Anoikis Resistance as a Further Trait of Acidic-Adapted Melanoma Cells

Establishment and validation of the prognostic risk model based on the anoikis-related genes in esophageal squamous cell carcinoma

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is a malignant condition in humans. Anoikis-related genes (ARGs) are crucial to cancer progression. Therefore, more studies on the relationship between ARGs and ESCC are warranted.

METHODS

The study acquired ESCC-related transcriptome data from TCGA. Differentially expressed ARGs (DE-ARGs) were obtained by differential analysis and candidates were filtered out by survival analysis. Prognostic genes were determined by Cox and LASSO regression. A risk model was constructed based on prognostic gene expressions. An immune infiltration study was done to explain how these genes contribute to ESCC development. The IC50 test was adopted to assess the clinical response of chemotherapy drugs. Single cell analysis was performed on the GSE145370 dataset. Moreover, the prognostic gene expressions were detected by qRT-PCR.

RESULTS

53 DE-ARGs were screened and four candidate genes including PBK, LAMC2, TNFSF10 and KL were obtained. Cox and LASSO regression identified the two prognostic genes, TNFSF10 and PBK. Immuno-infiltration analysis revealed positive associations of PBK with Macrophages M0 cells, and TNFSF10 with Macrophages M1 cells. The IC50 values of predicted drugs, in the case of Tozasertib 1096 and WIKI4 1940, were significantly variant between risk groups. Single cell analysis revealed that TNFSF10 and PBK levels were higher in epithelial cells than in other cells. The prognostic genes expression results by qRT-PCR were compatible with the dataset analysis.

CONCLUSION

The study established an ARG prognosis model of ESCC. It provided a reference for the research of ARGs in ESCC.

The oncogenic ADAMTS1-VCAN-EGFR cyclic axis drives anoikis resistance and invasion in renal cell carcinoma

BACKGROUND

Metastasis, the leading cause of renal cell carcinoma (RCC) mortality, involves cancer cells resisting anoikis and invading. Until now, the role of the matrix metalloproteinase (MMP)-related enzyme, A disintegrin and metalloprotease with thrombospondin motifs 1 (ADAMTS1), in RCC anoikis regulation remains unclear.

METHODS

The clinical significance of ADAMTS1 and its associated molecules in patients with RCC was investigated using data from the Gene Expression Omnibus (GEO) and TCGA datasets. Human phosphoreceptor tyrosine kinase (RTK) array, luciferase reporter assays, immunoprecipitation (IP) assays, western blotting, and real-time reverse-transcription quantitative polymerase chain reaction (RT-qPCR) were used to elucidate the underlying mechanisms of ADAMTS1. Functional assays, including anoikis resistance assays, invasion assays, and a Zebrafish xenotransplantation model, were conducted to assess the roles of ADAMTS1 in conferring resistance to anoikis in RCC.

RESULTS

This study found elevated ADAMTS1 transcripts in RCC tissues that were correlated with a poor prognosis. ADAMTS1 manipulation significantly affected cell anoikis through the mitochondrial pathway in RCC cells. Human receptor tyrosine kinase (RTK) array screening identified that epidermal growth factor receptor (EGFR) activation was responsible for ADAMTS1-induced anoikis resistance and invasion. Further investigations revealed that enzymatically active ADAMTS1-induced versican V1 (VCAN V1) proteolysis led to EGFR transactivation, which in turn, through positive feedback, regulated ADAMTS1. Additionally, ADAMTS1 can form a complex with p53 to influence EGFR signaling. In vivo, VCAN or EGFR knockdown reversed ADAMTS1-induced prometastatic characteristics of RCC. A clinical analysis revealed a positive correlation between ADAMTS1 and VCAN or the EGFR and patients with RCC with high ADAMTS1 and VCAN expression had the worst prognoses.

CONCLUSIONS

Our results collectively uncover a novel cyclic axis involving ADAMTS1-VCAN-EGFR, which significantly contributes to RCC invasion and resistance to anoikis, thus presenting a promising therapeutic target for RCC metastasis.

Anoikis-related genes in breast cancer patients: reliable biomarker of prognosis

BACKGROUND

Breast cancer (BC) is the most common cancer in women, and its progression is closely related to the phenomenon of anoikis. Anoikis, the specific programmed death resulting from a lack of contact between cells and the extracellular matrix, has recently been recognized as playing a critical role in tumor initiation, maintenance, and treatment. The ability of cancer cells to resist anoikis leads to cancer progression and metastatic colonization. However, the impact of anoikis on the prognosis of BC patients remains unclear.

METHOD

This study utilized data from the Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases to collect transcriptome and clinical data of BC patients. Anoikis-related genes (ARGs) were classified into subtypes A and B through consensus clustering. Subsequently, survival prognosis analysis, immune cell infiltration analysis, and functional enrichment analysis were performed for both subtypes. Using the Least Absolute Shrinkage and Selection Operator (LASSO) regression analysis, a set of 10 ARGs related to prognosis was identified. Immune cell infiltration and tumor microenvironment analyses were conducted on these 10 ARGs to develop a prognostic model. Furthermore, single-cell data analysis and real-time polymerase chain reaction (RT-PCR) analysis were employed to study the expression of the 10 identified prognostic ARGs in BC cells.

