Acidic tumor microenvironment in human melanoma

Targeting tumour metabolism in melanoma to enhance response to immune checkpoint inhibition: A balancing act

Immune checkpoint inhibition has transformed the treatment landscape of advanced melanoma and long-term survival of patients is now possible. However, at least half of the patients do not benefit sufficiently. Metabolic reprogramming is a hallmark of cancer cells and may contribute to both tumour growth and immune evasion by the tumour. Preclinical studies have indeed demonstrated that modulating tumour metabolism can reduce tumour growth while improving the functionality of immune cells. Since metabolic pathways are commonly shared between immune and tumour cells, it is essential to understand how modulating tumour metabolism in patients influences the intricate balance of pro-and anti-tumour immune effects in the tumour microenvironment. The key question is whether modulating tumour metabolism can inhibit tumour cell growth as well as facilitate an anti-tumour immune response. Here, we review current knowledge on the effect of tumour metabolism on the immune response in melanoma. We summarise metabolic pathways in melanoma and non-cancerous cells in the tumour microenvironment and discuss models and techniques available to study the metabolic-immune interaction. Finally, we discuss clinical use of these techniques to improve our understanding of how metabolic interventions can tip the balance towards a favourable, immune permissive microenvironment in melanoma patients.

Injectable Dendrimer Hydrogel Delivers Melphalan in Both Conjugated and Free Forms for Retinoblastoma

We report the successful synthesis of an injectable dendrimer hydrogel (DH) carrying melphalan, a clinical drug for retinoblastoma treatment, in both conjugated and free forms. Polyamidoamine (PAMAM) dendrimer generation 5 (G5) is surface-modified with an acid-sensitive acetal-dibenzocyclooctyne linker and then undergoes azide-alkyne cycloaddition with melphalan-PEG-N3 conjugate to form G5-acetal-melphalan. During the DH gelation between G5-acetal-melphalan and PEG-diacrylate, free melphalan is added, resulting in a hydrogel (G5-acetal-melphalan-DH/melphalan) that carries the drug in both conjugated and free forms. Melphalan is slowly released from G5-acetal-melphalan-DH/melphalan, with the conjugated melphalan released more quickly at pH 5.3 due to acid-triggered acetal bond cleavage. The formulation's in vitro safety and efficacy were established on human corneal epithelia (HCE-2) and retinoblastoma cells (Y79). In an in vivo Y79 tumor xenograft model of retinoblastoma, intratumorally injected G5-melphalan-DH formulation prolonged tumor suppression. This injectable, multimodal, pH-responsive formulation shows promise for intravitreal injection to treat retinoblastoma.

Tumor microenvironment: A playground for cells from multiple diverse origins

Tumor microenvironment is formed by various cellular and non-cellular components which interact with one another and form a complex network of interactions. Some of these cellular components also attain a secretory phenotype and release growth factors, cytokines, chemokines etc. in the surroundings which are capable of inducing even greater number of signalling networks. All these interactions play a decisive role in determining the course of tumorigenesis. The treatment strategies against cancer also exert their impact on the local microenvironment. Such interactions and anticancer therapies have been found to induce more deleterious outcomes like immunosuppression and chemoresistance in the process of tumor progression. Hence, understanding the tumor microenvironment is crucial for dealing with cancer and chemoresistance. This review is an attempt to develop some understanding about the tumor microenvironment and different factors which modulate it, thereby contributing to tumorigenesis. Along with summarising the major components of tumor microenvironment and various interactions taking place between them, it also throws some light on how the existing and potential therapies exert their impact on these dynamics.

Angiogenesis Still Plays a Crucial Role in Human Melanoma Progression

Angiogenesis plays a pivotal role in tumor progression, particularly in melanoma, the deadliest form of skin cancer. This review synthesizes current knowledge on the intricate interplay between angiogenesis and tumor microenvironment (TME) in melanoma progression. Pro-angiogenic factors, including VEGF, PlGF, FGF-2, IL-8, Ang, TGF-β, PDGF, integrins, MMPs, and PAF, modulate angiogenesis and contribute to melanoma metastasis. Additionally, cells within the TME, such as cancer-associated fibroblasts, mast cells, and melanoma-associated macrophages, influence tumor angiogenesis and progression. Anti-angiogenic therapies, while showing promise, face challenges such as drug resistance and tumor-induced activation of alternative angiogenic pathways. Rational combinations of anti-angiogenic agents and immunotherapies are being explored to overcome resistance. Biomarker identification for treatment response remains crucial for personalized therapies. This review highlights the complexity of angiogenesis in melanoma and underscores the need for innovative therapeutic approaches tailored to the dynamic TME.

CAR NK Cell Therapy for the Treatment of Metastatic Melanoma: Potential & Prospects

Melanoma is among the most lethal forms of cancer, accounting for 80% of deaths despite comprising just 5% of skin cancer cases. Treatment options remain limited due to the genetic and epigenetic mechanisms associated with melanoma heterogeneity that underlie the rapid development of secondary drug resistance. For this reason, the development of novel treatments remains paramount to the improvement of patient outcomes. Although the advent of chimeric antigen receptor-expressing T (CAR-T) cell immunotherapies has led to many clinical successes for hematological malignancies, these treatments are limited in their utility by their immune-induced side effects and a high risk of systemic toxicities. CAR natural killer (CAR-NK) cell immunotherapies are a particularly promising alternative to CAR-T cell immunotherapies, as they offer a more favorable safety profile and have the capacity for fine-tuned cytotoxic activity. In this review, the discussion of the prospects and potential of CAR-NK cell immunotherapies touches upon the clinical contexts of melanoma, the immunobiology of NK cells, the immunosuppressive barriers preventing endogenous immune cells from eliminating tumors, and the structure and design of chimeric antigen receptors, then finishes with a series of proposed design innovations that could improve the efficacy CAR-NK cell immunotherapies in future studies.

Nanomedicine Strategies in Conquering and Utilizing the Cancer Hypoxia Environment

Cancer with a complex pathological process is a major disease to human welfare. Due to the imbalance between oxygen (O2) supply and consumption, hypoxia is a natural characteristic of most solid tumors and an important obstacle for cancer therapy, which is closely related to tumor proliferation, metastasis, and invasion. Various strategies to exploit the feature of tumor hypoxia have been developed in the past decade, which can be used to alleviate tumor hypoxia, or utilize the hypoxia for targeted delivery and diagnostic imaging. The strategies to alleviate tumor hypoxia include delivering O2, in situ O2 generation, reprogramming the tumor vascular system, decreasing O2 consumption, and inhibiting HIF-1 related pathways. On the other side, hypoxia can also be utilized for hypoxia-responsive chemical construction and hypoxia-active prodrug-based strategies. Taking advantage of hypoxia in the tumor region, a number of methods have been applied to identify and keep track of changes in tumor hypoxia. Herein, we thoroughly review the recent progress of nanomedicine strategies in both conquering and utilizing hypoxia to combat cancer and put forward the prospect of emerging nanomaterials for future clinical transformation, which hopes to provide perspectives in nanomaterials design.

Molecular Basis for Mambalgin-2 Interaction with Heterotrimeric α-ENaC/ASIC1a/γ-ENaC Channels in Cancer Cells

Cancer progression is characterized by microenvironmental acidification. Tumor cells adapt to low environmental pH by activating acid-sensing trimeric ion channels of the DEG/ENaC family. The α-ENaC/ASIC1a/γ-ENaC heterotrimeric channel is a tumor-specific acid-sensing channel, and its targeting can be considered a new strategy for cancer therapy. Mambalgin-2 from the Dendroaspis polylepis venom inhibits the α-ENaC/ASIC1a/γ-ENaC heterotrimer more effectively than the homotrimeric ASIC1a channel, initially proposed as the target of mambalgin-2. Although the molecular basis of such mambalgin selectivity remained unclear. Here, we built the models of the complexes of mambalgin-2 with the α-ENaC/ASIC1a/γ-ENaC and ASIC1a channels, performed MD and predicted the difference in the binding modes. The importance of the 'head' loop region of mambalgin-2 for the interaction with the hetero-, but not with the homotrimeric channel was confirmed by site-directed mutagenesis and electrophysiology. A new mode of allosteric regulation of the ENaC channels by linking the thumb domain of the ASIC1a subunit with the palm domain of the γ-ENaC subunit was proposed. The data obtained provide new insights into the regulation of various types of acid-sensing ion channels and the development of new strategies for cancer treatment.

