The biological kinship of hypoxia with CSC and EMT and their relationship with deregulated expression of miRNAs and tumor aggressiveness

Hypoxia-induced epigenetic regulation of breast cancer progression and the tumour microenvironment

The events that control breast cancer progression and metastasis are complex and intertwined. Hypoxia plays a key role both in oncogenic transformation and in fueling the metastatic potential of breast cancer cells. Here we review the impact of hypoxia on epigenetic regulation of breast cancer, by interfering with multiple aspects of the tumour microenvironment. The co-dependent relationship between oxygen depletion and metabolic shift to aerobic glycolysis impacts on a range of enzymes and metabolites available in the cell, promoting posttranslational modifications of histones and chromatin, and changing the gene expression landscape to facilitate tumour development. Hormone signalling, particularly through ERα, is also tightly regulated by hypoxic exposure, with HIF-1α expression being a prognostic marker for therapeutic resistance in ER+ breast cancers. This highlights the strong need to understand the hypoxia-endocrine signalling axis and exploit it as a therapeutic target. Furthermore, hypoxia has been shown to enhance metastasis in TNBC cells, as well as promoting resistance to taxanes, radiotherapy and even immunotherapy through microRNA regulation and changes in histone packaging. Finally, several other mediators of the hypoxic response are discussed. We highlight a link between ionic dysregulation and hypoxia signalling, indicating a potential connection between HIF-1α and tumoural Na+ accumulation which would be worth further exploration; we present the role of Ca2+ in mediating hypoxic adaptation via chromatin remodelling, transcription factor recruitment and changes in signalling pathways; and we briefly summarise some of the findings regarding vesicle secretion and paracrine induced epigenetic reprogramming upon hypoxic exposure in breast cancer. By summarising these observations, this article highlights the heterogeneity of breast cancers, presenting a series of pathways with potential for therapeutic applications.

Reconstruction of single-cell lineage trajectories and identification of diversity in fates during the epithelial-to-mesenchymal transition

Exploring the complexity of the epithelial-to-mesenchymal transition (EMT) unveils a diversity of potential cell fates; however, the exact timing and mechanisms by which early cell states diverge into distinct EMT trajectories remain unclear. Studying these EMT trajectories through single-cell RNA sequencing is challenging due to the necessity of sacrificing cells for each measurement. In this study, we employed optimal-transport analysis to reconstruct the past trajectories of different cell fates during TGF-beta-induced EMT in the MCF10A cell line. Our analysis revealed three distinct trajectories leading to low EMT, partial EMT, and high EMT states. Cells along the partial EMT trajectory showed substantial variations in the EMT signature and exhibited pronounced stemness. Throughout this EMT trajectory, we observed a consistent downregulation of the EED and EZH2 genes. This finding was validated by recent inhibitor screens of EMT regulators and CRISPR screen studies. Moreover, we applied our analysis of early-phase differential gene expression to gene sets associated with stemness and proliferation, pinpointing ITGB4, LAMA3, and LAMB3 as genes differentially expressed in the initial stages of the partial versus high EMT trajectories. We also found that CENPF, CKS1B, and MKI67 showed significant upregulation in the high EMT trajectory. While the first group of genes aligns with findings from previous studies, our work uniquely pinpoints the precise timing of these upregulations. Finally, the identification of the latter group of genes sheds light on potential cell cycle targets for modulating EMT trajectories.

Polyploid giant cancer cells: origin, possible pathways of formation, characteristics, and mechanisms of regulation

Polyploid giant cancer cells (PGCCs) are characterized by the presence of either a single enlarged nucleus or multiple nuclei and are closely associated with tumor progression and treatment resistance. These cells contribute significantly to cellular heterogeneity and can arise from various stressors, including radiation, chemotherapy, hypoxia, and environmental factors. The formation of PGCCs can occur through mechanisms such as endoreplication, cell fusion, cytokinesis failure, mitotic slippage, or cell cannibalism. Notably, PGCCs exhibit traits similar to cancer stem cells (CSCs) and generate highly invasive progeny through asymmetric division. The presence of PGCCs and their progeny is pivotal in conferring resistance to chemotherapy and radiation, as well as facilitating tumor recurrence and metastasis. This review provides a comprehensive analysis of the origins, potential formation mechanisms, stressors, unique characteristics, and regulatory pathways of PGCCs, alongside therapeutic strategies targeting these cells. The objective is to enhance the understanding of PGCC initiation and progression, offering novel insights into tumor biology.

Hypoxia-inducible factor in breast cancer: role and target for breast cancer treatment

Globally, breast cancer stands as the most prevalent form of cancer among women. The tumor microenvironment of breast cancer often exhibits hypoxia. Hypoxia-inducible factor 1-alpha, a transcription factor, is found to be overexpressed and activated in breast cancer, playing a pivotal role in the anoxic microenvironment by mediating a series of reactions. Hypoxia-inducible factor 1-alpha is involved in regulating downstream pathways and target genes, which are crucial in hypoxic conditions, including glycolysis, angiogenesis, and metastasis. These processes significantly contribute to breast cancer progression by managing cancer-related activities linked to tumor invasion, metastasis, immune evasion, and drug resistance, resulting in poor prognosis for patients. Consequently, there is a significant interest in Hypoxia-inducible factor 1-alpha as a potential target for cancer therapy. Presently, research on drugs targeting Hypoxia-inducible factor 1-alpha is predominantly in the preclinical phase, highlighting the need for an in-depth understanding of HIF-1α and its regulatory pathway. It is anticipated that the future will see the introduction of effective HIF-1α inhibitors into clinical trials, offering new hope for breast cancer patients. Therefore, this review focuses on the structure and function of HIF-1α, its role in advancing breast cancer, and strategies to combat HIF-1α-dependent drug resistance, underlining its therapeutic potential.

Three-Dimensional Tumor Models to Study Cancer Stemness-Mediated Drug Resistance

Solid tumors often contain genetically different populations of cancer cells, stromal cells, various structural and soluble proteins, and other soluble signaling molecules. The American Cancer society estimated 1,958,310 new cancer cases and 609,820 cancer deaths in the United States in 2023. A major barrier against successful treatment of cancer patients is drug resistance. Gain of stem cell-like states by cancer cells under drug pressure or due to interactions with the tumor microenvironment is a major mechanism that renders therapies ineffective. Identifying approaches to target cancer stem cells is expected to improve treatment outcomes for patients. Most of our understanding of drug resistance and the role of cancer stemness is from monolayer cell cultures. Recent advances in cell culture technologies have enabled developing sophisticated three-dimensional tumor models that facilitate mechanistic studies of cancer drug resistance. This review summarizes the role of cancer stemness in drug resistance and highlights the various tumor models that are used to discover the underlying mechanisms and test potentially novel therapeutics.

Epigenetic alterations fuel brain metastasis via regulating inflammatory cascade

Brain metastasis (BrM) is a major threat to the survival of melanoma, breast, and lung cancer patients. Circulating tumor cells (CTCs) cross the blood-brain barrier (BBB) and sustain in the brain microenvironment. Genetic mutations and epigenetic modifications have been found to be critical in controlling key aspects of cancer metastasis. Metastasizing cells confront inflammation and gradually adapt in the unique brain microenvironment. Currently, it is one of the major areas that has gained momentum. Researchers are interested in the factors that modulate neuroinflammation during BrM. We review here various epigenetic factors and mechanisms modulating neuroinflammation and how this helps CTCs to adapt and survive in the brain microenvironment. Since epigenetic changes could be modulated by targeting enzymes such as histone/DNA methyltransferase, deacetylases, acetyltransferases, and demethylases, we also summarize our current understanding of potential drugs targeting various aspects of epigenetic regulation in BrM.

