In vitro topo II-DNA complex accumulation and cytotoxicity of etoposide inleukaemic cells from patients with acute myelogenous and chronic lymphocytic leukaemia

Topoisomerase II (topo II) is the target enzyme of etoposide, and DNA-topo II complex accumulation is considered crucial for the cytotoxic effect. We used a SDS-KCI precipitation assay to determine the complex accumulation in duced by etoposide in leukaemic cells isolated from 58 patients, 31 with ac ute myelogenous leukaemia (AML), and 27 with chronic lymphocytic leukaemia (CLL). To investigate whether the sensitivity towards etoposide was depende nt on the complex accumulation in the cells, we investigated the drug-induc ed DNA damage using a DNA unwinding assay and the in vitro cytotoxicity of etoposide using the MTT assay. AML cells had higher complex accumulation (P = 0.006) and more DNA damage (P = 0.029) compared with CLL cells. The data support a relationship between etoposide-induced complex accumulation and DNA damage in leukaemic cells from AML and CLL patients. However, the induc ed DNA damage did not translate to in vitro cytotoxicity, suggesting that o ther factors, such as DNA repair and apoptosis functions, also play importa nt roles to determine the etoposide sensitivity. (C) 2001 Elsevier Science Ltd. All rights reserved.