Metformin promotes anticancer activity of NK cells in a p38 MAPK dependent manner

A positive-feedback loop suppresses TNBC tumour growth by remodeling tumour immune microenvironment and inducing ferroptosis

Triple-negative breast cancer (TNBC) is a particularly aggressive subtype of breast cancer due to poor immunogenicity and limited immune cell infiltration, efficient therapeutics are still deficiency. Ferroptosis, a reactive oxygen species (ROS)-reliant cell death, can enhance cellular immunogenicity and then active immune system. To sustain a long-term "hot" tumour immune microenvironment (TIME), an immune-modulator is indispensable. Metformin (MET), a commonly used oral drug for type 2 diabetes, has played a vital role in fostering an immunostimulatory environment. Herein, we confirm the TIME can be remodeled by MET and further promotes ferroptosis via upregulating cellular concentration of l-Glutamine. In light of this, we have design a self-assembled MET-loaded Fe3+-doped polydopamine nanoparticle (Fe-PDA-MET NP) that can disorder the cellular redox homeostasis and induce robust ferroptosis under 808 nm irradiation, resulting in a strong immune response. Based on the function of MET, there is a marked increase in the infiltration of activated CD8+ T cells and NK cells, which subsequently augments ferroptosis to a greater extent. Taken together, Fe-PDA-MET NPs activate a ferroptotic positive-feedback loop for effectively control TNBC progression, which offers a promising therapeutic modality to enhance the immunogenicity and reshape the TIME.

Bibliometric analysis of metformin as an immunomodulator (2013-2024)

Background

Metformin, the frontline treatment for diabetes, has considerable potential as an immunomodulator; however, detailed bibliometric analyses on this subject are limited.

Methods

This study extracted 640 relevant articles from the Web of Science (WOS) Core Collection and conducted visual analyses using Microsoft Excel, VOSviewer, and CiteSpace.

Results

The findings showed that research on the immunomodulatory function of metformin has grown steadily since 2017, with China and the United States being the leading contributors. These studies have mostly been published in journals such as the International Journal of Molecular Sciences, Cancers, Frontiers in Immunology, and Scientific Reports. Keyword co-occurrence analysis highlighted metformin's role as an immunomodulator, particularly in the context of the tumor immune microenvironment, immunosuppressive checkpoints, and metformin derivatives. Recent research has highlighted metformin's application in aging, autoimmune diseases, COVID-19, and tuberculosis. Additionally, its role in regulating inflammation and gut microbiota is also being investigated.

Conclusion

Overall, the immunomodulatory effects of metformin were investigated in anti-tumor, antiviral, anti-aging, and autoimmune disease research. This highlights the scope of metformin use in these fields, while also significantly enhancing its clinical value as a repurposed drug.

Immunosenescence, Physical Exercise, and their Implications in Tumor Immunity and Immunotherapy

Aging is associated with a decline in immune function, termed immunosenescence, which compromises host defences and increases susceptibility to infections and cancer. Physical exercise is widely recognized for its myriad health benefits, including the potential to modulate the immune system. This review explores the bidirectional relationship between immunosenescence and physical exercise, focusing on their interplay in shaping antitumor immunity. We summarize the impact of aging on innate and adaptive immune cells, highlighting alterations that contribute to immunosenescence and cancer development. We further delineate the effects of exercise on immune cell function, demonstrating its potential to mitigate immunosenescence and enhance antitumor responses. We also discuss the implications of immunosenescence for the efficacy of immunotherapies, such as immune checkpoint inhibitors and adoptive T cell therapy, and explore the potential benefits of combining exercise with these interventions. Collectively, this review underscores the importance of understanding the complex relationship between immunosenescence, physical exercise, and antitumor immunity, paving the way for the development of innovative strategies to improve cancer outcomes in the aging population.

