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.

Nonalcoholic Steatohepatitis: Involvement of the Telomerase and Proinflammatory Mediators.

Nonalcoholic steatohepatitis or NASH is an excessive accumulation of fat in hepatocytes accompanied by inflammation and hepatic injury. Proinflammatory molecules such as IL-17, CCL20, S100A8, S100A9, and S100A8/A9 have been shown to be implicated in many types of cancer. Telomerase activity has been found to be associated with chronic inflammation and cancer. NASH can progress to fibrosis then cirrhosis and finally to hepatocellular carcinoma (HCC). Our objective is to try to find a relation between inflammation and the progression of NASH into HCC. We found that there was a significant elevation in the telomerase activity, detected by real-time PCR, between NASH and fibrotic NASH in the liver biopsies of patients. The expression of S100A8, S100A9, S100A8/A9, CCL20, and IL-17, detected by ELISA, is significantly increased in NASH patients with fibrosis in comparison with controls. But, in NASH patients, S100A9, S100A8/A9, and IL-17 only are significantly elevated in comparison with controls. The same, on the mRNA level, expression of IL-17, detected by RT-PCR, is significantly elevated in NASH patients in comparison with controls. Therefore, there is a direct link between the expression of IL-17, CCL20, telomerase, S100A8, and S100A9 in the fibrotic condition and the progression towards cancer.

Telomerase inhibition decreases alpha-fetoprotein expression and secretion by hepatocellular carcinoma cell lines: in vitro and in vivo study.

Alpha-fetoprotein (AFP) is a diagnostic marker for hepatocellular carcinoma (HCC). A direct relationship between poor prognosis and the concentration of serum AFP has been observed. Telomerase, an enzyme that stabilizes the telomere length, is expressed by 90% of HCC. The aim of this study was to investigate the effect of telomerase inhibition on AFP secretion and the involvement of the PI3K/Akt/mTOR signaling pathway. Proliferation and viability tests were performed using tetrazolium salt. Apoptosis was determined through the Annexin V assay using flow cytometry. The concentrations of AFP were measured using ELISA kits. The AFP mRNA expression was evaluated using RT-PCR, and cell migration was evaluated using a Boyden chamber assay. The in vivo effect of costunolide on AFP production was tested in NSG mice. Telomerase inhibition by costunolide and BIBR 1532 at 5 and 10 µM decreased AFP mRNA expression and protein secretion by HepG2/C3A cells. The same pattern was obtained with cells treated with hTERT siRNA. This treatment exhibited no apoptotic effect. The AFP mRNA expression and protein secretion by PLC/PRF/5 was decreased after treatment with BIBR1532 at 10 µM. In contrast, no effect was obtained for PLC/PRF/5 cells treated with costunolide at 5 or 10 µM. Inhibition of the PI3K/Akt/mTOR signaling pathway decreased the AFP concentration. In contrast, the MAPK/ERK pathway appeared to not be involved in HepG2/C3A cells, whereas ERK inhibition decreased the AFP concentration in PLC/PRF/5 cells. Modulation of the AFP concentration was also obtained after the inhibition or activation of PKC. Costunolide (30 mg/kg) significantly decreased the AFP serum concentration of NSG mice bearing HepG2/C3A cells. Both the inhibition of telomerase and the inhibition of the PI3K/Akt/mTOR signaling pathway decreased the AFP production of HepG2/C3A and PLC/PRF/5 cells, suggesting a relationship between telomerase and AFP expression through the PI3K/Akt/mTOR pathway.

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.