Action of topoisomerase targeting drugs on Non-Hodgkin's lymphoma and leukemia: Correlation of clinical and cell culture studies

In two different phase I clinical studies, Non-Hodgkin's lymphoma patients were treated with combination of topotecan (SKF 104864, Hycamptamine) and etoposide (VP16) while acute leukemia patients were treated with combination of topotecan and Ara-C. Peripheral blood samples were withdrawn from patients immediately after administration of topotecan or VP16, and mixed with Sarkosyl to trap the topoisomerase-DNA covalent complexes for the In Vivo Link assay (Topogen). Blood samples were collected in EDTA at the same time were used for preparation of leukocyte RNA. Semi-quantitative cDNA-PCR was performed to examine the levels of mRNA corresponding to topoisomerase I, topoisomerase II α and II β over the course of therapy. The formation of covalent topoisomerase-DNA complexes was found to vary between patients. There was a significant correlation between the clinical response and the formation of drug induced covalent complex in NHL patients. All patients with complete and partial remission formed drug induced covalent complex, while some of the patients with stable or progression of disease also formed the complex. The formation of protein-DNA covalent complex appeared to be necessary but not sufficient for clinical response. A consistent decline in the level of topoisomerase II α mRNA in the peripheral blood leukocytes of both NHL and leukemia were observed over the course of the treatments.;Based on the decrease in the mRNA level of topoisomerase II α, we hypothesized that increase in p53 level in response to drug induced DNA damage led to decreased topo II α mRNA level. In order to test this hypothesis two leukemic cell lines: ML-1 (wild type p53) and HL-60 (p53 null) were treated with camptothecin and the expression levels of topo II α mRNA and protein were determined by northern and western blot analyzes respectively. In ML-1 cell line p53 protein was induced while both topo II α mRNA and protein levels decreased below the pre-treatment level. In HL-60 cell line both topo II α mRNA and protein levels remained relatively the same. Thus it is highly probable that the decrease in topo II α mRNA in both NHL and leukemia patients after treatment with topotecan were due to the increase in p53 level. This should be considered in designing schedule for combination therapy using inhibitors of both topoisomerase I and II.