Flow cytometric double labeling technique for screening of multidrug resistance

Abstract

We investigated the capabilities of flow cytometry in the analysis of a multidrug resistant (MDR) human ovarian cancer cell line 2780AD and its drug sensitive parental A2780. A functional assay using daunorubicin (DNR) as a fluorescent probe was combined with an immunofluorescence assay of P‐glycoprotein (P‐gp) using the monoclonal antibody MRK‐16. Functionally MDR could be demonstrated by the lower DNR‐content of MDR cells compared to DNR‐content of drug sensitive cells. When incubation was performed with DNR in the presence of verapamil, DNR‐content increased in the MDR cells. However the content of the A2780 cells was never attained. Differences in DNR‐content were not related to differences in DNA‐content. In experimental cell lines immunofluorescence data were inversely related with those of DNR‐content: MDR cells had high levels of P‐gp expression and low levels of DNR‐content (and vice versa in drug sensitive cells). Both assays can be easily combined in a multiparametric flow cytometric procedure to evaluate both parameters simultaneously in the same cells. Analysis of clinical samples demonstrates the existence of aberrant subpopulations which would not be detected by using a single parameter assay. Copyright © 1991 Wiley‐Liss, Inc.