GPR4 in the pH-dependent migration of melanoma cells in the tumor microenvironment

Due to its high metastatic potential, malignant melanoma is one of the deadliest skin cancers. In melanoma as well as in other cancers, acidification of the tumor microenvironment (=TME, inverse pH-gradient) is a well-known driver of tumor progression and metastasis. Membrane-bound receptors, such as the proton-sensitive GPCR (pH-GPCR) GPR4, are considered as potential initiators of the signalling cascades relevant to malignant transformation. In this study, we investigated the pH-dependent migration of GPR4 wildtype/overexpressing SK-Mel-28 cells using an impedance-based electrical wounding and migration assay and classical Boyden chamber experiments. Migration of GPR4 overexpressing SK-Mel-28 cells was enhanced in a range of pH 6.5-7.5 as compared to controls in the impedance-based electrical wounding and migration assay. In Boyden chamber experiments, GPR4 overexpression only increased migration at pH 7.5 in a Matrigel-free setup, but not at pH 6.5. Results indicate that GPR4 is involved in the migration of melanoma cells, especially in the tumor periphery, and that this process is affected by pH in the TME.

Design of Nanoparticles in Cancer Therapy Based on Tumor Microenvironment Properties

Cancer is one of the leading causes of death worldwide, and battling cancer has always been a challenging subject in medical sciences. All over the world, scientists from different fields of study try to gain a deeper knowledge about the biology and roots of cancer and, consequently, provide better strategies to fight against it. During the past few decades, nanoparticles (NPs) have attracted much attention for the delivery of therapeutic and diagnostic agents with high efficiency and reduced side effects in cancer treatment. Targeted and stimuli-sensitive nanoparticles have been widely studied for cancer therapy in recent years, and many more studies are ongoing. This review aims to provide a broad view of different nanoparticle systems with characteristics that allow them to target diverse properties of the tumor microenvironment (TME) from nanoparticles that can be activated and release their cargo due to the specific characteristics of the TME (such as low pH, redox, and hypoxia) to nanoparticles that can target different cellular and molecular targets of the present cell and molecules in the TME.

Nucleic acid-triggered tumoral immunity propagates pH-selective therapeutic antibodies through tumor-driven epitope spreading

Important roles of humoral tumor immunity are often pointed out; however, precise profiles of dominant antigens and developmental mechanisms remain elusive. We systematically investigated the humoral antigens of dominant intratumor immunoglobulin clones found in human cancers. We found that approximately half of the corresponding antigens were restricted to strongly and densely negatively charged polymers, resulting in simultaneous reactivities of the antibodies to both densely sulfated glycosaminoglycans (dsGAGs) and nucleic acids (NAs). These anti-dsGAG/NA antibodies matured and expanded via intratumoral immunological driving force of innate immunity via NAs. These human cancer-derived antibodies exhibited acidic pH-selective affinity across both antigens and showed specific reactivity to diverse spectrums of human tumor cells. The antibody-drug conjugate exerted therapeutic effects against multiple cancers in vivo by targeting cell surface dsGAG antigens. This study reveals that intratumoral immunological reactions propagate tumor-oriented immunoglobulin clones and demonstrates a new therapeutic modality for the universal treatment of human malignancies.

The mitochondrial pyruvate carrier at the crossroads of intermediary metabolism

Pyruvate metabolism, a central nexus of carbon homeostasis, is an evolutionarily conserved process and aberrant pyruvate metabolism is associated with and contributes to numerous human metabolic disorders including diabetes, cancer, and heart disease. As a product of glycolysis, pyruvate is primarily generated in the cytosol before being transported into the mitochondrion for further metabolism. Pyruvate entry into the mitochondrial matrix is a critical step for efficient generation of reducing equivalents and ATP and for the biosynthesis of glucose, fatty acids, and amino acids from pyruvate. However, for many years, the identity of the carrier protein(s) that transported pyruvate into the mitochondrial matrix remained a mystery. In 2012, the molecular-genetic identification of the mitochondrial pyruvate carrier (MPC), a heterodimeric complex composed of protein subunits MPC1 and MPC2, enabled studies that shed light on the many metabolic and physiological processes regulated by pyruvate metabolism. A better understanding of the mechanisms regulating pyruvate transport and the processes affected by pyruvate metabolism may enable novel therapeutics to modulate mitochondrial pyruvate flux to treat a variety of disorders. Herein, we review our current knowledge of the MPC, discuss recent advances in the understanding of mitochondrial pyruvate metabolism in various tissue and cell types, and address some of the outstanding questions relevant to this field.

Dual-Mode Tumor Imaging Using Probes That Are Responsive to Hypoxia-Induced Pathological Conditions

Hypoxia in solid tumors is associated with poor prognosis, increased aggressiveness, and strong resistance to therapeutics, making accurate monitoring of hypoxia important. Several imaging modalities have been used to study hypoxia, but each modality has inherent limitations. The use of a second modality can compensate for the limitations and validate the results of any single imaging modality. In this review, we describe dual-mode imaging systems for the detection of hypoxia that have been reported since the start of the 21st century. First, we provide a brief overview of the hallmarks of hypoxia used for imaging and the imaging modalities used to detect hypoxia, including optical imaging, ultrasound imaging, photoacoustic imaging, single-photon emission tomography, X-ray computed tomography, positron emission tomography, Cerenkov radiation energy transfer imaging, magnetic resonance imaging, electron paramagnetic resonance imaging, magnetic particle imaging, and surface-enhanced Raman spectroscopy, and mass spectrometric imaging. These overviews are followed by examples of hypoxia-relevant imaging using a mixture of probes for complementary single-mode imaging techniques. Then, we describe dual-mode molecular switches that are responsive in multiple imaging modalities to at least one hypoxia-induced pathological change. Finally, we offer future perspectives toward dual-mode imaging of hypoxia and hypoxia-induced pathophysiological changes in tumor microenvironments.

Role of proton-activated G protein-coupled receptors in pathophysiology

Local acidification is a common feature of many disease processes such as inflammation, infarction, or solid tumor growth. Acidic pH is not merely a sequelae of disease but contributes to recruitment and regulation of immune cells, modifies metabolism of parenchymal, immune and tumor cells, modulates fibrosis, vascular permeability, oxygen availability and consumption, invasiveness of tumor cells, and impacts on cell survival. Thus, multiple pH-sensing mechanisms must exist in cells involved in these processes. These pH-sensors play important roles in normal physiology and pathophysiology, and hence might be attractive targets for pharmacological interventions. Among the pH-sensing mechanisms, OGR1 (GPR68), GPR4 (GPR4), and TDAG8 (GPR65) have emerged as important molecules. These G protein-coupled receptors are widely expressed, are upregulated in inflammation and tumors, sense changes in extracellular pH in the range between pH 8 and 6, and are involved in modulating key processes in inflammation, tumor biology, and fibrosis. This review discusses key features of these receptors and highlights important disease states and pathways affected by their activity.

