Reconstruction of functionally normal and malignant human breast tissues in mice

Humanization of the Prostate Microenvironment Reduces Homing of PC3 Prostate Cancer Cells to Human Tissue-Engineered Bone

The primary tumor microenvironment is inherently important in prostate cancer (PCa) initiation, growth and metastasis. However, most current PCa animal models are based on the injection of cancer cells into the blood circulation and bypass the first steps of the metastatic cascade, hence failing to investigate the influence of the primary tumor microenvironment on PCa metastasis. Here, we investigated the spontaneous metastasis of PC3 human PCa cells from humanized prostate tissue, containing cancer-associated fibroblasts (CAFs) and prostate lymphatic and blood vessel endothelial cells (BVECs), to humanized tissue-engineered bone constructs (hTEBCs) in NOD-SCID IL2Rγ^null (NSG) mice. The hTEBC formed a physiologically mature organ bone which allowed homing of metastatic PCa cells. Humanization of prostate tissue had no significant effect on the tumor burden at the primary site over the 4 weeks following intraprostatic injection, yet reduced the incidence and burden of metastases in the hTEBC. Spontaneous PCa metastases were detected in the lungs and spleen with no significant differences between the humanized and non-humanized prostate groups. A significantly greater metastatic tumor burden was observed in the liver when metastasis occurred from the humanized prostate. Together, our data suggests that the presence of human-derived CAFs and BVECs in the primary PCa microenvironment influences selectively the metastatic and homing behavior of PC3 cells in this model. Our orthotopic and humanized PCa model developed via convergence of cancer research and tissue engineering concepts provides a platform to dissect mechanisms of species-specific PCa bone metastasis and to develop precision medicine strategies.

Humanized Mouse Models for the Preclinical Assessment of Cancer Immunotherapy

Immunotherapy is one of the most exciting recent breakthroughs in the field of cancer treatment. Many different approaches are being developed and a number have already gained regulatory approval or are under investigation in clinical trials. However, learning from the past, preclinical animal models often insufficiently reflect the physiological situation in humans, which subsequently causes treatment failures in clinical trials. Due to species-specific differences in most parts of the immune system, the transfer of knowledge from preclinical studies to clinical trials is eminently challenging. Human tumor cell line-based or patient-derived xenografts in immunocompromised mice have been successfully applied in the preclinical testing of cytotoxic or molecularly targeted agents, but naturally these systems lack the human immune system counterpart. The co-transplantation of human peripheral blood mononuclear cells or hematopoietic stem cells is employed to overcome this limitation. This review summarizes some important aspects of the different available tumor xenograft mouse models, their history, and their implementation in drug development and personalized therapy. Moreover, recent progress, opportunities and limitations of different humanized mouse models will be discussed.

Obesity-Activated Adipose-Derived Stromal Cells Promote Breast Cancer Growth and Invasion

Obese women diagnosed with breast cancer have an increased risk for metastasis, and the underlying mechanisms are not well established. Within the mammary gland, adipose-derived stromal cells (ASCs) are heterogeneous cells with the capacity to differentiate into multiple mesenchymal lineages. To study the effects of obesity on ASCs, mice were fed a control diet (CD) or high-fat diet (HFD) to induce obesity, and ASCs were isolated from the mammary glands of lean and obese mice. We observed that obesity increased ASCs proliferation, decreased differentiation potential, and upregulated expression of α-smooth muscle actin, a marker of activated fibroblasts, compared to ASCs from lean mice. To determine how ASCs from obese mice impacted tumor growth, we mixed ASCs isolated from CD- or HFD-fed mice with mammary tumor cells and injected them into the mammary glands of lean mice. Tumor cells mixed with ASCs from obese mice grew significantly larger tumors and had increased invasion into surrounding adipose tissue than tumor cells mixed with control ASCs. ASCs from obese mice demonstrated enhanced tumor cell invasion in culture, a phenotype associated with increased expression of insulin-like growth factor-1 (IGF-1) and abrogated by IGF-1 neutralizing antibodies. Weight loss induced in obese mice significantly decreased expression of IGF-1 from ASCs and reduced the ability of the ASCs to induce an invasive phenotype. Together, these results suggest that obesity enhances local invasion of breast cancer cells through increased expression of IGF-1 by mammary ASCs, and weight loss may reverse this tumor-promoting phenotype.

Interaction between oral squamous cell carcinoma cells and fibroblasts through TGF-β1 mediated by podoplanin

Podoplanin is upregulated in the invasive front of oral squamous cell carcinoma (OSCC). Carcinoma-associated fibroblasts (CAFs) may mediate podoplanin expression. However, the role of podoplanin in OSCC cell and fibroblast interaction remains elusive. In the present study, we found that positive podoplanin expression in OSCC cells correlated with smooth muscle actin (α-SMA) expression in CAFs. Using CAFs and normal mucosal fibroblasts (NFs), we established indirect and direct co-culture systems mimicking the structure of OSCC. Podoplanin-overexpressing OSCC cells promoted NF activation; in direct co-culture, but not in indirect co-culture, podoplanin-overexpressing OSCC cells increased fibroblast invasion via matrix metalloproteinase 2 (MMP-2), MMP-14, and αv/β6 integrin receptor (ITGA5/ITGB6) signaling. CAFs also induced podoplanin expression through the transforming growth factor-β1 (TGF-β1)/Smad pathway. TGF-β1 increased the podoplanin-dependent activation of epidermal growth factor receptor (EGFR), AKT, and extracellular signal-regulated kinase (ERK) signaling. Additionally, CAFs promoted OSCC cell invasion by upregulating MMP-2 and MMP-14 expression in both indirect and direct co-culture. Taken together, our findings indicate that podoplanin regulates the interaction between OSCC cells and CAFs via the mutual paracrine effects of TGF-β1.

Stromal PTEN determines mammary epithelial response to radiotherapy

The importance of the tumor-associated stroma in cancer progression is clear. However, it remains uncertain whether early events in the stroma are capable of initiating breast tumorigenesis. Here, we show that in the mammary glands of non-tumor bearing mice, stromal-specific phosphatase and tensin homolog (Pten) deletion invokes radiation-induced genomic instability in neighboring epithelium. In these animals, a single dose of whole-body radiation causes focal mammary lobuloalveolar hyperplasia through paracrine epidermal growth factor receptor (EGFR) activation, and EGFR inhibition abrogates these cellular changes. By analyzing human tissue, we discover that stromal PTEN is lost in a subset of normal breast samples obtained from reduction mammoplasty, and is predictive of recurrence in breast cancer patients. Combined, these data indicate that diagnostic or therapeutic chest radiation may predispose patients with decreased stromal PTEN expression to secondary breast cancer, and that prophylactic EGFR inhibition may reduce this risk.

3D organizational mapping of collagen fibers elucidates matrix remodeling in a hormone-sensitive 3D breast tissue model

Hormones play an important role in normal and diseased breast tissue development. However, they can also disrupt cell-matrix interactions and their role in extracellular matrix reorganization during epithelial morphogenesis remains poorly understood, partly due to a lack of sensitive approaches for matrix characterization. Here, we assess the hormonal regulation of matrix reorganization in a three-dimensional (3D) breast tissue culture model using a novel metric, i.e., 3D directional variance, to characterize the 3D organization of collagen fibers visualized via high-resolution, second harmonic generation imaging. This metric enables resolving and quantifying patterns of spatial organization throughout the matrix surrounding epithelial structures treated with 17β-estradiol (E2) alone, and E2 in combination with either promegestone, a progestogen, or prolactin. Addition of promegestone results in the most disorganized fibers, while the E2 alone treatment leads to the most organized ones. Location-dependent organization mapping indicates that only the prolactin treatment leads to significant heterogeneities in the regional organization of collagen fibers, with higher levels of alignment observed at the end of the elongated epithelial structures. The observed collagen organization patterns for all groups persist for tens of micrometers. In addition, a comparison between 3D directional variance and typical 2D analysis approaches reveals an improved sensitivity of the 3D metric to identify organizational heterogeneities and differences among treatment groups. These results demonstrate that 3D directional variance is sensitive to subtle changes in the extracellular micro-environment and has the potential to elucidate reciprocal cell-matrix interactions in the context of numerous applications involving the study of normal and diseased tissue morphogenesis.

