Evidence for Hypoxia-Induced Shift in ATP Production from Glycolysis to Mitochondrial Respiration in Pulmonary Artery Smooth Muscle Cells in Pulmonary Arterial Hypertension.

BACKGROUND: The metabolic state of pulmonary artery smooth muscle cells (PASMCs) from patients with pulmonary arterial hypertension (PAH) is not well understood. In this study, we examined the balance between glycolysis and mitochondrial respiration in non-PAH-PASMCs and PAH-PASMCs under normoxia and hypoxia. METHODS: We investigated the enzymes involved in glycolysis and mitochondrial respiration, and studied the two major energy-yielding pathways (glycolysis and mitochondrial respiration) by measuring extracellular acidification rate (ECAR) and cellular oxygen consumption rate (OCR) using the Seahorse extracellular flux technology. RESULTS: Under both normoxia and hypoxia, the mRNA and protein levels of pyruvate dehydrogenase kinase 1 and pyruvate dehydrogenase were increased in PAH-PASMCs compared with non-PAH-PASMCs. The mRNA and protein levels of lactate dehydrogenase, as well as the intracellular lactate concentration, were also increased in PAH-PASMCs compared with non-PAH-PASMCs under normoxia. However, these were not significantly increased in PAH-PASMCs compared with non-PAH-PASMCs under hypoxia. Under normoxia, ATP production was significantly lower in PAH-PASMCs (59 ± 5 pmol/min) than in non-PAH-PASMCs (70 ± 10 pmol/min). On the other hand, ATP production was significantly higher in PAH-PASMCs (31 ± 5 pmol/min) than in non-PAH-PASMCs (14 ± 3 pmol/min) under hypoxia. CONCLUSIONS: There is an underlying change in the metabolic strategy to generate ATP production under the challenge of hypoxia.

Metabolic clogging of mannose triggers dNTP loss and genomic instability in human cancer cells.

Mannose has anticancer activity that inhibits cell proliferation and enhances the efficacy of chemotherapy. How mannose exerts its anticancer activity, however, remains poorly understood. Here, using genetically engineered human cancer cells that permit the precise control of mannose metabolic flux, we demonstrate that the large influx of mannose exceeding its metabolic capacity induced metabolic remodeling, leading to the generation of slow-cycling cells with limited deoxyribonucleoside triphosphates (dNTPs). This metabolic remodeling impaired dormant origin firing required to rescue stalled forks by cisplatin, thus exacerbating replication stress. Importantly, pharmacological inhibition of de novo dNTP biosynthesis was sufficient to retard cell cycle progression, sensitize cells to cisplatin, and inhibit dormant origin firing, suggesting dNTP loss-induced genomic instability as a central mechanism for the anticancer activity of mannose.

In order to grow and divide, cells require a variety of sugars. Breaking down sugars provides energy for cells to proliferate and allows them to make more complex molecules, such as DNA. Although this principle also applies to cancer cells, a specific sugar called mannose not only inhibits cancer cell division but also makes them more sensitive to chemotherapy. These anticancer effects of mannose are particularly strong in cells lacking a protein known as MPI, which breaks down mannose. Evidence from honeybees suggests that a combination of mannose and low levels of MPI leads to a build-up of a modified form of mannose, called mannose-6-phosphate, within cells. As a result, pathways required to release energy from glucose become disrupted, proving lethal to these insects. However, it was not clear whether the same processes were responsible for the anticancer effects of mannose. To investigate, Harada et al. removed the gene that encodes the MPI protein in two types of human cancer cells. The experiments showed that mannose treatment was not lethal to these cells but overall slowed the cell cycle ­ a fundamental process for cell growth and division. More detailed biochemical experiments showed that cancer cells with excess mannose-6-phosphate could not produce the molecules required to make DNA. This prevented them from doubling their DNA ­ a necessary step for cell division ­ and responding to stress caused by chemotherapy. Harada et al. also noticed that cancer cells lacking MPI did not all react to mannose treatment in exactly the same way. Therefore, future work will address these diverse reactions, potentially providing an opportunity to use the mannose pathway to search for new cancer treatments.

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-ROS-Nrf2 connection in the host defense mechanism against oxidative stress, apoptosis, cancers, and ageing.

