Ether lipids in oncology-welcoming address

Miltefosine – discovery of the antileishmanial activity of phospholipid derivatives

Miltefosine (hexadecylphosphocholine, Impavidotrade mark), a novel antiprotozoal drug used for the treatment of visceral and cutaneous leishmaniasis, was identified and evaluated independently in the early 1980s as a potential anticancer drug in Germany and as an antileishmanial drug in the UK. Although miltefosine is not the most active compound of its class against Leishmania parasites in vitro, the early demonstration of activity after oral administration in experimental models of visceral leishmaniasis helped to bring this compound to the attention of WHO TDR for further development in a unique collaboration model with the pharmaceutical industry (Zentaris GmbH). Miltefosine is active against most Leishmania species, including those that cause cutaneous disease.

Miltefosine: oral treatment of leishmaniasis

The well-known problems of classic treatment of the leishmaniases with pentavalent antimony (reduced efficacy), difficulties of administration and increasing frequency and severity of adverse events have stimulated the search for new drugs to treat these diseases. Other injectable, oral and topical drugs have not been consistently effective, especially in the modern World. Beginning in 1998, Indian researchers conducted several trials with hexadecylphosphocholine (miltefosine) in patients with visceral leishmaniasis, and in 1999, clinical studies were initiated in Colombia for cutaneous disease. More than 2500 patients have been treated, including patients with diffuse cutaneous leishmaniasis, mucosal disease and patients coinfected with HIV. Cure rates between 91 and 100% were reached with a dose of 2.5 mg/kg/day for 28 days, with no difference between treatment-naive and relapsing patients. Mild gastrointestinal events were present in 35-60% of patients and 10-20% had mild transaminase and creatinine elevations. Miltefosine has potent leishmanicidal activity as a consequence of its interference in parasite metabolic pathways and the induction of apoptosis. Miltefosine is the first effective and safe oral agent with the potential to treat all major clinical presentations of leishmaniasis.

Regulation of mammalian cell membrane biosynthesis

This review explores current information on the interrelationship between phospholipid biochemistry and cell biology. Phosphatidylcholine is the most abundant phospholipid and it biosynthesis has been studied extensively. The choline cytidylyltransferase regulates phosphatidylcholine production, and recent advances in our understanding of the mechanisms that govern cytidylyltransferase include the discovery of multiple isoforms and a more complete understanding of the lipid regulation of enzyme activity. Similarities between phosphatidylcholine formation and the phosphatidylethanolamine and phosphatidylinositol biosynthetic pathways are discussed, together with current insight into control mechanisms. Membrane phospholipid doubling during cell cycle progression is a function of periodic biosynthesis and degradation. Membrane homeostasis is maintained by a phospholipase A-mediated degradation of excess phospholipid, whereas insufficient phosphatidylcholine triggers apoptosis in cells.

Apoptosis triggered by 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine is prevented by increased expression of CTP:phosphocholine cytidylyltransferase

A HeLa cell line was constructed for the regulation of CTP:phosphocholine cytidylyltransferase (CCT) expression via a tetracycline-responsive promoter to test the role of CCT in apoptosis triggered by exposure of cells to the antineoplastic phospholipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3). Basal CCT expression in the engineered HeLa cell line was the same as in control HeLa cells lines, and CCT activity and protein were elevated 25-fold following 48 h of induction with doxycycline. Increased CCT expression prevented ET-18-OCH3-induced apoptosis. Acylation of exogenous lysophosphatidylcholine circumvented the requirement for CCT activity by providing an alternate route to phosphatidylcholine, and heightened CCT expression and lysophosphatidylcholine supplementation were equally effective in reversing the cytotoxic effect of ET-18-OCH3. Neither CCT overexpression nor lysophosphatidylcholine supplementation allowed the HeLa cells to proliferate in the presence of ET-18-OCH3, indicating that the cytostatic property of ET-18-OCH3 was independent of its effect on membrane phospholipid synthesis. These data provide compelling genetic evidence to support the conclusion that the interruption of phosphatidylcholine synthesis at the CCT step by ET-18-OCH3 is the primary physiological imbalance that accounts for the cytotoxic action of the drug.

Glyceryl-ether monooxygenase [EC 1.14.16.5]. A microsomal enzyme of ether lipid metabolism

The history, biological, and medical aspects of glyceryl ethers, as well as their chemical syntheses, biosynthesis, and their chemical and physical properties are briefly reviewed as background information for appreciating the importance of the enzyme glyceryl-ether monooxygenase, and for embarking on new studies of this enzyme. The occurrence, isolation and general properties of the microsomal, membrane-bound, glyceryl-ether monooxygenase from rat liver are described. Radiometric, nonradiometric, and coupled and direct spectrophotometric assays for this enzyme are detailed. The effects of detergents on the kinetics of this enzyme are described together with the stoichiometry and the effects of inhibitors. The structure-activity relationships of pterin cofactors and of ether lipid substrates, including their stereospecificities, have been summarized from enzyme kinetic data which are also tabulated. The mechanism of enzymic hydroxylation of glyceryl ethers and a model for the active site of glyceryl-ether monooxygenase are proposed from these apparent kinetic data. Notes on useful future studies of this monooxygenase have been made.

