Sca-1 identifies the tumor-initiating cells in mammary tumors of BALB-neuT transgenic mice

Tumor suppressor FRMD3 controls mammary epithelial cell fate determination via notch signaling pathway

The luminal-to-basal transition in mammary epithelial cells (MECs) is accompanied by changes in epithelial cell lineage plasticity; however, the underlying mechanism remains elusive. Here, we report that deficiency of Frmd3 inhibits mammary gland lineage development and induces stemness of MECs, subsequently leading to the occurrence of triple-negative breast cancer. Loss of Frmd3 in PyMT mice results in a luminal-to-basal transition phenotype. Single-cell RNA sequencing of MECs indicated that knockout of Frmd3 inhibits the Notch signaling pathway. Mechanistically, FERM domain-containing protein 3 (FRMD3) promotes the degradation of Disheveled-2 by disrupting its interaction with deubiquitinase USP9x. FRMD3 also interrupts the interaction of Disheveled-2 with CK1, FOXK1/2, and NICD and decreases Disheveled-2 phosphorylation and nuclear localization, thereby impairing Notch-dependent luminal epithelial lineage plasticity in MECs. A low level of FRMD3 predicts poor outcomes for breast cancer patients. Together, we demonstrated that FRMD3 is a tumor suppressor that functions as an endogenous activator of the Notch signaling pathway, facilitating the basal-to-luminal transformation in MECs.

Natural killer cell regulation of breast cancer stem cells mediates metastatic dormancy

Breast cancer patients with estrogen receptor positive tumors face a constant risk of disease recurrence for the remainder of their lives. Dormant tumor cells residing in tissues such as the bone marrow may generate clinically significant metastases many years after initial diagnosis. Previous studies suggest that dormant cells display "stem like" properties (CSCs), which may be regulated by the immune system. Although many studies have examined tumor cell intrinsic characteristics of dormancy, the role of the immune system in controlling dormancy and its escape is not well understood. This scientific gap is due, in part, to a lack of immunocompetent mouse models of breast cancer dormancy with many studies involving human xenografts in immunodeficient mice. To overcome this limitation, we studied dormancy in immunocompetent, syngeneic mouse breast cancer models. We find that PyMT, Met-1 and D2.0R cell lines contain CSCs that display both short- and long-term metastatic dormancy in vivo, which is dependent on the host immune system. Natural killer cells were key for the metastatic dormancy phenotype observed for D2.0R and the role of NK cells in regulating CSCs was further investigated.Quiescent D2.0R CSC are resistant to NK cytotoxicity, while proliferative D2.0R CSC were sensitive to NK cytotoxicity both in vitro and in vivo. This resistance was mediated, in part, by the expression of Bach1 and Sox2 transcription factors. NK killing was enhanced by the STING agonist MSA-2. Collectively, our findings demonstrate the important role of immune regulation of breast tumor dormancy and highlight the importance of utilizing immunocompetent models to study this phenomenon.

Deciphering Common Traits of Breast and Ovarian Cancer Stem Cells and Possible Therapeutic Approaches

Breast cancer (BC) and ovarian cancer (OC) are among the most common and deadly cancers affecting women worldwide. Both are complex diseases with marked heterogeneity. Despite the induction of screening programs that increase the frequency of earlier diagnosis of BC, at a stage when the cancer is more likely to respond to therapy, which does not exist for OC, more than 50% of both cancers are diagnosed at an advanced stage. Initial therapy can put the cancer into remission. However, recurrences occur frequently in both BC and OC, which are highly cancer-subtype dependent. Therapy resistance is mainly attributed to a rare subpopulation of cells, named cancer stem cells (CSC) or tumor-initiating cells, as they are capable of self-renewal, tumor initiation, and regrowth of tumor bulk. In this review, we will discuss the distinctive markers and signaling pathways that characterize CSC, their interactions with the tumor microenvironment, and the strategies they employ to evade immune surveillance. Our focus will be on identifying the common features of breast cancer stem cells (BCSC) and ovarian cancer stem cells (OCSC) and suggesting potential therapeutic approaches.

Pleiotropic effects of DCLK1 in cancer and cancer stem cells

Doublecortin-like kinase 1 (DCLK1), a protein molecule, has been identified as a tumor stem cell marker in the cancer cells of gastrointestinal, pancreas, and human colon. DCLK1 expression in cancers, such as breast carcinoma, lung carcinoma, hepatic cell carcinoma, tuft cells, and human cholangiocarcinoma, has shown a way to target the DCLK1 gene and downregulate its expression. Several studies have discussed the inhibition of tumor cell proliferation along with neoplastic cell arrest when the DCLK1 gene, which is expressed in both cancer and normal cells, was targeted successfully. In addition, previous studies have shown that DCLK1 plays a vital role in various cancer metastases. The correlation of DCLK1 with numerous stem cell receptors, signaling pathways, and genes suggests its direct or an indirect role in promoting tumorigenesis. Moreover, the impact of DCLK1 was found to be related to the functioning of an oncogene. The downregulation of DCLK1 expression by using targeted strategies, such as embracing the use of siRNA, miRNA, CRISPR/Cas9 technology, nanomolecules, specific monoclonal antibodies, and silencing the pathways regulated by DCLK1, has shown promising results in both in vitro and in vivo studies on gastrointestinal (GI) cancers. In this review, we will discuss about the present understanding of DCLK1 and its role in the progression of GI cancer and metastasis.

Toll-like receptor 2 promotes breast cancer progression and resistance to chemotherapy

Cancer stem cells (CSCs) are the main drivers of disease progression and chemotherapy resistance in breast cancer. Tumor progression and chemoresistance might then be prevented by CSC-targeted therapies. We previously demonstrated that Toll-like Receptor (TLR)2 is overexpressed in CSCs and fuels their self-renewal. Here, we show that high TLR2 expression is linked to poor prognosis in breast cancer patients, therefore representing a candidate target for breast cancer treatment. By using a novel mammary cancer-prone TLR2^KO mouse model, we demonstrate that TLR2 is required for CSC pool maintenance and for regulatory T cell induction. Accordingly, cancer-prone TLR2^KO mice display delayed tumor onset and increased survival. Transplantation of TLR2^WT and TLR2^KO cancer cells in either TLR2^WT or TLR2^KO hosts shows that tumor initiation is mostly sustained by TLR2 expression in cancer cells. TLR2 host deficiency partially impairs cancer cell growth, implying a pro-tumorigenic effect of TLR2 expression in immune cells. Finally, we demonstrate that doxorubicin-induced release of HMGB1 activates TLR2 signaling in cancer cells, leading to a chemotherapy-resistant phenotype. Unprecedented use of TLR2 inhibitors in vivo reduces tumor growth and potentiates doxorubicin efficacy with no negative impact on the host immune system, opening new perspectives for the treatment of breast cancer patients.

Sca-1 is a marker for cell plasticity in murine pancreatic epithelial cells and induced by IFN-β in vitro

BACKGROUND & AIMS

Sca-1 is a surface marker for murine hematopoietic stem cells (HSCs) and type-I interferon is a key regulator for Lin^-Sca-1⁺ HSCs expansion through Ifnar/Stat-1/Sca-1-signaling. In this study we aimed to characterize the role and regulation of Sca-1⁺ cells in pancreatic regeneration.

