Downregulation of estrogen receptor and modulation of growth of breast cancer cell lines mediated by paracrine stromal cell signals

Outlook and opportunities for engineered environments of breast cancer dormancy

Dormant, disseminated breast cancer cells resist treatment and may relapse into malignant metastases after decades of quiescence. Identifying how and why these dormant breast cancer cells are triggered into outgrowth is a key unsolved step in treating latent, metastatic breast cancer. However, our understanding of breast cancer dormancy in vivo is limited by technical challenges and ethical concerns with triggering the activation of dormant breast cancer. In vitro models avoid many of these challenges by simulating breast cancer dormancy and activation in well-controlled, bench-top conditions, creating opportunities for fundamental insights into breast cancer biology that complement what can be achieved through animal and clinical studies. In this review, we address clinical and preclinical approaches to treating breast cancer dormancy, how precisely controlled artificial environments reveal key interactions that regulate breast cancer dormancy, and how future generations of biomaterials could answer further questions about breast cancer dormancy.

The Role of Breast Cancer Cells in Bone Metastasis: Suitable Seeds for Nourishing Soil

PURPOSE OF REVIEW

The purpose of this review was to describe the characteristics of breast cancer cells prone to developing bone metastasis and determine how they are regulated by the bone microenvironment.

RECENT FINDINGS

The bone is a site of frequent breast cancer metastasis. Bone metastasis accounts for 70% of advanced breast cancer cases and remains incurable. It can lead to skeletal-related events, such as bone fracture and pain, and seriously affect the quality of life of patients. Breast cancer cells escape from the primary lesion and spread to the bone marrow in the early stages. They can then enter the dormant state and restore tumourigenicity after several years to develop overt metastasis. In the last few years, an increasing number of studies have reported on the factors promoting bone metastasis of breast cancer cells, both at the primary and metastatic sites. Identifying factors associated with bone metastasis aids in the early recognition of bone metastasis tendency. How to target these factors and minimize the side effects on the bone remains to be further explored.

Mathematical reconstruction of the metabolic network in an in-vitro multiple myeloma model

It is increasingly apparent that cancer cells, in addition to remodelling their metabolism to survive and proliferate, adapt and manipulate the metabolism of other cells. This property may be a telling sign that pre-clinical tumour metabolism studies exclusively utilising in-vitro mono-culture models could prove to be limited for uncovering novel metabolic targets able to translate into clinical therapies. Although this is increasingly recognised, and work towards addressing the issue is becoming routinary much remains poorly understood. For instance, knowledge regarding the biochemical mechanisms through which cancer cells manipulate non-cancerous cell metabolism, and the subsequent impact on their survival and proliferation remains limited. Additionally, the variations in these processes across different cancer types and progression stages, and their implications for therapy, also remain largely unexplored. This study employs an interdisciplinary approach that leverages the predictive power of mathematical modelling to enrich experimental findings. We develop a functional multicellular in-silico model that facilitates the qualitative and quantitative analysis of the metabolic network spawned by an in-vitro co-culture model of bone marrow mesenchymal stem- and myeloma cell lines. To procure this model, we devised a bespoke human genome constraint-based reconstruction workflow that combines aspects from the legacy mCADRE & Metabotools algorithms, the novel redHuman algorithm, along with 13C-metabolic flux analysis. Our workflow transforms the latest human metabolic network matrix (Recon3D) into two cell-specific models coupled with a metabolic network spanning a shared growth medium. When cross-validating our in-silico model against the in-vitro model, we found that the in-silico model successfully reproduces vital metabolic behaviours of its in-vitro counterpart; results include cell growth predictions, respiration rates, as well as support for observations which suggest cross-shuttling of redox-active metabolites between cells.

Breast cancer: molecular mechanisms of underlying resistance and therapeutic approaches

Breast cancer (BC) affects over 250,000 women in the US each year. Drug-resistant cancer cells are responsible for most breast cancer fatalities. Scientists are developing novel chemotherapeutic drugs and targeted therapy combinations to overcome cancer cell resistance. Combining drugs can reduce the chances of a tumor developing resistance to treatment. Clinical research has shown that combination chemotherapy enhances or improves survival, depending on the patient's response to treatment. Combination therapy is a highly successful supplemental cancer treatment. This review sheds light on intrinsic resistance to BC drugs and the importance of combination therapy for BC treatment. In addition to recurrence and metastasis of BC, the article discussed biomarkers for BC.

