Long non-coding NR2F1-AS1 is associated with tumor recurrence in estrogen receptor-positive breast cancers

The tenacity of late recurrence of estrogen receptor (ER)‐positive breast cancer remains a major clinical issue to overcome. The administration of endocrine therapies within the first 5 years substantially minimizes the risk of relapse; however, some tumors reappear 10–20 years after the initial diagnosis. Accumulating evidence has strengthened the notion that long noncoding RNAs (lncRNAs) are associated with cancer in various respects. Because lncRNAs may display high tissue/cell specificity, we hypothesized this might provide new insights to tumor recurrence. By comparing transcriptome profiles of 24 clinical primary tumors obtained from patients who developed distant metastases and patients with no signs of recurrence, we identified lncRNA NR2F1‐AS1 whose expression was associated with tumor recurrence. We revealed the relationship between NR2F1‐AS1 and the hormone receptor expressions in ER‐positive breast cancer cells. Gain of function of NR2F1‐AS1 steered cancer cells into quiescence‐like state by the upregulation of dormancy inducers and pluripotency markers, and activates representative events of the metastatic cascade. Our findings implicated NR2F1‐AS1 in the dynamics of tumor recurrence in ER‐positive breast cancers and introduce a new biomarker that holds a therapeutic potential, providing favorable prospects to be translated into the clinical field.

MiR-1285-5p/TMEM194A axis affects cell proliferation in breast cancer

The onset of breast cancer among young patients is a major issue in cancer etiology. Our previous study has shown that poor prognosis in young women with breast cancer is associated with lower expression of the microRNA miR‐1285‐5p. In this study, we showed that the expression of miR‐1285‐5p is lower in tumor tissues than in normal tissues. Accumulating evidence suggests that miR‐1285‐5p plays critical roles in various types of cancers. However, the functional role of miR‐1285‐5p in breast cancer remains to be elucidated. Here, we showed the tumor‐suppressive role of miR‐1285‐5p and detailed its mechanism of action in breast cancer. Overexpression of miR‐1285‐5p significantly inhibited cell proliferation in breast cancer cells regardless of the tumor subtype. Among the target genes of miR‐1285‐5p, we found that transmembrane protein 194A (TMEM194A) was directly regulated by miR‐1285‐5p. Notably, separation of centrosomes from the nuclear envelope was observed upon knockdown of TMEM194A or overexpression of miR‐1285‐5p. In conclusion, our findings show that miR‐1285‐5p is a tumor suppressor via TMEM194A inhibition in breast cancer.

Method to Convert Stem Cells into Cancer Stem Cells

The cancer stem cell (CSC) hypothesis suggests that tumors are sustained exclusively by a small population of the cells with stem cell properties. CSCs have been identified in most tumors and are responsible for the initiation, recurrence, and resistance of different cancers. In vitro CSC models will be of great help in revisiting the mechanism of cancer development, as well as the tumor microenvironment and the heterogeneity of cancer and metastasis. Our group recently described the generation of CSCs from induced pluripotent stem cells (iPSCs), which were reprogrammed from normal cells, and/or embryonic stem cells (ESCs). This procedure will improve the understanding of the essential niche involved in cancer initiation. The composition of this cancer-inducing niche, if identified, will let us know how normal cells convert to malignant in the body and how, in turn, cancer prevention could be achieved. Further, once developed, CSCs demonstrate the ability to differentiate into endothelial cells, cancer-associated fibroblasts, and other phenotypes establishing the CSC niche. These will be good materials for developing novel cancer treatments. In this protocol, we describe how to handle mouse iPSCs/ESCs and how to choose the critical time for starting the conversion into CSCs. This CSC generation protocol is essential for understanding the role of CSC in cancer initiation and progress.

