EFFECT OF CELL-DENSITY ON CYTOTOXICITY OF ETHER LIPID ANALOGS IN VARIANTS OF B16 MURINE MELANOMA

Ether lipids are defined here as analogues of naturally occurring lyso phosphatidylcholines with cytotoxic activity against neoplastic cells. The activity of -octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (E T18OMe) and ylmercapto-2-methoxymethyl-propyl-1-phosphocholine (Ilmofo sine(R)) (BM 41.440) was tested in variants of B16 murine melanoma, gr own in adhesion cultures (B16F1 with low metastatic potential; B16F10 and B16BL6 with high metastatic potential). Cytotoxicity was evaluated by counting the cells that survived after 24 h of drug exposure. Chol esterol, sphingomyelin, total phospholipid and phosphatidylcholine lev els were determined. After 24 h of drug exposure, cultures of the B16B L6 variant contained a larger number of cells, especially when high dr ug concentrations (100-250 muM) were used, than cultures of the B16F1 and B16F10 variants. The sensitivity to ET18OMe of the three variants was evaluated at different cell densities (at each density the dose wa s equalized per number of cells/well; 0.1 mumol/10(6) cells/well). In B16F1 and B16F10 cultures the dose-response curve was not affected by the number of cells/well, while in B16BL6 no more than 20% of the cell s were killed at all cell densities measured. A linear relationship wa s noted between cell density and cholesterol/phospholipid and sphingom yelin/phosphatidylcholine ratios in the resistant variant B16BL46, con firming that lipid composition modulates the cytotoxic activity of eth er lipids.