Tumor-derived mesenchymal stem cells and orthotopic site increase the tumor initiation potential of putative mouse mammary cancer stem cells derived from MMTV-PyMT mice

The ability to transplant mammary cancer stem cells, identified by the phenotype CD24⁺CD29⁺CD49f⁺Sca-1^low, is dependent on the microenvironment in which the cells are placed. Using the MMTV-PyMT mouse model of mammary cancer, we now report two methods of tumor growth enhancement: contributions of tumor stroma in the form of tumor-derived mesenchymal stem cells and orthotopic vs. heterotopic transplantation sites. To support evidence of stem cell function, tumor-derived mesenchymal stem cells differentiated into adipocyte- and osteocyte-like cells after culture in specific medium. Co-injection of tumor-initiating cells with tumor-derived mesenchymal stem cells significantly increased tumor initiation compared to subcutaneous injection of TICs alone; co-injection also allowed tumor initiation with a single TIC. Interestingly, we observed the formation of sarcomas after co-injections of tumor-derived mesenchymal stem cells or mouse embryonic fibroblasts with TICs; sarcomas are not observed in spontaneous MMTV-PyMT tumors and rarely observed in injections of TICs alone. Tumor initiation was also significantly increased in the orthotopic injection site compared to heterotopic injections. We conclude that tumor stroma and orthotopic sites both enhance tumor initiation by mammary cancer stem cells.     

Anti-matrix metalloproteinase-9 DNAzyme decreases tumor growth in the MMTV-PyMT mouse model of breast cancer

Introduction

Despite continued improvements in diagnosis, surgical techniques, and chemotherapy, breast cancer patients are still overcome by cancer metastasis. Tumor cell proliferation, invasion and metastasis are mediated, at least in part, through degradation of basement membrane by neutral matrix metalloproteinases (MMP) produced by tumor and stromal cells. Evidence suggests that MMP-9 plays a significant role in breast tumor cell invasion and metastasis. DNAzymes or catalytic oligonucleotides are new classes of gene targeting molecules that bind and cleave a specific mRNA, resulting in decreased protein expression.

Methods

The application of anti-MMP-9 DNAzyme (AM9D) for the treatment of primary and metastatic breast cancer was evaluated in vitro and in vivo using MDA-MB-231 cells and the MMTV-PyMT transgenic breast cancer mouse model. Spontaneously developed mammary tumors in MMTV-PyMT transgenic mice were treated intratumorally with naked AM9D, once a week for 4 weeks. The stability of DNAzyme was determined in vitro and in vivo using fluorescently labeled DNAzyme.

Results

AM9D specifically inhibited expression of MMP-9 in MDA-MB-231 cells resulting in reduced invasive property of these cells by 43%. Weekly intratumoral treatment of spontaneously developed mammary tumors in MMTV-PyMT transgenic mice was sufficient to significantly reduce the rate of tumor growth and final tumor load in a dose dependent and statistically significant manner (P < 0.05). This decrease in tumor growth was correlated with decreased MMP-9 protein production within the treated tumor tissues. Tumors treated with AM9D were also less vascularized and contained more apoptotic cells compared to control and untreated tumors.

Conclusions

These results show that targeting and down regulation of MMP-9 by AM9D could prove useful as a therapy against breast carcinoma tumor growth and invasion.     

乳腺干细胞和乳腺癌干细胞研究现状

<正>干细胞是机体内具有自我更新和多向分化潜能的细胞群体,并能通过分化产生特定组织的成熟细胞,理论上一个干细胞可以发育成为完整的生物个体或组织器官[1]。关于干细胞的概念,目前最广泛接受的是,干细胞是可以进行对称和非对称分裂的未分化的细胞群:分裂发生时,一个干细胞产生两个子细胞,一个与母细胞完全一致,具有母细胞同样的特征;另一个细胞可以分化形成不同的成熟细胞株。     

