Characterization and functional analysis of a slow cycling stem cell-like subpopulation in pancreas adenocarcinoma

Breast Cancer Stem Cells as Drivers of Tumor Chemoresistance, Dormancy and Relapse: New Challenges and Therapeutic Opportunities

Breast cancer is the most frequent cancer among women worldwide. Therapeutic strategies to prevent or treat metastatic disease are still inadequate although great progress has been made in treating early-stage breast cancer. Cancer stem-like cells (CSCs) that are endowed with high plasticity and self-renewal properties have been shown to play a key role in breast cancer development, progression, and metastasis. A subpopulation of CSCs that combines tumor-initiating capacity and a dormant/quiescent/slow cycling status is present throughout the clinical history of breast cancer patients. Dormant/quiescent/slow cycling CSCs are a key component of tumor heterogeneity and they are responsible for chemoresistance, tumor migration, and metastatic dormancy, defined as the ability of CSCs to survive in target organs and generate metastasis up to two decades after diagnosis. Understanding the strategies that are used by CSCs to resist conventional and targeted therapies, to interact with their niche, to escape immune surveillance, and finally to awaken from dormancy is of key importance to prevent and treat metastatic cancer. This review summarizes the current understanding of mechanisms involved in CSCs chemoresistance, dissemination, and metastasis in breast cancer, with a particular focus on dormant cells. Finally, we discuss how advancements in the detection, molecular understanding, and targeting of dormant CSCs will likely open new therapeutic avenues for breast cancer treatment.

BMP signaling mediates glioma stem cell quiescence and confers treatment resistance in glioblastoma

Despite advances in therapy, glioblastoma remains an incurable disease with a dismal prognosis. Recent studies have implicated cancer stem cells within glioblastoma (glioma stem cells, GSCs) as mediators of therapeutic resistance and tumor progression. In this study, we investigated the role of the transforming growth factor-β (TGF-β) superfamily, which has been found to play an integral role in the maintenance of stem cell homeostasis within multiple stem cell systems, as a mediator of stem-like cells in glioblastoma. We find that BMP and TGF-β signaling define divergent molecular and functional identities in glioblastoma, and mark relatively quiescent and proliferative GSCs, respectively. Treatment of GSCs with BMP inhibits cell proliferation, but does not abrogate their stem-ness, as measured by self-renewal and tumorigencity. Further, BMP pathway activation confers relative resistance to radiation and temozolomide chemotherapy. Our findings define a quiescent cancer stem cell population in glioblastoma that may be a cellular reservoir for tumor recurrence following cytotoxic therapy.

Mitochondrial membrane anchored photosensitive nano-device for lipid hydroperoxides burst and inducing ferroptosis to surmount therapy-resistant cancer

Rationale: Ferroptosis is a regulated process of cell death caused by iron-dependent accumulation of lipid hydroperoxides (LPO). It is sensitive to epithelial-to-mesenchymal transition (EMT) cells, a well-known therapy-resistant state of cancer. Previous studies on nanomaterials did not investigate the immense value of ferroptosis therapy (FT) in epithelial cell carcinoma during EMT. Herein, we describe an EMT-specific nanodevice for a comprehensive FT strategy involving LPO burst. Methods: Mitochondrial membrane anchored oxidation/reduction response and Fenton-Reaction-Accelerable magnetic nanophotosensitizer complex self-assemblies loading sorafenib (CSO-SS-Cy7-Hex/SPION/Srfn) were constructed in this study for LPO produced to overcome the therapy-resistant state of cancer. Both in vitro and in vivo experiments were performed using breast cancer cells to investigate the anti-tumor efficacy of the complex self-assemblies. Results: The nano-device enriched the tumor sites by magnetic targeting of enhanced permeability and retention effects (EPR), which were disassembled by the redox response under high levels of ROS and GSH in FT cells. Superparamagnetic iron oxide nanoparticles (SPION) released Fe²⁺ and Fe³⁺ in the acidic environment of lysosomes, and the NIR photosensitizer Cy7-Hex anchored to the mitochondrial membrane, combined sorafenib (Srfn) leading to LPO burst, which was accumulated ~18-fold of treatment group in breast cancer cells. In vivo pharmacodynamic test results showed that this nanodevice with small particle size and high cytotoxicity increased Srfn circulation and shortened the period of epithelial cancer treatment. Conclusion: Ferroptosis therapy had a successful effect on EMT cells. These findings have great potential in the treatment of therapy-resistant epithelial cell carcinomas.

Stem Cell Plasticity and Dormancy in the Development of Cancer Therapy Resistance

Cancer treatment with either standard chemotherapy or targeted agents often results in the emergence of drug-refractory cell populations, ultimately leading to therapy failure. The biological features of drug resistant cells are largely overlapping with those of cancer stem cells and include heterogeneity, plasticity, self-renewal ability, and tumor-initiating capacity. Moreover, drug resistance is usually characterized by a suppression of proliferation that can manifest as quiescence, dormancy, senescence, or proliferative slowdown. Alterations in key cellular pathways such as autophagy, unfolded protein response or redox signaling, as well as metabolic adaptations also contribute to the establishment of drug resistance, thus representing attractive therapeutic targets. Moreover, a complex interplay of drug resistant cells with the micro/macroenvironment and with the immune system plays a key role in dictating and maintaining the resistant phenotype. Recent studies have challenged traditional views of cancer drug resistance providing innovative perspectives, establishing new connections between drug resistant cells and their environment and indicating unexpected therapeutic strategies. In this review we discuss recent advancements in understanding the mechanisms underlying drug resistance and we report novel targeting agents able to overcome the drug resistant status, with particular focus on strategies directed against dormant cells. Research on drug resistant cancer cells will take us one step forward toward the development of novel treatment approaches and the improvement of relapse-free survival in solid and hematological cancer patients.

Cancer Stem Cells and Radioresistance: DNA Repair and Beyond

The current preclinical and clinical findings demonstrate that, in addition to the conventional clinical and pathological indicators that have a prognostic value in radiation oncology, the number of cancer stem cells (CSCs) and their inherent radioresistance are important parameters for local control after radiotherapy. In this review, we discuss the molecular mechanisms of CSC radioresistance attributable to DNA repair mechanisms and the development of CSC-targeted therapies for tumor radiosensitization. We also discuss the current challenges in preclinical and translational CSC research including the high inter- and intratumoral heterogeneity, plasticity of CSCs, and microenvironment-stimulated tumor cell reprogramming.

Identification of Breast Cancer Stem Cell Related Genes Using Functional Cellular Assays Combined With Single-Cell RNA Sequencing in MDA-MB-231 Cells

Breast cancer tumors display different cellular phenotypes. A growing body of evidence points toward a population of cancer stem cells (CSCs) that is important for metastasis and treatment resistance, although the characteristics of these cells are incomplete. We used mammosphere formation assay and label-retention assay as functional cellular approaches to enrich for cells with different degree of CSC properties in the breast cancer cell line MDA-MB-231 and performed single-cell RNA sequencing. We clustered the cells based on their gene expression profiles and identified three subpopulations, including a CSC-like population. The cell clustering into these subpopulations overlapped with the cellular enrichment approach applied. To molecularly define these groups, we identified genes differentially expressed between the three subpopulations which could be matched to enriched gene sets. We also investigated the transition process from CSC-like cells into more differentiated cell states. In the CSC population we found 14 significantly upregulated genes. Some of these potential breast CSC markers are associated to reported stem cell properties and clinical survival data, but further experimental validation is needed to confirm their cellular functions. Detailed characterization of CSCs improve our understanding of mechanisms for tumor progression and contribute to the identification of new treatment targets.