Ether lipid-induced cell damage of neuroblastoma cells is only weakly correlated with increased intracellular Ca2+ levels

The cell-damaging action of the ether lipid ET-18-OCH3 was studied in single NH15-CA2 neuroblastoma x glioma hybrid cells using light microscopy, and correlated with changes of the free intracellular calcium concentration, [Ca2+]i, as measured with the fluorescent Ca2+ indicator Fura-2. Addition of 3-100 microM ET-18-OCH3 to the cultures caused disintegration of neurites, cell rounding and detachment of the cells from the bottom of the culture dish. The effects occurred within 30-240 min, the faster, the higher the ET-18-OCH3 concentration. Also [Ca2+]i increased in a concentration-dependent manner, however, within seconds, and stayed high during the recording time of 20 min. The presence of 50 microM lanthanum or gadolinium ions prevented the ET-18-OCH3-induced increases of [Ca2+]i, but had no effect on neurite destruction and cell rounding. Preincubation with 1 mM diisopropylfluorphosphate or 100 microM leupeptin, both membrane-permeant inhibitors of intracellular proteases, did not prevent the effects. Nor was neurite destruction prohibited in the presence of 10 microM of the actin-stabilizing agent phalloidin or 2 microM taxol, a microtubule-stabilizer. We conclude that [Ca2+]i, although being increased during ET-18-OCH3-induced cell damage, is not the key factor of cell destruction.

Lysophosphatidylcholine attenuates the cytotoxic effects of the antineoplastic phospholipid 1-O-octadecyl-2-O-methyl-rac-glycero-3- phosphocholine

A colony-stimulating factor 1-dependent cell line was used to determine the relationship between the inhibition of phospholipid synthesis and the cytotoxic activity of the antineoplastic ether lipid, 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3). ET-18-OCH3 inhibited choline incorporation into phosphatidylcholine as well as total phospholipid synthesis. Exposure to ET-18-OCH3 at the G1/S boundary led to the accumulation of cells in G2, whereas the addition of ET-18-OCH3 in the G1 phase of the cell cycle prevented entry into the S phase. In both cases, ET-18-OCH3 treatment triggered DNA fragmentation and morphological changes associated with apoptosis within 10 h. The addition of lysophosphatidylcholine provided an exogenous source of cellular phospholipid and prevented ET-18-OCH3-dependent accumulation of cells in G2 and apoptosis. However, lysophosphatidylcholine did not overcome the ET-18-OCH3-dependent G1 block, although the growth-arrested cells remained viable. These data indicate that restoring phosphatidylcholine synthesis by supplementation with lysophosphatidylcholine overrides the cytotoxic but not the cytostatic activity of ET-18-OCH3.

Lysophosphatidylcholine and 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine inhibit the CDP-choline pathway of phosphatidylcholine synthesis at the CTP:phosphocholine cytidylyltransferase step

The regulation of the CDP-choline pathway of phosphatidylcholine synthesis at the CTP:phosphocholine cytidylyltransferase (CT) step by lysophosphatidylcholine (LPC) and the nonhydrolyzable LPC analog, 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3), was investigated in a colony-stimulating factor 1-dependent murine macrophage cell line. LPC inhibited phosphatidylcholine synthesis in vivo and led to the accumulation of choline and phosphocholine coupled to the disappearance of CDP-choline pointing to CT as the intracellular target. LPC neither inhibited cell growth nor decreased the cellular content of CT or altered the distribution of CT between soluble and particulate subcellular fractions. The inhibition of phosphatidylcholine synthesis was specific for LPC since lysophospholipids lacking the choline headgroup were not inhibitors. ET-18-OCH3 was a more potent inhibitor of phosphatidylcholine synthesis than LPC and caused the translocation of CT from the soluble compartment to the particulate compartment. Both LPC and ET-18-OCH3 were inhibitors of CT activity in vitro and kinetic analysis showed competitive inhibition with respect to the lipid activator. These data point to LPC as a negative regulator of de novo phosphatidylcholine synthesis that acts at the CT step and establish the mechanism for the inhibition of phosphatidylcholine biosynthesis by antineoplastic phospholipids.

Lyso platelet activating factor (LysoPAF) and its enantiomer. Total synthesis and carbon-13 NMR spectroscopy

Described is a reaction sequence for the total synthesis of lyso platelet activating factor (lysoPAF; 1-O-alkyl-sn-glycero-3-phosphocholine) and its enantiomer. The procedure is versatile and yields optically pure isomers of defined chain length. The synthesis is equally suited for the preparation of lysoPAF analogues and its enantiomers with unsaturation in the long aliphatic chain. First, rac-1(3)-O-alkylglycerol is prepared by alkylation of rac-isopropylideneglycerol with alkyl methanesulfonate followed by acid-catalyzed removal of the ketal group. The primary hydroxy group of alkylglycerol is then protected by tritylation, the secondary hydroxy group is acylated, and the protective trityl group is removed under mild acidic conditions with boric acid on silicic acid, essentially without acyl migration. Condensation of the diradylglycerol with bromoethyl dichlorophosphate in diethyl ether, hydrolysis of the resulting chloride, and nucleophilic displacement of the bromine with trimethylamine gives rac-1-O-alkyl-2-acylglycero-3-phosphocholine in good overall yield. The racemic alkylacylglycerophosphocholine is finally treated with snake venom phospholipase A2 (Ophiophagus hannah) which affords 1-O-alkyl-sn-glycero-3-phosphocholine (lysoPAF) of natural configuration in optically pure form. The "unnatural" 3-O-alkyl-2-O-acyl-sn-glycero-1-phosphocholine enantiomer, which is not susceptible to phospholipase A2 cleavage, gives 3-O-alkyl-sn-glycero-1-phosphocholine upon deacylation with methanolic sodium hydroxide. Homogeneity and structure of the intermediates and final products were ascertained by carbon-13 nuclear magnetic resonance spectroscopy on monomeric solutions.