Extracellular vesicles mediate the horizontal transfer of an active LINE-1 retrotransposon

Long interspersed element-1 (LINE-1 or L1) retrotransposons replicate through a copy-and-paste mechanism using an RNA intermediate. However, little is known about the physical transmission of retrotransposon RNA between cells. To examine the horizontal transfer of an active human L1 retrotransposon mediated by extracellular vesicles (EVs), human cancer cells were transfected with an expression construct containing a retrotransposition-competent human L1 tagged with a reporter gene. Using this model, active retrotransposition events were detected by screening for the expression of the reporter gene inserted into the host genome by retrotransposition. EVs including exosomes and microvesicles were isolated from cells by differential centrifugation. The enrichment of L1-derived reporter RNA transcripts were detected in EVs isolated from cells expressing active L1 retrotransposition. The delivery of reporter RNA was confirmed in recipient cells, and reporter genes were detected in the genome of recipient cells. Additionally, employing qRT-PCR, we found that host-encoded factors are activated in response to increased exposure to L1-derived RNA transcripts in recipient cells. Our results suggest that the horizontal transfer of retrotransposons can occur through the incorporation of RNA intermediates delivered via EVs and may have important implications for the intercellular regulation of gene expression and gene function.

Abstract 3055: A model of CSC converted from iPSC in the conditioned medium of HCC paving the way to establish HCC CSC

Hepatocellular carcinoma (HCC) represents the major histological subtype, accounting for 70%–85% of cases of primary liver cancer. Liver CSCs sustain their self-renewal remains largely unknown. The self-renewal and pluripotency of liver CSC are maintained by several signaling cascades. However, the mechanism of regulating these signaling is unknown.

In this study, we tried to convert mouse iPSCs into CSCs with the conditioned medium (CM) from human HCC cell line Huh7 cells without any genetic manipulation aiming at establishing liver CSCs.

First of all, CM was collected from confluent culture of Huh7 cells. Then, mouse iPSCs cells without MEF feeder cells were cultured in the presence of 50% CM for 4 weeks. The medium was changed every day with fresh medium containing 50% of CM. Mouse iPSCs cultured in the complete medium with LIF were used as a control.The survived cells (5x105 cells) were suspended in HBSS and injected into the liver of BALB/c nude mice. After 25 days malignant tumor was formed in the liver while benign teratoma was formed by the injection of iPSCs. Tumors were then excised and partly fixed in 10% neutral formalin buffer solution for HE staining and immunohistochemical analysis. The rest of tumors were subjected to rt-qPCR anaylsis and primary culture. Immunohistochemical analysis with GFP antibody showed that malignant tumor sustained GFP expression while teratoma from miPSCs did not. Immunocytochemistry of the primary cells from malignant tumor showed high expression of both glypican-3 (GPC3) and cytokeratin19 (CK19) when compared to that in miPSCs. Expression of stem cell markers (Nanog, Oct3/4, Sox2, Klf4) and CSC markers (CD44, EpCAM) were also confirmed by rt-qPCR in both the CSCs converted from iPSCs (miPS-Huh7cm cells) and the primary culture cells. These results indicate that the primary cells from the malignant tumor are rich in CSCs with high expression of GPC3 and CK19, which paves the way to establish a model of HCC CSC. This model should be very important and useful to assess the significant molecular mechanisms necessary to maintain HCC CSC, which will help develop effective therapy of liver cancer.

Citation Format: Said M Afify, Anna Sanchez Calle, Kazuki Kumon, Hend M Nawara, Apriliana C Khairani, Hafizah Mahmud, Aung Ko Ko Oo, Du Juan, Maram H Zahara, Akimasa Seno, Tomonari Kasai, Yoshiaki Iwasaki, Masaharu Seno. A model of CSC converted from iPSC in the conditioned medium of HCC paving the way to establish HCC CSC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3055.

Emerging roles of long non-coding RNA in cancer

Since comprehensive analysis of the mammalian genome revealed that the majority of genomic products are transcribed in long non‐coding RNA (lncRNA), increasing attention has been paid to these transcripts. The applied next‐generation sequencing technologies have provided accumulating evidence of dysregulated lncRNA in cancer. The implication of this finding can be seen in many forms and at multiple levels. With impacts ranging from integrating chromatin remodeling complexes to regulating transcription and post‐transcriptional processes, aberrant expression of lncRNA may have repercussions in cell proliferation, tumor progression or metastasis. lncRNA may act as enhancers, scaffolds or decoys by physically interacting with other RNA species or proteins, resulting in a direct impact on cell signaling cascades. Even though their functional classification is well‐established in the context of cancer, clearer characterization in terms of their phenotypic outputs is needed to optimize and identify suitable candidates that enable the development of new therapeutic strategies and the design of novel diagnostic approaches. The present article aims to outline different cancer‐associated lncRNA according to their contribution to tumor suppression or tumor promotion based on their most current functional annotations.