METHODS

To characterize Sca-1 in vivo, immunohistochemistry and immunofluorescence staining of Sca-1 was conducted in normal pancreas, in cerulein-mediated acute pancreatitis, and in Kras-triggered cancerous lesions. Ifnar/Stat-1/Sca-1-signaling was studied in type-I IFN-treated epithelial explants of adult wildtype, Ifnar^-/-, and Stat-1^-/- mice. Sca-1 induction was analyzed by gene expression and FACS analysis. After isolation of pancreatic epithelial Lin^-Sca-1⁺cells, pancreatosphere-formation and immunofluorescence-assays were carried out to investigate self-renewal and differentiation capabilities.

RESULTS

Sca-1⁺ cells were located in periacinar and periductal spaces and showed an enrichment during cerulein-induced acute pancreatitis (23.2/100 μm² ± 4.9 SEM) and in early inflammation-mediated carcinogenic lesions of the pancreas of Kras^G12D mice (35.8/100 μm² ± SEM 1.9) compared to controls (3.6/100 μm² ± 1.3 SEM). Pancreatic Lin^-Sca-1⁺ cells displayed a small population of 1.46% ± 0.12 SEM in FACS. In IFN-β treated pancreatic epithelial explants, Sca-1 expression was increased, and Lin^-Sca-1⁺ cells were enriched in vitro (from 1.49% ± 0.36 SEM to 3.85% ± 0.78 SEM). Lin^-Sca-1⁺ cells showed a 12 to 51-fold higher capacity for clonal self-renewal compared to Lin^-Sca-1^- cells and generated cells express markers of the acinar and ductal compartment.

CONCLUSIONS

Pancreatic Sca-1⁺ cells enriched during parenchymal damage showed a significant capacity for cell renewal and in vitro plasticity, suggesting that corresponding to the type I interferon-dependent regulation of Lin^-Sca-1⁺ hematopoietic stem cells, pancreatic Sca-1⁺ cells also employ type-I-interferon for regulating progenitor-cell-homeostasis.

The Antiviral Drug Efavirenz in Breast Cancer Stem Cell Therapy

Simple Summary

Cancer stem cells (CSCs) are responsible for tumour initiation, chemo- and radiotherapy resistance and cancer recurrence. CSCs display plasticity that enables them to alter their phenotype and function making them challenging to eliminate. In this study we explore the effects of an antiretroviral medication used to treat HIV/AIDS (Efavirenz) on cancer stem cells derived from multiple breast cancer cell lines. Efavirenz has been previously found to be effective in the treatment of triple-negative breast cancers, and here we show that it is also capable of altering CSC numbers, cell morphology, RNA/microRNA gene expression and levels of epithelial/mesenchymal CSC subtypes. This study shows that, with Efavirenz, it is possible to not only eliminate primary breast cancer cells, but also to promote changes in cell morphology.

Abstract

Although many breast cancer therapies show initial success in the treatment of the primary tumour, they often fail to eliminate a sub-population of cells known as cancer stem cells (CSCs). These cells are recognised for their self-renewal properties and for their capacity for differentiation often leading to chemo/radio-resistance. The antiviral drug Efavirenz has been shown to be effective in eliminating triple-negative breast cancer cells, and here we examine its effect on breast CSCs. The effects of Efavirenz on CSCs for several breast cancer cell lines were investigated by examining cellular changes upon drug treatment, including CSC numbers, morphology, RNA/microRNA expression and levels of epithelial/mesenchymal CSC subtypes. Efavirenz treatment resulted in a decrease in the size and number of tumorspheres and a reduction in epithelial-type CSC levels, but an increase in mesenchymal-type CSCs. Efavirenz caused upregulation of several CSC-related genes as well as miR-21, a CSC marker and miR-182, a CSC suppressor gene. We conclude that Efavirenz alters the phenotype and expression of key genes in breast CSCs, which has important potential therapeutic implications.

MicroRNA Regulation of Breast Cancer Stemness

Recent advances in our understanding of breast cancer have demonstrated that cancer stem-like cells (CSCs, also known as tumor-initiating cell (TICs)) are central for progression and recurrence. CSCs are a small subpopulation of cells present in breast tumors that contribute to growth, metastasis, therapy resistance, and recurrence, leading to poor clinical outcome. Data have shown that cancer cells can gain characteristics of CSCs, or stemness, through alterations in key signaling pathways. The dysregulation of miRNA expression and signaling have been well-documented in cancer, and recent studies have shown that miRNAs are associated with breast cancer initiation, progression, and recurrence through regulating CSC characteristics. More specifically, miRNAs directly target central signaling nodes within pathways that can drive the formation, maintenance, and even inhibition of the CSC population. This review aims to summarize these research findings specifically in the context of breast cancer. This review also discusses miRNAs as biomarkers and promising clinical therapeutics, and presents a comprehensive summary of currently validated targets involved in CSC-specific signaling pathways in breast cancer.

Human-derived osteoblast-like cells and pericyte-like cells induce distinct metastatic phenotypes in primary breast cancer cells

Approximately 70% of advanced breast cancer patients will develop bone metastases, which accounts for ∼90% of cancer-related mortality. Breast cancer circulating tumor cells (CTCs) establish metastatic tumors in the bone after a close interaction with local bone marrow cells including pericytes and osteoblasts, both related to resident mesenchymal stem/stromal cells (BM-MSCs) progenitors. In vitro recapitulation of the critical cellular players of the bone microenvironment and infiltrating CTCs could provide new insights into their cross-talk during the metastatic cascade, helping in the development of novel therapeutic strategies. Human BM-MSCs were isolated and fractionated according to CD146 presence. CD146+ cells were utilized as pericyte-like cells (PLCs) given the high expression of the marker in perivascular cells, while CD146- cells were induced into an osteogenic phenotype generating osteoblast-like cells (OLCs). Transwell migration assays were performed to establish whether primary breast cancer cells (3384T) were attracted to OLC. Furthermore, proliferation of 3384T breast cancer cells was assessed in the presence of PLC- and OLC-derived conditioned media. Additionally, conditioned media cultures as well as transwell co-cultures of each OLCs and PLCs were performed with 3384T breast cancer cells for gene expression interrogation assessing their induced transcriptional changes with an emphasis on metastatic potential. PLC as well as their conditioned media increased motility and invasion potential of 3384T breast cancer cells, while OLC induced a dormant phenotype, downregulating invasiveness markers related with migration and proliferation. Altogether, these results indicate that PLC distinctively drive 3384T cancer cells to an invasive and migratory phenotype, while OLC induce a quiescence state, thus recapitulating the different phases of the in vivo bone metastatic process. These data show that phenotypic responses from metastasizing cancer cells are influenced by neighboring cells at the bone metastatic niche during the establishment of secondary metastatic tumors.