Role of Amino Acid Transporter SNAT1/SLC38A1 in Human Melanoma

Simple Summary

Malignant melanoma originates from melanocytes. Due to its high metastatic potential and its increasing incidence, it is one of the most aggressive types of cancer. Cancer cells generally exhibit an elevated metabolism, consequently adapting their expression of transport proteins to meet the increased demand of nutrients, such as amino acids. The aim of this study was to analyze the expression and function of the amino acid transporter SNAT1 in human melanoma. In addition, we wanted to determine its role in development and progression of malignant melanoma. We revealed that SNAT1 is overexpressed in melanoma tissue samples, as well as primary and metastatic cell lines. Moreover, we were able to show that SNAT1 plays an important role in forcing proliferation, colony formation, migration and invasion, and inhibiting senescence of melanoma cells. Amino acid transporters like SNAT1 are therefore promising targets for the development of novel therapeutic strategies against melanoma.

Abstract

The tumor metabolism is an important driver of cancer cell survival and growth, as rapidly dividing tumor cells exhibit a high demand for energetic sources and must adapt to microenvironmental changes. Therefore, metabolic reprogramming of cancer cells and the associated deregulation of nutrient transporters are a hallmark of cancer cells. Amino acids are essential for cancer cells to synthesize the necessary amount of protein, DNA, and RNA. Although cancer cells can synthesize glutamine de novo, most cancer cells show an increased uptake of glutamine from the tumor microenvironment. Especially SNAT1/SLC38A1, a member of the sodium neutral amino acid transporter (SNAT) family, plays an essential role during major net import of glutamine. In this study, we revealed a significant upregulation of SNAT1 expression in human melanoma tissue in comparison to healthy epidermis and an increased SNAT1 expression level in human melanoma cell lines when compared to normal human melanocytes (NHEMs). We demonstrated that functional inhibition of SNAT1 with α-(methylamino) isobutyric acid (MeAIB), as well as siRNA-mediated downregulation reduces cancer cell growth, cellular migration, invasion, and leads to induction of senescence in melanoma cells. Consequently, these results demonstrate that the amino acid transporter SNAT1 is essential for cancer growth, and indicates a potential target for cancer chemotherapy.

Identification of Potential Biomarkers and Small Molecule Drugs for Cutaneous Melanoma Using Integrated Bioinformatic Analysis

Background: Cutaneous melanoma (CM) is a type of skin cancer with a high fatality rate, and its pathogenesis has not yet been fully elucidated.

Methods: We obtained the gene expression datasets of CM through the Gene Expression Omnibus (GEO) database. Subsequently, robust rank aggregation (RRA) method was used to identify differentially expressed genes (DEGs) between CM cases and normal skin controls. Gene functional annotation was performed to explore the potential function of the DEGs. We built the protein–protein interaction (PPI) network by the Interactive Gene database retrieval tool (STRING) and selected hub modules by Molecular Complexity Detection (MCODE). We furthered and validated our results using the TCGA-GTEX dataset. Finally, potential small molecule drugs were predicted by CMap database and verified by molecular docking method.

Results: A total of 135 DEGs were obtained by RRA synthesis analysis. GMPR, EMP3, SLC45A2, PDZD2, NPY1R, DLG5 and ADH1B were screened as potential targets for CM. Furazolidone was screened as a potential small molecule drug for the treatment of CM, and its mechanism may be related to the inhibition of CM cell proliferation by acting on GMPR.

Conclusion: We identified seven prognostic therapeutic targets associated with CM and furazolidone could be used as a potential drug for CM treatment, providing new prognostic markers, potential therapeutic targets and small molecule drugs for the treatment and prevention of CM.

Extracellular Vesicles Derived from Acidified Metastatic Melanoma Cells Stimulate Growth, Migration, and Stemness of Normal Keratinocytes

Metastatic melanoma is a highly malignant tumor. Melanoma cells release extracellular vesicles (EVs), which contribute to the growth, metastasis, and malignancy of neighboring cells by transfer of tumor-promoting miRNAs, mRNA, and proteins. Melanoma microenvironment acidification promotes tumor progression and determines EVs’ properties. We studied the influence of EVs derived from metastatic melanoma cells cultivated at acidic (6.5) and normal (7.4) pH on the morphology and homeostasis of normal keratinocytes. Acidification of metastatic melanoma environment made EVs more prooncogenic with increased expression of prooncogenic mi221 RNA, stemless factor CD133, and pro-migration factor SNAI1, as well as with downregulated antitumor mir7 RNA. Incubation with EVs stimulated growth and migration both of metastatic melanoma cells and keratinocytes and changed the morphology of keratinocytes to stem-like phenotype, which was confirmed by increased expression of the stemness factors KLF and CD133. Activation of the AKT/mTOR and ERK signaling pathways and increased expression of epidermal growth factor receptor EGFR and SNAI1 were detected in keratinocytes upon incubation with EVs. Moreover, EVs reduced the production of different cytokines (IL6, IL10, and IL12) and adhesion factors (sICAM-1, sICAM-3, sPecam-1, and sCD40L) usually secreted by keratinocytes to control melanoma progression. Bioinformatic analysis revealed the correlation between decreased expression of these secreted factors and worse survival prognosis for patients with metastatic melanoma. Altogether, our data mean that metastatic melanoma EVs are important players in the transformation of normal keratinocytes.

Nanozyme-Based Enhanced Cancer Immunotherapy

Catalytic nanoparticles with natural enzyme-mimicking properties, known as nanozymes, have emerged as excellent candidate materials for cancer immunotherapy. Owing to their enzymatic activities, artificial nanozymes not only serve as responsive carriers to load drugs and therapeutic molecules for cancer treatment, but also act as enzymes for modulating the immunosuppression of the tumor microenvironment (TME) via the catalytic activities of catalase, peroxidase, superoxide dismutase, and oxidase. The immunosuppressive pro-tumor TME can be reversed to the immunoactive anti-tumor TME by utilizing both reactive oxygen species (ROS)-generating and ROS-scavenging nanozymes, which enhance the efficacy of cancer immunotherapy. In this review, we introduce representative ROS-generating and ROS-scavenging nanozymes and discuss how artificial nanozymes respond to the conditions of the TME. Based on the mutual interaction between nanozymes and TME, recent therapeutic pathways to provoke anti-cancer immune responses using nanozymes are discussed.

Tumor Microenvironment Acidity Triggers Lipid Accumulation in Liver Cancer via SCD1 Activation

Acidification is recognized as the predominant characteristic of the tumor microenvironment (TME) and contributes to tumor progression. However, the mechanism of extracellular acidic TME directly influences intercellular pathological responses remains unclear. Meanwhile, acidic TME is mainly ascribed to aberrant metabolism of lipids and glucose, but whether and how acidity affects metabolic reprogramming, especially for lipid metabolism, is still unknown. We found that lipid was significantly accumulated in liver cancer cells when exposed to acidic TME. Moreover, proteomic analysis showed that differentially expressed proteins were mainly clustered into fatty acid pathways. Subsequently, we found that acidification increased the expression of SCD1 by activating PI3K/AKT signaling pathway. Interestingly, we found that SCD1 directly bound to PPARα in the acidic TME, which vanished after 2-day reverse incubation in pH7.4 medium, implying extracellular acidosis might influence intercellular function by mediating the binding affinity between SCD1 and PPARα under different pH gradients. In summary, our data revealed that acidosis could significantly trigger fatty acid synthesis to promote liver tumorigenesis by upregulating SCD1 in a PI3K/AKT activation dependent manner and simultaneously promote SCD1 binding to PPARα. Our study not only provides direct mechanistic evidence to support the vital role of acidosis in lipid metabolic reprogramming, but also provides novel insights for determining the binding affinity of functional proteins as a molecular mechanism to better understand the role of the acidic TME in tumor development. Implications: The acidic TME contributes to lipid accumulation in liver cancer by activating the PI3K/AKT signaling pathway and promoting SCD1-PPARα binding.

