Biological and clinical significance of cancer stem cell plasticity

KK-LC-1 as a therapeutic target to eliminate ALDH+ stem cells in triple negative breast cancer

Failure to achieve complete elimination of triple negative breast cancer (TNBC) stem cells after adjuvant therapy is associated with poor outcomes. Aldehyde dehydrogenase 1 (ALDH1) is a marker of breast cancer stem cells (BCSCs), and its enzymatic activity regulates tumor stemness. Identifying upstream targets to control ALDH⁺ cells may facilitate TNBC tumor suppression. Here, we show that KK-LC-1 determines the stemness of TNBC ALDH⁺ cells via binding with FAT1 and subsequently promoting its ubiquitination and degradation. This compromises the Hippo pathway and leads to nuclear translocation of YAP1 and ALDH1A1 transcription. These findings identify the KK-LC-1-FAT1-Hippo-ALDH1A1 pathway in TNBC ALDH⁺ cells as a therapeutic target. To reverse the malignancy due to KK-LC-1 expression, we employ a computational approach and discover Z839878730 (Z8) as an small-molecule inhibitor which may disrupt KK-LC-1 and FAT1 binding. We demonstrate that Z8 suppresses TNBC tumor growth via a mechanism that reactivates the Hippo pathway and decreases TNBC ALDH⁺ cell stemness and viability.

LncRNA MORT (ZNF667-AS1) in Cancer-Is There a Possible Role in Gynecological Malignancies?

Gynecological cancers (GCs) are currently among the major threats to female health. Moreover, there are different histologic subtypes of these cancers, which are defined as ‘rare’ due to an annual incidence of <6 per 100,000 women. The majority of these tend to be associated with a poor prognosis. Long non-coding RNAs (lncRNAs) play a critical role in the normal development of organisms as well as in tumorigenesis. LncRNAs can be classified into tumor suppressor genes or oncogenes, depending on their function within the cellular context and the signaling pathways in which they are involved. These regulatory RNAs are potential therapeutic targets for cancer due to their tissue and tumor specificity. However, there still needs to be a deeper understanding of the mechanisms by which lncRNAs are involved in the regulation of numerous biological functions in humans, both in normal health and disease. The lncRNA Mortal Obligate RNA Transcript (MORT; alias ZNF667-AS1) has been identified as a tumor-related lncRNA. ZNF667-AS1 gene, located in the human chromosome region 19q13.43, has been shown to be silenced by DNA hypermethylation in several cancers. In this review, we report on the biological functions of ZNF667-AS1 from recent studies and describe the regulatory functions of ZNF667-AS1 in human disease, including cancer. Furthermore, we discuss the emerging insights into the potential role of ZNF667-AS1 as a biomarker and novel therapeutic target in cancer, including GCs (ovarian, cervical, and endometrial cancers).

Role of MALAT1 in gynecological cancers: Pathologic and therapeutic aspects

Gynecological cancers, including breast, ovarian, uterine, vaginal, cervical and vulvar cancers are among the major threats to modern life, particularly to female health. Long non-coding RNAs (lncRNAs) play critical roles in normal development of organisms, as well as the tumorigenesis process, and metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) is a large infrequently spliced lncRNA, which have been implicated in different gynecological cancers. MALAT1 is overexpressed in breast, ovarian, cervical and endometrial cancers, which initiates cancer progression by inducing changes in the expression of several anti-apoptotic and epithelial-to-mesenchymal transition-related genes. Targeting MALAT1 is an important strategy to combat gynecological cancers, and application of RNA-interference technology and chemotherapeutic process are crucial to target and minimize MALAT1 activity. The present review discusses the role of MALAT1 in gynecological cancers, and potential strategies to target this lncRNA to develop cancer therapeutics. However, further clinical studies are required to determine the prognostic potential of MALAT1 in gynecological cancers.

MATHEMATICAL CHARACTERIZATION OF HETEROGENEITY IN A CANCER STEM CELL DRIVEN TUMOR GROWTH MODEL WITH NONLINEAR SELF-RENEWAL

The detection, in a wide variety of cancer types, of a population of highly tumorigenic cells that exhibit self-renewal and multipotency, which are hallmarks of stem cells, has transformed the current view of tumor initiation, progression, and treatment. Here, we develop and analyze a mathematical model for tumor growth that is based on the current biological understanding of the processes that underlie cellular expansion under the hierarchical guidelines of the cancer stem cell (CSC) hypothesis. Important features of the model include (i) a nonlinear probability of CSC self-renewal that reflects the fact that this key type of stem cell division can be regulated by extrinsic and intrinsic chemical signaling as well as environmental (niche) constraints and (ii) an amplification factor that captures the transient amplifying divisions that are a defining characteristic of progenitor cells. We present a thorough mathematical analysis of the model and highlight the conditions required for tumors to evolve toward either bounded or exponential growth. Numerical simulations further illustrate the impact of the various parameters on the tumor growth rate and on the heterogeneous cellular composition, which varies during progression.