Challenging the anticolorectal cancer capacity of quinoxaline-based scaffold via triazole ligation unveiled new efficient dual VEGFR-2/MAO-B inhibitors

Monoamine oxidases (MAOs) and vascular endothelial growth factor receptor-2 (VEGFR-2) are promoters of colorectal cancer (CRC) and central signaling nodes in epithelial-mesenchymal transition (EMT) induced by activating hypoxia-inducible factors (HIFs). Herein, a novel series of rationally designed triazole-tethered quinoxalines were synthesized and evaluated against HCT-116 CRC cells. The tailored scaffolds combine the pharmacophoric themes of both VEGFR-2 inhibitors and MAO inhibitors. All the synthesized derivatives were screened utilizing the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay for their possible cytotoxic effects on normal human colonocytes, then evaluated for their anticancer activities against HCT-116 cells overexpressing MAOs. The hit derivatives 11 and 14 exhibited IC50 = 18.04 and 7.850 µM, respectively, against HCT-116cells within their EC100 doses on normal human colonocytes. Wound healing assay revealed their efficient CRC antimetastatic activities recording HCT-116 cell migration inhibition exceeding 75 %. In vitro enzymatic assays demonstrated that both 11 and 14 efficiently inhibited VEGFR-2 (IC50 = 88.79 and 9.910 nM), MAO-A (IC50 = 0.763 and 629.1 nM) and MAO-B (IC50 = 0.488 and 209.6 nM) with observed MAO-B over MAO-A selectivity (SI = 1.546 and 3.001), respectively. Enzyme kinetics studies were performed for both compounds to identify their mode of MAO-B inhibition. Furthermore, qRT-PCR analysis showed that the hits efficiently downregulated HIF-1α in HCT-116cells by 3.420 and 16.96 folds relative to untreated cells. Docking studies simulated their possible binding modes within the active sites of VEGFR-2 and MAO-B to highlight their essential structural determinants of activities. Finally, they recorded in silico drug-like absorption, distribution, metabolism, excretion, and toxicity (ADMET) profiles as well as ligand efficiency metrics.

Cancer Stem Cells in Carcinogenesis and Potential Role in Pancreatic Cancer

A poor prognosis is associated with pancreatic cancer because of resistance during treatment and early distant metastases. The discovery of cancer stem cells has opened up novel avenues for research into the biology and treatment of cancer. Many investigations have pointed out the role of these types of stem cells in the oncogenesis and progression of hematologic and solid malignancies, specifically. Due to the existence of cancer stem cells in the proliferation and preservation of pancreatic tumors, such malignancies could be difficult to eradicate using conventional treatment techniques like chemotherapy and radiotherapy. It is hypothesized that pancreatic malignancies originate from a limited population of aberrant cancer stem cells to promote carcinogenesis, tumour metastasis, and therapeutic resistance. This review examines the role of pancreatic cancer stem cells in this disease and their significance in carcinogenesis, as well as the signals which modulate them, and also examines the ongoing clinical studies that are now being conducted with pancreatic stem cells.

AXL is required for hypoxia-mediated hypoxia-inducible factor-1 alpha function in glioblastoma

Glioblastoma (GBM) is the most aggressive type of central nervous system tumor. Molecular targeting may be important when developing efficient GBM treatment strategies. Sequencing of GBMs revealed that the receptor tyrosine kinase (RTK)/RAS/phosphatidylinositol-3-kinase pathway was altered in 88% of samples. Interestingly, AXL, a member of RTK, was proposed as a promising target in glioma therapy. However, the molecular mechanism of AXL modulation of GBM genesis and proliferation is still unclear. In this study, we investigated the expression and localization of hypoxia-inducible factor-1 alpha (HIF-1α) by AXL in GBM. Both AXL mRNA and protein are overexpressed in GBM. Short-interfering RNA knockdown of AXL in U251-MG cells reduced viability and migration. However, serum withdrawal reduced AXL expression, abolishing the effect on viability. AXL is also involved in hypoxia regulation. In hypoxic conditions, the reduction of AXL decreased the level and nuclear localization of HIF-1α. The co-expression of HIF-1α and AXL was found in human GBM samples but not normal tissue. This finding suggests a mechanism for GBM proliferation and indicates that targeting AXL may be a potential GBM therapeutic.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-023-00195-z.

Molecular Mechanisms of Tumor Cell Stemness Modulation during Formation of Spheroids

Cancer stem cells (CSCs), their properties and interaction with microenvironment are of interest in modern medicine and biology. There are many studies on the emergence of CSCs and their involvement in tumor pathogenesis. The most important property inherent to CSCs is their stemness. Stemness combines ability of the cell to maintain its pluripotency, give rise to differentiated cells, and interact with environment to maintain a balance between dormancy, proliferation, and regeneration. While adult stem cells exhibit these properties by participating in tissue homeostasis, CSCs behave as their malignant equivalents. High tumor resistance to therapy, ability to differentiate, activate angiogenesis and metastasis arise precisely due to the stemness of CSCs. These cells can be used as a target for therapy of different types of cancer. Laboratory models are needed to study cancer biology and find new therapeutic strategies. A promising direction is three-dimensional tumor models or spheroids. Such models exhibit properties resembling stemness in a natural tumor. By modifying spheroids, it becomes possible to investigate the effect of therapy on CSCs, thus contributing to the development of anti-tumor drug test systems. The review examines the niche of CSCs, the possibility of their study using three-dimensional spheroids, and existing markers for assessing stemness of CSCs.

Interleukin-6 and Hypoxia Synergistically Promote EMT-Mediated Invasion in Epithelial Ovarian Cancer via the IL-6/STAT3/HIF-1α Feedback Loop

Extensive peritoneal spread and capacity for distant metastasis account for the majority of mortality from epithelial ovarian cancer (EOC). Accumulating evidence shows that interleukin-6 (IL-6) promotes tumor invasion and migration in EOC, although the molecular mechanisms remain to be fully elucidated. Meanwhile, the hypoxic microenvironment has been recognized to cause metastasis by triggering epithelial-mesenchymal transition (EMT) in several types of cancers. Here, we studied the synergy between IL-6 and hypoxia in inducing EMT in two EOC cell lines, A2780 cells and SKOV3 cells. Exogenous recombination of IL-6 and autocrine production of IL-6 regulated by plasmids both induced EMT phenotype in EOC cells characterized by downregulated E-cadherin as well as upregulated expression of vimentin and EMT-related transcription factors. The combined effects of IL-6 and hypoxia were more significant than those of either one treatment on EMT. Suppression of hypoxia-inducible factor-1α (HIF-1α) before IL-6 treatment inhibited the EMT phenotype and invasion ability of EOC cells, indicating that HIF-1α occupies a key position in the regulatory pathway of EMT associated with IL-6. EMT score was found positively correlated with mRNA levels of IL-6, signal transducer and activator of transcription 3 (STAT3), and HIF-1α, respectively, in 489 ovarian samples from The Cancer Genome Atlas dataset. Next, blockade of the abovementioned molecules by chemical inhibitors reversed the alteration in the protein levels of EMT markers induced by either exogenous or endogenous IL-6. These findings indicate a positive feedback loop between IL-6 and HIF-1α, and induce and maintain EMT phenotype through STAT3 signaling, which might provide a novel rationale for prognostic prediction and therapeutic targets in EOC.

Role of HIF-1α in pathogenic mechanisms of keloids

BACKGROUDS AND OBJECTIVE

Keloids are defined as overrepairing products that develop after skin lesions. Keloids are characterized by the proliferation of fibroblasts and the overaccumulation of extracellular matrix components (mainly collagen), leading to a locally hypoxic microenvironment. Hence, this article was aimed to review hypoxia in pathogenesis of keloids.

