This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend 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 Matsumoto, Y. Articles by Fojo, T. Search for Related Content PubMed PubMed Citation Articles by Matsumoto, Y. Articles by Fojo, T.

Cellular Adaptation to Drug Exposure: Evolution of the Drug-resistant Phenotype

Medicine Branch, Division of Clinical Sciences, National Cancer Institute, NIH, Bethesda, Maryland 20892

The efficacy of all chemotherapeutic agents is limited by the occurrence of drug resistance. For etoposide (VP-16), increased expression of MDR-1 or MRP and alterations in topoisomerase II have been shown to confer tolerance. To further understand resistance to VP-16, three sublines, designated MCF-7-VP17, ZR-75B-VP13, and MDA-MB-231-VP7, were initially isolated as single clones from parental cells by exposure to VP-16. Subsequently, a population of cells from each subline was exposed to 3-fold higher drug concentrations, allowing stable sublines to be established at higher extracellular drug concentrations. Characterization of the resistant sublines demonstrates the adaptation that occurs with advancing drug concentrations during in vitro selections. Reduced topoisomerase II mRNA and protein levels were observed in the initial isolates. This reduction was accompanied by a decrease in topoisomerase II activity and cellular growth rate and was associated with 6–314-fold resistance to topoisomerase II poisons. With advancing resistance, MRP expression increased and VP-16 accumulation decreased. This adaptation allowed for partial restoration of topoisomerase II activity as a result of increased expression (MCF-7-VP17 and ZR-75B-VP13) or hyperphosphorylation (MDA-MB-231-VP7), with a resultant increase in growth rate. In MDA-MB-231-VP7 cells, hyperphosphorylation coincided with increased casein kinase II mRNA and protein levels, suggesting a role for this kinase in the acquired hyperphosphorylation. In this cell line, hyperphosphorylation mediated the increased activity despite a fall in topoisomerase II protein levels secondary to an acquired 600-bp deletion in one topoisomerase II allele, which resulted in reduced protein levels. In all three sublines, high levels of resistance were attained as a result of synergism between the reduced topoisomerase II levels and MRP overexpression. These studies demonstrate how cellular adaptation to increasing drug pressure occurs and how more than one mechanism can contribute to the resistant phenotype when increasing selecting pressure is applied. Reduced expression of topoisomerase II is sufficient to confer substantial resistance early in the selection process, with synergy from MRP overexpression helping to confer high levels of resistance.

¹ The order of the first two authors is to be considered arbitrary.

² To whom requests for reprints should be addressed, at Medicine Branch, Building 10, Room 12N226, NCI, NIH, 9000 Rockville Pike, Bethesda, MD, 20892.

Received 1/31/97. Accepted 9/19/97.

This article has been cited by other articles:

				R. A. Gatenby and T. L. Vincent Application of quantitative models from population biology and evolutionary game theory to tumor therapeutic strategies Mol. Cancer Ther., September 1, 2003; 2(9): 919 - 927. [Abstract] [Full Text] [PDF]

				M. R. Kang and I. K. Chung Down-Regulation of DNA Topoisomerase IIalpha in Human Colorectal Carcinoma Cells Resistant to a Protoberberine Alkaloid, Berberrubine Mol. Pharmacol., April 1, 2002; 61(4): 879 - 884. [Abstract] [Full Text] [PDF]

				M. M. van den Heuvel-Eibrink, E. A. C. Wiemer, M. J. de Boevere, B. van der Holt, P. J. M. Vossebeld, R. Pieters, and P. Sonneveld MDR1 gene-related clonal selection and P-glycoprotein function and expression in relapsed or refractory acute myeloid leukemia Blood, June 1, 2001; 97(11): 3605 - 3611. [Abstract] [Full Text] [PDF]

				Z. Zhou, L. A. Zwelling, Y. Kawakami, T. An, K. Kobayashi, C. Herzog, and E. S. Kleinerman Adenovirus-mediated Human Topoisomerase II{{alpha}} Gene Transfer Increases the Sensitivity of Etoposide-resistant Human Breast Cancer Cells Cancer Res., September 1, 1999; 59(18): 4618 - 4624. [Abstract] [Full Text] [PDF]

				M. Alvarez, R. Robey, V. Sandor, K. Nishiyama, Y. Matsumoto, K. Paull, S. Bates, and T. Fojo Using the National Cancer Institute Anticancer Drug Screen to Assess the Effect of MRP Expression on Drug Sensitivity Profiles Mol. Pharmacol., November 1, 1998; 54(5): 802 - 814. [Abstract] [Full Text]