Glucose uptake in the human gastric cancer cell line, MKN28, is increased by insulin stimulation

Progress in Metabolic Studies of Gastric Cancer and Therapeutic Implications

Background:

Worldwide, gastric cancer is ranked the fifth malignancy in incidence and the third malignancy in mortality. Gastric cancer causes an altered metabolism that can be therapeutically exploited.

Objective:

To provide an overview of the significant metabolic alterations caused by gastric cancer and propose a blockade.

Methods:

A comprehensive and up-to-date review of descriptive and experimental publications on the metabolic alterations caused by gastric cancer and their blockade. This is not a systematic review.

Results:

Gastric cancer causes high rates of glycolysis and glutaminolysis. There are increased rates of de novo fatty acid synthesis and cholesterol synthesis. Moreover, gastric cancer causes high rates of lipid turnover via fatty acid -oxidation. Preclinical data indicate that the individual blockade of these pathways via enzyme targeting leads to antitumor effects in vitro and in vivo. Nevertheless, there is no data on the simultaneous blockade of these five pathways, which is critical, as tumors show metabolic flexibility in response to the availability of nutrients. This means tumors may activate alternate routes when one or more are inhibited. We hypothesize there is a need to simultaneously blockade them to avoid or decrease the metabolic flexibility that may lead to treatment resistance.

Conclusions:

There is a need to explore the preclinical efficacy and feasibility of combined metabolic therapy targeting the pathways of glucose, glutamine, fatty acid synthesis, cholesterol synthesis, and fatty acid oxidation. This may have therapeutical implications because we have clinically available drugs that target these pathways in gastric cancer.

A multiscale agent-based framework integrated with a constraint-based metabolic network model of cancer for simulating avascular tumor growth

The integration of an agent-based framework with a constraint-based metabolic network model of cancer for simulating avascular tumor growth.

At the crossroad between obesity and gastric cancer

Obesity has reached epidemic proportions worldwide with disproportionate prevalence in different communities and ethnic groups. Recently, the American Medical Association recognized obesity as a disease, which is a significant milestone that opens the possibilities of treating obesity under standardized health plans. Obesity is an inflammatory disease characterized by elevated levels of biomarkers associated with abnormal lipid profiles, glucose levels, and blood pressure that lead to the onset of metabolic syndrome. Interestingly, inflammatory biomarkers, in particular, have been implicated in the risk of developing several types of cancer. Likewise, obesity has been linked to esophageal, breast, gallbladder, kidney, pancreatic, and colorectal cancers. Thus, there exists a link between obesity status and tumor appearance, which may be associated to the differential levels and the circulating profiles of several inflammatory molecules. For example, mediators of the inflammatory responses in both obesity and gastric cancer risk are the same: pro-inflammatory molecules produced by the activated cells infiltrating the inflamed tissues. These molecules trigger pathways of activation shared by obesity and cancer. Therefore, understanding how these different pathways are modulated would help reduce the impact that both diseases, and their concomitant existence, have on society.

Hesperetin impairs glucose uptake and inhibits proliferation of breast cancer cells

The flavanone hesperetin is known to decrease basal glucose uptake, although the inhibitory mechanism is largely unknown. Here, we used MDA-MB-231 breast cancer cells to investigate the molecular pathways affected by hesperetin. The results indicate that the suppression of glucose uptake is caused by the down-regulation of glucose transporter 1 (GLUT1). Hesperetin was also found to inhibit insulin-induced glucose uptake through impaired cell membrane translocation of glucose transporter 4 (GLUT4). In addition, the phosphorylation of the insulin receptor-beta subunit (IR-beta) and Akt was suppressed. Hesperetin also decreased cellular proliferation, which is likely due to the inhibition of glucose uptake. Cancer cells are highly dependent on glucose and hesperetin may, therefore, have potential application as an anticancer agent.

A new approach on the gastric absorption of anthocyanins

The bioavailability of anthocyanins is the most difficult one to assess amongst all flavonoid compounds as a result of their occurrence under different structures in equilibrium depending on pH. Due to their rapid appearance in plasma, the absorption of anthocyanins is likely to occur at the gastric level. Further investigations of the mechanisms by which anthocyanins are absorbed are limited by the lack of testable gastric epithelial cell models that form functional barriers. The methods available to evaluate the absorption of drugs at the gastric level make use of isolated gastric epithelial cells, which is both time and labour consuming. In the present study, a biologically relevant in vitro model of moderately differentiated adenocarcinoma stomach cells (MKN-28) was used as gastric barrier. The transepithelial electrical resistance (TEER) of MKN-28 cell monolayers was evaluated at pH values that cover the physiologic range of the stomach, ensuring the integrity of the cell monolayer . The immunofluorescence assay attested the localization of occludins at the cellular margins, which is associated with a non-disrupted membrane. Anthocyanins were found to cross MKN-28 cells in a time dependent manner and probably via a saturable transport mechanism.

