Induced multidrug resistance in murine leukemia L1210 and associated changes in a surface-membrane glycoprotein.

The aim of this study was to find out whether only resistant cells of the "multidrug-resistant" phenotype show the described changes of plasma membrane glycoprotein (170 kDa) or whether resistant cells that do not express this phenotype reveal corresponding results. Doxorubicin-resistant (L1210dox) and daunorubicin-resistant L1210 ascites tumor cells (L1210dnr) (multidrug-resistant tumor cells) were therefore compared with cytosine-arabino-side-resistant (L1210AraC) and cyclophosphamide-resistant L1210 ascites tumor cells (L1210ctx) (not multi-drug-resistant tumor cells). The resistant cell lines were generated in vivo in tumor-bearing mice and the resistance to cytostatic agents was evaluated in vivo and in vitro. Using the accumulation assay with rhodamine-123, the multidrug resistance can be detected. In order to determine alterations in the plasma membranes we used the monoclonal antibodies 265/F4 and C219, which were prepared against the membrane glycoprotein P170 (170 kDa) in colchicin-resistant Chinese hamster ovary cells. The results demonstrate that L1210dox and L1210dnr tumor cells show an intense immunostaining by the streptavidin/biotinylated-peroxidase-complex method and by the streptavidin/biotin/phycoerythrin immunofluorescence method. In contrast no specific immunostaining was observed in parental (sensitive) and L1210AraC or L1210ctx tumor lines. The results were confirmed by immunoblotting. To determine whether multidrug-resistant DNA sequences were expressed in the multidrug-resistant tumor cells, Northern blots with RNA od sensitive and resistant cells were performed using the clone pcDR1.5. Elevated RNA levels were detected only in resistant cells with the multidrug-resistant phenotype. Thus, the results of this study demonstrate that only resistant cells with the multidrug-resistant phenotype show an increased expression of the membrane 170-kDa glycoprotein.