Combined administration of naringenin and hesperetin with optimal ratio maximizes the anti-cancer effect in human pancreatic cancer via down regulation of FAK and p38 signaling pathway

BACKGROUND

We have previously reported the functional anti-cancer effects of the products of enzymatic hydrolysis of Citrus unshiu peel (εCUP) and fermented extraction of Citrus unshiu peel (ƒCUP) in human pancreatic cancer. Despite their different characteristics and effects, the underlying mechanism remains elusive.

PURPOSE

In this study, we further demonstrate the impact of ingredient contents of Citrus unshiu peel on the cancer's natural features.

METHODS

Anti-pancreatic cancer activities following combined treatment of naringenin and hesperetin were demonstrated in vitro and in vivo experiments.

RESULTS

Combined treatment with naringenin and hesperetin inhibited the growth of human pancreatic cancer cells (εCUP mimic condition, p < 0.001 for Miapaca-2 cells) through induction of caspase-3 cleavage compared to separate treatment with naringenin or hesperetin. Combined treatment with naringenin and hesperetin also inhibited the migration (εCUP mimic condition, p < 0.001 for Panc-1 cells) of human pancreatic cancer cells. The εCUP mimic condition had the most effective anti-cancer features; in contrast, which had no inhibitory effect on growth and migration of normal cells (HUVECs and Detroit551 cells). In addition, εCUP mimic condition inhibited the phosphorylation of focal adhesion kinase (FAK) and p38 signaling compared with separate treatment with naringenin or hesperetin. Of note, εCUP mimic condition showed a prominent anti-growth effect (p < 0.001) compared with control or ƒCUP mimic condition in vivo xenograft models.

CONCLUSION

These results suggest that combined treatment with naringenin and hesperetin might be a promising anti-cancer strategy for pancreatic cancers without eliciting toxicity on normal cells.

Anti-CD133 Monoclonal Antibody CMab-43 Exerts Antitumor Activity in a Mouse Xenograft Model of Colon Cancer

Cancer stem cells contribute to tumorigenesis, metastasis, recurrence, and chemoresistance. CD133/prominin-1-a pentaspan membrane glycoprotein-has been used as a stem cell biomarker for the isolation of stem-like cells from a variety of normal and pathological tissues. In our previous studies, we developed several anti-CD133 monoclonal antibodies using Cell-Based Immunization and Screening (CBIS) methods, followed by characterization of their efficacy by flow cytometry, western blotting, and immunohistochemical analyses. One of the 100 clones, CMab-43 (IgG_2a, kappa), demonstrated a sensitive and specific reaction against colon cancer cells. This study aimed to investigate the antitumor activity of CMab-43. Caco-2 cells (human colon cancer cell line) were subcutaneously implanted into the flanks of nude mice. CMab-43 and control mouse IgG were injected three times into the peritoneal cavity of mice. Tumor formation was observed in the control and CMab-43-treated mice of Caco-2 xenograft models. CMab-43 significantly reduced tumor development of Caco-2 xenograft in comparison with the control mouse IgG on days 12, 14, and 17. Our results cumulatively suggest that CMab-43 is useful for antibody therapy against CD133-expressing colon cancers.

Induction/reversal of drug resistance in gastric cancer by non-coding RNAs (Review)

Gastric cancer (GC) is one of the most prevalent and malignant types of cancer worldwide. In China, it is the second most common type of cancer and the malignancy with the highest incidence and mortality rate. Chemotherapy for GC is not always effective due to the development of drug resistance. Drug resistance, which is frequently observed in GC, undermines the success rate of chemotherapy and the survival of patients with GC. The dysregulation of non‑coding RNAs (ncRNAs), primarily microRNAs (miRNAs or miRs) and long non‑coding RNAs (lncRNAs), is involved in the development of GC drug resistance via numerous mechanisms. These mechanisms contribute to the involvement of a large and complex network of ncRNAs in drug resistance. In this review, we focus on and summarize the latest research on the specific mechanisms of action of miRNAs and lncRNAs that modulate drug resistance in GC. In addition, we discuss future prospects and clinical applications of ncRNAs as potential targeted therapies against the chemoresistance of GC.

Spontaneously slow-cycling subpopulations of human cells originate from activation of stress-response pathways

Slow-cycling subpopulations exist in bacteria, yeast, and mammalian systems. In the case of cancer, slow-cycling subpopulations have been proposed to give rise to drug resistance. However, the origin of slow-cycling human cells is poorly studied, in large part due to lack of markers to identify these rare cells. Slow-cycling cells pass through a noncycling period marked by low CDK2 activity and high p21 levels. Here, we use this knowledge to isolate these naturally slow-cycling cells from a heterogeneous population and perform RNA sequencing to delineate the transcriptome underlying the slow-cycling state. We show that cellular stress responses—the p53 transcriptional response and the integrated stress response (ISR)—are the most salient causes of spontaneous entry into the slow-cycling state. Finally, we show that cells’ ability to enter the slow-cycling state enhances their survival in stressful conditions. Thus, the slow-cycling state is hardwired to stress responses to promote cellular survival in unpredictable environments.

Single-cell time-lapse imaging and transcriptomic analysis reveal why some human cells proliferate more slowly than the majority of the population, with cellular stress responses triggering entry into a slow-cycling state to promote cellular survival in unpredictable environments.

Even within a genetically identical population, some cells proliferate more slowly than others. Slow-cycling cells have been implicated in resistance to antibiotics, antifungals, and cancer therapies, yet the origin of the slow-cycling state remains poorly understood. Here, we isolate a naturally slow-cycling subpopulation of human cells and find that the slow-cycling state is induced by moderate activation of stress responses. We further show that the ability to enter this slow-cycling state protects cells from further stress, consistent with its association with drug resistance. We propose that the existence of the slow-cycling state thereby promotes long-term survival of populations that occasionally experience mildly stressful environments.

Induced expression of GINS complex is an essential step for reactivation of quiescent stem-like tumor cells within the peri-necrotic niche in human glioblastoma

PURPOSE

Glioblastoma is still intractable despite the progress in therapies, and the intractability is attributable to a minor population of stem-like tumor cells. As a niche harboring quiescent stem-like tumor cells with potentially high tumorigenicity, we have specified an area around large ischemic necrosis, termed 'peri-necrotic niche', in glioblastoma. In this study, the behavior of tumor cells inside and outside the peri-necrotic niche was analyzed to find out molecules responsible for reactivation of quiescent stem-like tumor cells to proliferate outside the niche.

METHODS

Expression of Ki-67 and GINS complex composed of SLD5, PSF1, PSF2 and PSF3 was analyzed by immunohistochemistry in human glioblastoma tissue samples. Proliferation assays, immunoblotting and siRNA experiments were performed using a glioblastoma cell line.

RESULTS

Immunohistochemical analysis revealed quiescent and proliferative phenotypes of tumor cells inside and outside the niche, respectively, and the proliferation was spatially correlated with the expression of GINS components in tumor cells. To mimic the tissue microenvironment inside versus outside the niche, glioblastoma cells were cultured under hypoxic versus normoxic conditions, or without versus with serum. Quiescence and proliferation of tumor cells were reversibly determined by the microenvironment inside and outside the niche, respectively, and proliferative activities paralleled the expression levels of GINS components. Furthermore, the reactivation of proliferation after reoxygenation or serum replenishment was suppressed in quiescent tumor cells with PSF1 knockdown.