Landscape of targeted therapies for lung squamous cell carcinoma

Lung cancer, a common type of malignant neoplasm, has seen significant advancements in the treatment of lung adenocarcinoma (LUAD). However, the management of lung squamous cell carcinoma (LSCC) continues to pose challenges. Traditional treatment methods for LSCC encompass surgical resection, chemotherapy, and radiotherapy. The introduction of targeted therapy and immunotherapy has greatly benefited LSCC patients, but issues such as limited immune response rates and adverse reactions persist. Therefore, gaining a deeper comprehension of the underlying mechanisms holds immense importance. This review provides an in-depth overview of classical signaling pathways and therapeutic targets, including the PI3K signaling pathway, CDK4/6 pathway, FGFR1 pathway and EGFR pathway. Additionally, we delve into alternative signaling pathways and potential targets that could offer new therapeutic avenues for LSCC. Lastly, we summarize the latest advancements in targeted therapy combined with immune checkpoint blockade (ICB) therapy for LSCC and discuss the prospects and challenges in this field.

Paulownin elicits anti-tumor effects by enhancing NK cell cytotoxicity through JNK pathway activation

Paulownin, a natural compound derived from Paulownia tomentosa wood, exhibits various physiological functions, including anti-bacterial and anti-fungal effects. However, the impact of paulownin on natural killer (NK) cell immune activity remains largely unknown. In this study, we investigated the effect of paulownin on NK cell activity both in vitro and in vivo, and explored its potential mechanisms. NK-92 cells were used for in vitro experiments and a BALB/c mouse model with B16F10 cells injected subcutaneously were used for in vivo anti-tumor analysis. We found that paulownin enhanced the cytolytic activity of NK-92 cells against leukemia, human colon, and human lung cancer cell lines. Paulownin treatment increased the expression of the degranulation marker protein CD107a and cytolytic granules, including granzyme B and perforin in NK-92 cells. Moreover, these enhancements of cytotoxicity and the expression of cytolytic granules induced by paulownin were also observed in human primary NK cells. Signaling studies showed that paulownin promoted the phosphorylation of JNK. The increased perforin expression and elevated cytotoxic activity induced by paulownin were effectively inhibited by pre-treatment with a JNK inhibitor. In vivo studies demonstrated that the administration of paulownin suppressed the growth of B16F10 melanoma cells allografted into mice. Paulownin administration promoted the activation of NK cells in the spleen of mice, resulting in enhanced cytotoxicity against YAC-1 cells. Moreover, the anti-tumor effects of paulownin were reduced upon the depletion of NK cells. Therefore, these results suggest that paulownin enhances NK cell cytotoxicity by activating the JNK signaling pathway and provide significant implications for developing new strategies for cancer immunotherapy.

Harnessing Metformin's Immunomodulatory Effects on Immune Cells to Combat Breast Cancer

Metformin, a medication known for its anti-glycemic properties, also demonstrates potent immune system activation. In our study, using a 4T1 breast cancer model in BALB/C WT mice, we examined metformin's impact on the functional phenotype of multiple immune cells, with a specific emphasis on natural killer T (NKT) cells due to their understudied role in this context. Metformin administration delayed the appearance and growth of carcinoma. Furthermore, metformin increased the percentage of IFN-γ+ NKT cells, and enhanced CD107a expression, as measured by MFI, while decreasing PD-1+, FoxP3+, and IL-10+ NKT cells in spleens of metformin-treated mice. In primary tumors, metformin increased the percentage of NKp46+ NKT cells and increased FasL expression, while lowering the percentages of FoxP3+, PD-1+, and IL-10-producing NKT cells and KLRG1 expression. Activation markers increased, and immunosuppressive markers declined in T cells from both the spleen and tumors. Furthermore, metformin decreased IL-10+ and FoxP3+ Tregs, along with Gr-1+ myeloid-derived suppressor cells (MDSCs) in spleens, and in tumor tissue, it decreased IL-10+ and FoxP3+ Tregs, Gr-1+, NF-κB+, and iNOS+ MDSCs, and iNOS+ dendritic cells (DCs), while increasing the DCs quantity. Additionally, increased expression levels of MIP1a, STAT4, and NFAT in splenocytes were found. These comprehensive findings illustrate metformin's broad immunomodulatory impact across a variety of immune cells, including stimulating NKT cells and T cells, while inhibiting Tregs and MDSCs. This dynamic modulation may potentiate its use in cancer immunotherapy, highlighting its potential to modulate the tumor microenvironment across a spectrum of immune cell types.