METHODS

We reviewed and summarized the relevant published studies.

RESULTS

Hypoxia results in the accumulation of hypoxia-inducible factor 1α (HIF-1α) in keloids, contributing to overactivation of the fibrotic signaling pathway, epithelial-mesenchymal transition, and changes in metabolism, eventually leading to aggravated fibrosis, infiltrative growth, and radiotherapy resistance.

CONCLUSION

It is, therefore, essential to understand the role of HIF-1α in the pathogenic mechanisms of keloids in order to develop new therapeutic approaches.

Kalkitoxin: A Potent Suppressor of Distant Breast Cancer Metastasis

Bone metastasis resulting from advanced breast cancer causes osteolysis and increases mortality in patients. Kalkitoxin (KT), a lipopeptide toxin derived from the marine cyanobacterium Moorena producens (previously Lyngbya majuscula), has an anti-metastatic effect on cancer cells. We verified that KT suppressed cancer cell migration and invasion in vitro and in animal models in the present study. We confirmed that KT suppressed osteoclast-soup-derived MDA-MB-231 cell invasion in vitro and induced osteolysis in a mouse model, possibly enhancing/inhibiting metastasis markers. Furthermore, KT inhibits CXCL5 and CXCR2 expression, suppressing the secondary growth of breast cancer cells on the bone, brain, and lungs. The breast-cancer-induced osteolysis in the mouse model further reveals that KT plays a protective role, judging by micro-computed tomography and immunohistochemistry. We report for the first time the novel suppressive effects of KT on cancer cell migration and invasion in vitro and on MDA-MB-231-induced bone loss in vivo. These results suggest that KT may be a potential therapeutic drug for the treatment of breast cancer metastasis.

Targeting hypoxia-inducible factors for breast cancer therapy: A narrative review

Hypoxia-inducible factors (HIFs), central regulators for cells to adapt to low cellular oxygen levels, are often overexpressed and activated in breast cancer. HIFs modulate the primary transcriptional response of downstream pathways and target genes in response to hypoxia, including glycolysis, angiogenesis and metastasis. They can promote the development of breast cancer and are associated with poor prognosis of breast cancer patients by regulating cancer processes closely related to tumor invasion, metastasis and drug resistance. Thus, specific targeting of HIFs may improve the efficiency of cancer therapy. In this review, we summarize the advances in HIF-related molecular mechanisms and clinical and preclinical studies of drugs targeting HIFs in breast cancer. Given the rapid progression in this field and nanotechnology, drug delivery systems (DDSs) for HIF targeting are increasingly being developed. Therefore, we highlight the HIF related DDS, including liposomes, polymers, metal-based or carbon-based nanoparticles.

Hypoxia-Regulated Tumor-Derived Exosomes and Tumor Progression: A Focus on Immune Evasion

Tumor cells express a high quantity of exosomes packaged with unique cargos under hypoxia, an important characteristic feature in solid tumors. These hypoxic tumor-derived exosomes are, crucially, involved in the interaction of cancer cells with their microenvironment, facilitating not only immune evasion, but increased cell growth and survival, enhanced angiogenesis, epithelial–mesenchymal transition (EMT), therapeutic resistance, autophagy, pre-metastasis, and metastasis. This paper explores the tumor microenvironment (TME) remodeling effects of hypoxic tumor-derived exosome towards facilitating the tumor progression process, particularly, the modulatory role of these factors on tumor cell immune evasion through suppression of immune cells, expression of surface recognition molecules, and secretion of antitumor soluble factor. Tumor-expressed exosomes educate immune effector cells, including macrophages, monocytes, T cells, natural killer (NK) cells, dendritic cells (DCs), γδ T lymphocytes, regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs), mast cells, and B cells, within the hypoxic TME through the release of factors that regulate their recruitment, phenotype, and function. Thus, both hypoxia and tumor-derived exosomes modulate immune cells, growth factors, cytokines, receptor molecules, and other soluble factors, which, together, collaborate to form the immune-suppressive milieu of the tumor environment. Exploring the contribution of exosomal cargos, such as RNAs and proteins, as indispensable players in the cross-talk within the hypoxic tumor microenvironmental provides a potential target for antitumor immunity or subverting immune evasion and enhancing tumor therapies.

Dysregulation of EZH2/miR-138-5p Axis Contributes to Radiosensitivity in Hepatocellular Carcinoma Cell by Downregulating Hypoxia-Inducible Factor 1 Alpha (HIF-1α)

Enhancer of zeste homolog 2 (EZH2) is a histone methyltransferase involved in cell proliferation, invasion, angiogenesis, and metastasis in various cancers, including hepatocellular carcinoma (HCC). However, the role and molecular mechanisms of EZH2 in HCC radiosensitivity remain unclear. Here, we show that EZH2 is upregulated in HCC cells and the aberrantly overexpressed EZH2 is associated with the poor prognosis of HCC patients. Using miRNA databases, we identified miR-138-5p as a regulator of EZH2. We also found that miR-138-5p was suppressed by EZH2-induced H3K27me3 in HCC cell lines. MiR-138-5p overexpression and EZH2 knockdown enhanced cellular radiosensitivity while inhibiting cell migration, invasion, and epithelial-mesenchymal transition (EMT). Analysis of RNA-seq datasets revealed that the hypoxia-inducible factor-1 (HIF-1) signaling pathway was the main enrichment pathway for differential genes after miR-138-5p overexpression or EZH2 knockdown. Expression level of HIF-1α was significantly suppressed after miR-138-5p overexpression or silencing of EZH2. HIF-1α silencing mitigated resistance of HCC cells and inhibited EMT. This study establishes the EZH2/miR-138-5p/HIF-1α as a potential therapeutic target for sensitizing HCC to radiotherapy.

The low affinity A2B adenosine receptor enhances migratory and invasive capacity in vitro and angiogenesis in vivo of glioblastoma stem-like cells

Glioblastoma (GBM) is the most common and deadly malignant brain tumor, with a median survival of 15 to 17 months for a patient. GBM contains a cellular subpopulation known as GBM stem-like cells (GSCs) that persist in hypoxic niches and are capable of infiltrating into healthy brain tissue. For this reason, GSCs are considered one of the main culprits for GBM recurrence. A hypoxic microenvironment increases extracellular adenosine levels, activating the low affinity A2B adenosine receptor (A_2BAR). Adenosine, through A_2BAR, is capable of modulating invasiveness. However, its role in the invasion/migration of hypoxic-GSCs is still unknown. This study aims to understand the importance of A_2BAR in modulating the migratory/invasive capacity of GSCs under hypoxia. Data analysis from The Cancer Genome Atlas (TCGA) program correlates A_2BAR expression with high-grade glioma and hypoxic necrotic areas. U87MG and primary culture-derived GSCs under hypoxic conditions (0.5% O₂) increased A_2BAR mRNA and protein levels. As expected, the migratory and invasive capacity of GSCs increased under hypoxia, which was counteracted by blocking A_2BAR, through the downregulation of MMP9 activity and epithelial–mesenchymal transition marker expression. Finally, in a xenograft mouse model, we demonstrate that treatment with MRS1754 did not affect the tumor volume but could decrease blood vessel formation and VEGF expression. Our results suggest that extracellular adenosine, through the activation of A_2BAR, enhances the migratory and invasive capacity of GSCs in vitro under hypoxic conditions. Targeting A_2BAR can be an effective therapy for GBM recurrence.

Prognostic and predictive roles of cancer stem cell markers in head and neck squamous cell carcinoma patients receiving chemoradiotherapy with or without nimotuzumab

BACKGROUND

Anti-EGFR-based therapies have limited success in HNSCC patients. Predictive biomarkers are needed to identify the patients most likely to benefit from these therapies. Here, we present predictive and prognostic associations of different cancer stem cell markers in HPV-negative locally advanced (LA) HNSCC patients.

