Tumor Lactic Acidosis: Protecting Tumor by Inhibiting Cytotoxic Activity Through Motility Arrest and Bioenergetic Silencing

Identifying the critical oncogenic mechanism of LDHA based on a prognostic model of T-cell synthetic drivers

BACKGROUND

Despite its early success, immunotherapy focused on removing T-cell inhibition does not achieve the desired effect in most patients. New strategies that target antigen-driven T-cell activation are needed to improve immunotherapy outcomes. However, a comprehensive analysis of synthetic drivers of T-cells is greatly lacking in lung adenocarcinoma (LUAD) and other types of tumors.

METHODS

We comprehensively evaluated the patterns of LUAD patients based on T -cell synthetic drivers by unsupervised clustering analysis. A risk model was constructed using Lasso Cox regression analysis. The predicted survival and immunotherapy efficacy of the model was validated by independent cohorts. Finally, single-cell sequencing analysis, and a series of in vitro experiments were conducted to explore the role of lactate dehydrogenase A (LDHA) in the malignant progression of LUAD.

RESULTS

Patients in the high-risk group were characterized by survival disadvantage, a "cold" immune phenotype, and by not having benefitted from immunotherapy. LDHA was shown to promote LUAD cell proliferation, cell cycle, invasion, and migration. Secondly, we found that LDHA induced NF-κB pathway activation, tyrosine kinase inhibitor resistance and immunosuppressant microenvironment. Finally, LDHA was found to be highly expressed in fibroblasts, which may be involved in promoting TKI resistance and mediating the immune escape.

CONCLUSION

This study revealed that the T-cell synthetic driver-associated prognostic model developed herein significantly predicted prognosis and immunotherapy efficacy in LUAD. We further investigated the role of LDHA in the malignant phenotype of tumor cells and tumor microenvironment remodeling, providing a promising and novel therapeutic strategy for LUAD.

Human colorectal cancer: upregulation of the adaptor protein Rai in TILs leads to cell dysfunction by sustaining GSK-3 activation and PD-1 expression

BACKGROUND

The immunosuppressive tumor microenvironment (TME) of colorectal cancer (CRC) is a major hurdle for immune checkpoint inhibitor-based therapies. Hence characterization of the signaling pathways driving T cell exhaustion within TME is a critical need for the discovery of novel therapeutic targets and the development of effective therapies. We previously showed that (i) the adaptor protein Rai is a negative regulator of T cell receptor signaling and T helper 1 (Th1)/Th17 cell differentiation; and (ii) Rai deficiency is implicated in the hyperactive phenotype of T cells in autoimmune diseases.

METHODS

The expression level of Rai was measured by qRT-PCR in paired peripheral blood T cells and T cells infiltrating tumor tissue and the normal adjacent tissue in CRC patients. The impact of hypoxia-inducible factor (HIF)-1α on Rai expression was evaluated in T cells exposed to hypoxia and by performing chromatin immunoprecipitation assays and RNA interference assays. The mechanism by which upregulation of Rai in T cells promotes T cell exhaustion were evaluated by flow cytometric, qRT-PCR and western blot analyses.

RESULTS

We show that Rai is a novel HIF-1α-responsive gene that is upregulated in tumor infiltrating lymphocytes of CRC patients compared to patient-matched circulating T cells. Rai upregulation in T cells promoted Programmed cell Death protein (PD)-1 expression and impaired antigen-dependent degranulation of CD8+ T cells by inhibiting phospho-inactivation of glycogen synthase kinase (GSK)-3, a central regulator of PD-1 expression and T cell-mediated anti-tumor immunity.

CONCLUSIONS

Our data identify Rai as a hitherto unknown regulator of the TME-induced exhausted phenotype of human T cells.