RESULTS

One hundred thirty-five ARGs were identified as differentially expressed genes in the TCGA and GEO databases, with 42 of them associated with the survival prognosis of BC patients. Analyses involving Principal Component Analysis (PCA), t-Distributed Stochastic Neighbor Embedding (t-SNE), and Uniform Manifold Approximation and Projection (UMAP) revealed distinct expression patterns of ARGs between types A and B. Patients in type A exhibited worse survival prognosis and lower immune cell infiltration compared to type B. Subsequent analyses identified 10 key ARGs (YAP1, PIK3R1, BAK1, PHLDA2, EDA2R, LAMB3, CD24, SLC2A1, CDC25C, and SLC39A6) relevant to BC prognosis. Kaplan-Meier analysis indicated that high-risk patients based on these ARGs had a poorer BC prognosis. Additionally, Cox regression analysis established gender, age, T (tumor), N (nodes), and risk score as predictive factors in a nomogram model for BC. The model demonstrated diagnostic value for BC patients at 1, 3, and 5 years. Decision curve analysis (DCA) verified the risk score as a reliable predictor of BC patient survival rates. Moreover, RT-PCR results confirmed differential expressions of YAP1, PIK3R1, BAK1, PHLDA2, CD24, SLC2A1, and CDC25C in BC cells, with SLC39A6, EDA2R, and LAMB3 showing low expression levels.

CONCLUSION

ARGs markers can be used as BC biomarkers for risk stratification and survival prediction in BC patients. Besides, ARGs can be used as stratification factors for individualized and precise treatment of BC patients.

Survival mechanisms of circulating tumor cells and their implications for cancer treatment

Metastasis remains the principal trigger for relapse and mortality across diverse cancer types. Circulating tumor cells (CTCs), which originate from the primary tumor or its metastatic sites, traverse the vascular system, serving as precursors in cancer recurrence and metastasis. Nevertheless, before CTCs can establish themselves in the distant parenchyma, they must overcome significant challenges present within the circulatory system, including hydrodynamic shear stress (HSS), oxidative damage, anoikis, and immune surveillance. Recently, there has been a growing body of compelling evidence suggesting that a specific subset of CTCs can persist within the bloodstream, but the precise mechanisms of their survival remain largely elusive. This review aims to present an outline of the survival challenges encountered by CTCs and to summarize the recent advancements in understanding the underlying survival mechanisms, suggesting their implications for cancer treatment.

The critical role of glutamine and fatty acids in the metabolic reprogramming of anoikis-resistant melanoma cells

Introduction: Circulating tumor cells (CTCs) represent the sub-population of cells shed into the vasculature and able to survive in the bloodstream, adhere to target vascular endothelial cells, and re-growth into the distant organ. CTCs have been found in the blood of most solid tumor-bearing patients and are used as a diagnostic marker. Although a complex genotypic and phenotypic signature characterizes CTCs, the ability to survive in suspension constitutes the most critical property, known as resistance to anoikis, e.g., the ability to resist apoptosis resulting from a loss of substrate adhesion. Here, we selected melanoma cells resistant to anoikis, and we studied their metabolic reprogramming, with the aim of identifying new metabolic targets of CTCs. Methods: Subpopulations of melanoma cells expressing a high anoikis-resistant phenotype were selected by three consecutive rocking exposures in suspension and studied for their phenotypic and metabolic characteristics. Moreover, we tested the efficacy of different metabolic inhibitors targeting glycolysis (2DG), LDHA (LDHA-in-3), the mitochondrial electron transport chain complex I (rotenone), glutaminase (BPTES), fatty acid transporter (SSO), fatty acid synthase (denifanstat), CPT1 (etomoxir), to inhibit cell survival and colony formation ability after 24 h of rocking condition. Results: Anoikis-resistant cells displayed higher ability to grow in suspension on agarose-covered dishes respect to control cells, and higher cell viability and colony formation capability after a further step in rocking condition. They showed also an epithelial-to-mesenchymal transition associated with high invasiveness and a stemness-like phenotype. Anoikis-resistant melanoma cells in suspension showed a metabolic reprogramming from a characteristic glycolytic metabolism toward a more oxidative metabolism based on the use of glutamine and fatty acids, while re-adhesion on the dishes reversed the metabolism to glycolysis. The treatment with metabolic inhibitors highlighted the effectiveness of rotenone, BPTES, SSO, and etomoxir in reducing the viability and the colony formation ability of cells capable of surviving in suspension, confirming the dependence of their metabolism on oxidative phosphorylation, using glutamine and fatty acids as the most important fuels. Discussion: This finding opens up new therapeutic strategies based on metabolic inhibitors of glutaminase and fatty acid oxidation for the treatment of CTCs and melanoma metastases.