Steroid hormone receptor status of mouse mammary stem cells

The estrogen receptor alpha (ERalpha), progesterone receptor (PR), and erbB2 (Her2 in humans) are important prognostic markers of human breast cancer, and they are variably expressed in different subtypes of breast cancer. The basal subtype, for example, is negative for ERalpha, PR, and Her2 by immunohistochemistry. We investigated the expression of these signaling molecules in enriched populations of mouse mammary stem cells and luminal cells that were isolated according to their differential expression of CD24 and the alpha6beta1-integrin complex. We found that the basal population, which is enriched in mouse mammary stem cells, did not express ERalpha, PR, or ErbB2/Her2 but did express epidermal growth factor receptor (EGFR)/ErbB1, whereas the subset of cells enriched for luminal cells expressed ERalpha (37% of cells) and PR (40% of cells) but not ErbB2/Her2 or EGFR/ErbB1. Ovariectomy confirmed the importance of estrogen signaling to luminal cell proliferation but had no effect on the size of the mouse mammary stem cell-enriched population. Thus, mouse mammary stem cells were negative for ERalpha, PR, and ErbB2 and appeared to share common properties with poor-prognosis basal breast cancer.     

The mammary progenitor marker CD61/beta3 integrin identifies cancer stem cells in mouse models of mammary tumorigenesis

The cells of origin and mechanisms that underpin tumor heterogeneity in breast cancer are poorly understood. Here, we have examined three mouse models of mammary tumorigenesis (MMTV-wnt-1, MMTV-neu, and p53(+/-)) for changes in their epithelial cell hierarchy during the preneoplastic and neoplastic stages of tumor progression. In preneoplastic tissue, only MMTV-wnt-1 mice showed a perturbation in their epithelial subpopulations. In addition to an expanded mammary stem cell pool, repopulating cells capable of yielding extensive mammary outgrowths in vivo were revealed in the committed luminal progenitor population. These findings indicate that wnt-1 activation induces the appearance of aberrant progenitor cells, and suggest that both mammary stem and progenitor cells can serve as the cellular targets of wnt-1-induced tumorigenesis. In tumors arising in MMTV-wnt-1 tumors, the luminal epithelial progenitor marker CD61/beta3 integrin identified a cancer stem cell (CSC) population that was highly enriched for tumorigenic capability relative to the CD61(-) subset. CD61 expression also defined a CSC subset in 50% of p53(+/-)-derived tumors. No CSCs, however, could be identified in the more homogeneous MMTV-neu/erbB2 model, suggesting an alternative model of tumorigenesis. Overall, our findings show the utility of the progenitor marker CD61 in the identification of CSCs that sustain specific mammary tumors.     

小白菊内酯体内杀伤小鼠乳腺癌肿瘤干细胞

目的： 探讨小白菊内酯（parthenolide,PTL）对小鼠乳腺癌肿瘤干细胞（cancer stem cell,CSC）的杀伤作用,为临床应用PTL治疗乳腺癌提供实验依据。 方法： 采用5-氟尿嘧啶（5-fluorouracil, 5-FU）化疗法制备富含CSC的小鼠4T1细胞乳腺癌模型,随机分为对照组、5-FU组、PTL组。4周后脱颈处死小鼠,检测各组小鼠肿瘤的体积和重量,流式细胞术检测小鼠肿瘤组织中CD44+CD24-/low细胞比例,Hoechst33342染色法检测侧群（side population,SP）细胞的比例,免疫组化法检测CD55和乙醛脱氢酶1（aldehyde dehydrogenase1,ALDH1）蛋白的表达,倒置显微镜观察乳腺癌细胞微球体的形成。 结果： 成功制备富含CSC的小鼠乳腺癌细胞移植瘤模型,PTL可下调小鼠肿瘤组织中CD44+CD24-/low细胞的比例\[（42.5±3.7）% vs （68.7±32）%,P<0.05\],有效降低荷瘤小鼠肿瘤组织中SP细胞的比例\[（39.2±1.8）% vs （61.3±2.6）%,P<0.05\],下调小鼠移植瘤组织中CD55和ALDH1蛋白的表达\[（18.9±1.5）% vs （30.1±1.3）%,（8.1±2.3）% vs （18.0±1.4）%;均P<0.05\],抑制小鼠肿瘤细胞在无血清培养条件下形成微球体,并可抑制小鼠移植瘤的体积和重量\[（0.625±0.159）cm3 vs （1.715±0184）cm3,（1.467±0.373）g vs （3.367±0.398）g;均P<0.05\]。 结论： PTL在荷瘤小鼠体内可以明显降低肿瘤组织CSC含量,提示PTL可用来靶向杀伤乳腺癌CSC。     