Stromal Co-Cultivation for Modeling Breast Cancer Dormancy in the Bone Marrow

Cancers metastasize to the bone marrow before primary tumors can be detected. Bone marrow micrometastases are resistant to therapy, and while they are able to remain dormant for decades, they recur steadily and result in incurable metastatic disease. The bone marrow microenvironment maintains the dormancy and chemoresistance of micrometastases through interactions with multiple cell types and through structural and soluble factors. Modeling dormancy in vitro can identify the mechanisms of these interactions. Modeling also identifies mechanisms able to disrupt these interactions or define novel interactions that promote the reawakening of dormant cells. The in vitro modeling of the interactions of cancer cells with various bone marrow elements can generate hypotheses on the mechanisms that control dormancy, treatment resistance and reawakening in vivo. These hypotheses can guide in vivo murine experiments that have high probabilities of succeeding in order to verify in vitro findings while minimizing the use of animals in experiments. This review outlines the existing data on predominant stromal cell types and their use in 2D co-cultures with cancer cells.

Effects of iron modulation on mesenchymal stem cell-induced drug resistance in estrogen receptor-positive breast cancer

Patients with estrogen receptor-positive (ER+) breast cancer, the most common subtype, remain at risk for lethal metastatic disease years after diagnosis. Recurrence arises partly because tumor cells in bone marrow become resistant to estrogen-targeted therapy. Here, we utilized a co-culture model of bone marrow mesenchymal stem cells (MSCs) and ER+ breast cancer cells to recapitulate interactions of cancer cells in bone marrow niches. ER+ breast cancer cells in direct contact with MSCs acquire cancer stem-like (CSC) phenotypes with increased resistance to standard antiestrogenic drugs. We confirmed that co-culture with MSCs increased labile iron in breast cancer cells, a phenotype associated with CSCs and disease progression. Clinically approved iron chelators and in-house lysosomal iron-targeting compounds restored sensitivity to antiestrogenic therapy. These findings establish iron modulation as a mechanism to reverse MSC-induced drug resistance and suggest iron modulation in combination with estrogen-targeted therapy as a promising, translatable strategy to treat ER+ breast cancer.

Bone Marrow Mesenchymal Cells (BMSCs) on Breast Cancer Cell Proliferation and Metastasis by Regulating Phosphatase and Tensin Homolog 12

Among the newly diagnosed cancers in women, breast cancer metastasis is a key factor contributing to the poor prognosis. BMSCs are critical components for the malignant microenvironment. Studies have shown that the interaction between tumor cells and BMSCs support breast cancer progression. However, BMSCs’ effect on breast cancer cells is not yet clear. BMSCs and breast cancer cell MCF-7 were co-cultured to analyze tumor cell proliferation and apoptosis along with analysis of E-cadherin and Vimentin expression by real-time PCR, interleukin-6 and matrix protease-2 and PTEN12 expression. Co-culture of BMSCs promoted breast cancer cell proliferation, decreased apoptosis-related Caspase 3 activity and downregulated the expression of EMT related factors, upregulated IL-6 secretion and MMP-2, and downregulated PTEN12 expression (P < 0.05). In conclusion, BMSCs can promote breast cancer cell proliferation and survival and affect breast cancer transformation possibly through inhibiting the expression of PTEN12.