ELTD1 Function in Hepatocellular Carcinoma is Carcinoma-Associated Fibroblast-Dependent

Introduction: EGF, latrophilin, and seven transmembrane domain containing 1 (ELTD1) constitutes an orphan G-protein-coupled receptor (GPCR) of the adhesion family. High expression of ELTD1 is correlated with favorable prognosis of hepatocellular carcinoma (HCC). After silencing ELTD1 expression, however, tumor invasiveness is drastically reduced. The underlying mechanism of this apparent contradictory phenomenon is unknown. Because adhesion GPCRs couple extracellular adhesion to intracellular signaling, as a member of this family, ELTD1 function may be related to its tumor microenvironment. We therefore investigated the interaction between ELTD1 and the HCC tumor microenvironment. Methods: ELTD1 expression was assessed by immunohistochemical analyses of tissue samples from two independent groups of 333 patients with HCC. Correlations between the ELTD1 expression and the clinicopathological values were examined. We also constructed ELTD1 overexpression and knockdown HCC cell lines and conducted a series of in vivo and in vitro ELTD1 functional assays. We further collected carcinoma associated fibroblast (CAF) culture supernatants to culture HCC cell lines and repeat the respective functional assays in comparison with the control group. Results: Clinicopathologic correlations and in vivo models indicated ELTD1 as a tumor suppressor gene, whereas in vitro experiments suggested that ELTD1 could promote malignancy in HCC cell lines. Immunohistochemical staining of the generated ELTD1 overexpression xenograft tumors demonstrated that the CAF markers vimentin and α-SMA were highly expressed compared to the control group. This suggests that ELTD1 expression is correlated to CAF distribution. In addition, culturing with CAF supernatants inhibited HCC cell proliferation and invasion rates, confirming the correlation between CAF and ELTD1. Conclusion: The results of this study indicated that ELTD1 regulation of HCC progression is CAF-dependent, suggesting that ELTD1 function is regulated by its tumor microenvironment. Further investigation is required to determine the underlying mechanisms.

Fibroblasts in the Tumor Microenvironment: Shield or Spear?

Tumorigenesis is a complex process involving dynamic interactions between malignant cells and their surrounding stroma, including both the cellular and acellular components. Within the stroma, fibroblasts represent not only a predominant cell type, but also a major source of the acellular tissue microenvironment comprising the extracellular matrix (ECM) and soluble factors. Normal fibroblasts can exert diverse suppressive functions against cancer initiating and metastatic cells via direct cell-cell contact, paracrine signaling by soluble factors, and ECM integrity. The loss of such suppressive functions is an inherent step in tumor progression. A tumor cell-induced switch of normal fibroblasts into cancer-associated fibroblasts (CAFs), in turn, triggers a range of pro-tumorigenic signals accompanied by distraction of the normal tissue architecture, thus creating an optimal niche for cancer cells to grow extensively. To further support tumor progression and metastasis, CAFs secrete factors such as ECM remodeling enzymes that further modify the tumor microenvironment in combination with the altered adhesive forces and cell-cell interactions. These paradoxical tumor suppressive and promoting actions of fibroblasts are the focus of this review, highlighting the heterogenic molecular properties of both normal and cancer-associated fibroblasts, as well as their main mechanisms of action, including the emerging impact on immunomodulation and different therapy responses.

A functional genomic screen in vivo identifies CEACAM5 as a clinically relevant driver of breast cancer metastasis

Tumor cells disseminate early in tumor development making metastasis-prevention strategies difficult. Identifying proteins that promote the outgrowth of disseminated tumor cells may provide opportunities for novel therapeutic strategies. Despite multiple studies demonstrating that the mesenchymal-to-epithelial transition (MET) is critical for metastatic colonization, key regulators that initiate this transition remain unknown. We serially passaged lung metastases from a primary triple negative breast cancer xenograft to the mammary fat pads of recipient mice to enrich for gene expression changes that drive metastasis. An unbiased transcriptomic signature of potential metastatic drivers was generated, and a high throughput gain-of-function screen was performed in vivo to validate candidates. Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) was identified as a metastatic driver. CEACAM5 overproduction enriched for an epithelial gene expression pattern and facilitated tumor outgrowth at metastatic sites. Tissues from patients with metastatic breast cancer confirmed elevated levels of CEACAM5 in lung metastases relative to breast tumors, and an inverse correlation between CEACAM5 and the mesenchymal marker vimentin was demonstrated. Thus, CEACAM5 facilitates tumor outgrowth at metastatic sites by promoting MET, warranting its investigation as a therapeutic target and biomarker of aggressiveness in breast cancer.

A screen for drivers of metastasis has revealed a key protein involved in the spread of breast cancer into lung tissues. A US research team led by Helen Piwnica-Worms from the University of Texas MD Anderson Cancer Center in Houston enriched cells for genes involved in metastasis by engrafting mice with breast tumor biopsies taken from women with metastatic triple negative breast cancer and then metastases of these mice to mammary fat pads of recipient mice. The researchers pinpointed the gene encoding CEACAM5—a protein known to play a role in cell invasion and spread—as a key promoter of the cellular transition associated with metastasis. Tissues samples from patients confirmed that CEACAM5 levels were elevated in metastatic lung tumors relative to primary breast tumors. The protein provides a potential therapeutic target for drug development and candidate biomarker for patient stratification.

Patient-derived xenograft models in musculoskeletal malignancies

Successful oncological drug development for bone and soft tissue sarcoma is grossly stagnating. A major obstacle in this process is the lack of appropriate animal models recapitulating the complexity and heterogeneity of musculoskeletal malignancies, resulting in poor efficiency in translating the findings of basic research to clinical applications. In recent years, patient-derived xenograft (PDX) models generated by directly engrafting patient-derived tumor fragments into immunocompromised mice have recaptured the attention of many researchers due to their properties of retaining the principle histopathology, biological behaviors, and molecular and genetic characteristics of the original tumor, showing promising future in both basic and clinical studies of bone and soft tissue sarcoma. Despite several limitations including low take rate and long take time in PDX generation, deficient immune system and heterologous tumor microenvironment of the host, PDXs offer a more advantageous platform for preclinical drug screening, biomarker identification and clinical therapeutic decision guiding. Here, we provide a timely review of the establishment and applications of PDX models for musculoskeletal malignancies and discuss current challenges and future directions of this approach.

The origins of breast cancer associated with mammographic density: a testable biological hypothesis

Background

Our purpose is to develop a testable biological hypothesis to explain the known increased risk of breast cancer associated with extensive percent mammographic density (PMD), and to reconcile the apparent paradox that although PMD decreases with increasing age, breast cancer incidence increases.

Methods

We used the Moolgavkar model of carcinogenesis as a framework to examine the known biological properties of the breast tissue components associated with PMD that includes epithelium and stroma, in relation to the development of breast cancer. In this model, normal epithelial cells undergo a mutation to become intermediate cells, which, after further mutation, become malignant cells. A clone of such cells grows to become a tumor. The model also incorporates changes with age in the number of susceptible epithelial cells associated with menarche, parity, and menopause. We used measurements of the radiological properties of breast tissue in 4454 healthy subjects aged from 15 to 80+ years to estimate cumulative exposure to PMD (CBD) in the population, and we examined the association of CBD with the age-incidence curve of breast cancer in the population.

