Hypoxia Increases Thyroid Cancer Stem Cell-Enriched Side Population

Tumor microenvironment of cancer stem cells: Perspectives on cancer stem cell targeting

There are few tumor cell subpopulations with stem cell characteristics in tumor tissue, defined as cancer stem cells (CSCs) or cancer stem-like cells (CSLCs), which can reconstruct neoplasms with malignant biological behaviors such as invasiveness via self-renewal and unlimited generation. The microenvironment that CSCs depend on consists of various cellular components and corresponding medium components. Among these factors existing at a variety of levels and forms, cytokine networks and numerous signal pathways play an important role in signaling transduction. These factors promote or maintain cancer cell stemness, and participate in cancer recurrence, metastasis, and resistance. This review aims to summarize the recent molecular data concerning the multilayered relationship between CSCs and CSC-favorable microenvironments. We also discuss the therapeutic implications of targeting this synergistic interplay, hoping to give an insight into targeting cancer cell stemness for tumor therapy and prognosis.

Aberrantly expressed HIF-1α enhances HCC stem cell-like traits via Wnt/β-catenin signaling activation after insufficient radiofrequency ablation

BACKGROUND

Radiofrequency ablation has become a favorable treatment modality for small hepatocellular carcinoma (HCC) recently; however, insufficient radiofrequency ablation (RFA) was shown to lead to enhanced invasiveness and metastasis of HCC in our previous study, while the underlying molecular mechanism has not been understood.

MATERIALS AND METHODS

In order to explore the influence of the hypoxic microenvironment on residual cancer and cancer stem cell (CSC)-like characteristics of HCC cells in this process, an in vitro hypoxic model and an insufficient RFA mouse model were established with HCC cancer cell lines. Immunochemistry staining and western blot were used to examine the expression of hypoxia-inducible factor (HIF)-1α and liver CSC markers. The 3D colon formation assay, tumor cell invasion assay, and gene transfection assays were applied to test the change in liver CSC stemness and HCC cell invasion.

RESULTS

After insufficient RFA treatment, the upregulated HIF-1α expression was associated with an increase in the CSC-like population in residual cancer. In vitro, hypoxic tumor cells showed aggressive CSC-like properties and phenotypes. Wnt/β-catenin signaling activation was shown to be necessary for the acquisition of liver CSC-like characteristics under hypoxic conditions.

CONCLUSION

Overall, the aberrantly enhanced HIF-1α expression enhanced the liver CSC-like traits via abnormal Wnt/β-catenin signaling activation after insufficient RFA, and the overexpressed HIF-1α would be a vital factor and useful biomarker during the HCC recurrence and metastasis.

New findings on the action of hypericin in hypoxic cancer cells with a focus on the modulation of side population cells

The presence of key hypoxia regulators, namely, hypoxia-inducible factor (HIF)-1α or HIF-2α, in tumors is associated with poor patient prognosis. Hypoxia massively activates several genes, including the one encoding the BCRP transporter that proffers multidrug resistance to cancer cells through the xenobiotic efflux and is a determinant of the side population (SP) associated with cancer stem-like phenotypes. As natural medicine comes to the fore, it is instinctive to look for natural agents possessing powerful features against cancer resistance. Hypericin, a pleiotropic agent found in Hypericum plants, is a good example as it is a BCRP substrate and potential inhibitor, and an SP and HIF modulator. Here, we showed that hypericin efficiently accumulated in hypoxic cancer cells, degraded HIF-1/2α, and decreased BCRP efflux together with hypoxia, thus diminishing the SP population. On the contrary, this seemingly favorable result was accompanied by the stimulated migration of this minor population that preserved the SP phenotype. Because hypoxia unexpectedly decreased the BCRP level and SP fraction, we compared the SP and non-SP proteomes and their changes under hypoxia in the A549 cell line. We identified differences among protein groups connected to the epithelial-mesenchymal transition, although major changes were related to hypoxia, as the upregulation of many proteins, including serpin E1, PLOD2 and LOXL2, that ultimately contribute to the initiation of the metastatic cascade was detected. Altogether, this study helps in clarifying the innate and hypoxia-triggered resistance of cancer cells and highlights the ambivalent role of natural agents in the biology of these cells.

miR-210 Expression Is Strongly Hypoxia-Induced in Anaplastic Thyroid Cancer Cell Lines and Is Associated with Extracellular Vesicles and Argonaute-2

Hypoxia, or low oxygen tension, is frequently found in highly proliferative solid tumors such as anaplastic thyroid carcinoma (ATC) and is believed to promote resistance to chemotherapy and radiation. Identifying hypoxic cells for targeted therapy may thus be an effective approach to treating aggressive cancers. Here, we explore the potential of the well-known hypoxia-responsive microRNA (miRNA) miR-210-3p as a cellular and extracellular biological marker of hypoxia. We compare miRNA expression across several ATC and papillary thyroid cancer (PTC) cell lines. In the ATC cell line SW1736, miR-210-3p expression levels indicate hypoxia during exposure to low oxygen conditions (2% O₂). Furthermore, when released by SW1736 cells into the extracellular space, miR-210-3p is associated with RNA carriers such as extracellular vesicles (EVs) and Argonaute-2 (AGO2), making it a potential extracellular marker for hypoxia.

