Overcoming Hypoxia-Mediated Tumor Progression: Combinatorial Approaches Targeting pH Regulation, Angiogenesis and Immune Dysfunction

The Immune Landscape of Pheochromocytoma and Paraganglioma: Current Advances and Perspectives

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors derived from neural crest cells from adrenal medullary chromaffin tissues and extra-adrenal paraganglia, respectively. Although the current treatment for PPGLs is surgery, optimal treatment options for advanced and metastatic cases have been limited. Hence, understanding the role of the immune system in PPGL tumorigenesis can provide essential knowledge for the development of better therapeutic and tumor management strategies, especially for those with advanced and metastatic PPGLs. The first part of this review outlines the fundamental principles of the immune system and tumor microenvironment, and their role in cancer immunoediting, particularly emphasizing PPGLs. We focus on how the unique pathophysiology of PPGLs, such as their high molecular, biochemical, and imaging heterogeneity and production of several oncometabolites, creates a tumor-specific microenvironment and immunologically "cold" tumors. Thereafter, we discuss recently published studies related to the reclustering of PPGLs based on their immune signature. The second part of this review discusses future perspectives in PPGL management, including immunodiagnostic and promising immunotherapeutic approaches for converting "cold" tumors into immunologically active or "hot" tumors known for their better immunotherapy response and patient outcomes. Special emphasis is placed on potent immune-related imaging strategies and immune signatures that could be used for the reclassification, prognostication, and management of these tumors to improve patient care and prognosis. Furthermore, we introduce currently available immunotherapies and their possible combinations with other available therapies as an emerging treatment for PPGLs that targets hostile tumor environments.

Hallmarks of cancer resistance

This review explores the hallmarks of cancer resistance, including drug efflux mediated by ATP-binding cassette (ABC) transporters, metabolic reprogramming characterized by the Warburg effect, and the dynamic interplay between cancer cells and mitochondria. The role of cancer stem cells (CSCs) in treatment resistance and the regulatory influence of non-coding RNAs, such as long non-coding RNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs), are studied. The chapter emphasizes future directions, encompassing advancements in immunotherapy, strategies to counter adaptive resistance, integration of artificial intelligence for predictive modeling, and the identification of biomarkers for personalized treatment. The comprehensive exploration of these hallmarks provides a foundation for innovative therapeutic approaches, aiming to navigate the complex landscape of cancer resistance and enhance patient outcomes.

Biological characteristics and clinical treatment of pulmonary sarcomatoid carcinoma: a narrative review

Background and Objective

Pulmonary sarcomatoid carcinoma (PSC) is a subset of non-small cell lung cancer (NSCLC) with highly malignant, aggressive, and heterogeneous features. Patients with this disease account for approximately 0.1-0.4% of lung cancer cases. The absence of comprehensive summaries on the basic biology and clinical treatments for PSC means there is limited systematic awareness and understanding of this rare disease. This paper provides an overview of the biological characteristics of PSC and systematically summarizes various treatment strategies available for patients with this disease.

Methods

For this narrative review, we have searched literature related to the basic biology and clinical treatment approaches of PSC by searching the PubMed database for articles published from July 16, 1990 to August 29, 2023. The following keywords were used: "pulmonary sarcomatoid carcinoma", "genetic mutations", "immune microenvironment", "hypoxia", "angiogenesis", "overall survival", "surgery", "radiotherapy", "chemotherapy", and "immune checkpoint inhibitors".

Key Content and Findings

Classical PSC comprises epithelial and sarcomatoid components, with most studies suggesting a common origin. PSC exhibits a higher tumor mutational burden (TMB) and mutation frequency than other types of NSCLC. The tumor microenvironment (TME) of PSC is characterized by hypoxia, hypermetabolism, elevated programmed cell death protein 1/programmed cell death-ligand 1 expression, and high immune cell infiltration. Treatment strategies for advanced PSC are mainly based on traditional NSCLC treatments, but PSC exhibits resistance to chemotherapy and radiotherapy. The advancement of genome sequencing has introduced targeted therapies as an option for mutation-positive PSC cases. Moreover, due to the characteristics of the immune microenvironment of PSC, many patients positively respond to immunotherapy, demonstrating its potential for the management of PSC.

Conclusions

Although several studies have examined and assessed the TME of PSC, these are limited in quantity and quality, presenting challenges for research into the clinical treatment strategies for PSC. With the emergence of new technologies and the advancement of clinical research, for example, savolitinib's clinical study for MET exon 14 skipping mutations positive PSC patients have shown promising outcomes, more in-depth studies on PSC are eagerly anticipated.

Overcoming cold tumors: a combination strategy of immune checkpoint inhibitors

Immune Checkpoint Inhibitors (ICIs) therapy has advanced significantly in treating malignant tumors, though most 'cold' tumors show no response. This resistance mainly arises from the varied immune evasion mechanisms. Hence, understanding the transformation from 'cold' to 'hot' tumors is essential in developing effective cancer treatments. Furthermore, tumor immune profiling is critical, requiring a range of diagnostic techniques and biomarkers for evaluation. The success of immunotherapy relies on T cells' ability to recognize and eliminate tumor cells. In 'cold' tumors, the absence of T cell infiltration leads to the ineffectiveness of ICI therapy. Addressing these challenges, especially the impairment in T cell activation and homing, is crucial to enhance ICI therapy's efficacy. Concurrently, strategies to convert 'cold' tumors into 'hot' ones, including boosting T cell infiltration and adoptive therapies such as T cell-recruiting bispecific antibodies and Chimeric Antigen Receptor (CAR) T cells, are under extensive exploration. Thus, identifying key factors that impact tumor T cell infiltration is vital for creating effective treatments targeting 'cold' tumors.

Synthesis of new class of non-sulfonamide bis-benzimidazoles as antitumor agents by inhibiting carbonic anhydrase-IX enzyme

In several types of cancers, the expression of carbonic anhydrase-IX (CA-IX) enzyme is elevated than its normal level which ultimately plays a key role in the tumor growth of epithelial cells in breast and lung cancer by acidifying tumor microenvironment, therefore, inhibition of this target is important in antitumor therapy. We have synthesized bis-benzimidazole derivatives (1-25) by using 3,3'-diaminobenzidine and various aromatic aldehydes and characterized by various spectroscopic methods (UV/Visible, 1HNMR, 13CNMR, and mass spectrometry). Their inhibitory potential for human CA-IX (hCA-IX) was evaluated in-vitro, where several synthesized derivatives showed potent inhibition of hCA-IX (IC50 values in range of 5.23 ± 1.05 to 40.10 ± 1.78 μM) and compounds 3-5, 7-8, 13-16, 21 and 23 showed superior activity than the standard drug "acetazolamide" (IC50 = 18.24 ± 1.43 μM). Furthermore, all these compounds showed no toxicity on human fibroblast cell lines (BJ cell lines). Moreover, molecular docking was carried out to predict their binding modes in the active site of CA-IX and revealed a significant role of imidazole ring of synthesized entities in their effective binding with the specific residues of CA-IX. The obtained results paved the way for further in vivo and other pharmacological studies for the optimization of these molecules as possible anti-cancer agents.

