Endocrinology and hormone therapy in breast cancer: New insight into estrogen receptor-α function and its implication for endocrine therapy resistance in breast cancer

Recently multiple data accumulated concerning mutations in the ESR1 gene coding estrogen receptor α (mutESR1) and in the LYN gene coding non receptor tyrosine kinase SRC family member (mutLYN) that are associated with endocrine therapy resistance and that could be considered as markers of endocrine therapy efficiency. In case of gynecologic cancers including ovarian cancer the most frequent mutESR1 are ESR1L536H/P/R/V , ESR1Y537S/N/C/H, ESR1D538G that emerge in the course of hormonotherapy especially using aromatase inhibitors. mutLYN including LYNE159K, LYND189Y, LYNK209N, LYNA370T, LYNG418R, LYNA503D are also identified. mutESR1 and mutLYN increase transcriptional activity of estrogen receptor α (ERα) coded with ESR1 gene and catalytic activity of LYN kinase inducing endocrine therapy resistance. Interdependence of ESR1 and LYN genes is revealed at the level of proteins that they code as the kinases of the SRC family including LYN activate ERα-dependent transcription due to the phosphorylation of ERα at Y537 amino-acid residue that is the most frequently mutated in tumors with endocrine therapy resistance. The aim of the review is revealing the clinical correlations of mutESR1 and mutLYN with the ovarian cancer endocrine therapy resistance that opens perspectives of mutESR1 and mutLYN use as new predictive markers of ovarian cancer and development of more efficient anti-tumor medicaments. In the review the information obtained from PubMed database for the last 20 years using the following key words: ESR1, LYN, mutation(s), estrogen receptor α (ERα), LYN kinase, SRC family kinases, ovarian cancer, gynecologic(al) cancer is discussed.

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The Central Contributions of Breast Cancer Stem Cells in Developing Resistance to Endocrine Therapy in Estrogen Receptor (ER)-Positive Breast Cancer

Cancers ◽

10.3390/cancers11071028 ◽

2019 ◽

Vol 11 (7) ◽

pp. 1028 ◽

Cited By ~ 19

Author(s):

David Rodriguez ◽

Marc Ramkairsingh ◽

Xiaozeng Lin ◽

Anil Kapoor ◽

Pierre Major ◽

...

Keyword(s):

Breast Cancer ◽

Stem Cells ◽

Estrogen Receptor ◽

Cancer Stem Cells ◽

Hormone Therapy ◽

Endocrine Therapy ◽

Endocrine Resistance ◽

Therapy Resistance ◽

Breast Cancer Stem Cells ◽

Er Positive

Breast cancer stem cells (BCSC) play critical roles in the acquisition of resistance to endocrine therapy in estrogen receptor (ER)-positive (ER + ve) breast cancer (BC). The resistance results from complex alterations involving ER, growth factor receptors, NOTCH, Wnt/β-catenin, hedgehog, YAP/TAZ, and the tumor microenvironment. These mechanisms are likely converged on regulating BCSCs, which then drive the development of endocrine therapy resistance. In this regard, hormone therapies enrich BCSCs in ER + ve BCs under both pre-clinical and clinical settings along with upregulation of the core components of “stemness” transcriptional factors including SOX2, NANOG, and OCT4. SOX2 initiates a set of reactions involving SOX9, Wnt, FXY3D, and Src tyrosine kinase; these reactions stimulate BCSCs and contribute to endocrine resistance. The central contributions of BCSCs to endocrine resistance regulated by complex mechanisms offer a unified strategy to counter the resistance. ER + ve BCs constitute approximately 75% of BCs to which hormone therapy is the major therapeutic approach. Likewise, resistance to endocrine therapy remains the major challenge in the management of patients with ER + ve BC. In this review we will discuss evidence supporting a central role of BCSCs in developing endocrine resistance and outline the strategy of targeting BCSCs to reduce hormone therapy resistance.

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Abstract 1033: Estrogen receptor gene fusions drive endocrine therapy resistance in estrogen receptor positive breast cancer

10.1158/1538-7445.am2017-1033 ◽

2017 ◽

Author(s):

Jonathan T. Lei ◽

Jieya Shao ◽

Jin Zhang ◽

Michael Iglesia ◽

Doug W. Chan ◽

...

Keyword(s):

Breast Cancer ◽

Estrogen Receptor ◽

Endocrine Therapy ◽

Receptor Gene ◽

Therapy Resistance ◽

Gene Fusions ◽

Estrogen Receptor Gene ◽

Endocrine Therapy Resistance ◽

Estrogen Receptor Positive ◽

Positive Breast Cancer

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Estrogen-regulated feedback loop limits the efficacy of estrogen receptor–targeted breast cancer therapy

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1722617115 ◽

2018 ◽

Vol 115 (31) ◽

pp. 7869-7878 ◽

Cited By ~ 19

Author(s):

Tengfei Xiao ◽

Wei Li ◽

Xiaoqing Wang ◽

Han Xu ◽

Jixin Yang ◽

...