Up-Regulation of PI 3-Kinases and the Activation of PI3K-Akt Signaling Pathway in Cancer Stem-Like Cells Through DNA Hypomethylation Mediated by the Cancer Microenvironment

Previously, we have succeeded in converting induced pluripotent stem cells (iPSCs) into cancer stem cells (CSCs) by treating the iPSCs with conditioned medium of Lewis lung carcinoma (LLC) cells. The converted CSCs, named miPS-LLCcm cells, exhibited the self-renewal, differentiation potential, and potential to form malignant tumors with metastasis. In this study, we further characterized miPS-LLCcm cells both in vivo and in vitro. The tumors formed by subcutaneous injection showed the structures with pathophysiological features consisting of undifferentiated and malignant phenotypes generally found in adenocarcinoma. Metastasis in the lung was also observed as nodule structures. Excising from the tumors, primary cultured cells from the tumor and the nodule showed self-renewal, differentiation potential as well as tumor forming ability, which are the essential characters of CSCs. We then characterized the epigenetic regulation occurring in the CSCs. By comparing the DNA methylation level of CG rich regions, the differentially methylated regions (DMRs) were evaluated in all stages of CSCs when compared with the parental iPSCs. In DMRs, hypomethylation was found superior to hypermethylation in the miPS-LLCcm cells and its derivatives. The hypo- and hypermethylated genes were used to nominate KEGG pathways related with CSC. As a result, several categories were defined in the KEGG pathways from which most related with cancers, significant and high expression of components was PI3K-AKT signaling pathway. Simultaneously, the AKT activation was also confirmed in the CSCs. The PI3K-Akt signaling pathway should be an important pathway for the CSCs established by the treatment with conditioned medium of LLC cells.

A cancer stem cell model as the point of origin of cancer-associated fibroblasts in tumor microenvironment

Cancer-associated fibroblasts (CAFs) are one of the most prominent cell types in the stromal compartment of the tumor microenvironment. CAFs support multiple aspects of cancer progression, including tumor initiation, invasion, and metastasis. The heterogeneous nature of the stromal microenvironment is attributed to the multiple sources from which the cells in this compartment originate. The present study provides the first evidence that cancer stem cells (CSCs) are one of the key sources of CAFs in the tumor niche. We generated CSC-like cells by treating mouse induced pluripotent stem cells with conditioned medium from breast cancer cell lines. The resulting cell population expressed both CSC and pluripotency markers, and the sphere-forming CSC-like cells formed subcutaneous tumors in nude mice. Intriguingly, these CSC-like cells always formed heterogeneous populations surrounded by myofibroblast-like cells. Based on this observation, we hypothesized that CSCs could be the source of the CAFs that support tumor maintenance and survival. To address this hypothesis, we induced the differentiation of spheres and purified the myofibroblast-like cells. The resulting cells exhibited a CAF-like phenotype, suggesting that they had differentiated into the subpopulations of cells that support CSC self-renewal. These findings provide novel insights into the dynamic interplay between various microenvironmental factors and CAFs in the CSC niche.

Abstract 926: Generation of a potential breast cancer stem cell model from induced pluripotent stem cells

The role of cancer stem cells (CSC) in the present scenario of breast cancer research is perceived as indispensable in the development and progression of the disease. The CSC niche maintains a heirarchy of heterogeneous cells, which facilitates the inception of the tumor until its invasion. Therefore, our study focuses on the development of an effective breast cancer stem cell model from mouse induced pluripotent stem cells (miPSCs).

