Glucocorticoid resistance of migration and gene expression in a daughter MDA-MB-231 breast tumour cell line selected for high metastatic potential

A semiconductor 96-microplate platform for electrical-imaging based high-throughput phenotypic screening

High-content imaging for compound and genetic profiling is popular for drug discovery but limited to endpoint images of fixed cells. Conversely, electronic-based devices offer label-free, live cell functional information but suffer from limited spatial resolution or throughput. Here, we introduce a semiconductor 96-microplate platform for high-resolution, real-time impedance imaging. Each well features 4096 electrodes at 25 µm spatial resolution and a miniaturized data interface allows 8× parallel plate operation (768 total wells) for increased throughput. Electric field impedance measurements capture >20 parameter images including cell barrier, attachment, flatness, and motility every 15 min during experiments. We apply this technology to characterize 16 cell types, from primary epithelial to suspension cells, and quantify heterogeneity in mixed co-cultures. Screening 904 compounds across 13 semiconductor microplates reveals 25 distinct responses, demonstrating the platform's potential for mechanism of action profiling. The scalability and translatability of this semiconductor platform expands high-throughput mechanism of action profiling and phenotypic drug discovery applications.

Weakly migratory metastatic breast cancer cells activate fibroblasts via microvesicle-Tg2 to facilitate dissemination and metastasis

Cancer cell migration is highly heterogeneous, and the migratory capability of cancer cells is thought to be an indicator of metastatic potential. It is becoming clear that a cancer cell does not have to be inherently migratory to metastasize, with weakly migratory cancer cells often found to be highly metastatic. However, the mechanism through which weakly migratory cells escape from the primary tumor remains unclear. Here, utilizing phenotypically sorted highly and weakly migratory human breast cancer cells, we demonstrate that weakly migratory metastatic cells disseminate from the primary tumor via communication with stromal cells. While highly migratory cells are capable of single cell migration, weakly migratory cells rely on cell-cell signaling with fibroblasts to escape the primary tumor. Weakly migratory cells release microvesicles rich in tissue transglutaminase 2 (Tg2) which activate murine fibroblasts and lead weakly migratory cancer cell migration in vitro. These microvesicles also induce tumor stiffening and fibroblast activation in vivo and enhance the metastasis of weakly migratory cells. Our results identify microvesicles and Tg2 as potential therapeutic targets for metastasis and reveal a novel aspect of the metastatic cascade in which weakly migratory cells release microvesicles which activate fibroblasts to enhance cancer cell dissemination.

Reduction of Metastasis via Epigenetic Modulation in a Murine Model of Metastatic Triple Negative Breast Cancer (TNBC)

This study investigates the effects of a dual selective Class I histone deacetylase (HDAC)/lysine-specific histone demethylase 1A (LSD1) inhibitor known as 4SC-202 (Domatinostat) on tumor growth and metastasis in a highly metastatic murine model of Triple Negative Breast Cancer (TNBC). 4SC-202 is cytotoxic and cytostatic to the TNBC murine cell line 4T1 and the human TNBC cell line MDA-MB-231; the drug does not kill the normal breast epithelial cell line MCF10A. Furthermore, 4SC-202 reduces cancer cell migration. In vivo studies conducted in the syngeneic 4T1 model, which closely mimics human TNBC in terms of sites of metastasis, reveal reduced tumor burden and lung metastasis. The mechanism of action of 4SC-202 may involve effects on cancer stem cells (CSC) which can self-renew and form metastatic lesions. Approximately 5% of the total 4T1 cell population grown in three-dimensional scaffolds had a distinct CD44high/CD24low CSC profile which decreased after treatment. Bulk transcriptome (RNA) sequencing analyses of 4T1 tumors reveal changes in metastasis-related pathways in 4SC-202-treated tumors, including changes to expression levels of genes implicated in cell migration and cell motility. In summary, 4SC-202 treatment of tumors from a highly metastatic murine model of TNBC reduces metastasis and warrants further preclinical studies.