Anexelekto (AXL) no more: microRNA-155 (miR-155) controls the "Uncontrolled" in SARS-CoV-2

AXL is the gene that encodes the Anexelekto (AXL) receptor tyrosine kinase that demonstrates significant roles in various cellular processes, including cell growth, survival, and migration. Anexelekto is a Greek word meaning excessive and uncontrolled, semantically implying the crucial involvement of AXL in cancer and immune biology, and in promoting cancer metastasis. AXL overexpression appears to drive epithelial to mesenchymal transition, tumor angiogenesis, decreased antitumor immune response, and resistance to therapeutic agents. Recently, AXL has been reported to play important roles in several viral infections, including SARS-CoV-2. We have previously outlined the importance of microRNAs (miRNAs, miRs) and especially miR-155 in SARS-CoV-2 pathophysiology through regulation of the Renin-Angiotensin Aldosterone System (RAAS) and influence on several aspects of host innate immunity. MiRNAs are negative regulators of gene expression, decreasing the stability of target RNAs or limiting their translation and, enthrallingly, miR-155 is also involved in AXL homeostasis-both endogenously and pharmaceutically using repurposed drugs (e.g., metformin)-highlighting thrifty evolutionary host innate immunity mechanisms that successfully can thwart viral entry and replication. Cancer, infections, and immune system disturbances will increasingly involve miRNA diagnostics and therapeutics in the future.

Trial watch: beta-blockers in cancer therapy

Compelling evidence supports the hypothesis that stress negatively impacts cancer development and prognosis. Irrespective of its physical, biological or psychological source, stress triggers a physiological response that is mediated by the hypothalamic-pituitary-adrenal axis and the sympathetic adrenal medullary axis. The resulting release of glucocorticoids and catecholamines into the systemic circulation leads to neuroendocrine and metabolic adaptations that can affect immune homeostasis and immunosurveillance, thus impairing the detection and eradication of malignant cells. Moreover, catecholamines directly act on β-adrenoreceptors present on tumor cells, thereby stimulating survival, proliferation, and migration of nascent neoplasms. Numerous preclinical studies have shown that blocking adrenergic receptors slows tumor growth, suggesting potential clinical benefits of using β-blockers in cancer therapy. Much of these positive effects of β-blockade are mediated by improved immunosurveillance. The present trial watch summarizes current knowledge from preclinical and clinical studies investigating the anticancer effects of β-blockers either as standalone agents or in combination with conventional antineoplastic treatments or immunotherapy.

Targeting cellular metabolism in head and neck cancer precision medicine era: A promising strategy to overcome therapy resistance

Head and neck squamous cell carcinoma (HNSCC) is among the most prevalent cancer worldwide, with the most severe impact on quality of life of patients. Despite the development of multimodal therapeutic approaches, the clinical outcomes of HNSCC are still unsatisfactory, mainly caused by relatively low responsiveness to treatment and severe drug resistance. Metabolic reprogramming is currently considered to play a pivotal role in anticancer therapeutic resistance. This review aimed to define the specific metabolic programs and adaptations in HNSCC therapy resistance. An extensive literature review of HNSCC was conducted via the PubMed including metabolic reprogramming, chemo- or immune-therapy resistance. Glucose metabolism, fatty acid metabolism, and amino acid metabolism are closely related to the malignant biological characteristics of cancer, anti-tumor drug resistance, and adverse clinical results. For HNSCC, pyruvate, lactate and almost all lipid categories are related to the occurrence and maintenance of drug resistance, and targeting amino acid metabolism can prevent tumor development and enhance the response of drug-resistant tumors to anticancer therapy. This review will provide a better understanding of the altered metabolism in therapy resistance of HNSCC and promote the development of new therapeutic strategies against HNSCC, thereby contribute to a more efficacious precision medicine.

NK cells vs. obesity: A tale of dysfunction & redemption

Natural killer (NK) cells are critical in protecting the body against infection and cancer. NK cells can rapidly respond to these threats by directly targeting the infected or transformed cell using their cytotoxic machinery or by initiating and amplifying the immune response via their production of cytokines. Additionally, NK cells are resident across many tissues including adipose, were their role extends from host protection to tissue homeostasis. Adipose resident NK cells can control macrophage polarization via cytokine production, whilst also regulating stressed adipocyte fate using their cytotoxic machinery. Obesity is strongly associated with increased rates of cancer and a heightened susceptibility to severe infections. This is in part due to significant obesity-related immune dysregulation, including defects in both peripheral and adipose tissue NK cells. In this review, we detail the literature to date on NK cells in the setting of obesity - outlining the consequences, mechanisms and therapeutic interventions.