Taking into consideration the intertumor heterogeneity of breast cancer, three human breast cancer cell lines, namely BT549, SKBR3 and T47D representing three major hormone subtypes were used to derive respective conditioned medium. The miPSCs were treated with these conditioned media separately for a period of one month following the protocol previously established by our laboratory. The resulting survived cells were subcutaneously and orthotopically transplanted into Balb/c nude mice. Within a short span of 15-20 days, both subcutaneous and orthotopic tumors were developed. Serial transplantations in to nude mice also generated malignant tumors with same vigor. Histopathological studies of these tumors confirmed a malignant infiltrating ductal carcinoma with apparent desmoplasia in orthotopic tumor and Her2 expression in comparison with subcutaneous ones, all of which confirmed us the conversion of miPSCs to CSCs. Presence of lung metastatic nodes further ascertained the invasiveness of this in vitro generated CSCs. Marked expression of prominent CSC markers namely CD44, Nanog, Sox2 and CD49f were observed in primary cells generated from these tumors. Tumor sphere formation assay further confirmed the presence of a good population of self renewing CSC population in the tumor tissues.

This study attempts to recapitulate human breast cancer disease in mice without any genetic manipulation, but by exploiting the tumor microenvironment in the form of conditioned medium. This should pave the way for the establishment of personalized therapy and a model to assess effective therapeutic interventions.

Citation Format: Neha Nair, Anna Sanchez Calle, Maram Hussein Zahra, Aung Ko Ko Oo, Arun Vaidyanath, Shinobu Masuda, Tomonari Kasai, Masaharu Seno. Generation of a potential breast cancer stem cell model from induced pluripotent stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 926. doi:10.1158/1538-7445.AM2017-926

A new PDAC mouse model originated from iPSCs-converted pancreatic cancer stem cells (CSCcm)

Pancreatic ductal adenocarcinoma (PDAC) is the most representative form of pancreatic cancers. PDAC solid tumours are constituted of heterogeneous populations of cells including cancer stem cells (CSCs), differentiated cancer cells, desmoplastic stroma and immune cells. The identification and consequent isolation of pancreatic CSCs facilitated the generation of genetically engineered murine models. Nonetheless, the current models may not be representative for the spontaneous tumour occurrence. In the present study, we show the generation of a novel pancreatic iPSC-converted cancer stem cell lines (CSCcm) as a cutting-edge model for the study of PDAC. The CSCcm lines were achieved only by the influence of pancreatic cancer cell lines conditioned medium and were not subjected to any genetic manipulation. The xenografts tumours from CSCcm lines displayed histopathological features of ADM, PanIN and PDAC lesions. Further molecular characterization from RNA-sequencing analysis highlighted primary culture cell lines (1^st CSCcm) as potential candidates to represent the pancreatic CSCs and indicated the establishment of the pancreatic cancer molecular pattern in their subsequent progenies 2^nd CSCcm and 3^rd CSCcm. In addition, preliminary RNA-seq SNPs analysis showed that the distinct CSCcm lines did not harbour single point mutations for the oncogene Kras codon 12 or 13. Therefore, PDAC-CSCcm model may provide new insights about the actual occurrence of the pancreatic cancer leading to develop different approaches to target CSCs and abrogate the progression of this fatidic disease.