Characteristics of lactate metabolism phenotype in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a highly heterogeneous cancer, and more effective prognostic markers are needed. Lactic acid has been proved to be an important metabolite involved in cancer development, metastasis, and the tumor microenvironment, affecting the prognosis of patients. The role of lactic acid metabolism regulators (LAMRs) in HCC is still unclear. In this study, we analyzed the status of LAMRs, a gene list containing lactate from Molecular Signatures database, in HCC and consensus clustering was performed based on these LAMRs. Cluster B showed higher infiltrations of immune cells, higher TME scores, and a poorer prognosis. We further constructed a risk score based on DEGs using LASSO and COX regression analysis between two clusters, which could effectively predict the prognosis of TCGA-LIHC patients. The GSE14520 cohort confirmed the result. We also examined the correlation of risk scores with clinical characteristics, genetic mutations, drug sensitivity, immune checkpoint inhibitors(ICIs), and immunotherapy. In conclusion, our findings will facilitate a further understanding of the role of partial lactate metabolism related genes in HCC and suggest a new risk score to predict prognosis.

Circ_0006324 regulates cell proliferation, cell-cycle progression, apoptosis, and glycolysis of non-small cell lung cancer cells through miR-496/TRIM59 axis

Increasing evidence suggests that circular RNA (circRNA) plays an important role in non-small cell lung cancer (NSCLC) progression. This study aimed to investigate the role and potential molecular mechanism of circ_0006324 in NSCLC. The expression levels of circ_0006324, miR-496, miR-488-5p, and tripartite motif-containing 59 (TRIM59) mRNA were determined by quantitative real-time polymerase chain reaction (PCR). 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay, EdU assay, and flow cytometry were carried out to evaluate cell proliferation and apoptosis. The extracellular acidification rate and lactic acid production were examined to assess cell glycolysis. Western blot assay was used to detect protein levels. The target relationship of circ_0006324/miR-496/TRIM59 axis was validated by RNA pull-down assay, dual luciferase reporter assay, and radio immunoprecipitation assay. Xenograft tumor assay was performed to reveal the function of circ_0006324 in vivo. Circ_0006324 was upregulated in NSCLC and related to tumor node metastasis stage and distant metastasis. Knockdown of circ_00006324 impeded NSCLC cell proliferation, glycolysis, and promoted cell apoptosis. MiR-496 was verified as a target of circ_0006324 and circ_00006324 mediated the altering of cell proliferation, apoptosis, and glycolysis of NSCLC cells through targeting miR-496. TRIM59 was verified as a target of miR-496, and circ_0006324 positively regulated TRIM59 expression by targeting miR-496. Overexpression of TRIM59 could reverse the effects of circ_0006324 silencing on the proliferation, apoptosis, and glycolysis of NSCLC cells. Circ_0006324 knockdown impeded NSCLC tumor growth in vivo. Circ_0006324 functioned as a tumor promoter in NSCLC to promote cell proliferation, cell cycle progression, and glycolysis and inhibit cell apoptosis via miR-496/TRIM59 axis.

Reprogramming the immunosuppressive tumor microenvironment: exploiting angiogenesis and thrombosis to enhance immunotherapy

This review focuses on the immunosuppressive effects of tumor angiogenesis and coagulation on the tumor microenvironment (TME). We summarize previous research efforts leveraging these observations and targeting these processes to enhance immunotherapy outcomes. Clinical trials have documented improved outcomes when combining anti-angiogenic agents and immunotherapy. However, their overall survival benefit over conventional therapy remains limited and certain tumors exhibit poor response to anti-angiogenic therapy. Additionally, whilst preclinical studies have shown several components of the tumor coagulome to curb effective anti-tumor immune responses, the clinical studies reporting combinations of anticoagulants with immunotherapies have demonstrated variable treatment outcomes. By reviewing the current state of the literature on this topic, we address the key questions and future directions in the field, the answers of which are crucial for developing effective strategies to reprogram the TME in order to further the field of cancer immunotherapy.

