ETOPOSIDE-RESISTANCE IN THE MULTIDRUG-RESISTANT LZ-8 CELLS

The multidrug-resistant LZ-8 cells were found to exhibit marked resist ance to etoposide compared to wild-type, parental V79 cells. The multi drug resistant phenotype did not significantly contribute to this etop oside-resistance. Following exposure of LZ-8 cells and V79 cells to eq uivalent concentrations of etoposide, there was a dramatic reduction i n the number of etoposide-induced stabilized DNA-topoisomerase II comp lexes in the LZ-8 cells compared to V79 cells, however, this reduction was not found when nuclei isolated from LZ-8 and V79 cells were expos ed to equivalent concentrations of etoposide. These results suggest th at cytoplasmic factors are involved in the etoposide-resistance of LZ- 8 cells.