Original ResearchA molecular model for the mechanism of acquired tamoxifen resistance in breast cancer
Introduction
The clinical application of the laboratory strategy of long-term adjuvant antihormone therapy for the treatment of breast cancer [1] has significantly improved breast cancer survival. Selection of patients whose tumours express the oestrogen receptor (ER) are more likely to respond to long-term adjuvant tamoxifen (TAM) [2], [3] or aromatase inhibitors (AIs) [4] than those without ER. However, acquired resistance to antihormone therapy remains a challenge as adjuvant therapy is extended [3], [5].
The evolution of acquired resistance to TAM treatment was discovered using MCF-7 tumours transplanted in athymic mice to mimic years of adjuvant treatment in patients [6], [7], [8]. Long-term therapy generates selection pressure for cell populations that evolve from acquired TAM resistance, ubiquitously observed in metastatic breast cancer, to eventually expose a vulnerability that is expressed as oestrogen (E2)-induced apoptosis [8], [9], [10]. Acquired resistance to TAM or other selective ER modulators (SERMs) is unique in that the growth of resistant tumours is dependent on SERMs [6], [7], [8]. Acquired TAM resistance during the treatment of metastatic breast cancer occurs within one or two years [11], consistent with the model of SERM resistance in athymic mice [6], [8]. An AI (depleting E2) or fulvestrant (ICI 182,780; a pure antioestrogen that destroys the ER) is effective as second-line therapy after TAM failure [12], [13]. Thus, it appears that acquired resistance to SERMs is initially able to utilise either E2 or a SERM as the growth stimulus in ER-positive TAM-resistant breast tumours. However, no mechanism has been established to explain this paradox.
We describe a new model of antihormone-resistant breast cancer in vitro that exhibits the characteristics of acquired TAM resistance in vivo. The MCF-7:5C cell line emerged unexpectedly from an established MCF-7 cell line after long-term E2 deprivation, i.e. simulated AI resistance [14]. The E2-deprived cell lines [14], [15] created from MCF-7 cells have the unique ability to undergo E2-induced apoptosis that has clinical significance for the treatment [16] and prevention of breast cancer [17]. We discovered that if a c-Src inhibitor is applied, E2-induced apoptosis is initially blocked in MCF-7:5C cells [18], but with extended treatment, E2-stimulated growth re-emerges [19]. A stable cell line, MCF-7:PF is established [19], [20]. Unexpectedly, the derived cell line MCF-7:PF was found to mimic the SERM/E2-stimulated models in vivo [6], thereby providing the opportunity to decipher the mechanism of SERM-stimulated growth. Here, we provide evidence that 4-hydroxytamoxifen (4-OHT)-stimulated growth of MCF-7:PF is ER-dependent despite suppression of classical ER-target genes. However, 4-OHT functions as an agonist to enhance the non-genomic activity of ER and activates focal adhesion molecules to further increase phosphorylation of insulin-like growth factor-1 receptor beta (IGF-1Rβ). All of these events promote 4-OHT-stimulated cell growth. Overall, the sustained inhibition of nuclear ER-signalling causes broad activation of membrane-associated signalling to aid breast cancer cell survival during the selection process required for acquired TAM resistance.
Section snippets
Materials
Estradiol and focal adhesion kinase (FAK) inhibitor (PF573228) were purchased from Sigma–Aldrich (St. Louis, MO); ICI 182,780 (ICI) was purchased from Tocris (Park Ellisville, MO). SERMs: 4-hydroxytamoxifen (4-OHT) was purchased from Sigma–Aldrich (St. Louis, MO), raloxifene was a kind gift from Eli Lilly (Indianapolis, IN), endoxifen was gifted from Dr. James Ingle (Mayo Clinic, Rochester, MN), bazedoxifene (BZA) was gifted from Dr. Ronald Grigg (University of Leeds, United Kingdom (UK)),
The ER agonist activity of SERMs is significantly elevated in MCF-7:PF cells
Our recent publication shows the proliferative response to E2 in the selected and reprogrammed cell line, MCF-7:PF, occurs in an ER-dependent manner [19]. Here, we addressed the question of whether SERMs could block E2-stimulated growth. In long-term E2-deprived MCF-7:5C cells (simulating AI resistance), no SERM had an inhibitory effect except for bazedoxifene (BZA) [22], whereas all SERMs significantly stimulated cell growth in MCF-7:PF cells (Fig. 1A). Raloxifene did not stimulate MCF-7:PF
Discussion
Compelling evidence has shown that phosphorylation of c-Src is elevated in endocrine resistant cell models [29], [30], [31]. Our observation also demonstrates that phosphorylation of c-Src is enhanced in two E2-deprived breast cancer cell lines, MCF-7:5C and MCF-7:2A [32]. Further investigation reveals that c-Src plays a critical role in the mediation of stress responses which include oxidative stress, inflammatory stress and endoplasmic reticulum stress by E2 [18]. Thus, E2-induced apoptosis
Conflict of interest statement
None declared.