Identification of TENM4 as a Novel Cancer Stem Cell-Associated Molecule and Potential Target in Triple Negative Breast Cancer

Simple Summary

Patients with triple negative breast cancer (TNBC) experience shorter overall survival compared to non-TNBC patients because of the high incidence of recurrences and metastases. This is due to the capacity of aggressive cancer cell subpopulations named cancer stem cells (CSC) to resist current therapies. To design more effective therapeutic strategies for TNBC patients, in this study we sought to identify functional targets expressed on CSC. Our analyses led us to propose teneurin 4 (TENM4) as a promising candidate for drug- and immune-based therapies due to its role in CSC self-renewal and migratory capacity and the inverse correlation between its expression and survival of TNBC patients. In addition, TENM4 detection in the plasma of tumor-bearing patients endorses its potentiality as a disease detection marker.

Abstract

Triple-negative breast cancer (TNBC) is insensitive to endocrine and Her2-directed therapies, making the development of TNBC-targeted therapies an unmet medical need. Since patients with TNBC frequently show a quicker relapse and metastatic progression compared to other breast cancer subtypes, we hypothesized that cancer stem cells (CSC) could have a role in TNBC. To identify putative TNBC CSC-associated targets, we compared the gene expression profiles of CSC-enriched tumorspheres and their parental cells grown as monolayer. Among the up-regulated genes coding for cell membrane-associated proteins, we selected Teneurin 4 (TENM4), involved in cell differentiation and deregulated in tumors of different histotypes, as the object for this study. Meta-analysis of breast cancer datasets shows that TENM4 mRNA is up-regulated in invasive carcinoma specimens compared to normal breast and that high expression of TENM4 correlates with a shorter relapse-free survival in TNBC patients. TENM4 silencing in mammary cancer cells significantly impaired tumorsphere-forming ability, migratory capacity and Focal Adhesion Kinase (FAK) phosphorylation. Moreover, we found higher levels of TENM4 in plasma from tumor-bearing mice and TNBC patients compared to the healthy controls. Overall, our results indicate that TENM4 may act as a novel biomarker and target for the treatment of TNBC.

DNA vaccination against oncoantigens: A promise

The emerging evidence that DNA vaccines elicit a protective immune response in rodents, dogs and cancer patients, coupled with the US Food and Drug Administration (FDA) approval of an initial DNA vaccine to treat canine tumors is beginning to close the gap between the optimistic experimental data and their difficult application in a clinical setting. Here we review a series of conceptual and biotechnological advances that are working together to make DNA vaccines targeting molecules that play important roles during cancer progression (oncoantigens) a promise with near-term clinical impact.

Breast cancer stem cells: A review of their characteristics and the agents that affect them

The evolving concept that cancer stem cells (CSCs) are the driving element in cancer development, evolution and heterogeneity, has overridden the previous model of a tumor consisting of cells all with similar sequentially acquired mutations and a similar potential for renewal, invasion and metastasis. This paradigm shift has focused attention on therapeutically targeting CSCs directly as a means of eradicating the disease. In breast cancers, CSCs can be identified by cell surface markers and are characterized by their ability to self-renew and differentiate, resist chemotherapy and radiation, and initiate new tumors upon serial transplantation in xenografted mice. These functional properties of CSCs are regulated by both intracellular and extracellular factors including pluripotency-related transcription factors, intracellular signaling pathways and external stimuli. Several classes of natural products and synthesized compounds have been studied to target these regulatory elements and force CSCs to lose stemness and/or terminally differentiate and thereby achieve a therapeutic effect. However, realization of an effective treatment for breast cancers, focused on the biological effects of these agents on breast CSCs, their functions and signaling, has not yet been achieved. In this review, we delineate the intrinsic and extrinsic factors identified to date that control or promote stemness in breast CSCs and provide a comprehensive compilation of potential agents that have been studied to target breast CSCs, transcription factors and stemness-related signaling. Our aim is to stimulate further study of these agents that could become the basis for their use as stand-alone treatments or components of combination therapies effective against breast cancers.

Lung Adenocarcinoma Mouse Models Based on Orthotopic Transplantation of Syngeneic Tumor-Initiating Cells Expressing EpCAM, SCA-1, and Ly6d

Somatic mutations in EGFR and KRAS as well as chromosome rearrangements affecting ALK, ROS1, and RET have been identified in human lung adenocarcinoma (LUAD). We here developed organoid-based orthotopic and syngeneic mouse models for studies of the pathogenesis and treatment of LUAD. We isolated EpCAM-positive epithelial cells from mouse lungs and cultured them as organoids to maintain epithelial stem cell properties. These cells were transformed by KRAS(G12V) or EML4-ALK and then transplanted via the trachea into the lungs of the syngeneic mice, where they formed tumors that expressed the lung lineage marker TTF-1 and which closely recapitulated the pathology of human LUAD. Treatment with crizotinib suppressed the growth of tumors formed by the EML4-ALK-expressing lung epithelial cells in a subcutaneous transplantation model. Organoid culture of normal lung epithelial cells resulted in enrichment of EpCAM+SCA-1(Ly6a)+ cells as well as in that of cells expressing another member of the Ly6 protein family, Ly6d, which was found to be required for the growth of the LUAD-initiating cells expressing KRAS(G12V) or EML4-ALK. We also found that a high expression level of LY6D was associated with poor prognosis in human LUAD. Our results thus suggest that LY6D is a potential lung cancer stem cell marker.

The role of stem cell antigen-1/Lymphocyte antigen 6A-2/6E-1 knock out in murine epidermis

Stem Cell Antigen-1 (SCA-1) is a central positive marker for isolating stem cells in several tissues in the mouse. However, for the epidermis, this appears to be the opposite since lack of SCA-1 has been shown to identify keratinocyte populations with progenitor characteristics. This study investigates the effect of SCA-1 knockout in murine keratinocytes. We compared Sca-1^EGFP/EGFP knockout and wildtype mice with respect to the three-dimensional morphology of the epidermis, performed functional assays, and generated gene expression profiles on FACS sorted cells. There were no morphological abnormalities on skin, fur, or hair follicles in transgenic knockout mice compared to wild type mice. SCA-1 knockout keratinocytes showed significantly reduced colony-forming efficiency, colony size and proliferation rate in vitro, however, SCA-1 knockout did not alter wound healing efficiency or keratinocyte proliferation rate in vivo. Moreover, gene expression profiling shows that the effect from knockout of SCA-1 in keratinocytes is dissimilar from what has been observed in other tissues. Additionally, tumor assay indicated that SCA-1 knockout decreases the number of formed papillomas. The results indicate a more complex role for SCA-1, which might differ between epidermal keratinocytes during homeostasis and activated conditions.

TGF-β regulates Sca-1 expression and plasticity of pre-neoplastic mammary epithelial stem cells

The epithelial-mesenchymal plasticity, in tight association with stemness, contributes to the mammary gland homeostasis, evolution of early neoplastic lesions and cancer dissemination. Focused on cell surfaceome, we used mouse models of pre-neoplastic mammary epithelial and cancer stem cells to reveal the connection between cell surface markers and distinct cell phenotypes. We mechanistically dissected the TGF-β family-driven regulation of Sca-1, one of the most commonly used adult stem cell markers. We further provided evidence that TGF-β disrupts the lineage commitment and promotes the accumulation of tumor-initiating cells in pre-neoplastic cells.