Potential of Interleukin (IL)-12 Group as Antivirals: Severe Viral Disease Prevention and Management

The interleukin (IL)-12 family consists of pro- and anti-inflammatory cytokines that are able to signal the activation of host antiviral immunity while preventing over-reactive immune reactions due to active virus replication and viral clearance. Amongst others, IL-12 and IL-23 are produced and released by innate immune cells such as monocytes and macrophages to signal the proliferation of T cells and release of effector cytokines, which subsequently activate host defence against virus infections. Interestingly, the dualities of IL-27 and -35 are evidently shown in the course of virus infections; they regulate the synthesis of cytokines and antiviral molecules, proliferation of T cells, and viral antigen presentation in order to maximize virus clearance by the host immune system. In terms of anti-inflammatory reactions, IL-27 signals the formation of regulatory T cells (Treg) which in turn secrete IL-35 to control the scale of inflammatory response that takes place during virus infections. Given the multitasking of the IL-12 family in regards to the elimination of virus infections, its potential in antiviral therapy is unequivocally important. Thus, this work aims to delve deeper into the antiviral actions of the IL-12 family and their applications in antiviral therapies.

Extracellular Lactic Acidosis of the Tumor Microenvironment Drives Adipocyte-to-Myofibroblast Transition Fueling the Generation of Cancer-Associated Fibroblasts

Lactic acidosis characterizes the tumor microenvironment (TME) and is involved in the mechanisms leading to cancer progression and dissemination through the reprogramming of tumor and local host cells (e.g., endothelial cells, fibroblasts, and immune cells). Adipose tissue also represents a crucial component of the TME which is receiving increasing attention due to its pro-tumoral activity, however, to date, it is not known whether it could be affected by the acidic TME. Now, emerging evidence from chronic inflammatory and fibrotic diseases underlines that adipocytes may give rise to pathogenic myofibroblast-like cells through the adipocyte-to-myofibroblast transition (AMT). Thus, our study aimed to investigate whether extracellular acidosis could affect the AMT process, sustaining the acquisition by adipocytes of a cancer-associated fibroblast (CAF)-like phenotype with a pro-tumoral activity. To this purpose, human subcutaneous adipose-derived stem cells committed to adipocytes (acADSCs) were cultured under basal (pH 7.4) or lactic acidic (pH 6.7, 10 mM lactate) conditions, and AMT was evaluated with quantitative PCR, immunoblotting, and immunofluorescence analyses. We observed that lactic acidosis significantly impaired the expression of adipocytic markers while inducing myofibroblastic, pro-fibrotic, and pro-inflammatory phenotypes in acADSCs, which are characteristic of AMT reprogramming. Interestingly, the conditioned medium of lactic acidosis-exposed acADSC cultures was able to induce myofibroblastic activation in normal fibroblasts and sustain the proliferation, migration, invasion, and therapy resistance of breast cancer cells in vitro. This study reveals a previously unrecognized relationship between lactic acidosis and the generation of a new CAF-like cell subpopulation from adipocytic precursor cells sustaining tumor malignancy.

Postnatal administration of S-adenosylmethionine restores developmental AHR activation-induced deficits in CD8+ T cell function during influenza A virus infection

Developmental exposures can influence life-long health; yet, counteracting negative consequences is challenging due to poor understanding of cellular mechanisms. The aryl hydrocarbon receptor (AHR) binds many small molecules, including numerous pollutants. Developmental exposure to the signature environmental AHR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) significantly dampens adaptive immune responses to influenza A virus (IAV) in adult offspring. CD8+ cytotoxic T lymphocytes (CTL) are crucial for successful infection resolution, which depends on the number generated and the complexity of their functionality. Prior studies showed developmental AHR activation significantly reduced the number of virus-specific CD8+ T cells, but impact on their functions is less clear. Other studies showed developmental exposure was associated with differences in DNA methylation in CD8+ T cells. Yet, empirical evidence that differences in DNA methylation are causally related to altered CD8+ T cell function is lacking. The two objectives were to ascertain whether developmental AHR activation affects CTL function, and whether differences in methylation contribute to reduced CD8+ T cell responses to infection. Developmental AHR triggering significantly reduced CTL polyfunctionality, and modified the transcriptional program of CD8+ T cells. S-adenosylmethionine (SAM), which increases DNA methylation, but not Zebularine, which diminishes DNA methylation, restored polyfunctionality and boosted the number of virus-specific CD8+ T cells. These findings suggest that diminished methylation, initiated by developmental exposure to an AHR-binding chemical, contributes to durable changes in antiviral CD8+ CTL functions later in life. Thus, deleterious consequence of development exposure to environmental chemicals are not permanently fixed, opening the door for interventional strategies to improve health.