Pleiotropic functions of the tumor- and metastasis-suppressing matrix metalloproteinase-8 in mammary cancer in MMTV-PyMT transgenic mice

Introduction

Matrix metalloproteinase-8 (MMP-8; neutrophil collagenase) is an important regulator of innate immunity that has oncosuppressive actions in numerous tumor types.

Methods

We have intercrossed Mmp8-null mice with the Polyoma virus middle T oncogene-driven (MMTV-PyMT) mouse model of mammary cancer to explore the effects of loss of MMP-8 on the incidence and progression of mammary carcinomas.

Results

In this aggressive mouse model of breast cancer, loss of MMP-8 accelerated tumor onset even further, such that 90% of MMTV-PyMT; Mmp8-null female mice were tumor-bearing at the time of weaning. Throughout the 14 weeks of the model, tumor burden increased in homozygous Mmp8-null mice compared to Mmp8-wild-type and -heterozygote animals. Likewise, lung metastasis dramatically increased in the MMTV-PyMT; Mmp8-null mice. Immunohistochemistry revealed that tumors in wild-type, Mmp8-heterozygotes and -null animals had similar vascular density at 8 weeks, but at 10 weeks Mmp8-wild-type tumors had a lower vascularity than their heterozygote and null counterparts. No differences in macrophage infiltration were apparent throughout primary tumor development, though at 10 weeks a drop in neutrophil infiltrates was observed in Mmp8-wild-type tumors. Using quantitative real-time RT-PCR, we tracked the expression of the entire Mmp and Timp gene families, observing a significant decrease in Mmp3 expression in Mmp8-null tumors compared to wild-type and heterozygotes throughout the time course of the model, which was confirmed at the protein level.

Conclusions

These findings provide novel insight into the suppressive action of MMP-8 on mammary tumorigenesis and metastasis, and indicate that the loss of MMP-8 likely has pleiotropic effects on innate immunity and angiogenesis that are reflected in changes in the protease web.     

鼠乳腺干细胞研究进展

乳腺干细胞是乳腺组织内可以自我更新的细胞亚群,具有分化成导管、腺泡和肌上皮细胞的能力.近年来,多个实验室通过不同的方法确认乳腺干细胞,包括细胞表面标记Sca-1、Hoechst溢出实验、CD24、CD31-CD45-Ter119-CD24+CD29hi等,为阐明乳腺干细胞的自我更新机制,设计有效的乳腺癌治疗方法提供了新的工具.     

Characterization of sequences related to the mouse mammary tumor virus that are specific to MCF-7 breast cancer cells

Mouse mammary tumour virus (MuMTV) DNA hybridized more strongly to two human EcoRI fragments (6.6 and 9.5 kilobases) in DNA from the MCF-7 human breast cancer cell line than in DNA from normal human placenta. Seven recombinants (NMWV 1E1-7) containing these MuMTV-related sequences were identified. Hybridization of NMWV 1E probes to Southern transfers of human DNA suggested that these probes hybridize to multiple sequences in the human genome. The pattern obtained was very similar to that obtained using MuMTV gag-pol DNA. Analysis of the cloned DNA showed that the NMWV 1E MuMTV-related sequences are arranged as tandem repeats and are contained in EcoRI fragments of 6.6 or 9.5 kilobases. Only two NMWV 1E EcoRI fragments (9.5 and 15 kilobases) were detected in 17 DNA samples prepared from human placenta and blood. In contrast the 6.6-kilobase EcoRI fragment was detected in two (MCF-7 and EFM-19) of seven breast cancer cell lines and the MDA MB-231 cell line contained NMWV 1E sequences in an EcoRI fragment of 9.8 kilobases.     