Breast Cancer Stem Cells and Sex Steroid Hormones

Breast cancer stem cells (BCSCs) are a small population of tumor-initiating cells that express stem cell-associated markers. In recent years, their properties and mechanisms of regulation have become the focus of intense research due to their intrinsic resistance to conventional cancer therapies. This review describes breast cancer stem cell origin, signaling pathways involved in self-renewal, such as Wnt, Notch and Hedgehog, biomarkers linked to stemness, and the role of sex steroid hormones in BCSC regulation.

Breast Tumor Cells Highly Resistant to Drugs Are Controlled Only by the Immune Response Induced in an Immunocompetent Mouse Model

Background: The tumor cells responsible for metastasis are highly resistant to chemotherapy and have characteristics of stem cells, with a high capacity for self-regeneration and the use of detoxifying mechanisms that participate in drug resistance. In vivo models of highly resistant cells allow us to evaluate the real impact of the immune response in the control of cancer. Materials and Methods: A tumor population derived from the 4T1 breast cancer cell line that was stable in vitro and highly aggressive in vivo was obtained, characterized, and determined to exhibit cancer stem cell (CSC) phenotypes (CD44⁺, CD24⁺, ALDH⁺, Oct4⁺, Nanog⁺, Sox2⁺, and high self-renewal capacity). Orthotopic transplantation of these cells allowed us to evaluate their in vivo susceptibility to chemo and immune responses induced after vaccination. Results: The immune response induced after vaccination with tumor cells treated with doxorubicin decreased the formation of tumors and macrometastasis in this model, which allowed us to confirm the immune response relevance in the control of highly chemotherapy-resistant ALDH⁺ CSCs in an aggressive tumor model in immunocompetent animals. Conclusions: The antitumor immune response was the main element capable of controlling tumor progression as well as metastasis in a highly chemotherapy-resistant aggressive breast cancer model.

Fighting breast cancer stem cells through the immune-targeting of the xCT cystine-glutamate antiporter

Tumor relapse and metastatic spreading act as major hindrances to achieve complete cure of breast cancer. Evidence suggests that cancer stem cells (CSC) would function as a reservoir for the local and distant recurrence of the disease, due to their resistance to radio- and chemotherapy and their ability to regenerate the tumor. Therefore, the identification of appropriate molecular targets expressed by CSC may be critical in the development of more effective therapies. Our studies focused on the identification of mammary CSC antigens and on the development of CSC-targeting vaccines. We compared the transcriptional profile of CSC-enriched tumorspheres from an Her2+ breast cancer cell line with that of the more differentiated parental cells. Among the molecules strongly upregulated in tumorspheres we selected the transmembrane amino-acid antiporter xCT. In this review, we summarize the results we obtained with different xCT-targeting vaccines. We show that, despite xCT being a self-antigen, vaccination was able to induce a humoral immune response that delayed primary tumor growth and strongly impaired pulmonary metastasis formation in mice challenged with tumorsphere-derived cells. Moreover, immunotargeting of xCT was able to increase CSC chemosensitivity to doxorubicin, suggesting that it may act as an adjuvant to chemotherapy. In conclusion, our approach based on the comparison of the transcriptome of tumorspheres and parental cells allowed us to identify a novel CSC-related target and to develop preclinical therapeutic approaches able to impact on CSC biology, and therefore, hampering tumor growth and dissemination.

Genotoxic stress induces Sca-1-expressing metastatic mammary cancer cells

We describe a cell damage-induced phenotype in mammary carcinoma cells involving acquisition of enhanced migratory and metastatic properties. Induction of this state by radiation required increased activity of the Ptgs2 gene product cyclooxygenase 2 (Cox2), secretion of its bioactive lipid product prostaglandin E2 (PGE2), and the activity of the PGE2 receptor EP4. Although largely transient, decaying to low levels in a few days to a week, this phenotype was cumulative with damage and levels of cell markers Sca-1 and ALDH1 increased with treatment dose. The Sca-1+ , metastatic phenotype was inhibited by both Cox2 inhibitors and PGE2 receptor antagonists, suggesting novel approaches to radiosensitization.

Plac1 Is a Key Regulator of the Inflammatory Response and Immune Tolerance In Mammary Tumorigenesis

Plac1 is an X-linked trophoblast gene expressed at high levels in the placenta, but not in adult somatic tissues other than the testis. Plac1 however is re-expressed in several solid tumors and in most human cancer cell lines. To explore the role of Plac1 in cancer progression, Plac1 was reduced by RNA interference in EO771 mammary carcinoma cells. EO771 "knockdown" (KD) resulted in 50% reduction in proliferation in vitro and impaired tumor growth in syngeneic mice; however, tumor growth in SCID mice was equivalent to tumor cells expressing a non-silencing control RNA, suggesting that Plac1 regulated adaptive immunity. Gene expression profiling of Plac1 KD cells indicated reduction in several inflammatory and immune factors, including Cxcl1, Ccl5, Ly6a/Sca-1, Ly6c and Lif. Treatment of mice engrafted with wild-type EO771 cells with a Cxcr2 antagonist impaired tumor growth, reduced myeloid-derived suppressor cells and regulatory T cells, while increasing macrophages, dendritic cells, NK cells and the penetration of CD8+ T cells into the tumor bed. Cxcl1 KD phenocopied the effects of Plac1 KD on tumor growth, and overexpression of Cxcl1 partially rescued Plac1 KD cells. These results reveal that Plac1 modulates a tolerogenic tumor microenvironment in part by modulating the chemokine axis.

Disruption of IFN-I Signaling Promotes HER2/Neu Tumor Progression and Breast Cancer Stem Cells

Type I interferon (IFN-I) is a class of antiviral immunomodulatory cytokines involved in many stages of tumor initiation and progression. IFN-I acts directly on tumor cells to inhibit cell growth and indirectly by activating immune cells to mount antitumor responses. To understand the role of endogenous IFN-I in spontaneous, oncogene-driven carcinogenesis, we characterized tumors arising in HER2/neu transgenic (neuT) mice carrying a nonfunctional mutation in the IFNI receptor (IFNAR1). Such mice are unresponsive to this family of cytokines. Compared with parental neu^+/- mice (neuT mice), IFNAR1^-/- neu^+/- mice (IFNAR-neuT mice) showed earlier onset and increased tumor multiplicity with marked vascularization. IFNAR-neuT tumors exhibited deregulation of genes having adverse prognostic value in breast cancer patients, including the breast cancer stem cell (BCSC) marker aldehyde dehydrogenase-1A1 (ALDH1A1). An increased number of BCSCs were observed in IFNAR-neuT tumors, as assessed by ALDH1A1 enzymatic activity, clonogenic assay, and tumorigenic capacity. In vitro exposure of neuT⁺ mammospheres and cell lines to antibodies to IFN-I resulted in increased frequency of ALDH⁺ cells, suggesting that IFN-I controls stemness in tumor cells. Altogether, these results reveal a role of IFN-I in neuT-driven spontaneous carcinogenesis through intrinsic control of BCSCs. Cancer Immunol Res; 6(6); 658-70. ©2018 AACR.