Reactive oxygen species (ROS) acts as a second messenger to trigger biological responses in low concentrations, while it is implicated to be toxic to biomolecules in high concentrations. Mild inhibition of respiratory chain Complex I by metformin at physiologically relevant concentrations stimulates production of low-level mitochondrial ROS. The ROS seems to induce anti-oxidative stress response via activation of nuclear factor erythroid 2-related factor 2 (Nrf2) and glutathione peroxidase (GPx), which results in not only elimination of ROS but also activation of cellular responses including resistance to apoptosis, metabolic changes, cell proliferation, senescence prevention, lifespan extension, and immune T cell activation against cancers, regardless of its effect controlling blood glucose level and T2DM. Although metformin's effect against T2DM, cancers, and ageing, are believed mostly attributed to the activation of AMP-activated protein kinase (AMPK), the cellular responses involving metformin-ROS-Nrf2 axis might be another natural asset to improve healthspan and lifespan.

Blocking EP4 down-regulates tumor metabolism and synergizes with anti-PD-1 therapy to activate natural killer cells in a lung adenocarcinoma model.

Prostaglandin E2 (PGE2), a product of the cyclooxygenase (COX) pathway, is produced by tumors and surrounding stromal cells. It stimulates tumor progression, promotes angiogenesis and suppresses the anti-tumor response. Pharmacological inhibition of PGE2 synthesis has been shown to suppress tumor initiation and growth in vivo. In the current study, we demonstrated that the growth of the Ptgs2-deficient 3LL lung adenocarcinoma cell line was down-regulated in vivo through natural killer (NK) cell activation and a reduction in the population of polymorphonuclear leukocyte-myeloid-derived suppressor cells (PMN-MDSCs) and tumor-associated macrophages (TAMs). On the basis of these results, the therapeutic effect of ONO-AE3-208 (EP4i), an inhibitor of EP4 (a PGE2 receptor), combined with anti-PD-1 antibody was evaluated. EP4i, but not anti-PD-1 antibody, decreased tumor metabolism including glycolysis, fatty acid oxidation and oxidative phosphorylation. EP4i induced IFNγ production from only NK cells (not from T cells) and a shift from M2-like to M1-like macrophages in TAMs. These effects were further enhanced by anti-PD-1 antibody treatment. Although CD8 T-cell infiltration was increased, IFNγ production was not significantly altered, even with combination therapy. Tumor hypoxia was ameliorated by either EP4i or anti-PD-1 antibody treatment, which was further affected by the combination. Normalization of tumor vessels was significant only for the combination therapy. The results indicated a novel effect of EP4i for the metabolic reprogramming of tumors and revealed unique features of EP4i that can synergize with anti-PD-1 antibody to promote IFNγ production by NK cells, polarize TAMs into the M1 phenotype, and reduce hypoxia through normalization of the tumor vasculature.

Pharmacological effects on anaplerotic pathways alter the metabolic landscape in the tumor microenvironment, causing unpredictable, sustained anti-tumor immunity.

To achieve sustained anti-tumor immunity, tumor-infiltrating effector CD8 T lymphocytes (CD8 TILs) must be able to produce cytokines, including IFNγ, and proliferate robustly within the local tumor tissue upon antigen recognition. IFNγ production by CD8 TILs depends on glycolysis, whereas their proliferation additionally requires oxidative phosphorylation (OxPhos). The level of OxPhos, and hence the oxygen consumption rate, depends on mitochondrial biogenesis and requires the loading of metabolic precursors into the tricarboxylic acid cycle to keep it functioning. This is referred to as anaplerosis. Recent advances in the field of immuno-metabolism have shown the impact of pharmacological agents on anaplerotic pathways, resulting in metabolic down-regulation in tumor cells; in contrast, the agents trigger sustained anti-tumor immunity by up-regulating both glycolysis and OxPhos in CD8 TILs. The opposing effects of pharmacological inhibition (and/or activation) on anaplerosis in tumor cells and CD8 TILs are unpredictable. Careful dissection of the underlying mechanism might confer important knowledge, helping us to step into a new era for cancer immunotherapy.

Mitochondrial reactive oxygen species trigger metformin-dependent antitumor immunity via activation of Nrf2/mTORC1/p62 axis in tumor-infiltrating CD8T lymphocytes.