Prolactin-induced mouse mammary carcinomas model estrogen resistant luminal breast cancer

Introduction  

Tumors that express estrogen receptor alpha (ERα+) comprise 75% of breast cancers in women. While treatments directed against this receptor have successfully lowered mortality rates, many primary tumors initially or later exhibit resistance. The paucity of murine models of this "luminal" tumor subtype has hindered studies of factors that promote their pathogenesis and modulate responsiveness to estrogen-directed therapeutics. Since epidemiologic studies closely link prolactin and the development of ERα+ tumors in women, we examined characteristics of the aggressive ERα+ and ERα- carcinomas which develop in response to mammary prolactin in a murine transgenic model (neu-related lipocalin- prolactin (NRL-PRL)). To evaluate their relationship to clinical tumors, we determined phenotypic relationships among these carcinomas, other murine models of breast cancer, and features of luminal tumors in women.     

Polyphenols prevent cell shedding from mouse mammary cancer spheroids and inhibit cancer cell invasion in confrontation cultures derived from embryonic stem cells

The prognosis of cancer disease is worsened upon shedding of tumor cells from the primary tumor, which escape to the blood stream and form metastases at distant sites within the body. Inhibition of cell shedding from the primary tumor could therefore be exploited to avoid metastasis and delay the progression of the cancer disease. In the present study, we investigated the effects of the polyphenols resveratrol, baicalein, epicatechin, epigallocatechin and polyphenon 60 on cell shedding from multicellular tumor spheroids of the murine mammacarcinoma cell line 4T1, cell invasion into embryonic stem cell-derived tissues, generation of reactive oxygen species (ROS) and expression of matrix metalloproteinase 9 (MMP-9). With increasing tumor spheroid growth MMP-9 expression was upregulated and cells detached from tumor spheroids and formed subspheroids that displayed pronounced ROS generation. Upon incubation with polyphenols tumor growth was arrested and cell shedding was totally abolished. Polyphenol treatment decreased ROS generation and downregulated MMP-9 expression. Furthermore, polyphenols significantly inhibited invasion of tumor cells into embryonic stem cell-derived, vascularized tissues. Our data suggest, that polyphenols inhibit cell shedding and invasion by their anti-oxidative capacity and downregulation of MMP-9 expression.     

Towards an integrated model for breast cancer etiology: the crucial role of the number of mammary tissue-specific stem cells

Perinatal events and conditions, notably birth weight, are associated with breast cancer risk in offspring, and correlates of mammary gland mass are predictors of breast cancer risk. These findings may be interpreted as indicating that high levels of estrogens and components of the insulin-like growth factor system during pregnancy favour the generation of mammary tissue-specific stem cells, and that the number of these cells, which is positively associated with mammary gland mass, is an important determinant of breast cancer risk. Perinatal events and conditions may also affect risk for other malignancies, but the evidence in the case of breast cancer is prominent, possibly because estrogens and the insulin-like growth factor system are both involved in breast cancer etiology and affect birth weight.     

Mouse mammary stem cells express prognostic markers for triple-negative breast cancer

Introduction

Triple-negative breast cancer (TNBC) is a heterogeneous group of tumours in which chemotherapy, the current mainstay of systemic treatment, is often initially beneficial but with a high risk of relapse and metastasis. There is currently no means of predicting which TNBC will relapse. We tested the hypothesis that the biological properties of normal stem cells are re-activated in tumour metastasis and that, therefore, the activation of normal mammary stem cell-associated gene sets in primary TNBC would be highly prognostic for relapse and metastasis.

Methods

Mammary basal stem and myoepithelial cells were isolated by flow cytometry and tested in low-dose transplant assays. Gene expression microarrays were used to establish expression profiles of the stem and myoepithelial populations; these were compared to each other and to our previously established mammary epithelial gene expression profiles. Stem cell genes were classified by Gene Ontology (GO) analysis and the expression of a subset analysed in the stem cell population at single cell resolution. Activation of stem cell genes was interrogated across different breast cancer cohorts and within specific subtypes and tested for clinical prognostic power.