Pharmacotranscriptomic profiling of resistant triple-negative breast cancer cells treated with lapatinib and berberine shows upregulation of PI3K/Akt signaling under cytotoxic stress

Triple-negative breast cancer (TNBC) is the most incurable type of breast cancer, accounting for 15-20% of breast cancer cases. Lapatinib is a dual tyrosine kinase inhibitor targeting EGFR and Her2, and berberine (BBR) is a plant-based alkaloid suggested to inhibit several cancer signaling pathways. We previously reported that lapatinib activates the Akt oncoprotein in MDA-MB231 TNBC cells. The present study determined the mechanism(s) of Akt activation in response to lapatinib, BBR, and capivasertib (Akt inhibitor) as well as the role of Akt signaling in chemoresistance in TNBC cells. Genetic profiles of 10 TNBC cell lines and patients were analyzed using datasets obtained from Gene Expression Omnibus and The Cancer Genome Atlas Database. Then, the effects of lapatinib, BBR, and capivasertib on treated MDA-MB231 and MCF-7 cell lines were studied using cytotoxicity, immunoblot, and RNA-sequencing analyses. For further confirmation, we also performed real-time PCR for genes associated with PI3K signaling. MDA-MB231 and MCF-7 cell lines were both strongly resistant to capivasertib largely due to significant Akt activation in both breast cancer cell lines, while lapatinib and BBR only enhanced Akt signaling in MDA-MB231 cells. Next-generation sequencing, functional enrichment analysis, and immunoblot revealed downregulation of CDK6 and DNMT1 in response to lapatinib and BBR lead to a decrease in cell proliferation. Expression of placental, fibroblast growth factor, and angiogenic biomarker genes, which are significantly associated with Akt activation and/or dormancy in breast cancer cells, was significantly upregulated in TNBC cells treated with lapatinib and BBR. Lapatinib and BBR activate Akt through upregulation of alternative signaling, which lead to chemoresistance in TNBC cell. In addition, lapatinib overexpresses genes related to PI3K signaling in resistant TNBC cell model.

Autophagy and Cancer Dormancy

Metastasis and relapse account for the great majority of cancer-related deaths. Most metastatic lesions are micro metastases that have the capacity to remain in a non-dividing state called “dormancy” for months or even years. Commonly used anticancer drugs generally target actively dividing cancer cells. Therefore, cancer cells that remain in a dormant state evade conventional therapies and contribute to cancer recurrence. Cellular and molecular mechanisms of cancer dormancy are not fully understood. Recent studies indicate that a major cellular stress response mechanism, autophagy, plays an important role in the adaptation, survival and reactivation of dormant cells. In this review article, we will summarize accumulating knowledge about cellular and molecular mechanisms of cancer dormancy, and discuss the role and importance of autophagy in this context.

Syngeneic tobacco carcinogen-induced mouse lung adenocarcinoma model exhibits PD-L1 expression and high tumor mutational burden

Human lung adenocarcinoma (LUAD) in current or former smokers exhibits a high tumor mutational burden (TMB) and distinct mutational signatures. Syngeneic mouse models of clinically relevant smoking-related LUAD are lacking. We established and characterized a tobacco-associated, transplantable murine LUAD cell line, designated FVBW-17, from a LUAD induced by the tobacco carcinogen 4-(methylnitrosoamino)-1-(3-pyridyl)-1-butanone in the FVB/N mouse strain. Whole-exome sequencing of FVBW-17 cells identified tobacco-associated KrasG12D and Trp53 mutations and a similar mutation profile to that of classic alkylating agents with a TMB greater than 500. FVBW-17 cells transplanted subcutaneously, via tail vein, and orthotopically generated tumors that were histologically similar to human LUAD in FVB/N mice. FVBW-17 tumors expressed programmed death ligand 1 (PD-L1), were infiltrated with CD8+ T cells, and were responsive to anti-PD-L1 therapy. FVBW-17 cells were also engineered to express green fluorescent protein and luciferase to facilitate detection and quantification of tumor growth. Distant metastases to lung, spleen, liver, and kidney were observed from subcutaneously transplanted tumors. This potentially novel cell line is a robust representation of human smoking-related LUAD biology and provides a much needed preclinical model in which to test promising new agents and combinations, including immune-based therapies.