CONCLUSIONS

These findings indicate the essential role of GINS complex in the switch between quiescence and proliferation of tumor cells inside and outside the peri-necrotic niche.

Pharmacotherapeutic strategies for treating pancreatic cancer: advances and challenges

INTRODUCTION

Despite many efforts to improve the outcome of pancreatic ductal adenocarcinoma (PDAC), its prognosis remains poor, which is mostly related to late diagnosis and drug resistance. Improving systemic therapy is considered the major challenge in improving the outcome of this disease.

AREAS COVERED

This review covers novel chemotherapy and targeted agents in the treatment of PDAC, with a focus on advanced stage disease.

EXPERT OPINION

Current frontline therapies used in the treatment of patients with PDAC with favorable performance status are gemcitabine (GEM) and nab-paclitaxel or 5-fluorouracil, leucovorin, irinotecan, and oxaliplatin (FOLFIRINOX). PDAC has a number of genetic mutations that may explain its biological behavior, such as KRAS, p53 and CDK2NA, which occur in more than 90% of cases. Unfortunately, to this day, a specific targeting agent to any of those frequent gene mutations is lacking. Emerging areas of targeted therapies include the DNA repair, stroma, metabolism, and stem cells. Immunotherapy with either vaccines or immune checkpoint inhibitors has not produced any significant improvements in outcome of PDAC. Incorporating different approaches in therapy, including conventional, immunological, and others, is key in offering patients with the best possible care.

Chemotherapy resistance and stemness in mitotically quiescent human breast cancer cells identified by fluorescent dye retention

Metastatic recurrence in breast cancer is a major cause of mortality and often occurs many years after removal of the primary tumour. This process is driven by the reactivation of disseminated tumour cells that are characterised by mitotic quiescence and chemotherapeutic resistance. The ability to reliably isolate and characterise this cancer cell population is critical to enable development of novel therapeutic strategies for prevention of breast cancer recurrence. Here we describe the identification and characterisation of a sub-population of slow-cycling tumour cells in the MCF-7 and MDA-MB-231 human breast cancer cell lines based on their ability to retain the lipophilic fluorescent dye Vybrant^® DiD for up to six passages in culture. Vybrant^® DiD-retaining (DiD+) cells displayed significantly increased aldehyde dehydrogenase activity and exhibited significantly reduced sensitivity to chemotherapeutic agents compared to their rapidly dividing, Vybrant^® DiD-negative (DiD−) counterparts. In addition, DiD+ cells were exclusively capable of initiating population re-growth following withdrawal of chemotherapy. The DiD+ population displayed only partial overlap with the CD44⁺CD24^−/low cell surface protein marker signature widely used to identify breast cancer stem cells, but was enriched for CD44⁺CD24⁺ cells. Real-time qPCR profiling revealed differential expression of epithelial-to-mesenchymal transition and stemness genes between DiD+ and DiD− populations. This is the first demonstration that both MCF-7 and MDA-MB-231 human breast cancer lines contain a latent therapy-resistant population of slow-cycling cells capable of initiating population regrowth post-chemotherapy. Our data support that label-retaining cells can serve as a model for identification of molecular mechanisms driving tumour cell quiescence and de novo chemoresistance and that further characterisation of this prospective tumour-reinitiating population could yield novel therapeutic targets for elimination of the cells responsible for breast cancer recurrence.

Cancer stem cell populations in lymphoma in dogs and impact of cytotoxic chemotherapy

Cancer relapse following chemotherapy has been attributed in part to the presence of cancer stem cells (CSC), which drive tumour growth and metastasis and are highly resistant to the effects of cytotoxic chemotherapy. As a result, treatment with cytotoxic chemotherapy selects for drug-resistant CSC populations that eventually drive tumour recurrence. Little is known currently regarding the role of CSC in dogs with lymphoma, nor the impact of chemotherapy on CSC populations. Therefore, we prospectively quantitated CSC populations in dogs with B-cell (BCL) and T-cell lymphoma (TCL), using tumour aspirates and flow cytometric analysis with a panel of CSC markers. In addition, in vitro studies were carried out to determine the impact of chemotherapy resistance on the stem cell phenotype and stem cell properties of lymphoma cells. We found that the percentages of tumour cells expressing CSC markers were significantly increased in dogs with BCL, compared with B cells from normal lymph nodes. Similar findings were observed in dogs with TCL. In vitro studies revealed that lymphoma cells selected for resistance to CHOP chemotherapy had significantly upregulated expression of CSC markers, formed spheroids in culture more readily, and expressed significantly greater aldehyde dehydrogenase activity compared with chemotherapy-sensitive tumour cells. Similar results were observed in tumour samples dogs with relapsed BCL. These findings suggest that cytotoxic chemotherapy can lead to a relative enrichment of tumour cells with CSC properties, which may be associated with lymphoma recurrence.

MiR-30-5p suppresses cell chemoresistance and stemness in colorectal cancer through USP22/Wnt/β-catenin signaling axis

Colorectal cancer (CRC) remains both common and fatal, and its successful treatment is greatly limited by the development of stem cell‐like characteristics (stemness) and chemoresistance. MiR‐30‐5p has been shown to function as a tumor suppressor by targeting the Wnt/β‐catenin signaling pathway, but its activity in CRC has never been assessed. We hypothesized that miR‐30‐5p exerts anti‐oncogenic effects in CRC by regulating the USP22/Wnt/β‐catenin signaling axis. In the present study, we demonstrate that tissues from CRC patients and human CRC cell lines show significantly decreased miR‐30‐5p family expression. After identifying the 3’UTR of USP22 as a potential binding site of miR‐30‐5p, we constructed a luciferase reporter containing the potential miR‐30‐5p binding site and measured the effects on USP22 expression. Western blot assays showed that miR‐30‐5p decreased USP22 protein expression in HEK293 and Caco2 CRC cells. To evaluate the effects of miR‐30‐5p on CRC cell stemness, we isolated CD133 + CRC cells (Caco2 and HCT15). We then determined that, while miR‐30‐5p is normally decreased in CD133 + CRC cells, miR‐30‐5p overexpression significantly reduces expression of stem cell markers CD133 and Sox2, sphere formation, and cell proliferation. Similarly, we found that miR‐30‐5p expression is normally reduced in 5‐fluorouracil (5‐FU) resistant CRC cells, whereas miR‐30‐5p overexpression in 5‐FU resistant cells reduces sphere formation and cell viability. Inhibition of miR‐30‐5p reversed the process. Finally, we determined that miR‐30‐5p attenuates the expression of Wnt/β‐catenin signaling target genes (Axin2 and MYC), Wnt luciferase activity, and β‐catenin protein levels in CRC stem cells.

