A model of cancer stem cells derived from mouse induced pluripotent stem cells

Zebrafish-A Suitable Model for Rapid Translation of Effective Therapies for Pediatric Cancers

Pediatric cancers are the leading cause of disease-related deaths in children and adolescents. Most of these tumors are difficult to treat and have poor overall survival. Concerns have also been raised about drug toxicity and long-term detrimental side effects of therapies. In this review, we discuss the advantages and unique attributes of zebrafish as pediatric cancer models and their importance in targeted drug discovery and toxicity assays. We have also placed a special focus on zebrafish models of pediatric brain cancers-the most common and difficult solid tumor to treat.

Interconversion of Cancer Cells and Induced Pluripotent Stem Cells

Cancer cells, especially cancer stem cells (CSCs), share many molecular features with induced pluripotent stem cells (iPSCs) that enable the derivation of induced pluripotent cancer cells by reprogramming malignant cells. Conversely, normal iPSCs can be converted into cancer stem-like cells with the help of tumor microenvironment components and genetic manipulation. These CSC models can be utilized in oncogenic initiation and progression studies, understanding drug resistance, and developing novel therapeutic strategies. This review summarizes the role of pluripotency factors in the stemness, tumorigenicity, and therapeutic resistance of cancer cells. Different methods to obtain iPSC-derived CSC models are described with an emphasis on exposure-based approaches. Culture in cancer cell-conditioned media or cocultures with cancer cells can convert normal iPSCs into cancer stem-like cells, aiding the examination of processes of oncogenesis. We further explored the potential of reprogramming cancer cells into cancer-iPSCs for mechanistic studies and cancer dependencies. The contributions of genetic, epigenetic, and tumor microenvironment factors can be evaluated using these models. Overall, integrating iPSC technology into cancer stem cell research holds significant promise for advancing our knowledge of cancer biology and accelerating the development of innovative and tailored therapeutic interventions.

Expression and Functional Analysis of core stemness factors OSKM (OCT4, SOX2, KLF4, and MYC) in Pan-cancer

The dedifferentiation process of tumorigenesis and somatic cell reprogramming has some commonness and differences, which is the key question to cancer therapeutic strategy and stem cell applications. To further explore the commonalities and variance between carcinogenesis and induced pluripotent stem cell reprogramming, we investigated the role of stemness factors OSKM (OCT4, SOX2, KLF4, and MYC) in the pan-cancer process using public clinical data. Expression of OSKM in human pan-cancer was analyzed via the Genotype Tissue Expression (GTEx) and The Cancer Genome Atlas (TCGA) database based on the RNA-seq data of tissues. The correlation of expression between OSKM genes was analyzed via the Tumor Immune Evaluation Resource (TIMER) database, while the STRING tool was used to construct the protein-protein interaction network for OSKM. Prognostic impact of OSKM in pan-cancer was analyzed by Cox proportional hazards regression model. The relationships between OSKM and tumor stemness, tumor microenvironment and immune checkpoint and were performed by Sangerbox platform using Pearson correlation analysis. Our results showed that OSKM were universally expressed and significantly altered in tumors compared with adjacent normal tissues in most tumor types. In addition, correlation analysis revealed the relevance of OSKM genes to patient prognosis, cancer cell stemness, tumor microenvironment or immune checkpoint. However, there is little similarity between these genes in terms of how they function in each cancer type. This study elucidates the different roles of core stemness factors OSKM in pan-cancer, offering potential therapeutic targets for novel anti-cancer strategies and knowledge to minimize the potential carcinogenic effects during stem cell transplantation.

Exploring the promising potential of induced pluripotent stem cells in cancer research and therapy

The advent of iPSCs has brought about a significant transformation in stem cell research, opening up promising avenues for advancing cancer treatment. The formation of cancer is a multifaceted process influenced by genetic, epigenetic, and environmental factors. iPSCs offer a distinctive platform for investigating the origin of cancer, paving the way for novel approaches to cancer treatment, drug testing, and tailored medical interventions. This review article will provide an overview of the science behind iPSCs, the current limitations and challenges in iPSC-based cancer therapy, the ethical and social implications, and the comparative analysis with other stem cell types for cancer treatment. The article will also discuss the applications of iPSCs in tumorigenesis, the future of iPSCs in tumorigenesis research, and highlight successful case studies utilizing iPSCs in tumorigenesis research. The conclusion will summarize the advancements made in iPSC-based tumorigenesis research and the importance of continued investment in iPSC research to unlock the full potential of these cells.

Application of Induced Pluripotent Stem Cells in Malignant Solid Tumors

In the past decade, induced pluripotent stem cells (iPSCs) technology has significantly progressed in studying malignant solid tumors. This technically feasible reprogramming techniques can reawaken sequestered dormant regions that regulate the fate of differentiated cells. Despite the evolving therapeutic modalities for malignant solid tumors, treatment outcomes have not been satisfactory. Recently, scientists attempted to apply induced pluripotent stem cell technology to cancer research, from modeling to treatment. Induced pluripotent stem cells derived from somatic cells, cancer cell lines, primary tumors, and individuals with an inherited propensity to develop cancer have shown great potential in cancer modeling, cell therapy, immunotherapy, and understanding tumor progression. This review summarizes the evolution of induced pluripotent stem cells technology and its applications in malignant solid tumor. Additionally, we discuss potential obstacles to induced pluripotent stem cell technology.

iPSC-Derived Glioblastoma Cells Have Enhanced Stemness Wnt/β-Catenin Activity Which Is Negatively Regulated by Wnt Antagonist sFRP4

Growing evidence indicates that cancer stem cells (CSCs) endow the tumor with stem-like properties. Recently, induced pluripotent stem cells (iPSCs) have gained increased attention because of their easy derivation and availability and their potential to differentiate into any cell type. A CSC model derived from iPSCs of human origin would help understand the driving force of tumor initiation and early progression. We report the efficient generation of feeder-free SSEA4, TRA-1-60 and TRA-1-81 positive iPSCs from amniotic membrane-derived mesenchymal stem cells (AMMSCs), which successfully differentiated into three germ layers. We then developed human iPSC-derived glioblastoma multiforme (GBM) model using conditioned media (CM) from U87MG cell line and CSCs derived from U87MG, which confer iPSCs with GBM and GSC-like phenotypes within five days. Both cell types overexpress MGMT and GLI2, but only GSCs overexpress CD133, CD44, ABCG2 and ABCC2. We also observed overexpression of LEF1 and β-catenin in both cell types. Down-regulation of Wnt antagonist secreted frizzled-related protein 4 (sFRP4) in GBM and GSCs, indicating activation of the Wnt/β-catenin pathway, which could be involved in the conversion of iPSCs to CSCs. From future perspectives, our study will help in the creation of a rapid cell-based platform for understanding the complexity of GBM.

Deep learning models for cancer stem cell detection: a brief review

Cancer stem cells (CSCs), also known as tumor-initiating cells (TICs), are a subset of tumor cells that persist within tumors as a distinct population. They drive tumor initiation, relapse, and metastasis through self-renewal and differentiation into multiple cell types, similar to typical stem cell processes. Despite their importance, the morphological features of CSCs have been poorly understood. Recent advances in artificial intelligence (AI) technology have provided automated recognition of biological images of various stem cells, including CSCs, leading to a surge in deep learning research in this field. This mini-review explores the emerging trend of deep learning research in the field of CSCs. It introduces diverse convolutional neural network (CNN)-based deep learning models for stem cell research and discusses the application of deep learning for CSC research. Finally, it provides perspectives and limitations in the field of deep learning-based stem cell research.

