Glucose restriction induces AMPK-SIRT1-mediated circadian clock gene Per expression and delays NSCLC progression

The rhythmic expression of the circadian clock is intimately linked to the health status of the body. Disturbed circadian clock rhythms might lead to a wide range of metabolic diseases and even cancers. Our previous study showed that glucose restriction was able to inhibit non-small cell lung cancer (NSCLC). In the current study, we found that glucose restriction enhanced apoptosis and cell growth delay in NSCLC cells. In addition, we used GEPIA database analysis to derive different effects of each circadian clock gene on lung cancer tissue. Among these circadian clock genes, Per (Period) is lowly expressed in cancer tissues and highly expressed in normal tissues. Moreover, the higher expression of Per in cancer patients has a better prognostic significance. Furthermore, we revealed that glucose restriction induced the expression of the circadian clock gene Per in NSCLC cells by upregulating SIRT1 (Sirtuin1) via activation of the energy response factor AMPK (AMP-activated protein kinase). Changes in Per expression following upregulation or downregulation of AMPK were consistent with AMPK expression. Additionally, a low-carbohydrate ketogenic diet significantly delayed tumor progression in a xenograft tumor model of severe combined immunodeficiency (SCID) mice. Meanwhile, the ketogenic diet increased the expression of AMPK, SIRT1 and Per in vivo. Besides, the ketogenic diet was found to restore the normal rhythmic level of Per by Zeitgeber Time (ZT) experiments. Taken these together, these results indicated a novel mechanism that glucose restriction induces AMPK-SIRT1 mediated circadian clock gene Per expression and delays NSCLC progression, which provided more evidence for glucose restriction as an adjuvant clinical therapeutic strategy in NSCLC.

Inhibition of mitochondrial fusion via SIRT1/PDK2/PARL axis breaks mitochondrial metabolic plasticity and sensitizes cancer cells to glucose restriction therapy

Mitochondria dynamically change their morphology via fusion and fission, a process called mitochondrial dynamics. Dysregulated mitochondrial dynamics respond rapidly to metabolic cues, and are linked to the initiation and progression of diverse human cancers. Metabolic adaptations significantly contribute to tumor development and escape from tissue homeostatic defenses. In this work, we identified oroxylin A (OA), a dual GLUT1/mitochondrial fusion inhibitor, which restricted glucose catabolism of hepatocellular carcinoma cells and simultaneously inhibited mitochondrial fusion by disturbing SIRT1/PDK2/PARL axis. Based the dual action of OA in metabolic regulation and mitochondrial dynamics, further results revealed that mitochondrial functional status and spare respiratory capacity (SRC) of cancer cells had a close correlation with mitochondrial metabolic plasticity, and played important roles in the susceptibility to cancer therapy aiming at glucose restriction. Cancer cells with healthy mitochondria and high SRC exhibit greater metabolic flexibility and higher resistance to GLUT1 inhibitors. This phenomenon is attributed to the fact that high SRC cells fuse mitochondria in response to glucose restriction, enhancing tolerance to energy deficiency, but undergo less mitochondrial oxidative stress compared to low SRC cells. Thus, inhibiting mitochondrial fusion breaks mitochondrial metabolic plasticity and increases cancer cell susceptibility to glucose restriction therapy. Collectively, these finding indicate that combining a GLUT1 inhibitor with a mitochondrial fusion inhibitor can work synergistically in cancer therapy and, more broadly, suggest that the incorporations of mitochondrial dynamics and metabolic regulation may become the targetable vulnerabilities bypassing the genotypic heterogeneity of multiple malignancies.

Glucose restriction induces ROS-AMPK-mediated CTR1 expression and increases cisplatin efficiency in NSCLC

Cisplatin is one of the principal platinum-based chemotherapeutic agents for many types of cancer, including non-small-cell lung cancer (NSCLC). Copper transporter 1 (CTR1) plays a significant role in increasing cellular cisplatin uptake and sensitivity. The current study found that glucose restriction upregulated AMPK (AMP-activated protein kinase) through reactive oxygen species (ROS) to induce CTR1 expression in NSCLC cells. Direct upregulation of ROS levels also activated AMPK expression. The changes in CTR1 expression were consistent with glucose concentrations and AMPK expression. Feeding a low-carbohydrate ketogenic diet (a glucose restriction diet) to a severe combined immune deficiency (SCID) mouse xenograft model significantly enhanced the efficacy of cisplatin. The tumor size was significantly smaller in the group treated with cisplatin plus the low-carbohydrate ketogenic diet than in the group treated with cisplatin alone. Survival was longer in mice treated with the low-carbohydrate ketogenic diet than in the controls. Mice fed the low-carbohydrate ketogenic diet showed increased expression of CTR1 and AMPK in tumor tissues. These results suggest a novel mechanism whereby glucose restriction induces ROS-AMPK-mediated CTR1 expression in NSCLC, indicating glucose restriction as an effective adjuvant NSCLC therapy.