Molecular targets and therapeutic strategies for triple-negative breast cancer

Triple-negative breast cancer (TNBC) is known for its heterogeneous complexity and is often difficult to treat. TNBC lacks the expression of major hormonal receptors like estrogen receptor, progesterone receptor, and human epidermal growth factor receptor-2 and is further subdivided into androgen receptor (AR) positive and AR negative. In contrast, AR negative is also known as quadruple-negative breast cancer (QNBC). Compared to AR-positive TNBC, QNBC has a great scarcity of prognostic biomarkers and therapeutic targets. QNBC shows excessive cellular growth and proliferation of tumor cells due to increased expression of growth factors like EGF and various surface proteins. This study briefly reviews the limited data available as protein biomarkers that can be used as molecular targets in treating TNBC as well as QNBC. Targeted therapy and immune checkpoint inhibitors have recently changed cancer treatment. Many studies in medicinal chemistry continue to focus on the synthesis of novel compounds to discover new antiproliferative medicines capable of treating TNBC despite the abundance of treatments currently on the market. Drug repurposing is one of the therapeutic methods for TNBC that has been examined. Moreover, some additional micronutrients, nutraceuticals, and functional foods may be able to lower cancer risk or slow the spread of malignant diseases that have already been diagnosed with cancer. Finally, nanomedicines, or applications of nanotechnology in medicine, introduce nanoparticles with variable chemistry and architecture for the treatment of cancer. This review emphasizes the most recent research on nutraceuticals, medication repositioning, and novel therapeutic strategies for the treatment of TNBC.

Application of hyaluronic acid-based nanoparticles for cancer combination therapy

Cancer is a significant public health problem in the world. The treatment methods include surgery, chemotherapy, phototherapy, and immunotherapy. Due to their respective limitations, the treatment effect is often unsatisfactory, laying hidden dangers for metastasis and recurrence. Since their exceptional biocompatibility and excellent targeting capabilities, hyaluronic acid-based biomaterials have generated great interest as drug delivery methods for tumor therapy. Moreover, modified HA can self-assemble into hydrogels or nanoparticles (NPs) for precise drug administration. This article summarizes the application of HA-based NPs in combination therapy. Ultimately, it is anticipated that this research will offer guidance for creating various HA-based NPs utilized in numerous cancer therapies.

Construction of subtype classifiers and validation of a prognostic risk model based on hypoxia-associated lncRNAs for lung adenocarcinoma

BACKGROUND

Studies have shown that long non-coding RNAs (lncRNAs) are found to be hypoxia-regulated lncRNAs in cancer. Lung adenocarcinoma (LUAD) is the leading cause of cancer death worldwide, and despite early surgical removal, has a poor prognosis and a high recurrence rate. Thus, we aimed to identify subtype classifiers and construct a prognostic risk model using hypoxia-associated long noncoding RNAs (hypolncRNAs) for LUAD.

METHODS

Clinical data of LUAD samples with prognosis information obtained from the Gene Expression Omnibus (GEO), acted as validation dataset, and The Cancer Genome Atlas (TCGA) databases, served as training dataset, were used to screen hypolncRNAs in each dataset by univariate Cox regression analysis; the intersection set was used for subsequent analyses. Unsupervised clustering analysis was performed based on the expression of hypolncRNAs using the 'ConsensuClusterPlus' package. The tumor microenvironment (TME) was compared between LUAD subgroups by analyzing the expression of immune cell infiltration, immune components, stromal components, immune checkpoints, and chemokine secretion. To identify robust prognostically associated hypolncRNAs and construct a risk score model, multivariate Cox regression analysis was performed.

RESULTS

A total of 14 hypolncRNAs were identified. Based on the expression of these hypolncRNAs, patients with LUAD were classified into three hypolncRNA-regulated subtypes. The three subtypes differed significantly in immune cell infiltration, stromal score, specific immune checkpoints, and secretion of chemokines and their receptors. The Tumor Immune Dysfunction and Exclusion (TIDE) scores and myeloid-derived suppressor cell (MDSC) scores were also found to differ significantly among the three hypolncRNA-regulated subtypes. Four of the 14 hypolncRNAs were used to construct a signature to distinguish the overall survival (OS) in TCGA dataset (P<0.0001) and GEO dataset (P=0.0032) and sensitivity to targeted drugs in patients at different risks of LUAD.

CONCLUSIONS

We characterized three regulatory subtypes of hypolncRNAs with different TMEs. We developed a signature based on hypolncRNAs, contributing to the development of personalized therapy and representing a new potential therapeutic target for LUAD.

Prediction of prognosis and immunotherapy response in breast cancer based on neutrophil extracellular traps-related classification

Neutrophil extracellular traps (NETs), a network of DNA histone complexes and proteins released by activated neutrophils, have been demonstrated to be associated with inflammation, infection related immune response and tumorigenesis in previous reports. However, the relationship between NETs related genes and breast cancer remains controversial. In the study, we retrieved transcriptome data and clinical information of BRCA patients from The Cancer Genome Atlas (TCGA) database and Gene Expression Omnibus (GEO) datasets. The expression matrix of neutrophil extracellular traps (NETs) related genes was generated and consensus clustering was performed by Partitioning Around Medoid (PAM) to classify BRCA patients into two subgroups (NETs high group and NETs low group). Subsequently, we focus on the differentially expressed genes (DEGs) between the two NETs-related subgroups and further explored NETs enrichment related signaling pathways by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. In addition, we constructed a risk signature model by LASSO Cox regression analysis to evaluate the association between riskscore and prognosis. Even more, we explored the landscape of the tumor immune microenvironment and the expression of immune checkpoints related genes as well as HLA genes between two NETs subtypes in breast cancer patients. Moreover, we found and validated the correlation of different immune cells with risk score, as well as the response to immunotherapy in different subgroups of patients was detected by Tumor Immune Dysfunction and Exclusion (TIDE) database. Ultimately, a nomogram prognostic prediction model was established to speculate on the prognosis of breast cancer patients. The results suggest that high riskscore is associated with poor immunotherapy response and adverse clinical outcomes in breast cancer patients. In conclusion, we established a NETs-related stratification system that is beneficial for guiding the clinical treatment and predicting prognosis of BRCA.

Neutrophil extracellular traps induced by the hypoxic microenvironment in gastric cancer augment tumour growth

BACKGROUND

Inflammation-related predisposition to cancer plays an essential role in cancer progression and is associated with poor prognosis. A hypoxic microenvironment and neutrophil infiltration are commonly present in solid tumours, including gastric cancer (GC). Neutrophil extracellular traps (NETs) have also been demonstrated in the tumour immune microenvironment (TIME), but how NETs affect GC progression remains unknown. Here, we investigated the role of NET formation in the TIME and further explored the underlying mechanism of NETs in GC tumour growth.

METHODS

Hypoxia-induced factor-1α (HIF-1α), citrulline histone 3 (citH3) and CD66b expression in tumour and adjacent nontumor tissue samples was evaluated by western blotting, immunofluorescence and immunohistochemical staining. The expression of neutrophil-attracting chemokines in GC cells and their hypoxic-CM was measured by qRT‒PCR and ELISA. Neutrophil migration under hypoxic conditions was evaluated by a Transwell assay. Pathway activation in neutrophils in a hypoxic microenvironment were analysed by western blotting. NET formation was measured in vitro by immunofluorescence staining. The protumour effect of NETs on GC cells was identified by Transwell, wound healing and cell proliferation assays. In vivo, an lipopolysaccharide (LPS)-induced NET model and subcutaneous tumour model were established in BALB/c nude mice to explore the mechanism of NETs in tumour growth.