Conserved angio-immune subtypes of the tumor microenvironment predict response to immune checkpoint blockade therapy

Immune checkpoint blockade (ICB) therapy has revolutionized cancer treatment. However, only a fraction of patients respond to ICB therapy. Accurate prediction of patients to likely respond to ICB would maximize the efficacy of ICB therapy. The tumor microenvironment (TME) dictates tumor progression and therapy outcome. Here, we classify the TME by analyzing the transcriptome from 11,069 cancer patients based on angiogenesis and T cell activity. We find three distinct angio-immune TME subtypes conserved across 30 non-hematological cancers. There is a clear inverse relationship between angiogenesis and anti-tumor immunity in TME. Remarkably, patients displaying TME with low angiogenesis with strong anti-tumor immunity show the most significant responses to ICB therapy in four cancer types. Re-evaluation of the renal cell carcinoma clinical trials provides compelling evidence that the baseline angio-immune state is robustly predictive of ICB responses. This study offers a rationale for incorporating baseline angio-immune scores for future ICB treatment strategies.

Lactic acid and lactate: revisiting the physiological roles in the tumor microenvironment

Lactic acid production has been regarded as a mechanism by which malignant cells escape immunosurveillance. Recent technological advances in mass spectrometry and the use of cell culture media with a physiological nutrient composition have shed new light on the role of lactic acid and its conjugate lactate in the tumor microenvironment. Here, we review novel work identifying lactate as a physiological carbon source for mammalian tumors and immune cells. We highlight evidence that its use as a substrate is distinct from the immunosuppressive acidification of the extracellular milieu by lactic acid protons. Together, data suggest that neutralizing the effects of intratumoral acidity while maintaining physiological lactate metabolism in cytotoxic CD8+ T cells should be pursued to boost anti-tumor immunity.

LDHA: The Obstacle to T cell responses against tumor

Immunotherapy has become a successful therapeutic strategy in certain solid tumors and hematological malignancies. However, this efficacy of immunotherapy is impeded by limited success rates. Cellular metabolic reprogramming determines the functionality and viability in both cancer cells and immune cells. Extensive research has unraveled that the limited success of immunotherapy is related to immune evasive metabolic reprogramming in tumor cells and immune cells. As an enzyme that catalyzes the final step of glycolysis, lactate dehydrogenase A (LDHA) has become a major focus of research. Here, we have addressed the structure, localization, and biological features of LDHA. Furthermore, we have discussed the various aspects of epigenetic regulation of LDHA expression, such as histone modification, DNA methylation, N6-methyladenosine (m6A) RNA methylation, and transcriptional control by noncoding RNA. With a focus on the extrinsic (tumor cells) and intrinsic (T cells) functions of LDHA in T-cell responses against tumors, in this article, we have reviewed the current status of LDHA inhibitors and their combination with T cell-mediated immunotherapies and postulated different strategies for future therapeutic regimens.

Dendritic Cells or Macrophages? The Microenvironment of Human Clear Cell Renal Cell Carcinoma Imprints a Mosaic Myeloid Subtype Associated with Patient Survival

Since their initial description by Elie Metchnikoff, phagocytes have sparked interest in a variety of biologic disciplines. These important cells perform central functions in tissue repair and immune activation as well as tolerance. Myeloid cells can be immunoinhibitory, particularly in the tumor microenvironment, where their presence is generally associated with poor patient prognosis. These cells are highly adaptable and plastic, and can be modulated to perform desired functions such as antitumor activity, if key programming molecules can be identified. Human clear cell renal cell carcinoma (ccRCC) is considered immunogenic; yet checkpoint blockades that target T cell dysfunction have shown limited clinical efficacy, suggesting additional layers of immunoinhibition. We previously described "enriched-in-renal cell carcinoma" (erc) DCs that were often found in tight contact with dysfunctional T cells. Using transcriptional profiling and flow cytometry, we describe here that ercDCs represent a mosaic cell type within the macrophage continuum co-expressing M1 and M2 markers. The polarization state reflects tissue-specific signals that are characteristic of RCC and renal tissue homeostasis. ErcDCs are tissue-resident with increasing prevalence related to tumor grade. Accordingly, a high ercDC score predicted poor patient survival. Within the profile, therapeutic targets (VSIG4, NRP1, GPNMB) were identified with promise to improve immunotherapy.