Intrinsic and Extrinsic Factors Governing the Transcriptional Regulation of ESR1

Transcriptional regulation of ESR1, the gene that encodes for estrogen receptor α (ER), is critical for regulating the downstream effects of the estrogen signaling pathway in breast cancer such as cell growth. ESR1 is a large and complex gene that is regulated by multiple regulatory elements, which has complicated our understanding of how ESR1 expression is controlled in the context of breast cancer. Early studies characterized the genomic structure of ESR1 with subsequent studies focused on identifying intrinsic (chromatin environment, transcription factors, signaling pathways) and extrinsic (tumor microenvironment, secreted factors) mechanisms that impact ESR1 gene expression. Currently, the introduction of genomic sequencing platforms and additional genome-wide technologies has provided additional insight on how chromatin structures may coordinate with these intrinsic and extrinsic mechanisms to regulate ESR1 expression. Understanding these interactions will allow us to have a clearer understanding of how ESR1 expression is regulated and eventually provide clues on how to influence its regulation with potential treatments. In this review, we highlight key studies concerning the genomic structure of ESR1, mechanisms that affect the dynamics of ESR1 expression, and considerations towards affecting ESR1 expression and hormone responsiveness in breast cancer.

Modeling chemical effects on breast cancer: the importance of the microenvironment in vitro

Accumulating evidence suggests that our ability to predict chemical effects on breast cancer is limited by a lack of physiologically relevant in vitro models; the typical in vitro breast cancer model consists of the cancer cell and excludes the mammary microenvironment. As the effects of the microenvironment on cancer cell behavior becomes more understood, researchers have called for the integration of the microenvironment into in vitro chemical testing systems. However, given the complexity of the microenvironment and the variety of platforms to choose from, identifying the essential parameters to include in a chemical testing platform is challenging. This review discusses the need for more complex in vitro breast cancer models and outlines different approaches used to model breast cancer in vitro. We provide examples of the microenvironment modulating breast cancer cell responses to chemicals and discuss strategies to help pinpoint what components should be included in a model.

Estrogen Receptor Beta Inhibits The Proliferation, Migration, And Angiogenesis Of Gastric Cancer Cells Through Inhibiting Nuclear Factor-Kappa B Signaling

Purpose

This study aimed to investigate the regulatory roles of estrogen receptor beta (ERβ) on gastric cancer (GC) cells, and reveal the potential mechanisms relating to nuclear factor-kappa B (NF-κB) signaling.

Methods

GC cell lines SGC7901 and MKN45 were transfected with pEGFP-C1-ERβ to overexpress ERβ, and treated with PMA (a NF-κB activator) to activate NF-κB signaling. The cell proliferation and migration, as well as the formation of vessel-like structures in human venous endothelial cells (HUVECs) were detected. The expression of ERβ, NF-κB p65, p-NF-κB p65, Ki67 (a proliferation marker), vascular endothelial growth factor A (VEGF-A) and matrix metalloproteinase 2 (MMP-2), the DNA binding activity of NF-κB p65, the content of VEGF-A, and the activity of MMP-2 were detected in SGC7901 and MKN45 cells.

Results

The transfection of pEGFP-C1-ERβ significantly increased the expression of ERβ in SGC7901 and MKN45 cells (P < 0.05). Overexpression of ERβ in SGC7901 and MKN45 cells significantly decreased the cell activity, cell number in G2/M phase, cell migration, the expression of Ki67, VEGF-A and MMP-2, VEGF-A content, MMP-2 activity, as well as the number of vessel-like structures formed by HUVECs (P < 0.05). Overexpression of ERβ also significantly decreased the DNA binding activity and the expression of p-NF-κB p65 in SGC7901 and MKN45 cells (P < 0.05). The anti-tumor effect of ERβ overexpression on GC cells was reversed by the intervention of PMA (P < 0.05).

Conclusion

Overexpression of ERβ inhibited the proliferation, migration, and angiogenesis of GC cells through inhibiting NF-κB signaling.