RESULTS

GC generates a hypoxic microenvironment that recruits neutrophils and induces NET formation. High mobility group box 1 (HMGB1) was translocated to the cytoplasm from the nucleus of GC cells in the hypoxic microenvironment and mediated the formation of NETs via the toll-like receptor 4 (TLR4)/p38 MAPK signalling pathway in neutrophils. HMGB1/TLR4/p38 MAPK pathway inhibition abrogated hypoxia-induced neutrophil activation and NET formation. NETs directly induced GC cell invasion and migration but not proliferation and accelerated the augmentation of GC growth by increasing angiogenesis. This rapid tumour growth was abolished by treatment with the NET inhibitor deoxyribonuclease I (DNase I) or a p38 MAPK signalling pathway inhibitor.

CONCLUSIONS

Hypoxia triggers an inflammatory response and NET formation in the GC TIME to augment tumour growth. Targeting NETs with DNase I or HMGB1/TLR4/p38 MAPK pathway inhibitors is a potential therapeutic strategy to inhibit GC progression. Video Abstract.

Metabolic switch in cancer - Survival of the fittest

Cell metabolism is characterised by the highly coordinated conversion of nutrients into energy and biomass. In solid cancers, hypoxia, nutrient deficiencies, and tumour vasculature are incompatible with accelerated anabolic growth and require a rewiring of cancer cell metabolism. Driver gene mutations direct malignant cells away from oxidation to maximise energy production and biosynthesis while tumour-secreted factors degrade peripheral tissues to fuel disease progression and initiate metastasis. As it is vital to understand cancer cell metabolism and survival mechanisms, this review discusses the metabolic switch and current drug targets and clinical trials. In the future, metabolic markers may be included when phenotyping individual tumours to improve the therapeutic opportunities for personalised therapy.

Synergistic effect of combining sunitinib with a peptide-based vaccine in cancer treatment after microenvironment remodeling

Although it has proven difficult to demonstrate the clinical efficacy of therapeutic vaccination as a monotherapy in advanced cancers, its combination with an immunomodulatory treatment to reduce intra-tumor immunosuppression and improve vaccine efficacy is a very promising strategy. In this context, we are studying the combination of a vaccine composed of peptides of the tumor antigen survivin (SVX vaccine) with the anti-angiogenic agent sunitinib in a colorectal carcinoma model. To this end, we have been focusing on administration scheduling and have highlighted a therapeutic synergy between SVX vaccine and sunitinib when the vaccine was administered at the end of anti-angiogenic treatment. In this setting, a prolonged control of tumor growth associated with an important percentage of complete tumor regression was observed. Studying the remodeling induced by each therapy on the immunological and angiogenic tumor microenvironment over time we observed, during sunitinib treatment, a transient increase in polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) and a decrease in NK cells in the tumor microenvironment. In contrast, after sunitinib treatment was stopped, a decrease in PMN-MDSC populations has been observed in the tumor, associated with an increase in NK cells, pericyte coverage of tumor vessels and CD8⁺ T cell population and functionality. In conclusion, sunitinib treatment results in the promotion of an immune-favorable tumor microenvironment that can guide the optimal sequence of vaccine and anti-angiogenic combination to reinforce their synergy.

Co-delivery of carbonic anhydrase IX inhibitor and doxorubicin as a promising approach to address hypoxia-induced chemoresistance

Hypoxia, an oxygen-deprived condition of the tumor, is one of the major reasons for resistance to chemotherapy. Carbonic anhydrases are generally involved in pH homeostasis in normal conditions, but in solid tumors having a strong relation with hypoxia, the carbonic anhydrase IX (CA-IX) enzyme is overexpressed and results in an extracellular acidic environment. For most weakly basic anticancer drugs, including doxorubicin (Dox), the ionization in an acidic environment limits their cellular uptake, and consequently, the tumor exposure to the drug at sub-therapeutic concentration comes out as chemoresistance. Herein, a combined drug delivery system of liposomes and mesoporous silica nanoparticles (MSNPs) was developed for the co-delivery of the CA-IX enzyme inhibitor and Dox in hypoxic condition. The unique structure of MSNPs with higher surface area was utilized for higher drug loading and sustained release of Dox. Additionally, the biocompatible nature of liposomal coating as a second loading site for the CA-IX enzyme inhibitor has provided gatekeeping effects at pore opening to avoid premature drug release. Lipid coated MSNPs as a co-delivery system for Dox and the CA-IX inhibitor have synergistic cytotoxic effects against MDA-MB 231 breast cancer cells in hypoxic conditions. These findings assure the potential of this drug delivery system to overcome hypoxia-related chemoresistance.

Advances in 3D Bioprinting for Cancer Biology and Precision Medicine: From Matrix Design to Application

The tumor microenvironment is highly complex owing to its heterogeneous composition and dynamic nature. This makes tumors difficult to replicate using traditional 2D cell culture models that are frequently used for studying tumor biology and drug screening. This often leads to poor translation of results between in vitro and in vivo and is reflected in the extremely low success rates of new candidate drugs delivered to the clinic. Therefore, there has been intense interest in developing 3D tumor models in the laboratory that are representative of the in vivo tumor microenvironment and patient samples. 3D bioprinting is an emerging technology that enables the biofabrication of structures with the virtue of providing accurate control over distribution of cells, biological molecules, and matrix scaffolding. This technology has the potential to bridge the gap between in vitro and in vivo by closely recapitulating the tumor microenvironment. Here, a brief overview of the tumor microenvironment is provided and key considerations in biofabrication of tumor models are discussed. Bioprinting techniques and choice of bioinks for both natural and synthetic polymers are also outlined. Lastly, current bioprinted tumor models are reviewed and the perspectives of how clinical applications can greatly benefit from 3D bioprinting technologies are offered.

Prediction of immunotherapy efficacy and immunomodulatory role of hypoxia in colorectal cancer

Immunotherapy has been used in the clinical treatment of colorectal cancer (CRC); however, most patients fail to achieve satisfactory survival benefits. Biomarkers with high specificity and sensitivity are being increasingly developed to predict the efficacy of CRC immunotherapy. In addition to DNA alteration markers, such as microsatellite instability/mismatch repair and tumor mutational burden, immune cell infiltration and immune checkpoints (ICs), epigenetic changes and no-coding RNA, and gut microbiomes all show potential predictive ability. Recently, the hypoxic tumor microenvironment (TME) has been identified as a key factor mediating CRC immune evasion and resistance to treatment. Hypoxia-inducible factor-1α is the central transcription factor in the hypoxia response that drives the expression of a vast number of survival genes by binding to the hypoxia response element in cancer and immune cells in the TME. Hypoxia regulates angiogenesis, immune cell infiltration and activation, expression of ICs, and secretion of various immune molecules in the TME and is closely associated with the immunotherapeutic efficacy of CRC. Currently, various agents targeting hypoxia have been found to improve the TME and enhance the efficacy of immunotherapy. We reviewed current markers commonly used in CRC to predict therapeutic efficacy and the mechanisms underlying hypoxia-induced angiogenesis and tumor immune evasion. Exploring the mechanisms by which hypoxia affects the TME will assist the discovery of new immunotherapeutic predictive biomarkers and development of more effective combinations of agents targeting hypoxia and immunotherapy.