Keyword(s):

Breast Cancer ◽

Estrogen Receptor ◽

Endocrine Therapy ◽

Negative Feedback ◽

Feedback Loop ◽

Therapy Resistance ◽

Negative Feedback Loop ◽

Endocrine Therapy Resistance ◽

Estrogen Receptor Positive ◽

Underlying Mechanisms

Endocrine therapy resistance invariably develops in advanced estrogen receptor-positive (ER+) breast cancer, but the underlying mechanisms are largely unknown. We have identified C-terminal SRC kinase (CSK) as a critical node in a previously unappreciated negative feedback loop that limits the efficacy of current ER-targeted therapies. Estrogen directly drives CSK expression in ER+ breast cancer. At low CSK levels, as is the case in patients with ER+ breast cancer resistant to endocrine therapy and with the poorest outcomes, the p21 protein-activated kinase 2 (PAK2) becomes activated and drives estrogen-independent growth. PAK2 overexpression is also associated with endocrine therapy resistance and worse clinical outcome, and the combination of a PAK2 inhibitor with an ER antagonist synergistically suppressed breast tumor growth. Clinical approaches to endocrine therapy-resistant breast cancer must overcome the loss of this estrogen-induced negative feedback loop that normally constrains the growth of ER+ tumors.

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Long Non-Coding RNA H19 Acts as an Estrogen Receptor Modulator that is Required for Endocrine Therapy Resistance in ER+ Breast Cancer Cells

Cellular Physiology and Biochemistry ◽

10.1159/000495643 ◽

2018 ◽

Vol 51 (4) ◽

pp. 1518-1532 ◽

Cited By ~ 16

Author(s):

Pratima Basak ◽

Sumanta Chatterjee ◽

Vasudeva Bhat ◽

Alice Su ◽

Hyerang Jin ◽

...

Keyword(s):

Breast Cancer ◽

Estrogen Receptor ◽

Cancer Cells ◽

Endocrine Therapy ◽

Breast Cancer Cells ◽

Therapy Resistance ◽

Receptor Signaling ◽

Met Receptor ◽

Endocrine Therapy Resistance ◽

Organoid Cultures

Background/Aims: Blocking estrogen signaling with endocrine therapies (Tamoxifen or Fulverstrant) is an effective treatment for Estrogen Receptor-α positive (ER+) breast cancer tumours. Unfortunately, development of endocrine therapy resistance (ETR) is a frequent event resulting in disease relapse and decreased overall patient survival. The long noncoding RNA, H19, was previously shown to play a significant role in estrogen-induced proliferation of both normal and malignant ER+ breast epithelial cells. We hypothesized that H19 expression is also important for the proliferation and survival of ETR cells. Methods: Here we utilized established ETR cell models; the Tamoxifen (Tam)-resistant LCC2 and the Fulvestrant and Tam cross-resistant LCC9 cells. Gain and loss of H19 function were achieved through lentiviral transduction as well as pharmacological inhibitors of the Notch and c-Met receptor signaling pathways. The effects of altered H19 expression on cell viability and ETR were assessed using three-dimensional (3D) organoid cultures and 2D co-cultures with low passage tumour-associated fbroblasts (TAFs). Results: Here we report that treating ETR cells with Tam or Fulvestrant increases H19 expression and that it’s decreased expression overcomes resistance to Tam and Fulvestrant in these cells. Interestingly, H19 expression is regulated by Notch and HGF signaling in the ETR cells and pharmacological inhibitors of Notch and c-MET signaling together significantly reverse resistance to Tam and Fulvestrant in an H19-dependent manner in these cells. Lastly, we demonstrate that H19 regulates ERα expression at the transcript and protein levels in the ETR cells and that H19 protects ERα against Fulvestrant-mediated downregulation of ERα protein. We also observed that blocking Notch and the c-MET receptor signaling also overcomes Fulvestrant and Tam resistance in 3D organoid cultures by decreasing ERα and H19 expression in the ETR cells. Conclusion: In endocrine therapy resistant breast cancer cells Fulvestrant is ineffective in decreasing ERα levels. Our data suggest that in the ETR cells, H19 expression acts as an ER modulator and that its levels and subsequently ERα levels can be substantially decreased by blocking Notch and c-MET receptor signaling. Consequently, treating ETR cells with these pharmacological inhibitors helps overcome resistance to Fulvestrant and Tamoxifen.

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