METHODS

Pretreatment tumour tissues of 404 HPV-negative LA-HNSCCs patients, a subset of-phase 3-randomised study comparing cisplatin-radiation(CRT) and nimotuzumab plus cisplatin-radiation(NCRT) were examined. The expression levels of CD44, CD44v6, CD98hc, ALDH1A1, SOX2 and OCT4A were evaluated using immunohistochemistry. Progression-free survival(PFS), loco-regional control(LRC),- and overall survival(OS) were estimated by Kaplan-Meier method. Hazard ratios were estimated by Cox proportional hazard models.

RESULTS

NCRT showed significantly improved OS with low membrane expression of CD44 compared to CRT [HR (95% CI) = 0.63 (0.46-0.88)]. Patients with low CD44v6 also showed better outcomes with NCRT [LRC: HR (95% CI) = 0.25 (0.10-0.62); OS: HR (95% CI) = 0.38 (0.19-0.74)]. No similar benefit with NCRT observed in patients with high CD44 or CD44v6 expression. Bootstrap resampling confirmed the predictive effect of CD44 (Interaction P = 0.015) and CD44v6 (Interaction P = 0.041) for OS. Multivariable Cox analysis revealed an independent negative prognostic role of CD98hc membrane expression for LRC [HR (95% CI) = 0.63(0.39-1.0)] and OS[HR (95% CI) = 0.62 (0.40-0.95)].

CONCLUSIONS

CD44 and CD44v6 are potential predictive biomarkers for NCRT response. CD98hc emerged as an independent negative prognostic biomarker.

CLINICAL TRIAL REGISTRATION

Registered with the Clinical Trial Registry of India (Trial registration identifier-CTRI/2014/09/004980).

Inhibition of the HIF-1 Survival Pathway as a Strategy to Augment Photodynamic Therapy Efficacy

Photodynamic therapy (PDT) is a non-to-minimally invasive treatment modality that utilizes photoactivatable drugs called photosensitizers to disrupt tumors with locally photoproduced reactive oxygen species (ROS). Photosensitizer activation by light results in hyperoxidative stress and subsequent tumor cell death, vascular shutdown and hypoxia, and an antitumor immune response. However, sublethally afflicted tumor cells initiate several survival mechanisms that account for decreased PDT efficacy. The hypoxia inducible factor 1 (HIF-1) pathway is one of the most effective cell survival pathways that contributes to cell recovery from PDT-induced damage. Several hundred target genes of the HIF-1 heterodimeric complex collectively mediate processes that are involved in tumor cell survival directly and indirectly (e.g., vascularization, glucose metabolism, proliferation, and metastasis). The broad spectrum of biological ramifications culminating from the activation of HIF-1 target genes reflects the importance of HIF-1 in the context of therapeutic recalcitrance. This chapter elaborates on the involvement of HIF-1 in cancer biology, the hypoxic response mechanisms, and the role of HIF-1 in PDT. An overview of inhibitors that either directly or indirectly impede HIF-1-mediated survival signaling is provided. The inhibitors may be used as pharmacological adjuvants in combination with PDT to augment therapeutic efficacy.

Prognostic value of HIF-1α in digestive system malignancies: evidence from a systematic review and meta-analysis

Aim

This meta-analysis aimed to evaluate the association of HIF-1α expression with clinicopathological features and overall survival (OS) of patients with digestive system malignancies.

Background

Numerous studies have demonstrated that hypoxia-inducible factor-1α (HIF-1α) is abnormally expressed in various solid tumors. However, the clinicopathological features and prognostic value of HIF-1α expression in patients with digestive system malignancies remain controversial.

Methods

A literature search in PubMed, Web of Science, and Scopus databases was performed to identify all relevant studies published in English until 15 October 2020. The pooled effect was calculated to evaluate the association between HIF-1α expression and clinicopathological features and overall survival in cancer patients. Pooled odds ratios (ORs) or hazard ratios (HRs) with a 95% confidence interval (CI) were calculated using fixed- or random-effects model based on between-study heterogeneity.

Results

A total of 44 eligible studies with 5,964 patients were included. The pooled results indicated a positive association of HIF-1α overexpression with poor overall survival (OS) (HR=1.990, 95% CI: 1.615-2.453, p<0.001) and disease-free survival (DFS) (HR=1.90, 95% CI: 1.084-3.329, p=0.043). Meta-analysis results showed that HIF-1α level expression was significantly associated with positive lymph node metastasis (OR=1.869, 95% CI: 1.488-2.248, p<0.001), distance metastasis (OR=2.604, 95% CI: 1.500-4.519, p<0.001), tumor stage (OR=1.801, 95% CI: 1.437-2.257, p<0.001) and tumor size (OR=1.392. 95% CI: 1.068-1.815, p=0.014).

Conclusion

This meta-data suggest that HIF-1α expression might serve as an independent prognostic marker and a promising therapeutic target in patients with digestive system malignancies.

Epithelial-Mesenchymal Transition and Cancer Stem Cells

Epithelial-mesenchymal transition (EMT), a cellular phenotypic change from epithelial to mesenchymal-like features, is related to the resistance and metastasis of cancer stem cells (CSCs). Several signal transduction mechanisms induce EMT, which causes the gene expression alteration to induce the acquisition of resistance and metastasis in cancer. EMT is characterized with high gene expression of cadherin 2 (N-cadherin) and vimentin, and sparse cell-cell junction. The cells with EMT-phenotype have migration, metastasis and drug-resistance capacity, which are main characteristics of CSCs. It seems that the main population of CSCs exhibits EMT phenotype, whereas some populations consist of phenotypes other than EMT. In this chapter, EMT mechanism, phenotypic features of EMT and CSCs, signal transduction in EMT and CSCs, differences between EMT and CSCs, and the role of EMT in CSCs are described.

Mechanistic Insights Delineating the Role of Cholesterol in Epithelial Mesenchymal Transition and Drug Resistance in Cancer

Despite the significant advancements made in targeted anti-cancer therapy, drug resistance constitutes a multifaceted phenomenon leading to therapy failure and ultimately mortality. Emerging experimental evidence highlight a role of cholesterol metabolism in facilitating drug resistance in cancer. This review aims to describe the role of cholesterol in facilitating multi-drug resistance in cancer. We focus on specific signaling pathways that contribute to drug resistance and the link between these pathways and cholesterol. Additionally, we briefly discuss the molecular mechanisms related to the epithelial-mesenchymal transition (EMT), and the documented link between EMT, metastasis and drug resistance. We illustrate this by specifically focusing on hypoxia and the role it plays in influencing cellular cholesterol content following EMT induction. Finally, we provide a proposed model delineating the crucial role of cholesterol in EMT and discuss whether targeting cholesterol could serve as a novel means of combatting drug resistance in cancer progression and metastasis.

Cross-Talk between Oxidative Stress and m6A RNA Methylation in Cancer

Oxidative stress is a state of imbalance between oxidation and antioxidation. Excessive ROS levels are an important factor in tumor development. Damage stimulation and excessive activation of oncogenes cause elevated ROS production in cancer, accompanied by an increase in the antioxidant capacity to retain redox homeostasis in tumor cells at an increased level. Although moderate concentrations of ROS produced in cancer cells contribute to maintaining cell survival and cancer progression, massive ROS accumulation can exert toxicity, leading to cancer cell death. RNA modification is a posttranscriptional control mechanism that regulates gene expression and RNA metabolism, and m⁶A RNA methylation is the most common type of RNA modification in eukaryotes. m⁶A modifications can modulate cellular ROS levels through different mechanisms. It is worth noting that ROS signaling also plays a regulatory role in m⁶A modifications. In this review, we concluded the effects of m⁶A modification and oxidative stress on tumor biological functions. In particular, we discuss the interplay between oxidative stress and m⁶A modifications.