Nanomaterials for oncotherapies targeting the hallmarks of cancer

An increasing amount of evidence has demonstrated the diverse functionalities of nanomaterials in oncotherapies such as drug delivery, imaging, and killing cancer cells. This review aims to offer an authoritative guide for the development of nanomaterial-based oncotherapies and shed light on emerging yet understudied hallmarks of cancer where nanoparticles can help improve cancer control. With this aim, three nanomaterials, i.e. those based on gold, graphene, and liposome, were selected to represent and encompass metal inorganic, nonmetal inorganic, and organic nanomaterials, and four oncotherapies, i.e. phototherapies, immunotherapies, cancer stem cell therapies, and metabolic therapies, were characterized based on the differential hallmarks of cancer that they target. We also view physical plasma as a cocktail of reactive species and carrier of nanomaterials and focus on its roles in targeting the hallmarks of cancer provided with its unique traits and ability to selectively induce epigenetic and genetic modulations in cancer cells that halt tumor initiation and progression. This review provides a clear understanding of how the physico-chemical features of particles at the nanoscale contribute alone or create synergistic effects with current treatment modalities in combating each of the hallmarks of cancer that ultimately leads to desired therapeutic outcomes and shapes the toolbox for cancer control.

The issues with tissues: the wide range of cell fate separation enables the evolution of multicellularity and cancer

Our understanding of the rises of animal and cancer multicellularity face the same conceptual hurdles: what makes the clade originate and what makes it diversify. Between the events of origination and diversification lies complex tissue organization that gave rise to novel functionality for organisms and, unfortunately, for malignant transformation in cells. Tissue specialization with distinctly separated cell fates allowed novel functionality at organism level, such as for vertebrate animals, but also involved trade-offs at the cellular level that are potentially disruptive. These trade-offs are under-appreciated and here we discuss how the wide separation of cell phenotypes may contribute to cancer evolution by (a) how factors can reverse differentiated cells into a window of phenotypic plasticity, (b) the reversal to phenotypic plasticity coupled with asexual reproduction occurs in a way that the host cannot adapt, and (c) the power of the transformation factor correlates to the power needed to reverse tissue specialization. The role of reversed cell fate separation for cancer evolution is strengthened by how some tissues and organisms maintain high cell proliferation and plasticity without developing tumours at a corresponding rate. This demonstrates a potential proliferation paradox that requires further explanation. These insights from the cancer field, which observes tissue evolution in real time and closer than any other field, allow inferences to be made on evolutionary events in animal history. If a sweet spot of phenotypic and reproductive versatility is key to transformation, factors stimulating cell fate separation may have promoted also animal diversification on Earth.

Cell division symmetry control and cancer stem cells

Stem cells including cancer stem cells (CSC) divide symmetrically or asymmetrically. Usually symmetric cell division makes two daughter cells of the same fate, either as stem cells or more differentiated progenies; while asymmetric cell division (ACD) produces daughter cells of different fates. In this review, we first provide an overview of ACD, and then discuss more molecular details of ACD using the well-characterized Drosophila neuroblast system as an example. Aiming to explore the connections between cell heterogeneity in cancers and the critical need of ACD for self-renewal and generating cell diversity, we then examine how cell division symmetry control impacts common features associated with CSCs, including niche competition, cancer dormancy, drug resistance, epithelial-mesenchymal transition (EMT) and its reverse process mesenchymal-epithelial transition (MET), and cancer stem cell plasticity. As CSC may underlie resistance to therapy and cancer metastasis, understanding how cell division mode is selected and executed in these cells will provide possible strategies to target CSC.

A role for CBFβ in maintaining the metastatic phenotype of breast cancer cells

Epithelial to mesenchymal transition (EMT) is a dynamic process that drives cancer cell plasticity and is thought to play a major role in metastasis. Here we show, using MDA-MB-231 cells as a model, that the plasticity of at least some metastatic breast cancer cells is dependent on the transcriptional co-regulator CBFβ. We demonstrate that CBFβ is essential to maintain the mesenchymal phenotype of triple-negative breast cancer cells and that CBFβ-depleted cells undergo a mesenchymal to epithelial transition (MET) and re-organise into acini-like structures, reminiscent of those formed by epithelial breast cells. We subsequently show, using an inducible CBFβ system, that the MET can be reversed, thus demonstrating the plasticity of CBFβ-mediated EMT. Moreover, the MET can be reversed by expression of the EMT transcription factor Slug whose expression is dependent on CBFβ. Finally, we demonstrate that loss of CBFβ inhibits the ability of metastatic breast cancer cells to invade bone cell cultures and suppresses their ability to form bone metastases in vivo. Together our findings demonstrate that CBFβ can determine the plasticity of the metastatic cancer cell phenotype, suggesting that its regulation in different micro-environments may play a key role in the establishment of metastatic tumours.

In Silico Models Accurately Predict In Vivo Response for IL6 Blockade in Head and Neck Cancer

Malignant features of head and neck squamous cell carcinoma (HNSCC) may be derived from the presence of stem-like cells that are characterized by uniquely high tumorigenic potential. These cancer stem cells (CSC) function as putative drivers of tumor initiation, therapeutic evasion, metastasis, and recurrence. Although they are an appealing conceptual target, CSC-directed cancer therapies remain scarce. One promising CSC target is the IL6 pathway, which is strongly correlated with poor patient survival. In this study we created and validated a multiscale mathematical model to investigate the impact of cross-talk between tumor cell- and endothelial cell (EC)-secreted IL6 on HNSCC growth and the CSC fraction. We then predicted and analyzed the responses of HNSCC to tocilizumab (TCZ) and cisplatin combination therapy. The model was validated with in vivo experiments involving human ECs coimplanted with HNSCC cell line xenografts. Without artificial tuning to the laboratory data, the model showed excellent predictive agreement with the decrease in tumor volumes observed in TCZ-treated mice, as well as a decrease in the CSC fraction. This computational platform provides a framework for preclinical cisplatin and TCZ dose and frequency evaluation to be tested in future clinical studies. SIGNIFICANCE: A mathematical model is used to rapidly evaluate dosing strategies for IL6 pathway modulation. These results may lead to nonintuitive dosing or timing treatment schedules to optimize synergism between drugs.