GSK-3α/β and MEK inhibitors assist the microenvironment of tumor initiation

Induced pluripotent stem cells (iPSCs) are useful tools for modeling diseases and developing personalized medicine. We have been developing cancer stem cells (CSCs) from iPSCs with conditioned medium (CM) of cancer-derived cells as the mimicry of the microenvironment of tumor initiation. However, the conversion of human iPSCs has not always been efficient with only CM. In this study, human iPSCs reprogrammed from monocytes of healthy volunteers were cultured in a media containing 50% of the CM from human pancreatic cancer derived BxPC3 cells supplemented with a MEK inhibitor (AZD6244) and a GSK-3α/β inhibitor (CHIR99021). The survived cells were assessed for the characteristics of CSCs in vitro and in vivo. As a result, they exhibited CSC phenotypes of self-renewal, differentiation, and malignant tumorigenicity. Primary culture of the malignant tumors of the converted cells exhibited the elevated expression of CSC related genes CD44, CD24 and EPCAM maintaining the expression of stemness genes. In conclusion, the inhibition of GSK-3α/β and MEK and the microenvironment of tumor initiation mimicked by the CM can convert human normal stem cells into CSCs. This study could provide insights into establishing potentially novel personalized cancer models which could help investigate the tumor initiation and screening of personalized therapies on CSCs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-023-00575-1.

The evaluation of tumorigenicity and characterization of colonies in a soft agar colony formation assay using polymerase chain reaction

In regenerative medicine, the tumorigenic potency of cells in cellular therapy products (CTPs) is a major concern for their application to patients. This study presents a method-the soft agar colony formation assay using polymerase chain reaction (PCR)-to evaluate tumorigenicity. MRC-5 cells, contaminated with HeLa cells, were cultured for up to 4 weeks in soft agar medium. Cell-proliferation-related mRNAs, Ki-67 and cyclin B, could be detected in 0.01% of HeLa cells after 5 days of culture, whereas cyclin-dependent kinase 1 (CDK1) could be detected after 2 weeks. On the other hand, CDK2, proliferating cell nuclear antigen (PCNA), and minichromosome maintenance protein 7 (MCM7) were not useful to detect HeLa cells even after 4 weeks of culture. The cancer stem cell (CSC) markers, aldehyde dehydrogenase 1 (ALDH1) and CD133 in 0.01% of HeLa cells, could be detected 2 and 4 weeks after culture, respectively. However, another CSC marker CD44 was not useful because its expression was also detected in MRC-5 cells alone. This study suggests that the application of the PCR method to the soft agar colony formation assay could evaluate not only the tumorigenic potency in the short-term but also characterize the colonies, eventually improving the safety of CTPs.

Deep Learning of Phase-Contrast Images of Cancer Stem Cells Using a Selected Dataset of High Accuracy Value Using Conditional Generative Adversarial Networks

Artificial intelligence (AI) technology for image recognition has the potential to identify cancer stem cells (CSCs) in cultures and tissues. CSCs play an important role in the development and relapse of tumors. Although the characteristics of CSCs have been extensively studied, their morphological features remain elusive. The attempt to obtain an AI model identifying CSCs in culture showed the importance of images from spatially and temporally grown cultures of CSCs for deep learning to improve accuracy, but was insufficient. This study aimed to identify a process that is significantly efficient in increasing the accuracy values of the AI model output for predicting CSCs from phase-contrast images. An AI model of conditional generative adversarial network (CGAN) image translation for CSC identification predicted CSCs with various accuracy levels, and convolutional neural network classification of CSC phase-contrast images showed variation in the images. The accuracy of the AI model of CGAN image translation was increased by the AI model built by deep learning of selected CSC images with high accuracy previously calculated by another AI model. The workflow of building an AI model based on CGAN image translation could be useful for the AI prediction of CSCs.

Cancer metastasis is related to normal tissue stemness

The occurrence of cancer metastasis may be related to stem cells in normal tissues. We searched for patient IDs with both normal tissue stem cell values and TCGA (The Cancer Genome Atlas) clinical data for pairing and obtained 639 sets of data (stemness index of normal tissue, stemness index of tumor tissue, cancer stage, distant metastasis, tumor size) and invasion, and lymph node involvement). However, clinical data on cancer metastasis are of only four stages (e.g., Stage I, II, III, and IV), which cannot show subtle changes continuously. We need to find an effective data mining method to transform this four-valued clinical description into a numerical curve. We data-mine this data through numericalization, sorting, and noise reduction filtering. The results showed that: as the normal tissue stemness value (NS) increased, the tumor tissue stemness value (TS) increased proportionally (1.26 times NS). When NS >0.5, the rate of change in TS decelerated (0.43 times NS), and tumor metastasis began to occur. Clinical indicators, such as cancer stage, distant metastasis, tumor size and invasion, and lymph node involvement, showed that tumor metastasis became more and more severe with the increase of NS. This study suggests that tumor metastasis is triggered when the NS in the patient's body is more significant than 0.5.

Cancer stem cells induced by chronic stimulation with prostaglandin E2 exhibited constitutively activated PI3K axis

Previously, our group has demonstrated establishment of Cancer Stem Cell (CSC) models from stem cells in the presence of conditioned medium of cancer cell lines. In this study, we tried to identify the factors responsible for the induction of CSCs. Since we found the lipid composition could be traced to arachidonic acid cascade in the CSC model, we assessed prostaglandin E2 (PGE2) as a candidate for the ability to induce CSCs from induced pluripotent stem cells (iPSCs). Mouse iPSCs acquired the characteristics of CSCs in the presence of 10 ng/mL of PGE2 after 4 weeks. Since constitutive Akt activation and pik3cg overexpression were found in the resultant CSCs, of which growth was found independent of PGE2, chronic stimulation of the receptors EP-2/4 by PGE2 was supposed to induce CSCs from iPSCs through epigenetic effect. The bioinformatics analysis of the next generation sequence data of the obtained CSCs proposed not only receptor tyrosine kinase activation by growth factors but also extracellular matrix and focal adhesion enhanced PI3K pathway. Collectively, chronic stimulation of stem cells with PGE2 was implied responsible for cancer initiation enhancing PI3K/Akt axis.

Extracellular vesicles and particles impact the systemic landscape of cancer

Intercellular cross talk between cancer cells and stromal and immune cells is essential for tumor progression and metastasis. Extracellular vesicles and particles (EVPs) are a heterogeneous class of secreted messengers that carry bioactive molecules and that have been shown to be crucial for this cell-cell communication. Here, we highlight the multifaceted roles of EVPs in cancer. Functionally, transfer of EVP cargo between cells influences tumor cell growth and invasion, alters immune cell composition and function, and contributes to stromal cell activation. These EVP-mediated changes impact local tumor progression, foster cultivation of pre-metastatic niches at distant organ-specific sites, and mediate systemic effects of cancer. Furthermore, we discuss how exploiting the highly selective enrichment of molecules within EVPs has profound implications for advancing diagnostic and prognostic biomarker development and for improving therapy delivery in cancer patients. Altogether, these investigations into the role of EVPs in cancer have led to discoveries that hold great promise for improving cancer patient care and outcome.

Cancer-inducing niche: the force of chronic inflammation

The growth of cancer tissue is thought to be considered driven by a small subpopulation of cells, so-called cancer stem cells (CSCs). CSCs are located at the apex of a hierarchy in a cancer tissue with self-renewal, differentiation and tumorigenic potential that produce the progeny in the tissue. Although CSCs are generally believed to play a critical role in the growth, metastasis, and recurrence of cancers, the origin of CSCs remains to be reconsidered. We hypothesise that, chronic diseases, including obesity and diabetes, establish the cancer-inducing niche (CIN) that drives the undifferentiated/progenitor cells into CSCs, which then develop malignant tumours in vivo. In this context, a CIN could be traced to chronic inflammation that involves long-lasting tissue damage and repair after being exposed to factors such as cytokines and growth factors. This must be distinguished from the cancer microenvironment, which is responsible for cancer maintenance. The concept of a CIN is most important for cancer prevention as well as cancer therapy.