Cancer Metastasis-on-a-Chip for Modeling Metastatic Cascade and Drug Screening

Microfluidic chips are valuable tools for studying intricate cellular and cell-microenvironment interactions. Traditional in vitro cancer models lack accuracy in mimicking the complexities of in vivo tumor microenvironment. However, cancer-metastasis-on-a-chip (CMoC) models combine the advantages of 3D cultures and microfluidic technology, serving as powerful platforms for exploring cancer mechanisms and facilitating drug screening. These chips are able to compartmentalize the metastatic cascade, deepening the understanding of its underlying mechanisms. This article provides an overview of current CMoC models, focusing on distinctive models that simulate invasion, intravasation, circulation, extravasation, and colonization, and their applications in drug screening. Furthermore, challenges faced by CMoC and microfluidic technologies are discussed, while exploring promising future directions in cancer research. The ongoing development and integration of these models into cancer studies are expected to drive transformative advancements in the field.

Acidity and hypoxia of tumor microenvironment, a positive interplay in extracellular vesicle release by tumor cells

The complex and continuously evolving features of the tumor microenvironment, varying between tumor histotypes, are characterized by the presence of host cells and tumor cells embedded in a milieu shaped by hypoxia and low pH, resulting from the frequent imbalance between vascularity and tumor cell proliferation. These microenvironmental metabolic stressors play a crucial role in remodeling host cells and tumor cells, contributing to the stimulation of cancer cell heterogeneity, clonal evolution, and multidrug resistance, ultimately leading to progression and metastasis. The extracellular vesicles (EVs), membrane-enclosed structures released into the extracellular milieu by tumor/host cells, are now recognized as critical drivers in the complex intercellular communication between tumor cells and the local cellular components in a hypoxic/acidic microenvironment. Understanding the intricate molecular mechanisms governing the interactions between tumor and host cells within a hypoxic and acidic microenvironment, triggered by the release of EVs, could pave the way for innovative strategies to disrupt the complex interplay of cancer cells with their microenvironment. This approach may contribute to the development of an efficient and safe therapeutic strategy to combat cancer progression. Therefore, we review the major findings on the release of EVs in a hypoxic/acidic tumor microenvironment to appreciate their role in tumor progression toward metastatic disease.

Beyond Death: Unmasking the Intricacies of Apoptosis Escape

Apoptosis, or programmed cell death, maintains tissue homeostasis by eliminating damaged or unnecessary cells. However, cells can evade this process, contributing to conditions such as cancer. Escape mechanisms include anoikis, mitochondrial DNA depletion, cellular FLICE inhibitory protein (c-FLIP), endosomal sorting complexes required for transport (ESCRT), mitotic slippage, anastasis, and blebbishield formation. Anoikis, triggered by cell detachment from the extracellular matrix, is pivotal in cancer research due to its role in cellular survival and metastasis. Mitochondrial DNA depletion, associated with cellular dysfunction and diseases such as breast and prostate cancer, links to apoptosis resistance. The c-FLIP protein family, notably CFLAR, regulates cell death processes as a truncated caspase-8 form. The ESCRT complex aids apoptosis evasion by repairing intracellular damage through increased Ca2+ levels. Antimitotic agents induce mitotic arrest in cancer treatment but can lead to mitotic slippage and tetraploid cell formation. Anastasis allows cells to resist apoptosis induced by various triggers. Blebbishield formation suppresses apoptosis indirectly in cancer stem cells by transforming apoptotic cells into blebbishields. In conclusion, the future of apoptosis research offers exciting possibilities for innovative therapeutic approaches, enhanced diagnostic tools, and a deeper understanding of the complex biological processes that govern cell fate. Collaborative efforts across disciplines, including molecular biology, genetics, immunology, and bioinformatics, will be essential to realize these prospects and improve patient outcomes in diverse disease contexts.

Immune escape and metastasis mechanisms in melanoma: breaking down the dichotomy

Melanoma is one of the most lethal neoplasms of the skin. Despite the revolutionary introduction of immune checkpoint inhibitors, metastatic spread, and recurrence remain critical problems in resistant cases. Melanoma employs a multitude of mechanisms to subvert the immune system and successfully metastasize to distant organs. Concerningly, recent research also shows that tumor cells can disseminate early during melanoma progression and enter dormant states, eventually leading to metastases at a future time. Immune escape and metastasis have previously been viewed as separate phenomena; however, accumulating evidence is breaking down this dichotomy. Recent research into the progressive mechanisms of melanoma provides evidence that dedifferentiation similar to classical epithelial to mesenchymal transition (EMT), genes involved in neural crest stem cell maintenance, and hypoxia/acidosis, are important factors simultaneously involved in immune escape and metastasis. The likeness between EMT and early dissemination, and differences, also become apparent in these contexts. Detailed knowledge of the mechanisms behind "dual drivers" simultaneously promoting metastatically inclined and immunosuppressive environments can yield novel strategies effective in disabling multiple facets of melanoma progression. Furthermore, understanding progression through these drivers may provide insight towards novel treatments capable of preventing recurrence arising from dormant dissemination or improving immunotherapy outcomes.