Isolation of Stem-Like Cancer Cells in Primary Endometrial Cancer Using Cell Surface Markers CD133 and CXCR4

Endometrial cancer (EC) is the most common familiar gynecologic malignant tumor identified in the female reproductive system and has been increasing yearly. In this study, we will identify the surface markers and stem cell markers related with cancer stem cells (CSCs) of EC. Tissue samples were obtained from endometrial cancer patients during surgical procedures. Single cells were isolated from the tissues for culturing, transfection into nude mice, and histopathology analysis. RT-PCR demonstrated that the cultured cells strongly expressed stemness-related genes, such as c-Myc, Sox-2, Nanog, Oct 4A, ABCG2, BMI-1, CK-18, Nestin and β-actin. The expression of surface markers CD24, CD133, CD47, CD29, CD44, CXCR4, SSEA3 and SSEA4, CD24, and CD133 and chemokine markers such as CXCR4 were measured by flow cytometry. Then the double percentage of CD133+CXCR4+ cells constituted 7.2% and 9.3% in EC cells originated from two different patients, respectively. The CD133+CXCR4+ primary endometrial cancer cells grew faster, exhibited high expression of mRNA of stemness-related genes, produced more spheres, and had higher clonogenic ability than other subpopulations. They are also more resistant to anti-cancer drugs than other subpopulations. These findings indicate that CD133+CXCR4+ cells may possess some characteristics of CSCs in primary endometrial cancer. These cell surface markers may be useful for the development of drugs against CSC molecular targets or as a predictive marker for poor prognosis in primary endometrial cancer.

Salinomycin inhibits canine mammary carcinoma in vitro by targeting cancer stem cells

Salinomycin (SAL), a polyether ionophore antibiotic, has been demonstrated to selectively kill cancer stem cells (CSCs) in various types of human tumor. The aim of the present study was to investigate the effects of SAL on canine mammary CSCs. CSCs in canine mammary carcinoma cell lines (CMT7364 and CIPp) were identified using a sphere formation assay and flow cytometry. The chemoresistance, invasive potential and expression of stem cell-associated proteins of these spheres was then analyzed. This demonstrated that the spheres exhibited characteristics of CSCs, including a cluster of differentiation (CD)44⁺/CD24^-/low phenotype, upregulation of Wnt/β-catenin signaling pathway-associated proteins and chemoresistance. The viability of the spheres was decreased in a concentration- and time-dependent manner following treatment with SAL, and the spheres did not exhibit increased resistance to SAL compared with their parental cells. In addition, exposure to SAL inhibited sphere-formation and invasive potential in canine mammary CSCs in a dose-dependent manner. Furthermore, SAL decreased the CD44⁺/CD24^-/low population and downregulated the expression of Wnt/β-catenin signaling-associated proteins (β-catenin, Cyclin D1 and octamer-binding transcription factor 4) in the spheres. In conclusion, the present study demonstrated that SAL is an effective inhibitor of canine mammary CSCs in vitro, indicating that SAL is a promising chemotherapeutic agent for the treatment of canine mammary carcinoma.

Breast cancer stem cell: the roles and therapeutic implications

Breast cancers have been increasingly recognized as malignancies displaying frequent inter- and intra-tumor heterogeneity. This heterogeneity is represented by diverse subtypes and complexity within tumors, and impinges on response to therapy, metastasis, and prognosis. Cancer stem cells (CSCs), a subpopulation of cancer cells endowed with self-renewal and differentiation capacity, have been suggested to contribute to tumor heterogeneity. The CSC concept posits a hierarchical organization of tumors, at the apex of which are stem cells that drive tumor initiation, progression, and recurrence. In breast cancer, CSCs have been proposed to contribute to malignant progression, suggesting that targeting breast cancer stem cells (BCSCs) may improve treatment efficacy. Currently, several markers have been reported to identify BCSCs. However, there is objective variability with respect to the frequency and phenotype of BCSCs among different breast cancer cell lines and patients, and the regulatory mechanisms of BCSCs remain unclear. In this review, we summarize current literature about the diversity of BCSC markers, the roles of BCSCs in tumor development, and the regulatory mechanisms of BCSCs. We also highlight the most recent advances in BCSC targeting therapies and the challenges in translating the knowledge into clinical practice.

Immunization against HIF-1α Inhibits the Growth of Basal Mammary Tumors and Targets Mammary Stem Cells In Vivo

Purpose: Triple-negative breast cancer (TNBC) represents a cancer stem cell-enriched phenotype. Hypoxia-inducible factor-1α (HIF-1α) induces the expression of proteins associated with stemness and is highly upregulated in TNBC. We questioned whether HIF-1α was immunogenic and whether vaccination targeting HIF-1α would impact the growth of basal-like mammary tumors in transgenic mice.Experimental Design: We evaluated HIF-1α-specific IgG in sera from controls and patients with breast cancer. Class II epitopes derived from the HIF-1α protein sequence were validated by ELISPOT. To assess therapeutic efficacy, we immunized Tg-MMTVneu and C3(1)Tag mice with HIF-1α Th1-inducing peptides. Stem cells were isolated via magnetic bead separation. Levels of HIF-1α and stem cells in the tumor were quantitated by Western blotting and flow cytometry.Results: The magnitude (P < 0.001) and incidence (P < 0.001) of HIF-1α-specific IgG were elevated in TNBC patients compared with controls. Both breast cancer patients and donors showed evidence of HIF-1α-specific Th1 and Th2 immunity. Three HIF-1α-specific Th1 class II restricted epitopes that were highly homologous between species elicited type I immunity in mice. After HIF-1α vaccination, mammary tumor growth was significantly inhibited in only C3(1)Tag (basal-like/stem cell^high; P < 0.001) not TgMMTV-neu (luminal/neu/stem cell^low; P = 0.859) murine models. Vaccination increased type I T cells in the tumor (P = 0.001) and decreased cells expressing the stem cell marker, Sca-1, compared with controls (P = 0.004).Conclusions: An HIF-1α vaccine may be uniquely effective in limiting tumor growth in TNBC. Inhibiting outgrowth of breast cancer stem cells via active immunization in the adjuvant setting may impact disease recurrence. Clin Cancer Res; 23(13); 3396-404. ©2016 AACR.

Ly6E/K Signaling to TGFβ Promotes Breast Cancer Progression, Immune Escape, and Drug Resistance

Stem cell antigen Sca-1 is implicated in murine cancer stem cell biology and breast cancer models, but the role of its human homologs Ly6K and Ly6E in breast cancer are not established. Here we report increased expression of Ly6K/E in human breast cancer specimens correlates with poor overall survival, with an additional specific role for Ly6E in poor therapeutic outcomes. Increased expression of Ly6K/E also correlated with increased expression of the immune checkpoint molecules PDL1 and CTLA4, increased tumor-infiltrating T regulatory cells, and decreased natural killer (NK) cell activation. Mechanistically, Ly6K/E was required for TGFβ signaling and proliferation in breast cancer cells, where they contributed to phosphorylation of Smad1/5 and Smad2/3. Furthermore, Ly6K/E promoted cytokine-induced PDL1 expression and activation and binding of NK cells to cancer cells. Finally, we found that Ly6K/E promoted drug resistance and facilitated immune escape in this setting. Overall, our results establish a pivotal role for a Ly6K/E signaling axis involving TGFβ in breast cancer pathophysiology and drug response, and highlight this signaling axis as a compelling realm for therapeutic invention. Cancer Res; 76(11); 3376-86. ©2016 AACR.

