ANALYSIS OF DNA CONTENT IN MULTIDRUG-RESISTANT CELLS BY IMAGE AND FLOW-CYTOMETRY

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 CCR F-CEM) and to the MDR hamster LR73-R cell line obtained by transfectio n 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, e thidium bromide, or Hoechst 33342. This decrease was not accompanied b y changes in cell cycle phase distribution of cells. Moreover, image c ytometry of cells stained after various hydrolysis times in 5 M HCl in dicated that MDR cells displayed the same hydrolysis kinetics and sens itivity as drug-sensitive cells with a well-preserved stoichiometry of the Feulgen reaction. LR73-R cells transfected with mdr1 cDNA exhibit ed only a very limited change in propidium iodide staining as compared with sensitive LR73 cells, suggesting that mdr1 gene overexpression a lone could not account for the alterations in DNA content observed in the selected MDR cells.