iPSC-derived cancer stem cells provide a model of tumor vasculature

To grow beyond a size of approximately 1-2 mm³, tumor cells activate many processes to develop blood vasculature. Growing evidences indicate that the formation of the tumor vascular network is very complex, and is not restricted to angiogenesis. Cancer cell-derived tumor vasculatures have been recently described. Among them, endothelial differentiation of tumor cells have been directly related to cancer stem cells, which are cells within a tumor that possess the capacity to self-renew, and to exhibit multipotential heterogeneous lineages of cancer cells. Vasculogenic mimicry has been described to be formed by cancer cells expressing stemness markers. Thus, cancer stem cells have been proposed to contribute to vasculogenic mimicry, though its relation is yet to be clarified. Here, we analyzed the tumor vasculature by using a model of mouse cancer stem cells, miPS-LLCcm cells, which we have previously established from mouse induced pluripotent stem cells and we introduced the DsRed gene in miPS-LLCcm to trace them in vivo. Various features of vasculature were evaluated in ovo, in vitro, and in vivo. The tumors formed in allograft nude mice exhibited angiogenesis in chick chorioallantoic membrane assay. In those tumors, along with penetrated host endothelial vessels, we detected endothelial differentiation from cancer stem cells and formation of vasculogenic mimicry. The angiogenic factors such as VEGF-A and FGF2 were expressed predominantly in the cancer stem cells subpopulation of miPS-LLCcm cells. Our results suggested that cancer stem cells play key roles in not only the recruitment of host endothelial vessels into tumor, but also in maturation of endothelial linage of cancer stem cell's progenies. Furthermore, the undifferentiated subpopulation of the miPS-LLCcm participates directly in the vasculogenic mimicry formation. Collectively, we show that miPS-LLCcm cells have advantages to further study tumor vasculature and to develop novel targeting strategies in the future.

Abstract 1725: The significance of c-Kit proto-oncogene in iCSC-derived PDAC model

Our study is focused on the generation of a novel pancreatic iPS-derived cancer stem cell line (iCSC), as a cutting-edge model of study for PDAC, and the significance of the proto-oncogene c-Kit in PDAC, using the new model of iCSC-derived PDAC generated in vivo.

Pancreatic ductal adenocarcinoma (PDAC) is a neoplasia that originates within the pancreatic ducts. The mortality rate is high due to its rapid dissemination, the strong resistance to the radio and chemotherapy, along with the lack of prognostic approaches. Therefore, this highlights the urgent need to find novel therapies along with new pancreatic cancer markers towards the early detection of the primary stages of the PDAC.

The iCSC cells were orthotopically transplanted into the pancreas of Balb/c nude mice. After a short-time course of 15 days, PDAC progression was recapitulated not only at the level of the tumour phenotype, but also with the corresponding invasion towards specific hepatic metastatic nodes. iCSC cells were obtained from iPS, following the procedure previously established by our group, where the reprogramming is accomplished exclusively through conditioned medium, without any genetic modification, which may represent a substantial tool to study fairly about the insights on the actual tumour microenvironment. In order to confirm these experiments are reproducible, iPS were cultured with different pancreatic cancer cell line -PK-8, KLM-1 and PK-59-conditioned medium. Histochemistry assay of the tumour developed in vivo demonstrated the effectiveness of the conversion from iPS into iCSC among the cell lines, generating stroma-rich ductal adenocarcinoma structures that resemble the human tumour phenotype.

The tyrosine receptor c-Kit is expressed only during the embryonic pancreas differentiation, whereas adult pancreatic normal tissues lack the expression of the receptor. However in PDAC, its overexpression seems to be tightly correlated with the progression of the disease, and c-Kit has been suggested as a CSC marker.

The overexpression of c-Kit receptor was observed at protein and mRNA expression level, in the primary cultures of iCSC-derived PDAC tumours. Interestingly, this overexpression is directly related to the tumour phenotype, being the most disrupted ductal structures those, which show the c-Kit over-expression. Additionally, CSC from the primary cultures of iCSC-derived PDAC were isolated by puromycin selection as well as sphere formation, and after 7 days of culture the mRNA expression levels of Pax4 appears to be up-regulated, suggesting that iCSC cells indeed may differentiate into a tissue-specific lineage.

Hence, c-Kit might be a prominent candidate as a CSC marker in PDAC, and according to the current results we have generated a suitable PDAC model, which recapitulates the actual disease in a short-time course, and allows the study of the actual tumour microenvironment.

Citation Format: Anna Sanchez Calle, Kenta Hoshikawa, Neha Nair, Marta Prieto-Vila, Arun Vaidyanath, Tomonari Kasai, Masaharu Seno. The significance of c-Kit proto-oncogene in iCSC-derived PDAC model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1725.