Oncoviruses: Induction of cancer development and metastasis by increasing anoikis resistance

The phenomenon of cell death is a vital aspect in the regulation of aberrant cells such as cancer cells. Anoikis is a kind of cell death that occurs when cells get separated from the extracellular matrix. Some cancer cells can inhibit anoikis in order to progress metastasis. One of the key variables that might be implicated in anoikis resistance (AR) is viral infections. The most important viruses involved in this process are Epstein-Barr virus, human papillomavirus, hepatitis B virus, human herpes virus 8, human T-cell lymphotropic virus type 1, and hepatitis C virus. A better understanding of how carcinogenic viruses suppress anoikis might be helpful in developing an effective treatment for virus-associated cancers. In the current study, we review the role of the mentioned viruses and their gene products in anoikis inhibition.

Therapeutic targeting of anoikis resistance in cutaneous melanoma metastasis

The acquisition of resistance to anoikis, the cell death induced by loss of adhesion to the extracellular matrix, is an absolute requirement for the survival of disseminating and circulating tumour cells (CTCs), and for the seeding of metastatic lesions. In melanoma, a range of intracellular signalling cascades have been identified as potential drivers of anoikis resistance, however a full understanding of the process is yet to be attained. Mechanisms of anoikis resistance pose an attractive target for the therapeutic treatment of disseminating and circulating melanoma cells. This review explores the range of small molecule, peptide and antibody inhibitors targeting molecules involved in anoikis resistance in melanoma, and may be repurposed to prevent metastatic melanoma prior to its initiation, potentially improving the prognosis for patients.

Physicochemical aspects of the tumour microenvironment as drivers of vasculogenic mimicry

Tumour vascularisation is vital for cancer sustainment representing not only the main source of nutrients and oxygen supply but also an escape route for single or clustered cancer cells that, once detached from the primary mass, enter the blood circulation and disseminate to distant organs. Among the mechanisms identified to contribute to tumour vascularisation, vasculogenic mimicry (VM) is gaining increasing interest in the scientific community representing an intriguing target for cancer treatment. VM indeed associates with highly aggressive tumour phenotypes and strongly impairs patient outcomes. Differently from vessels of healthy tissues, tumour vasculature is extremely heterogeneous and tortuous, impeding efficient chemotherapy delivery, and at the meantime hyperpermeable and thus extremely accessible to metastasising cancer cells. Moreover, tumour vessel disorganisation creates a self-reinforcing vicious circle fuelling cancer malignancy and progression. Because of the inefficient oxygen delivery and metabolic waste removal from tumour vessels, many cells within the tumour mass indeed experience hypoxia and acidosis, now considered hallmarks of cancer. Being strong inducers of vascularisation, therapy resistance, inflammation and metastasis, hypoxia and acidosis create a permissive microenvironment for cancer progression and dissemination. Along with these considerations, we decided to focus our attention on the relationship between hypoxia/acidosis and VM. Indeed, besides tumour angiogenesis, VM is strongly influenced by both hypoxia and acidosis, which could potentiate each other and fuel this vicious circle. Thus, targeting hypoxia and acidosis may represent a potential target to treat VM to impair tumour perfusion and cancer cell sustainment.

miR-214-Enriched Extracellular Vesicles Released by Acid-Adapted Melanoma Cells Promote Inflammatory Macrophage-Dependent Tumor Trans-Endothelial Migration

Simple Summary

Cutaneous melanoma is the most aggressive form of skin cancer with high-metastatic ability. Despite the recent advancements in melanoma treatments, the prognosis of metastatic patients remains very poor. A better understanding of the molecular mechanisms leading to melanoma dissemination is urgently needed in order to develop novel therapeutical strategies to ameliorate patients’ outcomes. Extracellular vesicles (EV) released by tumor cells are key players in metastasis development: by conveying bioactive molecules with oncogenic activity, they can modulate the surrounding—and even the distant—microenvironment and reprogram recipient cells to facilitate the metastatic cascade. Here, we show that melanoma cells release a higher amount of miR-214-enriched EV when adapted to extracellular acidosis, which promote a macrophage activation state, capable of facilitating the trans-endothelial migration of melanoma cells. Thus, we disclose a new molecular mechanism to prevent melanoma intravasation based on miR-214 targeting.

Abstract

The understanding of the molecular mechanisms leading to melanoma dissemination is urgently needed in view of the identification of new targets and the development of innovative strategies to improve patients’ outcomes. Within the complexity of tumor intercellular communications leading to metastatic dissemination, extracellular vesicles (EV) released by tumor cells are central players. Indeed, the ability to travel through the circulatory system conveying oncogenic bioactive molecules even at distant sites makes EV capable of modulating recipient cells to facilitate metastatic dissemination. The dynamic remodeling of the tumor microenvironment might influence, along with a number of other events, tumoral EV release. We observed that, in melanoma, extracellular acidosis increases the release of EV enriched in miR-214, an onco-miRNA involved in melanoma metastasis. Then, miR-214-enriched EV were found to induce a state of macrophage activation, leading to an overproduction of proinflammatory cytokines and nitric oxide. Such an inflammatory microenvironment was able to alter the endothelial cell permeability, thereby facilitating the trans-endothelial migration of melanoma cells, a crucial step in the metastatic cascade. The use of synthetic miR-214 inhibitors and miR-214 overexpression allowed us to demonstrate the key role of miR-214 in the EV-dependent induction of macrophage activation. Overall, our in vitro study reveals that the release of tumor miR-214-enriched EV, potentiated by adapting tumor cells to extracellular acidosis, drives a macrophage-dependent trans-endothelial migration of melanoma cells. This finding points to miR-214 as a potential new therapeutic target to prevent melanoma intravasation.