Results

Extensive PMD is associated with a greater number of breast epithelial cells, lobules, and fibroblasts, and greater amounts of collagen and extracellular matrix. The known biological properties of these tissue components may, singly or in combination, promote the acquisition of mutations by breast epithelial cells specified by the Moolgavkar model, and the subsequent growth of a clone of malignant cells to form a tumor. We also show that estimated CBD in the population from ages 15 to 80+ years is closely associated with the age-incidence curve of breast cancer in the population.

Conclusions

These findings are consistent with the hypothesis that the biological properties of the breast tissue components associated with PMD increase the probability of the transition of normal epithelium to malignant cells, and that the accumulation of mutations with CBD may influence the age-incidence curve of breast cancer. This hypothesis gives rise to several testable predictions.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-0941-y) contains supplementary material, which is available to authorized users.

Sipa1 deficiency unleashes a host-immune mechanism eradicating chronic myelogenous leukemia-initiating cells

Chronic myelogenous leukemia (CML) caused by hematopoietic stem cells expressing the Bcr-Abl fusion gene may be controlled by Bcr-Abl tyrosine kinase inhibitors (TKIs). However, CML-initiating cells are resistant to TKIs and may persist as minimal residual disease. We demonstrate that mice deficient in Sipa1, which encodes Rap1 GTPase-activating protein, rarely develop CML upon transfer of primary hematopoietic progenitor cells (HPCs) expressing Bcr-Abl, which cause lethal CML disease in wild-type mice. Resistance requires both T cells and nonhematopoietic cells. Sipa1^−/− mesenchymal stroma cells (MSCs) show enhanced activation and directed migration to Bcr-Abl⁺ cells in tumor tissue and preferentially produce Cxcl9, which in turn recruits Sipa1^−/− memory T cells that have markedly augmented chemotactic activity. Thus, Sipa1 deficiency uncovers a host immune mechanism potentially capable of eradicating Bcr-Abl⁺ HPCs via coordinated interplay between MSCs and immune T cells, which may provide a clue for radical control of human CML.

Chronic myelogenous leukemia (CML)-initiating cells are resistant to kinase inhibitors. Here the authors show that deficiency of the Rap1 GTPase-activating protein Sipa1 in the tumor microenvironment releases an immune response that eradicates CML-initiating cells via interplay between stromal and T cells.

Matriptase regulates c-Met mediated proliferation and invasion in inflammatory breast cancer

The poor prognosis for patients with inflammatory breast cancer (IBC) compared to patients with other types of breast cancers emphasizes the need to better understand the molecular underpinnings of this disease with the goal of developing effective targeted therapeutics. Dysregulation of matriptase expression, an epithelial-specific member of the type II transmembrane serine protease family, has been demonstrated in many different cancer types. To date, no studies have assessed the expression and potential pro-oncogenic role of matriptase in IBC. We examined the functional relationship between matriptase and the HGF/c-MET signaling pathway in the IBC cell lines SUM149 and SUM190, and in IBC patient samples. Matriptase and c-Met proteins are localized on the surface membrane of IBC cells and their expression is strongly correlated in infiltrating cancer cells and in the cancer cells of lymphatic emboli in patient samples. Abrogation of matriptase expression by silencing with RNAi or inhibition of matriptase proteolytic activity with a synthetic inhibitor impairs the conversion of inactive pro-HGF to active HGF and subsequent c-Met-mediated signaling, leading to efficient impairment of proliferation and invasion of IBC cells. These data show the potential of matriptase inhibitors as a novel targeted therapy for IBC, and lay the groundwork for the development and testing of such drugs.

Razor-printed sticker microdevices for cell-based applications

Tape-based razor-printing is a flexible and affordable ultra-rapid prototyping approach for microscale device fabrication. However, integration of this prototyping approach into cell-based assay development has been limited to proof of principle demonstrations. This is in large part due to lack of an established or well-characterized option for biocompatible adhesive tape. Without such an option, integration of these areas will remain unexplored. Therefore, to address this critical hurdle, we characterized microscale devices made using a potentially biocompatible double-sided adhesive, ARCare 90106. We validated tape-based device performance against 96-well plates and PDMS microdevices with respect to cell viability, hydrophobic small molecule sequestration, the potential for leaching compounds, use in fluorescence microscopy, and outgassing (bubble formation). Results supported the tape as a promising tool for future cell-based assay development. Therefore, we subsequently demonstrated specific strengths enabled by the ultra-rapid (<1 h per prototype) and affordable (∼$1200 cutting plotter, <$0.05 per prototype) approach. Specifically, data demonstrate the ability to integrate disparate materials for advanced sticker-device functionality such as bonding of polystyrene devices to glass substrates for microscopy applications, inclusion of membranes, and incorporation of different electrospun biomaterials into a single device. Likewise, the approach allowed rapid adoption by uninitiated users. Overall, this study provides a necessary and unique contribution to the largely separate fields of tape-based razor-printing and cell-based microscale assay development by addressing a critical barrier to widespread integration and adoption while also demonstrating the potential for new and future applications.

Identifying biomarkers of breast cancer micrometastatic disease in bone marrow using a patient-derived xenograft mouse model

BACKGROUND

Disseminated tumor cells (DTCs) found in the bone marrow (BM) of patients with breast cancer portend a poor prognosis and are thought to be intermediaries in the metastatic process. To assess the clinical relevance of a mouse model for identifying possible prognostic and predictive biomarkers of these cells, we have employed patient-derived xenografts (PDX) for propagating and molecularly profiling human DTCs.

METHODS

Previously developed mouse xenografts from five breast cancer patients were further passaged by implantation into NOD/SCID mouse mammary fat pads. BM was collected from long bones at early, serial passages and analyzed for human-specific gene expression by qRT-PCR as a surrogate biomarker for the detection of DTCs. Microarray-based gene expression analyses were performed to compare expression profiles between primary xenografts, solid metastasis, and populations of BM DTCs. Differential patterns of gene expression were then compared to previously generated microarray data from primary human BM aspirates from patients with breast cancer and healthy volunteers.

RESULTS

Human-specific gene expression of SNAI1, GSC, FOXC2, KRT19, and STAM2, presumably originating from DTCs, was detected in the BM of all xenograft mice that also developed metastatic tumors. Human-specific gene expression was undetectable in the BM of those xenograft lines with no evidence of distant metastases and in non-transplanted control mice. Comparative gene expression analysis of BM DTCs versus the primary tumor of one mouse line identified multiple gene transcripts associated with epithelial-mesenchymal transition, aggressive clinical phenotype, and metastatic disease development. Sixteen of the PDX BM associated genes also demonstrated a statistically significant difference in expression in the BM of healthy volunteers versus the BM of breast cancer patients with distant metastatic disease.

CONCLUSION

Unique and reproducible patterns of differential gene expression can be identified that presumably originate from BM DTCs in mouse PDX lines. Several of these identified genes are also detected in the BM of patients with breast cancer who develop early metastases, which suggests that they may be clinically relevant biomarkers. The PDX model may also provide a clinically relevant system for analyzing and targeting these intermediaries of metastases.

Bovine Mammary Organoids: A Model to Study Epithelial Mammary Cells

Bovine mammary organoids are cell aggregates that are produced by an association of a mechanical and an enzymatic dissociation of mammary gland tissue. They provide a useful source to isolate mammary epithelial cells, but can also be frozen as an intermediate dissociation step.Due to the strong cell-cell interactions among epithelial cells, the production and isolation of organoids is an efficient way to remove unwanted cell population of non-epithelial origin like fibroblasts.

