Current Stem Cell Reports (2018) 4:81–94 https://doi.org/10.1007/s40778-018-0114-z CELL:CELL INTERACTIONS IN STEM CELL MAINTENANCE (D BONNET, SECTION EDITOR) The Role of Steroid Hormones in Breast and Effects on Cancer Stem Cells Denis G. Alferez1 & Bruno M. Simões1 & Sacha J. Howell1,2 & Robert B. Clarke1 Published online: 13 March 2018 # The Author(s) 2018 Abstract Purpose of Review This review will discuss how the steroid hormones, estrogen and progesterone, as well as treatments that target steroid receptors, can regulate cancer stem cell (CSC) activity. The CSC theory proposes a hierarchical organization in tumors where at its apex lies a subpopulation of cancer cells endowed with self-renewal and differentiation capacity. Recent Findings In breast cancer (BC), CSCs have been suggested to play a key role in tumor maintenance, disease progression, and the formation of metastases. In preclinical models of BC, only a few CSCs are required sustain tumor re-growth, especially after conventional anti-endocrine treatments. CSCs include therapy-resistant clones that survive standard of care treatments like chemotherapy, irradiation, and hormonal therapy. Summary The relevance of hormones for both normal mammary gland and BC development is well described, but it was only recently that the activities of hormones on CSCs have been investigated, opening new directions for future BC treatments and CSCs. Keywords Progenitor . Biomarker . Signal pathway . Therapy resistance . Breast cancer stem cells Introduction lineage− (named CD44+/CD24−/lo henceforth) cells (Table 1), isolated from human breast tumors by fluorescence activated The cancer stem cell (CSC) concept proposes a hierarchical cell sorting (FACS), were enriched for CSCs that were ade- organization of the cells within a tumor, where only a small quate to seed tumors in immune-deficient mice [14]. CD44+/ subset of cells, the CSCs, drives and sustains tumor growth. In CD24−/lo cells were serially passaged and gave rise to tumors preclinical studies using breast cancer models, CSCs are de- containing both CSCs (CD44+/CD24−/lo) and non-CSCs, sug- fined as self-renewing cells that can propagate the tumor, gesting self-renewal and differentiation, respectively. Breast which makes them very important in the processes of tumor cancers with high CD44 and low CD24 have been associated recurrence, metastasis, and resistance to therapy. These roles with the triple negative subtype (negative for estrogen recep- make them an important therapeutic target [1]. tor (ER), progesterone receptor (PR), and HER2 receptor) and The first report providing evidence for the presence of with poorer prognosis [15, 16]. breast CSCs (BCSCs) observed that CD44+/CD24low/ESA+/ Other strategies have also been used to identify BCSC enriched populations. Mammosphere formation, high alde- hyde dehydrogenase (ALDH) activity, and CD49f or CD133 This article is part of the Topical Collection on Cell:Cell Interactions in expression are properties that have been utilized to isolate Stem Cell Maintenance CSCs (Table 1). The mammosphere colony assay tests the capacity of BCSCs to survive in non-adherent culture condi- * Denis G. Alferez [email protected] tions and to form spherical colonies, called mammospheres [17–19]. The activity of ALDH1, which retinaldehyde to retinoic acid, is detected by an enzymatic assay 1 Breast Biology Group, Division of Cancer Sciences, School of (ALDEFLUOR) and flow cytometry [20]. The proportion of Medical Sciences, Faculty of Biology, Medicine, and Health, Manchester Cancer Research Centre, Wilmslow Road, cells with ALDH1 expression in breast cancer has been shown Manchester M20 4GJ, UK to correlate with poor prognosis [20–22]. Finally, CD49f and 2 Department of Medical Oncology, The University of Manchester, CD133 (Table 1) have recently been shown to enrich for CSCs The Christie NHS Foundation Trust, Manchester M20 4BX, UK in chemotherapy resistant triple negative and endocrine- 82 Curr Stem Cell Rep (2018) 4:81–94 Table 1 Markers of breast cancer stem cells Markers and reference Epitope function Expression in preclinical Expression in cancer Essays used to models subtypes evaluate activity CD44+/CD24−/low/EpCAM+ [2] CD44 is a ubiquitously Not detected in MCF7, T47D, Significantly In vitro CD44+/CD24−/low/EpCAM+/Lin− expressed receptor for ZR75,SKBR3,and associated with proliferation, hyaluronan and exerts MDA-MB-468 basal-like and migration, control over cell growth, luminal B subtypes, invasion, migration, and tumor but the inverse colony progression. associated with formation. CD44+/CD24−/low/Lin− CD24, also known as heat Highly expressed in luminal A [3]. In vivo tumor stable antigen (HSA), a MDA-MB-231, formation sialoprotein that is expressed MDA-MB-361, HCC1937 