Novel and Alternative Targets Against Breast Cancer Stemness to Combat Chemoresistance

Breast cancer stem cells (BCSCs) play a vital role in tumor progression and metastasis. They are heterogeneous and inherently radio- and chemoresistant. They have the ability to self-renew and differentiate into non-BCSCs. These determinants of BCSCs including the plasticity between the mesenchymal and epithelial phenotypes often leads to minimal residual disease (MRD), tumor relapse, and therapy failure. By studying the resistance mechanisms in BCSCs, a combinatorial therapy can be formulated to co-target BCSCs and bulk tumor cells. This review addresses breast cancer stemness and molecular underpinnings of how the cancer stemness can lead to pharmacological resistance. This might occur through rewiring of signaling pathways and modulated expression of various targets that support survival and self-renewal, clonogenicity, and multi-lineage differentiation into heterogeneous bulk tumor cells following chemotherapy. We explore emerging novel and alternative molecular targets against BC stemness and chemoresistance involving survival, drug efflux, metabolism, proliferation, cell migration, invasion, and metastasis. Strategic targeting of such vulnerabilities in BCSCs may overcome the chemoresistance and increase the longevity of the metastatic breast cancer patients.

Distinct biological characterization of the CD44 and CD90 phenotypes of cancer stem cells in gastric cancer cell lines

Recent study implicates that gastric cancer stem cells (CSCs) are capable of generating multiple types of cells to promote tumor growth and heterogeneity important for the development of gastric cancer. However, knowledge is limited regarding the expression and characteristics of marker-positive gastric CSCs. Therefore, gastric CSCs from a series of human gastric cancer cell lines (SNU-5, SNU-16, BGC-823, PAMC-82, MKN-45, and NCI-N87) using four putative CSC surface markers (CD44, CD90, CD133, and epithelial-cell adhesion molecule) were investigated the underlying mechanisms regulating such subpopulations. Only SNU-5 and SNU-16 exhibited independent co-expression of CD44⁺ and CD90⁺, which exhibited spheroid-colony formation in vitro and tumor formation in immunodeficient mice. Functional studies revealed that CD44⁺ cells were more invasive compared with CD90⁺ cells, whereas CD90⁺ cells exhibited higher levels of proliferation than CD44⁺ cells. Furthermore, serial xenotransplantation in mice of CD44⁺/CD90⁺ cells derived from SNU-5 and SNU-16 revealed rapid growth of CD90⁺ cells in subcutaneous lesions and a high metastatic capacity of CD44⁺ cells in the lung. Mechanistic analyses revealed that CD44⁺ cells underwent epithelial-to-mesenchymal transition (EMT) following acquisition of mesenchymal features, whereas CD90⁺ cells enhanced the activation of retinoblastoma phosphorylation at Ser780 and oncogenic cell cycle regulators. The expression of CD44 and CD90 in gastric cancer tissues was associated with distant metastasis and the differentiation state of tumors. These results demonstrated that CD44 and CD90 are specific biomarkers capable of identifying and isolating metastatic and tumorigenic CSCs through their ability to regulate EMT and the cell cycle in gastric cancer cell lines.

Targeting Cancer Stem Cell Redox Metabolism to Enhance Therapy Responses

Cancer has long been viewed as a disease of altered metabolism. Although it has long been recognized that the majority of cancer cells display increased dependence on glycolysis, the metabolism of "cancer stem-like cells" (CSCs) that drive tumor growth and metastasis is less well characterized. In this chapter, we review the current state of knowledge of CSC metabolism with an emphasis on the development of therapeutic strategies to exploit the metabolic vulnerabilities of these cells. We outline emerging evidence indicating distinct metabolic pathways active in the proliferative, epithelial- (E) and quiescent, mesenchymal-like (M) CSC states in triple negative breast cancer. These CSC states are characterized by their different redox potentials and divergent sensitivities to inhibitors of glycolysis and redox metabolism. We highlight the roles of two redox-regulated signaling pathways, hypoxia-inducible factor 1α and nuclear factor erythroid 2-related factor 2, in regulating CSC epithelial-mesenchymal plasticity during metabolic and/or oxidative stress, and discuss clinical strategies using combinations of pro-oxidant-based therapeutics simultaneously targeting E- and M-like CSCs. By specifically targeting CSCs of both states, these strategies have the potential to increase the therapeutic efficacy of traditional chemotherapy and radiation therapy.

TRIB3 Interacts With β-Catenin and TCF4 to Increase Stem Cell Features of Colorectal Cancer Stem Cells and Tumorigenesis

BACKGROUND & AIMS

Activation of Wnt signaling to β-catenin contributes to the development of colorectal cancer (CRC). Expression of tribbles pseudo-kinase 3 (TRIB3) is increased in some colorectal tumors and associated with poor outcome. We investigated whether increased TRIB3 expression promotes stem cell features of CRC cells and tumor progression by interacting with the Wnt signaling pathway.