Repurposed drug screen identifies cardiac glycosides as inhibitors of TGF-β-induced cancer-associated fibroblast differentiation

The tumor microenvironment, primarily composed of myofibroblasts, directly influences the progression of solid tumors. Through secretion of growth factors, extracellular matrix deposition, and contractile mechanotransduction, myofibroblasts, or cancer-associated fibroblasts (CAFs), support angiogenesis and cancer cell invasion and metastasis. The differentiation of fibroblasts to CAFs is primarily induced by TGF-β from cancer cells. To discover agents capable of blocking CAF differentiation, we developed a high content immunofluorescence-based assay to screen repurposed chemical libraries utilizing fibronectin expression as an initial CAF marker. Screening of the Prestwick chemical library and NIH Clinical Collection repurposed drug library, totaling over 1700 compounds, identified cardiac glycosides as particularly potent CAF blocking agents. Cardiac glycosides are traditionally used to regulate intracellular calcium by inhibiting the Na+/K+ ATPase to control cardiac contractility. Herein, we report that multiple cardiac glycoside compounds, including digoxin, are able to inhibit TGF-β-induced fibronectin expression at low nanomolar concentrations without undesirable cell toxicity. We found this inhibition to hold true for multiple fibroblast cell lines. Using real-time qPCR, we determined that digoxin prevented induction of multiple CAF markers. Furthermore, we report that digoxin is able to prevent TGF-β-induced fibroblast contraction of extracellular matrix, a major phenotypic consequence of CAF differentiation. Assessing the mechanism of inhibition, we found digoxin reduced SMAD promoter activity downstream of TGF-β, and we provide data that the effect is through inhibition of its known target, the Na+/K+ ATPase. These findings support a critical role for calcium signaling during CAF differentiation and highlight a novel, repurposable modality for cancer therapy.

Epithelial plasticity in the mammary gland

Many epithelial tissues rely on multipotent stem cells for the proper development and maintenance of their diverse cell lineages. Nevertheless, the identification of multipotent stem cell populations within the mammary gland has been a point of contention over the past decade. In this review, we provide a critical overview of the various lineage-tracing studies performed to address this issue and conclude that although multipotent stem cells exist in the embryonic mammary placode, the postnatal mammary gland instead contains distinct unipotent progenitor populations that contribute to stage-specific development and homeostasis. This begs the question of why differentiated mammary epithelial cells can exhibit stem cell behavior in culture. We speculate that such reprogramming potential is repressed in situ under normal conditions but revealed in vitro and might drive breast cancer development.

Breast Cancers Activate Stromal Fibroblast-Induced Suppression of Progenitors in Adjacent Normal Tissue

Human breast cancer cells are known to activate adjacent “normal-like” cells to enhance their own growth, but the cellular and molecular mechanisms involved are poorly understood. We now show by both phenotypic and functional measurements that normal human mammary progenitor cells are significantly under-represented in the mammary epithelium of patients' tumor-adjacent tissue (TAT). Interestingly, fibroblasts isolated from TAT samples showed a reduced ability to support normal EGF-stimulated mammary progenitor cell proliferation in vitro via their increased secretion of transforming growth factor β. In contrast, TAT fibroblasts promoted the proliferation of human breast cancer cells when these were co-transplanted in immunodeficient mice. The discovery of a common stromal cell-mediated mechanism that has opposing growth-suppressive and promoting effects on normal and malignant human breast cells and also extends well beyond currently examined surgical margins has important implications for disease recurrence and its prevention.

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Alterations to the breast tissue extend as far as 6 cm away from the primary tumors

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The matching contralateral non-tumor-bearing breast tissue remains unaltered

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Tumor-adjacent breast tissue contained significantly diminished progenitor pool

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Extending surgical margins may not be effective in reducing risk of tumor recurrence

Three-dimensional tumor model mimics stromal - breast cancer cells signaling

Tumor stroma is a major contributor to the biological aggressiveness of cancer cells. Cancer cells induce activation of normal fibroblasts to carcinoma-associated fibroblasts (CAFs), which promote survival, proliferation, metastasis, and drug resistance of cancer cells. A better understanding of these interactions could lead to new, targeted therapies for cancers with limited treatment options, such as triple negative breast cancer (TNBC). To overcome limitations of standard monolayer cell cultures and xenograft models that lack tumor complexity and/or human stroma, we have developed a high throughput tumor spheroid technology utilizing a polymeric aqueous two-phase system to conveniently model interactions of CAFs and TNBC cells and quantify effects on signaling and drug resistance of cancer cells. We focused on signaling by chemokine CXCL12, a hallmark molecule secreted by CAFs, and receptor CXCR4, a driver of tumor progression and metastasis in TNBC. Using three-dimensional stromal-TNBC cells cultures, we demonstrate that CXCL12 – CXCR4 signaling significantly increases growth of TNBC cells and drug resistance through activation of mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) pathways. Despite resistance to standard chemotherapy, upregulation of MAPK and PI3K signaling sensitizes TNBC cells in co-culture spheroids to specific inhibitors of these kinase pathways. Furthermore, disrupting CXCL12 – CXCR4 signaling diminishes drug resistance of TNBC cells in co-culture spheroid models. This work illustrates the capability to identify mechanisms of drug resistance and overcome them using our engineered model of tumor-stromal interactions.

TGF-β Family Signaling in Tumor Suppression and Cancer Progression

Transforming growth factor-β (TGF-β) induces a pleiotropic pathway that is modulated by the cellular context and its integration with other signaling pathways. In cancer, the pleiotropic reaction to TGF-β leads to a diverse and varied set of gene responses that range from cytostatic and apoptotic tumor-suppressive ones in early stage tumors, to proliferative, invasive, angiogenic, and oncogenic ones in advanced cancer. Here, we review the knowledge accumulated about the molecular mechanisms involved in the dual response to TGF-β in cancer, and how tumor cells evolve to evade the tumor-suppressive responses of this signaling pathway and then hijack the signal, converting it into an oncogenic factor. Only through the detailed study of this complexity can the suitability of the TGF-β pathway as a therapeutic target against cancer be evaluated.

Analysis of Normal Human Mammary Epigenomes Reveals Cell-Specific Active Enhancer States and Associated Transcription Factor Networks

The normal adult human mammary gland is a continuous bilayered epithelial system. Bipotent and myoepithelial progenitors are prominent and unique components of the outer (basal) layer. The inner (luminal) layer includes both luminal-restricted progenitors and a phenotypically separable fraction that lacks progenitor activity. We now report an epigenomic comparison of these three subsets with one another, with their associated stromal cells, and with three immortalized, non-tumorigenic human mammary cell lines. Each genome-wide analysis contains profiles for six histone marks, methylated DNA, and RNA transcripts. Analysis of these datasets shows that each cell type has unique features, primarily within genomic regulatory regions, and that the cell lines group together. Analyses of the promoter and enhancer profiles place the luminal progenitors in between the basal cells and the non-progenitor luminal subset. Integrative analysis reveals networks of subset-specific transcription factors.

Ionizing radiation-mediated premature senescence and paracrine interactions with cancer cells enhance the expression of syndecan 1 in human breast stromal fibroblasts: the role of TGF-β

The cell surface proteoglycan syndecan 1 (SDC1) is overexpressed in the malignant breast stromal fibroblasts, creating a favorable milieu for tumor cell growth. In the present study, we found that ionizing radiation, a well-established treatment in human breast cancer, provokes premature senescence of human breast stromal fibroblasts in vitro, as well as in the breast tissue in vivo. These senescent cells were found to overexpress SDC1 both in vitro and in vivo. By using a series of specific inhibitors and siRNA approaches, we showed that this SDC1 overexpression in senescent cells is the result of an autocrine action of Transforming Growth Factor-β (TGF-β) through the Smad pathway and the transcription factor Sp1, while the classical senescence pathways of p53 or p38 MAPK - NF-kB are not involved. In addition, the highly invasive human breast cancer cells MDA-MB-231 (in contrast to the low-invasive MCF-7) can also enhance SDC1 expression, both in early-passage and senescent fibroblasts via a paracrine action of TGF-β. The above suggest that radiation-mediated premature senescence and invasive tumor cells, alone or in combination, enhance SDC1 expression in breast stromal fibroblasts, a poor prognostic factor for cancer growth, and that TGF-β plays a crucial role in this process.

