Alkyl lysophospholipids inhibit phorbol ester-stimulated phospholipase D activity and DNA synthesis in fibroblasts

The antineoplastic alkyl lysophospholipids (ALP) 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3) and 1-S-hexadecylthio-2-methoxymethyl-2-deoxy-rac-glycero-3-phosphocho line (BM41.440) were found to alter phospholipase D (PLD)-mediated phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) hydrolysis in NIH 3T3 fibroblasts. After a shorter (50 min) treatment, 2.5-7.5 microg/ml concentrations of ALP stimulated PtdCho, but not PtdEtn, hydrolysis 2-4-fold. At the same time, 7.5-25 microg/ml concentrations of ALP significantly inhibited the larger (5.8-6.5-fold) stimulatory effects of phorbol 12-myristate 13-acetate (PMA) on both PtdCho and PtdEtn hydrolysis. When a brief (30 min) exposure of cells to 1-2.5 microg/ml concentrations of BM 41.440 was followed by incubation of washed cells for 3-16 h prior to the assay of PLD activity or DNA synthesis, the treated cells exhibited no increased PtdCho hydrolysis, while their responses to the stimulatory PMA effects on both PLD activity and DNA synthesis were strongly reduced. The results suggest that the PLD and protein kinase C systems may be important cellular targets of ALP actions.