Synthesis and characterization of a novel pH-responsive drug-releasing nanocomposite hydrogel for skin cancer therapy and wound healing

Local skin cancer recurrence occurs in ∼12% of the patients post-surgery due to persistent growth of residual cancer cells. Wound infection is another significant complication following surgery. We report a novel in situ-forming nanocomposite hydrogel (NCH) containing PLGA-carboxymethyl chitosan nanoparticles (186 nm) for localized pH-responsive skin cancer therapy and wound healing. This injectable hydrogel, comprising of a citric acid-derived polymer backbone, gelled within 5 minutes, and demonstrated excellent swelling (283% of dry weight) and compressive strengths (∼5.34 MPa). Nanoparticle incorporation did not significantly affect hydrogel properties. The NCH effluents were cytocompatible with human dermal fibroblasts at 500 μg ml-1 concentration and demonstrated pH-dependent drug release and promising therapeutic efficacy against A431 and G361 skin cancer cells in vitro. Significant zones of inhibition were observed in S. aureus and E. coli cultures on NCH treatment, confirming its antibacterial properties. Our studies show that the pH-responsive NCH can be potentially used for adjuvant skin cancer treatment and wound healing.

Normalization of the tumor microvasculature based on targeting and modulation of the tumor microenvironment

Angiogenesis is an essential process for tumor development. Owing to the imbalance between pro- and anti-angiogenic factors, the tumor vasculature possesses the characteristics of tortuous, hyperpermeable vessels and compressive force, resulting in a reduction in the effect of traditional chemotherapy and radiotherapy. Anti-angiogenesis has emerged as a promising strategy for cancer treatment. Tumor angiogenesis, however, has been proved to be a complex process in which the tumor microenvironment (TME) plays a vital role in the initiation and development of the tumor microvasculature. The host stromal cells in the TME, such as cancer associated fibroblasts (CAFs), tumor associated macrophages (TAMs) and Treg cells, contribute to angiogenesis. Furthermore, the abnormal metabolic environment, such as hypoxia and acidosis, leads to the up-regulated expression of angiogenic factors. Indeed, normalization of the tumor microvasculature via targeting and modulating the TME has become a promising strategy for anti-angiogenesis and anti-tumor therapy. In this review, we summarize the abnormalities of the tumor microvasculature, tumor angiogenesis induced by an abnormal metabolic environment and host stromal cells, as well as drug delivery therapies to restore the balance between pro- and anti-angiogenic factors by targeting and normalizing the tumor vasculature in the TME.

Mambalgin-2 Inhibits Growth, Migration, and Invasion of Metastatic Melanoma Cells by Targeting the Channels Containing an ASIC1a Subunit Whose Up-Regulation Correlates with Poor Survival Prognosis

Melanoma is an aggressive cancer characterized by the acidification of the extracellular environment. Here, we showed for the first time that extracellular media acidification increases proliferation, migration, and invasion of patient-derived metastatic melanoma cells and up-regulates cell-surface expression of acid-sensitive channels containing the ASIC1a, α-ENaC, and γ-ENaC subunits. No influence of media acidification on these processes was found in normal keratinocytes. To control metastatic melanoma progression associated with the ASIC1a up-regulation, we proposed the ASIC1a inhibitor, -mambalgin-2 from Dendpoaspis polylepis venom. Recombinant analog of mambalgin-2 cancelled acidification-induced proliferation, migration, and invasion of metastatic melanoma cells, promoted apoptosis, and down-regulated cell-surface expression of prooncogenic factors CD44 and Frizzled 4 and phosphorylation of transcription factor SNAI. Confocal microscopy and affinity purification revealed that mambalgin-2 interacts with heterotrimeric ASIC1a/α-ENaC/γ-ENaC channels on the surface of metastatic melanoma cells. Using the mutant variant of mambalgin-2 with reduced activity toward ASIC1a, we confirmed that the principal molecular target of mambalgin-2 in melanoma cells is the ASIC1a subunit. Bioinformatic analysis confirmed up-regulation of the ASIC1 expression as a marker of poor survival prognosis for patients with metastatic melanoma. Thus, targeting ASIC1a by drugs such as mambalgin-2 could be a promising strategy for metastatic melanoma treatment.

Recent advances in MOF-based nanoplatforms generating reactive species for chemodynamic therapy

Still today, cancer remains a threat to human health. Possible common treatments to cure this disease include chemotherapy (CT), radiotherapy (RT), photothermal therapy (PTT), and surgical resection, which give unreasonable results because of their limited efficiency and also lead to side-effects. Hence, different strategies are now being exploited to not only enhance the efficiency of these traditional therapeutic methods or treat the tumor cells but also curtail the side effects. A latest method with authentic proof of chemodynamic therapy (CDT) utilizing the Fenton reaction is now gaining importance. This approach, which is developed based on the high level of hydrogen peroxide (H2O2) in a tumor microenvironment (TME), can be used to catalyze the Fenton reaction to generate cancer cell-killing reactive oxygen species (ROS). The selection of materials is extremely important and nanomaterials offer the most likely method to facilitate CDT. Among various materials, metal-organic frameworks (MOFs) which have been extensively applied in medical areas are regarded as a promising material and possess potential for the next generation of nanotechnology. This review focuses on summarizing the use of MOFs in CDT and their synergetic therapeutics as well as the challenges, obstacles, and development.

How Neural Crest Transcription Factors Contribute to Melanoma Heterogeneity, Cellular Plasticity, and Treatment Resistance

Cutaneous melanoma represents one of the deadliest types of skin cancer. The prognosis strongly depends on the disease stage, thus early detection is crucial. New therapies, including BRAF and MEK inhibitors and immunotherapies, have significantly improved the survival of patients in the last decade. However, intrinsic and acquired resistance is still a challenge. In this review, we discuss two major aspects that contribute to the aggressiveness of melanoma, namely, the embryonic origin of melanocytes and melanoma cells and cellular plasticity. First, we summarize the physiological function of epidermal melanocytes and their development from precursor cells that originate from the neural crest (NC). Next, we discuss the concepts of intratumoral heterogeneity, cellular plasticity, and phenotype switching that enable melanoma to adapt to changes in the tumor microenvironment and promote disease progression and drug resistance. Finally, we further dissect the connection of these two aspects by focusing on the transcriptional regulators MSX1, MITF, SOX10, PAX3, and FOXD3. These factors play a key role in NC initiation, NC cell migration, and melanocyte formation, and we discuss how they contribute to cellular plasticity and drug resistance in melanoma.

Influence of Tumor Microenvironment and Fibroblast Population Plasticity on Melanoma Growth, Therapy Resistance and Immunoescape

Cutaneous melanoma (CM) tissue represents a network constituted by cancer cells and tumor microenvironment (TME). A key feature of CM is the high structural and cellular plasticity of TME, allowing its evolution with disease and adaptation to cancer cell and environmental alterations. In particular, during melanoma development and progression each component of TME by interacting with each other and with cancer cells is subjected to dramatic structural and cellular modifications. These alterations affect extracellular matrix (ECM) remodelling, phenotypic profile of stromal cells, cancer growth and therapeutic response. The stromal fibroblast populations of the TME include normal fibroblasts and melanoma-associated fibroblasts (MAFs) that are highly abundant and flexible cell types interacting with melanoma and stromal cells and differently influencing CM outcomes. The shift from the normal microenvironment to TME and from normal fibroblasts to MAFs deeply sustains CM growth. Hence, in this article we review the features of the normal microenvironment and TME and describe the phenotypic plasticity of normal dermal fibroblasts and MAFs, highlighting their roles in normal skin homeostasis and TME regulation. Moreover, we discuss the influence of MAFs and their secretory profiles on TME remodelling, melanoma progression, targeted therapy resistance and immunosurveillance, highlighting the cellular interactions, the signalling pathways and molecules involved in these processes.