Extracellular superoxide dismutase inhibits hepatocyte growth factor-mediated breast cancer-fibroblast interactions

We have previously shown tumor suppressive effects of extracellular superoxide dismutase, EcSOD in breast cancer cells. In this study, an RTK signaling array revealed an inhibitory effect of EcSOD on c-Met phosphorylation and its downstream kinase c-Abl in MDA-MB231 cells. Moreover, an extracellular protein array showed that thrombospondin 1 (TSP-1), a scavenger of the c-Met ligand, hepatocyte growth factor (HGF) is significantly up-regulated in EcSOD overexpressing cells (Ec.20). We further determined the effects of EcSOD on HGF/c-Met-mediated cancer-fibroblast interactions by co-culturing normal fibroblasts (RMF) or RMF which overexpresses HGF (RMF-HGF) with MDA-MB231 cells. We observed that while RMF-HGF significantly promoted Matrigel growth of MDA-MB231, overexpression of EcSOD inhibited the HGF-stimulated growth. Similarly, a SOD mimetic, MnTE-2-PyP, inhibited HGF-induced growth and invasion of MDA-MB231. In addition, a long-term heterotypic co-culture study not only showed that Ec.20 cells are resistant to RMF-HGF-induced invasive stimulation but RMF-HGF that were co-cultured with Ec.20 cells showed an attenuated phenotype, suggesting an oxidative-mediated reciprocal interaction between the two cell types. In addition, we demonstrated that RMF-HGF showed an up-regulation of an ROS-generating enzyme, NADPH oxidase 4 (Nox4). Targeting this pro-oxidant significantly suppressed the activated phenotype of RMF-HGF in a collagen contraction assay, suggesting that RMF-HGF contributes to the oxidative tumor microenvironment. We have further shown that scavenging ROS with EcSOD significantly inhibited RMF-HGF-stimulated orthotopic tumor growth of MDA-MB231. This study suggests the loss of EcSOD in breast cancer plays a pivotal role in promoting the HGF/c-Met-mediated cancer-fibroblast interactions.

The effect of co-transplantation of nerve fibroblasts and Schwann cells on peripheral nerve repair

Combinations of fibroblasts (Fbs) and corresponding epithelial cells have been widely used in many tissues, such as the skin and breast tissues, to augment tissue repair and remodeling. Recently, a large amount of new data has indicated that nerve Fbs play critical roles in Schwann cells (SCs) and axons in vitro. However, little is known regarding the effects of co-transplanting nerve Fbs and SCs on peripheral nerve repair in vivo. The aim of this study was to investigate the effect of co-transplanting sciatic nerve Fbs (SN-Fbs) and sciatic nerve SCs (SN-SCs) on nerve regeneration. We developed a 5 mm nerve-defect model in mice using a polyurethane (PUR) catheter and then injected one of four different mixtures of cells into the catheters to form the following four groups: pure Matrigel (Control group), SN-Fbs alone (SN-Fb group), SN-Fbs combined with SN-SCs at a ratio of 1:2 (Fb&SC group) and SN-SCs alone (SN-SC group). Histological and functional analyses were performed 3 months later. The results indicated that in vitro, the expression levels of NGF, BDNF and GDNF were significantly higher, and in vivo, a more moderate amount of extracellular matrix was produced in the Fb&SC group than in the SN-SC group. Compared to the other groups, co-transplanting SN-Fbs with SCs at a 1:2 ratio had significantly positive effects on nerve regeneration and functional recovery.

Notch Shapes the Innate Immunophenotype in Breast Cancer

Notch activation, which is associated with basal-like breast cancer (BLBC), normally directs tissue patterning, suggesting that it may shape the tumor microenvironment. Here, we show that Notch in tumor cells regulates the expression of two powerful proinflammatory cytokines, IL1β and CCL2, and the recruitment of tumor-associated macrophages (TAM). Notch also regulates TGFβ-mediated activation of tumor cells by TAMs, closing a Notch-dependent paracrine signaling loop between these two cell types. We use a mouse model in which Notch can be regulated in spontaneous mammary carcinoma to confirm that IL1β and CCL2 production, and macrophage recruitment are Notch-dependent. In human disease, expression array analyses demonstrate a striking association between Notch activation, IL1β and CCL2 production, macrophage infiltration, and BLBC. These findings place Notch at the nexus of a vicious cycle of macrophage infiltration and amplified cytokine secretion and provide immunotherapeutic opportunities in BLBC.Significance: BLBC is aggressive and has an unmet need for effective targeted treatment. Our data highlight immunotherapeutic opportunities in Notch-activated BLBC. Effective IL1β and CCL2 antagonists are currently in clinical review to treat benign inflammatory disease, and their transition to the cancer clinic could have a rapid impact. Cancer Discov; 7(11); 1320-35. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 1201.

The deleterious interplay between tumor epithelia and stroma in cholangiocarcinoma

Prognosis of cholangiocarcinoma, a devastating liver epithelial malignancy characterized by early invasiveness, remains very dismal, though its incidence has been steadily increasing. Evidence is mounting that in cholangiocarcinoma, tumor epithelial cells establish an intricate web of mutual interactions with multiple stromal components, largely determining the pervasive behavior of the tumor. The main cellular components of the tumor microenvironment (i.e. myofibroblasts, macrophages, lymphatic endothelial cells), which has been recently termed as 'tumor reactive stroma', are recruited and activated by neoplastic cells, and in turn, deleteriously mold tumor behavior by releasing a huge variety of paracrine signals, including cyto/chemokines, growth factors, morphogens and proteinases. An abnormally remodeled and stiff extracellular matrix favors and supports these cell interactions. Although the mechanisms responsible for the generation of tumor reactive stroma are largely uncertain, hypoxia presumably plays a central role. In this review, we will dissect the intimate relationship among the different cell elements cooperating within this complex 'ecosystem', with the ultimate goal to pave the way for a deeper understanding of the mechanisms underlying cholangiocarcinoma aggressiveness, and possibly, to foster the development of innovative, combinatorial therapies aimed at halting tumor progression. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

Ex vivo expanded natural killer cells from breast cancer patients and healthy donors are highly cytotoxic against breast cancer cell lines and patient-derived tumours

BACKGROUND

Natural killer (NK) cells play a critical role in cancer immunosurveillance. Recent developments in NK cell ex-vivo expansion makes it possible to generate millions of activated NK cells from a small volume of peripheral blood. We tested the functionality of ex vivo expanded NK cells in vitro against breast cancer cell lines and in vivo using a xenograft mouse model. The study aim was to assess functionality and phenotype of expanded NK cells from breast cancer patients against breast cancer cell lines and autologous primary tumours.

METHODS

We used a well-established NK cell co-culture system to expand NK cells ex vivo from healthy donors and breast cancer patients and examined their surface marker expression. Moreover, we tested the ability of expanded NK cells to lyse the triple negative breast cancer and HER2-positive breast cancer cell lines MDA-MB-231 and MDA-MB-453, respectively. We also tested their ability to prevent tumour growth in vivo using a xenograft mouse model. Finally, we tested the cytotoxicity of expanded NK cells against autologous and allogeneic primary breast cancer tumours in vitro.

