Alkyl-lysophospholipids (ALP) are a new family of compounds which have demonstrated antitumor activity in vitro and in vivo against a variety of neoplastic cells. The most active compound to date has been 1-octadecyl-2-methoxy-glycero-3-phosphatidylcholine (ET18-OCH3). We have synthesized this compound in our laboratories. It has been suggested that the antitumor activity is selective, in that normal cells contain an 0-alkyl cleavage enzyme which metabolizes the drug, whereas neoplastic cells largely lack this enzyme resulting in accumulation of ALP which interferes with intermediate phospholipid metabolism. We have observed that two human leukemic cell lines, HL60 and K562 have different sensitivities to comparable concentrations of ALP when measured by tritiated thymidine incorporation, viability and clonogenicity in soft agar. We wish to explore the reasons for this difference in these two cell lines by 1) comparing uptake and intracellular distribution of radiolabelled ALP, 2) measuring 0-alkyl cleavage enzyme activity, 3) comparing the effect on phosphatidylcholine and phosphatidylethanolamine synthesis, 4) investigating the mechanisms, characteristics and effects on phospholipid sensitive-Ca2+ dependent protein phosphorylation, 5) measuring Na transport and identifying small mobile metabolites using NMR spectroscopy. Furthermore, we plan to synthesize other ether analogs of lysophosphatidylcholine and compare their activity to that of ET18-OCH3. These studies should extend our knowledge concerning the mechanism for sensitivity and resistance of these cell lines to these new antineoplastic agents which are beginning clinical trials.
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