Results

A set of 323 genes was identified that was expressed significantly more highly in the purified basal stem cells compared to all other cells of the mammary epithelium. A total of 109 out of 323 genes had been associated with stem cell features in at least one other study in addition to our own, providing further support for their involvement in the biology of this cell type. GO analysis demonstrated an enrichment of these genes for an association with cell migration, cytoskeletal regulation and tissue morphogenesis, consistent with a role in invasion and metastasis. Single cell resolution analysis showed that individual cells co-expressed both epithelial- and mesenchymal-associated genes/proteins. Most strikingly, we demonstrated that strong activity of this stem cell gene set in TNBCs identified those tumours most likely to rapidly progress to metastasis.

Conclusions

Our findings support the hypothesis that the biological properties of normal stem cells are drivers of metastasis and that these properties can be used to stratify patients with a highly heterogeneous disease such as TNBC.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-015-0539-6) contains supplementary material, which is available to authorized users.     

Loss of Stat5a delays mammary cancer progression in a mouse model

A genetic study was conducted to determine if activated Stat5a contributes to mammary carcinogenesis and to evaluate the mechanism. Similar to human breast cancers, a proportion of mammary adenocarcinomas in the WAP-TAg transgenic mouse model demonstrate constitutive Stat5a/b and Stat3 activation. Stat5a activation is linked to mammary epithelial cell survival and differentiation, and proliferation in hematopoetic cell lineages. Breeding WAP-TAg mice to mice carrying germ-line deletions of the Stat5a gene generated mice with reduced levels of Stat5a. Hemizygous loss of the Stat5a allele significantly reduced levels of Stat5a expression without altering mammary gland development or transgene expression levels. In comparison to mice carrying two wild-type Stat5a alleles, hemizygous loss of the Stat5a allele reduced the number of mice with palpable tumors at 7 months of age (67% from 100%, P<0.05), resulted in smaller tumors at 7 months of age (3.8 cm3 from 7.6 cm3, P=0.003), delayed first tumor appearance (208 days from 188 days, P=0.01), and increased the apoptotic index in the adenocarcinomas (4.3+/-0.3 from 1.2+/-0.2, P=0.016). Neither cell proliferation nor differentiation in the cancers was altered. Decreasing Stat5a activation levels could be a therapeutic approach for reducing survival of breast cancer cells.     

Biomarkers of phenethyl isothiocyanate-mediated mammary cancer chemoprevention in a clinically relevant mouse model

Background Phenethyl isothiocyanate (PEITC) is a natural plant compound with chemopreventative potential against some cancers and the ability to induce apoptosis in breast cancer cells. Methods Female mouse mammary tumor virus-neu mice were fed a control AIN-76A diet (n = 35) or the same diet supplemented with 3 μmol PEITC/g diet (n = 33) for 29 weeks, at which time they were killed. Breast tissue sections were stained with hematoxylin and eosin for histopathological assessments, and incidence and size of macroscopic mammary tumors were assessed. Cell proliferation (Ki-67 staining), apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick-labeling), and neoangiogenesis (CD31 staining) were determined in tumor sections. Plasma levels of transthyretin were measured in treated and control mice. Expression of proteins in mammary tumor sections was determined by immunohistochemistry. Proteomic profiling was performed by two-dimensional gel electrophoresis followed by mass spectrometry. All statistical tests were two-sided. Results Administration of PEITC for 29 weeks was associated with 53.13% decreased incidence of macroscopic mammary tumors (mean tumor incidence, PEITC-supplemented diet vs control diet, 18.75% vs 40.00%, difference = -21.25%, 95% confidence interval [CI] = -43.19% to 0.69%, P = .07) and with a 56.25% reduction in microscopic mammary carcinoma lesions greater than 2mm(2) (mean incidence, PEITC-supplemented diet vs control diet, 18.75% vs 42.86%, difference = -24.11%, 95% CI = -46.35% to -1.86%, P = .04). PEITC-mediated mammary cancer growth inhibition was not because of suppression of human epidermal growth factor receptor-2 expression but was associated with reduced cellular proliferation and neoangiogenesis, increased apoptosis, and altered expression of several proteins, including decreased ATP synthase in the tumor and increased plasma levels of transthyretin. Conclusions PEITC inhibits the growth of mammary cancers in a mouse model with similarities to human breast cancer progression. ATP synthase and transthyretin appear to be novel biomarkers associated with PEITC exposure.     