studies on B cells, T cells, keratinocytes, and myofiber synaptic nuclei and is upregulated in a wide variety of cancers. ALDH1+ [4] Aldehyde dehydrogenases Highly expressed in Significantly In vivo tumor ALDH1+/CD44+/CD24− (ALDHs) detoxify aldehydes MDA-MB-468, associated with formation by oxidizing them to MDA-MB-231, HCC1937, HER2+ and studies. carboxylic acids. ALDH1A1 SKBR3, MCF7, ZR75 [5]. basal-Like BC, but is a cytosolic enzyme that Not detected in T47D, negative associated preferentially oxidizes MDA-MB-361 [5]. Detected with luminal A [3]. retinaldehyde to retinoic in BT-20, MDA-MB-157, acid. and MDA-MB-231 [6]. CD133+ [7••, CD133 (also known as Highly expressed in Significantly In vivo tumor 8, prominin 1) is a plasma MDA-MB-468. Not associated staining formation 9] membrane protein known to detected in MCF-7, T47D, in Triple negative studies be expressed on neural stem ZR75, SKBR3, (71%) [9]. Mediating cells and hematopoietic stem MDA-MB-231, Low expression metastatic cells.CD133highcellsmay MDA-MB-361, and (staining) in Her2+ progression. predict for refractory HCC1937 [5]. (38%) and Luminal metastatic disease following Not detected in: BT-20 and (26%) tumors [9]. neoadjuvant endocrine MDA-MB-157 [6]. therapy. Detected in MCF-7 ER-low, Associated with higher MCF-7 + Fulv, ZR75 + Fulv self-renewal potential and and in a Resistant vascular mimicry. PDX-TamR [7••]. Associated with CSC in Brca1Δ11p53+/− mammary tumors CD24+/CD29high [10] Integrin beta-1/CD29: A MMTV-wnt (Balb-C) mice NA Tumor membrane receptors formation involved in cell adhesion and studies recognition in a variety of processes including embryogenesis, hemostasis, tissue repair, immune response, and metastatic diffusion of tumor cells CD24+/CD29−/low/CD61+ Integrin beta-3 (β3)/CD61: CSC population in MMTV-wnt NA integral cell-surface proteins (Balb-C) tumors known to participate in cell Half of the CSC population in adhesion as well as BALB/c-p53+/− cell-surface-mediated signaling. CD24+/CD29+/CD49f+ [11, 12] Integrin alpha-6/CD49f: a cell CSC population in NA surface proteins integral Brca1-mutant cell-surface involved in cell primary mammary adhesion as well as tumors(Balb-C) cell-surface mediated signaling. CD49f has novel and dynamic roles in Curr Stem Cell Rep (2018) 4:81–94 83 Table 1 (continued) Markers and reference Epitope function Expression in preclinical Expression in cancer Essays used to models subtypes evaluate activity regulating the differentiation potential of hMSCs and maintaining pluripotency Tumor formation, migration, and metastasis studies CD24high/CD49fhigh/DNERhigh [13] DNER: Delta and Notch-like Epithelial cells from Colony CD24high/CD49fhigh/DLL1high epidermal growth reductive formation factor-related receptor mammoplasties. Sphere-form- CD49f+/DLL1high/DNERhigh DLL1: a member of the ing study delta/serrate/jagged family In vivo tumor involved in cell-to-cell formation communication studies Basal-like cell lines including MDA-MB-468, MDA-MB-231, and HCC1937; luminal-like cell lines such as T47D, MCF-7, ZR-75, and SKBR-3 EpCAM epithelial cell adhesion molecule, ALDH aldehyde dehydrogenase, Fulv fulvestrant, BC breast cancer, CSC cancer stem cell resistant breast cancer, respectively [7••, 23]. The establish- physiological form of estrogen, than does ERβ [29]. ment of BCSC markers suitable for all tumors is hindered by Transcription factors need nuclear receptor co-regulators to intra-tumor and inter-tumor heterogeneity of CSC mediate their action on target DNA sequences; in this case, populations. ER signaling is dependent on FOXA1 expression, which pro- At the present time, the most robust enrichment for BCSCs motes local DNA unwinding facilitating the access of ER to is achieved through the use of CD44+/CD24−/lo and ALDH+. DNA [30]. These two cell populations have been demonstrated to mark Around three out of four breast tumors express ERα.Its BCSCs in different states and with gene expression resem- expression is associated with luminal differentiation markers bling either mesenchymal (CD44+/CD24−/lo cells) or epitheli- and with a more favorable breast cancer prognosis and is the al characteristics (ALDH+ cells) [24]. A small overlapping most important breast cancer predictive factor for endocrine population of cells which is both CD44+/CD24−/lo and responsiveness [31, 32]. Exposure to high levels of estrogen ALDH+ was identified, which suggested that BCSCs possess during women’s lifetime is established to be associated with cellular plasticity and can dynamically switch between mes- increased risk of postmenopausal breast cancer [33]. enchymal and epithelial states. The epithelial–mesenchymal However, exogenous estrogen used as hormone replacement transition and vice-versa (mesenchymal–epithelial