Abstract
In a variety of adult and childhood leukaemia cell samples collected at different states of the disease, we analysed in a series of sequentially performed slot-blot or Northern-blot hybridisation experiments the expression of genes possibly involved in multiple drug resistance (MDR) (mdr1/P-glycoprotein, DNA topoisomerase II, glutathione-S-transferase pi), and the expression of the DNA topoisomerase I and histone 3.1 genes. Occasionally, P-glycoprotein gene expression was additionally examined by indirect immunocytofluorescence using the monoclonal antibody C219. No significant difference in mdr1/P-glycoprotein mRNA levels between primary and relapsed state acute lymphocytic leukaemias (ALL) was seen on average. Second or third relapses, however, showed a distinct tendency to an elevated expression of this multidrug transporter gene (up to 10-fold) in part well beyond the value seen in the moderately cross-resistant T-lymphoblastoid CCRF-CEM subline CCRF VCR 100. Increased mdr1/P-glycoprotein mRNA levels were also found in relapsed state acute myelogenous leukaemias (AML), and in chronic lymphocytic leukaemias (CLL) treated with chlorambucil and/or prednisone for several years. Topoisomerase I and topoisomerase II mRNA levels were found to be very variable. Whereas in all but one case of CLL topoisomerase II mRNA was not detected by slot-blot hybridizations, strong topoisomerase I and topoisomerase II gene expression levels, frequently exceeding the levels monitored in the CCRF-CEM cell line, were seen in many cell samples of acute leukaemia. If topoisomerase II mRNA was undetectable, expression of topoisomerase I was clearly visible throughout. These observations might be valuable considering the possible treatment with specific topoisomerase I or topoisomerase II inhibitors. Significant positive correlations were found (i) for topoisomerase I and histone 3.1 gene expression levels in general (P less than 0.001), and (ii) in the CLL samples additionally for the expression levels of the mdr1 gene, and the histone 3.1, topoisomerase I, and glutathione-S-transferase pi genes, respectively.
Highlights
Failure of chemotherapy during treatment of leukaemia is supposedly caused by the resistance of the tumour cells to antineoplastic drugs (Goldie & Coldman, 1984)
Two different mechanisms confering resistance on these cells to a wide variety of structurally unrelated cytotoxic agents have been identified so far at the molecular level, (i) the enhanced expression of the mdrl gene coding for an ATP-dependent, transmembrane drug efflux pump called P-glycoprotein, and (ii) an altered activity of the DNA topoisomerase II, a nuclear enzyme possessing DNA double-strand passing activity by an ATP-dependent cleaving and rejoining process
In series of sequentially performed slot-blot hybridisation experiments the RNA samples prepared from cell lines, healthy donors or leukaemia cell samples were evaluated for gene expression using the mdrl/P-glycoprotein, topoisomerase I, topoisomerase II, histon 3.1, glutathione-S-transferase class, or P-actin specific gene probes
Summary
Failure of chemotherapy during treatment of leukaemia is supposedly caused by the resistance of the tumour cells to antineoplastic drugs (Goldie & Coldman, 1984). Two different mechanisms confering resistance on these cells to a wide variety of structurally unrelated cytotoxic agents have been identified so far at the molecular level, (i) the enhanced expression of the mdrl gene coding for an ATP-dependent, transmembrane drug efflux pump called P-glycoprotein, and (ii) an altered activity of the DNA topoisomerase II, a nuclear enzyme possessing DNA double-strand passing activity by an ATP-dependent cleaving and rejoining process. 'Classical' multiple drug resistance (MDR) of cell lines selected in vitro is basically mediated by the P-glycoprotein (for review see Endicott & Ling, 1989). Point to further as yet unrecognised mechanisms or a multifactorial emergence of MDR of in vitro selected cell lines (McGrath & Center, 1988; Deffie et al, 1988; Harker et al, 1989)
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