BACKGROUND: Metformin (Met) is the first-line treatment for type 2 diabetes mellitus and plays an effective role in treating various diseases, such as cardiovascular disease, neurodegenerative disease, cancer, and aging. However, the underlying mechanism of Met-dependent antitumor immunity remains to be elucidated. METHODS: MitoTEMPO, a scavenger of mitochondrial superoxide, abolished the antitumor effect of Met, but not antiprogrammed cell death (PD-1) antibody (Ab) treatment. Consequently, we studied the mechanism of the Met-induced antitumor effect. Expressions of glucose transporter (Glut)-1, mitochondrial reactive oxygen species (mtROS), interferon (IFN)-γ, Ki67, autophagy markers, activation markers for NF-E2-related factor 2 (Nrf2), and mammalian target of rapamaycin complex 1 (mTORC1) in CD8+ tumor-infiltrating T lymphocytes (CD8TILs) were examined by flow cytometry analysis. In addition, conditional knockout mice for Nrf2 and p62 were used to detect these markers, together with the monitoring of in vivo tumor growth. RNA sequencing was performed for CD8TILs and tumor cells. Melanoma cells containing an IFN-γ receptor (IFNγR) cytoplasmic domain deletion mutant was overexpressed and used for characterization of the metabolic profile of those tumor cells using a Seahorse Flux Analyzer. RESULTS: Met administration elevates mtROS and cell surface Glut-1, resulting in the production of IFN-γ in CD8TILs. mtROS activates Nrf2 in a glycolysis-dependent manner, inducing activation of autophagy, glutaminolysis, mTORC1, and p62/SQSTM1. mTORC1-dependent phosphorylation of p62 at serine 351 (p-p62(S351)) is also involved in activation of Nrf2. Conditional deletion of Nrf2 in CD8TILs abrogates mTORC1 activation and antitumor immunity by Met. In synergy with the effect of anti-PD-1 Ab, Met boosts CD8TIL proliferation and IFN-γ secretion, resulting in decreased glycolysis and oxidative phosphorylation in tumor cells. Consequently, Glut-1 is elevated in CD8TILs, together with the expansion of activated dendritic cells. Moreover, tumor cells lacking in IFNγR signaling abolish IFN-γ production and proliferation of CD8TILs. CONCLUSIONS: We found that Met stimulates production of mtROS, which triggers Glut-1 elevation and Nrf2 activation in CD8TILs. Nrf2 activates mTORC1, whereas mTORC1 activates Nrf2 in a p-p62(S351)-dependent manner, thus creating a feedback loop that ensures CD8TILs' proliferation. In combination with anti-PD-1 Ab, Met stimulates robust proliferation of CD8TILs and IFN-γ secretion, resulting in an IFN-γ-dependent reprogramming of the tumor microenvironment.

Metformin Prevents Peritoneal Dissemination via Immune-suppressive Cells in the Tumor Microenvironment.

BACKGROUND/AIM: Metformin, a drug for type 2 diabetes, also exerts anticancer effects. This study addressed the immunological effects of metformin on peritoneal dissemination. MATERIALS AND METHODS: We developed a mouse model of peritoneal dissemination via intraperitoneal injection of RLmale1, an X-ray-induced leukemia cell line, into BALB/c mice. Cell-surface markers, cytokine production, and myeloid-derived suppressor cells (MDSCs) were examined in cells from spleen and peritoneal lavage fluid. RESULTS: Metformin-treated mice exhibited suppressed intraperitoneal tumor growth and extended survival, and these effects were lost in mice with severe combined immunodeficiency. MDSCs induction was inhibited in metformin-treated mice. Although MDSC mobilization into the peritoneal cavity was correlated with suppression of interferon-γ production by tumor-infiltrating lymphocytes, the T-helper 1 ability of these lymphocytes was preserved in metformin-treated mice. CONCLUSION: Our findings demonstrate the action of metformin on both intraperitoneal tumors and immune-suppressive cells and might contribute to the development of immunotherapy against peritoneal dissemination.

Metformin induces CD11b+-cell-mediated growth inhibition of an osteosarcoma: implications for metabolic reprogramming of myeloid cells and anti-tumor effects.

CD11b+ myeloid subpopulations, including myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs), play crucial roles in the suppression of T-cell-mediated anti-tumor immunity. Regulation of these cell types is a primary goal for achieving efficient cancer immunotherapy. We found that metformin (Met) induces CD11b+-cell-mediated growth inhibition of a K7M2neo osteosarcoma independent of T cells, as growth inhibition of K7M2neo was still observed in wild-type (WT) mice depleted of T cells by antibodies and in SCID; this contrasted with the effect of Met on Meth A fibrosarcoma, which was entirely T-cell-dependent. Moreover, the inhibitory effect seen in SCID was abrogated by anti-CD11b antibody injection. PMN-MDSCs were significantly reduced in both spleens and tumors following Met treatment. In TAMs, production of IL-12 and TNF-α, but not IL-10, became apparent, and elevation of MHC class II with reduction of CD206 was observed, indicating a shift from an M2- to M1-like phenotype via Met administration. Metabolically, Met treatment decreased basal respiration and the oxygen consumption rate (OCR)/extracellular acidification rate (ECAR) ratio of CD11b+ cells in tumors, but not in the spleen. In addition, decreased reactive oxygen species (ROS) production and proton leakage in MDSCs and TAMs were consistently observed in tumors. Uptake of both 2-deoxy-2-d-glucose (2-NBDG) and BODIPY® decreased in MDSCs, but only BODIPY® incorporation was decreased in TAMs. Overall, our results suggest that Met redirects the metabolism of CD11b+ cells to lower oxidative phosphorylation (OXPHOS) while elevating glycolysis, thereby pushing the microenvironment to a state that inhibits the growth of certain tumors.