Temporal and Locational Values of Images Affecting the Deep Learning of Cancer Stem Cell Morphology

Deep learning is being increasingly applied for obtaining digital microscopy image data of cells. Well-defined annotated cell images have contributed to the development of the technology. Cell morphology is an inherent characteristic of each cell type. Moreover, the morphology of a cell changes during its lifetime because of cellular activity. Artificial intelligence (AI) capable of recognizing a mouse-induced pluripotent stem (miPS) cell cultured in a medium containing Lewis lung cancer (LLC) cell culture-conditioned medium (cm), miPS-LLCcm cell, which is a cancer stem cell (CSC) derived from miPS cell, would be suitable for basic and applied science. This study aims to clarify the limitation of AI models constructed using different datasets and the versatility improvement of AI models. The trained AI was used to segment CSC in phase-contrast images using conditional generative adversarial networks (CGAN). The dataset included blank cell images that were used for training the AI but they did not affect the quality of predicting CSC in phase contrast images compared with the dataset without the blank cell images. AI models trained using images of 1-day culture could predict CSC in images of 2-day culture; however, the quality of the CSC prediction was reduced. Convolutional neural network (CNN) classification indicated that miPS-LLCcm cell image classification was done based on cultivation day. By using a dataset that included images of each cell culture day, the prediction of CSC remains to be improved. This is useful because cells do not change the characteristics of stem cells owing to stem cell marker expression, even if the cell morphology changes during culture.

Diphenyleneiodonium efficiently inhibits the characteristics of a cancer stem cell model derived from induced pluripotent stem cells

Diphenyleneiodonium (DPI) has long been evaluated as an anticancer drug inhibiting NADPH oxidase, the IC₅₀ in several cancer cell lines was reported 10 µM, which is too high for efficacy. In this study, we employed miPS-Huh7cmP cells, which we previously established as a cancer stem cell (CSC) model from induced pluripotent stem cells, to reevaluate the efficacy of DPI because CSCs are currently one of the main foci of therapeutic strategy to treat cancer, but generally considered resistant to chemotherapy. As a result, the conventional assay for the cell growth inhibition by DPI accounted for an IC₅₀ at 712 nM that was not enough to define the effectiveness as an anticancer drug. Simultaneously, the wound-healing assay revealed an IC₅₀ of approximately 500 nM. Comparatively, the IC₅₀ values shown on sphere formation, colony formation, and tube formation assays were 5.52, 12, and 8.7 nM, respectively. However, these inhibitory effects were not observed by VAS2780, also a reputed NADPH oxidase inhibitor. It is noteworthy that these three assays are evaluating the characteristic of CSCs and are designed in the three-dimensional (3D) culture methods. We concluded that DPI could be a suitable candidate to target mitochondrial respiration in CSCs. We propose that the 3D culture assays are more efficient to screen anti-CSC drug candidates and better mimic tumor microenvironment when compared to the adherent monolayer of 2D culture system used for a conventional assay, such as cell growth inhibition and wound-healing assays.

The significance of ErbB2/3 in the conversion of induced pluripotent stem cells into cancer stem cells

Cancer stem cells (CSCs) are suggested to be responsible for drug resistance and aggressive phenotypes of tumors. Mechanisms of CSC induction are still under investigation. Our lab has established a novel method to generate CSCs from iPSCs under a cancerous microenvironment mimicked by the conditioned medium (CM) of cancer-derived cells. Here, we analyzed the transcriptome of CSCs, which were converted from iPSCs with CM from pancreatic ductal adenocarcinoma cells. The differentially expressed genes were identified and used to explore pathway enrichment. From the comparison of the CSCs with iPSCs, genes with elevated expression were related to the ErbB2/3 signaling pathway. Inhibition of either ErbB2 with lapatinib as a tyrosine kinase inhibitor or ErbB3 with TX1-85-1 or siRNAs arrested cell proliferation, inhibited the in vitro tumorigenicity, and lead to loss of stemness in the converting cells. The self-renewal and tube formation abilities of cells were also abolished while CD24 and Oct3/4 levels were reduced, and the MAPK pathway was overactivated. This study shows a potential involvement of the ErbB2/ErbB3 pathway in CSC generation and could lead to new insight into the mechanism of tumorigenesis and the way of cancer prevention.

Different pancreatic cancer microenvironments convert iPSCs into cancer stem cells exhibiting distinct plasticity with altered gene expression of metabolic pathways

BACKGROUND

Cancer stem cells (CSCs) are generated under irregular microenvironment in vivo, of which mimic is quite difficult due to the lack of enough information of the factors responsible for cancer initiation. Here, we demonstrated that mouse induced pluripotent cells (miPSCs) reprogrammed from normal embryonic fibroblasts were susceptible to the microenvironment affected by cancer cells to convert into CSCs in vivo.

METHODS

Three different pancreatic cancer line cells, BxPC3, PANC1, and PK8 cells were mixed with miPSCs and subcutaneously injected into immunodeficient mice. Tumors were evaluated by histological analysis and cells derived from iPSCs were isolated and selected from tumors. The isolated cells were characterized for cancer stem cell characters in vitro and in vivo as well as their responses to anticancer drugs. The impact of co-injection of iPSCs with cancer cells on transcriptome and signaling pathways of iPSCs was investigated.

RESULTS

The injection of miPSCs mixed with human pancreatic cancer cells into immunodeficient mice maintained the stemness of miPSCs and changed their phenotype. The miPSCs acquired CSC characteristics of tumorigenicity and self-renewal. The drug responses and the metastatic ability of CSCs converted from miPSCs varied depending on the microenvironment of cancer cells. Interestingly, transcriptome profiles of these cells indicated that the pathways related with aggressiveness and energy production were upregulated from the levels of miPSCs.

CONCLUSIONS

Our result suggests that cancer-inducing microenvironment in vivo could rewire the cell signaling and metabolic pathways to convert normal stem cells into CSCs.

The efficacy of PI3Kγ and EGFR inhibitors on the suppression of the characteristics of cancer stem cells

Cancer stem cells (CSCs) are capable of continuous proliferation, self-renewal and are proposed to play significant roles in oncogenesis, tumor growth, metastasis and cancer recurrence. We have established a model of CSCs that was originally developed from mouse induced pluripotent stem cells (miPSCs) by proposing miPSCs to the conditioned medium (CM) of cancer derived cells, which is a mimic of carcinoma microenvironment. Further research found that not only PI3K-Akt but also EGFR signaling pathway was activated during converting miPSCs into CSCs. In this study, we tried to observe both of PI3Kγ inhibitor Eganelisib and EGFR inhibitor Gefitinib antitumor effects on the models of CSCs derived from miPSCs (miPS-CSC) in vitro and in vivo. As the results, targeting these two pathways exhibited significant inhibition of cell proliferation, self-renewal, migration and invasion abilities in vitro. Both Eganelisib and Gefitinib showed antitumor effects in vivo while Eganelisib displayed more significant therapeutic efficacy and less side effects than Gefitinib on all miPS-CSC models. Thus, these data suggest that the inhibitiors of PI3K and EGFR, especially PI3Kγ, might be a promising therapeutic strategy against CSCs defeating cancer in the near future.

Cancer Stem Cells and the Tumor Microenvironment in Gastric Cancer

Gastric cancer (GC) remains one of the leading causes of cancer-related death worldwide. Cancer stem cells (CSCs) might be responsible for tumor initiation, relapse, metastasis and treatment resistance of GC. The tumor microenvironment (TME) comprises tumor cells, immune cells, stromal cells and other extracellular components, which plays a pivotal role in tumor progression and therapy resistance. The properties of CSCs are regulated by cells and extracellular matrix components of the TME in some unique manners. This review will summarize current literature regarding the effects of CSCs and TME on the progression and therapy resistance of GC, while emphasizing the potential for developing successful anti-tumor therapy based on targeting the TME and CSCs.

