ALTERATIONS IN PHOSPHATIDYLCHOLINE SYNTHESIS ARE ASSOCIATED WITH TAXOL RESISTANCE (PHOSPHOLIPIDS, MULTI-DRUG)
SORBARA, LYNN ROSE
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A taxol resistant variant (J7/TAX-50) of the murine macrophage-like cell line J774.2 has been developed in vitro. The LD(,50) of taxol for the resistant cells is 800-fold greater than that for the parental cell line. The J7/TAX-50 cells display the following phenotypic traits which are associated with multidrug resistance: (1) cross-resistance to unrelated hydrophobic drugs; (2) reduced steady-state accumulation of taxol; and (3) the presence of a 135-150 kDa membrane phosphoglycoprotein. J7/TAX-50 is unstably resistant and must be maintained in the presence of taxol. Cells grown in the absence of taxol for 30 days revert to drug sensitivity, and the membrane phosphoglycoprotein is lost. In contrast, the return to a normal level of drug accumulation is prolonged and requires over 8 months of growth in the absence of taxol.;To characterize further the parental, resistant and revertant cell lines, the major lipids have been analyzed by 2D-chromatography and HPLC. The steady-state level of phosphatidylcholine (PC) in J7/TAX-50 is greater than in the parental or revertant cell lines. The rate of synthesis of PC is increased (TURN)2-fold by both the salvage and de novo pathways in J7/TAX-50. Pulse-chase studies performed with ('14)C-choline or ('32)P-orthophosphate demonstrated an increase in the turnover of PC in J7/TAX-50. Analysis by gas chromatography/mass spectrometry of the composition of the major phospholipids indicated that fatty acids attached to the sn1- and 2-positions of PC are the same in the resistant and parental cell lines. These studies suggest that an increased level of PC in the membrane may be related to drug resistance and responsible for the prolonged decrease in steady-state drug association in J7/TAX-50 grown in the absence of taxol.
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