Hypoxia and Extracellular Acidification as Drivers of Melanoma Progression and Drug Resistance

Hypoxia and elevated extracellular acidification are prevalent features of solid tumors and they are often shown to facilitate cancer progression and drug resistance. In this review, we have compiled recent and most relevant research pertaining to the role of hypoxia and acidification in melanoma growth, invasiveness, and response to therapy. Melanoma represents a highly aggressive and heterogeneous type of skin cancer. Currently employed treatments, including BRAF V600E inhibitors and immune therapy, often are not effective due to a rapidly developing drug resistance. A variety of intracellular mechanisms impeding the treatment were discovered. However, the tumor microenvironment encompassing stromal and immune cells, extracellular matrix, and physicochemical conditions such as oxygen level or acidity, may also influence the therapy effectiveness. Hypoxia and acidification are able to reprogram the metabolism of melanoma cells, enhance their survival and invasiveness, as well as promote the immunosuppressive environment. For this reason, these physicochemical features of the melanoma niche and signaling pathways related to them emerge as potential therapeutic targets.

pH-Responsive Release of Ruthenium Metallotherapeutics from Mesoporous Silica-Based Nanocarriers

Ruthenium complexes are attracting interest in cancer treatment due to their potent cytotoxic activity. However, as their high toxicity may also affect healthy tissues, efficient and selective drug delivery systems to tumour tissues are needed. Our study focuses on the construction of such drug delivery systems for the delivery of cytotoxic Ru(II) complexes upon exposure to a weakly acidic environment of tumours. As nanocarriers, mesoporous silica nanoparticles (MSN) are utilized, whose surface is functionalized with two types of ligands, (2-thienylmethyl)hydrazine hydrochloride (H1) and (5,6-dimethylthieno[2,3-d]pyrimidin-4-yl)hydrazine (H2), which were attached to MSN through a pH-responsive hydrazone linkage. Further coordination to ruthenium(II) center yielded two types of nanomaterials MSN-H1[Ru] and MSN-H2[Ru]. Spectrophotometric measurements of the drug release kinetics at different pH (5.0, 6.0 and 7.4) confirm the enhanced release of Ru(II) complexes at lower pH values, which is further supported by inductively coupled plasma optical emission spectrometry (ICP-OES) measurements. Furthermore, the cytotoxicity effect of the released metallotherapeutics is evaluated in vitro on metastatic B16F1 melanoma cells and enhanced cancer cell-killing efficacy is demonstrated upon exposure of the nanomaterials to weakly acidic conditions. The obtained results showcase the promising capabilities of the designed MSN nanocarriers for the pH-responsive delivery of metallotherapeutics and targeted treatment of cancer.

Intelligent stimuli-responsive nano immunomodulators for cancer immunotherapy

Cancer immunotherapy is a revolutionary treatment method in oncology, which uses a human's own immune system against cancer. Many immunomodulators that trigger an immune response have been developed and applied in cancer immunotherapy. However, there is the risk of causing an excessive immune response upon directly injecting common immunomodulators into the human body to trigger an immune response. Therefore, the development of intelligent stimuli-responsive immunomodulators to elicit controlled immune responses in cancer immunotherapy is of great significance. Nanotechnology offers the possibility of designing smart nanomedicine to amplify the antitumor response in a safe and effective manner. Progress relating to intelligent stimuli-responsive nano immunomodulators for cancer immunotherapy is highlighted as a new creative direction in the field. Considering the clinical demand for cancer immunotherapy, we put forward some suggestions for constructing new intelligent stimuli-responsive nano immunomodulators, which will advance the development of cancer immunotherapy.

Traceable metallic antigen release for enhanced cancer immunotherapy

Tumor vaccine has shown outstanding advantages and good therapeutic effects in tumor immunotherapy. However, antigens in tumor vaccines can be easily cleared by the reticuloendothelium system in advance, which leads to poor therapeutic effect of tumor vaccines. Moreover, it was still hard to monitor the fate and distribution of antigens. To address these limitations, we synthesized a traceable nanovaccine based on gold nanocluster-labeled antigens and upconversion nanoparticles (UCNPs) for the treatment of melanoma in this study. PH-sensitive Schiff base bond is introduced between UCNPs and gold nanocluster-labeled ovalbumin antigens for monitoring antigens release. Our studies demonstrated that UCNPs conjugated metallic antigen showed excellent biocompatibility, pH-sensitive and therapeutic effect.

Identification of immune-related genes with prognostic significance in the microenvironment of cutaneous melanoma

Cutaneous melanoma is one of the most aggressive cancers characterized by increasing incidence and mortality. In recent years, the emergence of immunotherapy has greatly raised the survival rate of patients suffering from cutaneous melanoma, yet some sufferers remain to have poor outcomes after treatment mainly due to the tumor microenvironment (TME). In this study, cutaneous melanoma-associated TME was systematically analyzed using the ESTIMATE algorithm based on the gene transcriptome data obtained from the TCGA database. Totally, 471 patients were included and 553 TME-related genes were screened. Afterwards, a 3-gene signature-based model (CLEC4A, GBP4, KIR2DL4) was constructed via univariate Cox, LASSO, and multivariate Cox regression analyses. To validate the validity of this model, ROC analysis was conducted, and the model was further validated to be an independent prognostic biomarker through univariate and multivariate regression analyses. Finally, the three genes in the model were studied by GSEA and GSVA for their biological significance. We found that the three genes could promote cancer immune response predominantly through affecting immune-related pathways such as antigen processing and presentation, and they may help tumor cells in escaping from surveillance of the immune system when their expression levels were decreased. Additionally, we as well discovered that the expression of the three genes was significantly and positively correlated with the infiltration of related immune cells, but negatively associated with tumor purity. Overall, this study comprehensively analyzed the TME of cutaneous melanoma, identified related biomarkers, and discovered their association with immune system.

Lactate in the Tumor Microenvironment: An Essential Molecule in Cancer Progression and Treatment

Simple Summary

The role of lactate in cancer described by Otto Warburg in 1927 states that cancer cells uptake high amount of glucose with a marked increase in lactate production, this is known as the “Warburg effect”. Since then lactate turn out to be a major signaling molecule in cancer progression. Its release from tumor cells is accompanied by acidification ranging from 6.3 to 6.9 in the tumor microenvironment (TME) which favors processes such as tumor promotion, angiogenesis, metastasis, tumor resistance and more importantly, immunosuppression which has been associated with a poor outcome. The goal of this review is to examine and discuss in deep detail the recent studies that address the role of lactate in all these cancerous processes. Lastly, we explore the efforts to target the lactate production and its transport as a promising approach for cancer therapeutics.

Abstract

Cancer is a complex disease that includes the reprogramming of metabolic pathways by malignant proliferating cells, including those affecting the tumor microenvironment (TME). The “TME concept” was introduced in recognition of the roles played by factors other than tumor cells in cancer progression. In response to the hypoxic or semi-hypoxic characteristic of the TME, cancer cells generate a large amount of lactate via the metabolism of glucose and glutamine. Export of this newly generated lactate by the tumor cells together with H+ prevents intracellular acidification but acidifies the TME. In recent years, the importance of lactate and acidosis in carcinogenesis has gained increasing attention, including the role of lactate as a tumor-promoting metabolite. Here we review the existing literature on lactate metabolism in tumor cells and the ability of extracellular lactate to direct the metabolic reprogramming of those cells. Studies demonstrating the roles of lactate in biological processes that drive or sustain carcinogenesis (tumor promotion, angiogenesis, metastasis and tumor resistance) and lactate’s role as an immunosuppressor that contributes to tumor evasion are also considered. Finally, we consider recent therapeutic efforts using available drugs directed at and interfering with lactate production and transport in cancer treatment.

