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.
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.
Mensah-Osman
Edith J
EJ
Division of Hematology and Oncology, Department of Internal Medicine, Karmanos Cancer Institute, Detroit, Michigan 48201, USA.
Al-Katib
Ayad M
AM
Wu
Hai-Young
HY
Osman
Nadir I
NI
Mohammad
Ramzi M
RM
D000951:Antigens, Neoplasm; D015153:Blotting, Western; D016895:Culture Media, Serum-Free; D004247:DNA / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D007150:Immunohistochemistry; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000097:blood; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009368:Neoplasm Transplantation; D020033:Protein Isoforms; D011810:Quinoxalines / Q000494:pharmacology*; D013997:Time Factors; D014407:Tumor Cells, Cultured; D015854:Up-Regulation; D008258:Waldenstrom Macroglobulinemia / Q000188:drug therapy / Q000378:metabolism
D000951:Antigens, Neoplasm; D016895:Culture Media, Serum-Free; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D020033:Protein Isoforms; D011810:Quinoxalines; C118180:XK 469; D005047:Etoposide; D004247:DNA; D004250:DNA Topoisomerases, Type II