Regulation of cancer stem cells in triple negative breast cancer

Triple Negative Breast Cancer (TNBC) is the most lethal subtype of breast cancer. Despite the successes of emerging targeted therapies, relapse, recurrence, and therapy failure rates in TNBC significantly outpace other subtypes of breast cancer. Mounting evidence suggests accumulation of therapy resistant Cancer Stem Cell (CSC) populations within TNBCs contributes to poor clinical outcomes. These CSCs are enriched in TNBC compared to non-TNBC breast cancers. The mechanisms underlying CSC accumulation have been well-characterized and discussed in other reviews. In this review, we focus on TNBC-specific mechanisms that allow the expansion and activity of self-renewing CSCs. We highlight cellular signaling pathways and transcription factors, specifically enriched in TNBC over non-TNBC breast cancer, contributing to stemness. We also analyze publicly available single-cell RNA-seq data from basal breast cancer tumors to highlight the potential of emerging bioinformatic approaches in identifying novel drivers of stemness in TNBC and other cancers.

MiR-139 Modulates Cancer Stem Cell Function of Human Breast Cancer through Targeting CXCR4

Elevated expression of C-X-C motif chemokine receptor 4 (CXCR4) correlates with chemotaxis, invasion, and cancer stem cell (CSC) properties within several solid-tumor malignancies. Recent studies reported that microRNA (miRNA) modulates the stemness of embryonic stem cells. We aimed to investigate the role of miRNA, via CXCR4-modulation, on CSC properties in breast cancer using cell lines and xenotransplantation mouse model and evaluated miR-193 levels in 191 patients with invasive ductal carcinoma. We validated miR-139 directly targets the 3'-untranslated region of CXCR4. Hoechst 33342 fluorescence-activated cell sorting (FACS) and sphere-forming assay were used to identify CSCs. MiR-139 suppressed breast CSCs with mesenchymal traits; led to decreased migration and invasion abilities through down-regulating CXCR4/p-Akt signaling. In lung cancer xenograft model of nude mice transplanted with human miR-139-carrying MDA-MB-231 cells, metastatic lung nodules were suppressed. Clinically, microdissected breast tumor tissues showed miR-139 reduction, compared to adjacent non-tumor tissues, that was significantly associated with worse clinicopathological features, including larger tumor size, advanced tumor stage and lymph node metastasis; moreover, reduced miR-139 level was predominately occurred in late-stage HER2-oreexpression tumors. Collectively, our findings highlight miR-139-mediated suppression of CXCR4/p-Akt signaling and thereby affected mesenchymal stem-cell genesis, indicating its potential as a therapeutic target for invasive breast cancer.

Hypoxia in Breast Cancer-Scientific Translation to Therapeutic and Diagnostic Clinical Applications

Breast cancer has been the leading cause of female cancer deaths for decades. Intratumoral hypoxia, mainly caused by structural and functional abnormalities in microvasculature, is often associated with a more aggressive phenotype, increased risk of metastasis and resistance to anti-malignancy treatments. The response of cancer cells to hypoxia is ascribed to hypoxia-inducible factors (HIFs) that activate the transcription of a large battery of genes encoding proteins promoting primary tumor vascularization and growth, stromal cell recruitment, extracellular matrix remodeling, cell motility, local tissue invasion, metastasis, and maintenance of the cancer stem cell properties. In this review, we summarized the role of hypoxia specifically in breast cancer, discuss the prognostic and predictive value of hypoxia factors, potential links of hypoxia and endocrine resistance, cancer hypoxia measurements, further involved mechanisms, clinical application of hypoxia-related treatments and open questions.

HIF-Prolyl Hydroxylase Domain Proteins (PHDs) in Cancer-Potential Targets for Anti-Tumor Therapy?

Solid tumors are typically associated with unbridled proliferation of malignant cells, accompanied by an immature and dysfunctional tumor-associated vascular network. Consequent impairment in transport of nutrients and oxygen eventually leads to a hypoxic environment wherein cells must adapt to survive and overcome these stresses. Hypoxia inducible factors (HIFs) are central transcription factors in the hypoxia response and drive the expression of a vast number of survival genes in cancer cells and in cells in the tumor microenvironment. HIFs are tightly controlled by a class of oxygen sensors, the HIF-prolyl hydroxylase domain proteins (PHDs), which hydroxylate HIFs, thereby marking them for proteasomal degradation. Remarkable and intense research during the past decade has revealed that, contrary to expectations, PHDs are often overexpressed in many tumor types, and that inhibition of PHDs can lead to decreased tumor growth, impaired metastasis, and diminished tumor-associated immune-tolerance. Therefore, PHDs represent an attractive therapeutic target in cancer research. Multiple PHD inhibitors have been developed that were either recently accepted in China as erythropoiesis stimulating agents (ESA) or are currently in phase III trials. We review here the function of HIFs and PHDs in cancer and related therapeutic opportunities.

Therapeutic Strategies Against Cancer Stem Cells in Esophageal Carcinomas

Cancer stem cells (CSCs) in esophageal cancer have a key role in tumor initiation, progression and therapy resistance. Novel therapeutic strategies to target CSCs are being tested, however, more in-depth research is necessary. Eradication of CSCs can result in successful therapeutic approaches against esophageal cancer. Recent evidence suggests that targeting signaling pathways, miRNA expression profiles and other properties of CSCs are important strategies for cancer therapy. Wnt/β-catenin, Notch, Hedgehog, Hippo and other pathways play crucial roles in proliferation, differentiation, and self-renewal of stem cells as well as of CSCs. All of these pathways have been implicated in the regulation of esophageal CSCs and are potential therapeutic targets. Interference with these pathways or their components using small molecules could have therapeutic benefits. Similarly, miRNAs are able to regulate gene expression in esophageal CSCs, so targeting self-renewal pathways with miRNA could be utilized to as a potential therapeutic option. Moreover, hypoxia plays critical roles in esophageal cancer metabolism, stem cell proliferation, maintaining aggressiveness and in regulating the metastatic potential of cancer cells, therefore, targeting hypoxia factors could also provide effective therapeutic modalities against esophageal CSCs. To conclude, additional study of CSCs in esophageal carcinoma could open promising therapeutic options in esophageal carcinomas by targeting hyper-activated signaling pathways, manipulating miRNA expression and hypoxia mechanisms in esophageal CSCs.

Hypoxic tumor-derived exosomal circular RNA SETDB1 promotes invasive growth and EMT via the miR-7/Sp1 axis in lung adenocarcinoma

Hypoxia is a common feature of solid tumors and has been associated with tumor aggressiveness and poor prognosis. Exosomes are involved in mediating cellular-environment interactions. Circular RNAs (circRNAs) are a class of non-coding RNA broadly found in cells and exosomes. However, the functions and regulatory mechanisms of exosomal circRNAs induced by hypoxia remain poorly understood in lung adenocarcinoma (LUAD) development. Differentially expressed circRNAs were identified between exosomes extracted from hypoxic and normoxic conditions through microarray analysis. We focused on hsa-circ-0003439 found on chromosome 1 and derived from SET domain bifurcated histone lysine methyltransferase 1 (SETDB1), and thus we named it circSETDB1. We discovered that exosomes obtained from hypoxic LUAD cells improved the migration, invasion, and proliferation capacity of normoxic LUAD cells. circSETDB1 was found to be significantly upregulated in hypoxia-induced exosomes from LUAD cell lines compared with exosomes in the normal condition. Moreover, knockdown of circSETDB1 significantly inhibited cell malignant growth in vitro. Importantly, we showed that circSETDB1 was upregulated in serum exosomes in LUAD patients, and exosomal circSETDB1 levels were closely associated with disease stage. Finally, using RNA immunoprecipitation (RIP), bioinformatics, and luciferase reporter assays, we elucidated the implication of a circSETDB1/miR-7/specificity protein 1 (Sp1) axis in the development and epithelial-mesenchymal transition (EMT) of lung adenocarcinoma.