Hypoxia-Driven TGFβ Modulation of Side Population Cells in Breast Cancer: The Potential Role of ERα

Epithelial-to-mesenchymal transition (EMT) is known to be important in regulating the behaviour of cancer cells enabling them to acquire stem cell characteristics or by enhancing the stem cell characteristics of cancer stem cells, resulting in these cells becoming more migratory and invasive. EMT can be driven by a number of mechanisms, including the TGF-β1 signalling pathway and/or by hypoxia. However, these drivers of EMT differ in their actions in regulating side population (SP) cell behaviour, even within SPs isolated from the same tissue. In this study we examined CoCl2 exposure and TGF-β driven EMT on SP cells of the MDA-MB-231 and MCF7 breast cancer cell lines. Both TGF-β1 and CoCl2 treatment led to the depletion of MDA-MB-231 SP. Whilst TGF-β1 treatment significantly reduced the MCF7 SP cells, CoCl2 exposure led to a significant increase. Single cell analysis revealed that CoCl2 exposure of MCF7 SP leads to increased expression of ABCG2 and HES1, both associated with multi-drug resistance. We also examined the mammosphere forming efficiency in response to CoCl2 exposure in these cell lines, and saw the same effect as seen with the SP cells. We suggest that these contrasting effects are due to ERα expression and the inversely correlated expression of TGFB-RII, which is almost absent in the MCF7 cells. Understanding the EMT-mediated mechanisms of the regulation of SP cells could enable the identification of new therapeutic targets in breast cancer.

Efficient Multitask Multiple Kernel Learning With Application to Cancer Research

Multitask multiple kernel learning (MKL) algorithms combine the capabilities of incorporating different data sources into the prediction model and using the data from one task to improve the accuracy on others. However, these methods do not necessarily produce interpretable results. Restricting the solutions to the set of interpretable solutions increases the computational burden of the learning problem significantly, leading to computationally prohibitive run times for some important biomedical applications. That is why we propose a multitask MKL formulation with a clustering of tasks and develop a highly time-efficient solution approach for it. Our solution method is based on the Benders decomposition and treating the clustering problem as finding a given number of tree structures in a graph; hence, it is called the forest formulation. We use our method to discriminate early-stage and late-stage cancers using genomic data and gene sets and compare our algorithm against two other algorithms. The two other algorithms are based on different approaches for linearization of the problem while all algorithms make use of the cutting-plane method. Our results indicate that as the number of tasks and/or the number of desired clusters increase, the forest formulation becomes increasingly favorable in terms of computational performance.

Impact of transforming growth factor beta 1 on normal and thyroid cancer side population cells

PURPOSE

To determine the impact of exogenous transforming growth factor beta 1 (TGF-β1) on side population (SP) cells isolated from normal, papillary thyroid cancer and anaplastic thyroid cancer cell lines and from human thyroid tissues.

METHODS

All cell populations were stained with Hoechst 33342 and analysed using dual wavelength flow cytometry to identify SP cells. This SP assay was used to assess the impact of TGF-β1 treatment and withdrawal of treatment on SP percentages. Semi-quantitative and quantitative PCR were used for molecular analysis of cells pre and post TGF-β1 treatment.

RESULTS

All cell lines expressed mRNA for both TGFB1 and its receptors, as well as showing variable expression of CDH1 and CDH2, with expressing of CDH1 being highest and CDH2 being lowest in the normal cell line. Exposure to exogenous TGF-β1 resulted in a reduction in mRNA expression of ABCG2 compared to controls which was significant between control and treated cancer cell lines. SP cells were isolated from primary human thyroid tissues, with numbers being significantly higher in papillary thyroid cancers. Exposure to TGF-β1 decreased the SP percentage in both thyroid cancer cell lines and completely abrogated these cells in the primary papillary thyroid cancer cultures. On withdrawal of TGF-β1 the SP phenotype was restored in the cancer cell lines and SP percentages increased to above that of untreated cells.

