Endoxifen, a Secondary Metabolite of Tamoxifen, and 4-OH-Tamoxifen Induce Similar Changes in Global Gene Expression Patterns in MCF-7 Breast Cancer Cells
- Young Chai Lim,
- Lang Li,
- Zeruesenay Desta,
- Qianqian Zhao,
- James M. Rae,
- David A. Flockhart and
- Todd C. Skaar
- Division of Clinical Pharmacology (Y.C.L., Z.D., D.A.F., T.C.S.) and Division of Biostatistics (L.L., Q.Z.), Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; Research Institute of Medical Sciences, Chonnam National University and Clinical Trial Center, Chonnam National University Hospital, Kwangju, Korea (Y.C.L.); and Division of Hematology Oncology, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, Michigan (J.M.R.)
- Address correspondence to:
Dr. Todd C. Skaar, Division of Clinical Pharmacology, Indiana University School of Medicine, 1001 West 10th Street, WD Myers Bldg., W7123, Indianapolis, IN 46202. E-mail: tskaar{at}iupui.edu
Abstract
We recently demonstrated that endoxifen (4-hydroxy-N-desmethyl-tamoxifen), a pharmacogenetically regulated metabolite of tamoxifen, is equipotent to 4-hydroxy-tamoxifen (4-OH-Tam) with respect to estrogen receptor binding and inhibition of 17β-estradiol (E2)-induced cell proliferation. Endoxifen was also found to be more abundant in human plasma than 4-OH-Tam, and its formation has been shown to be primarily catalyzed by cytochrome P450 2D6 (CYP2D6). Here, we report studies evaluating the effects of endoxifen, 4-OH-Tam, and E2 on gene expression in MCF-7 cells using Affymetrix U133A GeneChip Arrays (Santa Clara, CA). We detected 4062 genes that were E2-regulated (1924 induced; 2138 suppressed), and the ratio of E2-induced versus E2-suppressed genes was consistent regardless of the cutoff value. In the presence of E2, 2444 and 2390 genes were affected by 4-OH-Tam and endoxifen, respectively, when no minimal -fold change cutoff was implemented. The majority of genes regulated by the tamoxifen metabolites were also E2-responsive (74.4 and 73.3%, respectively). Endoxifen and 4-OH-Tam had overlapping effects on 1365 E2-sensitive genes, whose -fold effects between these metabolites were highly correlated (R2 = 0.99). A significant correlation was also found between the -fold effects of 249 E2-insensitive genes coregulated by both metabolites (R2 = 0.99). Hierarchical clustering analysis demonstrated similar gene regulation patterns between these metabolites, which were distinct from E2 or vehicle treatment patterns. Using real time-polymerase chain reaction, we validated the gene expression patterns of five genes that were differentially regulated by endoxifen and 4-OH-Tam. We conclude that endoxifen and 4-OH-Tam have similar effects on global gene expression patterns in MCF-7 cells and that the majority of the affected genes are estrogen-regulated genes.
Footnotes
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This study was supported in part by Pharmacogenetics Research Network Grants 2U-01 GM61373 (to D.A.F.) and K24RR020815 (to D.A.F.), National Institutes of Health Clinical Pharmacology Training Grant 5T32-GM-08425 (to D.A.F.), the Indiana University Center for Medical Genomics Core Facility, a grant of the Korea Health 21 R&D Project, Ministry of Health and Welfare, Republic of Korea (A050174; to Y.C.L.) and a grant from the Basic Research Program of the Korean Science and Engineering Foundation (R01-2006-000-11087-0; to Y.C.L.).
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.105.100511.
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ABBREVIATIONS: SERM, selective estrogen receptor modulator; endoxifen, 4-hydroxy-N-desmethyl-tamoxifen, IMEM, improved minimum essential medium; PharmGKB, the Pharmacogenetics and Pharmacogenomics Knowledge Base; E2, estradiol; PCR, polymerase chain reaction; GO, gene ontology; ER, estrogen receptor; 4-OH-Tam, 4-hydroxy-tamoxifen.
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- Received December 22, 2005.
- Accepted May 9, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
