identification of a novel topoisomerase inhibitor effective in cells overexpressing drug efflux transporters新颖的拓扑异构酶抑制剂有效的识别细胞overexpressing药物外排转运蛋白.pdfVIP

Identification of a Novel Topoisomerase Inhibitor Effective in Cells Overexpressing Drug Efflux Transporters 1 ˚ ¨ 2 1 ¨ 1 2 1 Walid Fayad , Marten Fryknas , Slavica Brnjic , Maria Hagg Olofsson , Rolf Larsson , Stig Linder * 1 Department of Oncology and Pathology, Karolinska Institute and Hospital, Stockholm, Sweden, 2 Department of Medical Sciences, Division of Clinical Pharmacology, University Hospital, Uppsala University, Uppsala, Sweden Abstract Background: Natural product structures have high chemical diversity and are attractive as lead structures for discovery of new drugs. One of the disease areas where natural products are most frequently used as therapeutics is oncology. Method and Findings: A library of natural products (NCI Natural Product set) was screened for compounds that induce apoptosis of HCT116 colon carcinoma cells using an assay that measures an endogenous caspase-cleavage product. One of the apoptosis-inducing compounds identified in the screen was thaspine (taspine), an alkaloid from the South American tree Croton lechleri. The cortex of this tree is used for medicinal purposes by tribes in the Amazonas basin. Thaspine was found to induce conformational activation of the pro-apoptotic proteins Bak and Bax, mitochondrial cytochrome c release and mitochondrial membrane permeabilization in HCT116 cells. Analysis of the gene expression signature of thaspine- treated cells suggested that thaspine is a topoisomerase inhibitor. Inhibition of both topoisomerase I and II was observed using in vitro assays, and thaspine was found to have a reduced cytotoxic effect on a cell line with a mutated topoisomerase II enzyme. Interestingly, in contrast to the topoisomerase II inhibitors doxorubicin, etoposide and mitoxantron