CONCLUSIONS

TGF-β1 exposure transiently regulates thyroid cancer SP cells, leading to a reduction in SP percentages, while withdrawal of TGF-β1 results in restoration of the SP phenotype.

Imaging the Human Thyroid Using Three-Dimensional Diffuse Optical Tomography: A Preliminary Study

Thyroid cancer is usually diagnosed by ultrasound imaging and fine-needle aspiration biopsy. However, diagnosis of follicular thyroid carcinomas (FTC) is difficult because FTC lacks nuclear atypia and a consensus on histological interpretation. Diffuse optical tomography (DOT) offers the potential to diagnose FTC because it can measure tumor hypoxia, while image reconstruction of the thyroid is still challenging mainly due to the complex anatomical features of the neck. In this study, we attempted to solve this issue by creating a finite element model of the human neck excluding the trachea (a void region). By reconstruction of the absorption coefficients at three wavelengths, 3D tissue oxygen saturation maps of the human thyroid are obtained for the first time by DOT.

The Effect of Hypoxia on the Expression of CXC Chemokines and CXC Chemokine Receptors-A Review of Literature

Hypoxia is an integral component of the tumor microenvironment. Either as chronic or cycling hypoxia, it exerts a similar effect on cancer processes by activating hypoxia-inducible factor-1 (HIF-1) and nuclear factor (NF-κB), with cycling hypoxia showing a stronger proinflammatory influence. One of the systems affected by hypoxia is the CXC chemokine system. This paper reviews all available information on hypoxia-induced changes in the expression of all CXC chemokines (CXCL1, CXCL2, CXCL3, CXCL4, CXCL5, CXCL6, CXCL7, CXCL8 (IL-8), CXCL9, CXCL10, CXCL11, CXCL12 (SDF-1), CXCL13, CXCL14, CXCL15, CXCL16, CXCL17) as well as CXC chemokine receptors—CXCR1, CXCR2, CXCR3, CXCR4, CXCR5, CXCR6, CXCR7 and CXCR8. First, we present basic information on the effect of these chemoattractant cytokines on cancer processes. We then discuss the effect of hypoxia-induced changes on CXC chemokine expression on the angiogenesis, lymphangiogenesis and recruitment of various cells to the tumor niche, including myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), tumor-associated neutrophils (TANs), regulatory T cells (T_regs) and tumor-infiltrating lymphocytes (TILs). Finally, the review summarizes data on the use of drugs targeting the CXC chemokine system in cancer therapies.

Hypoxia in Solid Tumors: How Low Oxygenation Impacts the "Six Rs" of Radiotherapy

Radiotherapy is an important component of cancer treatment, with approximately 50% of all cancer patients receiving radiation therapy during their course of illness. Nevertheless, solid tumors frequently exhibit hypoxic areas, which can hinder therapies efficacy, especially radiotherapy one. Indeed, hypoxia impacts the six parameters governing the radiotherapy response, called the « six Rs of radiation biology » (for Radiosensitivity, Repair, Repopulation, Redistribution, Reoxygenation, and Reactivation of anti-tumor immune response), by inducing pleiotropic cellular adaptions, such as cell metabolism rewiring, epigenetic landscape remodeling, and cell death weakening, with significant clinical repercussions. In this review, according to the six Rs, we detail how hypoxia, and associated mechanisms and pathways, impact the radiotherapy response of solid tumors and the resulting clinical implications. We finally illustrate it in hypoxic endocrine cancers through a focus on anaplastic thyroid carcinomas.

3D culture technologies of cancer stem cells: promising ex vivo tumor models

Cancer stem cells have been shown to be important in tumorigenesis processes, such as tumor growth, metastasis, and recurrence. As such, many three-dimensional models have been developed to establish an ex vivo microenvironment that cancer stem cells experience under in vivo conditions. Cancer stem cells propagating in three-dimensional culture systems show physiologically related signaling pathway profiles, gene expression, cell-matrix and cell-cell interactions, and drug resistance that reflect at least some of the tumor properties seen in vivo. Herein, we discussed the presently available Cancer stem cell three-dimensional culture models that use biomaterials and engineering tools and the biological implications of these models compared to the conventional ones.