Abstract LB-278: Cancer stem cells as the novel origin of cancer-associated fibroblast-like cells

Cancer associated fibroblast (CAF) is an indispensible component of stromal microenvironment mediating cancer progression notably in breast, prostate and pancreatic carcinoma. CAF heterogeneity is attributed to its possible multiple origin majorly from tumor resident fibroblast, mesenchymal stem cells, epithelial cells. The present work analyses the possibility of cancer stem cells (CSC) as the source of CAF like cells. For this, we have used the model of CSC established in our laboratory derived from mouse induced pluripotent cells (miPSCs) by culturing with conditioned medium from cancer cell lines mimicking tumor microenvironment. In the present study, human breast cancer derived T47D and BT549 cells have been cultured to collect the conditioned medium. Since the green fluorescent protein (GFP) gene was integrated under the control of Nanog promoter in the miPSCs used in this study, the resulting CSCs was assessed by the expression of GFP for the undifferentiated state. The differentiation of CSCs was tracked by the attenuation of GFP.

The CSC population was multiplied by serial subcutaneous and orthotropic transplantation in nude mice. This population was further enriched by sphere formation. Then these spheres were allowed to differentiate into adhesive cells. The CAF-like cells were separated from the differentiated population. The expression of prominent CAF markers fibroblast specific protein (FSP), fibroblast activation protein (FAP), vimentin, collagen type1 α1, and smooth muscle actin (SMA) were assessed by real time PCR. Immuno-cytochemistry of the cells for the expression of FSP, FAP and SMA was further confirmed for the evidence that cancer stem cells should be a possible source of CAF. This model should elaborate the functional heterogeneity amongst CAFs and help design therapeutic interventions to inhibit such conversions.

Citation Format: Neha Nair, Arun Vaidyanath, Kenta Hoshikawa, Anna Sanchez Calle, Tomonari Kasai, Masaharu Seno. Cancer stem cells as the novel origin of cancer-associated fibroblast-like cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-278.

Abstract LB-144: Derivation of a model of cancer stem cell from human induced pluripotent stem cells

The existence of cancer stem cell (CSC) has been considered as one of the important reason as to why patients have a poor prognosis. However, heterotopic transplantation of embryonic stem cells and induced pluripotent stem cells has been shown to form teratoma, but not malignant teratoma. Since the microenvironment niche is playing a significant role for the proper differentiation of stem cells, the cancerous niche should drive stem cells into malignant cells in vivo. According to this hypothesis, we tried to generate cancer cells from human induced pluripotent stem (hiPS) cells. For the conversion into CSC, the conditioned medium from different human cancer cell lines was collected from confluent dishes and filtered using 0.22 micrometer filter. Then, hiPS cells, without MEF feeder cells, were maintained in the conditioned medium (CM) in the ratio of 1:1. The medium was changed every day with CM for 4 weeks. hiPS cells with the complete medium were used as control. For transplantation studies, 10^4 cells were suspended in HBSS and were xenotransplantated into NOD-SCID mice. After 3 months, tumors were excised and fixed in 10% neutral formalin buffer solution, or subjected to primary culture. The converted cells and primary cultured cells formed spheroids in suspension culture, and had tumorigenicity in vivo. The stemness of living cells was checked under fluorescent microscopy observation with rBC2LCN-FITC staining. The RNAs were extracted from converted cells and microarray analysis was perfomed. The RNA expression patterns of cell lines were visualized by sphered self-organizing map (sSOM) analysis. The sSOM analysis perfomed based upon various parameters shows the converted CSCs can be characterized into various cell types. Utilizing this method, we successfully established two different hiPS-CSC lines using CM from A172 and RERF-LC-KJ.

The comprehensive understanding of cancer could be realized as the heterogeneity of cancer tissues is clarified and their component cells are identified. This study will lead to the development of the true personalized therapy of cancer in the future.

Citation Format: Tomonari Kasai, Kenta Hoshikawa, Shuto Takejiri, Masashi Ikeda, Kazuki Kumon, Anna Sanchez Calle, Arun Vaidyanath, Akifumi Mizutani, Chen Ling, Masaharu Seno. Derivation of a model of cancer stem cell from human induced pluripotent stem cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-144. doi:10.1158/1538-7445.AM2015-LB-144