Nuclear DNA content was assessed in multidrug-resistant (MDR) cells by image and flow cytometry. Two human MDR cell lines (K562-Dox and CEM-VLB) obtained by in vitro drug selection and overexpressing mdr1 gene were compared to their respective sensitive counterparts (K562 and CCRF-CEM) and to the MDR hamster LR73-R cell line obtained by transfection of mouse mdr1 cDNA. Both cell lines obtained by selection displayed a decreased DNA content, as measured by image cytometry after Feulgen staining, or by flow cytometry after staining with propidium iodide, ethidium bromide, or Hoechst 33342. This decrease was not accompanied by changes in cell cycle phase distribution of cells. Moreover, image cytometry of cells stained after various hydrolysis times in 5 M HCl indicated that MDR cells displayed the same hydrolysis kinetics and sensitivity as drug-sensitive cells with a well-preserved stoichiometry of the Feulgen reaction. LR73-R cells transfected with mdr1 cDNA exhibited only a very limited change in propidium iodide staining as compared with sensitive LR73 cells, suggesting that mdr1 gene overexpression alone could not account for the alterations in DNA content observed in the selected MDR cells.

Adriamycin (ADM) can increase sialic acid content in K 562 cells and reduce their susceptibility to NK-mediated lysis. In this report, hypothetical relationship between this resistance and augmentation in sialylation has been investigated. Variations in the time of exposure to ADM showed that 12 hours were sufficient to cause maximal recruitment of benzidine-positive cells, growth inhibition and resistance to NK-mediated lysis. On the contrary, the membrane sialic acid density seemed stable and 24 hours of drug exposure were necessary to observe a clear rise in sialic acid. Neuraminidase treatment of control and ADM-treated K 562 cells was associated with an obvious enhancement in their susceptibility to NK-mediated lysis which can be explained by an increase in the target-effector binding ability as assessed by a direct conjugate-forming cell assay. However, the neuraminidase treatment did not modify the sensitivity difference to lysis between untreated and ADM-treated cells. As compared to control the reactivity of ADM-treated cells was higher with an antiglycophorin A (GPA) MAb and lower with an antitransferrin receptor (TFR) MAb. Kinetic studies suggested that GPA expression is a better index of ADM-induced resistance to NK-mediated lysis than TFR expression. In addition, neuraminidase treatment showed that TFR and GPA modulations induced by ADM can be correlated with sialylation alterations.

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