Carbonic anhydrase IX: A tumor acidification switch in heterogeneity and chemokine regulation

The primary physiological process of respiration produces carbon dioxide (CO₂) that reacts with water molecules which subsequently liberates bicarbonate (HCO-₃) and protons. Carbonic anhydrases (CAs) are the primary catalyst involved in this conversion. More than 16 isoforms of human CAs show organ or subcellular specific activity. Dysregulation of each CA is associated with multiple pathologies. Out of these members, the overexpression of membrane-bound carbonic anhydrase IX (CAIX) is associated explicitly with hypoxic tumors or various solid cancers. CAIX helps tumors deal with higher CO₂ by sequestering it with bicarbonate ions and helping cancer cells to grow in a comparatively hypoxic or acidic environment, thus acting as a pH adaptation switch. CAIX-mediated adaptations in cancer cells include angiogenesis, metabolic alterations, tumor heterogeneity, drug resistance, and regulation of cancer-specific chemokines. This review comprehensively collects and describe the cancer-specific expression mechanism and role of CAIX in cancer growth, progression, heterogeneity, and its structural insight to develop future combinatorial targeted cancer therapies.

Role of hypoxia in the tumor microenvironment and targeted therapy

Tumor microenvironment (TME), which is characterized by hypoxia, widely exists in solid tumors. As a current research hotspot in the TME, hypoxia is expected to become a key element to break through the bottleneck of tumor treatment. More and more research results show that a variety of biological behaviors of tumor cells are affected by many factors in TME which are closely related to hypoxia. In order to inhibiting the immune response in TME, hypoxia plays an important role in tumor cell metabolism and anti-apoptosis. Therefore, exploring the molecular mechanism of hypoxia mediated malignant tumor behavior and therapeutic targets is expected to provide new ideas for anti-tumor therapy. In this review, we discussed the effects of hypoxia on tumor behavior and its interaction with TME from the perspectives of immune cells, cell metabolism, oxidative stress and hypoxia inducible factor (HIF), and listed the therapeutic targets or signal pathways found so far. Finally, we summarize the current therapies targeting hypoxia, such as glycolysis inhibitors, anti-angiogenesis drugs, HIF inhibitors, hypoxia-activated prodrugs, and hyperbaric medicine.

Identification of COX4I2 as a hypoxia-associated gene acting through FGF1 to promote EMT and angiogenesis in CRC

Background

Current evidence suggests that the hypoxic tumor microenvironment further aggravates tumor progression, leading to poor therapeutic outcomes. There is as yet no biomarker capable of evaluating the hypoxic state of the tumor. The cytochrome c oxidase (COX) subunit is crucial to the mitochondrial respiratory chain.

Methods

We investigated the potential oncogenic role of COX subunit 4 isoform 2 gene (COX4I2) in colorectal cancer (CRC) by least absolute shrinkage and selection operator (LASSO) and COX regression analysis to examine whether COX4I2 overexpression can predict colorectal cancer (CRC) prognosis. The association of COX4I2 levels with clinical features and its biological actions were evaluated both in vitro and in vivo.

Results

Our analysis showed that elevated COX4I2 levels were correlated with poor clinical outcomes. We also observed that that COX4I2 may be involved in epithelial-mesenchymal transition, activation of cancer-related fibroblasts and angiogenesis in relation to fibroblast growth factor 1.

Conclusions

The COX4I2 level may be a predictor of outcome in CRC and may represent a novel target for treatment development.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s11658-022-00380-2.

Tumor acidity: From hallmark of cancer to target of treatment

Tumor acidity is one of the cancer hallmarks and is associated with metabolic reprogramming and the use of glycolysis, which results in a high intracellular lactic acid concentration. Cancer cells avoid acid stress major by the activation and expression of proton and lactate transporters and exchangers and have an inverted pH gradient (extracellular and intracellular pHs are acid and alkaline, respectively). The shift in the tumor acid–base balance promotes proliferation, apoptosis avoidance, invasiveness, metastatic potential, aggressiveness, immune evasion, and treatment resistance. For example, weak-base chemotherapeutic agents may have a substantially reduced cellular uptake capacity due to “ion trapping”. Lactic acid negatively affects the functions of activated effector T cells, stimulates regulatory T cells, and promotes them to express programmed cell death receptor 1. On the other hand, the inversion of pH gradient could be a cancer weakness that will allow the development of new promising therapies, such as tumor-targeted pH-sensitive antibodies and pH-responsible nanoparticle conjugates with anticancer drugs. The regulation of tumor pH levels by pharmacological inhibition of pH-responsible proteins (monocarboxylate transporters, H⁺-ATPase, etc.) and lactate dehydrogenase A is also a promising anticancer strategy. Another idea is the oral or parenteral use of buffer systems, such as sodium bicarbonate, to neutralize tumor acidity. Buffering therapy does not counteract standard treatment methods and can be used in combination to increase effectiveness. However, the mechanisms of the anticancer effect of buffering therapy are still unclear, and more research is needed. We have attempted to summarize the basic knowledge about tumor acidity.

How the Potassium Channel Response of T Lymphocytes to the Tumor Microenvironment Shapes Antitumor Immunity

Competent antitumor immune cells are fundamental for tumor surveillance and combating active cancers. Once established, tumors generate a tumor microenvironment (TME) consisting of complex cellular and metabolic elements that serve to suppress the function of antitumor immune cells. T lymphocytes are key cellular elements of the TME. In this review, we explore the role of ion channels, particularly K+ channels, in mediating the suppressive effects of the TME on T cells. First, we will review the complex network of ion channels that mediate Ca2+ influx and control effector functions in T cells. Then, we will discuss how multiple features of the TME influence the antitumor capabilities of T cells via ion channels. We will focus on hypoxia, adenosine, and ionic imbalances in the TME, as well as overexpression of programmed cell death ligand 1 by cancer cells that either suppress K+ channels in T cells and/or benefit from regulating these channels’ activity, ultimately shaping the immune response. Finally, we will review some of the cancer treatment implications related to ion channels. A better understanding of the effects of the TME on ion channels in T lymphocytes could promote the development of more effective immunotherapies, especially for resistant solid malignancies.

Metabolic reprograming of MDSCs within tumor microenvironment and targeting for cancer immunotherapy

A number of emerging studies in field of immune metabolism have indicated that cellular metabolic reprograming serves as a major administrator in maintaining the viability and functions of both tumor cells and immune cells. As one of the most important immunosuppressive cells in tumor stroma, myeloid-derived suppressor cells (MDSCs) dynamically orchestrate their metabolic pathways in response to the complicated tumor microenvironment (TME), a process that consequently limits the therapeutic effectiveness of anti-cancer treatment modalities. In this context, the metabolic vulnerabilities of MDSCs could be exploited as a novel immune metabolic checkpoint upon which to intervene for promoting the efficacy of immunotherapy. Here, we have discussed about recent studies highlighting the important roles of the metabolic reprograming and the core molecular pathways involved in tumor-infiltrating MDSCs. In addition, we have also summarized the state-of-the-art strategies that are currently being employed to target MDSC metabolism and improve the efficacy of antineoplastic immunotherapy.

Hypoxia-inducible factors: cancer progression and clinical translation

Hypoxia-inducible factors (HIFs) are master regulators of oxygen homeostasis that match O2 supply and demand for each of the 50 trillion cells in the adult human body. Cancer cells co-opt this homeostatic system to drive cancer progression. HIFs activate the transcription of thousands of genes that mediate angiogenesis, cancer stem cell specification, cell motility, epithelial-mesenchymal transition, extracellular matrix remodeling, glucose and lipid metabolism, immune evasion, invasion, and metastasis. In this Review, the mechanisms and consequences of HIF activation in cancer cells are presented. The current status and future prospects of small-molecule HIF inhibitors for use as cancer therapeutics are discussed.