Functional and Molecular Characters of Cancer Stem Cells Through Development to Establishment

Cancer stem cells (CSCs) are small subpopulation sharing similar properties like normal stem such as self-renewal and differentiation potential to direct tumor growth. Last few years, scientists considered CSCs as the cause of phenotypic heterogeneity in diverse cancer types. Also, CSCs contribute to cancer metastasis and recurrence. The cellular and molecular regulators influence on the CSCs' phenotype changing their behaviors in different stages of cancer progression. CSC markers play significance roles in cancer diagnosis and characterization. We delineate the cross-talks between CSCs and the tumor microenvironment that supports their intrinsic properties including survival, stemness, quiescence and their cellular and molecular adaptation. An insight into the markers of CSCs specific to organs is described.

ERBB Signaling Pathway in Cancer Stem Cells

The epidermal growth factor receptor (EGFR) was first tyrosine kinase receptor linked to human cancers. EGFR or ERBB1 is a member of ERBB subfamily, which consists of four type I transmembrane receptor tyrosine kinases, ERBB1, 2, 3 and 4. ERBBs form homo/heterodimers after ligand binding except ERBB2 and consequently becomes activated. Different signal pathways, such as phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT), RAS/RAF/MEK/ERK, phospholipase Cγ and JAK-STAT, are triggered by ERBB activation. Since ERBBs, through these pathways, regulate stemness and differentiation of cancer stem cells (CSCs), their roles in CSC tumorigenicity have extensively been investigated. The hyperactivation of ERBBs and its downstream pathways stimulated by either genetic and/or epigenetic factors are frequently described in many types of human cancers. Their dysregulations make cells acquiring CSC characters such as survival, tumorigenicity and stemness. Because of the roles in tumor growth and progress, ERBBs are considered to be one of the drug targets as cancer treatment strategy. In this chapter, we will summarize the structure, function and roles of ERBB subfamily along with their relative pathways regulating the stemness and tumorigenicity of CSCs. Finally, we will discuss the targeting therapy strategies of cancer along with ERBBs in addition to some challenges and future perspectives.

Differentiation of cancer stem cells into erythroblasts in the presence of CoCl2

Cancer stem cells (CSCs) are subpopulations in the malignant tumors that show self-renewal and multilineage differentiation into tumor microenvironment components that drive tumor growth and heterogeneity. In previous studies, our group succeeded in producing a CSC model by treating mouse induced pluripotent stem cells. In the current study, we investigated the potential of CSC differentiation into blood cells under chemical hypoxic conditions using CoCl₂. CSCs and miPS-LLCcm cells were cultured for 1 to 7 days in the presence of CoCl₂, and the expression of VEGFR1/2, Runx1, c-kit, CD31, CD34, and TER-119 was assessed by RT-qPCR, Western blotting and flow cytometry together with Wright-Giemsa staining and immunocytochemistry. CoCl₂ induced significant accumulation of HIF-1α changing the morphology of miPS-LLCcm cells while the morphological change was apparently not related to differentiation. The expression of VEGFR2 and CD31 was suppressed while Runx1 expression was upregulated. The population with hematopoietic markers CD34⁺ and c-kit⁺ was immunologically detected in the presence of CoCl₂. Additionally, high expression of CD34 and, a marker for erythroblasts, TER-119, was observed. Therefore, CSCs were suggested to differentiate into erythroblasts and erythrocytes under hypoxia. This differentiation potential of CSCs could provide new insight into the tumor microenvironment elucidating tumor heterogenicity.

The Potential of Induced Pluripotent Stem Cells to Advance the Treatment of Pancreatic Ductal Adenocarcinoma

Simple Summary

Despite improvements in the treatment of several cancer types, the extremely poor prognosis of pancreatic cancer patients has remained unchanged over the last decades. Therefore, new therapeutic regimens for pancreatic cancer are highly needed. In this review, we will discuss the potential of induced pluripotent stem cells (iPSCs) to generate representative pancreatic cancer models that can aid the development of novel diagnostics and therapeutic strategies. Furthermore, the potential of iPSCs as pancreatic cancer vaccines or as a basis for cellular therapies will be discussed. With promising preclinical results and ongoing clinical trials, the potential of iPSCs to further the treatment of pancreatic cancer is being explored and, in turn, will hopefully provide additional therapies to increase the poor survival rates of this patient population.

Abstract

Advances in the treatment of pancreatic ductal adenocarcinoma (PDAC) using neoadjuvant chemoradiotherapy, chemotherapy, and immunotherapy have had minimal impact on the overall survival of patients. A general lack of immunogenic features and a complex tumor microenvironment (TME) are likely culprits for therapy refractoriness in PDAC. Induced pluripotent stem cells (iPSCs) should be explored as a means to advance the treatment options for PDAC, by providing representative in vitro models of pancreatic cancer development. In addition, iPSCs could be used for tailor-made cellular immunotherapies or as a source of tumor-associated antigens in the context of vaccination.

Cancer Stem Cells in Tumor Modeling: Challenges and Future Directions

Microfluidic tumors-on-chips models have revolutionized anticancer therapeutic research by creating an ideal microenvironment for cancer cells. The tumor microenvironment (TME) includes various cell types and cancer stem cells (CSCs), which are postulated to regulate the growth, invasion, and migratory behavior of tumor cells. In this review, the biological niches of the TME and cancer cell behavior focusing on the behavior of CSCs are summarized. Conventional cancer models such as three-dimensional cultures and organoid models are reviewed. Opportunities for the incorporation of CSCs with tumors-on-chips are then discussed for creating tumor invasion models. Such models will represent a paradigm shift in the cancer community by allowing oncologists and clinicians to predict better which cancer patients will benefit from chemotherapy treatments.

Evaluation of the Efficacy of Stem Cell Therapy in Ovariectomized Osteoporotic Rats Based on Micro-CT and Dual-Energy X-Ray Absorptiometry: A Systematic Review and Meta-Analysis

Objective

Osteoporosis is an abnormal bone metabolism disease characterized by microstructural degeneration of bone tissue and reduction in bone mass, resulting in increased brittleness of bone tissue and susceptibility to fracture. Due to the tissue regenerative potential of stem cell transplantation, it is now used in the treatment of various disease models such as osteoporosis. The purpose of this work is to carry out a systematic review and meta-analysis of the efficacy of stem cell therapy in ovariectomized (OVX) osteoporotic rats.

Methods

PubMed, Cochrane Library, ScienceDirect, Embase, CNKI, and Wanfang Databases were used to search for articles that met the inclusion criteria. Two researchers independently screened the articles that met the inclusion criteria. RevMan 5.3 and STATA 16.0 were used for data analysis. This meta-analysis was registered at INPLASY with reference number ID: INPLASY202150017.

Results

Thirteen eligible studies were selected, including 405 rats. The sources of stem cells are divided into four main categories: bone marrow mesenchymal stem cells (BMSCs), adipose-derived stem cells (ADSCs), amniotic membrane mesenchymal stem cells (AM-MSCs), and human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs). Compared with the OVX group, both stem cell transplantation groups had higher bone mineral density (BMD) (BMSCs: SMD = 2.01, 95% CI: [1.38, 2.63], P < 0.001, I² = 76.6%; ADSCs: SMD = 2.24, 95% CI: [0.79, 3.69], P = 0.003, I² = 86.7%) and bone volume/total volume (BV/TV) (hUCB-MSCs: SMD = 1.71, 95% CI: [0.97, 2.44], P < 0.001, I² = 0%; ADSCs: SMD = 2.16, 95% CI: [0.27, 4.04], P = 0.025, I² = 82.6%). In the BMSC treatment groups, the trabecular numbers (Tb.N) (SMD = 4.28, 95% CI: [0.91, 7.64], P = 0.013, I² = 94.9%) were significantly higher, whereas the results for trabecular thickness (Tb.Th) (SMD = 2.7, 95% CI: [-0.34, 5.73], P = 0.081, I² = 95.4%) and trabecular spacing (Tb.Sp) (SMD = −3.08, 95% CI: [-6.55, 0.38], P = 0.081, I² = 96.3%) were not statistically significant compared to those of the OVX group. The stem cell transplantation group had a low BMD, BV/TV, and Tb.N compared to the sham operation group.