Mechanisms behind context-dependent role of glucocorticoids in breast cancer progression

Glucocorticoids (GCs), mostly dexamethasone (dex), are routinely administered as adjuvant therapy to manage side effects in breast cancer. However, recently, it has been revealed that dex triggers different effects and correlates with opposite outcomes depending on the breast cancer molecular subtype. This has raised new concerns regarding the generalized use of GC and suggested that the context-dependent effects of GCs can be taken into potential consideration during treatment design. Based on this, attention has recently been drawn to the role of the glucocorticoid receptor (GR) in development and progression of breast cancer. Therefore, in this comprehensive review, we aimed to summarize the different mechanisms behind different context-dependent GC actions in breast cancer by applying a multilevel examination, starting from the association of variants of the GR-encoding gene to expression at the mRNA and protein level of the receptor, and its interactions with other factors influencing GC action in breast cancer. The role of GCs in chemosensitivity and chemoresistance observed during breast cancer therapy is discussed. In addition, experiences using GC targeting therapeutic options (already used and investigated in preclinical and clinical trials), such as classic GC dexamethasone, selective glucocorticoid receptor agonists and modulators, the GC antagonist mifepristone, and GR coregulators, are also summarized. Evidence presented can aid a better understanding of the biology of context-dependent GC action that can lead to further advances in the personalized therapy of breast cancer by the evaluation of GR along with the conventional estrogen receptor (ER) and progesterone receptor (PR) in the routine diagnostic procedure.

High-throughput microfluidic compressibility cytometry using multi-tilted-angle surface acoustic wave

Cellular mechanical properties (e.g. compressibility) are important biophysical markers in relation to cellular processes and functionality. Among the methods for cell mechanical measurement, acoustofluidic methods appear to be advantageous due to tunability, biocompatibility and acousto-mechanical nature. However, the previous acoustofluidic methods were limited in throughput and number of measurements. In this study, we developed a high-throughput microfluidic compressibility cytometry approach using multi-tilted-angle surface acoustic wave, which can provide thousands of single-cell compressibility measurements within minutes. The compressibility cytometer was constructed to drag microparticles or cells towards the microfluidic channel sidewall at different segments based on their biophysical properties (such as size and compressibility), as a result of the varied balance between acoustics and flow. Mathematical analysis and computational simulation revealed that the compressibility of a cell could be estimated from the position of collision with the sidewall. Microbeads of different materials and sizes were experimentally tested to validate the simulation and to demonstrate the capability to characterise size and compressibility. MDA MB231 cells, of the triple negative breast cancer subtype, were treated with the microtubule disrupting agent colchicine which increased compressibility and treated with the actin disrupting agent cytochalasin B which increased cell size but did not change compressibility. Moreover, the highly metastatic variant MDA MB231 LNm5 cell line showed increased compressibility compared to the parent MDA MB231 cells, indicating the potential utility of high-throughput mechanophenotyping for tumour cell characterisation.

Annexin A1 Is Required for Efficient Tumor Initiation and Cancer Stem Cell Maintenance in a Model of Human Breast Cancer

Simple Summary

Triple-negative breast cancer (TNBC) has a poor outcome compared to the other major breast cancer subtypes and new therapies are needed. We sought to clarify the functions of a ubiquitous protein, Annexin A1, in the development and progression of TNBC. We found that Annexin A1 expression correlated with poor patient prognosis in basal-like breast tumors and also in the basal like-2 subset of TNBCs. Stable knockdown of Annexin A1 attenuated the growth of SUM149 xenografts, which model basal-like 2 tumors. In a polyoma middle T antigen-driven allograft model of breast cancer, Annexin A1 depletion markedly delayed tumor formation, induced epithelial to mesenchymal transition and upregulated basal markers. Finally, loss of Annexin A1 resulted in the loss of a discrete CD24⁺/Sca1⁻ population containing putative tumor-initiating cells. Collectively, our data demonstrate a novel cell-autonomous role for Annexin A1 in the promotion of tumor-forming capacity in certain TNBC tumors.