The role of hypoxia in the tumor microenvironment and development of cancer stem cell: a novel approach to developing treatment

Hypoxia is a common feature of solid tumors, and develops because of the rapid growth of the tumor that outstrips the oxygen supply, and impaired blood flow due to the formation of abnormal blood vessels supplying the tumor. It has been reported that tumor hypoxia can: activate angiogenesis, thereby enhancing invasiveness and risk of metastasis; increase survival of tumor, as well as suppress anti-tumor immunity and hamper the therapeutic response. Hypoxia mediates these effects by several potential mechanisms: altering gene expression, the activation of oncogenes, inactivation of suppressor genes, reducing genomic stability and clonal selection. We have reviewed the effects of hypoxia on tumor biology and the possible strategiesto manage the hypoxic tumor microenvironment (TME), highlighting the potential use of cancer stem cells in tumor treatment.

Glioma stem cells and their roles within the hypoxic tumor microenvironment

Tumor microenvironments are the result of cellular alterations in cancer that support unrestricted growth and proliferation and result in further modifications in cell behavior, which are critical for tumor progression. Angiogenesis and therapeutic resistance are known to be modulated by hypoxia and other tumor microenvironments, such as acidic stress, both of which are core features of the glioblastoma microenvironment. Hypoxia has also been shown to promote a stem-like state in both non-neoplastic and tumor cells. In glial tumors, glioma stem cells (GSCs) are central in tumor growth, angiogenesis, and therapeutic resistance, and further investigation of the interplay between tumor microenvironments and GSCs is critical to the search for better treatment options for glioblastoma. Accordingly, we summarize the impact of hypoxia and acidic stress on GSC signaling and biologic phenotypes, and potential methods to inhibit these pathways.

Hypoxia-Mediated Decrease of Ovarian Cancer Cells Reaction to Treatment: Significance for Chemo- and Immunotherapies

Hypoxia, a common factor ruling the microenvironment composition, leads to tumor progression. In this hypoxic context, cytokines and cells cooperate to favor cancer development and metastasis. Tumor hypoxia is heterogeneously distributed. Oxygen gradients depend on the vicinity, functionality of blood vessels, and oxygen ability to diffuse into surrounding tissues. Thus, the vasculature state modulates the microenvironment of the tumor cells. Cells sense and react to small variations in oxygen tension, which explains the lack of tumor cells’ unicity in their reaction to drugs. Ovarian cancers are highly hypoxia-dependent, ascites worsening the access to oxygen, in their reactions to both chemotherapy and new immunotherapy. Consequently, hypoxia affects the results of immunotherapy, and is thus, crucial for the design of treatments. Controlling key immunosuppressive factors and receptors, as well as immune checkpoint molecule expression on tumor, immune and stromal cells, hypoxia induces immunosuppression. Consequently, new approaches to alleviate hypoxia in the tumor microenvironment bring promises for ovarian cancer immunotherapeutic strategies. This review focuses on the effects of hypoxia in the microenvironment and its consequences on tumor treatments. This opens the way to innovative combined treatments to the advantage of immunotherapy outcome in ovarian cancers.

Long non-coding RNAs in breast cancer metastasis

Breast cancer is the leading cause of cancer-related death among women. Recurrence of primary tumor and metastasis to distant body parts are major causes of breast cancer-associated mortality. The 5-year survival rate for women with metastatic breast cancer is only 25-30%. Breast cancer metastasis is a series of processes involved with EMT, invasion, loss of cell to cell adhesion, alteration in cell phenotype, extravasation, microenvironment of the tumor, and colonization to the secondary sites. Epigenetic modification is involved in the transformation of the distant stromal cell into a secondary tumor. LncRNAs, are one the key epigenetic modifiers, are the largest endogenous non-coding RNAs with approximate base-pair lengths from 200 nt to 100 kb. LncRNA plays a crucial role in breast cancer metastasis by sponging miRNA, by degrading or silencing specific mRNA, or else by targeting the enzymes and microprocessor subunits involved in the biogenesis of miRNA. LncRNA also alters the expression of several genes involved in breast cancer metastasis and modulating different cell signaling pathways. The goal of this review is to provide a better understanding of the role of lncRNA in the regulation of breast cancer metastasis. We also summarized some of the key lncRNAs that regulate the genes and signaling pathways involved in breast cancer invasion and metastasis.

CHIP-mediated CIB1 ubiquitination regulated epithelial-mesenchymal transition and tumor metastasis in lung adenocarcinoma

CIB1 is a homolog of calmodulin that regulates cell adhesion, migration, and differentiation. It has been considered as an oncogene in many tumor cells; however, its role in lung adenocarcinoma (LAC) has not been studied. In this study, the expression levels of CIB1 in LAC tissues and adjacent normal tissues were examined by immunohistochemistry, and the relationship between CIB1 expression and patient clinicopathological characteristics was analyzed. The effects of CIB1 on epithelial–mesenchymal transition (EMT), migration, and metastasis of LAC cells were determined in vitro and vivo. Proteins interacting with CIB1 were identified using electrospray mass spectrometry (LS-MS), and CHIP was selected in the following assays. Carboxyl-terminus of Hsp70-interacting protein (CHIP) is a ubiquitin E3 ligase. We show that CHIP can degrade CIB1 via promoting polyubiquitination of CIB1 and its subsequent proteasomal degradation. Besides, lysine residue 10 and 65 of CIB1 is the ubiquitinated site of CIB1. Furthermore, CHIP-mediated CIB1 downregulation is critical for the suppression of metastasis and migration of LAC. These results indicated that CHIP-mediated CIB1 ubiquitination could regulate epithelial–mesenchymal and tumor metastasis in LAC.

The modern views of the clinical, morphological and molecular biological predictors of breast cancer sensitivity to chemotherapy

In the treatment of breast cancer, the neoadjuvant chemotherapy is vitally important and the evaluation of its effectiveness is crucial for determining the further therapy treatment, as well as the prognosis of the disease. This review provides current data of the physical, instrumental, morphological, molecular biology and genetics analysis used for the estimation of the neoadjuvant treatment effectiveness. Thus, review discusses the data concerning association of the disease peculiarities with the efficient therapeutic response to neoadjuvant chemotherapy including characteristics of patients (age, status of regional lymph nodes, presence of the lymphovascular invasion) and tumors (size, histological type, degree of differentiation, severity of the lymphoid tumor infiltration, molecular biological and genetic peculiarities). Particular attention is paid to such a promising predictive marker of the breast cancer response to chemotherapy as the level of tissue hypoxia. This section discusses the currently known mechanisms that might enable the effect of tissue hypoxia on the sensitivity of the tumor to drug treatment. The prospects for the use of a comprehensive analysis of predictive markers of the effectiveness of chemotherapeutic treatment are discussed.