The role and therapeutic significance of the anoikis pathway in renal clear cell carcinoma

Anoikis is a specialized mode of programmed cell death. Specifically, once cells detach from the original extracellular matrix, an apoptotic program is initiated, preventing colonization of the cells in distant parts of the organ. Therefore, both distant metastasis and colonization of cancer cells rely on the anoikis resistance of cancer cells. Bioinformatics analysis was performed to confirm the relation of anoikis to kidney renal cell carcinoma (KIRC). To construct a prognostic model for patients with KIRC, we investigated several genes of the anoikis pathway most closely related to KIRC and also contrasted the effects of common anticancer drugs on the KIRC pathway. Besides KIRC, we explored the expression of anoikis-related genes in various other cancers. We classified patients with KIRC into three clusters based on the coefficients and mRNA expression levels of anoikis-related genes selected using the GSVA algorithm. We used the GDSC database to predict the response of the anoikis pathway to common anticancer drugs and explored the potential targets of the anoikis pathway in KIRC. We then analyzed the response of common immunotherapies to the anoikis pathway to analyze the correlation between anoikis and immune checkpoint inhibitor therapy. Finally, eleven cancer-related genes were screened and a prognostic model was constructed using LASSO regression.

An Oleocanthal-Enriched EVO Oil Extract Induces the ROS Production in Gastric Cancer Cells and Potentiates the Effect of Chemotherapy

Oleocanthal, a minor polar compound in extra-virgin olive (EVO) oil, contains anticancer properties, which should be encouraged in its use in oncology. Gastric Cancer (GC), a very aggressive human cancer, is often diagnosed at advanced stages, when surgery is substituted or supported by chemotherapy (CT). However, CT frequently fails due to the patient’s resistance to the treatment. Thus, the aim of this study is to verify whether an OC-enriched EVO oil extract fraction (OCF) may be useful in order to overcome a resistance to GC. We evaluated the OCF effects on an AGS gastric adenocarcinoma cell line wild type (AGS wt) and on its subpopulations resistant to 5-fluorouracil (5FUr), Paclitaxel (TAXr) or cisplatin (CISr). We found that a 60 µM dose of the OCF acts on the AGS wt, 5FUr and TAXr, leading to the cell cycle inhibition and to a ROS production, but not on CISr cells. Resistance of CISr to the OCF seems to be due to higher levels of antioxidant-enzymes that can counteract the OCF-induced ROS production. Moreover, using the OCF plus 5-fluorouracil, Paclitaxel or cisplatin, we found a potentiating effect compared with a mono-treatment in all resistant GC cells, including CISr. In conclusion, the use of the OCF in the management of GC has shown very interesting advantages, opening-up the possibility to evaluate the efficacy of the OCF in vivo, as a valid adjuvant in the treatment of resistant GC.

Anoikis resistance in diffuse glioma: The potential therapeutic targets in the future

Glioma is the most common malignant intracranial tumor and exhibits diffuse metastasis and a high recurrence rate. The invasive property of glioma results from cell detachment. Anoikis is a special form of apoptosis that is activated upon cell detachment. Resistance to anoikis has proven to be a protumor factor. Therefore, it is suggested that anoikis resistance commonly occurs in glioma and promotes diffuse invasion. Several factors, such as integrin, E-cadherin, EGFR, IGFR, Trk, TGF-β, the Hippo pathway, NF-κB, eEF-2 kinase, MOB2, hypoxia, acidosis, ROS, Hsp and protective autophagy, have been shown to induce anoikis resistance in glioma. In our present review, we aim to summarize the underlying mechanism of resistance and the therapeutic potential of these molecules.

Proton export upregulates aerobic glycolysis

INTRODUCTION

Aggressive cancers commonly ferment glucose to lactic acid at high rates, even in the presence of oxygen. This is known as aerobic glycolysis, or the "Warburg Effect." It is widely assumed that this is a consequence of the upregulation of glycolytic enzymes. Oncogenic drivers can increase the expression of most proteins in the glycolytic pathway, including the terminal step of exporting H+ equivalents from the cytoplasm. Proton exporters maintain an alkaline cytoplasmic pH, which can enhance all glycolytic enzyme activities, even in the absence of oncogene-related expression changes. Based on this observation, we hypothesized that increased uptake and fermentative metabolism of glucose could be driven by the expulsion of H+ equivalents from the cell.