Lactate metabolism in human health and disease

The current understanding of lactate extends from its origins as a byproduct of glycolysis to its role in tumor metabolism, as identified by studies on the Warburg effect. The lactate shuttle hypothesis suggests that lactate plays an important role as a bridging signaling molecule that coordinates signaling among different cells, organs and tissues. Lactylation is a posttranslational modification initially reported by Professor Yingming Zhao’s research group in 2019. Subsequent studies confirmed that lactylation is a vital component of lactate function and is involved in tumor proliferation, neural excitation, inflammation and other biological processes. An indispensable substance for various physiological cellular functions, lactate plays a regulatory role in different aspects of energy metabolism and signal transduction. Therefore, a comprehensive review and summary of lactate is presented to clarify the role of lactate in disease and to provide a reference and direction for future research. This review offers a systematic overview of lactate homeostasis and its roles in physiological and pathological processes, as well as a comprehensive overview of the effects of lactylation in various diseases, particularly inflammation and cancer.

Obstacles for T-lymphocytes in the tumour microenvironment: Therapeutic challenges, advances and opportunities beyond immune checkpoint

The tumour microenvironment (TME) imposes a major obstacle to infiltrating T-lymphocytes and suppresses their function. Several immune checkpoint proteins that interfere with ligand/receptor interactions and impede T-cell anti-tumour responses have been identified. Immunotherapies that block immune checkpoints have revolutionized the treatment paradigm for many patients with advanced-stage tumours. However, metabolic constraints and soluble factors that exist within the TME exacerbate the functional exhaustion of tumour-infiltrating T-cells. Here we review these multifactorial constraints and mechanisms – elevated immunosuppressive metabolites and enzymes, nutrient insufficiency, hypoxia, increased acidity, immense amounts of extracellular ATP and adenosine, dysregulated bioenergetic and purinergic signalling, and ionic imbalance - that operate in the TME and collectively suppress T-cell function. We discuss how scientific advances could help overcome the complex TME obstacles for tumour-infiltrating T-lymphocytes, aiming to stimulate further research for developing new therapeutic strategies by harnessing the full potential of the immune system in combating cancer.

Lactic acidosis promotes aggressive features of cholangiocarcinoma cells via upregulating ALDH1A3 expression through EGFR axis

AIMS

Lactic acidosis (LA) generated in tumor microenvironment promotes tumor metastasis and drug resistance. This study aimed to demonstrate the impacts and the mechanisms of LA on aldehyde dehydrogenase1A3 (ALDH1A3) in promoting aggressiveness and gemcitabine resistance in cholangiocarcinoma (CCA) cell lines. The clinical relevance and the molecular pathway related to the upregulation of ALDH1A3 in LA cells will be revealed.

MAIN METHODS

ALDH1A3 expression and its clinical significances in CCA tissues were analyzed using the GEO databases. Human CCA cell lines, KKU-213A-LA and KKU-213B-LA maintained in the LA medium were studied and compared with its parental cells cultured in normal medium. Aggressive features-proliferation, colony formation, migration, invasion, and gemcitabine response were determined. Expression of ALDH1A3, EGFR and the downstream effectors were analyzed using real-time PCR and Western blotting.

KEY FINDINGS

ALDH1A3 was upregulated in patient CCA tissues and correlated with LDHA and shorter survival of CCA patients. mRNA and protein of ALDH1A3 were increased in LA cells. Attenuation of ALDH1A3 expression by siRNA significantly reduced cell proliferation, colony formation, migration, invasion, and gemcitabine resistance of LA cells, and gemcitabine resistant cells. The EGF/EGFR signaling via Erk and STAT3 was pinned to be involved in the induction of ALDH1A3 expression in LA cells. The transcriptomic analysis from TCGA dataset supported the links between LDHA, EGFR and ALDH1A3 in several tumor tissues.