Aging-associated genes TNFRSF12A and CHI3L1 contribute to thyroid cancer: An evidence for the involvement of hypoxia as a driver

The prevalence of thyroid cancer (TC) is high in the elderly. The present study was based on the hypothesis that genes, which have increased activity with aging, may play a role in the development of TC. A large-scale literature-based data analysis was conducted to explore the genes that are implicated in both TC and aging. Subsequently, a mega-analysis of 16 RNA expression datasets (1,222 samples: 439 healthy controls, and 783 patients with TC) was conducted to test a set of genes associated with aging but not TC. To uncover a possible link between these genes and TC, a functional pathway analysis was conducted, and the results were validated by analysis of gene co-expression. A multiple linear regression (MLR) model was employed to study the possible influence of sample size, population region and study age on the gene expression levels in TC. A total of 262 and 816 genes were identified to have increased activity with aging and TC, respectively; with a significant overlap of 63 genes (P<3.82×10⁻³⁵). The mega-analysis revealed two aging-associated genes (CHI3L1 and TNFRSF12A) to be significantly associated with TC (P<2.05×10⁻⁸), and identified the association with multiple hypoxia-driven pathways through functional pathway analysis, also confirmed by the co-expression analysis. The MLR analysis identified population region as a significant factor contributing to the expression levels of CHI3L1 and TNFRSF12A in TC samples (P<3.24×10⁻⁴). The determination of genes that promote aging was warranted due to their possible involvement in TC. The present study suggests CHI3L1 and TNFRSF12A as novel common risk genes associated with both aging and TC.

Herbal Active Ingredients: An Emerging Potential for the Prevention and Treatment of Papillary Thyroid Carcinoma

Papillary thyroid carcinoma (PTC) is the most common subtype of differentiated thyroid cancers in Asian coastal cities, where the patients have increased risk of potentially high or excessive iodine intake. Given the high metastasis and recurrence of patients with BRAF^V600E mutation, the mortality rate of thyroid cancer has recently shown an upward trend. A variety of therapies, including surgery, radiotherapy, and chemotherapy, have been used to treat thyroid cancer, but these therapies still have limitations, including postoperative complications, drug resistance, poor efficacy, or serious side effects. Recent studies have shown the potential of active ingredients derived from herbal medicine in inhibiting PTC via various cell signaling pathways. Some plant-derived compounds, such as apigenin, genistein, and curcumin, are also known to prevent and treat PTC. This article summarizes the recent advances in the structure-functional impact of anti-PTC active ingredients and their effects on PTC cells and tumor microenvironments with an emphasis on their challenges from basic research to clinical practice.

[Protein kinase D1 regulates the growth and metabolism of oral squamous carcinoma cells in tumor microenvironment]

OBJECTIVE

To observe the effect of protein kinase D1 (PKD1) on the growth and metabolism of oral squamous cell carcinoma HSC-4 cells and related molecular mechanisms in the tumor microenvironment.

METHODS

HSC-4 cell lines were transfected with shRNA plasmids. Three groups (Wild, control-shRNA, and PKD1-shRNA) were cultured under acidic or hypoxic environment for a certain time. Western blot was used to detect the expression of autophagy-related and glycolytic-related proteins. The proliferation changes were detected by CCK-8 kits.

RESULTS

The PKD1-knockdown HSC-4 cell line was established. PKD1 silencing increased autophagy activity. Under hypoxic and acidic conditions, the PKD1-knockdown HSC-4 cells showed lower proliferation than the parental cells. PKD1-knockdown also decreased the expression of hypoxia induciblefactor 1α (HIF-1α) and pyruvate kinase M2 (PKM2).

CONCLUSIONS

Under hypoxic and acidic conditions, PKD1 gene silencing can increase apoptotic autophagy activity. Downregulated PKD1 gene expression can reduce the glycolysis of oral squamous cell carcinoma cells and inhibit tumor cell proliferation. This study revealed the important role of PKD1 in the metabolism and growth of oral squamous cell carcinoma, making it a possible target for the treatment of oral squamous cell carcinoma.

Functions of stem cells of thyroid glands in health and disease

Thyroid gland has been implicated in the regulation of many functions using endocrine, paracrine and autocrine signals. Functional thyroid follicular cells derived from stem cells attracted a great interest from researchers as a strategy for thyroid's regenerative therapy. Thyroid has a very low rate of turnover; however, studies showed that the regenerative ability is enhanced following diseases or thyroidectomy, which promotes the role of stem cell. The objective of this review is to summarize the morphological characterization and the expression of stem cell genes/markers in the thyroid. Also, to highlight the mechanisms of tumor formation in thyroid via its stem cells. The most important thyroid stem cell's markers are: stem cell antigen 1 (SCA-1), octamer-binding transcription 4 (OCT-4), p63, CD34+ CD45-, paired box gene 8 (PAX-8), thyroid transcription factor 1 (TTF-1), thyroid transcription factor 2 (TTF-2), hematopoietically expressed homeobox protein HHEX, the transcription factor GATA-4, hepatocyte nuclear factor 4-α (HNF-4-α) and homeobox transcription factor Nanog (hNanog). This review highlights the functional characterization describing the mechanisms of stem cell's differentiation into functional thyroid follicle and proposing mechanisms involving in cancer formation through one of these cell types: fetal cell, thyroblasts, prothyrocytes, certain genetic mutation in the mature thyroid cells or presence of a special type of cells (cancer stem cell) which are responsible for different types of cancer formation. Understanding the mechanisms of thyroid's stem cell in cancer formation and the expression of the biomarkers in normal and abnormal thyroid status are promising physiological tools in promoting thyroid regeneration and in provision management for thyroid cancer.