In vitro comparative models for canine and human breast cancers

During the past four decades, an increased number of similarities between canine mammary tumors and human breast cancer have been reported: molecular, histological, morphological, clinical and epidemiological, which lead to comparative oncological studies. One of the most important goals in human and veterinary oncology is to discover potential molecular biomarkers that could detect breast cancer in an early stage and to develop new effective therapies. Recently, cancer cell lines have successfully been used as an in vitro model to study the biology of cancer, to investigate molecular pathways and to test the efficiency of anticancer drugs. Moreover, establishment of an experimental animal model for the study of human breast cancer will improve testing potential anti-cancer therapies and the discovery of effective therapeutic schemes suitable for human clinical trials.

In this review, we collected data from previous studies that strengthen the value of canine mammary cancer cell lines as an in vitro model for the study of human breast cancer.

Breast Cancer Stem Cell Isolation

Cells within the tumor are highly heterogeneous. Only a small portion of the cells within the tumor is capable to generate a new tumor. These cells are called cancer stem cells. Theoretically, cancer stem cells are originally from normal stem cells or early progenitor cells which accumulate the random mutations and undergo an altered version of the normal differentiation process. The cancer stem cell drives tumor progression and its recurrence. Thus, the technique to identify and purify the cancer stem cell is the key in any cancer stem cell research. In this protocol, we provide the basic technology of identification and purification of breast cancer stem cells as well as further functional assays to help the researchers achieve their research goals.

Immunotargeting of Antigen xCT Attenuates Stem-like Cell Behavior and Metastatic Progression in Breast Cancer

Resistance to therapy and lack of curative treatments for metastatic breast cancer suggest that current therapies may be missing the subpopulation of chemoresistant and radioresistant cancer stem cells (CSC). The ultimate success of any treatment may well rest on CSC eradication, but specific anti-CSC therapies are still limited. A comparison of the transcriptional profiles of murine Her2(+) breast tumor TUBO cells and their derived CSC-enriched tumorspheres has identified xCT, the functional subunit of the cystine/glutamate antiporter system xc(-), as a surface protein that is upregulated specifically in tumorspheres. We validated this finding by cytofluorimetric analysis and immunofluorescence in TUBO-derived tumorspheres and in a panel of mouse and human triple negative breast cancer cell-derived tumorspheres. We further show that downregulation of xCT impaired tumorsphere generation and altered CSC intracellular redox balance in vitro, suggesting that xCT plays a functional role in CSC biology. DNA vaccination based immunotargeting of xCT in mice challenged with syngeneic tumorsphere-derived cells delayed established subcutaneous tumor growth and strongly impaired pulmonary metastasis formation by generating anti-xCT antibodies able to alter CSC self-renewal and redox balance. Finally, anti-xCT vaccination increased CSC chemosensitivity to doxorubicin in vivo, indicating that xCT immunotargeting may be an effective adjuvant to chemotherapy.

OTX2 exhibits cell-context-dependent effects on cellular and molecular properties of human embryonic neural precursors and medulloblastoma cells

Medulloblastoma (MB) is the most common malignant primary pediatric brain tumor and is currently divided into four subtypes based on different genomic alterations, gene expression profiles and response to treatment: WNT, Sonic Hedgehog (SHH), Group 3 and Group 4. This extensive heterogeneity has made it difficult to assess the functional relevance of genes to malignant progression. For example, expression of the transcription factor Orthodenticle homeobox2 (OTX2) is frequently dysregulated in multiple MB variants; however, its role may be subtype specific. We recently demonstrated that neural precursors derived from transformed human embryonic stem cells (trans-hENs), but not their normal counterparts (hENs), resemble Groups 3 and 4 MB in vitro and in vivo. Here, we tested the utility of this model system as a means of dissecting the role of OTX2 in MB using gain- and loss-of-function studies in hENs and trans-hENs, respectively. Parallel experiments with MB cells revealed that OTX2 exerts inhibitory effects on hEN and SHH MB cells by regulating growth, self-renewal and migration in vitro and tumor growth in vivo. This was accompanied by decreased expression of pluripotent genes, such as SOX2, and was supported by overexpression of SOX2 in OTX2+ SHH MB and hENs that resulted in significant rescue of self-renewal and cell migration. By contrast, OTX2 is oncogenic and promotes self-renewal of trans-hENs and Groups 3 and 4 MB independent of pluripotent gene expression. Our results demonstrate a novel role for OTX2 in self-renewal and migration of hENs and MB cells and reveal a cell-context-dependent link between OTX2 and pluripotent genes. Our study underscores the value of human embryonic stem cell derivatives as alternatives to cell lines and heterogeneous patient samples for investigating the contribution of key developmental regulators to MB progression.

Summary: Human embryonic stem cell neural derivatives can be used to model the molecular and cellular properties of medulloblastoma.

Blockade of Wnt/β-catenin signaling suppresses breast cancer metastasis by inhibiting CSC-like phenotype

The identification of cancer stem cells (CSCs) represents an important milestone in the understanding of chemodrug resistance and cancer recurrence. More specifically, some studies have suggested that potential metastasis-initiating cells (MICs) might be present within small CSC populations. The targeting and eradication of these cells represents a potential strategy for significantly improving clinical outcomes. A number of studies have suggested that dysregulation of Wnt/β-catenin signaling occurs in human breast cancer. Consistent with these findings, our previous data have shown that the relative level of Wnt/β-catenin signaling activity in breast cancer stem cells (BCSCs) is significantly higher than that in bulk cancer cells. These results suggest that BCSCs could be sensitive to therapeutic approaches targeting Wnt/β-catenin signaling pathway. In this context, abnormal Wnt/β-catenin signaling activity may be an important clinical feature of breast cancer and a predictor of poor survival. We therefore hypothesized that Wnt/β-catenin signaling might regulate self-renewal and CSC migration, thereby enabling metastasis and systemic tumor dissemination in breast cancer. Here, we investigated the effects of inhibiting Wnt/β-catenin signaling on cancer cell migratory potential by examining the expression of CSC-related genes, and we examined how this pathway links metastatic potential with tumor formation in vitro and in vivo.