Conclusion

Stem cell therapy may increase bone strength, bone volume, and the number of trabeculae in OVX osteoporotic rats. The results of this meta-analysis showed the potential therapeutic effect of stem cell transplantation in OVX osteoporotic rats, bringing new therapeutic ideas and directions to the clinical treatment of osteoporosis. Due to the limited number and quality of studies related to some outcomes, more high-quality RCTs are still needed in the future to complement the existing findings.

Chronic exposure to FGF2 converts iPSCs into cancer stem cells with an enhanced integrin/focal adhesion/PI3K/AKT axis

We previously demonstrated the conversion of normal stem cells, including induced pluripotent stem cells (iPSCs), into cancer stem cells (CSCs) without genetic manipulation. Herein, we designed a meta-analysis to assess gene expression profiles in different breast cancer cell lines focusing on the secretory factors responsible for conversion. As a result, fibroblast growth factor 2 (FGF2) was found to be the best candidate in T47D and BT549 cells, of which conditioned medium was previously successful in inducing CSCs. When treated with 3.1 μg/ml FGF2, mouse iPSCs not only maintained survival without LIF for three weeks but also acquired growth ability independent of FGF2. The resultant cells exhibited expression of stemness and cancer stem cell markers, sphere-forming ability, differentiation, and tumorigenicity with malignancy. The primary cultures of the tumor confirmed the signatures of CSCs with two different phenotypes with or without GFP expression under control of the Nanog promoter. Bioinformatic analysis of gene expression profiles suggested constitutive autocrine activation of the FGF receptor, integrins, focal adhesions, and PI3K/AKT pathways. FGF2 could potently initiate cancer as a component of the inflammatory microenvironment.

Metformin suppresses self-renewal and stemness of cancer stem cell models derived from pluripotent stem cells

Metformin exhibits anti-cancer activities in various types of tumours while it is prescribed as the first-line drug for type 2 diabetes. Since new evidence has recently suggested that metformin could target cancer stem cells (CSCs) and prevent their recurrence, repositioning of metformin could be considered as a candidate for anti-CSC agent. In this study, we assessed the effect of metformin on the cancer stem cells developed from induced pluripotent stem cells. As the result, metformin significantly suppressed the self-renewal ability of CSCs when assessed by 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and cell counting methods exhibiting the IC₅₀ as approximately 20 mM, which suppressed tube formation by CSCs on Matrigel reducing the angiogenic potential of CSCs. Cell cycle analysis showed that metformin reduced the percentage of cells in the S phase increasing the percentage of cells in G0/G1 phase. Moreover, the tumorigenicity of CSCs was found to be attenuated when the cells were injected with metformin. From these results, we concluded that metformin could be promising for targeted therapy by repositioning the widely available drugs with safety. SIGNIFICANCE OF THE STUDY: Metformin could target CSCs and prevent their recurrence, repositioning of metformin could be considered as a candidate for the anti-CSC agent. In this paper, we assessed the effect of metformin on the CSCs developed from induced pluripotent stem cells. Here, we show that metformin suppresses the self-renewal and tube formation abilities of CSCs. We also show that metformin reduces the percentage of cells in the S phase increasing the percentage of cells in G0/G1 phase. Moreover, the tumorigenicity of CSCs was found to be attenuated when grafted in vivo after treatment with metformin.

Microenvironment of mammary fat pads affected the characteristics of the tumors derived from the induced cancer stem cells

Breast cancer is the first common cause of cancer-related death in women worldwide. Since the malignancy and aggressiveness of breast cancer have been correlated with the presence of breast cancer stem cells, the establishment of a disease model with cancer stem cells is required for the development of a novel therapeutic strategy. Here, we aimed to evaluate the availability of cancer stem cell models developed from mouse induced pluripotent stem cells with the conditioned medium of different subtypes of breast cancer cell lines, the hormonal-responsive T47D cell line and the triple-negative breast cancer BT549 cell line, to generate in vivo tumor models. When transplanted into the mammary fat pads of BALB/c nude mice, these two model cells formed malignant tumors exhibiting pronounced histopathological characteristics similar to breast cancers. Serial transplantation of the primary cultured cells into mammary fat pads evoked the same features of breast cancer, while this result was perturbed following subcutaneous transplantation. The tumors formed in the mammary fat pads exhibited immune reactivities to prolactin receptor, progesterone receptor, green florescent protein, Ki67, CD44, estrogen receptor α/β and cytokeratin 8, while all of the tumors and their derived primary cells exhibited immunoreactivity to estrogen receptor α/β and cytokeratin 8. Cancer stem cells can be developed from pluripotent stem cells via the secretory factors of cancer-derived cells with the capacity to inherit tissue specificity. However, cancer stem cells should be plastic enough to be affected by the microenvironment of specific tissues. In summary, we successfully established a breast cancer tumor model using mouse induced pluripotent stem cells developed from normal fibroblasts without genetic manipulation.

Cancer Stem Cell Initiation by Tumor-Derived Extracellular Vesicles

Cancer stem cells (CSCs) are capable of continuous proliferation and self-renewal and are proposed to play significant roles in oncogenesis, tumor growth, metastasis, and cancer recurrence. CSCs are considered derived from normal stem cells affected by the inflammatory microenvironment. Stem cells, are considered to be induced into progenitor cells, which differentiate into various normal phenotypes depending on the normal niche. We hypothesized that CSCs could be derived from stem cells in the cancer-inducing niche, which is a condition of chronic inflammation rich in growth factors, interleukins, chemokines, etc. Exosomes are considered to be the key mediators responsible for the cell-to-cell communications carrying proteins, nucleic acids, metabolites, etc., to shuttle between cells. If these cells are in the environment of chronic inflammation, the exosomes should be reflecting the conditions. In this chapter, we detail the method of CSC initiation using extracellular vesicles (EVs) derived from cancer cell. The stem cells treated with the EVs acquired characteristics of CSCs showing spheroids expressing stemness markers in the suspension culture and high tumorigenicity in Balb/c nude mice. EVs might perform as suitable inducer for initiating CSCs from stem cells or progenitor cells. The model of CSCs and the procedure of their establishment with EVs will help study the exact effect of EVs in the cancer-inducing niche and tumor microenvironment.

Pluripotent Stem Cells: Cancer Study, Therapy, and Vaccination

INTRODUCTION

Pluripotent stem cells (PSCs) are promising tools for modern regenerative medicine applications because of their stemness properties, which include unlimited self-renewal and the ability to differentiate into all cell types in the body. Evidence suggests that a rare population of cells within a tumor, termed cancer stem cells (CSCs), exhibit stemness and phenotypic plasticity properties that are primarily responsible for resistance to chemotherapy, radiotherapy, metastasis, cancer development, and tumor relapse. Different therapeutic approaches that target CSCs have been developed for tumor eradication.

RESULTS AND DISCUSSION

In this review, we first provide an overview of different viewpoints about the origin of CSCs. Particular attention has been paid to views believe that CSCs are probably appeared through dysregulation of very small embryonic-like stem cells (VSELs) which reside in various tissues as the main candidate for tissue-specific stem cells. The expression of pluripotency markers in these two types of cells can strengthen the validity of this theory. In this regard, we discuss the common properties of CSCs and PSCs, and highlight the potential of PSCs in cancer studies, therapeutic applications, as well as educating the immune system against CSCs.

CONCLUSION

In conclusion, the resemblance of CSCs to PSCs can provide an appropriate source of CSC-specific antigens through cultivation of PSCs which brings to light promising ideas for prophylactic and therapeutic cancer vaccine development.