Research Progress of Metformin in the Treatment of Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) is one of the most common malignancies and has a high mortality, posing a great threat to both human physical and mental health. With the advancement of scientific research, a variety of cancer therapies have been used for OSCC treatment. However, the prognosis of OSCC shows no significant improvement. Metformin has been recognized as the first-line drug for the treatment of diabetes, and recent studies have shown that metformin has a remarkable suppressive effect on tumor progression. Metformin can not only affect the energy metabolism of tumor cells but also play an antitumor role by modulating the tumor microenvironment and cancer stem cells. In this review, the molecular mechanism of metformin and its anticancer mechanism in OSCC are summarized. In addition, this article summarizes the side effects of metformin and the future prospects of its application in the treatment of OSCC.

The Impact of Metformin on Tumor-Infiltrated Immune Cells: Preclinical and Clinical Studies

The tumor microenvironment (TME) plays a pivotal role in the fate of cancer cells, and tumor-infiltrating immune cells have emerged as key players in shaping this complex milieu. Cancer is one of the leading causes of death in the world. The most common standard treatments for cancer are surgery, radiation therapy, and chemotherapeutic drugs. In the last decade, immunotherapy has had a potential effect on the treatment of cancer patients with poor prognoses. One of the immune therapeutic targeted approaches that shows anticancer efficacy is a type 2 diabetes medication, metformin. Beyond its glycemic control properties, studies have revealed intriguing immunomodulatory properties of metformin. Meanwhile, several studies focus on the impact of metformin on tumor-infiltrating immune cells in various tumor models. In several tumor models, metformin can modulate tumor-infiltrated effector immune cells, CD8+, CD4+ T cells, and natural killer (NK) cells, as well as suppressor immune cells, T regulatory cells, tumor-associated macrophages (TAMs), and myeloid-derived suppressor cells (MDSCs). In this review, we discuss the role of metformin in modulating tumor-infiltrating immune cells in different preclinical models and clinical trials. Both preclinical and clinical studies suggest that metformin holds promise as adjunctive therapy in cancer treatment by modulating the immune response within the tumor microenvironment. Nonetheless, both the tumor type and the combined therapy have an impact on the specific targets of metformin in the TME. Further investigations are warranted to elucidate the precise mechanisms underlying the immunomodulatory effects of metformin and to optimize its clinical application in cancer patients.

Cycloartenyl ferulate improves natural killer (NK) cell immunity against cancer by binding to IFNγ receptor 1

Cycloartenyl ferulate (CF) is abundant in brown rice with multiple biologic functions. It has been reported to possess antitumor activity; however, the related mechanism of action of CF has not been clarified. Herein, we unexpectedly uncover the immunological regulation effects of CF and its molecular mechanism. We discovered that CF directly enhanced the killing capacity of natural killer (NK) cells for various cancer cells in vitro. In vivo, CF also improved cancer surveillance in mouse models of lymphoma clearance and metastatic melanoma dependent on NK cells. In addition, CF promoted anticancer efficacy of the anti-PD1 antibody with improvement of tumor immune microenvironment. Mechanistically, we first unveiled that CF acted on the canonical JAK1/2-STAT1 signaling pathway to enhance the immunity of the NK cells by selectively binding to interferon γ receptor 1. Collectively, our results indicate that CF is a promising immunoregulation agent worthy of attention in clinical application in the future. Due to broad biological significance of interferon γ, our findings also provide a capability to understand the diverse functions of CF.

Metformin as a booster of cancer immunotherapy

Metformin, a biguanide antidiabetic, has been studied for its repurposing effects in oncology. Although a modest effect was observed in a single-agent regimen, metformin can synergize the anti-tumor effects of other modalities. The promising combination for cancer treatment is with immunotherapy. Despite high efficacy for some cancers, immunotherapy could be limited by modulation of the tumor immune microenvironment and the immune exhaustion of cytotoxic immune cells. Combining immunotherapy with metformin, thus, exerted a rescuing effect of immunotherapy and potentiated the anti-tumor effects of each other. Although not fully understood, metformin shows promoting effects of immunotherapy by several mechanisms. Those proposed mechanisms have been partially proven and are suggested for possible therapeutic strategies for cancer treatment. In this review, a state-of-the-art of metformin's boosting effects on immunotherapy is reviewed and discussed. The future directions for metformin research in preclinical and clinical immunotherapy are also suggested.