Characterization of Nestin, a Selective Marker for Bone Marrow Derived Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are multipotent cells capable of differentiating into multiple cell lineages and contributing to tissue repair and regeneration. Characterization of the physiological function of MSCs has been largely hampered by lack of unique markers. Nestin, originally found in neuroepithelial stem cells, is an intermediate filament protein expressed in the early stages of development. Increasing studies have shown a particular association between Nestin and MSCs. Nestin could characterize a subset of bone marrow perivascular MSCs which contributed to bone development and closely contacted with hematopoietic stem cells (HSCs). Nestin expressing (Nes(+)) MSCs also play a role in the progression of various diseases. However, Nes(+) cells were reported to participate in angiogenesis as MSCs or endothelial progenitor cells (EPCs) in several tissues and be a heterogeneous population comprising mesenchymal cells and endothelial cells in the developing bone marrow. In this review article, we will summarize the progress of the research on Nestin, particularly the function of Nes(+) cells in bone marrow, and discuss the feasibility of using Nestin as a specific marker for MSCs.

Targeting the hsp70 gene delays mammary tumor initiation and inhibits tumor cell metastasis

Elevated levels of the inducible heat-shock protein 70 (Hsp72) have been implicated in mammary tumorigenesis in histological investigations of human breast cancer. We therefore examined the role of Hsp72 in mice, using animals in which the hsp70 gene was inactivated. We used a spontaneous tumor system with mice expressing the polyomavirus middle T (PyMT) oncogene under control of the mouse mammary tumor virus (MMTV) long-terminal repeat (MMT mice). These mice developed spontaneous, metastatic mammary cancer. We then showed Hsp72 to be upregulated in a fraction of mammary cancer initiating cells (CIC) within the MMT tumor cell population. These cells were characterized by elevated surface levels of stem cell markers CD44 and Sca1 and by rapid metastasis. Inactivation of the hsp70 gene delayed the initiation of mammary tumors. This delay in tumor initiation imposed by loss of hsp70 was correlated with a decreased pool of CIC. Interestingly, hsp70 knockout significantly reduced invasion and metastasis by mammary tumor cells and implicated its product Hsp72 in cell migration and formation of secondary neoplasms. Impaired tumorigenesis and metastasis in hsp70-knockout MMT mice was associated with downregulation of the met gene and reduced activition of the oncogenic c-Met protein. These experiments therefore showed Hsp72 to be involved in the growth and progression of mammary carcinoma and highlighted this protein as a potential target for anticancer drug development.

Wnt/β-Catenin Small-Molecule Inhibitor CWP232228 Preferentially Inhibits the Growth of Breast Cancer Stem-like Cells

Breast cancer stem cells (BCSC) are resistant to conventional chemotherapy and radiotherapy, which may destroy tumor masses but not all BCSC that can mediate relapses. In the present study, we showed that the level of Wnt/β-catenin signaling in BCSC is relatively higher than in bulk tumor cells, contributing to a relatively higher level of therapeutic resistance. We designed a highly potent small-molecule inhibitor, CWP232228, which antagonizes binding of β-catenin to T-cell factor (TCF) in the nucleus. Notably, although CWP232228 inhibited the growth of both BCSC and bulk tumor cells by inhibiting β-catenin-mediated transcription, BCSC exhibited greater growth inhibition than bulk tumor cells. We also documented evidence of greater insulin-like growth factor-I (IGF-I) expression by BCSC than by bulk tumor cells and that CWP232228 attenuated IGF-I-mediated BCSC functions. These results suggested that the inhibitory effect of CWP232228 on BCSC growth might be achieved through the disruption of IGF-I activity. Taken together, our findings indicate that CWP232228 offers a candidate therapeutic agent for breast cancer that preferentially targets BCSC as well as bulk tumor cells.

Antitumor immunization of mothers delays tumor development in cancer-prone offspring

Maternal immunization is successfully applied against some life-threatening infectious diseases as it can protect the mother and her offspring through the passive transfer of maternal antibodies. Here, we sought to evaluate whether the concept of maternal immunization could also be applied to cancer immune-prevention. We have previously shown that antibodies induced by DNA vaccination against rat Her2 (neu) protect heterozygous neu-transgenic female (BALB-neuT) mice from autochthonous mammary tumor development. We, herein, seek to evaluate whether a similar maternal immunization can confer antitumor protection to BALB-neuT offspring. Significantly extended tumor-free survival was observed in BALB-neuT offspring born and fed by mothers vaccinated against neu, as compared to controls. Maternally derived anti-neu immunoglobulin G (IgG) was successfully transferred from mothers to newborns and was responsible for the protective effect. Vaccinated mothers and offspring also developed active immunity against neu as revealed by the presence of T-cell-mediated cytotoxicity against the neu immunodominant peptide. This active response was due to the milk transfer of immune complexes that were formed between the neu extracellular domain, shed from vaccine-transfected muscle cells, and the anti-neu IgG induced by the vaccine. These findings show that maternal immunization has the potential to hamper mammary cancer in genetically predestinated offspring and to develop into applications against lethal neonatal cancer diseases for which therapeutic options are currently unavailable.

Syngeneic Murine Ovarian Cancer Model Reveals That Ascites Enriches for Ovarian Cancer Stem-Like Cells Expressing Membrane GRP78

Patients with ovarian cancer are generally diagnosed at FIGO (International Federation of Gynecology and Obstetrics) stage III/IV, when ascites is common. The volume of ascites correlates positively with the extent of metastasis and negatively with prognosis. Membrane GRP78, a stress-inducible endoplasmic reticulum chaperone that is also expressed on the plasma membrane ((mem)GRP78) of aggressive cancer cells, plays a crucial role in the embryonic stem cell maintenance. We studied the effects of ascites on ovarian cancer stem-like cells using a syngeneic mouse model. Our study demonstrates that ascites-derived tumor cells from mice injected intraperitoneally with murine ovarian cancer cells (ID8) express increased (mem)GRP78 levels compared with ID8 cells from normal culture. We hypothesized that these ascites-associated (mem)GRP78(+) cells are cancer stem-like cells (CSC). Supporting this hypothesis, we show that (mem)GRP78(+) cells isolated from murine ascites exhibit increased sphere forming and tumor initiating abilities compared with (mem)GRP78(-) cells. When the tumor microenvironment is recapitulated by adding ascites fluid to cell culture, ID8 cells express more (mem)GRP78 and increased self-renewing ability compared with those cultured in medium alone. Moreover, compared with their counterparts cultured in normal medium, ID8 cells cultured in ascites, or isolated from ascites, show increased stem cell marker expression. Antibodies directed against the carboxy-terminal domain of GRP78: (i) reduce self-renewing ability of murine and human ovarian cancer cells preincubated with ascites and (ii) suppress a GSK3α-AKT/SNAI1 signaling axis in these cells. Based on these data, we suggest that (mem)GRP78 is a logical therapeutic target for late-stage ovarian cancer.

A mathematical-biological joint effort to investigate the tumor-initiating ability of Cancer Stem Cells

The involvement of Cancer Stem Cells (CSCs) in tumor progression and tumor recurrence is one of the most studied subjects in current cancer research. The CSC hypothesis states that cancer cell populations are characterized by a hierarchical structure that affects cancer progression. Due to the complex dynamics involving CSCs and the other cancer cell subpopulations, a robust theory explaining their action has not been established yet. Some indications can be obtained by combining mathematical modeling and experimental data to understand tumor dynamics and to generate new experimental hypotheses. Here, we present a model describing the initial phase of ErbB2⁺ mammary cancer progression, which arises from a joint effort combing mathematical modeling and cancer biology. The proposed model represents a new approach to investigate the CSC-driven tumorigenesis and to analyze the relations among crucial events involving cancer cell subpopulations. Using in vivo and in vitro data we tuned the model to reproduce the initial dynamics of cancer growth, and we used its solution to characterize observed cancer progression with respect to mutual CSC and progenitor cell variation. The model was also used to investigate which association occurs among cell phenotypes when specific cell markers are considered. Finally, we found various correlations among model parameters which cannot be directly inferred from the available biological data and these dependencies were used to characterize the dynamics of cancer subpopulations during the initial phase of ErbB2⁺ mammary cancer progression.