RESULTS

After 3 weeks of culture we observed over 1000-fold expansion of NK cells isolated from either breast cancer patients or healthy donors. We also showed that the phenotype of expanded NK cells is comparable between those from healthy donors and cancer patients. Moreover, our results confirm the ability of ex vivo expanded NK cells to lyse tumour cell lines in vitro. While the cell lines examined had differential sensitivity to NK cell killing we found this was correlated with level of major histocompatibility complex (MHC) class I expression. In our in vivo model, NK cells prevented tumour establishment and growth in immunocompromised mice. Finally, we showed that NK cells expanded from the peripheral blood of breast cancer patients show high cytotoxicity against allogeneic and autologous patient-derived tumour cells in vitro.

CONCLUSION

NK cells from breast cancer patients can be expanded similarly to those from healthy donors, have a high cytotoxic ability against breast cancer cell lines and patient-derived tumour cells, and can be compatible with current cancer treatments to restore NK cell function in cancer patients.

Pathomimetic avatars reveal divergent roles of microenvironment in invasive transition of ductal carcinoma in situ

BACKGROUND

The breast tumor microenvironment regulates progression of ductal carcinoma in situ (DCIS) to invasive ductal carcinoma (IDC). However, it is unclear how interactions between breast epithelial and stromal cells can drive this progression and whether there are reliable microenvironmental biomarkers to predict transition of DCIS to IDC.

METHODS

We used xenograft mouse models and a 3D pathomimetic model termed mammary architecture and microenvironment engineering (MAME) to study the interplay between human breast myoepithelial cells (MEPs) and cancer-associated fibroblasts (CAFs) on DCIS progression.

RESULTS

Our results show that MEPs suppress tumor formation by DCIS cells in vivo even in the presence of CAFs. In the in vitro MAME model, MEPs reduce the size of 3D DCIS structures and their degradation of extracellular matrix. We further show that the tumor-suppressive effects of MEPs on DCIS are linked to inhibition of urokinase plasminogen activator (uPA)/urokinase plasminogen activator receptor (uPAR)-mediated proteolysis by plasminogen activator inhibitor 1 (PAI-1) and that they can lessen the tumor-promoting effects of CAFs by attenuating interleukin 6 (IL-6) signaling pathways.

CONCLUSIONS

Our studies using MAME are, to our knowledge, the first to demonstrate a divergent interplay between MEPs and CAFs within the DCIS tumor microenvironment. We show that the tumor-suppressive actions of MEPs are mediated by PAI-1, uPA and its receptor, uPAR, and are sustained even in the presence of the CAFs, which themselves enhance DCIS tumorigenesis via IL-6 signaling. Identifying tumor microenvironmental regulators of DCIS progression will be critical for defining a robust and predictive molecular signature for clinical use.

TGF-β, Bone Morphogenetic Protein, and Activin Signaling and the Tumor Microenvironment

The cellular and noncellular components surrounding the tumor cells influence many aspects of tumor progression. Transforming growth factor β (TGF-β), bone morphogenetic proteins (BMPs), and activins have been shown to regulate the phenotype and functions of the microenvironment and are attractive targets to attenuate protumorigenic microenvironmental changes. Given the pleiotropic nature of the cytokines involved, a full understanding of their effects on numerous cell types in many contexts is necessary for proper clinical intervention. In this review, we will explore the various effects of TGF-β, BMP, and activin signaling on stromal phenotypes known to associate with cancer progression. We will summarize these findings in the context of their tumor suppressive or promoting effects, as well as the molecular changes that these cytokines induce to influence stromal phenotypes.

Expression pattern of cancer-associated fibroblast and its clinical relevance in intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma (ICC) is a highly malignant neoplasm and lack of effective treatment, characterized by dense desmoplastic stroma rich in cancer-associated fibroblasts (CAFs), which have been indicated to facilitate tumor progression in several types of human cancer. However, the clinical relevance of CAFs in ICC has not been fully characterized. Here, we evaluated the histological phenotype of CAFs and immunohistochemical expressions of α-SMA, FSP-1, and PDGFRβ in 71 ICC cases, and found that immature CAF phenotype was significantly associated with lymph node metastasis (P=.045), advanced TNM stage (P=.025) and poor 5-year overall survival (OS) (38.5% versus 78.6%, P=.015). In addition, α-SMA, FSP-1, and PDGFRβ were positively expressed in stromal fibroblasts in 63.4% (45/71), 84.5% (60/71), and 78.9% (56/71) of patients, respectively. Positive expression of α-SMA was correlated with poor differentiation (P=.032); FSP-1 expression in stromal fibroblasts was linked with lymph node metastasis (P=.022) and immature phenotype (P=.048). What's more, positive expression of FSP-1 in cancer cells was observed in 22.5% (16/71) of cases and was correlated with worse 5-year OS (36.4% versus 76.7%, P=.014). Importantly, in multivariate analysis, histological CAF phenotype was an independent prognostic factor for OS in ICC. Our findings demonstrated histological categorization of CAFs was a useful predictor for prognosis, providing new evidence that CAFs play a crucial role in tumor progression and can serve as potential therapeutic targets in ICC.

A stemness-related ZEB1-MSRB3 axis governs cellular pliancy and breast cancer genome stability

Chromosomal instability (CIN), a feature of most adult neoplasms from their early stages onward, is a driver of tumorigenesis. However, several malignancy subtypes, including some triple-negative breast cancers, display a paucity of genomic aberrations, thus suggesting that tumor development may occur in the absence of CIN. Here we show that the differentiation status of normal human mammary epithelial cells dictates cell behavior after an oncogenic event and predetermines the genetic routes toward malignancy. Whereas oncogene induction in differentiated cells induces massive DNA damage, mammary stem cells are resistant, owing to a preemptive program driven by the transcription factor ZEB1 and the methionine sulfoxide reductase MSRB3. The prevention of oncogene-induced DNA damage precludes induction of the oncosuppressive p53-dependent DNA-damage response, thereby increasing stem cells' intrinsic susceptibility to malignant transformation. In accord with this model, a subclass of breast neoplasms exhibit unique pathological features, including high ZEB1 expression, a low frequency of TP53 mutations and low CIN.

The Influence of Biomaterials on Cytokine Production in 3D Cultures

As a result of improved relevance to in vivo physiology, in vitro studies are increasingly performed in diverse, three-dimensional (3D) biomaterials. However, material-cell type pairing effects on cytokine availability remain unclear. We cultured five cell types in agarose, alginate, collagen, Matrigel, or RGD-functionalized polyethylene glycol (PEG) hydrogels. We measured 21 cytokines in the conditioned media, and we identified differences in measured cytokine levels that were cell-type- or material-dependent. We further evaluated our data using principal component analysis. Interestingly, component one identified two classes of biomaterials with characteristic cytokine expression levels. Component two identified cell-type-dependent differences in cytokines related to the wound response. Although elements of soluble cytokine availability are shared despite parameter differences, material and cellular properties variably influenced cytokine levels, underlining the influence of biomaterial-cell type pairings on in vitro assay outcomes. Relationships between material properties, cellular responses, and cytokine availability in 3D in vitro models warrant further investigation.

