2-[4-(7-chloro-2-quinoxalinyloxyphenoxy]-propionic acid (XK469), an inhibitor of topoisomerase (Topo) IIbeta, up-regulates Topo IIalpha and enhances Topo IIalpha-mediated cytotoxicity
| Autor: | Edith J, Mensah-Osman, Ayad M, Al-Katib, Hai-Young, Wu, Nadir I, Osman, Ramzi M, Mohammad |
|---|---|
| Rok vydání: | 2003 |
| Předmět: |
Microscopy
Confocal Time Factors Blotting Western DNA Immunohistochemistry Leukemia Lymphocytic Chronic B-Cell Culture Media Serum-Free Up-Regulation DNA-Binding Proteins DNA Topoisomerases Type II Microscopy Fluorescence Antigens Neoplasm Quinoxalines Tumor Cells Cultured Humans Protein Isoforms Enzyme Inhibitors Waldenstrom Macroglobulinemia Neoplasm Transplantation Etoposide |
| Zdroj: | Molecular cancer therapeutics. 1(14) |
| ISSN: | 1535-7163 |
| Popis: | Topoisomerase (Topo) IIalpha has proven to be an adequate anticancer target for tumors expressing this enzyme. In this study, we elucidated the effect of 2-[4-(7-chloro-2-quinoxalinyloxyphenoxy]-propionic acid (XK469; a new Topo IIbeta inhibitor) in the modulation of Topo IIalpha levels and sensitivity to Topo IIalpha poisons. We demonstrate by Western blot analysis that indolent B-cell tumors express undetectable levels of this enzyme and are refractory to the effects of Topo IIalpha poisons such as VP16. Using the Waldenstrom's macroglobulinemia (WM) cell line WSU-WM, we show that XK469 induced the expression of Topo IIalpha protein by 24 h compared with control. Immunofluorescence studies by confocal microscopy using a specific monoclonal antibody against Topo IIalpha supported the immunoblot findings with high intensity staining in XK469-exposed cells. To determine the effect of up-regulating Topo IIalpha on sensitivity of Topo IIalpha-directed inhibitors, WSU-WM cells were exposed to simultaneous, sequential, and reverse order XK469 and VP16. We demonstrate that 24 h of exposure to XK469 before VP16 resulted in a maximum synergistic response. In contrast, simultaneous or reverse order exposure resulted in an antagonistic effect. A similar trend was observed with cells obtained from chronic lymphocytic leukemia patients, but not in normal lymphocytes. This increase in VP16 sensitivity after 24 h of XK469 exposure was associated with VP16-dependent DNA cleavage, as demonstrated by formation of a smeared DNA band in a SDS-KCL DNA cleavage assay. From this study, we concluded that XK469 up-regulates Topo IIalpha levels and consequently sensitizes indolent malignant B cells to the cytotoxic effect of VP16 in a schedule-dependent manner. |
| Databáze: | OpenAIRE |
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