FINDING THE DRUG-RESISTANT TUMOR-CELL BY MOLECULAR AND CELLULAR-ASSAYS - THE ALTERED TOPOISOMERASE PARADIGM - ASSAYS FOR DRUG-RESISTANCE

Because drug resistance is a barrier to the cure of many neoplastic di seases, identification of mechanisms of resistance to different classe s of anticancer drugs and development of assays to recognize individua l drug-resistant tumor cells are justified. We have focused our recent efforts on cells expressing multidrug resistance due to altered (decr eased) activity of DNA topoisomerase II (at-MDR). We discuss herein mo lecular and cellular assays that permit the detection of single cells expressing the at-MDR phenotype, and suggest that these assays may hav e more general applicability to cells expressing other mechanisms of m ultidrug resistance.