Expression of drug resistance-associated mdr-1, GST π, and topoisomerase II genes during cell cycle traverse

Abstract The expression of drug resistance-associated mdr -1, GST π, and topoisomerase II genes was analyzed in cell cycle phase enriched populations of doxorubicin-resistant murine leukemic P388/R-84 cells. Flow cytometric analysis of bromodeoxyuridine (BrdU) incorporation and staining with anti-BrdU antibodies was used to confirm the purity of cell cycle phase enriched populations obtained by centrifugal elutriation. Doxorubicin (DOX) and daunorubicin (DNR) accumulation was significantly lower in S-phase cells, and coincubation with verapamil (VPL) or chlorpromazine (CPZ) enhanced DOX and DNR accumulation more in S-phase than in G 1 - and G 2 M - phase cells. While the cellular content of mdr -1 and topoisomerase II mRNAs changed, GST π mRNA content remained constant during the cell cycle. S-phase cells had about 3-fold higher mdr -1 mRNA content than G 1 - and G 2 M - phase cells. In G 1 cells, P-glycoprotein expression, as determined by C219 monoclonal antibody, was 12% less than that of S and G 2 M cells. Topoisomerase II mRNA content increased with the progression of cell cycle and peaked in G 2 M cells. These observations suggest that cell cycle stage related changes in expression of drug resistance markers may have a major bearing on chemosensitivity of drug-resistant cells.