RESULTS

To test this hypothesis, we stably transfected lowly glycolytic MCF-7, U2-OS, and glycolytic HEK293 cells to express proton-exporting systems: either PMA1 (plasma membrane ATPase 1, a yeast H+-ATPase) or CA-IX (carbonic anhydrase 9). The expression of either exporter in vitro enhanced aerobic glycolysis as measured by glucose consumption, lactate production, and extracellular acidification rate. This resulted in an increased intracellular pH, and metabolomic analyses indicated that this was associated with an increased flux of all glycolytic enzymes upstream of pyruvate kinase. These cells also demonstrated increased migratory and invasive phenotypes in vitro, and these were recapitulated in vivo by more aggressive behavior, whereby the acid-producing cells formed higher-grade tumors with higher rates of metastases. Neutralizing tumor acidity with oral buffers reduced the metastatic burden.

CONCLUSIONS

Therefore, cancer cells which increase export of H+ equivalents subsequently increase intracellular alkalization, even without oncogenic driver mutations, and this is sufficient to alter cancer metabolism towards an upregulation of aerobic glycolysis, a Warburg phenotype. Overall, we have shown that the traditional understanding of cancer cells favoring glycolysis and the subsequent extracellular acidification is not always linear. Cells which can, independent of metabolism, acidify through proton exporter activity can sufficiently drive their metabolism towards glycolysis providing an important fitness advantage for survival.

Understanding the cell survival mechanism of anoikis-resistant cancer cells during different steps of metastasis

Anchorage-independent survival of cancer cells is associated with metastasis as it enables cells to travel to secondary target sites. Tissue integrity is generally maintained by detachment-induced cell death called 'anoikis', but cancer cells undergoing the multistep metastatic process show resistance to anoikis. Anoikis resistance enables these cells to survive through the extracellular matrix (ECM) deprived phase, which starts when cancer cells detach and move into the circulation till cells reach to the secondary target site. Comprehensive analysis of the molecular and functional biology of anoikis resistance in cancer cells will provide crucial details about cancer metastasis, enabling us to identify novel therapeutic targets against cancer cell dissemination and ultimately secondary tumor formation. This review broadly summarizes recent advances in the understanding of cellular and molecular events leading to anoikis and anoikis resistance. It further elaborates more about the signaling cross-talk in anoikis resistance and its regulation during metastasis.

Identification of distinct slow mode of reversible adaptation of pancreatic ductal adenocarcinoma to the prolonged acidic pH microenvironment

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is the most common pancreatic neoplasm with high metastatic potential and poor clinical outcome. Like other solid tumors, PDAC in the early stages is often asymptomatic, and grows very slowly under a distinct acidic pHe (extracellular pH) microenvironment. However, most previous studies have only reported the fate of cancerous cells upon cursory exposure to acidic pHe conditions. Little is known about how solid tumors-such as the lethal PDAC originating within the pancreatic duct-acinar system that secretes alkaline fluids-evolve to withstand and adapt to the prolonged acidotic microenvironmental stress.

METHODS

Representative PDAC cells were exposed to various biologically relevant periods of extracellular acidity. The time effects of acidic pHe stress were determined with respect to tumor cell proliferation, phenotypic regulation, autophagic control, metabolic plasticity, mitochondrial network dynamics, and metastatic potentials.

RESULTS

Unlike previous short-term analyses, we found that the acidosis-mediated autophagy occurred mainly as an early stress response but not for later adaptation to microenvironmental acidification. Rather, PDAC cells use a distinct and lengthy process of reversible adaptive plasticity centered on the early fast and later slow mitochondrial network dynamics and metabolic adjustment. This regulates their acute responses and chronic adaptations to the acidic pHe microenvironment. A more malignant state with increased migratory and invasive potentials in long-term acidosis-adapted PDAC cells was obtained with key regulatory molecules being closely related to overall patient survival. Finally, the identification of 34 acidic pHe-related genes could be potential targets for the development of diagnosis and treatment against PDAC.

CONCLUSIONS

Our study offers a novel mechanism of early rapid response and late reversible adaptation of PDAC cells to the stress of extracellular acidosis. The presence of this distinctive yet slow mode of machinery fills an important knowledge gap in how solid tumor cells sense, respond, reprogram, and ultimately adapt to the persistent microenvironmental acidification.