Infiltrative and drug-resistant slow-cycling cells support metabolic heterogeneity in glioblastoma

Metabolic reprogramming has been described in rapidly growing tumors, which are thought to mostly contain fast-cycling cells (FCCs) that have impaired mitochondrial function and rely on aerobic glycolysis. Here, we characterize the metabolic landscape of glioblastoma (GBM) and explore metabolic specificities as targetable vulnerabilities. Our studies highlight the metabolic heterogeneity in GBM, in which FCCs harness aerobic glycolysis, and slow-cycling cells (SCCs) preferentially utilize mitochondrial oxidative phosphorylation for their functions. SCCs display enhanced invasion and chemoresistance, suggesting their important role in tumor recurrence. SCCs also demonstrate increased lipid contents that are specifically metabolized under glucose-deprived conditions. Fatty acid transport in SCCs is targetable by pharmacological inhibition or genomic deletion of FABP7, both of which sensitize SCCs to metabolic stress. Furthermore, FABP7 inhibition, whether alone or in combination with glycolysis inhibition, leads to overall increased survival. Our studies reveal the existence of GBM cell subpopulations with distinct metabolic requirements and suggest that FABP7 is central to lipid metabolism in SCCs and that targeting FABP7-related metabolic pathways is a viable therapeutic strategy.

Long non-coding RNA AFAP1-AS1/miR-320a/RBPJ axis regulates laryngeal carcinoma cell stemness and chemoresistance

AFAP1-AS1 is a long non-coding RNA that is associated with tumorigenesis and poor prognosis in a variety of cancers. We have been suggested that AFAP1-AS1 increases tumorigenesis in laryngeal carcinoma specifically by enhancing stemness and chemoresistance. We assessed AFAP1-AS1 expression in human laryngeal specimens, paired adjacent normal tissues and human HEp-2 cells. Indeed, we found not only that AFAP1-AS1 was up-regulated in laryngeal carcinoma specimens and cells, but also that stemness-associated genes were overexpressed. Silencing of AFAP1-AS1 promoted HEp-2 cell chemoresistance under cisplatin treatment. Expression of AFAP1-AS1 was increased in drug-resistant Hep-2 cells. We then probed the mechanism of AFAP1-AS1 activity and determined that miR-320a was a potential molecular target of AFAP1-AS1. Luciferase reporter and qRT-PCR assays of AFAP1-AS1 and miR-320a levels in human specimens and cell cultures indicated that AFAP1-AS1 negatively regulates miR-320a. To discover the molecular mechanism of miR-320a, we again used the DIANA Tools algorithm to predict its genetic target, RBPJ. After cloning the 3'-untranslated regions (3'-UTR) of RBPJ into a luciferase reporter, we determined that miR-320a did in fact reduce RBPJ mRNA and protein levels. Ultimately, we determined that AFAP1-AS1 increases RBPJ expression by negatively regulating miR-320a and RBPJ overexpression rescues stemness and chemoresistance inhibited by AFAP1-AS1 silencing. Taken together, these results suggest that AFAP1-AS1 can serve as a prognostic biomarker in laryngeal carcinoma and that miR-320a has the potential to improve standard therapeutic approaches to the disease, especially for cases in which cancer cell stemness and drug resistance present significant barriers to effective treatment.

Loss of PDPK1 abrogates resistance to gemcitabine in label-retaining pancreatic cancer cells

BACKGROUND

Label-retaining cancer cells (LRCC) have been proposed as a model of slowly cycling cancer stem cells (CSC) which mediate resistance to chemotherapy, tumor recurrence, and metastasis. The molecular mechanisms of chemoresistance in LRCC remain to-date incompletely understood. This study aims to identify molecular targets in LRCC that can be exploited to overcome resistance to gemcitabine, a standard chemotherapy agent for the treatment of pancreas cancer.

METHODS

LRCC were isolated following Cy5-dUTP staining by flow cytometry from pancreatic cancer cell lines. Gene expression profiles obtained from LRCC, non-LRCC (NLRCC), and bulk tumor cells were used to generate differentially regulated pathway networks. Loss of upregulated targets in LRCC on gemcitabine sensitivity was assessed via RNAi experiments and pharmacological inhibition. Expression patterns of PDPK1, one of the upregulated targets in LRCC, was studied in patients' tumor samples and correlated with pathological variables and clinical outcome.

RESULTS

LRCC are significantly more resistant to gemcitabine than the bulk tumor cell population. Non-canonical EGF (epidermal growth factor)-mediated signal transduction emerged as the top upregulated network in LRCC compared to non-LRCC, and knock down of EGF signaling effectors PDPK1 (3-phosphoinositide dependent protein kinase-1), BMX (BMX non-receptor tyrosine kinase), and NTRK2 (neurotrophic receptor tyrosine kinase 2) or treatment with PDPK1 inhibitors increased growth inhibition and induction of apoptosis in response to gemcitabine. Knockdown of PDPK1 preferentially increased growth inhibition and reduced resistance to induction of apoptosis upon gemcitabine treatment in the LRCC vs non-LRCC population. These findings are accompanied by lower expression levels of PDPK1 in tumors compared to matched uninvolved pancreas in surgical resection specimens and a negative association of membranous localization on IHC with high nuclear grade (p < 0.01).

CONCLUSION

Pancreatic cancer cell-derived LRCC are relatively resistant to gemcitabine and harbor a unique transcriptomic profile compared to bulk tumor cells. PDPK1, one of the members of an upregulated EGF-signaling network in LRCC, mediates resistance to gemcitabine, is found to be dysregulated in pancreas cancer specimens, and might be an attractive molecular target for combination therapy studies.

Epithelial-to-mesenchymal transition in cancer: complexity and opportunities

The cell-biological program termed the epithelial-to-mesenchymal transition (EMT) plays an important role in both development and cancer progression. Depending on the contextual signals and intracellular gene circuits of a particular cell, this program can drive fully epithelial cells to enter into a series of phenotypic states arrayed along the epithelial-mesenchymal phenotypic axis. These cell states display distinctive cellular characteristics, including stemness, invasiveness, drug-resistance and the ability to form metastases at distant organs, and thereby contribute to cancer metastasis and relapse. Currently we still lack a coherent overview of the molecular and biochemical mechanisms inducing cells to enter various states along the epithelial-mesenchymal phenotypic spectrum. An improved understanding of the dynamic and plastic nature of the EMT program has the potential to yield novel therapies targeting this cellular program that may aid in the management of high-grade malignancies.

Metformin influences drug sensitivity in pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive, highly metastatic malignancy and accounts for 85% of pancreatic cancers. PDAC patients have poor prognosis with a five-year survival of only 5-10% after diagnosis and treatment. Pancreatic cancer has been associated with type II diabetes as the frequency of recently diagnosed diabetics that develop pancreatic cancer within a 10-year period of initial diagnosis of diabetes in increased in comparison to non-diabetic patients. Metformin is a very frequently prescribed drug used to treat type II diabetes. Metformin acts in part by stimulating AMP-kinase (AMPK) and results in the suppression of mTORC1 activity and the induction of autophagy. In the following studies, we have examined the effects of metformin in the presence of various chemotherapeutic drugs, signal transduction inhibitors and natural products on the growth of three different PDAC lines. Metformin, by itself, was not effective at suppressing growth of the pancreatic cancer cell lines at concentration less than 1000 nM, however, in certain PDAC lines, a suboptimal dose of metformin (250 nM) potentiated the effects of various chemotherapeutic drugs used to treat pancreatic cancer (e.g., gemcitabine, cisplatin, 5-fluorouracil) and other cancer types (e.g., doxorubicin, docetaxel). Furthermore, metformin could increase anti-proliferative effects of mTORC1 and PI3K/mTOR inhibitors as well as natural products such as berberine and the anti-malarial drug chloroquine in certain PDAC lines. Thus, metformin can enhance the effects of certain drugs and signal transduction inhibitors which are used to treat pancreatic and various other cancers.