Cancer Stem Cell Microenvironment Models with Biomaterial Scaffolds In Vitro

Defined by its potential for self-renewal, differentiation and tumorigenicity, cancer stem cells (CSCs) are considered responsible for drug resistance and relapse. To understand the behavior of CSC, the effects of the microenvironment in each tissue are a matter of great concerns for scientists in cancer biology. However, there are many complicated obstacles in the mimicking the microenvironment of CSCs even with current advanced technology. In this context, novel biomaterials have widely been assessed as in vitro platforms for their ability to mimic cancer microenvironment. These efforts should be successful to identify and characterize various CSCs specific in each type of cancer. Therefore, extracellular matrix scaffolds made of biomaterial will modulate the interactions and facilitate the investigation of CSC associated with biological phenomena simplifying the complexity of the microenvironment. In this review, we summarize latest advances in biomaterial scaffolds, which are exploited to mimic CSC microenvironment, and their chemical and biological requirements with discussion. The discussion includes the possible effects on both cells in tumors and microenvironment to propose what the critical factors are in controlling the CSC microenvironment focusing the future investigation. Our insights on their availability in drug screening will also follow the discussion.

Metastasis Model of Cancer Stem Cell-Derived Tumors

Metastasis includes the dissemination of cancer cells from a malignant tumor and seed in distant sites inside the body forming secondary tumors. Metastatic cells from the primary tumor can move even before the cancer is detected. Therefore, metastases are responsible for more than 90% of cancer-related deaths. Over recent decades there has been adequate evidence suggesting the existence of CSCs with self-renewing and drug-resistant potency within heterogeneous tumors. Cancer stem cells (CSCs) act as a tumor initiating cells and have roles in tumor retrieve and metastasis. Our group recently developed a unique CSC model from mouse induced pluripotent stem cells cultured in the presence of cancer cell-conditioned medium that mimics tumors microenvironment. Using this model, we demonstrated a new method for studying metastasis by intraperitoneal transplantation of tumors and investigate the metastasis ability of cells from these segments. First of all, CSCs were injected subcutaneously in nude mice. The developed malignant tumors were minimized then transplanted into the peritoneal cavity. Following this, the developed tumor in addition to lung, pancreas and liver were then excised and analyzed. Our method showed the metastatic potential of CSCs with the ability of disseminated and moving to blood circulation and seeding in distant organs such as lung and pancreas. This method could provide a good model to study the mechanisms of metastasis according to CSC theory.

Signaling Inhibitors Accelerate the Conversion of mouse iPS Cells into Cancer Stem Cells in the Tumor Microenvironment

Cancer stem cells (CSCs) are a class of cancer cells characterized by self-renewal, differentiation and tumorigenic potential. We previously established a model of CSCs by culturing mouse induced pluripotent stem cells (miPSCs) for four weeks in the presence of a conditioned medium (CM) of cancer cell lines, which functioned as the tumor microenvironment. Based on this methodology of developing CSCs from miPSCs, we assessed the risk of 110 non-mutagenic chemical compounds, most of which are known as inhibitors of cytoplasmic signaling pathways, as potential carcinogens. We treated miPSCs with each compound for one week in the presence of a CM of Lewis lung carcinoma (LLC) cells. However, one-week period was too short for the CM to convert miPSCs into CSCs. Consequently, PDO325901 (MEK inhibitor), CHIR99021 (GSK-3β inhibitor) and Dasatinib (Abl, Src and c-Kit inhibitor) were found to confer miPSCs with the CSC phenotype in one week. The tumor cells that survived exhibited stemness markers, spheroid formation and tumorigenesis in Balb/c nude mice. Hence, we concluded that the three signal inhibitors accelerated the conversion of miPSCs into CSCs. Similarly to our previous study, we found that the PI3K-Akt signaling pathway was upregulated in the CSCs. Herein, we focused on the expression of relative genes after the treatment with these three inhibitors. Our results demonstrated an increased expression of pik3ca, pik3cb, pik3r5 and pik3r1 genes indicating class IA PI3K as the responsible signaling pathway. Hence, AKT phosphorylation was found to be up-regulated in the obtained CSCs. Inhibition of Erk1/2, tyrosine kinase, and/or GSK-3β was implied to be involved in the enhancement of the PI3K-AKT signaling pathway in the undifferentiated cells, resulting in the sustained stemness, and subsequent conversion of miPSCs into CSCs in the tumor microenvironment.

Deep Learning of Cancer Stem Cell Morphology Using Conditional Generative Adversarial Networks

Deep-learning workflows of microscopic image analysis are sufficient for handling the contextual variations because they employ biological samples and have numerous tasks. The use of well-defined annotated images is important for the workflow. Cancer stem cells (CSCs) are identified by specific cell markers. These CSCs were extensively characterized by the stem cell (SC)-like gene expression and proliferation mechanisms for the development of tumors. In contrast, the morphological characterization remains elusive. This study aims to investigate the segmentation of CSCs in phase contrast imaging using conditional generative adversarial networks (CGAN). Artificial intelligence (AI) was trained using fluorescence images of the Nanog-Green fluorescence protein, the expression of which was maintained in CSCs, and the phase contrast images. The AI model segmented the CSC region in the phase contrast image of the CSC cultures and tumor model. By selecting images for training, several values for measuring segmentation quality increased. Moreover, nucleus fluorescence overlaid-phase contrast was effective for increasing the values. We show the possibility of mapping CSC morphology to the condition of undifferentiation using deep-learning CGAN workflows.

Paclitaxel and Sorafenib: The Effective Combination of Suppressing the Self-Renewal of Cancer Stem Cells

“Combination therapy”, which is a treatment modality combining two or more therapeutic agents, is considered a cornerstone of cancer therapy. The combination of anticancer drugs, of which functions are different from the other, enhances the efficiency compared to the monotherapy because it targets cancer cells in a synergistic or an additive manner. In this study, the combination of paclitaxel and sorafenib in low concentration was evaluated to target cancer stem cells, miPS-BT549cmP and miPS-Huh7cmP cells, developed from mouse induced pluripotent stem cells. The synergistic effect of paclitaxel and sorafenib on cancer stem cells was assessed by the inhibition of proliferation, self-renewal, colony formation, and differentiation. While the IC₅₀ values of paclitaxel and sorafenib were approximately ranging between 250 and 300 nM and between 6.5 and 8 µM, respectively, IC₅₀ of paclitaxel reduced to 20 and 25 nM, which was not toxic in a single dose, in the presence of 1 µM sorafenib, which was not toxic to the cells. Then, the synergistic effect was further assessed for the potential of self-renewal of cancer stem cells by sphere formation ability. As a result, 1 µM of sorafenib significantly enhanced the effect of paclitaxel to suppress the number of spheres. Simultaneously, paclitaxel ranging in 1 to 4 nM significantly suppressed not only the colony formation but also the tube formation of the cancer stem cells in the presence of 1 µM sorafenib. These results suggest the combination therapy of paclitaxel and sorafenib in low doses should be an attractive approach to target cancer stem cells with fewer side effects.

Cancer Stem Cell Functions in Hepatocellular Carcinoma and Comprehensive Therapeutic Strategies

Hepatocellular carcinoma (HCC) is a significant cause of cancer-related mortality owing to resistance to traditional treatments and tumor recurrence after therapy, which leads to poor therapeutic outcomes. Cancer stem cells (CSC) are a small subset of tumor cells with the capability to influence self-renewal, differentiation, and tumorigenesis. A number of surface markers for liver cancer stem cell (LCSC) subpopulations (EpCAM, CD133, CD44, CD13, CD90, OV-6, CD47, and side populations) in HCC have been identified. LCSCs play critical roles in regulating HCC stemness, self-renewal, tumorigenicity, metastasis, recurrence, and therapeutic resistance via genetic mutations, epigenetic disruption, signaling pathway dysregulation, or alterations microenvironment. Accumulating studies have shown that biomarkers for LCSCs contribute to diagnosis and prognosis prediction of HCC, supporting their utility in clinical management and development of therapeutic strategies. Preclinical and clinical analyses of therapeutic approaches for HCC using small molecule inhibitors, oncolytic measles viruses, and anti-surface marker antibodies have demonstrated selective, efficient, and safe targeting of LCSC populations. The current review focuses on recent reports on the influence of LCSCs on HCC stemness, tumorigenesis, and multiple drug resistance (MDR), along with LCSC-targeted therapeutic strategies for HCC.