Abstract

Triple-negative breast cancer (TNBC) has a poor outcome compared to other breast cancer subtypes, and new therapies that target the molecular alterations driving tumor progression are needed. Annexin A1 is an abundant multi-functional Ca²⁺ binding and membrane-associated protein. Reported roles of Annexin A1 in breast cancer progression and metastasis are contradictory. Here, we sought to clarify the functions of Annexin A1 in the development and progression of TNBC. The association of Annexin A1 expression with patient prognosis in subtypes of TNBC was examined. Annexin A1 was stably knocked down in a panel of human and murine TNBC cell lines with high endogenous Annexin A1 expression that were then evaluated for orthotopic growth and spontaneous metastasis in vivo and for alterations in cell morphology in vitro. The impact of Annexin A1 knockdown on the expression of genes involved in mammary epithelial cell differentia tion and epithelial to mesenchymal transition was also determined. Annexin A1 mRNA levels correlated with poor patient prognosis in basal-like breast tumors and also in the basal-like 2 subset of TNBCs. Unexpectedly, loss of Annexin A1 expression had no effect on either primary tumor growth or spontaneous metastasis of MDA-MB-231_HM xenografts, but abrogated the growth rate of SUM149 orthotopic tumors. In an MMTV-PyMT driven allograft model of breast cancer, Annexin A1 depletion markedly delayed tumor formation in both immuno-competent and immuno-deficient mice and induced epithelial to mesenchymal transition and upregulation of basal markers. Finally, loss of Annexin A1 resulted in the loss of a discrete CD24⁺/Sca1⁻ population containing putative tumor initiating cells. Collectively, our data demonstrate a novel cell-autonomous role for Annexin A1 in the promotion of tumor-forming capacity in a model of human breast cancer and suggest that some basal-like TNBCs may require high endogenous tumor cell Annexin A1 expression for continued growth.

The In Vivo Selection Method in Breast Cancer Metastasis

Metastasis is a complex event in cancer progression and causes most deaths from cancer. Repeated transplantation of metastatic cancer cells derived from transplanted murine organs can be used to select the population of highly metastatic cancer cells; this method is called as in vivo selection. The in vivo selection method and highly metastatic cancer cell lines have contributed to reveal the molecular mechanisms of cancer metastasis. Here, we present an overview of the methodology for the in vivo selection method. Recent comparative analysis of the transplantation methods for metastasis have revealed the divergence of metastasis gene signatures. Even cancer cells that metastasize to the same organ show various metastatic cascades and gene expression patterns by changing the transplantation method for the in vivo selection. These findings suggest that the selection of metastasis models for the study of metastasis gene signatures has the potential to influence research results. The study of novel gene signatures that are identified from novel highly metastatic cell lines and patient-derived xenografts (PDXs) will be helpful for understanding the novel mechanisms of metastasis.

Effect of dexamethasone on the antileukemic effect of cytarabine: role of deoxycytidine kinase

Dexamethasone (DEX) is often used in the initial treatment of leukemia. Earlier we demonstrated that DEX decreased the activity of deoxycytidine kinase (dCK) which is essential for the activation of cytarabine (ara-C). Therefore we investigated the effect of DEX on the in vivo sensitivity of acute myeloid leukemia (AML) to ara-C and another deoxycytidine analog, gemcitabine, in the Brown Norway Myeloid Leukemia (BNML) rat model for AML, and its ara-C resistant variant B-araC, in relation to the effects on dCK activity.The antileukemic effect was evaluated as survival of the rats, while dCK activity was measured in leukemic spleen (completely consisting of BNML cells) with liver as representative normal tissue, 24 hr after treatment with ara-C or DEX with radioactive deoxycytidine (CdR) as a substrate.Treatment with ara-C increased life-span of BNML by 200%, which was not affected by DEX. Gemcitabine was ineffective. In the liver of BNML bearing rats DEX decreased dCK activity 33%, while ara-C increased dCK activity slightly (to 129%), but in the combination of ara-C/DEX dCK activity was also decreased. In the livers of Bara-C bearing rats dCK was 2.7-fold higher compared to BNML rats, which was increased 179% in the gemcitabine-DEX treated rats. In BNML leukemic spleens DEX decreased dCK activity 41% and gem/dex 46%, but ara-C increased dCK activity to 123%, but in the combination this effect was neutralized. In Bara-C spleens only ara-C/dex decreased dCK activity (32%).In conclusion; in an AML rat model DEX did not affect the antileukemic effect of ara-C, nor the dCK activity.