Predicting the clinical outcome of melanoma using an immune-related gene pairs signature

OBJECTIVE

Melanoma is rare but dangerous skin cancer, and it can spread rather quickly in the advanced stages of the tumor. Abundant evidence suggests the relationship between tumor development and progression and the immune system. A robust gene risk model could provide an accurate prediction of clinical outcomes. The present study aimed to explore a robust signature of immune-related gene pairs (IRGPs) for estimating overall survival (OS) in malignant melanoma.

METHODS

Clinical and genetic data of skin cutaneous melanoma (SKCM) patients from The Cancer Genome Atlas (TCGA) was performed as a training dataset to identify candidate IRGPs for the prognosis of melanoma. Two independent datasets from the Gene Expression Omnibus (GEO) database (GSE65904) and TCGA dataset (TCGA-UVM) were selected for external validation. Univariate and multivariate Cox regression analyses were then performed to explore the prognostic power of the IRGPs signature and other clinical factors. CIBERSORTx was applied to estimate the fractions of infiltrated immune cells in bulk tumor tissues.

RESULTS

A signature consisted of 33 IRGPs was established which was significantly associated with patients' survival in the TCGA-SKCM dataset (P = 2.0×10-16, Hazard Ratio (HR) = 4.220 (2.909 to 6.122)). We found the IRGPs signature exhibited an independent prognostic factor in all the three independent cohorts in both the univariate and multivariate Cox analysis (P<0.01). The prognostic efficacy of the signature remained unaffected regardless of whether BRAF or NRAS was mutated. As expected, the results were verified in the GSE65904 dataset and the TCGA-UVM dataset. We found an apparent shorter OS in patients of the high-risk group in the GSE65904 dataset (P = 2.1×10-3; HR = 1.988 (1.309 to 3.020)). The trend in the results of the survival analysis in TCGA-UVM was as we expected, but the result was not statistically significant (P = 0.117, HR = 4.263 (1.407 to 12.91)). CD8 T cells, activated dendritic cells (DCs), regulatory T cells (Tregs), and activated CD4 memory T cells presented a significantly lower fraction in the high-risk group in the TCGA-SKCM dataset(P <0.01).

CONCLUSION

The results of the present study support the IRGPs signature as a promising marker for prognosis prediction in melanoma.

Membrane Transporters and Channels in Melanoma

Recent research has revealed that ion channels and transporters can be important players in tumor development, progression, and therapy resistance in melanoma. For example, members of the ABC family were shown to support cancer stemness-like features in melanoma cells, while several members of the TRP channel family were reported to act as tumor suppressors.Also, many transporter proteins support tumor cell viability and thus suppress apoptosis induction by anticancer therapy. Due to the high number of ion channels and transporters and the resulting high complexity of the field, progress in understanding is often focused on single molecules and is in total rather slow. In this review, we aim at giving an overview about a broad subset of ion transporters, also illustrating some aspects of the field, which have not been addressed in detail in melanoma. In context with the other chapters in this special issue on "Transportome Malfunctions in the Cancer Spectrum," a comparison between melanoma and these tumors will be possible.

pH sensing in skin tumors: Methods to study the involvement of GPCRs, acid-sensing ion channels and transient receptor potential vanilloid channels

Solid tumors exhibit an inversed pH gradient with increased intracellular pH (pH_i ) and decreased extracellular pH (pH_e ). This inside-out pH gradient is generated via sodium/hydrogen antiporter 1, vacuolar-type H + ATPases, monocarboxylate transporters, (bi)carbonate (co)transporters and carboanhydrases. Our knowledge on how pH_e -signals are sensed and what the respective receptors induce inside cells is scarce. Some pH-sensitive receptors (GPR4, GPR65/TDAG8, GPR68/OGR1, GPR132/G2A, possibly GPR31 and GPR151) and ion channels (acid-sensing ion channels ASICs, transient receptor potential vanilloid receptors TRPVs) transduce signals inside cells. As little is known on the expression and function of these pH sensors, we used immunostainings to study tissue samples from common and rare skin cancers. Our current and future work is directed towards investigating the impact of all the pH-sensing receptors in different skin tumors using cell culture techniques with selective knockdown/knockout (siRNA/CRISPR-Cas9). To study cell migration and proliferation, novel impedance-based wound healing assays have been developed and are used. The field of pH sensing in tumors and wounds holds great promise for the development of pH-targeting therapies, either against pH regulators or sensors to inhibit cell proliferation and migration.

pH- and Time-Dependent Release of Phytohormones from Diruthenium Complexes

The controlled release of functionally active compounds is important in a variety of applications. Here, we have synthesized, characterized, and studied the magnetic properties of three novel metal-metal-bonded tris(formamidinato) Ru₂⁵⁺ complexes. We have used different auxin-related hormones, indole-3-acetate (IAA), 2,4-dichlorophenoxyacetate (2,4-D), and 1-naphthaleneacetate (NAA), to generate [Ru₂Cl(μ-DPhF)₃(μ-IAA)] (RuIAA), [Ru₂Cl(μ-DPhF)₃(μ-2,4-D)] (Ru2,4-D), and [Ru₂Cl(μ-DPhF)₃(μ-NAA)] (RuNAA) (DPhF = N,N'-diphenylformamidinate). The crystal structures of RuIAA, RuIAA·THF, Ru2,4-D·CH₂Cl₂, and RuNAA·0.5THF have been determined by single-crystal X-ray diffraction. To assess the releasing capacity of the bound hormone, we have employed a biological assay that relied on Arabidopsis thaliana plants expressing an auxin reporter gene and we demonstrate that the release of the phytohormones from RuIAA, Ru2,4-D, and RuNAA is pH- and time-dependent. These studies serve as a proof of concept showing the potential of these types of compounds as biological molecule carriers.

Metabolic Plasticity of Melanoma Cells and Their Crosstalk With Tumor Microenvironment

Cutaneous melanoma (CM) is a highly aggressive and drug resistant solid tumor, showing an impressive metabolic plasticity modulated by oncogenic activation. In particular, melanoma cells can generate adenosine triphosphate (ATP) during cancer progression by both cytosolic and mitochondrial compartments, although CM energetic request mostly relies on glycolysis. The upregulation of glycolysis is associated with constitutive activation of BRAF/MAPK signaling sustained by BRAF^V600E kinase mutant. In this scenario, the growth and progression of CM are strongly affected by melanoma metabolic changes and interplay with tumor microenvironment (TME) that sustain tumor development and immune escape. Furthermore, CM metabolic plasticity can induce a metabolic adaptive response to BRAF/MEK inhibitors (BRAFi/MEKi), associated with the shift from glycolysis toward oxidative phosphorylation (OXPHOS). Therefore, in this review article we survey the metabolic alterations and plasticity of CM, its crosstalk with TME that regulates melanoma progression, drug resistance and immunosurveillance. Finally, we describe hallmarks of melanoma therapeutic strategies targeting the shift from glycolysis toward OXPHOS.

Predicting the Risk of Melanoma Metastasis Using an Immune Risk Score in the Melanoma Cohort

Melanoma is a highly aggressive cancer, attracting increasing attention worldwide. The 5-year survival rate of patients with metastatic melanoma is low. Therefore, it is critical to identify potential effective biomarkers for diagnosis of melanoma metastasis. In the present study, the melanoma cohort and immune genes were obtained from the Cancer Genome Atlas (TCGA) database and the ImmPort database, respectively. Then, we constructed the immune risk score (IRS) using univariate and multivariate logistic analysis. The area under the curve (AUC) of IRS in sequencing samples and the initial diagnosis patients was 0.90 and 0.80, respectively. Besides, IRS could add benefits for metastasis diagnosis. For sequencing samples, IRS (OR = 16.35, 95% CI = 8.74–30.59) increased the odds for melanoma metastasis. Similar results were obtained in the initial diagnosis patients (OR = 8.93, 95% CI = 3.53–22.61). A composite nomogram was built based on IRS and clinical information with well-fitted calibration curves. We further used other independent melanoma cohorts from Gene Expression Omnibus (GEO) databases to confirm the reliability and validity of the IRS (AUC > 0.75, OR > 1.04, and P value < 0.01 in all cohorts). In conclusion, IRS is significantly associated with melanoma metastasis and can be a novel effective signature for predicting the metastasis risk.