METHODS

We performed studies with C57BL/6J-Apc^Min/J mice injected with an adeno-associated virus vector that expresses a small hairpin RNA against Trib3 mRNA (Apc^Min/J-Trib3^KD) or a control vector (Apc^Min/J-Ctrl). We created BALB/c mice that overexpress TRIB3 from an adeno-associated virus vector and mice with small hairpin RNA-mediated knockdown of β-catenin. The mice were given azoxymethane followed by dextran sodium sulfate to induce colitis-associated cancer. Intestinal tissues were collected and analyzed by histology, gene expression profiling, immunohistochemistry, and immunofluorescence. Leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5)-positive (LGR5^Pos) and LGR5-negative (LGR5^Neg) HCT-8 CRC cells, with or without knockdown or transgenic expression of TRIB3, were sorted and analyzed in sphere-formation assays. We derived organoids from human and mouse colorectal tumors to analyze the function of TRIB3 and test the effect of a peptide inhibitor. Wnt signaling to β-catenin was analyzed in dual luciferase reporter, chromatin precipitation, immunofluorescence, and immunoblot assays. Proteins that interact with TRIB3 were identified by immunoprecipitation. CRC cell lines were grown in nude mice as xenograft tumors.

RESULTS

At 10 weeks of age, more than half the Apc^Min/J-Ctrl mice developed intestinal high-grade epithelial neoplasia, whereas Apc^Min/J-Trib3^KD mice had no intestinal polyps and normal histology. Colon tissues from Apc^Min/J-Trib3^KD mice expressed lower levels of genes regulated by β-catenin and genes associated with cancer stem cells. Mice with overexpression of Trib3 developed more tumors after administration of azoxymethane and dextran sodium sulfate than BALB/c mice. Mice with knockdown of β-catenin had a lower tumor burden after administration of azoxymethane and dextran sodium sulfate, regardless of Trib3 overexpression. Intestinal tissues from mice with overexpression of Trib3 and knockdown of β-catenin did not have activation of Wnt signaling or expression of genes regulated by β-catenin. LGR5^Pos cells sorted from HCT-8 cells expressed higher levels of TRIB3 than LGR5^Neg cells. CRC cells that overexpressed TRIB3 had higher levels of transcription by β-catenin and formed larger spheroids than control CRC cells; knockdown of β-catenin prevented the larger organoid size caused by TRIB3 overexpression. TRIB3 interacted physically with β-catenin and transcription factor 4 (TCF4). TRIB3 overexpression increased, and TRIB3 knockdown decreased, recruitment of TCF4 and β-catenin to the promoter region of genes regulated by Wnt. Activated β-catenin increased expression of TRIB3, indicating a positive-feedback loop. A peptide (P2-T3A6) that bound β-catenin disrupted its interaction with TRIB3 and TCF4. In primary CRC cells and HCT-8 cells, P2-T3A6 decreased expression of genes regulated by β-catenin and genes associated with cancer stem cells and decreased cell viability and migration. Injection of C57BL/6J-Apc^Min/J mice with P2-T3A6 decreased the number and size of tumor nodules and colon expression of genes regulated by β-catenin. P2-T3A6 increased 5-fluorouracil-induced death of CRC cells and survival times of mice with xenograft tumors.

CONCLUSION

TRIB3 interacts with β-catenin and TCF4 in intestine cells to increase expression of genes associated with cancer stem cells. Knockdown of TRIB3 decreases colon neoplasia in mice, migration of CRC cells, and their growth as xenograft tumors in mice. Strategies to block TRIB3 activity might be developed for treatment of CRC.

Therapeutic implications of cancer epithelial-mesenchymal transition (EMT)

The epithelial-mesenchymal transition (EMT) comprises an essential biological process involving cancer progression as well as initiation. While the EMT has been regarded as a phenotypic conversion from epithelial to mesenchymal cells, recent evidence indicates that it plays a critical role in stemness, metabolic reprogramming, immune evasion and therapeutic resistance of cancer cells. Interestingly, several transcriptional repressors including Snail (SNAI1), Slug (SNAI2) and the ZEB family constitute key players for EMT in cancer as well as in the developmental process. Note that the dynamic conversion between EMT and epithelial reversion (mesenchymal-epithelial transition, MET) occurs through variable intermediate-hybrid states rather than being a binary process. Given the close connection between oncogenic signaling and EMT repressors, the EMT has emerged as a therapeutic target or goal (in terms of MET reversion) in cancer therapy. Here we review the critical role of EMT in therapeutic resistance and the importance of EMT as a therapeutic target for human cancer.

Novel and Alternative Targets Against Breast Cancer Stemness to Combat Chemoresistance

Breast cancer stem cells (BCSCs) play a vital role in tumor progression and metastasis. They are heterogeneous and inherently radio- and chemoresistant. They have the ability to self-renew and differentiate into non-BCSCs. These determinants of BCSCs including the plasticity between the mesenchymal and epithelial phenotypes often leads to minimal residual disease (MRD), tumor relapse, and therapy failure. By studying the resistance mechanisms in BCSCs, a combinatorial therapy can be formulated to co-target BCSCs and bulk tumor cells. This review addresses breast cancer stemness and molecular underpinnings of how the cancer stemness can lead to pharmacological resistance. This might occur through rewiring of signaling pathways and modulated expression of various targets that support survival and self-renewal, clonogenicity, and multi-lineage differentiation into heterogeneous bulk tumor cells following chemotherapy. We explore emerging novel and alternative molecular targets against BC stemness and chemoresistance involving survival, drug efflux, metabolism, proliferation, cell migration, invasion, and metastasis. Strategic targeting of such vulnerabilities in BCSCs may overcome the chemoresistance and increase the longevity of the metastatic breast cancer patients.