The role of the Hedgehog signaling pathway in cancer: A comprehensive review

The Hedgehog (Hh) signaling pathway was first identified in the common fruit fly. It is a highly conserved evolutionary pathway of signal transmission from the cell membrane to the nucleus. The Hh signaling pathway plays an important role in the embryonic development. It exerts its biological effects through a signaling cascade that culminates in a change of balance between activator and repressor forms of glioma-associated oncogene (Gli) transcription factors. The components of the Hh signaling pathway involved in the signaling transfer to the Gli transcription factors include Hedgehog ligands (Sonic Hh [SHh], Indian Hh [IHh], and Desert Hh [DHh]), Patched receptor (Ptch1, Ptch2), Smoothened receptor (Smo), Suppressor of fused homolog (Sufu), kinesin protein Kif7, protein kinase A (PKA), and cyclic adenosine monophosphate (cAMP). The activator form of Gli travels to the nucleus and stimulates the transcription of the target genes by binding to their promoters. The main target genes of the Hh signaling pathway are PTCH1, PTCH2, and GLI1. Deregulation of the Hh signaling pathway is associated with developmental anomalies and cancer, including Gorlin syndrome, and sporadic cancers, such as basal cell carcinoma, medulloblastoma, pancreatic, breast, colon, ovarian, and small-cell lung carcinomas. The aberrant activation of the Hh signaling pathway is caused by mutations in the related genes (ligand-independent signaling) or by the excessive expression of the Hh signaling molecules (ligand-dependent signaling - autocrine or paracrine). Several Hh signaling pathway inhibitors, such as vismodegib and sonidegib, have been developed for cancer treatment. These drugs are regarded as promising cancer therapies, especially for patients with refractory/advanced cancers.

Targeting hypoxic microenvironment of pancreatic xenografts with the hypoxia-activated prodrug TH-302

Previous reports have suggested that the hypoxic microenvironment provides a niche that supports tumor stem cells, and that this might explain clinical observations linking hypoxia to metastasis. To test this, we examined the effects of a hypoxia-activated prodrug, TH-302, on the tumor-initiating cell (TIC) frequency of patient-derived pancreatic xenografts (PDX).

The frequencies of TIC, measured by limiting dilution assay, varied widely in 11 PDX models, and were correlated with rapid growth but not with the levels of hypoxia. Treatment with either TH-302 or ionizing radiation (IR), to target hypoxic and well-oxygenated regions, respectively, reduced TIC frequency, and the combination of TH-302 and IR was much more effective in all models tested. The combination was also more effective than TH-302 or IR alone controlling tumor growth, particularly treating the more rapidly-growing/hypoxic models. These findings support the clinical utility of hypoxia targeting in combination with radiotherapy to treat pancreatic cancers, but do not provide strong evidence for a hypoxic stem cell niche.

Using Carboxy Fluorescein Succinimidyl Ester (CFSE) to Identify Quiescent Glioblastoma Stem-Like Cells

Tumor resistance to conventional therapies is a major challenge toward the eradication of cancer, a life-threatening disease. This resistance mainly results from tumor heterogeneity and more specifically from the existence of "stem-like" cells that remain in a quiescent state for long periods of time and thus escape commonly used anti-cancer drugs resulting in treatment failure. Therefore, targeting this subpopulation would present a viable strategy to overcome tumor burden. This daunting task requires a deep and thorough understanding of the biology of the quiescent stem-cell population, their interaction with tumor microenvironments, and mechanisms used to sustain themselves despite aggressive therapies. In this chapter, we describe detailed technical procedures for the isolation of quiescent or infrequently dividing stem-like cells in cultured glioblastoma tumor cells using carboxy fluorescein succinimidyl ester (CFSE) staining and flow cytometric analysis. Quiescent glioblastoma cells with stem-like features are characterized and subsequently isolated based on their ability to retain the CFSE labeling.

Cancer stem cells as targets for immunotherapy

Current cancer therapies target the bulk of the tumour, while a population of highly resistant tumour cells may be able to repopulate the tumour and metastasize to new sites. Cancer cells with such stem cell-like characteristics can be identified based on their phenotypical and/or functional features which may open up ways for their targeted elimination. In this review we discuss potential off-target effects of inhibiting cancer stem-cell self-renewal pathways on immune cells, and summarize some recent immunological studies specifically targeting cancer stem cells based on their unique antigen expression.

Drug Resistance Driven by Cancer Stem Cells and Their Niche

Drug resistance represents one of the greatest challenges in cancer treatment. Cancer stem cells (CSCs), a subset of cells within the tumor with the potential for self-renewal, differentiation and tumorigenicity, are thought to be the major cause of cancer therapy failure due to their considerable chemo- and radioresistance, resulting in tumor recurrence and eventually metastasis. CSCs are situated in a specialized microenvironment termed the niche, mainly composed of fibroblasts and endothelial, mesenchymal and immune cells, which also play pivotal roles in drug resistance. These neighboring cells promote the molecular signaling pathways required for CSC maintenance and survival and also trigger endogenous drug resistance in CSCs. In addition, tumor niche components such as the extracellular matrix also physically shelter CSCs from therapeutic agents. Interestingly, CSCs contribute directly to the niche in a bilateral feedback loop manner. Here, we review the recent advances in the study of CSCs, the niche and especially their collective contribution to resistance, since increasingly studies suggest that this interaction should be considered as a target for therapeutic strategies.

Time-lapse microscopic observation of non-dividing cells in cultured human osteosarcoma MG-63 cell line

Cancer stem cells resemble normal tissue-specific stem cells in many aspects, such as self-renewal and plasticity. Like their non-malignant counterparts, cancer stem cells are suggested to exhibit a relative quiescence. The established cancer cell lines reportedly harbor slow-proliferating cells that are positive for some cancer stem cells markers. However, the fate of these cells and their progeny remains unknown. We used time-lapse microscopy and the contrast-based segmentation algorithm to identify and monitor actively dividing and non-dividing cells in human osteosarcoma MG-63 cell line. Within the monitored field of view the non-dividing cells were represented by three cells that never divided, and one cell that attempted to divide, but failed cytokinesis, and later, after significantly prolonged division, produced the progeny with enlarged segmented nuclei, thus pointing to a possible mitotic catastrophe. Together, these cells initially constituted about 6.2% of the total number of seeded cells, yet only 0.02% of all cells at the end of the observation period when cells became confluent. Non-dividing cells were characterized by rounded shape, dark nuclei, random cytoplasmic streaming and subtle oscillatory movement, however, they did not migrate and rarely formed cell-cell contacts as compared to actively dividing cells. Our data indicate that the observed non-dividing MG-63 cells do not have a growth advantage over other cells and, therefore, they do not contribute to the cancer stem cells pool.

Establishment of CMab-43, a Sensitive and Specific Anti-CD133 Monoclonal Antibody, for Immunohistochemistry

CD133, also known as prominin-1, was first described as a cell surface marker on early progenitor and hematopoietic stem cells. It is a five-domain transmembrane protein composed of an N-terminal extracellular tail, two small cytoplasmic loops, two large extracellular loops containing seven potential glycosylation sites, and a short C-terminal intracellular tail. CD133 has been used as a marker to identify cancer stem cells derived from primary solid tumors and as a prognostic marker of gliomas. Herein, we developed novel anti-CD133 monoclonal antibodies (mAbs) and characterized their efficacy in flow cytometry, Western blot, and immunohistochemical analyses. We expressed the full length of CD133 in LN229 glioblastoma cells, immunized mice with LN229/CD133 cells, and performed the first screening using flow cytometry. After limiting dilution, we established 100 anti-CD133 mAbs, reacting with LN229/CD133 cells but not with LN229 cells. Subsequently, we performed the second and third screening with Western blot and immunohistochemical analyses, respectively. Among 100 mAbs, 11 strongly reacted with CD133 in Western blot analysis. One of 11 clones, CMab-43 (IgG_2a, kappa), showed a sensitive and specific reaction against colon cancer cells, warranting the use of CMab-43 in detecting CD133 in pathological analyses of CD133-expressing cancers.