[Culture and identification of tumor stem cells from surgically resected colorectal cancer tissues]

OBJECTIVE

To obtain cancer stem cells (CSCs) from surgically resected colorectal cancer specimens and identify their stem cell characteristics.

METHODS

Colorectal cancer tissue specimen obtained from a patient undergoing radical resection of colorectal cancer were implanted in nude mice, and the xenograft was harvested 1 month later to obtain purified tumor cells by enzyme digestion and adherent culture. The CSCs were screened by limiting dilution method and serum-free culture to identify their phenotypes. Soft agar colony assay was used to assess the proliferative ability of the CSCs and human colorectal cancer cell line SW480. The tumorigenic ability of the isolated CSCs and SW480 cells was evaluated by observing their subcutaneous tumor formation in nude mice. Western blotting and immunofluorescence assay were used to detect the immunophenotype of the CSCs and SW480 cells.

RESULTS

The primary cultured CSCs from clinical specimens of colorectal cancer underwent differentiation in the presence of serum in the culture. Soft agar colony formation assay showed that the CSCs had a colony formation rate above 50%, significantly higher than the rate of colorectal cancer SW480 cells (4.41%; P < 0.01). In nude mice, subcutaneous injection of 500 CSCs was sufficient to result in subcutaneous tumor formation, while the injection of 500 SW480 cells failed to form any subcutaneous tumors. The CSCs expressed CD133 and CD44 but not CK7, while SW480 cells expressed CK7 but not CD133 or CD44.

CONCLUSIONS

CSCs can be derived by primary culture of cancer cells obtained from surgically resected colorectal cancer tissue followed by serum-free culture, and the CSCs obtained have self-renewal and differentiation abilities.

Inhibition of Cancer Stem-Like Phenotype by Curcumin and Deguelin in CAL-62 Anaplastic Thyroid Cancer Cells

Background:

Anaplastic Thyroid Cancer (ATC) is one of the most lethal and aggressive human malignancies. Studies have shown that Cancer Stem-Cell (CSC) phenotype is mainly responsible for ATC aggressiveness. Cytostatic compounds are mostly ineffective because of multidrug resistance mechanisms driven by the CSC phenotype. Taxanes have limited efficacy. Recently, CSC inhibition using plant-derived, less toxic compounds, which have anti-cancer efficacy, has become a novel treatment modality. The aim of the study was to evaluate the anti-cancer activity of two natural compounds (curcumin and deguelin) on ATC cells and their CSC properties. In addition, the efficacies of these compounds were compared with that of docetaxel.

Methods:

Besides control, five treatment groups were formed. ATC cells (CAL-62) were treated with curcumin, deguelin, docetaxel, and their combinations (curcumin+docetaxel, deguelin+docetaxel) at previously determined IC50 doses. Stemness was analyzed by quantitative estimation of sphere formation in matrigel, expression of several cell surface markers (CD133, CD90, Nanog, and OCT3/4) using flow cytometry, and quantification of the hypoxic status [Oxidative Stress Index (OSI) and Superoxide Dismutase (SOD) activity]. The anti-cancer efficacies of these compounds and their combinations were evaluated by determining the alterations in the cell cycle, apoptosis, and tumoral cell migration.

Results:

Both the natural compounds (particularly curcumin) significantly suppressed the spheroid formation and cellular motility in matrigel as well as suppressed the accumulation of cells in the G0/1 phase, in which the maximum CSC activity is observed. The compounds did not suppress the expression of CSC markers, but twothirds of the cells expressed CD90. Deguelin was found to be particularly effective in inducing apoptosis similar to docetaxel at IC50 concentrations. Curcumin reduced the OSI and deguelin enhanced the SOD activity, even in docetaxel pre-treated cells.

Conclusion:

A large proportion of anaplastic tumors might consist of heterogeneous CSC population. Curcumin and deguelin have anti-cancer and several anti-stem cell activities against ATC cells. These natural compounds are capable of altering the aggressive behavior of ATC cells through the inhibition of the CSC phenotype. As a novel therapeutic target, CD90 should be investigated in other ATC cell lines and in vivo models.