Revisiting Cancer Stem Cells as the Origin of Cancer-Associated Cells in the Tumor Microenvironment: A Hypothetical View from the Potential of iPSCs

The tumor microenvironment (TME) has an essential role in tumor initiation and development. Tumor cells are considered to actively create their microenvironment during tumorigenesis and tumor development. The TME contains multiple types of stromal cells, cancer-associated fibroblasts (CAFs), Tumor endothelial cells (TECs), tumor-associated adipocytes (TAAs), tumor-associated macrophages (TAMs) and others. These cells work together and with the extracellular matrix (ECM) and many other factors to coordinately contribute to tumor growth and maintenance. Although the types and functions of TME cells are well understood, the origin of these cells is still obscure. Many scientists have tried to demonstrate the origin of these cells. Some researchers postulated that TME cells originated from surrounding normal tissues, and others demonstrated that the origin is cancer cells. Recent evidence demonstrates that cancer stem cells (CSCs) have differentiation abilities to generate the original lineage cells for promoting tumor growth and metastasis. The differentiation of CSCs into tumor stromal cells provides a new dimension that explains tumor heterogeneity. Using induced pluripotent stem cells (iPSCs), our group postulates that CSCs could be one of the key sources of CAFs, TECs, TAAs, and TAMs as well as the descendants, which support the self-renewal potential of the cells and exhibit heterogeneity. In this review, we summarize TME components, their interactions within the TME and their insight into cancer therapy. Especially, we focus on the TME cells and their possible origin and also discuss the multi-lineage differentiation potentials of CSCs exploiting iPSCs to create a society of cells in cancer tissues including TME.

A novel model of liver cancer stem cells developed from induced pluripotent stem cells

Background

Liver cancer is the second most common cause of cancer-related death. Every type of tumours including liver cancer contains cancer stem cells (CSCs). To date, the molecular mechanism regulating the development of liver CSCs remains unknown.

Methods

In this study, we tried to generate a new model of liver CSCs by converting mouse induced pluripotent stem cells (miPSCs) with hepatocellular carcinoma (HCC) cell line Huh7 cells conditioned medium (CM). miPSCs treated with CM were injected into the liver of BALB/c nude mice. The developed tumours were then excised and analysed.

Results

The primary cultured cells from the malignant tumour possessed self-renewal capacity, differentiation potential and tumorigenicity in vivo, which were found rich in liver cancer-associated markers as well as CSC markers.

Conclusions

We established a model of liver CSCs converting from miPS and showed different stages of stemness during conversion process. Our CSC model will be important to assess the molecular mechanisms necessary to develop liver CSCs and could help in defeating liver cancer.

Hematopoietic Cells Derived from Cancer Stem Cells Generated from Mouse Induced Pluripotent Stem Cells

Cancer stem cells (CSCs) represent the subpopulation of cancer cells with the ability to differentiate into other cell phenotypes and initiated tumorigenesis. Previously, we reported generating CSCs from mouse induced pluripotent stem cells (miPSCs). Here, we investigated the ability of the CSCs to differentiate into hematopoietic cells. First, the primary cells were isolated from malignant tumors that were formed by the CSCs. Non-adherent cells (NACs) that arose from adherent cells were collected and their viability, as well as the morphology and expression of hematopoietic cell markers, were analyzed. Moreover, NACs were injected into the tail vein of busulfan conditioned Balb/c nude mice. Finally, CSCs were induced to differentiate to macrophages while using IL3 and SCF. The round nucleated NACs were found to be viable, positive for hematopoietic lineage markers and CD34, and expressed hematopoietic markers, just like homing to the bone marrow. When NACs were injected into mice, Wright–Giemsa staining showed that the number of white blood cells got higher than those in the control mice after four weeks. CSCs also showed the ability to differentiate toward macrophages. CSCs were demonstrated to have the potential to provide progenies with hematopoietic markers, morphology, and homing ability to the bone marrow, which could give new insight into the tumor microenvironment according to the plasticity of CSCs.

The Histone Demethylase KDM3A, Increased in Human Pancreatic Tumors, Regulates Expression of DCLK1 and Promotes Tumorigenesis in Mice

BACKGROUND & AIMS

The histone lysine demethylase 3A (KDM3A) demethylates H3K9me1 and H3K9Me2 to increase gene transcription and is upregulated in tumors, including pancreatic tumors. We investigated its activities in pancreatic cancer cell lines and its regulation of the gene encoding doublecortin calmodulin-like kinase 1 (DCLK1), a marker of cancer stem cells.

METHODS

We knocked down KDM3A in MiaPaCa-2 and S2-007 pancreatic cancer cell lines and overexpressed KDM3A in HPNE cells (human noncancerous pancreatic ductal cell line); we evaluated cell migration, invasion, and spheroid formation under hypoxic and normoxic conditions. Nude mice were given orthotopic injections of S2-007 cells, with or without (control) knockdown of KDM3A, and HPNE cells, with or without (control) overexpression of KDM3A; tumor growth was assessed. We analyzed pancreatic tumor tissues from mice and pancreatic cancer cell lines by immunohistochemistry and immunoblotting. We performed RNA-sequencing analysis of MiaPaCa-2 and S2-007 cells with knockdown of KDM3A and evaluated localization of DCLK1 and KDM3A by immunofluorescence. We analyzed the cancer genome atlas for levels of KDM3A and DCLK1 messenger RNA in human pancreatic ductal adenocarcinoma (PDAC) tissues and association with patient survival time.

RESULTS

Levels of KDM3A were increased in human pancreatic tumor tissues and cell lines, compared with adjacent nontumor pancreatic tissues, such as islet and acinar cells. Knockdown of KDM3A in S2-007 cells significantly reduced colony formation, invasion, migration, and spheroid formation, compared with control cells, and slowed growth of orthotopic tumors in mice. We identified KDM3A-binding sites in the DCLK1 promoter; S2-007 cells with knockdown of KDM3A had reduced levels of DCLK1. HPNE cells that overexpressed KDM3A formed foci and spheres in culture and formed tumors and metastases in mice, whereas control HPNE cells did not. Hypoxia induced sphere formation and increased levels of KDM3A in S2-007 cells and in HPNE cells that overexpressed DCLK1, but not control HPNE cells. Levels of KDM3A and DCLK1 messenger RNA were higher in human PDAC than nontumor pancreatic tissues and correlated with shorter survival times of patients.

CONCLUSIONS

We found human PDAC samples and pancreatic cancer cell lines to overexpress KDM3A. KDM3A increases expression of DCLK1, and levels of both proteins are increased in human PDAC samples. Knockdown of KDM3A in pancreatic cancer cell lines reduced their invasive and sphere-forming activities in culture and formation of orthotopic tumors in mice. Hypoxia increased expression of KDM3A in pancreatic cancer cells. Strategies to disrupt this pathway might be developed for treatment of pancreatic cancer.