Targeting of the Eukaryotic Translation Initiation Factor 4A Against Breast Cancer Stemness

Breast cancer stem cells (BCSCs) are intrinsically chemoresistant and capable of self-renewal. Following chemotherapy, patients can develop minimal residual disease due to BCSCs which can repopulate into a relapsed tumor. Therefore, it is imperative to co-target BCSCs along with the bulk tumor cells to achieve therapeutic success and prevent recurrence. So, it is vital to identify actionable molecular targets against both BCSCs and bulk tumor cells. Previous findings from our lab and others have demonstrated that inhibition of the emerging drug target eIF4A with Rocaglamide A (RocA) was efficacious against triple-negative breast cancer cells (TNBC). RocA specifically targets the pool of eIF4A bound to the oncogenic mRNAs that requires its helicase activity for their translation. This property enables specific targeting of tumor cells. The efficacy of RocA against BCSCs is unknown. In this study, we postulated that eIF4A could be a vulnerable node in BCSCs. In order to test this, we generated a paclitaxel-resistant TNBC cell line which demonstrated an elevated level of eIF4A along with increased levels of cancer stemness markers (ALDH activity and CD44), pluripotency transcription factors (SOX2, OCT4, and NANOG) and drug transporters (ABCB1, ABCG2, and ABCC1). Furthermore, genetic ablation of eIF4A resulted in reduced expression of ALDH1A1, pluripotency transcription factors and drug transporters. This pointed out that eIF4A is likely associated with selected set of proteins that are critical to BCSCs, and hence targeting eIF4A may eliminate BCSCs. Therefore, we isolated BCSCs from two TNBC cell lines: MDA-Bone-Un and SUM-159PT. Following RocA treatment, the self-renewal ability of the BCSCs was significantly reduced as determined by the efficiency of the formation of primary and secondary mammospheres. This was accompanied by a reduction in the levels of NANOG, OCT4, and drug transporters. Exposure to RocA also induced cell death of the BCSCs as evaluated by DRAQ7 and cell viability assays. RocA treatment induced apoptosis with increased levels of cleaved caspase-3. Overall, we identified that RocA is effective in targeting BCSCs, and eIF4A is an actionable molecular target in both BCSCs and bulk tumor cells. Therefore, anti-eIF4A inhibitors could potentially be combined synergistically with existing chemo-, radio- and/or immunotherapies.

Targeting Breast Cancer Stem Cell State Equilibrium through Modulation of Redox Signaling

Although breast cancer stem cells (BCSCs) display plasticity transitioning between quiescent mesenchymal-like (M) and proliferative epithelial-like (E) states, how this plasticity is regulated by metabolic or oxidative stress remains poorly understood. Here, we show that M- and E-BCSCs rely on distinct metabolic pathways and display markedly different sensitivities to inhibitors of glycolysis and redox metabolism. Metabolic or oxidative stress generated by 2DG, H₂O₂, or hypoxia promotes the transition of ROS^lo M-BCSCs to a ROS^hi E-state. This transition is reversed by N-acetylcysteine and mediated by activation of the AMPK-HIF1α axis. Moreover, E-BCSCs exhibit robust NRF2-mediated antioxidant responses, rendering them vulnerable to ROS-induced differentiation and cytotoxicity following suppression of NRF2 or downstream thioredoxin (TXN) and glutathione (GSH) antioxidant pathways. Co-inhibition of glycolysis and TXN and GSH pathways suppresses tumor growth, tumor-initiating potential, and metastasis by eliminating both M- and E-BCSCs. Exploiting metabolic vulnerabilities of distinct BCSC states provides a novel therapeutic approach targeting this critical tumor cell population.

Human Endogenous Retrovirus K in the Crosstalk Between Cancer Cells Microenvironment and Plasticity: A New Perspective for Combination Therapy

Abnormal activation of human endogenous retroviruses (HERVs) has been associated with several diseases such as cancer, autoimmunity, and neurological disorders. In particular, in cancer HERV activity and expression have been specifically associated with tumor aggressiveness and patient outcomes. Cancer cell aggressiveness is intimately linked to the acquisition of peculiar plasticity and heterogeneity based on cell stemness features, as well as on the crosstalk between cancer cells and the microenvironment. The latter is a driving factor in the acquisition of aggressive phenotypes, associated with metastasis and resistance to conventional cancer therapies. Remarkably, in different cell types and stages of development, HERV expression is mainly regulated by epigenetic mechanisms and is subjected to a very precise temporal and spatial regulation according to the surrounding microenvironment. Focusing on our research experience with HERV-K involvement in the aggressiveness and plasticity of melanoma cells, this perspective aims to highlight the role of HERV-K in the crosstalk between cancer cells and the tumor microenvironment. The implications for a combination therapy targeted at HERVs with standard approaches are discussed.

Non-Coding RNAs and Resistance to Anticancer Drugs in Gastrointestinal Tumors

Non-coding RNAs are important regulators of gene expression and transcription. It is well established that impaired non-coding RNA expression especially the one of long non-coding RNAs and microRNAs is involved in a number of pathological conditions including cancer. Non-coding RNAs are responsible for the development of resistance to anticancer treatments as they regulate drug resistance-related genes, affect intracellular drug concentrations, induce alternative signaling pathways, alter drug efficiency via blocking cell cycle regulation, and DNA damage response. Furthermore, they can prevent therapeutic-induced cell death and promote epithelial-mesenchymal transition (EMT) and elicit non-cell autonomous mechanisms of resistance. In this review, we summarize the role of non-coding RNAs for different mechanisms resulting in drug resistance (e.g., drug transport, drug metabolism, cell cycle regulation, regulation of apoptotic pathways, cancer stem cells, and EMT) in the context of gastrointestinal cancers.