Drug resistance and cancer stem cells: the shared but distinct roles of hypoxia-inducible factors HIF1α and HIF2α

Chemotherapy resistance is a major contributor to poor treatment responses and tumour relapse, the development of which has been strongly linked to the action of cancer stem cells (CSCs). Mounting evidence suggests that CSCs are reliant on low oxygen conditions and hypoxia-inducible factors 1α and 2α (HIF1α and HIF2α) to maintain their stem cell features. Research in the last decade has begun to clarify the functional differences between the two HIFα subtypes (HIFαs). Here, we review and discuss these differences in relation to CSC-associated drug resistance. Both HIFαs contribute to CSC survival but play different roles -HIF1α being more responsible for survival functions and HIF2α for stemness traits such as self-renewal - and are sensitive to different degrees of hypoxia. Failure to account for physiologically relevant oxygen concentrations in many studies may influence the current understanding of the roles of HIFαs. We also discuss how hypoxia and HIFαs contribute to CSC drug resistance via promotion of ABC drug transporters Breast cancer resistance protein (BCRP), MDR1, and MRP1 and through maintenance of quiescence. Additionally, we explore the PI3K/AKT cell survival pathway that may support refractory cancer by promoting CSCs and activating both HIF1α and HIF2α. Accordingly, HIF1α and HIF2α inhibition, potentially via PI3K/AKT inhibitors, could reduce chemotherapy resistance and prevent cancer relapse.

Blockade of Stearoyl-CoA-desaturase 1 activity reverts resistance to cisplatin in lung cancer stem cells

Poor prognosis in lung cancer has been attributed to the presence of lung cancer stem cells (CSCs) which resist chemotherapy and cause disease recurrence. Hence, the strong need to identify mechanisms of chemoresistance and to develop new combination therapies. We have previously shown that Stearoyl-CoA-desaturase 1 (SCD1), the enzyme responsible for the conversion of saturated to monounsaturated fatty acids is upregulated in 3D lung cancer spheroids and is an upstream activator of key proliferation pathways β-catenin and YAP/TAZ. Here we first show that SCD1 expression, either alone or in combination with a variety of CSCs markers, correlates with poor prognosis in adenocarcinoma (ADC) of the lung. Treatment of lung ADC cell cultures with cisplatin enhances the formation of larger 3D tumor spheroids and upregulates CSCs markers. In contrast, co-treatment with cisplatin and the SCD1 inhibitor MF-438 reverts upregulation of CSCs markers, strongly synergizes in the inhibition of 3D spheroids formation and induces CSCs apoptosis. Mechanistically, SCD1 inhibition activates endoplasmic reticulum stress response and enhances autophagy. These data all together support the use of combination therapy with SCD1 inhibitors to achieve better control of lung cancer.

Characterization and functional analysis of a slow-cycling subpopulation in colorectal cancer enriched by cell cycle inducer combined chemotherapy

The concept of cancer stem cells has been proposed in various malignancies including colorectal cancer. Recent studies show direct evidence for quiescence slow-cycling cells playing a role in cancer stem cells. There exists an urgent need to isolate and better characterize these slow-cycling cells. In this study, we developed a new model to enrich slow-cycling tumor cells using cell-cycle inducer combined with cell cycle-dependent chemotherapy in vitro and in vivo. Our results show that Short-term exposure of colorectal cancer cells to chemotherapy combined with cell-cycle inducer enriches for a cell-cycle quiescent tumor cell population. Specifically, these slow-cycling tumor cells exhibit increased chemotherapy resistance in vitro and tumorigenicity in vivo. Notably, these cells are stem-cell like and participate in metastatic dormancy. Further exploration indicates that slow-cycling colorectal cancer cells in our model are less sensitive to cytokine-induced-killer cell mediated cytotoxic killing in vivo and in vitro. Collectively, our cell cycle inducer combined chemotherapy exposure model enriches for a slow-cycling, dormant, chemo-resistant tumor cell sub-population that are resistant to cytokine induced killer cell based immunotherapy. Studying unique signaling pathways in dormant tumor cells enriched by cell cycle inducer combined chemotherapy treatment is expected to identify novel therapeutic targets for preventing tumor recurrence.

MHY451 induces cell cycle arrest and apoptosis by ROS generation in HCT116 human colorectal cancer cells

Colorectal cancer (CRC) is the third most frequently diagnosed cancer and cause of cancer-related deaths. Despite advancements in conventional therapeutic approaches to CRC, most patients with CRC die of their disease. There is a need to develop novel therapeutic agents for this malignancy. Therefore, the present study aimed to examine the anticancer effects and elucidate the underlying mechanism of MHY451 in HCT116 human colorectal cancer cells. Treatment with MHY451 inhibited cell growth in a time- and concentration-dependent manner. MHY451 increased the accumulation of cell cycle progression at the G2/M phase. This agent decreased the protein level of cyclin B1 and its activating partners, Cdc25c and Cdc2, whereas it increased the cell cycle inhibitor p21WAF/CIP. The induction of apoptosis was observed by decreased viability, cleavage of poly(ADP-ribose) polymerase (PARP), alteration in the ratio of Bax/Bcl-2 protein expression and reduction of procaspase-8 and -9. Pretreatment with Z-VAD-FMK, a pan-caspase inhibitor, inhibited MHY451-induced apoptosis, indicating that apoptotic cell death by MHY451 was mediated through caspases. Moreover, the apoptotic effect of MHY451 was reactive oxygen species (ROS)-dependent, evidenced by the inhibition of MHY451-induced PARP cleavage and ROS generation by N-acetylcysteine-induced ROS scavenging. Taken together, these results demonstrate that MHY451 exerts anticancer effects by regulating the cell cycle, inducing apoptosis through caspase activation and generating ROS. These results suggest that MHY451 has considerable potential for chemoprevention or treatment of CRC or both.

Overexpression of TRIM44 is related to invasive potential and malignant outcomes in esophageal squamous cell carcinoma

Recent studies have shown that some members of the tripartite motif-containing protein family function as important regulators for carcinogenesis. In this study, we investigated whether tripartite motif-containing protein 44 acts as a cancer-promoting gene through its overexpression in esophageal squamous cell carcinoma. We analyzed esophageal squamous cell carcinoma cell lines to evaluate malignant potential and also analyzed 68 primary tumors to evaluate clinical relevance of tripartite motif-containing protein 44 protein in esophageal squamous cell carcinoma patients. Expression of the tripartite motif-containing protein 44 protein was detected in esophageal squamous cell carcinoma cell lines (8/14 cell lines; 57%) and primary tumor samples of esophageal squamous cell carcinoma (39/68 cases; 57%). Knockdown of tripartite motif-containing protein 44 expression in esophageal squamous cell carcinoma cells using several specific small interfering RNAs inhibited cell migration and invasion, but not cell proliferation. Immunohistochemical analysis demonstrated that the overexpression of the tripartite motif-containing protein 44 protein in the tumor infiltrated region was associated with the status of lymph node metastasis ( p = 0.049), and the overall survival rates were significantly worse among patients with tripartite motif-containing protein 44-overexpressing tumors than those with non-expressing tumors ( p = 0.029). Moreover, multivariate Cox regression model identified that overexpression of the tripartite motif-containing protein 44 protein was an independent worse prognostic factor (hazard ratio = 2.815; p = 0.041), as well as lymphatic invasion (hazard ratio = 2.735; p = 0.037). These results suggest that tripartite motif-containing protein 44 protein could play a crucial role in tumor invasion through its overexpression and highlight its usefulness as a predictor and potential therapeutic target in esophageal squamous cell carcinoma.