BS148 Reduces the Aggressiveness of Metastatic Melanoma via Sigma-2 Receptor Targeting

The management of advanced-stage melanoma is clinically challenging, mainly because of its resistance to the currently available therapies. Therefore, it is important to develop alternative therapeutic strategies. The sigma-2 receptor (S2R) is overexpressed in proliferating tumor cells and represents a promising vulnerability to target. Indeed, we have recently identified a potent S2R modulator (BS148) that is effective in melanoma. To elucidate its mechanism of action, we designed and synthesized a BS148 fluorescent probe that enters SK-MEL-2 melanoma cells as assessed using confocal microscopy analysis. We show that S2R knockdown significantly reduces the anti-proliferative effect induced by BS148 administration, indicating the engagement of S2R in BS148-mediated cytotoxicity. Interestingly, BS148 treatment showed similar molecular effects to S2R RNA interference-mediated knockdown. We demonstrate that BS148 administration activates the endoplasmic reticulum stress response through the upregulation of protein kinase R-like ER kinase (PERK), activating transcription factor 4 (ATF4) genes, and C/EBP homologous protein (CHOP). Furthermore, we show that BS148 treatment downregulates genes related to the cholesterol pathway and activates the MAPK signaling pathway. Finally, we translate our results into patient-derived xenograft (PDX) cells, proving that BS148 treatment reduces melanoma cell viability and migration. These results demonstrate that BS148 is able to inhibit metastatic melanoma cell proliferation and migration through its interaction with the S2R and confirm its role as a promising target to treat cancer.

The development and benefits of metformin in various diseases

Metformin has been used for the treatment of type II diabetes mellitus for decades due to its safety, low cost, and outstanding hypoglycemic effect clinically. The mechanisms underlying these benefits are complex and still not fully understood. Inhibition of mitochondrial respiratory-chain complex I is the most described downstream mechanism of metformin, leading to reduced ATP production and activation of AMP-activated protein kinase (AMPK). Meanwhile, many novel targets of metformin have been gradually discovered. In recent years, multiple pre-clinical and clinical studies are committed to extend the indications of metformin in addition to diabetes. Herein, we summarized the benefits of metformin in four types of diseases, including metabolic associated diseases, cancer, aging and age-related diseases, neurological disorders. We comprehensively discussed the pharmacokinetic properties and the mechanisms of action, treatment strategies, the clinical application, the potential risk of metformin in various diseases. This review provides a brief summary of the benefits and concerns of metformin, aiming to interest scientists to consider and explore the common and specific mechanisms and guiding for the further research. Although there have been countless studies of metformin, longitudinal research in each field is still much warranted.

The function, mechanisms, and clinical applications of metformin: potential drug, unlimited potentials

Metformin has been used clinically for more than 60 years. As time goes by, more and more miraculous effects of metformin beyond the clinic have been discovered and discussed. In addition to the clinically approved hypoglycemic effect, it also has a positive metabolic regulation effect on the human body that cannot be ignored. Such as anti-cancer, anti-aging, brain repair, cardiovascular protection, gastrointestinal regulation, hair growth and inhibition of thyroid nodules, and other nonclinical effects. Metformin affects almost the entire body in the situation taking it over a long period, and the preventive effects of metformin in addition to treating diabetes are also beginning to be recommended in some guidelines. This review is mainly composed of four parts: the development history of metformin, the progress of clinical efficacy, the nonclinical efficacy of metformin, and the consideration and prospect of its application.