Microenvironment, oncoantigens, and antitumor vaccination: lessons learned from BALB-neuT mice

The tyrosine kinase human epidermal growth factor receptor 2 (HER2) gene is amplified in approximately 20% of human breast cancers and is associated with an aggressive clinical course and the early development of metastasis. Its crucial role in tumor growth and progression makes HER2 a prototypic oncoantigen, the targeting of which may be critical for the development of effective anticancer therapies. The setup of anti-HER2 targeting strategies has revolutionized the clinical outcome of HER2⁺ breast cancer. However, their initial success has been overshadowed by the onset of pharmacological resistance that renders them ineffective. Since the tumor microenvironment (TME) plays a crucial role in drug resistance, the design of more effective anticancer therapies should depend on the targeting of both cancer cells and their TME as a whole. In this review, starting from the successful know-how obtained with a HER2⁺ mouse model of mammary carcinogenesis, the BALB-neuT mice, we discuss the role of TME in mammary tumor development. Indeed, a deeper knowledge of antigens critical for cancer outbreak and progression and of the mechanisms that regulate the interplay between cancer and stromal cell populations could advise promising ways for the development of the best anticancer strategy.

Sca1⁺ murine pituitary adenoma cells show tumor-growth advantage

The role of tumor stem cells in benign tumors such as pituitary adenomas remains unclear. In this study, we investigated whether the cells within pituitary adenomas that spontaneously develop in Rb+/- mice are hierarchically distributed with a subset being responsible for tumor growth. Cells derived directly from such tumors grew as spheres in serum-free culture medium supplemented with epidermal growth factor and basic fibroblast growth factor. Some cells within growing pituitary tumor spheres (PTS) expressed common stem cell markers (Sca1, Sox2, Nestin, and CD133), but were devoid of hormone-positive differentiated cells. Under subsequent differentiating conditions (matrigel-coated growth surface), PTS expressed all six pituitary hormones. We next searched for specific markers of the stem cell population and isolated a Sca1(+) cell population that showed increased sphere formation potential, lower mRNA hormone expression, higher expression of stem cell markers (Notch1, Sox2, and Nestin), and increased proliferation rates. When transplanted into non-obese diabetic-severe combined immunodeficiency gamma mice brains, Sca1(+) pituitary tumor cells exhibited higher rates of tumor formation (brain tumors observed in 11/11 (100%) vs 7/12 (54%) of mice transplanted with Sca1(+) and Sca1(-) cells respectively). Magnetic resonance imaging and histological analysis of brain tumors showed that tumors derived from Sca1(+) pituitary tumor cells were also larger and plurihormonal. Our findings show that Sca1(+) cells derived from benign pituitary tumors exhibit an undifferentiated expression profile and tumor-proliferative advantages, and we propose that they could represent putative pituitary tumor stem/progenitor cells.

Acute lymphoid leukemia cells with greater stem cell antigen-1 (Ly6a/Sca-1) expression exhibit higher levels of metalloproteinase activity and are more aggressive in vivo

Stem cell antigen-1 (Ly6a/Sca-1) is a gene that is expressed in activated lymphocytes, hematopoietic stem cells and stem cells of a variety of tissues in mice. Despite decades of study its functions remain poorly defined. These studies explored the impact of expression of this stem cell associated gene in acute lymphoid leukemia. Higher levels of Ly6a/Sca-1 expression led to more aggressive leukemia growth in vivo and earlier death of hosts. Leukemias expressing higher levels of Ly6a/Sca-1 exhibited higher levels of matrix metalloproteinases. The results suggest the hypothesis that the more aggressive behavior of Ly6a/Sca-1 expressing leukemias is due at least in part to greater capacity to degrade microenvironmental stroma and invade tissues.

The in-vitro spheroid culture induces a more highly differentiated but tumorigenic population from melanoma cell lines

Cancer stem cells (CSCs) have been identified in various malignancies, and different properties have been examined to characterize CSCs: tumorigenicity in immunocompromised mice, stem cell surface markers, label-retaining properties, and proliferation as nonadherent spheres. This study explored the consistency and efficiency among these methods. Among the melanoma cell lines examined (A375, A875, MUM-2b, and MUM-2c), only A375 and MUM-2c grew as nonadherent spheres and continuously propagated in a defined serum-free medium in vitro. Flow cytometry and immunofluorescence analysis indicated that sphere-derived cells contained a smaller proportion of cells expressing the candidate surface markers of melanoma stem cells such as ABCB5, CD133, CD20 and CD271, and a larger proportion of cells expressing melanocytic differentiation markers such as HMB45 and S100 protein, compared with adherent cells. Surprisingly, the more highly differentiated sphere-derived melanoma cells exhibited increased tumorigenic potential in vivo, as indicated by shorter tumor incubation (A375) and smaller number of cells required to initiate tumor formation (A375 and MUM-2c) compared with those of parental cells. Despite the similarity in histopathological characteristics, the expression profile indicated that xenografts derived from sphere-derived melanoma cells exhibited a more tumorigenic phenotype with respect to the stem or the differentiation markers detected by immunohistochemical analysis. Therefore, sphere formation in nonadherent cultures may not be a preferred surrogate in-vitro method for enriching melanoma stem cells according to candidate markers but may be a favorable condition for activating potential CSCs.

IFN-γ Rα is a key determinant of CD8+ T cell-mediated tumor elimination or tumor escape and relapse in FVB mouse

During the past decade, the dual function of the immune system in tumor inhibition and tumor progression has become appreciated. We have previously reported that neu-specific T cells can induce rejection of neu positive mouse mammary carcinoma (MMC) and also facilitate tumor relapse by inducing neu antigen loss and epithelial to mesenchymal transition (EMT). Here, we sought to determine the mechanism by which CD8+ T cells either eliminate the tumor, or maintain tumor cells in a dormant state and eventually facilitate tumor relapse. We show that tumor cells that express high levels of IFN-γ Rα are eliminated by CD8+ T cells. In contrast, tumor cells that express low levels of IFN-γ Rα do not die but remain dormant and quiescent in the presence of IFN-γ producing CD8+ T cells until they hide themselves from the adaptive immune system by losing the tumor antigen, neu. Relapsed tumor cells show CD44+CD24- phenotype with higher rates of tumorigenesis, in vivo. Acquisition of CD44+CD24- phenotype in relapsed tumors was not solely due to Darwinian selection. Our data suggest that tumor cells control the outcome of tumor immune surveillance through modulation of the expression of    IFN-γ Rα.