Topo ii beta activity determinescellular sensitivity toanthracyclines andep1podophyl lotoxinesinaml

By virtue of their different pH optima in the réaction buffer, two different topo If activities witti activity optima at pH 7.9 and at pH 8.9 under high can be quantified stringency conditions. The activities could be identified as topo II beta activity (pH 7.9) and topo II alpha activity (pH 8,9) by their different sensitivities to topo II alpha inhibitors, dephosphorylation experiments and immunoprecipitation with potyclonal antibodies. 72 bone marrow or blood samples from patients with AML have been examined and their in vitro sensitivities correlated to the activities of topo II alpha and topo II beta. Although the topo II alpha activity could be directly inhibited by incubation of the cells, no correlation between the topo II alpha activity and the sensitivity of the cells could be found. In contrast, the topo II beta activity, which was not substantially inhibited by the drugs, inversely correlated with the sensitivity of the cells (idarubicin P=O.OI7, daunorubicin P=0.006). Vice versa, resistant cells (1C90 > median) had a higher topo II beta activity. Cells from patients which relapsed after initial anthracyclin-containing treatment had a higher topo II alpha / beta activity ratio (P=0.0276). The sensitivity of AML-cells is substantially influenced by the activity of the resistant topo II (topo IE beta) which gives evidence that the remaining topo II activity after treatment helps the cell to survive the DNA repair phase.