Metabolism of NK cells during viral infections

Cellular metabolism is essential for the correct function of immune system cells, including Natural Killer cells (NK). These cells depend on energy to carry out their effector functions, especially in the early stages of viral infection. NK cells participate in the innate immune response against viruses and tumors. Their main functions are cytotoxicity and cytokine production. Metabolic changes can impact intracellular signals, molecule production, secretion, and cell activation which is essential as the first line of immune defense. Metabolic variations in different immune cells in response to a tumor or pathogen infection have been described; however, little is known about NK cell metabolism in the context of viral infection. This review summarizes the activation-specific metabolic changes in NK cells, the immunometabolism of NK cells during early, late, and chronic antiviral responses, and the metabolic alterations in NK cells in SARS-CoV2 infection. The modulation points of these metabolic routes are also discussed to explore potential new immunotherapies against viral infections.

Diabetes medications and risk of HCC

Type 2 diabetes mellitus is a recognized risk factor for HCC in patients with liver disease, independent from the etiology of their liver disease. Hence, prevention and treatment of type 2 diabetes mellitus and its underlying cause, insulin resistance, should be considered a treatment target for patients with liver disease. The drug armamentarium for diabetes is wide and consists of agents with insulin-sensitizing activity, agents that stimulate insulin secretion, insulin itself, and agents that reduce gastrointestinal and urinary glucose absorption. From an endocrinology perspective, the main goal of treatment is the achievement of euglycemia; however, in patients at risk of, or with known underlying liver disease, the choice of diabetic medication as it relates to potential hepatic carcinogenesis remains complex and should be carefully considered. In the last decade, increasing evidence has suggested that metformin may reduce the risk of HCC, whereas evidence for other classes of diabetic medications, particularly some of the newer agents including the sodium glucose cotransporter-2 inhibitors and glucagon-like peptide-1 receptor agonists, is fewer and often inconsistent. In this review, we aim to summarize the current evidence on the potential effects of the most widely used diabetic agents on liver cancer tumorigenesis.

Diabetes and skin cancers: Risk factors, molecular mechanisms and impact on prognosis

Diabetes and skin cancers have emerged as threats to public health worldwide. However, their association has been less intensively studied. In this narrative review, we explore the common risk factors, molecular mechanisms, and prognosis of the association between cutaneous malignancies and diabetes. Hyperglycemia, oxidative stress, low-grade chronic inflammation, genetic, lifestyle, and environmental factors partially explain the crosstalk between skin cancers and this metabolic disorder. In addition, diabetes and its related complications may interfere with the appropriate management of cutaneous malignancies. Antidiabetic medication seems to exert an antineoplastic effect, however, future large, observation studies with a prospective design are needed to clarify its impact on the risk of malignancy in diabetes. Screening for diabetes in skin cancers, as well as close follow-up for the development of cutaneous malignancies in subjects suffering from diabetes, is warranted.

Tumor accomplice: T cell exhaustion induced by chronic inflammation

The development and response to treatment of tumor are modulated by inflammation, and chronic inflammation promotes tumor progression and therapy resistance. This article summarizes the dynamic evolution of inflammation from acute to chronic in the process of tumor development, and its effect on T cells from activation to the promotion of exhaustion. We review the mechanisms by which inflammatory cells and inflammatory cytokines regulate T cell exhaustion and methods for targeting chronic inflammation to improve the efficacy of immunotherapy. It is great significance to refer to the specific state of inflammation and T cells at different stages of tumor development for accurate clinical decision-making of immunotherapy and improving the efficiency of tumor immunotherapy.

Immunosenescence, inflammaging, and cancer immunotherapy efficacy

INTRODUCTION

Immunosenescence is a progressive remodeling of immune functions associated with a decreased ability of the immune system to set up an efficient immune response, both innate and adaptive, with an increase of highly differentiated T cells at the expense of naive T cells. The incidence and prevalence of most cancers increase with age, which can partly be explained by tumor escape mechanisms and decreased immunosurveillance. Aging is also associated with inflammaging, a low-grade proinflammatory state characterized by an increase in inflammatory mediators. Anti-cancer immunotherapy has profoundly changed the landscape of oncology therapy in the last 10 years. Modern T-cell targeted therapies such as bispecific T cell engagers, CAR-T cells, or immune checkpoint blockers may be theoretically affected by immunosenescence or inflammaging.

AREAS COVERED

A bibliographic review through PubMed and Embase was carried out using the following search terms: 'immunosenescence,' 'immunotherapy,' 'inflammaging,' 'bispecific antibodies,' 'CAR-T cells,' 'immune checkpoint blockers,' and 'older patients.'