NAD+ depletion radiosensitizes 2-DG-treated glioma cells by abolishing metabolic adaptation

Two-deoxy-d-glucose (2-DG) mediated glucose restriction (GR) has been applied as a potential therapeutic strategy for tumor clinical treatments. However, increasing evidences have indicated that 2-DG alone is inefficient in killing tumor cells, and the effect of 2-DG on modifying tumor radio-responses also remains controversial. In this study, we found that 2-DG triggered metabolic adaption in U87 glioma cells by up-regulating nicotinamide phosphoribosyltransferase (NAMPT) and cellular NAD+ content, which abolished 2-DG-induced potential radiosensitizing effect in glioma cells. Strikingly, NAD+ depletion evoked notable oxidative stress by NADPH reduction and hence re-radiosensitized 2-DG-treated glioma cells. Furthermore, isocitrate dehydrogenase-1 (IDH1) mutant U87 glioma cells with deficiency in the rate-limiting enzyme of Preiss-Handler pathway nicotinate phosphoribosyltransferase (Naprt1) revealed notable 2-DG-induced oxidative stress and radiosensitization. Our findings implied that targeting NAD+ could radiosensitize gliomas with GR, and 2-DG administration could be benefit for tumor patients with IDH1 mutation.

Glucose restriction delays senescence and promotes proliferation of HUVECs via the AMPK/SIRT1-FOXA3-Beclin1 pathway

Caloric restriction (CR) is an important means to delay senescence, and glucose restriction is one of the measures to achieve CR. On the basis of our previous work and bioinformatics analysis, we hypothesized that glucose restriction can up-regulate autophagy, inhibit senescence and promote proliferation via the AMPK/SIRT1-FOXA3-Beclin1 pathway in human umbilical vein endothelial cells (HUVECs). We found that compared with 5.5 mmol/L and 25 mmol/L glucose, 2.5 mmol/L glucose restriction significantly reduced senescence, enhanced autophagy, increased migration speed, relieved G₀/G₁ phase arrest and enhanced proliferation of HUVECs. Furthermore, glucose restriction up-regulated AMPKα1, SIRT1, FOXA3 and Beclin1 expression in HUVECs. Additionally, we demonstrated that AMPKα1 phosphorylated FOXA3 at S170 and S305 in the cytoplasm and promoted FOXA3 nuclear translocation under glucose restriction. FOXA3 in the nucleus was deacetylated by SIRT1 at K214 and K221. Deacetylated FOXA3 specifically bound to +109 C in the Beclin1 transcriptional regulatory region, and significantly enhanced Beclin1 transcription and expression. siRNA knock down of AMPKα1, SIRT1, FOXA3 or Beclin1 expression impaired the glucose restriction-induced inhibition of senescence, enhanced autophagy, increased migration, and induced proliferation of HUVECs. This study confirmed that glucose restriction can enhance autophagy, inhibit senescence, and enhance proliferation of HUVECs through the AMPK/SIRT1-FOXA3-Beclin1 pathway.

Glucose restriction reverses the Warburg effect and modulates PKM2 and mTOR expression in breast cancer cell lines