Tight Junction Protein Claudin-2 Promotes Self-Renewal of Human Colorectal Cancer Stem-like Cells

Posttreatment recurrence of colorectal cancer, the third most lethal cancer worldwide, is often driven by a subpopulation of cancer stem cells (CSC). The tight junction (TJ) protein claudin-2 is overexpressed in human colorectal cancer, where it enhances cell proliferation, colony formation, and chemoresistance in vitro While several of these biological processes are features of the CSC phenotype, a role for claudin-2 in the regulation of these has not been identified. Here, we report that elevated claudin-2 expression in stage II/III colorectal tumors is associated with poor recurrence-free survival following 5-fluorouracil-based chemotherapy, an outcome in which CSCs play an instrumental role. In patient-derived organoids, primary cells, and cell lines, claudin-2 promoted colorectal cancer self-renewal in vitro and in multiple mouse xenograft models. Claudin-2 enhanced self-renewal of ALDH^High CSCs and increased their proportion in colorectal cancer cell populations, limiting their differentiation and promoting the phenotypic transition of non-CSCs toward the ALDH^High phenotype. Next-generation sequencing in ALDH^High cells revealed that claudin-2 regulated expression of nine miRNAs known to control stem cell signaling. Among these, miR-222-3p was instrumental for the regulation of self-renewal by claudin-2, and enhancement of this self-renewal required activation of YAP, most likely upstream from miR-222-3p. Taken together, our results indicate that overexpression of claudin-2 promotes self-renewal within colorectal cancer stem-like cells, suggesting a potential role for this protein as a therapeutic target in colorectal cancer.Significance: Claudin-2-mediated regulation of YAP activity and miR-222-3p expression drives CSC renewal in colorectal cancer, making it a potential target for therapy. Cancer Res; 78(11); 2925-38. ©2018 AACR.

Long Non Coding RNA Expression Intersecting Cancer and Spermatogenesis: A Systematic Review

Background: Numerous similarities have been noted between gametogenic and tumorigenic programs in features such as global hypomethylation, immune evasion, immortalization, meiosis induction, and migration. In addition, aberrant expression of testis specific genes has been detected in various cancers which has led to categorization of these genes as “cancer-testis genes”. Most of the examples identified in this category are protein encoding. However, recent studies have revealed that non-coding RNAs, including long non coding RNAs (lncRNAs), may have essential regulatory roles in telomere biology, chromatin dynamics, modulation of gene expression and genome structural organization. All of these functions are implicated in both gametogenic and tumorigenic programs. Methods: In the present study, we conducted a computerized search of the MEDLINE/PUBMED and Embase databases with the key words lncRNA, gametogenesis, testis and cancer. Results: We found a number of lncRNAs with essential roles and notable expression in both gametogenic and cancer tissues. Conclusions: Comparison between cancer tissues and gametogenic tissues has shown that numerous lncRNAs are expressed in both, playing similar roles in processes modulated by signaling pathways such as Wnt/β-catenin and PI3K/AKT/mTOR. Evaluation of expression patterns and functions of these genes should pave the way to discovery of biomarkers for early detection, prognostic assessment and evaluation of therapeutic responses in cancers.

Nano Let‑7b sensitization of eliminating esophageal cancer stem‑like cells is dependent on blockade of Wnt activation of symmetric division

The poor therapy response and poor prognosis of esophageal cancer has made it one of the most malignant carcinoma, and the complicated multidisciplinary treatment failed to achieve a long-term disease-free survival. To diagnose esophageal cancer at an earlier stage, and to improve the effect of anticancer therapy would improve the therapeutic efficacy. After retrospective analysis of the cancer samples of patients who received esophagectomy, we found the relevance between ratio of either ALDH1 or CD133-positive cancer stem cells and 2-year recurrence. Higher ratios of cancer stem cells indicated later clinical stages, and Wnt signaling activation was more frequent in later esophageal carcinoma. Further in bench studies, we explored the suppressive roles and the mechanisms involved in Let‑7 on self-renewal in ECA‑109 and ECA‑9706 esophageal cancer stem cells. Isolated cancer stem cells naturally divide symmetrically and are therapy resistant. Therapy of fluorouracil and docetaxel both enriched the stem cells, proving the resistant characteristics of cancer stem cells. Wnt activation stimulated more symmetric division of stem cells, resulting in self-renewal promotion, which could be blocked by Let‑7 overexpression. Furthermore, enforced Let‑7 sensitized the stem cells to chemotherapies in a Wnt pathway inhibition-dependent manner, contributing to Let‑7 sensitization of chemotherapeutic response. Wnt activation weakened the suppressive Let‑7b through the sponge functions of CCAT-1, forming the negative feedback loop of Let‑7b/Wnt/CCAT1. These results identified the crucial participation of stem cells in esophageal cancer occurrence and progression as the potent indicator, and also indicate the potential powerful agent of Let‑7 nano-particles in treatment of cancer.