Glucocorticoids rapidly inhibit cell migration through a novel, non-transcriptional HDAC6 pathway

Glucocorticoids (GCs) act through the glucocorticoid receptor (GR, also known as NR3C1) to regulate immunity, energy metabolism and tissue repair. Upon ligand binding, activated GR mediates cellular effects by regulating gene expression, but some GR effects can occur rapidly without new transcription. Here, we show that GCs rapidly inhibit cell migration, in response to both GR agonist and antagonist ligand binding. The inhibitory effect on migration is prevented by GR knockdown with siRNA, confirming GR specificity, but not by actinomycin D treatment, suggesting a non-transcriptional mechanism. We identified a rapid onset increase in microtubule polymerisation following GC treatment, identifying cytoskeletal stabilisation as the likely mechanism of action. HDAC6 overexpression, but not knockdown of αTAT1, rescued the GC effect, implicating HDAC6 as the GR effector. Consistent with this hypothesis, ligand-dependent cytoplasmic interaction between GR and HDAC6 was demonstrated by quantitative imaging. Taken together, we propose that activated GR inhibits HDAC6 function, and thereby increases the stability of the microtubule network to reduce cell motility. We therefore report a novel, non-transcriptional mechanism whereby GCs impair cell motility through inhibition of HDAC6 and rapid reorganization of the cell architecture.This article has an associated First Person interview with the first author of the paper.

Glucocorticoid receptors are required effectors of TGFβ1-induced p38 MAPK signaling to advanced cancer phenotypes in triple-negative breast cancer

BACKGROUND

Altered signaling pathways typify breast cancer and serve as direct inputs to steroid hormone receptor sensors. We previously reported that phospho-Ser134-GR (pS134-GR) species are elevated in triple-negative breast cancer (TNBC) and cooperate with hypoxia-inducible factors, providing a novel avenue for activation of GR in response to local or cellular stress.

METHODS

We probed GR regulation by factors (cytokines, growth factors) that are rich within the tumor microenvironment (TME). TNBC cells harboring endogenous wild-type (wt) or S134A-GR species were created by CRISPR/Cas knock-in and subjected to transwell migration, invasion, soft-agar colony formation, and tumorsphere assays. RNA-seq was employed to identify pS134-GR target genes that are regulated both basally (intrinsic) or by TGFβ1 in the absence of exogenously added GR ligands. Regulation of selected basal and TGFβ1-induced pS134-GR target genes was validated by qRT-PCR and chromatin immunoprecipitation assays. Bioinformatics tools were used to probe public data sets for expression of pS134-GR 24-gene signatures.

RESULTS

In the absence of GR ligands, GR is transcriptionally activated via p38-dependent phosphorylation of Ser134 as a mechanism of homeostatic stress-sensing and regulated upon exposure of TNBC cells to TME-derived agents. The ligand-independent pS134-GR transcriptome encompasses TGFβ1 and MAPK signaling gene sets associated with TNBC cell survival and migration/invasion. Accordingly, pS134-GR was essential for TNBC cell anchorage-independent growth in soft-agar, migration, invasion, and tumorsphere formation, an in vitro readout of cancer stemness properties. Both pS134-GR and expression of the MAPK-scaffolding molecule 14-3-3ζ were essential for a functionally intact p38 MAPK signaling pathway downstream of MAP3K5/ASK1, indicative of a feedforward signaling loop wherein self-perpetuated GR phosphorylation enables cancer cell autonomy. A 24-gene pS134-GR-dependent signature induced by TGFβ1 predicts shortened overall survival in breast cancer patients.

CONCLUSIONS

Phospho-S134-GR is a critical downstream effector of p38 MAPK signaling and TNBC migration/invasion, survival, and stemness properties. Our studies define a ligand-independent role for GR as a homeostatic "sensor" of intrinsic stimuli as well as extrinsic factors rich within the TME (TGFβ1) that enable potent activation of the p38 MAPK stress-sensing pathway and nominate pS134-GR as a therapeutic target in aggressive TNBC.