Diabetes, cancer, and metformin: connections of metabolism and cell proliferation

Diabetes is associated with an increased risk of developing and dying from cancer. This increased risk may be due to hyperglycemia, hyperinsulinemia, and insulin resistance or other factors. Metformin has recently gained much attention as it appears to reduce cancer incidence and improve prognosis of patients with diabetes. In vitro data and animal studies support these findings from human epidemiological studies. Metformin has multiple potential mechanisms by which it inhibits cancer development and growth. For example, metaformin inhibits hepatic gluconeogenesis, thus decreasing circulating glucose levels, and it increases insulin sensitivity, thus reducing circulating insulin levels. Intracellularly, metformin activates AMPK, which decreases protein synthesis and cell proliferation. Metaformin also reduces aromatase activity in the stromal cells of the mammary gland. Finally, metformin may diminish the recurrence and aggressiveness of tumors by reducing the stem cell population and inhibiting epithelial to mesenchymal transition. Here, we discuss the metabolic abnormalities that occur in tumor development and some of the mechanisms through which metformin may alter these pathways and reduce tumor growth.

Targeting the delivery of glycan-based paclitaxel prodrugs to cancer cells via glucose transporters

This report describes the synthesis of four novel paclitaxel based prodrugs with glycan conjugation (1-4). Glycans were conjugated using an ester or ether bond as the linker between 2'-paclitaxel and the 2'-glucose or glucuronic acid moiety. These prodrugs showed good water solubility and selective cytotoxicity against cancer cell lines, but showed reduced toxicity toward normal cell lines and cancer cell lines with low expression levels of GLUTs. The ester conjugated prodrug 1 showed the most cytotoxicity among the prodrugs examined and could be transported into cells via GLUTs. Fluorescent and confocal microscopy demonstrated that targeted cells exhibited morphological changes in tubulin and chromosomal alterations that were similar to those observed with paclitaxel treatment. Therefore, these glycan-based prodrugs may be good drug candidates for cancer therapy, and the glycan conjugation approach is an alternative method to enhance the targeted delivery of other drugs to cancer cells that overexpress GLUTs.

Synthesis of 2'-paclitaxel methyl 2-glucopyranosyl succinate for specific targeted delivery to cancer cells

A novel glucose-conjugated paclitaxel 5 was synthesized using succinic acid as linker between 2'-paclitaxel and methyl 2'-glucopyranose. 5 has not only improved the pharmaceutical properties of paclitaxel, such as solubility and stability, but also enhanced the specific target delivery to MCF-7 cells without the cytotoxicity against normal cells. Therefore, the glucose conjugation may be potentially used in the targeted delivery of other drugs into cells via glucose transporters (GLUTs) for cancer therapy.

Therapeutic effect of imatinib in gastrointestinal stromal tumors: AKT signaling dependent and independent mechanisms

Most gastrointestinal stromal tumors (GISTs) possess a gain-of-function mutation in c-KIT. Imatinib mesylate, a small-molecule inhibitor against several receptor tyrosine kinases, including KIT, platelet-derived growth factor receptor-alpha, and BCR-ABL, has therapeutic benefit for GISTs both via KIT and via unknown mechanisms. Clinical evidence suggests that a potential therapeutic benefit of imatinib might result from decreased glucose uptake as measured by positron emission tomography using 18-fluoro-2-deoxy-d-glucose. We sought to determine the mechanism of and correlation to altered metabolism and cell survival in response to imatinib. Glucose uptake, cell viability, and apoptosis in GIST cells were measured following imatinib treatment. Lentivirus constructs were used to stably express constitutively active AKT1 or AKT2 in GIST cells to study the role of AKT signaling in metabolism and cell survival. Immunoblots and immunofluorescent staining were used to determine the levels of plasma membrane-bound glucose transporter Glut4. We show that oncogenic activation of KIT maximizes glucose uptake in an AKT-dependent manner. Imatinib treatment markedly reduces glucose uptake via decreased levels of plasma membrane-bound Glut4 and induces apoptosis or growth arrest by inhibiting KIT activity. Importantly, expression of constitutively active AKT1 or AKT2 does not rescue cells from the imatinib-mediated apoptosis although glucose uptake was not blocked, suggesting that the potential therapeutic effect of imatinib is independent of AKT activity and glucose deprivation. Overall, these findings contribute to a clearer understanding of the molecular mechanisms involved in the therapeutic benefit of imatinib in GIST and suggest that a drug-mediated decrease in tumor metabolism observed clinically may not entirely reflect therapeutic efficacy of treatment.

Placental leucine aminopeptidase (P-LAP) and glucose transporter 4 (GLUT4) expression in benign, borderline, and malignant ovarian epithelia

OBJECTIVE

Increased glucose consumption is a characteristic of malignant cells. Glucose is transported into the cell via facilitative glucose transporters, which are known to be members of a supergene family. The insulin-responsive GLUT4 isoform is expressed almost exclusively in insulin target tissues. P-LAP is a cell surface aminopeptidase, and is a synonym for oxytocinase. P-LAP is also referred to as insulin-regulated membrane aminopeptidase (IRAP) associated with GLUT4-containing vesicle. The authors evaluated P-LAP and GLUT4 expression in benign, borderline, and malignant ovarian epithelia.