Molecular insights into phytochemicals-driven break function in tumor microenvironment

Advanced knowledge about the role of tumor microenvironment (TME) in cancer progression has opened various ways to target the vast signaling pathways for cancer treatment. Failures of the currently used drugs have raised out the need to look for novel drugs which can target various crucial aspects of cancer progression (e.g., angiogenesis, uncontrolled cell division, and metastasis). Phytochemicals behaving as potent anticancer agents shows promise as therapeutics. Various phytochemicals, such as curcumin, Epigallocatechin Gallate (EGCG), resveratrol, plumbagin, genistein, and others, have been identified with modulatory effect on TME. These phytochemicals often target the molecular pathways that reside in the tumor vicinity associated with endothelial cells, cancer-associated fibroblasts, immune cells, mesenchymal stem cells, other cell types, vascular and lymphatic networks, and extracellular matrix which are important for tumor progression and development. Some phytochemicals also target the internal signaling pathways, including STAT3, NF-қB, ERK-1/2, and PI3K/Akt signaling of noncancer cell, residing in the microenvironment, and thus inhibiting the supportive effect from these cells in tumor development. However, much information needs to be acquired before using these phytochemicals in cancer treatment. The primary objective of this review is to provide a better knowledge about the role of TME in cancer progression and development, focusing on the different targets which can be used for therapeutic approach, and then to give a brief account on some known phytochemicals to date, which have shown remarkable TME modulatory effects. PRACTICAL APPLICATIONS: For the use of phytochemicals as therapeutics, it is highly recommended that their precise target should be known; therefore studies should be encouraged such that the effects of these phytochemicals can be evaluated on the individual cellular level like how the phytochemical is targeting the tumor-associated macrophage, or any other cell residing in the tumor microenvironment (TME), and the compound should target a specific component of TME to avoid off target effects.

Mechanisms for Modulating Anoikis Resistance in Cancer and the Relevance of Metabolic Reprogramming

The attachment of cells to the extracellular matrix (ECM) is the hallmark of structure–function stability and well-being. ECM detachment in localized tumors precedes abnormal dissemination of tumor cells culminating in metastasis. Programmed cell death (PCD) is activated during tumorigenesis to clear off ECM-detached cells through “anoikis.” However, cancer cells develop several mechanisms for abrogating anoikis, thus promoting their invasiveness and metastasis. Specific factors, such as growth proteins, pH, transcriptional signaling pathways, and oxidative stress, have been reported as drivers of anoikis resistance, thus enhancing cancer proliferation and metastasis. Recent studies highlighted the key contributions of metabolic pathways, enabling the cells to bypass anoikis. Therefore, understanding the mechanisms driving anoikis resistance could help to counteract tumor progression and prevent metastasis. This review elucidates the dynamics employed by cancer cells to impede anoikis, thus promoting proliferation, invasion, and metastasis. In addition, the authors have discussed other metabolic intermediates (especially amino acids and nucleotides) that are less explored, which could be crucial for anoikis resistance and metastasis.

The Carbonic Anhydrase IX inhibitor SLC-0111 as emerging agent against the mesenchymal stem cell-derived pro-survival effects on melanoma cells

Mesenchymal stem cells (MSC) take part to solid tumour-associated stroma and critically influence progression of malignancy. Our study represents a striking example of melanoma progression to a more malignant and resistant phenotype promoted by MSC and the possibility to contrast this diabolic liaison using CAIX inhibitors. In particular, we demonstrated that melanoma cells exposed to a MSC-conditioned medium switch to a more malignant phenotype, characterised by resistance to programmed cell death and endowed with an epithelial-to-mesenchymal transition and stem cell characteristics. These effects were reversed abrogating MSC CAIX activity using SLC-0111, a CAIX inhibitor. Moreover, the acquisition by melanoma cells of a Vemurafenib-resistant phenotype upon MSC-conditioned medium exposure was removed when MSC were treated with SLC-0111. Therefore, MSC may profoundly reprogramme melanoma cells towards a wide resistant phenotype through CAIX involvement, as the use of SLC-0111 is able to contrast the development of this highly risky adaptation for disease progression.

YAP activation in melanoma contributes to anoikis resistance and metastasis

Melanoma is inherently heterogeneous, providing resistance to apoptosis. Anoikis resistance is a hallmark feature of metastatic melanoma to escape apoptosis when cells lose contact with adjacent cells or extracellular matrix. The yes-associated protein transcription co-activator is the effector of Hippo pathway. Herein, we investigated the function of yes-associated protein in anoikis resistance of melanoma cells. When melanoma cells were grown under anchorage-independent condition, anoikis-resistant cells displayed higher levels of yes-associated protein activation than the cells that were attached to the basement membrane, as evidenced by downregulated phosphorylated yes-associated protein at Ser127 and higher expression of downstream genes BCL2 and MCL-1. Yes-associated protein overexpression directly enhanced the anoikis resistance and metastatic potential of melanoma cells. Conversely, yes-associated protein inhibitor CA3 exhibited Dose-dependent induction of anoikis in resistant melanoma cells and exerted great inhibition on cell migration. Knockdown of yes-associated protein expression by shRNA also rendered melanoma cells susceptible to anoikis and interrupted cell invasiveness. Yes-associated protein inhibition in anoikis-resistant cells also reduced the number of metastatic nodules in the lung sections of SCID mice. Clinically, higher yes-associated protein level in the lung metastasis tissues correlated with higher BCL2 and MCL1 expressions compared with the non-metastasis tissues. Overall, our finding suggests that the aberrant activation of yes-associated protein exerts important role on anoikis resistance and metastatic capability of melanoma cells.