FGF13 promotes metastasis of triple-negative breast cancer

Triple-negative breast cancer (TNBC) represents 10-20% of all human ductal adenocarcinomas and has a poor prognosis relative to other subtypes, due to the high propensity to develop distant metastases. Hence, new molecular targets for therapeutic intervention are needed for TNBC. We recently conducted a rigorous phenotypic and genomic characterization of four isogenic populations of MDA-MB-231 human triple-negative breast cancer cells that possess a range of intrinsic spontaneous metastatic capacities in vivo, ranging from nonmetastatic (MDA-MB-231_ATCC) to highly metastatic to lung, liver, spleen and spine (MDA-MB-231_HM). Gene expression profiling of primary tumours by RNA-Seq identified the fibroblast growth factor homologous factor, FGF13, as highly upregulated in aggressively metastatic MDA-MB-231_HM tumours. Clinically, higher FGF13 mRNA expression was associated with significantly worse relapse free survival in both luminal A and basal-like human breast cancers but was not associated with other clinical variables and was not upregulated in primary tumours relative to normal mammary gland. Stable FGF13 depletion restricted in vitro colony forming ability in MDA-MB-231_HM TNBC cells but not in oestrogen receptor (ER)-positive MCF-7 or MDA-MB-361 cells. However, despite augmenting MDA-MB-231_HM cell migration and invasion in vitro, FGF13 suppression almost completely blocked the spontaneous metastasis of MDA-MB-231_HM orthotopic xenografts to both lung and liver while having negligible impact on primary tumour growth. Together, these data indicate that FGF13 may represent a therapeutic target for blocking metastatic outgrowth of certain TNBCs. Further evaluation of the roles of individual FGF13 protein isoforms in progression of the different subtypes of breast cancer is warranted.

MicroRNA-708 activation by glucocorticoid receptor agonists regulate breast cancer tumorigenesis and metastasis via downregulation of NF-κB signaling

Therapeutic administration of glucocorticoids (GCs) is frequently used as add-on chemotherapy for palliative purposes during breast cancer treatment. Recent studies have shown that GC treatment induces microRNA-708 in ovarian cancer cells, resulting in impaired tumor cell proliferation and metastasis. However, the regulatory functions of GCs on miR-708 and its downstream target genes in human breast cancer cells (BCCs) are poorly understood. In this study, we found that treatment with either the synthetic GC dexamethasone (DEX) or the natural GC mimic, antcin A (ATA) significantly increased miR-708 expression by transactivation of glucocorticoid receptor alpha (GRα) in MCF-7 and MDA-MB-231 human BCCs. Induction of miR-708 by GR agonists resulted in inhibition of cell proliferation, cell-cycle progression, cancer stem cell (CSC)-like phenotype and metastasis of BCCs. In addition, GR agonist treatment or miR-708 mimic transfection remarkably inhibited IKKβ expression and suppressed nuclear factor-kappaB (NF-κB) activity and its downstream target genes, including COX-2, cMYC, cyclin D1, Matrix metalloproteinase (MMP)-2, MMP-9, CD24, CD44 and increased p21CIP1 and p27KIP1 that are known to be involved in proliferation, cell-cycle progression, metastasis and CSC marker protein. BCCs xenograft models indicate that treatment with GR agonists significantly reduced tumor growth, weight and volume. Overall, our data strongly suggest that GR agonists induced miR-708 and downstream suppression of NF-κB signaling, which may be applicable as a novel therapeutic intervention in breast cancer treatment.

All-Trans Retinoic Acid Enhances Matrix Metalloproteinase 2 Expression and Secretion in Human Myeloid Leukemia THP-1 Cells

All-trans retinoic acid (ATRA) is an effective drug for the induction therapy of acute promyelocytic leukemia. However, the treatment is associated with adverse events such as retinoic acid syndrome (RAS) in some patients, whose histologic characteristics included organ infiltration by leukemic cells. Matrix metalloproteinase 2 (MMP-2) is often upregulated in tumor cells and plays a role in tumor cell migration and invasion by degrading the extracellular matrix. In this study, we examined the possible modulatory effects of ATRA on MMP-2 expression and secretion in human myeloid leukemia cell line THP-1. The cells were treated with various concentrations of ATRA, and MMP-2 expression and secretion were examined. MMP-2 expression and secretion started to increase with ATRA concentration as low as 0.1 nM and gradually increased thereafter. Agonists of retinoic acid receptor (RAR) or retinoid X receptor (RXR) alone could enhance MMP-2 secretion, and RAR or RXR antagonists alone could reverse ATRA-induced MMP-2 secretion. ATRA increased intracellular calcium ion levels, and a calcium-channel blocker inhibited ATRA-induced MMP-2 secretion. Dexamethasone suppressed ATRA-induced MMP-2 secretion. Our results suggest that ATRA enhances MMP-2 expression and secretion in human myeloid leukemia THP-1 cells in a calcium ion dependent manner through RAR/RXR signaling pathways, and this enhanced expression and secretion may be associated with the possible mechanisms of RAS.

