title: Endoxifen, a secondary metabolite of tamoxifen, and 4-OH-tamoxifen induce similar changes in global gene expression patterns in MCF-7 breast cancer cells.
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 17beta-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.
authors.affiliation: Division of Clinical Pharmacology, Indiana University School of Medicine, 1001 West 10th Street, WD Myers Bldg., W7123, Indianapolis, IN 46202, USA.
authors.forename: Young Chai
authors.initials: YC
authors.lastname: Lim
authors.forename: Lang
authors.initials: L
authors.lastname: Li
authors.forename: Zeruesenay
authors.initials: Z
authors.lastname: Desta
authors.forename: Qianqian
authors.initials: Q
authors.lastname: Zhao
authors.forename: James M
authors.initials: JM
authors.lastname: Rae
authors.forename: David A
authors.initials: DA
authors.lastname: Flockhart
authors.forename: Todd C
authors.initials: TC
authors.lastname: Skaar
mesh_terms: D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism*; D045744:Cell Line, Tumor; D016000:Cluster Analysis; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D020411:Oligonucleotide Array Sequence Analysis; D012334:RNA, Neoplasm / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020845:Selective Estrogen Receptor Modulators / Q000494:pharmacology*; D013629:Tamoxifen / Q000031:analogs & derivatives* / Q000493:pharmacokinetics* / Q000494:pharmacology
chemical_list: D012334:RNA, Neoplasm; D020845:Selective Estrogen Receptor Modulators; D013629:Tamoxifen; C016601:afimoxifene; C055492:4-hydroxy-N-desmethyltamoxifen; D004958:Estradiol