METHODS

Histologic sections of formalin-fixed, paraffin-embedded specimens from 11 patients with benign serous or mucinous cystadenomas, 14 patients with serous or mucinous borderline tumors, and 80 patients with epithelial-ovarian adenocarcinomas (29 serous, 17 endometrioid, 14 mucinous, and 20 clear cell adenocarcinomas) were stained for P-LAP and GLUT4 using each polyclonal antibody. Expressions of P-LAP and GLUT-4 in ovarian cancer cells were detected by Western blotting.

RESULTS

P-LAP immunoreactivity was detected in 2 of 11 benign cystadenomas. None of the 11 benign ovarian tumors showed any immunoreactivity for GLUT4. Seven of 14 borderline tumors demonstrated P-LAP immunoreactivity, while 5 of 14 borderline tumors demonstrated GLUT4 immunoreactivity. P-LAP was expressed in 23 of 29 in serous, 15 of 17 endometrioid, 13 of 14 mucinous, and all clear-cell adenocarcinomas. The tendency toward increased P-LAP expression with advancing grade was observed in serous adenocarcinomas. GLUT4 was expressed in 13 of 29 serous, 13 of 17 endometrioid, 13 of 14 mucinous, and 18 of 20 clear-cell adenocarcinomas. In invasive carcinomas, there was a direct correlation between P-LAP immunoreactivity and GLUT4 immunoreactivity (correlation coefficient [r] = 0.58; P < 0.01). Furthermore, P-LAP overexpression in SKOV3 cells induced the GLUT4 expression.

CONCLUSIONS

P-LAP and GLUT4 are available not only for the evaluation of ovarian epithelial malignancy, but also as targets for molecular therapy. Further study to investigate the roles of P-LAP and GLUT4 in ovarian carcinoma is needed.

Naringenin Inhibits Glucose Uptake in MCF-7 Breast Cancer Cells: A Mechanism for Impaired Cellular Proliferation

Certain flavonoids inhibit glucose uptake in cultured cells. In this report, we show that the grapefruit flava-none naringenin inhibited insulin-stimulated glucose uptake in proliferating and growth-arrested MCF-7 breast cancer cells. Our findings indicate that naringenin inhibits the activity of phosphoinositide 3-kinase (PI3K), a key regulator of insulin-induced GLUT4 translocation, as shown by impaired phosphorylation of the downstream signaling molecule Akt. Naringenin also inhibited the phosphorylation of p44/p42 mitogen-activated protein kinase (MAPK). Inhibition of the MAPK pathway with PD98059, a MAPK kinase inhibitor, reduced insulin-stimulated glucose uptake by approximately 60%. The MAPK pathway therefore appears to contribute significantly to insulin-stimulated glucose uptake in breast cancer cells. Importantly, decreasing the availability of glucose by lowering the glucose concentration of the culture medium inhibited proliferation, as did treatment with naringenin. Collectively, our findings suggest that naringenin inhibits the proliferation of MCF-7 cells via impaired glucose uptake. Because a physiologically attainable dose of 10 micro M naringenin reduced insulin-stimulated glucose uptake by nearly 25% and also reduced cell proliferation, naringenin may possess therapeutic potential as an anti-proliferative agent.

Gene expression of GLUT isoforms and VHL in oral squamous cell carcinoma

In human oral squamous cell carcinoma (OSCC) cell lines, we detected atypical mRNA expression of GLUT2 and/or GLUT4 in addition to enhanced expression of GLUT1 mRNA using RT-PCR. In semi-quantitative reverse transcription-polymerase chain reaction analysis of mRNA expression in OSCC cell lines, we found an inverse relationship between mRNA expression of von Hippel-Lindau (VHL) and that of GLUT1, with no apparent influence on the expression of other GLUTs. These findings suggest that the reduction of VHL may play a critical role in glucose uptake of OSCC cell lines, with enhancement of GLUT1 expression.

Suppression of facilitative glucose transporter 1 mRNA can suppress tumor growth

We attempted to suppress glucose transporter 1 (GLUT1) expression by transfecting MKN45 cells with cDNA for antisense GLUT1. Glucose transport was significantly decreased in cells with antisense GLUT1 compared with wild-type cells or cells with vector alone. Suppression of GLUT1 mRNA resulted in a decreased number of cells in the S phase. This was accompanied by overexpression of p21 protein. Tumorigenicity in the nude mice injected with antisense GLUT1 expressing cells was significantly slower than in those with wild-type MKN45 cells. These results suggest that antisense GLUT1 mRNA inhibits tumor growth through a G(1) arrest and that expression of antisense GLUT1 mRNA via gene therapy can be used as a tool in the treatment of cancer.