SIGNIFICANCE

Lactic acidosis upregulated EGFR and ALDH1A3 expression, leading to the aggressiveness of CCA cells. The EGFR/ALDH1A3 axis could be a novel therapeutic target to eradicate metastatic CCA.

Targeting Tumour-Associated Fibroblasts in Cancers

Tumours develop within complex tissue environments consisting of aberrant oncogenic cancer cells, diverse innate and adaptive immune cells, along with structural stromal cells, extracellular matrix and vascular networks, and many other cellular and non-cellular soluble constituents. Understanding the heterogeneity and the complex interplay between these cells remains a key barrier in treating tumours and cancers. The immune status of the pre-tumour and tumour milieu can dictate if the tumour microenvironment (TME) supports either a pro-malignancy or an anti-malignancy phenotype. Identification of the factors and cell types that regulate the dysfunction of the TME is crucial in order to understand and modulate the immune status of tumours. Among these cell types, tumour-associated fibroblasts are emerging as a major component of the TME that is often correlated with poor prognosis and therapy resistance, including immunotherapies. Thus, a deeper understanding of the complex roles of tumour-associated fibroblasts in regulating tumour immunity and cancer therapy could provide new insight into targeting the TME in various human cancers. In this review, we summarize recent studies investigating the role of immune and key stromal cells in regulating the immune status of the TME and discuss the therapeutic potential of targeting stromal cells, especially tumour-associated fibroblasts, within the TME as an adjuvant therapy to sensitize immunosuppressive tumours and prevent cancer progression, chemo-resistance and metastasis.

The acidic tumour microenvironment: Manipulating the immune response to elicit escape

The success of cancer treatment relies on the composition of the tumour microenvironment which is comprised of tumour cells, blood vessels, stromal cells, immune cells, and extracellular matrix components. Barriers to effective cancer treatment need to be overcome, and the acidic microenvironment of the tumour provides a key target for treatment. This review intends to provide an overview of the effects that low extracellular pH has on components of the tumour microenvironment and how they contribute to immune escape. Further, potential therapeutic targets will be discussed.

The impact of hypoxia on immune state in cancer

Hypoxia is a known feature of solid tumors and a critical promoter of tumor hallmarks. Hypoxia influences tumor immunity in a way favoring immune evasion and resistance. Extreme hypoxia and aberrant hypoxia-inducible factor-1 (HIF-1) activity in tumor microenvironment (TME) is a drawback for effective immunotherapy. Infiltration and activity of CD8⁺ T cells is reduced in such condition, whereas regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) show high activities. Highly hypoxic TME also impairs maturation and activity of dendritic cell (DCs) and natural killer (NK) cells. In addition, the hypoxic TME positively is linked positively with metabolic changes in cells of immune system. These alterations are indicative of a need for hypoxia modulation as a complementary targeting strategy to go with immune checkpoint inhibitor (ICI) therapy.

Lactate Is a Metabolic Mediator That Shapes Immune Cell Fate and Function

Lactate and the associated H⁺ ions are still introduced in many biochemistry and general biology textbooks and courses as a metabolic by-product within fast or oxygen-independent glycolysis. However, the role of lactate as a fuel source has been well-appreciated in the field of physiology, and the role of lactate as a metabolic feedback regulator and distinct signaling molecule is beginning to gain traction in the field of immunology. We now know that while lactate and the associated H⁺ ions are generally immunosuppressive negative regulators, there are cell, receptor, mediator, and microenvironment-specific effects that augment T helper (Th)17, macrophage (M)2, tumor-associated macrophage, and neutrophil functions. Moreover, we are beginning to uncover how lactate and H⁺ utilize different transporters and signaling cascades in various immune cell types. These immunomodulatory effects may have a substantial impact in cancer, sepsis, autoimmunity, wound healing, and other immunomodulatory conditions with elevated lactate levels. In this article, we summarize the known effects of lactate and H⁺ on immune cells to hypothesize potential explanations for the divergent inflammatory vs. anti-inflammatory effects.