Acknowledgements
VCJ is supported by the Department of Defense Breast Program under Award number W81XWH-06-1-0590 Center of Excellence; subcontract under the SU2C (AACR) Grant number SU2C-AACR-DT0409; the Susan G. Komen for the Cure Foundation under Award number SAC100009; GHUCCTS CTSA (Grant # UL1RR031975) and the Lombardi Comprehensive Cancer Center Support Grant (CCSG) Core Grant NIH P30 CA051008. We are particularly grateful to the Avon Foundation for supporting this work.
References (47)
Tamoxifen as the first targeted long-term adjuvant therapy for breast cancer
Endocr Relat Cancer
(2014)- et al.
Relevance of breast cancer hormone receptors and other factors to the efficacy of adjuvant tamoxifen: patient-level meta-analysis of randomised trials
Lancet
(2011) - et al.
Long-term effects of continuing adjuvant tamoxifen to 10 years versus stopping at 5 years after diagnosis of oestrogen receptor-positive breast cancer: ATLAS, a randomised trial
Lancet
(2013) - et al.
Meta-analysis of breast cancer outcomes in adjuvant trials of aromatase inhibitors versus tamoxifen
J Clin Oncol
(2010) - et al.
Efficacy of letrozole extended adjuvant therapy according to estrogen receptor and progesterone receptor status of the primary tumor: National Cancer Institute of Canada Clinical Trials Group MA.17
J Clin Oncol
(2007) - et al.
Development of tamoxifen-stimulated growth of MCF-7 tumors in athymic mice after long-term antiestrogen administration
Cancer Res
(1988) - et al.
Differential ability of antiestrogens to stimulate breast cancer cell (MCF-7) growth in vivo and in vitro
Cancer Res
(1989) - et al.
Antitumor action of physiological estradiol on tamoxifen-stimulated breast tumors grown in athymic mice
Clin Cancer Res
(2000) The 38th David A. Karnofsky lecture: the paradoxical actions of estrogen in breast cancer–survival or death?
J Clin Oncol
(2008)- et al.
Estrogen induces apoptosis in estrogen deprivation-resistant breast cancer through stress responses as identified by global gene expression across time
Proc Natl Acad Sci USA
(2011)
Randomized clinical trial of diethylstilbestrol versus tamoxifen in postmenopausal women with advanced breast cancer
N Engl J Med
Double-blind, randomized trial comparing the efficacy and tolerability of fulvestrant versus anastrozole in postmenopausal women with advanced breast cancer progressing on prior endocrine therapy: results of a North American trial
J Clin Oncol
Fulvestrant, formerly ICI 182,780, is as effective as anastrozole in postmenopausal women with advanced breast cancer progressing after prior endocrine treatment
J Clin Oncol
Intrinsic mechanism of estradiol-induced apoptosis in breast cancer cells resistant to estrogen deprivation
J Natl Cancer Inst
Effect of long-term estrogen deprivation on apoptotic responses of breast cancer cells to 17beta-estradiol
J Natl Cancer Inst
Lower-dose vs high-dose oral estradiol therapy of hormone receptor-positive, aromatase inhibitor-resistant advanced breast cancer: a phase 2 randomized study
JAMA
Conjugated equine oestrogen and breast cancer incidence and mortality in postmenopausal women with hysterectomy: extended follow-up of the Women’s Health Initiative randomised placebo-controlled trial
Lancet Oncol
c-Src modulates estrogen-induced stress and apoptosis in estrogen-deprived breast cancer cells
Cancer Res
Inhibition of c-Src blocks oestrogen-induced apoptosis and restores oestrogen-stimulated growth in long-term oestrogen-deprived breast cancer cells
Eur J Cancer
Acquired resistance to selective estrogen receptor modulators (SERMs) in clinical practice (tamoxifen & raloxifene) by selection pressure in breast cancer cell populations
Steroids
Molecular mechanism of action of bisphenol and bisphenol A mediated by oestrogen receptor alpha in growth and apoptosis of breast cancer cells
Br J Pharmacol
The selective estrogen receptor modulator bazedoxifene inhibits hormone-independent breast cancer cell growth and down-regulates estrogen receptor α and cyclin D1
Mol Pharmacol
Pharmacological characterization of 4-hydroxy-N-desmethyl tamoxifen, a novel active metabolite of tamoxifen
Breast Cancer Res Treat
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Current address: Department of Pathology, Dunedin School of Medicine, Dunedin 9054, New Zealand.