Endothelium originated from colorectal cancer stem cells constitute cancer blood vessels

Tumor growth depends on the formation of blood vessels that provide the supply of nutrients and oxygen. Previous data have shown that glioblastoma stem cells are able to give rise to vascular cells to constitute the functional vessels in tumor tissues. However, which kinds of vascular cells are generated from glioblastoma stem cells is largely debated. In addition, there is little evidence showing that the stem cells from other kinds of tumors can produce vascular cells to constitute the functional blood vessels in tumor tissues. Here we show that cancer stem cells of human colorectal carcinomas (CoCSC) can give rise to vascular endothelial cells and compose the vasculatures in cancer tissues. The human‐cell‐specific nuclear antigen NuMA⁺ vascular endothelial cells were detected in the blood vessels in xenografts derived from CoCSC. NuMA⁺ endothelial cells incorporated into functional blood vessels. Our data indicate that the cancer stem cells derived from human colorectal carcinomas have the capacity to generate functional blood vessels and provide a new mechanism for tumor vasculogenesis in carcinoma.

Human Cytomegalovirus-Infected Glioblastoma Cells Display Stem Cell-Like Phenotypes

A role for HCMV in GBMs remains controversial for several reasons. Some studies find HCMV in GBM tumors, while others do not. Few cells within a GBM may harbor HCMV, making it unclear how the virus could be contributing to the tumor phenotype without infecting every cell. Finally, HCMV does not overtly transform cells in vitro. However, tumors induced by other viruses can be treated with antiviral remedies, and initial results indicate that this may be true for anti-HCMV therapies and GBMs. With such a poor prognosis for GBM patients, any potential new intervention deserves exploration. Our work here describes an evidence-based model for how HCMV could contribute to GBM biology while infecting very few cells and without transforming them. It also illuminates why anti-HCMV treatments may be beneficial to GBM patients. Our observations provide blueprints for future in vitro studies examining how HCMV manipulates stem cell-specific pathways and future clinical studies of anti-HCMV measures as GBM therapeutics.

Glioblastoma multiforme (GBM) is the most common brain tumor in adults. Human cytomegalovirus (HCMV) genomes are present in GBM tumors, yielding hope that antiviral treatments could prove therapeutic and improve the poor prognosis of GBM patients. We discovered that GBM cells infected in vitro with HCMV display properties of cancer stem cells. HCMV-infected GBM cells grow more slowly than mock-infected controls, demonstrate a higher capacity for self-renewal determined by a sphere formation assay, and display resistance to the chemotherapeutic drug temozolomide. Our data suggest that HCMV, while present in only a minority of the cells within a tumor, could contribute to the pathogenesis of GBMs by promoting or prolonging stem cell-like phenotypes, thereby perpetuating tumors in the face of chemotherapy. Importantly, we show that temozolomide sensitivity is restored by the antiviral drug ganciclovir, indicating a potential mechanism underlying the positive effects observed in GBM patients treated with antiviral therapy.

IMPORTANCE A role for HCMV in GBMs remains controversial for several reasons. Some studies find HCMV in GBM tumors, while others do not. Few cells within a GBM may harbor HCMV, making it unclear how the virus could be contributing to the tumor phenotype without infecting every cell. Finally, HCMV does not overtly transform cells in vitro. However, tumors induced by other viruses can be treated with antiviral remedies, and initial results indicate that this may be true for anti-HCMV therapies and GBMs. With such a poor prognosis for GBM patients, any potential new intervention deserves exploration. Our work here describes an evidence-based model for how HCMV could contribute to GBM biology while infecting very few cells and without transforming them. It also illuminates why anti-HCMV treatments may be beneficial to GBM patients. Our observations provide blueprints for future in vitro studies examining how HCMV manipulates stem cell-specific pathways and future clinical studies of anti-HCMV measures as GBM therapeutics.

Blocking epithelial-to-mesenchymal transition in glioblastoma with a sextet of repurposed drugs: the EIS regimen

This paper outlines a treatment protocol to run alongside of standard current treatment of glioblastoma- resection, temozolomide and radiation. The epithelial to mesenchymal transition (EMT) inhibiting sextet, EIS Regimen, uses the ancillary attributes of six older medicines to impede EMT during glioblastoma. EMT is an actively motile, therapy-resisting, low proliferation, transient state that is an integral feature of cancers’ lethality generally and of glioblastoma specifically. It is believed to be during the EMT state that glioblastoma’s centrifugal migration occurs. EMT is also a feature of untreated glioblastoma but is enhanced by chemotherapy, by radiation and by surgical trauma. EIS Regimen uses the antifungal drug itraconazole to block Hedgehog signaling, the antidiabetes drug metformin to block AMP kinase (AMPK), the analgesic drug naproxen to block Rac1, the anti-fibrosis drug pirfenidone to block transforming growth factor-beta (TGF-beta), the psychiatric drug quetiapine to block receptor activator NFkB ligand (RANKL) and the antibiotic rifampin to block Wnt- all by their previously established ancillary attributes. All these systems have been identified as triggers of EMT and worthy targets to inhibit. The EIS Regimen drugs have a good safety profile when used individually. They are not expected to have any new side effects when combined. Further studies of the EIS Regimen are needed.

Modeling the process of human tumorigenesis

Modelling the genesis of human cancers is at a scientific turning point. Starting from primary sources of normal human cells, it is now possible to reproducibly generate several types of malignant cell populations. Powerful methods for clonally tracking and manipulating their appearance and progression in serially transplanted immunodeficient mice are also in place. These developments circumvent historic drawbacks inherent in analyses of cancers produced in model organisms, established human malignant cell lines, or highly heterogeneous patient samples. In this review, we survey the advantages, contributions and limitations of current de novo human tumorigenesis strategies and note several exciting prospects on the horizon.

A better understanding of the earliest stages of human cancer formation can enable future improvements in early detection, diagnosis and treatment. In this review, the authors summarize the methods enabling de novo tumorigenesis protocols to be applied to human cells and the insights derived from them to date, as well as the exciting and relevant technical developments anticipated to extend even further the utility of these strategies.