Aerobic glycolysis, known as the "Warburg effect", is one of several hallmarks of cancer cells. The conversion of phosphoenolpyruvate (PEP) to pyruvate can be down regulated by the re-expression of the embryonic isoform 2 of pyruvate kinase (PKM2). This mechanism allows the accumulation of glycolytic intermediates for the biosynthesis of macromolecules, such as proteins, lipids and nucleic acids. PKM2 is favored by the well-known PI3K/Akt/mTOR proliferative pathway. This pathway is induced by high glucose levels, and the mTOR kinase is the central activator of the Warburg effect. In this study, we investigated the role of glucose restriction (GR) and mTOR inhibition  in reversing the Warburg effect in MDA-MB 231 and MCF-7 breast cancer cell lines. PKM2 expression was measured by western blot. Lactate production by cells was determined by a colorimetric assay. The concentration of glucose in the supernatant of cells was measured using the Trinder method. ATP level  was evaluated by using a Colorimetric/Fluorometric ATP Assay Kit. Our results showed that MDA-MB 231 cells increased glucose consumption when the glucose concentration was 0 g/L (P <0.01). In MCF-7 cells, glucose deprivation reduced lactate secretion by 80% (P =0.0001) but tripled glucose consumption (P = 0.0041). ATP concentration increased approximately when MCF-7 cells were deprived of glucose (P = 0.02). GSK1059615 does not significantly modulate lactate secretion and glucose uptake in both cell lines. Glucose restriction contribute to the reduction of the Warburg effect through mTOR inhibition and regulation of PKM2 kinases.

Nuclear translocation of PKM2/AMPK complex sustains cancer stem cell populations under glucose restriction stress

Cancer cells encounter metabolic stresses such as hypoxia and nutrient limitations because they grow and divide more quickly than their normal counterparts. In response to glucose restriction, we found that nuclear translocation of the glycolic enzyme, pyruvate kinase M2 (PKM2), helped cancer cells survive under the metabolic stress. Restriction of glucose stimulated AMPK activation and resulted in co-translocation of AMPK and PKM2 through Ran-mediated nuclear transport. Nuclear PKM2 subsequently bound to Oct4 and promoted the expression of cancer stemness-related genes, which might enrich the cancer stem cell population under the metabolic stress. Nuclear PKM2 was also capable of promoting cancer metastasis in an orthotopic xenograft model. In summary, we found that cytosolic AMPK helped PKM2 carry out its nonmetabolic functions in the nucleus under glucose restriction and that nuclear PKM2 promoted cancer stemness and metastasis. These findings suggested a potential new targeting pathway for cancer therapy in the future.

The accumulation of assembly intermediates of the mitochondrial complex I matrix arm is reduced by limiting glucose uptake in a neuronal-like model of MELAS syndrome

Ketogenic diet (KD) which combined carbohydrate restriction and the addition of ketone bodies has emerged as an alternative metabolic intervention used as an anticonvulsant therapy or to treat different types of neurological or mitochondrial disorders including MELAS syndrome. MELAS syndrome is a severe mitochondrial disease mainly due to the m.3243A > G mitochondrial DNA mutation. The broad success of KD is due to multiple beneficial mechanisms with distinct effects of very low carbohydrates and ketones. To evaluate the metabolic part of carbohydrate restriction, transmitochondrial neuronal-like cybrid cells carrying the m.3243A > G mutation, shown to be associated with a severe complex I deficiency was exposed during 3 weeks to glucose restriction. Mitochondrial enzyme defects were combined with an accumulation of complex I (CI) matrix intermediates in the untreated mutant cells, leading to a drastic reduction in CI driven respiration. The severe reduction of CI was also paralleled in post-mortem brain tissue of a MELAS patient carrying high mutant load. Importantly, lowering significantly glucose concentration in cell culture improved CI assembly with a significant reduction of matrix assembly intermediates and respiration capacities were restored in a sequential manner. In addition, OXPHOS protein expression and mitochondrial DNA copy number were significantly increased in mutant cells exposed to glucose restriction. The accumulation of CI matrix intermediates appeared as a hallmark of MELAS pathophysiology highlighting a critical pathophysiological mechanism involving CI disassembly, which can be alleviated by lowering glucose fuelling and the induction of mitochondrial biogenesis, emphasizing the usefulness of metabolic interventions in MELAS syndrome.

Metabolic reprogramming of hydrogenosomal amino acids in Trichomonas vaginalis under glucose restriction

BACKGROUND

Glucose is the major energy source that is converted to pyruvate for ATP generation in the trichomonad hydrogenosome. Under glucose restriction (GR), the regulation of amino acids metabolism is crucial for trichomonad growth and survival. RNA-sequencing (RNA-seq) analysis has been used to identify differentially expressed genes in Trichomonas vaginalis under GR, leading to significant advances in understanding adaptive responses of amino acid metabolism to GR. However, the levels of amino acid metabolites modulated by GR are unknown in T. vaginalis.

