Diverse Gene Expression and DNA Methylation Profiles Correlate with Differential Adaptation of Breast Cancer Cells to the Antiestrogens Tamoxifen and Fulvestrant

Abstract

The development of targeted therapies for antiestrogenresistant breast cancer requires a detailed understanding of its molecular characteristics. To further elucidate the molecular events underlying acquired resistance to the antiestrogens tamoxifen and fulvestrant, we established drug-resistant sublines from a single colony of hormonedependent breast cancer MCF7 cells. These model systems allowed us to examine the cellular and molecular changes induced by antiestrogens in the context of a uniform clonal background. Global changes in both basal and estrogeninduced gene expression profiles were determined in hormonesensitive and hormonal-resistant sublines using Affymetrix Human Genome U133 Plus 2.0 Arrays. Changes in DNA methylation were assessed by differential methylation hybridization, a high-throughput promoter CpG island microarray analysis. By comparative studies, we found distinct gene expression and promoter DNA methylation profiles associated with acquired resistance to fulvestrant versus tamoxifen. Fulvestrant resistance was characterized by pronounced upregulation of multiple growth-stimulatory pathways, resulting in estrogen receptor A (ERA)-independent, autocrineregulated proliferation. Conversely, acquired resistance to tamoxifen correlated with maintenance of the ERA-positive phenotype, although receptor-mediated gene regulation was altered. Activation of growth-promoting genes, due to promoter hypomethylation, was more frequently observed in antiestrogen-resistant cells compared with gene inactivation by promoter hypermethylation, revealing an unexpected insight into the molecular changes associated with endocrine resistance. In summary, this study provides an in-depth understanding of the molecular changes specific to acquired resistance to clinically important antiestrogens. Such knowledge of resistance-associated mechanisms could allow for identification of therapy targets and strategies for resensitization to these well-established antihormonal agents. (Cancer Res 2006; 66(24): 11954-66)

Anti-microRNA-222 (Anti-miR-222) and -181B Suppress Growth of Tamoxifen-resistant Xenografts in Mouse by Targeting TIMP3 Protein and Modulating Mitogenic Signal

“…Cell Culture and Tissue Procurement-Tamoxifen-sensitive MCF-7 cells and resistant OHT R cells were obtained from Dr. Kenneth P. Nephew (Indiana University) and maintained as described (11). T47D cells were obtained from the ATCC (American Type Culture Collection) and maintained as instructed.…”

PARP and CHK inhibitors interact to cause DNA damage and cell death in mammary carcinoma cells

“…1A). 28 Similar data were obtained in other breast cancer cell lines exposed to the CHK1 inhibitor LY2603618 and to the PARP inhibitors AZD2281 and AG014699 ( Fig. 1B and C).…”

Selective recruitment of breast cancer anti-estrogen resistance genes and relevance for breast cancer progression and tamoxifen therapy response

“…The probability of recovery of a particular gene under different selection conditions may depend on the integration position modulating its level of expression and on the consequences of the particular anti-estrogen on the biology of the ZR-75-1 cells. Our observations that the mechanisms underlying resistance against diverse anti-estrogens differ are in line with previous observations in breast cancer cell models (Soulez & Parker 2001, Faridi et al 2003, Frasor et al 2004, Martin et al 2005, Fan et al 2006, Kuske et al 2006, Scafoglio et al 2006, Shaw et al 2006, Osipo et al 2007. Accordingly, patients with breast tumors failing on tamoxifen have been shown to respond to the pure anti-estrogen fulvestrant (Howell et al 2002, Osborne et al 2002, Howell 2006, indicating subtle differences in the underlying mechanisms of tumor growth control.…”