Tumour Microenvironment in Skin Carcinogenesis

Tumour microenvironment is a complex system comprising cells and molecules that will provide the necessary conditions for tumour development and progression. Cells residing in the tumour microenvironment gain specific phenotypes and specific functions that are pro-tumorigenic. Tumour progression is in fact a combination between tumour cell characteristics and its interplay with tumour microenvironment. This dynamic network will allow tumour cells to grow, migrate and invade tissues. In the present chapter, we are highlighting some traits that characterise tumour microenvironment in basal cell carcinoma, squamous cell carcinoma and cutaneous melanoma. In skin cancers, there are some common tumour microenvironment characteristics such as the presence of tumour-associated macrophages and regulatory T lymphocytes that are non-tumour cells promoting tumorigenesis. There are also skin cancer type differences in terms of tumour microenvironment characteristics. Thus, markers such as macrophage migration inhibitory factor in melanoma or the extraordinary diverse genetic make-up in the cancer-associated fibroblasts associated to squamous cell carcinoma are just a few of specific traits in skin cancer types. New technological advances for evaluation of tumour environment are presented. Thus, non-invasive skin imaging techniques such as reflectance confocal microscopy can evaluate skin tumour inflammatory infiltrates for density and cellular populations. Analysing tumour micromedium in depth may offer new insights into cancer therapy and identify new therapy targets.

Anti-Metastatic Effects on Melanoma via Intravenous Administration of Anti-NF-κB siRNA Complexed with Functional Peptide-Modified Nano-Micelles

Controlling metastasis is an important strategy in cancer treatment. Nanotechnology and nucleic acids with novel modalities are promising regulators of cancer metastasis. We aimed to develop a small interfering RNA (siRNA) systemic delivery and anti-metastasis system using nanotechnology. We previously reported that polyethylene glycol-polycaprolactone (PEG-PCL) and functional peptide CH2R4H2C nano-micelle (MPEG-PCL-CH2R4H2C) has high siRNA silencing effects, indicated by increased drug accumulation in tumor-bearing mice, and has an anti-tumor effect on solid tumors upon systemic injection. In this study, we aimed to apply our micelles to inhibit metastasis and evaluated the inhibitory effect of anti-RelA siRNA (siRelA), which is a subunit of NF-κB conjugated with MPEG-PCL-CH2R4H2C, via systemic administration. We report that siRelA/MPEG-PCL-CH2R4H2C had a high cellular uptake and suppressed the migration/invasion of cells in B16F10 cells without toxicity. In addition, in a lung metastasis mouse model using intravenous administration of B16F10 cells treated with siRelA/MPEG-PCL-CH2R4H2C, the number of lung nodules in lung tissue significantly decreased compared to naked siRelA and siControl/MPEG-PCL-CH2R4H2C micelle treatments. Hence, we show that RelA expression can reduce cancer metastasis, and MPEG-PCL-CH2R4H2C is an effective siRNA carrier for anti-metastasis cancer therapies.

Acidic Microenvironment Regulates the Severity of Hepatic Ischemia/Reperfusion Injury by Modulating the Generation and Function of Tregs via the PI3K-mTOR Pathway

Hepatic ischemia/reperfusion injury (HIRI) is a major cause of liver dysfunction and even liver failure after liver transplantation and hepatectomy. One of the critical mechanisms that lead to HIRI is an acidic microenvironment, which develops due to the accumulation of high acid-like substances such as lactic acid and ketone bodies. Previous studies have shown that the adoptive transfer of induced regulatory T cells (iTregs) attenuates HIRI; however, little is known about the function of Tregs in the acidic microenvironment of a HIRI model. In the present study, we examined the effect of acidic microenvironment on Tregs in vitro and in vivo. Here, we report that microenvironment acidification and dysfunction of the liver is induced during HIRI in humans and mice and that an acidic microenvironment can inhibit the generation and function of CD4⁺CD25⁺Foxp3⁺ iTregs via the PI3K/Akt/mTOR signaling pathway. By contrast, the reversal of the acidic microenvironment restored Foxp3 expression and iTreg function. In addition, the results of cell culture in vitro indicated that the proton pump inhibitor omeprazole improves decreased iTreg differentiation caused by the acidic microenvironment, suggesting the potential clinical use of proton pump inhibitors as immunoregulatory therapy in the treatment of HIRI. Furthermore, our findings demonstrate that buffering the acidic microenvironment to attenuate HIRI in mice has an inseparable relationship with Tregs. Thus, an acidic microenvironment is a key regulator in HIRI, involved in modulating the generation and function of Tregs.

Dissimilar Appearances Are Deceptive-Common microRNAs and Therapeutic Strategies in Liver Cancer and Melanoma

: In this review, we summarize the current knowledge on miRNAs as therapeutic targets in two cancer types that were frequently described to be driven by miRNAs-melanoma and hepatocellular carcinoma (HCC). By focusing on common microRNAs and associated pathways in these-at first sight-dissimilar cancer types, we aim at revealing similar molecular mechanisms that are evolved in microRNA-biology to drive cancer progression. Thereby, we also want to outlay potential novel therapeutic strategies. After providing a brief introduction to general miRNA biology and basic information about HCC and melanoma, this review depicts prominent examples of potent oncomiRs and tumor-suppressor miRNAs, which have been proven to drive diverse cancer types including melanoma and HCC. To develop and apply miRNA-based therapeutics for cancer treatment in the future, it is essential to understand how miRNA dysregulation evolves during malignant transformation. Therefore, we highlight important aspects such as genetic alterations, miRNA editing and transcriptional regulation based on concrete examples. Furthermore, we expand our illustration by focusing on miRNA-associated proteins as well as other regulators of miRNAs which could also provide therapeutic targets. Finally, design and delivery strategies of miRNA-associated therapeutic agents as well as potential drawbacks are discussed to address the question of how miRNAs might contribute to cancer therapy in the future.

Cell-in-Cell Phenomenon and Its Relationship With Tumor Microenvironment and Tumor Progression: A Review

The term cell-in-cell, morphologically, refers to the presence of one cell within another. This phenomenon can occur in tumors but also among non-tumor cells. The cell-in-cell phenomenon was first observed 100 years ago, and it has since been found in a variety of tumor types. Recently, increasing attention has been paid to this phenomenon and the underlying mechanism has gradually been elucidated. There are three main related process: cannibalism, emperipolesis, and entosis. These processes are affected by many factors, including the tumor microenvironment, mitosis, and genetic factors. There is considerable evidence to suggest that the cell-in-cell phenomenon is associated with the prognosis of cancers, and it promotes tumor progression in most situations. Notably, in pancreatic cancer, the cell-in-cell phenomenon is associated with reduced metastasis, which is the opposite of what happens in other tumor types. Thus, it can also inhibit tumor progression. Studies show that cell-in-cell structure formation is affected by the tumor microenvironment, and that it may lead to changes in cellular characteristics. In this review, we summarize the different cell-in-cell processes and discuss their role in tumor progression and how they are regulated by different mechanisms.