Metastasis of Cancer Stem Cells Developed in the Microenvironment of Hepatocellular Carcinoma

Metastasis develops when cancer cells spread from the primary site of a malignant tumor to the surrounding and distant tissues, and it is the most critical problem in cancer treatment. Our group developed cancer stem cells (CSCs) from induced pluripotent stem cells (iPSCs) in the presence of a conditioned medium (CM) of cancer-derived cells. The CSCs were characterized by the formation of malignant tumors in vivo, followed by metastasis. In this study, CSCs converted from mouse iPSCs in the presence of CM from hepatocellular carcinoma (HCC) cell line Huh7 cells. These converted cells (miPS-Huh7cm cells) were established as the metastatic cells. The generated CSCs were injected into the liver or spleen of nude mice. Almost one month after transplantation, the tumors were excised, and the primary cultured cells derived from the malignant tumors and metastatic nodules were evaluated by stemness and metastatic markers to compare their differences. The miPS-Huh7cm cells exhibited metastatic potential, and efficiently formed malignant tumors with lung and/or liver lesions in vivo, whereas the injected miPS formed teratoma. The primary cultured cells derived from the malignant tumors and metastatic nodules sustained the expression of stemness markers, such as Nanog, Klf4 and c-Myc, and acquired cancer stem markers, such as CD90, CD44 and ALDH1. Simultaneously, the expression of metastatic markers, such as Slug, Twist1 and vimentin, in primary cells derived from the malignant tumors, was higher than in metastatic nodules. The CSCs derived from iPSCs, forming malignant tumors and displaying high metastasis, will provide a good animal model to study the mechanisms of metastasis.

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.

Cancer stem cell induction from mouse embryonic stem cells

Although cancers are often removed by surgery and treated by chemotherapy and/or radiation therapies, they often reoccur following treatment due to the presence of resistant residual cells such as cancer stem cells (CSCs). CSCs are characterized by their self-renewal, pluripotency, and tumorigenicity properties, and are promising therapeutic targets for the complete therapy of cancers; however, the number of CSCs in cancer tissue is typically too small to investigate fully. We have previously reported that CSCs could be established from induced pluripotent stem cells (iPSCs) using a conditioned medium during cancer cell culture. In the present study, mouse embryonic stem cells (mESCs) were observed to be converted to CSCs (mES-CSCs). This demonstrated that CSC induction does not exclusively occur following gene editing in somatic cells, and that conditioned medium from cancer cells may contain factors that can induce CSCs. Therefore, not only iPSCs but also mESCs, were demonstrated to be able to produce CSCs as one of the potentials of pluripotency of stem cells, suggesting that the conversion to CSCs is not specific to iPSCs. The resultant mES-CSCs would be also useful to generate tissue specific cancers and these naturally occurring cancers can contribute to drug screenings, but also undergo further investigation in order to reveal cancer mechanisms.

The Evolving Landscape of Cancer Stem Cells and Ways to Overcome Cancer Heterogeneity

Cancer stem cells (CSCs) with therapeutic resistance and plasticity can be found in various types of tumors and are recognized as attractive targets for treatments. As CSCs are derived from tissue stem or progenitor cells, and/or dedifferentiated mature cells, their signal transduction pathways are critical in the regulation of CSCs; chronic inflammation causes the accumulation of genetic mutations and aberrant epigenetic changes in these cells, potentially leading to the production of CSCs. However, the nature of CSCs appears to be stronger than the treatments of the past. To improve the treatments targeting CSCs, it is important to inhibit several molecules on the signaling cascades in CSCs simultaneously, and to overcome cancer heterogeneity caused by the plasticity. To select suitable target molecules for CSCs, we have to explore the landscape of CSCs from the perspective of cancer stemness and signaling systems, based on the curated databases of cancer-related genes. We have been studying the integration of a broad range of knowledge and experiences from cancer biology, and also from other interdisciplinary basic sciences. In this review, we have introduced the concept of developing novel strategies targeting CSCs.

Conversion of Stem Cells to Cancer Stem Cells: Undercurrent of Cancer Initiation

Cancer stem cells (CSCs) also known as cancer-initiating cells (CIC), are responsible for the sustained and uncontrolled growth of malignant tumors and are proposed to play significant roles in metastasis and recurrence. Several hypotheses have proposed that the events in either stem and/or differentiated cells, such as genomic instability, inflammatory microenvironment, cell fusion, and lateral gene transfer, should be considered as the possible origin of CSCs. However, until now, the exact origin of CSC has been obscure. The development of induced pluripotent stem cells (iPSCs) in 2007, by Yamanaka's group, has been met with much fervency and hailed as a breakthrough discovery by the scientific and research communities, especially in regeneration therapy. The studies on the development of CSC from iPSCs should also open a new page of cancer research, which will help in designing new therapies applicable to CSCs. Currently most reviews have focused on CSCs and CSC niches. However, the insight into the niche before the CSC niche should also be of keen interest. This review introduces the novel concept of cancer initiation introducing the conversion of iPSCs to CSCs and proposes a relationship between the inflammatory microenvironment and cancer initiation as the key concept of the cancer-inducing niche responsible for the development of CSC.

Sulforaphane Suppresses the Growth of Triple-negative Breast Cancer Stem-like Cells In vitro and In vivo

Triple-negative breast cancer (TNBC) represents the poorest prognosis among all of breast cancer subtypes with no currently available effective therapy. In this study, we hypothesized that sulforaphane, a dietary component abundant in broccoli and its sprouts, can inhibit malignant cell proliferation and tumor sphere formation of cancer stem-like cells (CSC) in TNBC. CSC population was isolated using FACS analysis with the combined stem cell surface markers, CD44⁺/CD24^-/CD49f⁺ The effect of sulforaphane on a stem-related embryonic oncogene CRIPTO-1/TDGF1 (CR1) was evaluated via ELISA. In vivo, BalbC/nude mice were supplemented with sulforaphane before and after TNBC cell inoculation (daily intraperitoneal injection of 50 mg sulforaphane/kg for 5 and 3 weeks, respectively), and the effects of sulforaphane during mammary tumor initiation and growth were accessed with NanoString gene analysis. We found that sulforaphane can inhibit cell proliferation and mammosphere formation of CSCs in TNBC. Further analysis of gene expression in these TNBC tumor cells revealed that sulforaphane significantly decreases the expression of cancer-specific CR1, CRIPTO-3/TDGF1P3 (CR3, a homologue of CR1), and various stem cell markers including Nanog, aldehyde dehydrogenase 1A1 (ALDH1A1), Wnt3, and Notch4. Our results suggest that sulforaphane may control the malignant proliferation of CSCs in TNBC via Cripto-mediated pathway by either suppressing its expression and/or by inhibiting Cripto/Alk4 protein complex formation. Thus, the use of sulforaphane for chemoprevention of TNBC is plausible and warrants further clinical evaluation.

Exogenous Cripto-1 Suppresses Self-Renewal of Cancer Stem Cell Model

Cripto-1 is a glycophosphatidylinositol (GPI) anchored signaling protein of epidermal growth factor (EGF)-Cripto-1-FRL1-Cryptic (CFC) family and plays a significant role in the early developmental stages and in the different types of cancer cells, epithelial to mesenchymal transition and tumor angiogenesis. Previously, we have developed cancer stem cells (miPS-LLCcm) from mouse iPSCs by culturing them in the presence of conditioned medium of Lewis Lung Carcinoma (LLC) cells for four weeks. Nodal and Cripto-1 were confirmed to be expressed in miPS-LLCcm cells by quantitative reverse transcription PCR (rt-qPCR) implying that Cr-1 was required in maintaining stemness. To investigate the biological effect of adding exogenous soluble CR-1 to the cancer stem cells, we have prepared a C-terminally truncated soluble form of recombinant human CR-1 protein (rhsfCR-1), in which the GPI anchored moiety was removed by substitution of a stop codon through site-directed mutagenesis. rhsfCR-1 effectively suppressed the proliferation and sphere forming ability of miPS-LLCcm cells in a dose-dependent manner in the range of 0 to 5 µg/mL, due to the suppression of Nodal-Cripto-1/ALK4/Smad2 signaling pathway. Frequency of sphere-forming cells was dropped from 1/40 to 1/69 by rhsfCR-1 at 1 µg/mL. Moreover, rhsfCR-1 in the range of 0 to 1 µg/mL also limited the differentiation of miPS-LLCcm cells into vascular endothelial cells probably due to the suppression of self-renewal, which should reduce the number of cells with stemness property. As demonstrated by a soluble form of exogenous Cripto-1 in this study, the efficient blockade would be an attractive way to study Cripto-1 dependent cancer stem cell properties for therapeutic application.