Hypoxia-activated neuropeptide Y/Y5 receptor/RhoA pathway triggers chromosomal instability and bone metastasis in Ewing sarcoma

Adverse prognosis in Ewing sarcoma (ES) is associated with the presence of metastases, particularly in bone, tumor hypoxia and chromosomal instability (CIN). Yet, a mechanistic link between these factors remains unknown. We demonstrate that in ES, tumor hypoxia selectively exacerbates bone metastasis. This process is triggered by hypoxia-induced stimulation of the neuropeptide Y (NPY)/Y5 receptor (Y5R) pathway, which leads to RhoA over-activation and cytokinesis failure. These mitotic defects result in the formation of polyploid ES cells, the progeny of which exhibit high CIN, an ability to invade and colonize bone, and a resistance to chemotherapy. Blocking Y5R in hypoxic ES tumors prevents polyploidization and bone metastasis. Our findings provide evidence for the role of the hypoxia-inducible NPY/Y5R/RhoA axis in promoting genomic changes and subsequent osseous dissemination in ES, and suggest that targeting this pathway may prevent CIN and disease progression in ES and other cancers rich in NPY and Y5R.

Ewing sarcoma tumour cells frequently metastasize to the bone but the molecular mechanisms governing this process are not well understood. Here, the authors show that neuropeptide Y/Y5 receptor pathway is activated in the hypoxic tumour microenvironment, which results in cytokinesis defects and chromosomal instability, leading to bone invasion.

Understanding autophagy role in cancer stem cell development

Cancer stem cells (CSCs) are a small subpopulation of immature cells located in the tumor mass. These cells are responsible for tumor development, proliferation, resistance and spreading. CSCs are characterized by three unique features: the ability to self-renew, differentiation and tumor formation. CSCs are similar to stem cells, but they differ in the malignant phenotype. CSCs become immortal and survive harsh environmental conditions such as hypoxia, starvation and oxidative stress. However, this harsh tumor microenvironment induces the activation of autophagy, which further increases the CSCs stemness profile, and all these features further increase tumorigenicity and metastasis capacity. Autophagy is induced by the extracellular and cellular microenvironment. Hypoxia is one of the most common factors that highly increases the activity of autophagy in CSCs. Therefore, hypoxia-induced autophagy and CSCs proliferation should be elucidated in order to find a novel cure to defeat cancer cells (CSCs and non-CSCs). The remaining challenges to close the gap between the laboratory bench and the development of therapies, to use autophagy against CSCs in patients, could be addressed by adopting a 3D platform to better-mimic the natural environment in which these cells reside. Ultimately allowing to obtain the blueprints for bioprocess scaling up and to develop the production pipeline for safe and cost-effective autophagy-based novel biologics.

CA9-Related Acidic Microenvironment Mediates CD8+ T Cell Related Immunosuppression in Pancreatic Cancer

PURPOSE

This study aims to integrate pancreatic cancer TCGA, GEO, and single-cell RNA-sequencing (scRNA-seq) datasets, and explore the potential prognostic markers and underlying mechanisms of the immune microenvironment of pancreatic cancer through bioinformatics methods, in vitro and in vivo assays.

METHODS

Expression data and clinicopathological data of pancreatic cancer TCGA, GEO (GSE131050), single cell sequencing (PAAD_CRA001160) dataset were downloaded. We used R/Bioconductor edgeR for differential expression analysis. ClusterProfiler was utilized to perform GO enrichment analysis on differentially expressed genes. The online software CIBERSORT was used to reanalyze the mRNA expression data of pancreatic cancer. CellRanger, RunPCA, FindNeighbors, FindClusters, RunTSNE and RunUMAP were used to perform preprocessing, cell clustering and expression profile analysis on single-cell sequencing data sets. We analyzed intracellular pH with or without CA9 inhibitor SLC-0111. Indirect co-culture model of human pancreatic cancer cell lines and healthy individual-derived PBMCs were used to determine the effect of CA9-related Acidic Microenvironment on CD8+ T cells.

RESULTS

The CIBERSORT analysis of TCGA pancreatic cancer transcriptome sequencing data showed that among the 22 immune microenvironment components, CD8+ T cell infiltration was significantly correlated with the prognosis of pancreatic cancer patients. The differential expression analysis of the TCGA data grouped by the level of CD8+ T cell infiltration indicates that the expression of carbonic anhydrase 9 (CA9) is the most significant, and the survival analysis suggests that CA9 is associated with the overall survival of pancreatic cancer. TCGA data and GEO data set GSE131050 expression correlation analysis suggests that CA9 and CD8 expression are closely related. Pancreatic cancer single-cell sequencing data set PAAD_CRA001160 analysis results show that CA9 is mainly expressed in pancreatic cancer cell clusters, and the expression of the cancer cell subgroup CA9 in the single-cell data set is correlated with CD8+ T cell infiltration.

CONCLUSION

Pancreatic cancer cells may inhibit the infiltration of CD8+ T cells through CA9. Further exploration of its related mechanisms can be used to explore the immune escape pathway of pancreatic cancer and provides new perspectives immune targeted therapy.

Recent advances in nanomedicines for photodynamic therapy (PDT)-driven cancer immunotherapy

Cancer immunotherapy has made tremendous clinical progress in advanced-stage malignancies. However, patients with various tumors exhibit a low response rate to immunotherapy because of a powerful immunosuppressive tumor microenvironment (TME) and insufficient immunogenicity of tumors. Photodynamic therapy (PDT) can not only directly kill tumor cells, but also elicit immunogenic cell death (ICD), providing antitumor immunity. Unfortunately, limitations from the inherent nature and complex TME significantly reduce the efficiency of PDT. Recently, smart nanomedicine-based strategies could subtly modulate the pharmacokinetics of therapeutic compounds and the TME to optimize both PDT and immunotherapy, resulting in an improved antitumor effect. Here, the emerging nanomedicines for PDT-driven cancer immunotherapy are reviewed, including hypoxia-reversed nanomedicines, nanosized metal-organic frameworks, and subcellular targeted nanoparticles (NPs). Moreover, we highlight the synergistic nanotherapeutics used to amplify immune responses combined with immunotherapy against tumors. Lastly, the challenges and future expectations in the field of PDT-driven cancer immunotherapy are discussed.

Microenvironment of Cancer Stem Cells

Microenvironment of cancer stem cells (CSCs) consists of a variety of cells and inter-cellular matrix and communications of the components. The microenvironment of CSCs maintains the stemness feature of the CSCs. Several cell types which communicate each other via signaling molecules surrounding CSCs are main factors of the CSC microenvironment. A key question is "What kind of information the cells exchange in the CSC microenvironment?" to reveal the microenvironment and CSC features. Components and molecular markers of CSC microenvironment, signaling cross-talks in CSC microenvironment, and targeting CSC microenvironment are focused in this review.

Hypoxia as a driver of resistance to immunotherapy

Hypoxia, a hallmark of solid tumors, determines the selection of invasive and aggressive malignant clones displaying resistance to radiotherapy, conventional chemotherapy or targeted therapy. The recent introduction of immunotherapy, based on immune checkpoint inhibitors (ICPIs) and chimeric antigen receptor (CAR) T-cells, has markedly transformed the prognosis in some tumors but also revealed the existence of intrinsic or acquired drug resistance. In the current review we highlight hypoxia as a culprit of immunotherapy failure. Indeed, multiple metabolic cross talks between tumor and stromal cells determine the prevalence of immunosuppressive populations within the hypoxic tumor microenvironment and confer upon tumor cells resistance to ICPIs and CAR T-cells. Notably, hypoxia-triggered angiogenesis causes immunosuppression, adding another piece to the puzzle of hypoxia-induced immunoresistance. If these factors concurrently contribute to the resistance to immunotherapy, they also unveil an unexpected Achille's heel of hypoxic tumors, providing the basis for innovative combination therapies that may rescue the efficacy of ICPIs and CAR T-cells. Although these treatments reveal both a bright side and a dark side in terms of efficacy and safety in clinical trials, they represent the future solution to enhance the efficacy of immunotherapy against hypoxic and therapy-resistant solid tumors.

