Magnetic resonance spectroscopy of cellular lipid extracts from sensitive, resistant and reverting K562 cells and flow cytometry for investigating the P‐glycoprotein function in resistance reversion

The proton NMR spectra of K562 cells contain resonances of lipids. When these cells acquire multidrug resistance phenotype, the NMR lipid signals are modified and partially recovered when the resistance is reversed. The goals of the present study are to elucidate the mechanism of the resistance phenotype reversion and to investigate the possible origin of lipid signals detected in whole cells with proton NMR spectroscopy. Therefore, the K562 drug-sensitive cell line, its adriamycin resistant counterpart and two reverting derivates, obtained by verapamil treatment and long term culture in drug-free medium, were used in this study. The P-glycoprotein (P-gp) pump function was measured by flow cytometry and lipids were extracted to be analysed by proton and phosphorus spectroscopy. The phenotype reversion is due to the decrease of the P-gp function and an increased entrance of anthracycline drug when compared with the resistant cells. The spectra obtained on extracts showed no modification of the fatty acid composition and of the ratio of total cholesterol to fatty acid content. A different phospholipid composition in sensitive and resistant cells was found, but the reversion of resistance did not produce a recovery of these lipids. Thus, the lipid NMR spectra of extracts could not explain the spectral modifications observed on whole cells, in relation to acquiring and reverting drug resistance. These results are in favour of a different lipid organization or of localization within the cell.