Defining lung cancer stem cells exosomal payload of miRNAs in clinical perspective

Since the first publication regarding the existence of stem cells in cancer [cancer stem cells (CSCs)] in 1994, many studies have been published providing in-depth information about their biology and function. This research has paved the way in terms of appreciating the role of CSCs in tumour aggressiveness, progression, recurrence and resistance to cancer therapy. Targeting CSCs for cancer therapy has still not progressed to a sufficient degree, particularly in terms of exploring the mechanism of dynamic interconversion between CSCs and non-CSCs. Besides the CSC scenario, the problem of cancer dissemination has been analyzed in-depth with the identification and isolation of microRNAs (miRs), which are now considered to be compelling molecular markers in the diagnosis and prognosis of tumours in general and specifically in patients with non-small cell lung cancer. Paracrine release of miRs via “exosomes” (small membrane vesicles (30-100 nm), the derivation of which lies in the luminal membranes of multi-vesicular bodies) released by fusion with the cell membrane is gaining popularity. Whether exosomes play a significant role in maintaining a dynamic equilibrium state between CSCs and non-CSCs and their mechanism of activity is as yet unknown. Future studies on CSC-related exosomes will provide new perspectives for precision-targeted treatment strategies.

Cancer Stem Cells as a Potential Target to Overcome Multidrug Resistance

Multidrug resistance (MDR), which is a significant impediment to the success of cancer chemotherapy, is attributable to various defensive mechanisms in cancer. Initially, overexpression of ATP-binding cassette (ABC) transporters such as P-glycoprotein (P-gp) was considered the most important mechanism for drug resistance; hence, many investigators for a long time focused on the development of specific ABC transporter inhibitors. However, to date their efforts have failed to develop a clinically applicable drug, leaving only a number of problems. The concept of cancer stem cells (CSCs) has provided new directions for both cancer and MDR research. MDR is known to be one of the most important features of CSCs and thus plays a crucial role in cancer recurrence and exacerbation. Therefore, in recent years, research targeting CSCs has been increasing rapidly in search of an effective cancer treatment. Here, we review the drugs that have been studied and developed to overcome MDR and CSCs, and discuss the limitations and future perspectives.

Differential mechanisms of autophagy in cancer stem cells: Emphasizing gastrointestinal cancers

Gastrointestinal (GI) cancers are one of the most common forms of malignancies and still are the most important cause of cancer-related mortality worldwide. Autophagy is a conserved catabolic pathway involving lysosomal degradation and recycling of whole cellular components, which is essential for cellular homeostasis. For instance, it acts as a pivotal intracellular quality control and repair mechanism but also implicated in cell reformation during cell differentiation and development. Indeed, GI cancer stem cells (CSCs) are thought to be responsible for tumour initiation, traditional therapies resistance, metastasis and tumour recurrence. Molecular mechanisms of autophagy in normal vs CSCs gain great interest worldwide. Here, we shed light on the role of autophagy in normal stem cells differentiation for embryonic progression and its role in maintaining the activity and self-renewal capacity of CSCs which offer novel viewpoints on promising cancer therapeutic strategies based on the differential roles of autophagy in CSCs.

ROS and oncogenesis with special reference to EMT and stemness

Elevation of the level of intracellular reactive oxygen species (ROS) has immense implication in the biological system. On the one hand, ROS promote the signaling cascades for the maintenance of normal physiological functions, the phenomenon referred to as redox biology, and on the other hand increased ROS can cause damages to the cellular macromolecules as well as genetic material, the process known as oxidative stress. Oxidative stress acts as an etiological factor for wide varieties of pathologies, cancer being one of them. ROS is regarded as a "double-edged sword" with respect to oncogenesis. It can suppress as well as promote the malignant progression depending on the type of signaling pathway it uses. Moreover, the attribution of ROS in promoting phenotypic plasticity as well as acquisition of stemness during neoplasia has become a wide area of research. The current review discussed all the aspects of ROS in the perspective of tumor biology with special reference to epithelial-mesenchymal transition (EMT) and cancer stem cells.

P4HA2 contributes to cervical cancer progression via inducing epithelial-mesenchymal transition

Background: Cervical cancer is one of the most common gynaecological malignancies. Emerging studies have documented that prolyl-4-hydroxylase α subunit 2 (P4HA2) is involved in multiple processes of cancer progression. However, the functional roles of P4HA2 in cervical cancer progression remain to be elucidated.

Methods: P4HA2 mRNA and protein levels were examined in cervical cancer tissues and cell line by qRT-PCR and western blot. The correlation of the P4HA2 expression levels and prognosis of cervical cancer patients were analysed in TCGA cervical cancer cohort and tissue microarray (TMA) cohort. P4HA2 was silenced to evaluate its function on cervical cancer progression both in vitro and in vivo. Bioinformatics analysis was performed to investigate the underlying regulation mechanism of cervical cancer by P4HA2.

Results: We found that P4HA2 are markedly upregulated in cervical cancer tissues in comparison with adjacent non-neoplastic tissues. In addition, upregulation of P4HA2 was associated with shorter overall survival (OS) and relapse-free survival (RFS). Functionally, we demonstrated that P4HA2 knockdown attenuated cell proliferation, migration and invasion of cervical cancer cells. Furthermore, xenograft tumor mouse model experiment showed silencing P4HA2 significantly inhibited tumor growth in vivo. Mechanistically, bioinformatics analysis revealed that epithelial-mesenchymal transition (EMT) was involved in cervical cancer progression regulated by P4HA2 and we further confirmed knockdown P4HA2 suppressed the EMT process.

Conclusion: our results suggest that P4HA2 functions as an oncogene in promoting cervical cancer cell proliferation, migration and invasion by inducing EMT, which might be a promising prognostic factor and therapeutic target for cervical cancer.

Exosomes Derived from Hypoxic Colorectal Cancer Cells Transfer miR-410-3p to Regulate Tumor Progression

Hypoxia is a common characteristic of solid tumors and is associated with cancer progression and poor outcomes. However, the roles and specific mechanisms of exosomes and hypoxia during cancer progression still remain unclear. Herein, we found that exosomes secreted from hypoxic colorectal cancer (CRC) cells promoted the proliferation, migration, invasion, and metastasis of normoxic CRC cells, and these hypoxic exosomes exerted their biological effects depending on miR-410-3p. We discovered that miR-410-3p was highly enriched in hypoxic CRC-derived exosomes in a HIF1α or HIF2α-dependent manner, and miR-410-3p levels positively associated with poor prognosis of CRC. Moreover, decreased PTEN levels caused by hypoxic CRC cells-derived exosomal miR-410-3p increased activation of PI3K/Akt as well as tumor progression. Conversely, inhibition of miR-410-3p or PI3K/Akt signaling pathway effectively decreased hypoxic CRC cells-derived exosomes-mediated tumor progression. In conclusion, our findings indicate that the hypoxic microenvironment in CRC may promote tumor cells to release miR-410-3p-rich exosomes that are transferred to normoxic cells to enhance tumor progression, revealing a new investigation into the therapeutic targets of exosome for CRC treatment.

Hypoxia in solid tumors: a key promoter of cancer stem cell (CSC) resistance

PURPOSE

Cancer stem cells (CSCs) are highly tumorigenic cell types that reside within specific areas of tumor microenvironment (TME), and are endowed with self-renewal and resistance properties. Here, we aimed to discuss mechanisms involved in hypoxia-derived CSC resistance and targeting for effective cancer therapy.

RESULTS

Preferential localization within hypoxic niches would help CSCs develop adaptive mechanisms, mediated through the modification of responses to various stressors and, as a result, show a more aggressive behavior.

CONCLUSION

Hypoxia, in fact, serves as a multi-tasking strategy to nurture CSCs with this adaptive capacity, complexing targeted therapies.