Loss of exosomal miR-320a from cancer-associated fibroblasts contributes to HCC proliferation and metastasis

Cancer-associated fibroblasts (CAFs) play a pivotal role in regulating tumour progression. Therefore, understanding how CAFs communicate with hepatocellular carcinoma (HCC) is crucial for HCC therapy. Recently, exosomes have been considered an important "messenger" between cells. In this study, we performed microRNA (miRNA) sequencing of exosomes derived from CAFs and corresponding para-cancer fibroblasts (PAFs) of HCC patients. We found a significant reduction in the miR-320a level in CAF-derived exosomes. Using exogenous miRNAs, we demonstrated that stromal cells could transfer miRNA to HCC cells. In vitro and in vivo studies further revealed that miR-320a could function as an antitumour miRNA by binding to its direct downstream target PBX3 to suppress HCC cell proliferation, migration and metastasis. The miR-320a-PBX3 pathway inhibited tumour progression by suppressing the activation of the MAPK pathway, which could induce the epithelial-mesenchymal transition and upregulate cyclin-dependent kinase 2 (CDK2) and MMP2 expression to promote cell proliferation and metastasis. In xenograft experiments involving CAFs mixed with MHCC97-H cells, miR-320a overexpression in CAFs could inhibit tumourigenesis. Therefore, these data suggest that CAF-mediated HCC tumour progression is partially related to the loss of antitumour miR-320a in the exosomes of CAFs and that promoting the transfer of stromal cell-derived miR-320a might be a potential treatment option to overcome HCC progression.

Therapeutic vaccination based on side population cells transduced by the granulocyte-macrophage colony-stimulating factor gene elicits potent antitumor immunity

Among cancer immunotherapies, granulocyte-macrophage colony-stimulating factor (GM-CSF) gene-transduced tumor cell vaccine (GVAX) therapies appear promising and have been shown to be safe and effective in multiple clinical trials. However, the antitumor efficacies of GVAX therapy alone are in some cases limited. Here we showed that GVAX therapy targeting cancer stem cells (CSCs) substantially suppressed tumor development in syngeneic immunocompetent mice recapitulating normal immune systems. CSCs were isolated as side population (SP) cells from 4T1 murine breast carcinoma cell line and transduced with GM-CSF gene delivered by non-transmissible Sendai virus (4T1-SP/GM). Impaired tumorigenicity of subcutaneously injected 4T1-SP/GM depended on CD8⁺ T cells in concert with CD4⁺ T cells and natural killer cells. Mice therapeutically vaccinated with irradiated 4T1-SP/GM cells had markedly suppressed tumor development of subcutaneously transplanted 4T1-SP cells compared with those treated with irradiated cells of non-transduced 4T1-SP cells or non-SP (4T1-NSP/GM) cells. Tumor suppression was accompanied by the robust accumulation of mature dendritic cells at vaccination sites and T-helper type 1-skewed systemic cellular immunity. Our results suggested that CSC cell-based GVAX immunotherapy might be clinically useful for inducing potent tumor-specific antitumor immunity.

Patient-derived xenograft (PDX) models in basic and translational breast cancer research

Patient-derived xenograft (PDX) models of a growing spectrum of cancers are rapidly supplanting long-established traditional cell lines as preferred models for conducting basic and translational preclinical research. In breast cancer, to complement the now curated collection of approximately 45 long-established human breast cancer cell lines, a newly formed consortium of academic laboratories, currently from Europe, Australia, and North America, herein summarizes data on over 500 stably transplantable PDX models representing all three clinical subtypes of breast cancer (ER+, HER2+, and "Triple-negative" (TNBC)). Many of these models are well-characterized with respect to genomic, transcriptomic, and proteomic features, metastatic behavior, and treatment response to a variety of standard-of-care and experimental therapeutics. These stably transplantable PDX lines are generally available for dissemination to laboratories conducting translational research, and contact information for each collection is provided. This review summarizes current experiences related to PDX generation across participating groups, efforts to develop data standards for annotation and dissemination of patient clinical information that does not compromise patient privacy, efforts to develop complementary data standards for annotation of PDX characteristics and biology, and progress toward "credentialing" of PDX models as surrogates to represent individual patients for use in preclinical and co-clinical translational research. In addition, this review highlights important unresolved questions, as well as current limitations, that have hampered more efficient generation of PDX lines and more rapid adoption of PDX use in translational breast cancer research.

Epithelial Plasticity During Human Breast Morphogenesis and Cancer Progression

Understanding the complex events leading to formation of an epithelial-based organ such as the breast requires a detailed insight into the crosstalk between epithelial and stromal compartments. These interactions occur both through heterotypic cellular interactions and between cells and matrix components. While in vivo models may partially capture these complex interactions, there is a need for in- vitro models to study these events. In this review we discuss cell-cell interactions in breast development focusing on the stem cell niche and branching morphogenesis. Given the recent understanding that the basic developmental events underlying branching morphogenesis are closely related to pathways important to cancer progression, i.e. epithelial plasticity and epithelial to mesenchymal transition (EMT), we will also discuss aspects relevant to cancer progression. In cancer, the adoption of mesenchymal phenotype by the malignant cells allows stromal invasion and subsequent intravasation to blood- or lymphatic vessels, a route that is a prerequisite for metastasis. A number of publications have demonstrated that tumor initiating cells, sometimes referred to as cancer stem cells adapt an EMT phenotype that renders them more resistant to apoptosis and drug therapy. The mechanism behind this phenomenon is currently unknown but this may partially explain relapse in breast cancer patients. Increased understanding of branching morphogenesis in the breast gland and the regulation of EMT and its reverse process mesenchymal to epithelial transition (MET) may hold the keys for future development of methods/drugs that neutralize the invading properties of cancer cells.

Metronomic chemotherapy prevents therapy-induced stromal activation and induction of tumor-initiating cells

Chan et al. report that treatment of tumor-bearing mice with low-dose metronomic chemotherapy prevents stromal secretion of ELR⁺ chemokines and induction of tumor-initiating cells usually observed with administration of drugs at maximum tolerated dose.

Although traditional chemotherapy kills a fraction of tumor cells, it also activates the stroma and can promote the growth and survival of residual cancer cells to foster tumor recurrence and metastasis. Accordingly, overcoming the host response induced by chemotherapy could substantially improve therapeutic outcome and patient survival. In this study, resistance to treatment and metastasis has been attributed to expansion of stem-like tumor-initiating cells (TICs). Molecular analysis of the tumor stroma in neoadjuvant chemotherapy–treated human desmoplastic cancers and orthotopic tumor xenografts revealed that traditional maximum-tolerated dose chemotherapy, regardless of the agents used, induces persistent STAT-1 and NF-κB activity in carcinoma-associated fibroblasts. This induction results in the expression and secretion of ELR motif–positive (ELR⁺) chemokines, which signal through CXCR-2 on carcinoma cells to trigger their phenotypic conversion into TICs and promote their invasive behaviors, leading to paradoxical tumor aggression after therapy. In contrast, the same overall dose administered as a low-dose metronomic chemotherapy regimen largely prevented therapy-induced stromal ELR⁺ chemokine paracrine signaling, thus enhancing treatment response and extending survival of mice carrying desmoplastic cancers. These experiments illustrate the importance of stroma in cancer therapy and how its impact on treatment resistance could be tempered by altering the dosing schedule of systemic chemotherapy.

TGF-β1 induces PGP9.5 expression in CAFs to promote the growth of colorectal cancer cells

Numerous studies indicate that the interaction between cancer-associated fibroblasts (CAFs) and tumors is manifested in the entire process of colorectal cancer (CRC) cell development, in which TGF-β1 plays a key role and has a significant effect on promoting the activation of CAFs. However, there are few studies on the mechanisms involved in the activation of CAFs by TGF-β1 to produce an influence on tumor cells. TGF-β1 was added to CAFs for further culture, and the expression of α-SMA was significantly enhanced as shown by immunofluorescence assay. Western blot analysis was performed, and the results showed that TGF-β1 promoted expression of PGP9.5 in a time-dependent manner. After siRNA was used to inhibit the expression of Smad2 or Smad3, the TGF-β1-induced PGP9.5 expression in CAFs was obviously suppressed. In addition, TGF-β1 was also found to promote the expression of PGP9.5 through the ERK1/2 and PI3K pathways. CAFs were cultured on the upper layer of a Transwell plate and TGF-β1 was added. Simultaneously, CRC cells were cultured on the lower layer. The biological behaviors of the cancer cells were detected. According to the results, TGF-β1 promoted the proliferation and invasion of CRC cells and inhibited their apoptosis while activating CAFs. This effect was achieved by induction of the expression of PGP9.5. However, when PGP9.5 was inhibited, the impact of TGF-β1 on tumor cells after activation of CAFs was not fully blocked. Therefore, TGF-β1 can promote PGP9.5 expression in CAFs to facilitate the growth of cancer cells. This finding aids in the identification of new targets for treating CRC.