Early vascular deficits are correlated with delayed mammary tumorigenesis in the MMTV-PyMT transgenic mouse following genetic ablation of the NG2 proteoglycan

Introduction

The neuron-glial antigen 2 (NG2) proteoglycan promotes pericyte recruitment and mediates pericyte interaction with endothelial cells. In the absence of NG2, blood vessel development is negatively impacted in several pathological models. Our goal in this study was to determine the effect of NG2 ablation on the early development and function of blood vessels in mammary tumors in the mammary tumor virus-driven polyoma middle T (MMTV-PyMT) transgenic mouse, and to correlate these vascular changes with alterations in mammary tumor growth.

Methods

Three different tumor paradigms (spontaneous tumors, transplanted tumors, and orthotopic allografts of tumor cell lines) were used to investigate the effects of NG2 ablation on breast cancer progression in the MMTV-PyMT transgenic mouse. In addition to examining effects of NG2 ablation on mammary tumor growth, we also investigated effects on the structure and function of tumor vasculature.

Results

Ablation of NG2 led to reduced early progression of spontaneous, transplanted, and orthotopic allograft mammary tumors. NG2 was not expressed by the mammary tumor cells themselves, but instead was found on three components of the tumor stroma. Microvascular pericytes, myeloid cells, and adipocytes were NG2-positive in both mouse and human mammary tumor stroma. The effect of NG2 on tumor progression therefore must be stromal in nature. Ablation of NG2 had several negative effects on early development of the mammary tumor vasculature. In the absence of NG2, pericyte ensheathment of endothelial cells was reduced, along with reduced pericyte maturation, reduced sprouting of endothelial cells, reduced assembly of the vascular basal lamina, and reduced tumor vessel diameter. These early deficits in vessel structure are accompanied by increased vessel leakiness, increased tumor hypoxia, and decreased tumor growth. NG2 ablation also diminishes the number of tumor-associated and TEK tyrosine kinase endothelial (Tie2) expressing macrophages in mammary tumors, providing another possible mechanism for reducing tumor vascularization and growth.

Conclusions

These results emphasize the importance of NG2 in mediating pericyte/endothelial cell communication that is required for proper vessel maturation and function. In the absence of normal pericyte/endothelial cell interaction, poor vascular function results in diminished early progression of mammary tumors.     

Mesenchymal stem cells in mammary adipose tissue stimulate progression of breast cancer resembling the basal-type

Data are accumulating to support a role for adipose-derived mesenchymal stem cells (MSCs) in breast cancer progression; however, to date most studies have relied on adipose MSCs from non-breast sources. There is a particular need to investigate the role of adipose MSCs in the pathogenesis of basal-like breast cancer, which develops at a disproportionate rate in pre-menopausal African-American women with a gain in adiposity. The aim of this study was to better understand how breast adipose MSCs (bMSCs) contribute to the progression of basal-like breast cancers by relying on isogenic HMT-3255 S3 (pre-invasive) and T4-2 (invasive) human cells that upon transplantation into nude mice resemble this tumor subtype. In vitro results suggested that bMSCs may contribute to breast cancer progression in multiple ways. bMSCs readily penetrate extracellular matrix components in part through their expression of matrix metalloproteinases 1 and 3, promote the invasion of T4-2 cells and efficiently chemoattract endothelial cells via a bFGF-independent, VEGF-A-dependent manner. As mixed xenografts, bMSCs stimulated the growth, invasion and desmoplasia of T4-2 tumors, yet these resident stem cells showed no observable effect on the progression of pre-invasive S3 cells. While bMSCs form vessel-like structures within Matrigel both in vitro and in vivo and chemoattract endothelial cells, there appeared to be no difference between T4-2/bMSC mixed xenografts and T4-2 xenografts with regard to intra- or peri-tumoral vascularity. Collectively, our data suggest that bMSCs may contribute to the progression of basal-like breast cancers by stimulating growth and invasion but not vasculogenesis or angiogenesis.