Pseudopterosin Inhibits Proliferation and 3D Invasion in Triple-Negative Breast Cancer by Agonizing Glucocorticoid Receptor Alpha

Pseudopterosin, produced by the sea whip of the genus Antillogorgia, possesses a variety of promising biological activities, including potent anti-inflammatory effects. However, few studies examined pseudopterosin in the treatment of cancer cells and, to our knowledge, the ability to inhibit triple-negative breast cancer (TNBC) proliferation or invasion has not been explored. Thus, we evaluated the as-yet unknown mechanism of action of pseudopterosin: Pseudopterosin was able to inhibit proliferation of TNBC. Interestingly, analyzing breast cancer cell proliferation after knocking down glucocorticoid receptor α (GRα) revealed that the antiproliferative effects of pseudopterosin were significantly inhibited when GRα expression was reduced. Furthermore, pseudopterosin inhibited the invasion of MDA-MB-231 3D tumor spheroids embedded in an extracellular-like matrix. Remarkably, the knockdown of GRα in 3D tumor spheroids revealed increased ability of cells to invade the surrounding matrix. In a coculture, encompassing peripheral blood mononuclear cells (PBMC) and MDA-MB-231 cells, and the production of interleukin 6 (IL-6) and interleukin 8 (IL-8) significantly increased compared to a monoculture. Notably, pseudopterosin indicated to block cytokine elevation, representing key players in tumor progression in the coculture. Thus, our results reveal pseudopterosin treatment as a potential novel approach in TNBC therapy.

Functional and genomic characterisation of a xenograft model system for the study of metastasis in triple-negative breast cancer

Triple-negative breast cancer (TNBC) represents 10-20% of all human ductal adenocarcinomas and has a poor prognosis relative to other subtypes. Hence, new molecular targets for therapeutic intervention are necessary. Analyses of panels of human or mouse cancer lines derived from the same individual that differ in their cellular phenotypes but not in genetic background have been instrumental in defining the molecular players that drive the various hallmarks of cancer. To determine the molecular regulators of metastasis in TNBC, we completed a rigorous in vitro and in vivo characterisation of four populations of the MDA-MB-231 human breast cancer line ranging in aggressiveness from non-metastatic to spontaneously metastatic to lung, liver, spleen and lymph node. Single nucleotide polymorphism (SNP) array analyses and genome-wide mRNA expression profiles of tumour cells isolated from orthotopic mammary xenografts were compared between the four lines to define both cell autonomous pathways and genes associated with metastatic proclivity. Gene set enrichment analysis (GSEA) demonstrated an unexpected association between both ribosome biogenesis and mRNA metabolism and metastatic capacity. Differentially expressed genes or families of related genes were allocated to one of four categories, associated with either metastatic initiation (e.g. CTSC, ENG, BMP2), metastatic virulence (e.g. ADAMTS1, TIE1), metastatic suppression (e.g. CST1, CST2, CST4, CST6, SCNNA1, BMP4) or metastatic avirulence (e.g. CD74). Collectively, this model system based on MDA-MB-231 cells should be useful for the assessment of gene function in the metastatic cascade and also for the testing of novel experimental therapeutics for the treatment of TNBC.This article has an associated First Person interview with the first author of the paper.

Progesterone suppresses the invasion and migration of breast cancer cells irrespective of their progesterone receptor status - a short report

PURPOSE

Pre-operative progesterone treatment of breast cancer has been shown to confer survival benefits to patients independent of their progesterone receptor (PR) status. The underlying mechanism and the question whether such an effect can also be observed in PR negative breast cancer cells remain to be resolved.

METHODS

We performed proteome profiling of PR-positive and PR-negative breast cancer cells in response to progesterone using a phospho-kinase array platform. Western blotting was used to validate the results. Cell-based phenotypic assays were conducted using PR-positive and PR-negative breast cancer cells to assess the effect of progesterone.

RESULTS

We found that progesterone induces de-phosphorylation of 12 out of 43 kinases tested, which are mostly involved in cellular invasion and migration regulation. Consistent with this observation, we found through cell-based phenotypic assays that progesterone inhibits the invasion and migration of breast cancer cells independent of their PR status.

CONCLUSION

Our results indicate that progesterone can inhibit breast cancer cell invasion and migration mediated by the de-phosphorylation of kinases. This inhibition appears to be independent of the PR status of the breast cancer cells. In a broader context, our study may provide a basis for an association between progesterone treatment and recurrence reduction in breast cancer patients, thereby providing a lead for modelling a randomized in vitro study.