membrane and the membrane lipid composition may modulate it. As a continuation of previous reports, we now present data showing that cholesterol concentration modulates EL toxicity in the K562, U937 and MOLT4 leukemic cell lines in vitro. Cells become sensitive to otherwise ineffective doses of EL when their cholesterol content is lowered. Cell cholesterol levels were reduced by exposure to an egg lipid mixture (neutral glycerides, phosphatidylcholine and phosphatidylethanolamine, AL721). The data contribute to an understanding of the EL mechanism of action on membranes and suggest that the cellular cholesterol concentration must be considered a major factor in modulating the cytotoxic effects of EL.

The ability of 2 recent ether-lipid derivatives, aza-phospholipids BN52205 and BN52211, to induce apoptosis in different leukemia cell lines was investigated using I-octadecyl-2-methyl-rac-glycero-3- phosphocholine (ET-18-OCH3) as a positive control. HL60, K562, Molt-4 and U937 cells were exposed for 24 hr to 20 microM of drug. The 2 aza-derivatives were as cytotoxic as ET-18-OCH3: BN52205 and BN52211 selectively induced apoptotic death in HL60, Molt-4 and U937 cells, but not in the K562-resistant cell line. Around 50% of DNA was fragmented in HL60 cells after exposure to the aza-derivatives, and 34% and 20% of DNA was fragmented in Molt-4 and U937 cells respectively. Similar results were obtained when cells were exposed to ET-18-OCH3. Our data confirm that ether lipids induce apoptosis in a variety of human leukemic cells, providing a possible explanation for their selectivity and mechanism of action.

To investigate whether the endogenous vasoactive substrate, leukotriene B4 (LTB4), was induced in adverse reactions observed after intravenous injection of iodinated contrast media (CM), the authors measured the in vitro production and metabolism of LTB4 by human polymorphonuclear leukocytes (PMNs) after stimulation with different doses of commercial CM preparations: iopamidol, 300 mg I/mL; iodamide, 300 mg I/mL; iohexol, 300 mg I/mL; ioxaglate, 320 mg I/mL; and the experimental preparation, iomeprolo. This study showed that the CM studied do not stimulate the production or metabolism of LTB4 by isolated human blood PMNs. All of the CM studied except iodamide do not inhibit the production or metabolism of LTB4 in PMNs stimulated by A23187. The in vitro hepatic microsomal oxidation of exogenous LTB4 to (omega-1)OH LTB4 and omega-OH LTB4 was inhibited by all the CM studied. LTB4 production by PMNs seems not to play a major role in anaphylactoid reactions observed after iodinated CM. However, a transient blockade by CM of LTB4 metabolism, leading to an increase of steady-state concentrations of LTB4, could not be excluded by these experiments.