Dual-Energy CT Perfusion of Invasive Tumor Front in Non-Small Cell Lung Cancers

Background Active endothelial cell proliferation occurs at the tumor edge, known as the invading-tumor front. This study focused on perfusion analysis of non-small cell lung cancers. Purpose To analyze dual-phase, dual-energy CT perfusion according to the degree of tumor hypoxia. Materials and Methods This prospective study was performed 2016-2017. A two-phase dual-energy CT protocol was obtained for consecutive participants with operable non-small cell lung cancer. The first pass and delayed iodine concentration within the tumor and normalized iodine uptake, corresponding to the iodine concentration within the tumor normalized to iodine concentration within the aorta, were calculated for the entire tumor and within three peripheral layers automatically segmented (ie, 2-mm-thick concentric subvolumes). The expression of the membranous carbonic anhydrase (mCA) IX, a marker of tumor hypoxia, was assessed in tumor specimens. Comparative analyses according to the histologic subtypes, type of resected tumors, and mCA IX expression were performed. Results There were 33 mCA IX-positive tumors and 16 mCA IX-negative tumors. In the entire tumor, the mean normalized iodine uptake was higher on delayed than on first-pass acquisitions (0.35 ± 0.17 vs 0.13 ± 0.15, respectively; P < .001). A single layer, located at the edge of the tumor, showed higher values of the iodine concentration (median, 0.53 mg/mL vs 0.21 mg/mL, respectively; P = .03) and normalized iodine uptake (0.04 vs 0.02, respectively; P = .03) at first pass in mCA IX-positive versus mCA IX-negative tumors. Within this layer, a functional profile of neovascularization was found in 23 of 33 (70%) of mCA IX-positive tumors, and the median mCA IX score of these tumors was higher than in tumors with a nonfunctional profile of neovascularization (median mCA IX score, 20 vs 2, respectively; P = .03). Conclusion A two-phase dual-energy CT examination depicted higher perfusion between the tumor edge and lung parenchyma in hypoxic tumors. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Murphy and Ryan in this issue.

Heme Sequestration Effectively Suppresses the Development and Progression of Both Lung Adenocarcinoma and Squamous Cell Carcinoma

Lung adenocarcinoma (ADC) and squamous cell carcinoma (SCC) are two most common subtypes of lung cancer. Here, to identify new, targetable molecular properties of both subtypes, we monitored changes in the levels of heme- and oxidative phosphorylation (OXPHOS)-related proteins during lung tumorigenesis. Heme is a central molecule for oxidative metabolism and ATP generation via OXPHOS. Notably, both lung ADC and SCC tumors can be induced in the genetically engineered KL_Luc mouse model harboring the G12D Kras mutation and a conditional Lkb1 knockout. We found that the levels of the rate-limiting heme synthesis enzyme ALAS1 and uptake protein SLC48A1, along with OXPHOS complex subunits, progressively increased as lung tumorigenesis advanced. Our data demonstrated that elevated levels of heme- and OXPHOS-related proteins were associated with both ADC and SCC. Importantly, treatment of KL_Luc mice with a heme-sequestering protein, HeSP2, that inhibits heme uptake in tumor cells effectively arrested lung tumor progression, and both ADC and SCC tumors were strongly suppressed. Additionally, HeSP2 effectively suppressed the growth of both SCC and ADC tumor xenografts in NOD/SCID mice. Further analyses indicated that HeSP2 effectively diminished OXPHOS in both ADC and SCC, reduced angiogenesis, alleviated tumor hypoxia, and suppressed cell proliferation. These results show that the advancing of lung tumorigenesis requires progressive increase in cellular heme synthesis and uptake, leading to intensified OXPHOS activity and ATP generation and promoting aggressive tumorigenic functions. IMPLICATIONS: Heme sequestration is an effective strategy for the suppression of both ADC and SCC tumor initiation and development.

Uncovering the interplay between pH receptors and immune cells: Potential drug targets (Review)

Extracellular acidosis is associated with various immunopathological states. The microenvironment of numerous solid tumours and inflammatory responses during acute or chronic infection are all related to a pH range of 5.5‑7.0. The relationship between inflammation and immune escape, cancer metabolism, and immunologic suppression drives researchers to focus on the effects of low pH on diverse components of disease immune monitoring. The potential effect of low extracellular pH on the immune function reveals the importance of pH in inflammatory and immunoreactive processes. In this review, the mechanism of how pH receptors, including monocarboxylate transporters (MCTs), Na⁺/H⁺ exchanger 1, carbonic anhydrases (CAs), vacuolar‑ATPase, and proton‑sensing G‑protein coupled receptors (GPCRs), modulate the immune system in disease, especially in cancer, were studied. Their role in immunocyte growth and signal transduction as part of the immune response, as well as cytokine production, have been documented in great detail. Currently, immunotherapy strategies have positive therapeutic effects for patients. However, the acidic microenvironment may block the effect of immunotherapy through compensatory feedback mechanisms, leading to drug resistance. Therefore, we highlight promising therapeutic developments regarding pH manipulation and provide a framework for future research.

The current knowledge concerning solid cancer and therapy

Solid cancers comprise a large number of new cases and deaths from cancer each year globally. There are a number of strategies for addressing tumors raised from solid organs including surgery, chemotherapy, radiotherapy, targeted therapy, immunotherapy, combinational therapy, and stem cell and extracellular vesicle (EV) therapy. Surgery, radiotherapy, and chemotherapy are the dominant cures, but are not always effective, in which even in a localized tumor there is a possibility of tumor relapse after surgical resection. Over half of the cancer patients will receive radiotherapy as a part of their therapeutic schedule. Radiotherapy can cause an abscopal response for boosting the activity of the immune system outside the local field of radiation, but it may also cause an unwanted bystander effect, predisposing nonradiated cells into carcinogenesis. In the context of immunotherapy, immune checkpoint inhibition is known as the standard-of-care, but the major concern is in regard with cold cancers that show low responses to such therapy. Stem-cell therapy can be used to send prodrugs toward the tumor area; this strategy, however, has its own predicaments, such as unwanted attraction toward the other sites including healthy tissues and its instability. A substitute to such therapy and quite a novel strategy is to use EVs, by virtue of their stability and potential to cross biological barriers and long-term storage of contents. Combination therapy is the current focus. Despite advances in the field, there are still unmet concerns in the area of effective cancer therapy, raising challenges and opportunities for future investigations.