Bone Marrow Stromal Cells Transcriptionally Repress ESR1 but Cannot Overcome Constitutive ESR1 Mutant Activity

Estrogen receptor α (ER) is the target of endocrine therapies in ER-positive breast cancer (BC), but their therapeutic effectiveness diminishes with disease progression. Most metastatic BCs retain an ER-positive status, but ER expression levels are reduced. We asked how the bone tumor microenvironment (TME) regulates ER expression. We observed ESR1 mRNA and ER protein downregulation in BC cells treated with conditioned media (CM) from patient-derived, cancer-activated bone marrow stromal cells (BMSCs) and the BMSC cell line HS5. Decreases in ESR1 mRNA were attributed to decreases in nascent transcripts as well as decreased RNA polymerase II occupancy and H3K27Ac levels on the ESR1 promoter and/or distal enhancer (ENH1). Repression extended to neighboring genes of ESR1, including ARMT1 and SYNE1. Although ERK/MAPK signaling pathway can repress ER expression by other TME cell types, MAPK inhibition did not reverse decreases in ER expression by BMSC-CM. ESR1 mRNA and ER protein half-lives in MCF7 cells were unchanged by BMSC-CM treatment. Whereas ER phosphorylation was induced, ER activity was repressed by BMSC-CM as neither ER occupancy at known binding sites nor estrogen response element-luciferase activity was detected. BMSC-CM also repressed expression of ER target genes. In cells expressing the Y537S and D538G ESR1 mutations, BMSC-CM reduced ESR1, but expression of target genes PGR and TFF1 remained significantly elevated compared with that of control wild-type cells. These studies demonstrate that BMSCs can transcriptionally corepress ESR1 with neighboring genes and inhibit receptor activity, but the functional consequences of the BMSC TME can be limited by metastasis-associated ESR1 mutations.

Chemoresistance mechanisms of breast cancer and their countermeasures

Chemoresistance is one of the major challenges for the breast cancer treatment. Owing to its heterogeneous nature, the chemoresistance mechanisms of breast cancer are complicated, and not been fully elucidated. The existing treatments fall short of offering adequate solution to drug resistance, so more effective approaches are desperately needed to improve existing therapeutic regimens. To overcome this hurdle, a number of strategies are being investigated, such as novel agents or drug carriers and combination treatment. In addition, some new therapeutics including gene therapy and immunotherapy may be promising for dealing with the resistance. In this article, we review the mechanisms of chemoresistance in breast cancer. Furthermore, the potential therapeutic methods to overcome the resistance were discussed.

IL-1 induces p62/SQSTM1 and autophagy in ERα+ /PR+ BCa cell lines concomitant with ERα and PR repression, conferring an ERα- /PR- BCa-like phenotype

Estrogen receptor α (ERα)^low/- tumors are associated with breast cancer (BCa) endocrine resistance, where ERα low tumors show a poor prognosis and a molecular profile similar to triple negative BCa tumors. Interleukin-1 (IL-1) downregulates ERα accumulation in BCa cell lines, yet the cells can remain viable. In kind, IL-1 and ERα show inverse accumulation in BCa patient tumors and IL-1 is implicated in BCa progression. IL-1 represses the androgen receptor hormone receptor in prostate cancer cells concomitant with the upregulation of the prosurvival, autophagy-related protein, Sequestome-1 (p62/SQSTM1; hereinafter, p62); and given their similar etiology, we hypothesized that IL-1 also upregulates p62 in BCa cells concomitant with hormone receptor repression. To test our hypothesis, BCa cell lines were exposed to conditioned medium from IL-1-secreting bone marrow stromal cells (BMSCs), IL-1, or IL-1 receptor antagonist. Cells were analyzed for the accumulation of ERα, progesterone receptor (PR), p62, or the autophagosome membrane protein, microtubule-associated protein 1 light chain 3 (LC3), and for p62-LC3 interaction. We found that IL-1 is sufficient to mediate BMSC-induced ERα and PR repression, p62 and autophagy upregulation, and p62-LC3 interaction in ERα⁺ /PR⁺ BCa cell lines. However, IL-1 does not significantly elevate the high basal p62 accumulation or high basal autophagy in the ERα^- /PR^- BCa cell lines. Thus, our observations imply that IL-1 confers a prosurvival ERα^- /PR^- molecular phenotype in ERα⁺ /PR⁺ BCa cells that may be dependent on p62 function and autophagy and may underlie endocrine resistance.