Long non-coding RNA CCAT1/miR-218/ZFX axis modulates the progression of laryngeal squamous cell cancer

Long non-coding RNAs have been proved to be closely associated with different cancers. This study was designed to elucidate the function and mechanisms of colon cancer-associated transcript-1 in the progression of human laryngeal squamous cell cancer. Expressions of colon cancer-associated transcript-1, microRNA-218, and zinc finger protein, X-linked messenger RNA were measured using quantitative real-time polymerase chain reaction, and the expression level of zinc finger protein, X-linked protein was detected using western blot. Proliferation and invasion of laryngeal squamous cell cancer cell lines were detected by Cell Counting Kit-8 assay and Transwell invasion assay, respectively. Luciferase assay was used to confirm whether microRNA-218 is a target of colon cancer-associated transcript-1 and whether microRNA-218 directly binds to 3'-untranslated region of zinc finger protein, X-linked messenger RNA. Effect of colon cancer-associated transcript-1 on tumor growth was observed through xenograft mice models in vivo. The results showed that expressions of colon cancer-associated transcript-1 and zinc finger protein, X-linked were significantly higher while microRNA-218 expression was significantly lower in the laryngeal squamous cell cancer tissues than those in the adjacent normal tissues. MicroRNA-218 overexpression or zinc finger protein, X-linked silencing significantly suppressed proliferation and invasion of laryngeal squamous cell cancer cells. Moreover, knockdown of colon cancer-associated transcript-1 significantly inhibited proliferation and invasion of laryngeal squamous cell cancer cells, which were reversed by microRNA-218 downregulation or zinc finger protein, X-linked upregulation. Finally, colon cancer-associated transcript-1 silencing inhibited xenograft tumor growth of laryngeal squamous cell cancer in vivo. In conclusion, colon cancer-associated transcript-1 knockdown inhibits proliferation and invasion of laryngeal squamous cell cancer cells through enhancing zinc finger protein, X-linked by sponging microRNA-218, elucidating a novel colon cancer-associated transcript-1-microRNA-218-zinc finger protein, X-linked regulatory axis in laryngeal squamous cell cancer and providing a promising therapeutic target for laryngeal squamous cell cancer patients.

Down-regulation of LncRNA TUG1 enhances radiosensitivity in bladder cancer via suppressing HMGB1 expression

Background

Long non-coding RNAs (lncRNAs) have been reported to regulate the sensitivity of different cancer cells to chemoradiotherapy. Aberrant expression of lncRNA Taurine-upregulated gene 1 (TUG1) has been found to be involved in the development of bladder cancer, however, its function and underlying mechanism in the radioresistance of bladder cancer remains unclear.

Methods

Quantitative real-time PCR (qRT-PCR) was conducted to measure the expression of TUG1 and HMGB1 mRNA in bladder cancer tissues and cell lines. HMGB1 protein levels were tested by western blot assays. Different doses of X-ray were used for radiation treatment of bladder cancer cells. Colony survival and cell viability were detected by clonogenic assay and CCK-8 Kit, respectively. Cell apoptosis was determined by flow cytometry. A xenograft mouse model was constructed to observe the effect of TUG1 on tumor growth in vivo.

Results

The levels of TUG1 and HMGB1 were remarkably increased in bladder cancer tissues and cell lines. Radiation treatment markedly elevated the expression of TUG1 and HMGB1. TUG1 knockdown inhibited cell proliferation, promoted cell apoptosis and decreased colony survival in SW780 and BIU87 cells under radiation. Moreover, TUG1 depletion suppressed the HMGB1 mRNA and protein levels. Furthermore, overexpression of HMGB1 reversed TUG1 knockdown-induced effect in bladder cancer cells. Radiation treatment dramatically reduced the tumor volume and weight in xenograft model, and this effect was more obvious when combined with TUG1 silencing.

Conclusion

LncRNA TUG1 knockdown enhances radiosensitivity of bladder cancer by suppressing HMGB1 expression. TUG1 acts as a potential regulator of radioresistance of bladder cancer, and it may represent a promising therapeutic target for bladder cancer patients.

Induction of metastasis, cancer stem cell phenotype, and oncogenic metabolism in cancer cells by ionizing radiation

Radiation therapy is one of the major tools of cancer treatment, and is widely used for a variety of malignant tumours. Radiotherapy causes DNA damage directly by ionization or indirectly via the generation of reactive oxygen species (ROS), thereby destroying cancer cells. However, ionizing radiation (IR) paradoxically promotes metastasis and invasion of cancer cells by inducing the epithelial-mesenchymal transition (EMT). Metastasis is a major obstacle to successful cancer therapy, and is closely linked to the rates of morbidity and mortality of many cancers. ROS have been shown to play important roles in mediating the biological effects of IR. ROS have been implicated in IR-induced EMT, via activation of several EMT transcription factors—including Snail, HIF-1, ZEB1, and STAT3—that are activated by signalling pathways, including those of TGF-β, Wnt, Hedgehog, Notch, G-CSF, EGFR/PI3K/Akt, and MAPK. Cancer cells that undergo EMT have been shown to acquire stemness and undergo metabolic changes, although these points are debated. IR is known to induce cancer stem cell (CSC) properties, including dedifferentiation and self-renewal, and to promote oncogenic metabolism by activating these EMT-inducing pathways. Much accumulated evidence has shown that metabolic alterations in cancer cells are closely associated with the EMT and CSC phenotypes; specifically, the IR-induced oncogenic metabolism seems to be required for acquisition of the EMT and CSC phenotypes. IR can also elicit various changes in the tumour microenvironment (TME) that may affect invasion and metastasis. EMT, CSC, and oncogenic metabolism are involved in radioresistance; targeting them may improve the efficacy of radiotherapy, preventing tumour recurrence and metastasis. This study focuses on the molecular mechanisms of IR-induced EMT, CSCs, oncogenic metabolism, and alterations in the TME. We discuss how IR-induced EMT/CSC/oncogenic metabolism may promote resistance to radiotherapy; we also review efforts to develop therapeutic approaches to eliminate these IR-induced adverse effects.