Immune-mediated antitumor effect by type 2 diabetes drug, metformin.

Metformin, a prescribed drug for type 2 diabetes, has been reported to have anti-cancer effects; however, the underlying mechanism is poorly understood. Here we show that this mechanism may be immune-mediated. Metformin enabled normal but not T-cell-deficient SCID mice to reject solid tumors. In addition, it increased the number of CD8(+) tumor-infiltrating lymphocytes (TILs) and protected them from apoptosis and exhaustion characterized by decreased production of IL-2, TNFα, and IFNγ. CD8(+) TILs capable of producing multiple cytokines were mainly PD-1(-)Tim-3(+), an effector memory subset responsible for tumor rejection. Combined use of metformin and cancer vaccine improved CD8(+) TIL multifunctionality. The adoptive transfer of antigen-specific CD8(+) T cells treated with metformin concentrations as low as 10 µM showed efficient migration into tumors while maintaining multifunctionality in a manner sensitive to the AMP-activated protein kinase (AMPK) inhibitor compound C. Therefore, a direct effect of metformin on CD8(+) T cells is critical for protection against the inevitable functional exhaustion in the tumor microenvironment.

Etoposide modulates the effects of oral morphine analgesia by targeting the intestinal P-glycoprotein.

OBJECTIVES: Opioids and anticancer compounds such as etoposide (ETP) are substrates of P-glycoprotein (P-gp), an ATP-dependent efflux pump. Chemotherapy compounds may impact on the analgesic effect of opioids such as morphine when the two drugs are co-administered. In this study, we used a mouse model to determine if there is a pharmacological interaction between ETP and morphine, focusing on the involvement of intestinal P-gp. METHODS: P-gp drug efflux activity was measured by an in-situ closed loop method with Rhodamine 123, a P-gp substrate. The analgesic effect of morphine was determined by the tail-flick test. Intestinal P-gp expression levels were determined by Western blot. KEY FINDINGS: ETP and morphine significantly decreased the intestinal Rhodamine 123 efflux activity of P-gp. Oral morphine analgesia was significantly enhanced when co-administered with ETP. However, repeated pretreatment (7 days) with oral ETP significantly decreased the oral morphine-induced analgesia, in a cyclosporine A (a P-gp inhibitor) reversible manner. Furthermore, repeated ETP significantly up-regulated intestinal P-gp expression. CONCLUSIONS: It may be important to consider aspects of therapeutic design such as the administration route or scheduling of drugs in patients receiving concurrent chemotherapy and opioid therapy to avoid pharmacokinetic interactions between the two agents.

The antinociceptive and anti-inflammatory action of the CHCl3-soluble phase and its main active component, damnacanthal, isolated from the root of Morinda citrifolia.

Morinda citrifolia (Rubiaceae, Noni) is a traditional medicine with various pharmacological activities. We investigated if the MeOH-, CHCl(3)- and BuOH-soluble phase and its main active component, damnacanthal, isolated from the Noni root, have antinociceptive and anti-inflammatory actions in mice. The CHCl(3)-soluble phase (3 g/kg, per os (p.o.)) significantly reduced pain-related behavior observed in the formalin test. These effects were not suppressed by pretreatment with naloxone (1 mg/kg, intraperitoneally (i.p.)), an opioid receptor antagonist. The CHCl(3)-soluble phase (3 g/kg, p.o.) significantly reduced histamine-induced paw edema. The MeOH- and BuOH-soluble phase had no effect in either test. Furthermore, damnacanthal (10-100 mg/kg, p.o.) exerted an antinociceptive effect on chemical nociceptive stimuli, and decreased histamine-induced paw edema. Damnacanthal was weakly bound to the histamine H(1) receptor. These data suggest that the CHCl(3)-soluble phase of the Noni root has antinociceptive and anti-inflammatory effects. Furthermore, these effects of damnacanthal isolated from the Noni root is mediated in part by the histamine H(1) receptor.