The Impact of Environmental and Endogenous Damage on Somatic Mutation Load in Human Skin Fibroblasts

Accumulation of somatic changes, due to environmental and endogenous lesions, in the human genome is associated with aging and cancer. Understanding the impacts of these processes on mutagenesis is fundamental to understanding the etiology, and improving the prognosis and prevention of cancers and other genetic diseases. Previous methods relying on either the generation of induced pluripotent stem cells, or sequencing of single-cell genomes were inherently error-prone and did not allow independent validation of the mutations. In the current study we eliminated these potential sources of error by high coverage genome sequencing of single-cell derived clonal fibroblast lineages, obtained after minimal propagation in culture, prepared from skin biopsies of two healthy adult humans. We report here accurate measurement of genome-wide magnitude and spectra of mutations accrued in skin fibroblasts of healthy adult humans. We found that every cell contains at least one chromosomal rearrangement and 600–13,000 base substitutions. The spectra and correlation of base substitutions with epigenomic features resemble many cancers. Moreover, because biopsies were taken from body parts differing by sun exposure, we can delineate the precise contributions of environmental and endogenous factors to the accrual of genetic changes within the same individual. We show here that UV-induced and endogenous DNA damage can have a comparable impact on the somatic mutation loads in skin fibroblasts.

Somatic genomes are constantly accumulating changes caused by endogenous lesions, errors in DNA replication and repair, as well as environmental insults. Despite the importance of somatic genome instability in aging and age-related pathologies, including cancers, accurate measurements of mutation loads in healthy cells is still missing. In this study, we developed an experimental approach to accurately determine the somatic genome changes accrued in cell lineages over the lifetime of healthy humans. We show that the amounts and types of mutations in skin cells resemble many cancers, thus indicating that the mechanisms that lead to carcinogenesis are also functional in healthy cells. Moreover, sun-exposed skin cells have a higher mutation load attributable to ultraviolet radiation (UV) unlike cells from hips that were protected by clothing. Our work provides precise measurements of the mutation loads in single cells in human skin. Furthermore our data allowed defining the mutagenic impacts of environmental and endogenous processes within the same individual and led to conclusion that these processes have a comparable impact on the somatic mutation load.

The Role of Cyclooxygenase-2 in Colorectal Carcinogenesis

Colorectal cancer is a major worldwide health care problem that accounts for 1 million new cases each year. The risk factors for this disease include hereditary factors, environmental agents, and inflammatory stimuli that affect the gastrointestinal tract. Among these risk factors, cyclooxygenase-2 (COX-2) is one of the major players in the progression of colorectal cancer; however, the detailed mechanism of its role in causing colorectal cancer is still not well understood. In addition, the role of COX-2 signaling through the interaction in the epithelial and stromal compartments on colorectal carcinogenesis has not been fully illustrated. In the present review, we provide published evidence to demonstrate that (1) COX-2 signaling plays a major role in the progression of colorectal cancer, (2) activation of COX-2 in the stromal compartment also contributes to colorectal carcinogenesis, and (3) inhibition of COX-2 signaling by COX-2 inhibitors might be an effective method to control colorectal cancer. We have also summarized recent advances and insights from mechanistic studies of colorectal cancer to help prevent and control this deadly disease and provide our opinion regarding the importance of risk reduction and disease prevention for colorectal cancer.

In vitro models of cancer stem cells and clinical applications

Cancer cells, stem cells and cancer stem cells have for a long time played a significant role in the biomedical sciences. Though cancer therapy is more effective than it was a few years ago, the truth is that still none of the current non-surgical treatments can cure cancer effectively. The reason could be due to the subpopulation called “cancer stem cells” (CSCs), being defined as those cells within a tumour that have properties of stem cells: self-renewal and the ability for differentiation into multiple cell types that occur in tumours.

The phenomenon of CSCs is based on their resistance to many of the current cancer therapies, which results in tumour relapse. Although further investigation regarding CSCs is still needed, there is already evidence that these cells may play an important role in the prognosis of cancer, progression and therapeutic strategy. Therefore, long-term patient survival may depend on the elimination of CSCs. Consequently, isolation of pure CSC populations or reprogramming of cancer cells into CSCs, from cancer cell lines or primary tumours, would be a useful tool to gain an in-depth knowledge about heterogeneity and plasticity of CSC phenotypes and therefore carcinogenesis. Herein, we will discuss current CSC models, methods used to characterize CSCs, candidate markers, characteristic signalling pathways and clinical applications of CSCs. Some examples of CSC-specific treatments that are currently in early clinical phases will also be presented in this review.

The mammary ducts create a favourable microenvironment for xenografting of luminal and molecular apocrine breast tumours

There is a paucity of models for hormone receptor-positive (HR+) breast cancer because of the difficulty of establishing xenografts from these tumours. We show that this obstacle can be overcome by injecting human tumour cells directly into the mammary ducts of immunodeficient mice. Tumours from 31 patients were infected overnight with a lentiviral vector expressing tdTomato and injected through the nipple into the mammary ducts of NOD-SCID-IL2RG-/- mice. Tumours formed in the mice in 77% of cases after the first injection (6/8 luminal A, 15/20 luminal B, and 3/3 molecular apocrine). Four luminal A and one molecular apocrine graft were tested in secondary and tertiary grafts: all were successfully passaged in secondary and 4/5 in tertiary grafts. None of the samples engrafted when injected subcutaneously. The morphology, oestrogen receptor (ER), progesterone receptor (PR), androgen receptor (AR), and Ki-67 profiles of the clinical samples were maintained in the tertiary grafts. We also show that the intraductal approach can be used to test the response to targeted therapy with fulvestrant and palbociclib, using a genetically defined ER+ model. We conclude that the mammary ducts create a microenvironment that is uniquely favourable to the survival and growth of tumours derived from mammary hormone-sensing cells. This approach opens the door to testing genomically targeted treatment of HR+ tumours in precision medicine programmes. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The Zebrafish Xenograft Platform: Evolution of a Novel Cancer Model and Preclinical Screening Tool

Animal xenografts of human cancers represent a key preclinical tool in the field of cancer research. While mouse xenografts have long been the gold standard, investigators have begun to use zebrafish (Danio rerio) xenotransplantation as a relatively rapid, robust and cost-effective in vivo model of human cancers. There are several important methodological considerations in the design of an informative and efficient zebrafish xenotransplantation experiment. Various transgenic fish strains have been created that facilitate microscopic observation, ranging from the completely transparent casper fish to the Tg(fli1:eGFP) fish that expresses fluorescent GFP protein in its vascular tissue. While human cancer cell lines have been used extensively in zebrafish xenotransplantation studies, several reports have also used primary patient samples as the donor material. The zebrafish is ideally suited for transplanting primary patient material by virtue of the relatively low number of cells required for each embryo (between 50 and 300 cells), the absence of an adaptive immune system in the early zebrafish embryo, and the short experimental timeframe (5-7 days). Following xenotransplantation into the fish, cells can be tracked using in vivo or ex vivo measures of cell proliferation and migration, facilitated by fluorescence or human-specific protein expression. Importantly, assays have been developed that allow for the reliable detection of in vivo human cancer cell growth or inhibition following administration of drugs of interest. The zebrafish xenotransplantation model is a unique and effective tool for the study of cancer cell biology.