Shaping the synthesis of surfactant-stabilized oxygen microbubbles to accommodate encapsulated drug

We have developed oxygen filled microbubbles, SE61_O2, for localized, ultrasound-triggered oxygen delivery to hypoxic tumors prior to radiation therapy. Microbubbles, created by sonication, have a shell composed of D-α-Tocopherol polyethylene glycol 1000 succinate (TPGS) and sorbitan monostearate. Preliminary studies in mice with breast tumor xenographs showed that increases in oxygen partial pressure levels lasted less than 3 min, which is insufficient for most clinical applications. Hence, we investigated the potential of incorporating a hydrophobic antiglycolytic drug, modeled with Nile red. A new fabrication method was developed by first creating drug-loaded TPGS micelles. The resulting microbubbles had similar shell compositions, physical size, morphology, and acoustic properties as the original method. However, microbubble yield was more than doubled, resulting in twice the encapsulation efficiency. For the TPGS micelle method these include similar shell compositions (94.4 ± 0.6 % Montane 60), physical size post freeze-drying and reconstitution (1.57 ± 0.42 μm), morphology (spherical), and acoustic properties (maximum enhancement 19.92 ± 0.55 dB). However, microbubble yield was more than doubled, resulting in twice the encapsulation efficiency (up to 10.49 %). We propose that a nonideal mixture is formed when the surfactants are combined by the standard method, resulting in the formation of mixed micelles that are more stable, making microbubble creation more difficult during the sonication step.

Next-generation multimodality of nutrigenomic cancer therapy: sulforaphane in combination with acetazolamide actively target bronchial carcinoid cancer in disabling the PI3K/Akt/mTOR survival pathway and inducing apoptosis

OBJECTIVE

Aberrations in the PI3K/AKT/mTOR survival pathway in many cancers are the most common genomic abnormalities. The phytochemical and bioactive agent sulforaphane (SFN) has nutrigenomic potential in activating the expression of several cellular protective genes via the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2). Nrf2 is primarily related to mechanisms of endogenous cellular defense and survival. The efficacy of SFN in combination with acetazolamide (AZ) was investigated in reducing typical H727 and atypical H720 BC survival, migration potential, and apoptosis in vitro and in vivo preclinical xenograft tissues.

MATERIALS AND METHODS

Microscopic imaging, immunocytochemistry, wound healing assay, caspase-cleaved cytokeratin 18 (M30, CCK18) CytoDeath ELISA assay, immunofluorescence labeling assays for apoptosis, hypoxia, Western Blotting, Tunnel assay, measurement of 5-HT secretion by carbon fiber amperometry assay, quantitative methylation-specific PCR (qMSP), morphologic changes, cell viability, apoptosis activity and the expression levels of phospho-Akt1, Akt1, HIF-1α, PI3K, p21, CAIX, 5-HT, phospho-mTOR, and mTOR in xenografts derived from typical H727 and atypical H720 BC cell lines.

RESULTS

Combining AZ+SFN reduced tumor cell survival compared to each agent alone, both in vitro and in vivo xenograft tissues. AZ+SFN targeted multiple pathways involved in cell cycle, serotonin secretion, survival, and growth pathways, highlighting its therapeutic approach. Both H727 and H720 cells were associated with induction of apoptosis, upregulation of the p21 cell cycle inhibitor, and downregulation of the PI3K/Akt/mTOR pathway, suggesting that the PI3K/Akt/mTOR pathway is a primary target of the AZ+SFN combination therapy.

CONCLUSIONS

Combining SFN+AZ significantly inhibits the PI3K/Akt/mTOR pathway and significantly reducing 5-HT secretion in carcinoid syndrome.

Overcoming chemoresistance by targeting reprogrammed metabolism: the Achilles' heel of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the leading causes of cancer-related death due to its late diagnosis that removes the opportunity for surgery and metabolic plasticity that leads to resistance to chemotherapy. Metabolic reprogramming related to glucose, lipid, and amino acid metabolism in PDAC not only enables the cancer to thrive and survive under hypovascular, nutrient-poor and hypoxic microenvironments, but also confers chemoresistance, which contributes to the poor prognosis of PDAC. In this review, we systematically elucidate the mechanism of chemotherapy resistance and the relationship of metabolic programming features with resistance to anticancer drugs in PDAC. Targeting the critical enzymes and/or transporters involved in glucose, lipid, and amino acid metabolism may be a promising approach to overcome chemoresistance in PDAC. Consequently, regulating metabolism could be used as a strategy against PDAC and could improve the prognosis of PDAC.

Turning cold tumors into hot tumors by improving T-cell infiltration

Immunotherapy, represented by immune checkpoint inhibitors (ICIs), has greatly improved the clinical efficacy of malignant tumor therapy. ICI-mediated antitumor responses depend on the infiltration of T cells capable of recognizing and killing tumor cells. ICIs are not effective in "cold tumors", which are characterized by the lack of T-cell infiltration. To realize the full potential of immunotherapy and solve this obstacle, it is essential to understand the drivers of T-cell infiltration into tumors. We present a critical review of our understanding of the mechanisms underlying “cold tumors”, including impaired T-cell priming and deficient T-cell homing to tumor beds. “Hot tumors” with significant T-cell infiltration are associated with better ICI efficacy. In this review, we summarize multiple strategies that promote the transformation of "cold tumors" into “hot tumors” and discuss the mechanisms by which these strategies lead to increased T-cell infiltration. Finally, we discuss the application of nanomaterials to tumor immunotherapy and provide an outlook on the future of this emerging field. The combination of nanomedicines and immunotherapy enhances cross-presentation of tumor antigens and promotes T-cell priming and infiltration. A deeper understanding of these mechanisms opens new possibilities for the development of multiple T cell-based combination therapies to improve ICI effectiveness.

Microfluidic tumor-on-a-chip model to evaluate the role of tumor environmental stress on NK cell exhaustion

Solid tumors generate a suppressive environment that imposes an overwhelming burden on the immune system. Nutrient depletion, waste product accumulation, hypoxia, and pH acidification severely compromise the capacity of effector immune cells such as T and natural killer (NK) cells to destroy cancer cells. However, the specific molecular mechanisms driving immune suppression, as well as the capacity of immune cells to adapt to the suppressive environment, are not completely understood. Thus, here, we used an in vitro microfluidic tumor-on-a-chip platform to evaluate how NK cells respond to the tumor-induced suppressive environment. The results demonstrated that the suppressive environment created by the tumor gradually eroded NK cell cytotoxic capacity, leading to compromised NK cell surveillance and tumor tolerance. Further, NK cell exhaustion persisted for an extended period of time after removing NK cells from the microfluidic platform. Last, the addition of checkpoint inhibitors and immunomodulatory agents alleviated NK cell exhaustion.

VISTA: A Mediator of Quiescence and a Promising Target in Cancer Immunotherapy

V-domain Ig suppressor of T cell activation (VISTA) is a B7 family member that maintains T cell and myeloid quiescence and is a promising target for combination cancer immunotherapy. During inflammatory challenges, VISTA activity reprograms macrophages towards reduced production of proinflammatory cytokines and increased production of interleukin (IL)-10 and other anti-inflammatory mediators. The interaction of VISTA with its ligands is regulated by pH, and the acidic pH ~6.0 in the tumor microenvironment (TME) facilitates VISTA binding to P-selectin glycoprotein ligand 1 (PSGL-1). Targeting intratumoral pH might be a way to reduce the immunoinhibitory activity of the VISTA pathway and enhance antitumor immune responses. We review differences among VISTA therapeutics under development as candidate immunotherapies, focusing on VISTA binding partners and the unique structural features of this interaction.