Exosomes: New insights into cancer mechanisms

Exosomes are mobile extracellular vesicles with a diameter 40 to 150 nm. They play a critical role in several processes such as the development of cancers, intercellular signaling, drug resistance mechanisms, and cell-to-cell communication by fusion onto the cell membrane of recipient cells. These vesicles contain endogenous proteins and both noncoding and coding RNAs (microRNA and messenger RNAs) that can be delivered to various types of cells. Furthermore, exosomes exist in body fluids such as plasma, cerebrospinal fluid, and urine. Therefore, they could be used as a novel carrier to deliver therapeutic nucleic-acid drugs for cancer therapy. It was recently documented that, hypoxia promotes exosomes secretion in different tumor types leading to the activation of vascular cells and angiogenesis. Cancer cell-derived exosomes (CCEs) have been used as prognostic and diagnostic markers in many types of cancers because exosomes are stable at 4°C and -70°C. CCEs have many functional roles in tumorigenesis, metastasis, and invasion. Consequently, this review presents the data about the therapeutic application of exosomes and the role of CCEs in cancer invasion, drug resistance, and metastasis.

Hypoxia‑inducible factors in hepatocellular carcinoma (Review)

Maintenance of an appropriate oxygen concentration is essential for the function of the liver. However, in many pathological conditions, and particularly in the tumor microenvironment, cells and tissues are frequently in a hypoxic state. In the presence of hypoxia, the cells adapt to the low oxygen levels through the hypoxia-inducible factor (HIF) pathway. Overgrowth of tumor cells restricts the diffusion of oxygen in tumors, leading to insufficient blood supply and the creation of a hypoxic microenvironment, and, as a consequence, activation of the expression of HIFs. HIFs possess a wide range of target genes, which function to control a variety of signaling pathways; thus, HIFs modulate cellular metabolism, immune escape, angiogenesis, metastasis, extracellular matrix remodeling, cancer stem cells and other properties of the tumor. Given their crucial role in the occurrence and development of tumors, HIFs are expected to become new targets of precise treatment of hepatocellular carcinoma.

Why Be One Protein When You Can Affect Many? The Multiple Roles of YB-1 in Lung Cancer and Mesothelioma

Lung cancers and malignant pleural mesothelioma (MPM) have some of the worst 5-year survival rates of all cancer types, primarily due to a lack of effective treatment options for most patients. Targeted therapies have shown some promise in thoracic cancers, although efficacy is limited only to patients harboring specific mutations or target expression. Although a number of actionable mutations have now been identified, a large population of thoracic cancer patients have no therapeutic options outside of first-line chemotherapy. It is therefore crucial to identify alternative targets that might lead to the development of new ways of treating patients diagnosed with these diseases. The multifunctional oncoprotein Y-box binding protein-1 (YB-1) could serve as one such target. Recent studies also link this protein to many inherent behaviors of thoracic cancer cells such as proliferation, invasion, metastasis and involvement in cancer stem-like cells. Here, we review the regulation of YB-1 at the transcriptional, translational, post-translational and sub-cellular levels in thoracic cancer and discuss its potential use as a biomarker and therapeutic target.

Tumor Dormancy and Interplay with Hypoxic Tumor Microenvironment

The tumor microenvironment is a key factor in disease progression, local resistance, immune-escaping, and metastasis. The rapid proliferation of tumor cells and the aberrant structure of the blood vessels within tumors result in a marked heterogeneity in the perfusion of the tumor tissue with regions of hypoxia. Although most of the tumor cells die in these hypoxic conditions, a part of them can adapt and survive for many days or months in a dormant state. Dormant tumor cells are characterized by cell cycle arrest in G0/G1 phase as well as a low metabolism, and are refractive to common chemotherapy, giving rise to metastasis. Despite these features, the cells retain their ability to proliferate when conditions improve. An understanding of the regulatory machinery of tumor dormancy is essential for identifying early cancer biomarkers and could provide a rationale for the development of novel agents to target dormant tumor cell populations. In this review, we examine the current knowledge of the mechanisms allowing tumor dormancy and discuss the crucial role of the hypoxic microenvironment in this process.

Immunohistochemical Features of Epithelial-Mesenchymal Transition in Feline Oral Squamous Cell Carcinoma

Feline oral squamous cell carcinoma (FOSCC) is an aggressive malignancy with invasive and metastatic behavior. It is poorly responsive to chemotherapy and radiation. Neoplastic epithelial-mesenchymal transition (EMT) portends highly malignant behavior and enhances resistance to therapy. In transitioning to a more malignant phenotype, carcinoma stem cells undergo transformation mediated by expression of proteins, endowing them with mesenchymal properties advantageous to cell survival. The goal of the current study was to identify proteins associated with EMT in FOSCC. This study documents protein expression patterns in 10 FOSCC biopsies and 3 FOSCC cell lines (SCCF1, SCCF2, SCCF3), compatible with an EMT phenotype. As markers of EMT, P-cadherin, N-cadherin, vimentin, nuclear transcription factors Twist and Snail, hypoxia inducible factor 1α (HIF-1α), programmed death ligand 1, and vascular endothelial growth factor D, as well as E-cadherin, were examined using immunohistochemistry, Western blot, and enzyme-linked immunosorbent assay. P-cadherin, Twist, HIF-1α, and programmed death ligand 1 were commonly expressed in biopsies and cell lines. N-cadherin, classically associated with EMT, was not highly expressed, and E-cadherin was coexpressed along with proteins characteristic of EMT in all specimens. Production of vascular endothelial growth factor A by cell lines, a process regulated by HIF-1α expression, was suppressed by the small-molecule inhibitor dasatinib. These data are consistent with EMT in FOSCC and shed light on cellular changes that could contribute to the aggressive behavior of FOSCC.

Poor outcome in hypoxic endometrial carcinoma is related to vascular density

Background

Identification of endometrial carcinoma (EC) patients at high risk of recurrence is lacking. In this study, the prognostic role of hypoxia and angiogenesis was investigated in EC patients.

Methods

Tumour slides from EC patients were stained by immunofluorescence for carbonic anhydrase IX (CAIX) as hypoxic marker and CD34 for assessment of microvessel density (MVD). CAIX expression was determined in epithelial tumour cells, with a cut-off of 1%. MVD was assessed according to the Weidner method. Correlations with disease-specific survival (DSS), disease-free survival (DFS) and distant disease-free survival (DDFS) were calculated using Kaplan–Meier curves and Cox regression analysis.

Results

Sixty-three (16.4%) of 385 ECs showed positive CAIX expression with high vascular density. These ECs had a reduced DSS compared to tumours with either hypoxia or high vascular density (log-rank p = 0.002). Multivariable analysis showed that hypoxic tumours with high vascular density had a reduced DSS (hazard ratio [HR] 3.71, p = 0.002), DDFS (HR 2.68, p = 0.009) and a trend for reduced DFS (HR 1.87, p = 0.054).

Conclusions

This study has shown that adverse outcome in hypoxic ECs is seen in the presence of high vascular density, suggesting an important role of angiogenesis in the metastatic process of hypoxic EC. Differential adjuvant treatment might be indicated for these patients.

Mechanobiology of Cancer Stem Cells and Their Niche

Though the existence of cancer stem cells remained enigmatic initially, over the time their participation in tumorigenesis and tumor progression has become highly evident. Today, they are also appreciated as the causal element for tumor heterogeneity and drug-resistance. Cancer stem cells activate a set of molecular pathways some of which are triggered by the unique mechanical properties of the tumor tissue stroma. A relatively new field called mechanobiology has emerged, which aims to critically evaluate the mechanical properties associated with biological events like tissue morphogenesis, cell-cell or cell-matrix interactions, cellular migration and also the development and progression of cancer. Development of more realistic model systems and biophysical instrumentation for observation and manipulation of cell-dynamics in real-time has invoked a hope for some novel therapeutic modalities against cancer in the future. This review discusses the fundamental concepts of cancer stem cells from an intriguing viewpoint of mechanobiology and some important breakthroughs to date.