Gene mutation-based and specific therapies in precision medicine

Precision medicine has been initiated and gains more and more attention from preclinical and clinical scientists. A number of key elements or critical parts in precision medicine have been described and emphasized to establish a systems understanding of precision medicine. The principle of precision medicine is to treat patients on the basis of genetic alterations after gene mutations are identified, although questions and challenges still remain before clinical application. Therapeutic strategies of precision medicine should be considered according to gene mutation, after biological and functional mechanisms of mutated gene expression or epigenetics, or the correspondent protein, are clearly validated. It is time to explore and develop a strategy to target and correct mutated genes by direct elimination, restoration, correction or repair of mutated sequences/genes. Nevertheless, there are still numerous challenges to integrating widespread genomic testing into individual cancer therapies and into decision making for one or another treatment. There are wide‐ranging and complex issues to be solved before precision medicine becomes clinical reality. Thus, the precision medicine can be considered as an extension and part of clinical and translational medicine, a new alternative of clinical therapies and strategies, and have an important impact on disease cures and patient prognoses.

Regulatory roles of epigenetic modulators, modifiers and mediators in lung cancer

Lung cancer as the leading cause of cancer-related deaths can be initiated and progressed by the interaction between dynamically genetic and epigenetic elements, although mechanisms mediating lung cancer development and progression remain unclear. Tumor progenitor genes may contribute to lung carcinogenesis and cancer progression, are epigenetically disrupted at the early stages of malignancies even before mutations, and alter cell differentiation throughout tumor evolution. The present review explores potential roles and mechanisms of epigenetic modulators, modifiers and mediators in the development of lung cancer. We also overviewed potential mechanisms by which epigenetic modulators, modifiers and mediators control and regulate 3D nuclear architectures, and discussed translational efforts to epigenetic modifications for treatment of lung cancer. Deep understanding of epigenetic modulators, modifiers and mediators will benefit the discovery and development of new diagnostics and therapies for lung cancer.

Characterization of Biomarkers of Tumorigenic and Chemoresistant Cancer Stem Cells in Human Gastric Carcinoma

Purpose: Gastric carcinomas are heterogeneous, and the current therapy remains essentially based on surgery with conventional chemotherapy and radiotherapy. This study aimed to characterize biomarkers allowing the detection of cancer stem cells (CSC) in human gastric carcinoma of different histologic types.Experimental Design: The primary tumors from 37 patients with intestinal- or diffuse-type noncardia gastric carcinoma were studied, and patient-derived tumor xenograft (PDX) models in immunodeficient mice were developed. The expressions of 10 putative cell surface markers of CSCs, as well as aldehyde dehydrogenase (ALDH) activity, were studied, and the tumorigenic properties of cells were evaluated by in vitro tumorsphere assays and in vivo xenografts by limiting dilution assays.Results: We found that a subpopulation of gastric carcinoma cells expressing EPCAM, CD133, CD166, CD44, and a high ALDH activity presented the properties to generate new heterogeneous tumorspheres in vitro and tumors in vivo CD44 and CD166 were coexpressed, representing 6.1% to 37.5% of the cells; ALDH activity was detected in 1.6% to 15.4% of the cells; and the ALDH⁺ cells represented a core within the CD44⁺/CD166⁺ subpopulation that contained the highest frequency of tumorigenic CSCs in vivo The ALDH⁺ cells possessed drug efflux properties and were more resistant to standard chemotherapy than the ALDH^- cells, a process that was partially reversed by verapamil treatment.Conclusions: CD44 and ALDH are the most specific biomarkers to detect and isolate tumorigenic and chemoresistant gastric CSCs in noncardia gastric carcinomas independently of the histologic classification of the tumor. Clin Cancer Res; 23(6); 1586-97. ©2016 AACR.

Gene heterogeneity in metastasis of colorectal cancer to the lung

Colorectal cancer (CRC) as a heterogeneous disease, is one of the most common and serious cancers with high metastases and mortality. Lung is one of the most common sites of CRC metastases with high heterogeneity between cells, pathways, or molecules. The present review will focus on potential roles of gene heterogeneity in KRAS pathway in the development of CRC metastasis to lung and clinical therapies, which would lead to better understanding of the metastatic control and benefit to the treatment of metastases. KRAS is the central relay for pathways originating at the epidermal growth factor receptor (EGFR) family. KRAS mutation exists in about 40% CRC, associated with higher cumulative incidence of CRC lung metastasis, and acts as an independent predictor of metastasis to lung. Mutations in KRAS can lead to poor response of patients to panitumumab, and inferior progression-free survival. However, most patients with KRAS wild-type tumors still do not respond, which indicates other mutations. Phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) mutation was associated with lung metastases in metastatic colorectal cancer. PIK3CA mutation in exon 20 was found to be correlated with patient survival in the metastatic setting after the treatment with cetuximab and chemotherapy. The heterogeneity of KRAS pathway was found in the phosphatase and tensin homologue deleted on chromosome ten loss, disheveled binding antagonist of beta catenin 2 overexpression and increased dual-specificity protein phosphatase 4 expression of CRC lung metastasis.