METHODS

Herein, we describe a comprehensive metabolomic analysis of amino acid metabolites in the hydrogenosome using liquid chromatography Fourier transform ion cyclotron resonance mass spectrometry (LC-FT MS). The relative abundance of 17 hydrogenosomal amino acids was analyzed under GR and high-glucose (HG) conditions.

RESULTS

Levels of most amino acids were higher in GR culture. Arginine was not detectable in either HG or GR cultures; however, its metabolic end-product proline was slightly increased under GR, suggesting that the arginine dihydrolase pathway was more activated by GR. Additionally, methionine catabolism was less stimulated under GR because of greater methionine accumulation. Furthermore, branched chain amino acids (BCAA), including leucine, isoleucine and valine, as well as phenylalanine and alanine, markedly accumulated under GR, indicating that glutamate-related metabolic pathways were remarkably enhanced in this setting. Our metabolomic analysis combined with previous RNA-seq data confirm the existence of several amino acid metabolic pathways in the hydrogenosome and highlight their potentially important roles in T. vaginalis under glucose deprivation.

Real-time cell analysis of the inhibitory effect of vitamin K2 on adhesion and proliferation of breast cancer cells

Breast cancer is the most prevalent cancer type worldwide. Continued efforts to improve treatment strategies for patients with breast cancer will be instrumental in reducing the death rates associated with this disease. In particular, the triple-negative breast cancer subtype of breast cancer has no targeted therapy available so it is essential to continue to work on any potential therapies. Vitamin K (VK) is known for its essential role in the clotting cascade. The antitumor properties of VK derivatives have been reported in both hepatocellular carcinoma and glioblastoma. Our hypothesis was that menaquinone-4, the most common form of vitamin K2 (VK2), is an effective anticancer agent against breast cancer cell types. In this study, we used a novel impedance-based live cell monitoring platform (xCELLigence) to determine the effects of VK derivatives on the triple-negative breast cancer cell line, MDA-MB-231, and the HER2+ breast cancer cell line, MDA-MB-453. Cells were treated with varying concentrations of menaquinone-4 (VK2) previously reported to have an antiproliferative effect on human glioblastoma cells. After initial testing, these concentrations were adjusted to 100, 125, and 150 μmol/L. A significant dose-dependent, growth inhibitory effect was found when cells were treated at these concentrations. These effects were seen in both adhesion and proliferation phases and show a dramatic reduction in cell growth. Additional analysis of MDA-MB-231 cells treated with VK2 (100 μmol/L) in combination with a low-glucose nutrient media showed a further decrease in adhesion and viability. This is the first study of its kind showing the real-time effects of VK derivatives on breast cancer cells and suggests that dietary factors may be an important consideration for patients.

Glucose restriction decreases telomerase activity and enhances its inhibitor response on breast cancer cells: possible extra-telomerase role of BIBR 1532

Background

Considerable progress has been made to understand the association between lifestyle and diet in cancer initiation and promotion. Because excessive glucose consumption is a key metabolic hallmark of cancer cells, glucose restriction (GR) decreases the proliferation, and promotes the differentiation and transformation of cancer cells to quiescent cells. The immortality of cancerous cells is largely assured by telomerase, which is an interesting target for inhibition by BIBR 1532. In this study, we investigated the effect of GR on telomerase activity and on the efficacy of its inhibition by BIBR 1532.

Methods

Breast cancer MDA-MB 231 and MCF-7 cells were cultured in DMEM (Dulbecco’s modified eagle’s media) with 0, 1 or 4.5 g/l of glucose. The telomerase activity was measured via quantitative Real-Time PCR, and the two telomerase subunits were semi-quantified by RT-PCR. Proliferation test and mitochondrial metabolism were assessed via tetrazolium salt reduction and cell counts; apoptosis was assessed via caspase-3 quantification and flow cytometry.

Results

A decrease in the telomerase activity of more than 75% was associated with a significant reduction in the mRNA expression of its catalytic subunit hTERT (Reverse Transcriptase) and a decrease in the mitochondrial metabolism by more than 80% under restricted glucose conditions. In addition, GR increased the effect of BIBR 1532. Glucose deprivation induces apoptosis via BIBR 1532-mediated telomerase inhibition in triple negative breast cancer cells, as assessed by caspase-3 measurements and Annexin analysis.

Conclusions

Taken together, our results suggest that the effect of BIBR 1532 is potentiated by GR to induce triple negative breast cancer cell death.