Targeting Tumor Microenvironment by Small-Molecule Inhibitors

The tumor microenvironment (TME) is a hypoxic, acidic, and immune/inflammatory cell–enriched milieu that plays crucial roles in tumor development, growth, progression, and therapy resistance. Targeting TME is an attractive strategy for the treatment of solid tumors. Conventional cancer chemotherapies are mostly designed to directly kill cancer cells, and the effectiveness is always compromised by their penetration and accessibility to cancer cells. Small-molecule inhibitors, which exhibit good penetration and accessibility, are widely studied, and many of them have been successfully applied in clinics for cancer treatment. As TME is more penetrable and accessible than tumor cells, a lot of efforts have recently been made to generate small-molecule inhibitors that specifically target TME or the components of TME or develop special drug-delivery systems that release the cytotoxic drugs specifically in TME. In this review, we briefly summarize the recent advances of small-molecule inhibitors that target TME for the tumor treatment.

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Tumor microenvironment (TME) is an indispensable part of tumor and is an important therapeutic target.

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TME is more penetrable and accessible than tumor cell area.

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Small-molecule inhibitors that target TME are very promising.

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The target efficiency can be improved by specific deliver and release systems.

PGM5 is a promising biomarker and may predict the prognosis of colorectal cancer patients

Background

Phosphoglucomutase (PGM), a key enzyme in the metabolism of glucose-1-phosphate and glucose-6-phosphate, has been found to be associated with proliferation, invasion, and metastasis of cancer. However, the expression and function of PGM5 in colorectal cancer (CRC) remains unknown.

Methods

We tested PGM5 mRNA and protein expression levels in 79 CRC tissue and their matched adjacent tissue samples by qRT-PCR and immunohistochemistry, respectively. Overall survival (OS) was estimated with the Kaplan-Meier method and compared between groups with the log-rank test. We performed multivariable Cox regression analyses to identify factors associated with CRC risk. The cell proliferation, migration and invasion abilities of CRC cells were detected by using CCK-8, Transwell migration and invasion assays, respectively.

Results

The PGM5 protein levels expression in CRC tissues were significantly lower than those in the adjacent tissues (t = 5.035, P < 0.001), and Kaplan-Meier analysis indicated that low PGM5 expression were significantly associated with poor overall survival (P = 0.0069). Univariate and multivariate analyses demonstrated that PGM5 was an independent risk factor for overall survival (hazard ratio = 0.3951, P = 0.014). PGM5 overexpression significantly inhibited the proliferation, invasion and migration abilities of CRC cells. On the contrary, knockdown of PGM5 promotes the invasion and migration of CRC cells.

Conclusions

PMG5 regulates proliferation, invasion, and migration in the CRC and decreased PGM5 is associated with poor prognosis. Therefore, PGM5 is a promising biomarker in CRC and decreased PGM5 may predict poor overall survival in patients with CRC.

Warburg effect and its role in tumourigenesis

Glucose is a crucial molecule in energy production and produces different end products in non-tumourigenic- and tumourigenic tissue metabolism. Tumourigenic cells oxidise glucose by fermentation and generate lactate and adenosine triphosphate even in the presence of oxygen (Warburg effect). The Na⁺/H⁺-antiporter is upregulated in tumourigenic cells resulting in release of lactate- and H⁺ ions into the extracellular space. Accumulation of lactate- and proton ions in the extracellular space results in an acidic environment that promotes invasion and metastasis. Otto Warburg reported that tumourigenic cells have defective mitochondria that produce less energy. However, decades later it became evident that these mitochondria have adapted with alterations in mitochondrial content, structure, function and activity. Mitochondrial biogenesis and mitophagy regulate the formation of new mitochondria and degradation of defective mitochondria in order to combat accumulation of mutagenic mitochondrial deoxyribonucleic acid. Tumourigenic cells also produce increase reactive oxygen species (ROS) resulting from upregulated glycolysis leading to pathogenesis including cancer. Moderate ROS levels exert proliferative- and prosurvival signaling, while high ROS quantities induce cell death. Understanding the crosstalk between aberrant metabolism, redox regulation, mitochondrial adaptions and pH regulation provides scientific- and medical communities with new opportunities to explore cancer therapies.

Extracellular acidosis triggers a senescence-like phenotype in human melanoma cells

Acidosis of the tumor microenvironment is a characteristic of solid tumors such as malignant melanoma. Main causes of the extracellular acidification are metabolic alterations in cancer cells. While numerous studies showed that acidosis promotes tumor invasiveness, metastasis, and neoangiogenesis resulting in malignant progression, contrary data reported that acidosis induces cell apoptosis, inhibits cell proliferation, and mediates cell autophagy. Here, we show that low pH (pH 6.7) induces senescent/quiescent phenotype in melanoma cells after long-time treatment defined by induction of SA-ß-galactosidase, upregulation of p21, G₁ /G₀ cell cycle arrest, and reduction of proliferation. Moreover, we revealed that extracellular acidosis triggers the inhibition of eIF2α and subsequently the activation of ATF4 expression, a key component of the integrated stress response (ISR), indicating an acid-mediated translation reprogramming. Interestingly, we also demonstrated that acidosis represses microphthalmia-associated transcription factor (MITF) and activates the expression of the receptor tyrosine kinase AXL. This MITF^low /AXL^high phenotype is correlated with drug resistance and therapeutic outcome in melanoma. Our results suggest that acidosis is an important microenvironmental factor triggering phenotypic plasticity and promoting tumor progression.

Metabolic flexibility in melanoma: A potential therapeutic target

Cutaneous melanoma (CM) represents one of the most metastasizing and drug resistant solid tumors. CM is characterized by a remarkable metabolic plasticity and an important connection between oncogenic activation and energetic metabolism. In fact, melanoma cells can use both cytosolic and mitochondrial compartments to produce adenosine triphosphate (ATP) during cancer progression. However, the CM energetic demand mainly depends on glycolysis, whose upregulation is strictly linked to constitutive activation of BRAF/MAPK pathway affected by BRAF^V600E kinase mutant. Furthermore, the impressive metabolic plasticity of melanoma allows the development of resistance mechanisms to BRAF/MEK inhibitors (BRAFi/MEKi) and the adaptation to microenvironmental changes. The metabolic interaction between melanoma cells and tumor microenvironment affects the immune response and CM growth. In this review article, we describe the regulation of melanoma metabolic alterations and the metabolic interactions between cancer cells and microenvironment that influence melanoma progression and immune response. Finally, we summarize the hallmarks of melanoma therapies and we report BRAF/MEK pathway targeted therapy and mechanisms of metabolic resistance.

Tumor Microenvironment and Cell Fusion

Cell fusion is a highly regulated biological process that occurs under both physiological and pathological conditions. The cellular and extracellular environment is critical for the induction of the cell-cell fusion. Aberrant cell fusion is initiated during tumor progression. Tumor microenvironment is a complex dynamic system formed by the interaction between tumor cells and their surrounding cells. Cell-cell fusion mediates direct interaction between tumor cells and their surrounding cells and is associated with tumor initiation and progression. Various microenvironmental factors affect cell fusion in tumor microenvironment and generate hybrids that acquire genomes of both parental cells and exhibit novel characteristics, such as tumor stem cell-like properties, radioresistance, drug resistance, immune evasion, and enhanced migration and invasion abilities, which are closely related to the initiation, invasion, and metastasis of tumor. The phenotypic characteristics of hybrids are based on the phenotypes of parental cells, and the fusion of tumor cells with diverse types of microenvironmental fusogenic cells is concomitant with phenotypic heterogeneity. This review highlights the types of fusogenic cells in tumor microenvironment that can fuse with tumor cells and their specific significance and summarizes the various microenvironmental factors affecting tumor cell fusion. This review may be used as a reference to develop strategies for future research on tumor cell fusion and the exploration of cell fusion-based antitumor therapies.