This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Oloumi, A. Articles by Olive, P. L. Search for Related Content PubMed PubMed Citation Articles by Oloumi, A. Articles by Olive, P. L.

Changes in Subcellular Distribution of Topoisomerase II Correlate with Etoposide Resistance in Multicell Spheroids and Xenograft Tumors¹

British Columbia Cancer Research Centre, Vancouver, British Columbia, V5Z 1L3 Canada

The outer cells of Chinese hamster V79 spheroids are about 10 times more resistant than monolayers to DNA damage and cell killing by the topoisomerase (topo) II inhibitor etoposide. Although the amount and catalytic activity of topo II are identical for monolayers or the outer cells of spheroids, and the cell proliferation rate is the same, our previous results indicated that phosphorylation of topo II is at least 10 times higher in V79 monolayers than in spheroids. Because phosphorylation of topo II has been associated with nuclear translocation, we examined subcellular distribution of Topo II in monolayers, spheroids, and xenograft tumors using immunohistochemistry. Topo II was located predominantly in the nucleus of V79, human SiHa, and rat C6 monolayers but was found mainly in the cytoplasm of the proliferating outer cells of spheroids formed from these cell lines. Conversely, the outer cells of WiDr human colon carcinoma spheroids showed predominantly nuclear localization of topo II, and only WiDr cells showed no increase in resistance to etoposide when grown as spheroids. Cells sorted from xenografts resembled the spheroids in terms of sensitivity to etoposide and location of topo II. When the outer cells of V79 spheroids were returned to monolayer growth, the rate of redistribution of topo II to the nucleus occurred with similar kinetics as the increase in sensitivity to killing by etoposide. Removal and return of individual outer V79 spheroid cells to suspension culture resulted in the translocation of topo II to the nucleus for the first 24 h, accompanied by an increase in sensitivity to DNA damage by etoposide. Therefore, the cytoplasmic topo II distribution in outer spheroid cells and tumors appears to correlate not with morphological changes associated with growth in suspension but rather with the presence of neighboring, noncycling cells.

This article has been cited by other articles:

				A. Di Leo and E. Moretti Anthracyclines: The First Generation of Cytotoxic Targeted Agents? A Possible Dream J. Clin. Oncol., November 1, 2008; 26(31): 5011 - 5013. [Full Text] [PDF]

				J. G. Turner, R. Engel, J. A. Derderian, R. Jove, and D. M. Sullivan Human topoisomerase II{alpha} nuclear export is mediated by two CRM-1-dependent nuclear export signals J. Cell Sci., June 15, 2004; 117(14): 3061 - 3071. [Abstract] [Full Text] [PDF]

				L. A. Kunz-Schughart, J. P. Freyer, F. Hofstaedter, and R. Ebner The Use of 3-D Cultures for High-Throughput Screening: The Multicellular Spheroid Model J Biomol Screen, June 1, 2004; 9(4): 273 - 285. [Abstract] [PDF]

				K. O. Hicks, F. B. Pruijn, J. R. Sturman, W. A. Denny, and W. R. Wilson Multicellular Resistance to Tirapazamine Is Due to Restricted Extravascular Transport: A Pharmacokinetic/Pharmacodynamic Study in HT29 Multicellular Layer Cultures Cancer Res., September 15, 2003; 63(18): 5970 - 5977. [Abstract] [Full Text] [PDF]

				E. J. Mensah-Osman, A. M. Al-Katib, H.-Y. Wu, N. I. Osman, and R. M. Mohammad 2-[4-(7-Chloro-2-quinoxalinyloxy)phenoxy]-propionic Acid (XK469), an Inhibitor of Topoisomerase (Topo) II{beta}, Up-Regulates Topo II{alpha} and Enhances Topo II{alpha}-mediated Cytotoxicity Mol. Cancer Ther., December 1, 2002; 1(14): 1321 - 1326. [Abstract] [Full Text] [PDF]

				J. S. Coon, E. Marcus, S. Gupta-Burt, S. Seelig, K. Jacobson, S. Chen, V. Renta, G. Fronda, and H. D. Preisler Amplification and Overexpression of Topoisomerase II{alpha} Predict Response to Anthracycline-based Therapy in Locally Advanced Breast Cancer Clin. Cancer Res., April 1, 2002; 8(4): 1061 - 1067. [Abstract] [Full Text] [PDF]

				K. H. Shain, T. H. Landowski, and W. S. Dalton Adhesion-Mediated Intracellular Redistribution of c-Fas-Associated Death Domain-Like IL-1-Converting Enzyme-Like Inhibitory Protein-Long Confers Resistance to CD95-Induced Apoptosis in Hematopoietic Cancer Cell Lines J. Immunol., March 1, 2002; 168(5): 2544 - 2553. [Abstract] [Full Text] [PDF]

				K. H. Shain and W. S. Dalton Cell Adhesion Is a Key Determinant in de Novo Multidrug Resistance (MDR): New Targets for the Prevention of Acquired MDR Mol. Cancer Ther., November 1, 2001; 1(1): 69 - 78. [Abstract] [Full Text] [PDF]

				L. A. Hazlehurst, N. Valkov, L. Wisner, J. A. Storey, D. Boulware, D. M. Sullivan, and W. S. Dalton Reduction in drug-induced DNA double-strand breaks associated with {beta}1 integrin-mediated adhesion correlates with drug resistance in U937 cells Blood, September 15, 2001; 98(6): 1897 - 1903. [Abstract] [Full Text] [PDF]