EXPERT OPINION

This review explores the potential impact of immunosenescence and inflammaging on anti-cancer immunotherapy and therapeutic strategies that could counter immune senescence. A more dedicated research on immunosenescence biomarkers in future clinical trials is warranted for the development of new, more effective and safer therapies.

Nutrient Condition in the Microenvironment Determines Essential Metabolisms of CD8+ T Cells for Enhanced IFNγ Production by Metformin

Metformin (Met), a first-line drug for type 2 diabetes, lowers blood glucose levels by suppressing gluconeogenesis in the liver, presumably through the liver kinase B1-dependent activation of AMP-activated protein kinase (AMPK) after inhibiting respiratory chain complex I. Met is also implicated as a drug to be repurposed for cancers; its mechanism is believed identical to that of gluconeogenesis inhibition. However, AMPK activation requires high Met concentrations at more than 1 mM, which are unachievable in vivo. The immune-mediated antitumor response might be the case in a low dose Met. Thus, we proposed activating or expanding tumor-infiltrating CD8⁺ T cells (CD8TILs) in a mouse model by orally administering Met in free drinking water. Here we showed that Met, at around 10 μM and a physiologically relevant concentration, enhanced production of IFNγ,TNFα and expression of CD25 of CD8⁺ T cells upon TCR stimulation. Under a glucose-rich condition, glycolysis was exclusively involved in enhancing IFNγ production. Under a low-glucose condition, fatty acid oxidation or autophagy-dependent glutaminolysis, or both, was also involved. Moreover, phosphoenolpyruvate carboxykinase 1 (PCK1), converting oxaloacetate to phosphoenolpyruvate, became essential. Importantly, the enhanced IFNγ production was blocked by a mitochondrial ROS scavenger and not by an inhibitor of AMPK. In addition, IFNγ production by CD8TILs relied on pyruvate translocation to the mitochondria and PCK1. Our results revealed a direct effect of Met on IFNγ production of CD8⁺ T cells that was dependent on differential metabolic pathways and determined by nutrient conditions in the microenvironment.

Metformin and Cancer, an Ambiguanidous Relationship

The deregulation of energetic and cellular metabolism is a signature of cancer cells. Thus, drugs targeting cancer cell metabolism may have promising therapeutic potential. Previous reports demonstrate that the widely used normoglycemic agent, metformin, can decrease the risk of cancer in type 2 diabetics and inhibit cell growth in various cancers, including pancreatic, colon, prostate, ovarian, and breast cancer. While metformin is a known adenosine monophosphate-activated protein kinase (AMPK) agonist and an inhibitor of the electron transport chain complex I, its mechanism of action in cancer cells as well as its effect on cancer metabolism is not clearly established. In this review, we will give an update on the role of metformin as an antitumoral agent and detail relevant evidence on the potential use and mechanisms of action of metformin in cancer. Analyzing antitumoral, signaling, and metabolic impacts of metformin on cancer cells may provide promising new therapeutic strategies in oncology.

Metformin combined with local irradiation provokes abscopal effects in a murine rectal cancer model

Although preoperative chemoradiation therapy can down-stage locally advanced rectal cancer (LARC), it has little effect on distant metastases. Metformin exerts an anti-cancer effect partly through the activation of host immunity. LuM1, a highly lung metastatic subclone of colon 26, was injected subcutaneously (sc) in BALB/c mice and treated with metformin and/or local radiation (RT). Lung metastases and the primary tumors were evaluated and the phenotypes of immune cells in the spleen and lung metastases were examined with flow cytometry and immunohistochemistry. Local RT, but not metformin, partially delayed the growth of sc tumor which was augmented with metformin. Lung metastases were unchanged in metformin or RT alone, but significantly reduced in the combined therapy. The ratios of splenic T cells tended to be low in the RT group, which were increased by the addition of metformin. IFN-γ production of the splenic CD4(+) and CD8(+) T cells was enhanced and CD49b (+) CD335(+) activated NK cells was increased after combined treatment group. Density of NK cells infiltrating in lung metastases was increased after combination treatment. Metformin effectively enhances local and abscopal effects of RT though the activation of cell-mediated immunity and might be clinically useful for LARC.