Enhanced cancer stem cell properties of a mitotically quiescent subpopulation of p75NTR-positive cells in esophageal squamous cell carcinoma

Mitotically quiescent cancer stem cells (CSCs) possess higher malignant potential than other CSCs, indicating their higher contribution to therapeutic resistance than that of other CSCs. In esophageal squamous cell carcinoma (ESCC), p75 neurotrophin receptor (p75NTR) is expressed in a candidate CSC population showing high tumorigenicity and chemoresistance. In the present study, we isolated and characterized quiescent CSCs population in ESCC based on p75NTR expression and cell cycle status. Expression of p75NTR and Ki-67 in ESCC cell lines (KYSE cells) and surgically resected ESCC specimens was detected by performing immunocytochemical analysis. p75NTR-positive KYSE cells were fractionated into quiescent and proliferating cells by performing flow cytometry with a fluorescent DNA-staining dye to determine their CSC phenotype. Immunocytochemical analysis showed that 21.8 and 36.5% of the p75NTR-positive cells were Ki-67-negative (G0), which accounted for 11.4 and 15.7% of cells in KYSE-30 and KYSE-140 cell lines, respectively. Flow cytometric cell sorting showed that p75NTR-positive cells in the G0-G1 phase (p75NTR-positive/G0-1 cells) but not in the S-G2-M phase (p75NTR-positive/S-G2-M cells) showed strong expression of stem cell-related genes Nanog, BMI-1, and p63; high colony formation ability; high tumorigenicity in a mouse xenograft model; and strong chemoresistance against cisplatin because of the expression of drug resistance genes ABCG2 and ERCC1. Label-retention assay showed that 3.4% p75NTR-positive cells retained fluorescent cell-tracing dye, but p75NTR-negative cells did not. Immunohistochemical analysis of ESCC specimens showed p75NTR expression in 39 of 95 (41.1%) patients, with a median of 13.2% (range, 3.0-80.1%) p75NTR-positive/Ki-67-negative cells, which were found to be associated with poorly differentiated histology. Our results suggest that p75NTR-positive/G0-1 cells represent quiescent CSCs in ESCC and indicate that these cells can be used as targets to investigate molecular processes regulating CSC phenotype and to develop novel therapeutic strategies.

Generation of patient-derived xenografts from fine needle aspirates or core needle biopsy

BACKGROUND

Patient-derived xenografts have recently become a powerful tool for cancer research and may be used to guide personalized therapy. Thus far, patient-derived xenografts have been grown from tumor tissue obtained after operative resection; however, many cancer patients never undergo operative intervention for a variety of reasons. We hypothesized that xenograft tumors could be grown from smaller volumes of patient tissue, such as those obtained during diagnostic biopsies.

METHODS

Surgical specimens were obtained after resection of primary or metastatic lesions of the following cancers: pancreatic carcinoma, non-small cell lung cancer, bladder (urothelial) carcinoma, and melanoma. At least 10 cases of each cancer were included in this study. To mimic clinical biopsies, small fragments of the surgical specimens were biopsied with a 22-gauge needle, and the needle contents were injected subcutaneously in immunocompromised mice. The tumor fragment from which the biopsy was taken was also implanted subcutaneously in the contralateral side of the same mouse as a control.

RESULTS

Success rates of the traditional method of xenograft implantation ranged from 27.3%-70%. Success rates of the fine needle aspirate technique ranged from 0%-36.4%. An attempt to engraft a percutaneous core needle liver biopsy of a metastatic pancreatic adenocarcinoma also was successful.

CONCLUSION

We have found that it is possible to engraft fine needle aspirates and core biopsies of solid tumors in order to generate patient-derived xenografts. This may open up xenografting to a wider cancer patient population than previously possible.

The epithelial to mesenchymal transition (EMT) and cancer stem cells: implication for treatment resistance in pancreatic cancer

The mechanical properties of epithelial to mesenchymal transition (EMT) and a pancreatic cancer subpopulation with stem cell properties have been increasingly recognized as potent modulators of the effective of therapy. In particular, pancreatic cancer stem cells (PCSCs) are functionally important during tumor relapse and therapy resistance. In this review we have surveyed recent advances in the role of EMT and PCSCs in tumor progression, metastasis and treatment resistance, and the mechanisms of integrated with biochemical signals and the underlying pathways involved in treatment resistance of pancreatic cancer. These findings highlight the importance of confirming stem-cells markers and complex molecular signaling pathways controlling EMT and cancer stem cells in pancreatic cancer during tumor formation, progression, and response to therapy.

Bulk pancreatic cancer cells can convert into cancer stem cells(CSCs) in vitro and 2 compounds can target these CSCs

Increasing evidence has confirmed the existence of cancer stem cells (CSCs) in both hematological malignancies and solid tumors. However, the origin of CSCs is still uncertain, and few agents have been capable of eliminating CSCs till now. The aim of this study was to investigate whether bulk pancreatic cancer cells could convert into CSCs under certain conditions and explore whether metformin and curcumin can kill pancreatic CSCs. Aspc1, Bxpc3 and Panc1 pancreatic cancer cells were cultured in stem cell culture medium (serum-free Dulbecco's modified Eagle medium/Nutrient Mixture F-12 containing basic fibroblast growth factor, epidermal growth factor, B27 and insulin) for 5 days and it was found that all the pancreatic cancer cells aggregated into spheres and expressed pancreatic cancer stem cell surface markers. Then characteristics of Panc1 sphere cells were analyzed and cytotoxicity assays were performed. The results show that Panc1 sphere cells exhibited CSC characteristics and were more resistant to conventional chemotherapy and more sensitive to metformin and curcumin than their parent cells. These findings suggested that bulk pancreatic cancer cells could acquire CSC characteristics under certain conditions, which may support the "yin-yang" model of CSCs (interconversion between bulk cancer cells and CSCs). These results also showed that metformin and curcumin could be candidate drugs for targeting pancreatic CSCs.

Cancer stem cells don't waste their time cleaning-low proteasome activity, a marker for cancer stem cell function

A population of stem-like cells in tumors, the so-called cancer stem cells (CSCs), are being held responsible for therapy resistance and tumor recurrence. In analogy with normal stem cells, CSCs possess the capacity of long term self-renewal and multilineage differentiation. CSCs are believed to be more resistant to various therapies compared to their differentiated offspring and therefore the cause of tumor relapse. Markers for CSCs have been identified using xenograft transplantation assays and lineage tracing in mouse models, however the specificity and validity of many of these markers is under debate. Recently, low proteasome activity has been postulated as a novel CSC marker. In several solid malignancies a small subset of low proteasomal activity cells with CSC characteristics were identified, suggesting that proteasomal activity might be a functional marker for CSCs. In this perspective, we will discuss a recent study by Munakata et al., describing a population of colorectal cancer cells with CSC properties, characterized by low proteasome activity and treatment resistance. We will put this finding in a broader view by discussing the challenges and issues inherent with CSC identification, as well as some emerging insights in the CSC concept.

Current evidence for cancer stem cells in gastrointestinal tumors and future research perspectives

Cancer stem cells (CSCs) are a very heterogeneous subpopulation of "stem-like" cancer cells that have been identified in many cancers, including leukemias and solid tumors. It is believed that CSCs drive tumor growth, malignant behavior and are responsible for the initiation of metastatic spread. In addition, CSCs have been implicated in chemotherapy and radiotherapy resistance. Current evidence supports the theory that CSCs share at least two main features of normal stem cells: self-renewal and differentiation, properties that contribute to tumor survival even in the presence of aggressive chemotherapy; however, the mechanism(s) governing the unique biology of CSCs remain unclear. In the field of gastrointestinal cancer, where we face very low survival rates across different tumor types, unraveling the role of CSCs in gastrointestinal tumors should improve our knowledge of cancer biology and chemoresistance, ultimately benefiting patient survival. Towards this end, much effort is being invested in the characterization of CSCs as a means of overcoming drug resistance and controlling metastatic spread. In this review we will cover the concept of CSCs, the current evidence for CSCs in gastrointestinal tumors and future research directions.