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

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

Metabolic interventions: A new insight into the cancer immunotherapy

Metabolic reprogramming confers cancer cells plasticity and viability under harsh conditions. Such active alterations lead to cell metabolic dependency, which can be exploited as an attractive target in development of effective antitumor therapies. Similar to cancer cells, activated T cells also execute global metabolic reprogramming for their proliferation and effector functions when recruited to the tumor microenvironment (TME). However, the high metabolic activity of rapidly proliferating cancer cells can compete for nutrients with immune cells in the TME, and consequently, suppressing their anti-tumor functions. Thus, therapeutic strategies could aim to restore T cell metabolism and anti-tumor responses in the TME by targeting the metabolic dependence of cancer cells. In this review, we highlight current research progress on metabolic reprogramming and the interplay between cancer cells and immune cells. We also discuss potential therapeutic intervention strategies for targeting metabolic pathways to improve cancer immunotherapy efficacy.

Targeting hypoxia in the tumor microenvironment: a potential strategy to improve cancer immunotherapy

With the success of immune checkpoint inhibitors (ICIs), significant progress has been made in the field of cancer immunotherapy. Despite the long-lasting outcomes in responders, the majority of patients with cancer still do not benefit from this revolutionary therapy. Increasing evidence suggests that one of the major barriers limiting the efficacy of immunotherapy seems to coalesce with the hypoxic tumor microenvironment (TME), which is an intrinsic property of all solid tumors. In addition to its impact on shaping tumor invasion and metastasis, the hypoxic TME plays an essential role in inducing immune suppression and resistance though fostering diverse changes in stromal cell biology. Therefore, targeting hypoxia may provide a means to enhance the efficacy of immunotherapy. In this review, the potential impact of hypoxia within the TME, in terms of key immune cell populations, and the contribution to immune suppression are discussed. In addition, we outline how hypoxia can be manipulated to tailor the immune response and provide a promising combinational therapeutic strategy to improve immunotherapy.

Hypoxia Dictates Metabolic Rewiring of Tumors: Implications for Chemoresistance

Hypoxia is a condition commonly observed in the core of solid tumors. The hypoxia-inducible factors (HIF) act as hypoxia sensors that orchestrate a coordinated response increasing the pro-survival and pro-invasive phenotype of cancer cells, and determine a broad metabolic rewiring. These events favor tumor progression and chemoresistance. The increase in glucose and amino acid uptake, glycolytic flux, and lactate production; the alterations in glutamine metabolism, tricarboxylic acid cycle, and oxidative phosphorylation; the high levels of mitochondrial reactive oxygen species; the modulation of both fatty acid synthesis and oxidation are hallmarks of the metabolic rewiring induced by hypoxia. This review discusses how metabolic-dependent factors (e.g., increased acidification of tumor microenvironment coupled with intracellular alkalinization, and reduced mitochondrial metabolism), and metabolic-independent factors (e.g., increased expression of drug efflux transporters, stemness maintenance, and epithelial-mesenchymal transition) cooperate in determining chemoresistance in hypoxia. Specific metabolic modifiers, however, can reverse the metabolic phenotype of hypoxic tumor areas that are more chemoresistant into the phenotype typical of chemosensitive cells. We propose these metabolic modifiers, able to reverse the hypoxia-induced metabolic rewiring, as potential chemosensitizer agents against hypoxic and refractory tumor cells.

Inhibitory activity against carbonic anhydrase IX and XII as a candidate selection criterion in the development of new anticancer agents

Analysis of the literature data reveals that while inhibition of cancer-related carbonic anhydrase IX and XII isoforms continues to be an important enrichment factor for designing anticancer agent development libraries, exclusive reliance on the in vitro inhibition of these two recombinant isozymes in nominating candidate compounds for evaluation of their effects on cancer cells may lead not only to identifying numerous compounds devoid of the desired cellular efficacy but also to overlooking many promising candidates which may not display the best potency in biochemical inhibition assay. However, SLC-0111, now in phase Ib/II clinical trials, was developed based on the excellent agreement between the in vitro, in vivo and more recently, in-patient data.

Malic Enzyme 1 Is Associated with Tumor Budding in Oral Squamous Cell Carcinomas

Budding at the tumor invasive front has been correlated with the malignant properties of many cancers. Malic enzyme 1 (ME1) promotes the Warburg effect in cancer cells and induces epithelial–mesenchymal transition (EMT) in oral squamous cell carcinoma (OSCC). Therefore, we investigated the role of ME1 in tumor budding in OSCC. Tumor budding was measured in 96 human OSCCs by immunostaining for an epithelial marker (AE1/AE3), and its expression was compared with that of ME1. A significant correlation was observed between tumor budding and ME1 expression. The correlation increased with the progression of cancer. In human OSCC cells, lactate secretion decreased when lactate fermentation was suppressed by knockdown of ME1 and lactate dehydrogenase A or inhibition of pyruvate dehydrogenase (PDH) kinase. Furthermore, the extracellular pH increased, and the EMT phenotype was suppressed. In contrast, when oxidative phosphorylation was suppressed by PDH knockdown, lactate secretion increased, extracellular pH decreased, and the EMT phenotype was promoted. Induction of chemical hypoxia in OSCC cells by CoCl₂ treatment resulted in increased ME1 expression along with HIF1α expression and promotion of the EMT phenotype. Hypoxic conditions also increased matrix metalloproteinases expression and decreased mitochondrial membrane potential, mitochondrial oxidative stress, and extracellular pH. Furthermore, the hypoxic treatment resulted in the activation of Yes-associated protein (YAP), which was abolished by ME1 knockdown. These findings suggest that cancer cells at the tumor front in hypoxic environments increase their lactate secretion by switching their energy metabolism from oxidative phosphorylation to glycolysis owing to ME1 overexpression, decrease in extracellular pH, and YAP activation. These alterations enhance EMT and the subsequent tumor budding. Tumor budding and ME1 expression are thus considered useful markers of OSCC malignancy, and ME1 is expected to be a relevant target for molecular therapy.

Metabolic programming of tumor associated macrophages in the context of cancer treatment

Tumor associated macrophages (TAMs) are important components of the tumor microenvironment (TME). They are characterized by a remarkable functional plasticity, thereby mostly promoting cancer progression. Changes in immune cell metabolism are paramount for this functional adaptation. Here, we review the functional consequences of the metabolic programming of TAMs and the influence of local and systemic targeted therapies on the metabolic characteristics of the TME that shape the functional phenotype of the TAMs. Understanding these metabolic changes within the context of the cross-talk between the different components of the TME including the TAMs and the tumor cells is an essential step that can pave the way towards identifications of ways to improve responses to different treatments, to overcome resistance to treatments, tumor progression and reduce treatment-specific toxicity.

Targeting Hypoxia-Driven Metabolic Reprogramming to Constrain Tumor Progression and Metastasis

Hypoxia in locally advanced solid tumors develops due to uncontrollable cell proliferation, altered metabolism, and the severe structural and functional abnormality of the tumor vasculature, leading to an imbalance between oxygen supply and consumption in the fast-growing tumors and negative impact on the therapeutic outcome. Several hypoxia-responsive molecular determinants, such as hypoxia-inducible factors, guide the cellular adaptation to hypoxia by gene activation, which is critical for promoting malignant progression in the hostile tumor microenvironment. Over time, a large body of evidence exists to suggest that tumor hypoxia also influences the tumor metabolic reprogramming, resulting in neoangiogenesis, metastasis, and immune evasion. In this respect, our review aims to understand the biological processes, key events, and consequences regarding the hypoxia-driven metabolic adaptation of tumor cells. We also assess the potential therapeutic impact of hypoxia and highlight our review by discussing possible therapeutic strategies targeting hypoxia, which would advance the current understanding of hypoxia-associated tumor propagation and malignant progression and improve the management of tumor hypoxia.