The acidic tumor microenvironment drives a stem-like phenotype in melanoma cells

Abstract

Acidosis characterizes the microenvironment of most solid tumors and is considered a new hallmark of cancer. It is mainly caused by both “aerobic” and “anaerobic” glycolysis of differently adapted cancer cells, with the final product lactic acid being responsible of the extracellular acidification. Many evidences underline the role of extracellular acidosis in tumor progression. Among the different findings, we demonstrated that acidosis-exposed cancer cells are characterized by an epithelial-to-mesenchymal transition phenotype with high invasive ability, high resistance to apoptosis, anchorage-independent growth, and drug therapy. Acidic melanoma cells over-express SOX2, which is crucial for the maintenance of their oxidative metabolism, and carbonic anhydrase IX, that correlates with poor prognosis of cancer patients. Considering these evidences, we realized that the profile outlined for acid cancer cells inevitably remind us the stemness profile. Therefore, we wondered whether extracellular acidosis might induce in cancer cells the acquisition of stem-like properties and contribute to the expansion of the cancer stem cell sub-population. We found that a chronic adaptation to acidosis stimulates in cancer cells the expression of stem-related markers, also providing a high in vitro/in vivo clonogenic and trans-differentiating ability. Moreover, we observed that the acidosis-induced stem-like phenotype of melanoma cells was reversible and related to the EMT induction. These findings help to characterize a further aspect of stem cell niche, contributing to the sustainment and expansion of cancer stem cell subpopulation. Thus, the usage of agents controlling tumor extracellular acidosis might acquire great importance in the clinic for the treatment of aggressive solid tumor.

Key messages

• Extracellular acidosis up-regulates EMT and stem-related markers in melanoma cells

• Acidic medium up-regulates in vitro self-renewal capacity of melanoma cells

• Chronic acidosis adaptation induces trans-differentiation ability in melanoma cells

• Melanoma cells adapted to acidosis show higher tumor-initiating potential than control cells

• Extracellular acidosis promotes a stem-like phenotype in prostate and colorectal carcinoma cells

Cancer Glycolytic Dependence as a New Target of Olive Leaf Extract

Oleuropein (Ole), the main bioactive phenolic component of Olea europaea L. has recently attracted the scientific attention for its several beneficial properties, including its anticancer effects. This study is intended to investigate whether an olive leaf extract enriched in Ole (OLEO) may counteract the aerobic glycolysis exploited by tumor cells. We found that OLEO decreased melanoma cell proliferation and motility. OLEO was also able to reduce the rate of glycolysis of human melanoma cells without affecting oxidative phosphorylation. This reduction was associated with a significant decrease of glucose transporter-1, protein kinase isoform M2 and monocarboxylate transporter-4 expression, possible drivers of such glycolysis inhibition. Extending the study to other tumor histotypes, we observed that the metabolic effects of OLEO are not confined to melanoma, but also confirmed in colon carcinoma, breast cancer and chronic myeloid leukemia. In conclusion, OLEO represents a natural product effective in reducing the glycolytic metabolism of different tumor types, revealing an extended metabolic inhibitory activity that may be well suited in a complementary anti-cancer therapy.

Cellular and Extracellular Components in Tumor Microenvironment and Their Application in Early Diagnosis of Cancers

Tumors are surrounded by complex environmental components, including blood and lymph vessels, fibroblasts, endothelial cells, immune cells, cytokines, extracellular vesicles, and extracellular matrix. All the stromal components together with the tumor cells form the tumor microenvironment (TME). In addition, extracellular physical and chemical factors, including extracellular pH, hypoxia, elevated interstitial fluid pressure, and fibrosis, are closely associated with tumor progression, metastasis, immunosuppression, and drug resistance. Cellular and extracellular components in TME contribute to nearly all procedures of carcinogenesis. By summarizing the recent work in this field, we make a comprehensive review on the role of cellular and extracellular components in the process of carcinogenesis and their potential application in early diagnosis of cancer. We hope that a systematic review of the diverse aspects of TME will help both research scientists and clinicians in this field.

Potential Role of HLA Class I Antigens in the Glycolytic Metabolism and Motility of Melanoma Cells

Besides playing a crucial role in immune surveillance, human leukocyte antigens (HLA) possess numerous non-immune functions involved in cell communication. In the present study, screening of a panel of HLA class I- and HLA class II-specific monoclonal antibodies (mAbs) for their effects on the metabolism of human melanoma cells showed for the first time that the HLA-B,C-specific mAb B1.23.2 reduced the expression level of key glycolytic enzymes, but did not affect that of mitochondrial respiration effectors. As a result, the metabolism of melanoma cells shifted from a Warburg metabolism to a more oxidative phosphorylation. In addition, the HLA-B,C-specific mAb B1.23.2 downregulated the expression of glutamine transporter and glutaminase enzyme participating in the reduction of tricarboxylic acid cycle. The HLA-B,C-specific mAb B1.23.2-mediated reduction in energy production was associated with a reduction of melanoma cell motility. On the whole, the described results suggest that HLA class I antigens, and in particular the gene products of HLA-B and C loci play a role in the motility of melanoma cells by regulating their metabolism.