The Tumor Microenvironment as a Regulator of Endocrine Resistance in Breast Cancer

Estrogen receptor positive breast neoplasias represent over 70% of diagnosed breast cancers. Depending on the stage at which the tumor is detected, HER2 status and genomic risk, endocrine therapy is combined with either radio, chemo and/or targeted therapy. A growing amount of evidence supports the notion that components of the tumor microenvironment play specific roles in response to treatment and that strategies targeting these key interactions with tumor cells could pave the way to a new generation of therapies. In this review, we analyze the evidence suggesting different components of the tumor microenvironment play a role in hormone receptor positive breast cancer progression. In particular we focus on the immune system, carcinoma associated fibroblasts and the extracellular matrix. Further insight into the cross talk between these constituents of the microenvironment and the tumor cells may lead to therapies that eliminate disseminated metastatic cells early on, and thus reduce distant disease relapse which is the leading cause of death for patients who are diagnosed with this illness.

Hyaluronan arrests human breast cancer cell growth by prolonging the G0/G1 phase of the cell cycle

In clinical breast cancer patients, quiescent disseminated tumor cells (DTCs) can persist for a long time in the bone marrow (BM) under the influence of microenvironmental cues. As a high molecular weight polysaccharide, hyaluronan (HA) not only has been shown to regulate cancer processes including cell invasion, metastasis, migration, and proliferation, but also is a major component of the BM extracellular matrix. Here, we tested whether HA promotes breast cancer cell quiescence through detecting cell proliferation, cell cycle phase distribution, and the expression of cell cycle-related regulator proteins. In our results, HA slowed the growth and prolonged the G0/G1 phase of the highly metastatic, bone-seeking human breast cancer MDA-MB-231BO cell line, which is consistent with results that HA activated p38α/β, inhibited phospho-ERK1/2 levels and reduced the ERK/p38 signaling ratio. Additionally, we examined the crucial cell cycle factors p21cip1 and Cyclin D1, both of which influence the transition from G1 to S phase. The results revealed that p21cip1 expression was up-regulated by HA, which was consequently accompanied by a decrease in Cyclin D1 level. Further research with a 3D culture model indicated that HA maintained low Ki-67 and high p21cip1 expression levels in MDA-MB-231BO cells. In summary, our work revealed that HA might contribute to DTC quiescence.

Signaling pathways and steroid receptors modulating estrogen receptor α function in breast cancer

Estrogen receptor α (ER) is the major driver of ∼75% of breast cancers, and multiple ER targeting drugs are routinely used clinically to treat patients with ER+ breast cancer. However, many patients relapse on these targeted therapies and ultimately develop metastatic and incurable disease, and understanding the mechanisms leading to drug resistance is consequently of utmost importance. It is now clear that, in addition to estrogens, ER function is modulated by other steroid receptors and multiple signaling pathways (e.g., growth factor and cytokine signaling), and many of these pathways affect drug resistance and patient outcome. Here, we review the mechanisms through which these pathways impact ER function and drug resistance as well as discuss the clinical implications.

Mechanisms of resistance to selective estrogen receptor down-regulator in metastatic breast cancer

Based on the prominent role estrogen receptor (ER) plays in breast cancer, endocrine therapy has been developed to block the ER pathway and has shown great effectiveness. Fulvestrant, the first selective ER down-regulator (SERD), was demonstrated to completely suppress ERα and notably efficient. However, resistance to fulvestrant occurs, either intrinsic or acquired during the treatment. Several potential mechanisms inducing fulvestrant resistance have been proposed, composed of activated ERα-independent compensatory growth factor signaling, stimulated downstream kinases, altered cell cycle mediators, etcetera. Experimentally, combinations of fulvestrant with targeted treatments were reported to eliminate the resistance and improve the effect of fulvestrant. Meanwhile, some clinical trials associated with the targeted combination therapies are in progress. This review focuses on the underlying mechanisms that contribute to fulvestrant resistance in ER-positive breast cancer and provides an overview of combined fulvestrant with targeted agents to shed light on optimal therapies for patients with ER-positive breast cancer.