Metformin attenuates ovarian cancer cell growth in an AMP-kinase dispensable manner

Metformin limits the adipocyte tumor-promoting effect on ovarian cancer

Omental adipocytes promote ovarian cancer by secretion of adipokines, cytokines and growth factors, and acting as fuel depots. We investigated if metformin modulates the ovarian cancer promoting effects of adipocytes. Effect of conditioned media obtained from differentiated mouse 3T3L1 preadipoctes on the proliferation and migration of a mouse ovarian surface epithelium cancer cell line (ID8) was estimated. Conditioned media from differentiated adipocytes increased the proliferation and migration of ID8 cells, which was attenuated by metformin. Metformin inhibited adipogenesis by inhibition of key adipogenesis regulating transcription factors (CEBPα, CEBPß, and SREBP1), and induced AMPK. A targeted Cancer Pathway Finder RT-PCR (real-time polymerase chain reaction) based gene array revealed 20 up-regulated and 2 down-regulated genes in ID8 cells exposed to adipocyte conditioned media, which were altered by metformin. Adipocyte conditioned media also induced bio-energetic changes in the ID8 cells by pushing them into a highly metabolically active state; these effects were reversed by metformin. Collectively, metformin treatment inhibited the adipocyte mediated ovarian cancer cell proliferation, migration, expression of cancer associated genes and bio-energetic changes. Suggesting, that metformin could be a therapeutic option for ovarian cancer at an early stage, as it not only targets ovarian cancer, but also modulates the environmental milieu.

Metformin and gynecologic cancers

IMPORTANCE

The obese population in the United States is reaching epic proportions, and obesity is linked to an increased risk for several cancers including gynecologic cancers. Obesity is not only a risk factor but also a marker of poor prognosis. It is crucial to develop novel treatment strategies to target this population. Metformin is a biguanide drug, typically used for diabetes treatment, currently being studied to evaluate its role in the treatment and prevention of gynecologic cancers.

OBJECTIVE

The aim of this study was to review the underlying biologic mechanisms of metformin's antitumorigenic effects. We assessed the epidemiologic and preclinical data that support the use of metformin in patients with endometrial and ovarian cancer. Finally, we reviewed current clinical trials that incorporate metformin as a prevention or treatment strategy for gynecologic cancers.

EVIDENCE ACQUISITION

A thorough search of PubMed for all current literature was performed. All preclinical, clinical, and epidemiologic reviews were evaluated across all cancers, with a focus on gynecologic cancer.

RESULTS

The preclinical, epidemiologic, and clinical data evaluated in this review are strongly supportive of the use of metformin for the prevention and treatment of gynecologic cancer. On the basis of these data, centers are currently enrolling for clinical trials using metformin in patients diagnosed with gynecologic malignancies.

CONCLUSIONS AND RELEVANCE

The data supporting the use of metformin in the prevention and treatment of cancers are building, including that of endometrial and ovarian cancer. The association between obesity, insulin resistance, as well as increased risk and poor outcomes in endometrial and ovarian cancer patients makes metformin an attractive agent for the prevention and treatment of these diseases.

Metformin inhibits thyroid cancer cell growth, migration, and EMT through the mTOR pathway

Mammalian target of rapamycin (mTOR) signaling pathways have been shown to be activated in thyroid cancer. Recent evidences have demonstrated that the antidiabetic agent metformin, an activator of 5'-AMP-activated protein kinase, can impair the proliferation and migration of cancer cells via inhibition of mTOR. However, the underlying mechanisms remain unclear. In this study, we show that metformin can inhibit mTOR pathway to impair growth and migration of the thyroid cancer cell lines. Cyclin D1 and c-Myc are important regulators of cancer cell growth, and we observed that treatment of thyroid cancer cells with metformin reduced c-Myc and cyclin D1 expression through suppression of mTOR and subsequent inhibition of P70S6K1 and 4E-BP1 phosphorylation. Metformin reduced epithelial to mesenchymal transition (EMT) in thyroid carcinoma cells. Moreover, metformin regulated expression of the EMT-related markers E-cadherin, N-cadherin, and Snail. Additionally, knockdown of TSC2, the upstream regulatory molecule of mTOR pathway, or treatment of rapamycin, the mTOR inhibitor, could abolish the effects of metformin to regulate thyroid cancer cell proliferation, migration, EMT, and mTOR pathway molecules. These results indicate that metformin can suppress the proliferation, migration, and EMT of thyroid cancer cell lines by inhibiting mTOR signaling. These findings suggest that metformin and its molecular targets may be useful in thyroid carcinoma therapy.

Metformin inhibits ovarian cancer growth and increases sensitivity to paclitaxel in mouse models

OBJECTIVE

There is increasing preclinical evidence indicating that metformin, a medication commonly used for type 2 diabetes mellitus, may protect against cancer. Motivated by this emerging evidence we asked 2 questions: (1) can metformin prevent ovarian cancer growth by altering metabolism and (2) will metformin increase sensitivity to chemotherapy.

STUDY DESIGN

The effect of metformin in ovarian cancer was tested in vitro and with 2 different mouse models. In vitro, cell lines (n = 6) were treated with metformin (10-40 mmol/L) or phosphate-buffered saline solution and cellular proliferation and metabolic alterations (adenosine monophosphate-activated protein kinase activity, glycolysis, and lipid synthesis) were compared between the 2 groups. In mouse models, a prevention study was performed by treating mice with metformin (250 mg/kg/d intraperitoneally) or placebo for 2 weeks followed by intraperitoneal injection of the SKOV3ip1 human ovarian cancer cell line, and the mean number of tumor implants in each treatment group was compared. In a treatment study, the LSL-K-ras(G12D/+)/PTEN(floxP/floxP) genetic mouse model of ovarian cancer was used. Mice were treated with placebo, paclitaxel (3 mg/kg/wk intraperitoneally for 7 weeks), metformin (100 mg/kg/d in water for 7 weeks), or paclitaxel plus metformin, and tumor volume was compared among treatment groups.

RESULTS

In vitro, metformin decreased proliferation of ovarian cancer cell lines and induced cell cycle arrest, but not apoptosis. Further analysis showed that metformin altered several aspects of metabolism including adenosine monophosphate-activated protein kinase activity, glycolysis, and lipid synthesis. In the prevention mouse model, mice that were pretreated with metformin had 60% fewer tumor implants compared with controls (P < .005). In the treatment study, mice that were treated with paclitaxel plus metformin had a 60% reduction in tumor weight compared with controls (P = .02), which is a level of tumor reduction greater than that resulting from either paclitaxel or metformin alone.

CONCLUSION

Based on these results, we conclude that metformin alters metabolism in ovarian cancer cells, prevents tumor growth, and increases sensitivity to chemotherapy in vitro and in mouse models. These preclinical findings suggest that metformin warrants further investigation for use as an ovarian cancer therapeutic.

Effects of fucoidan on proliferation, AMP-activated protein kinase, and downstream metabolism- and cell cycle-associated molecules in poorly differentiated human hepatoma HLF cells

Survival rates are low in patients with poorly differentiated hepatocellular carcinoma (HCC). Fucoidan, a sulfated polysaccharide derived from brown seaweed, has anticancer activity; however, the effects of fucoidan on poorly differentiated HCC remain unclear. In this study, we investigated the effects of fucoidan on AMP-activated protein kinase (AMPK), a proliferation regulator, and its downstream metabolism- and cell cycle-related molecules in a poorly differentiated human hepatoma HLF cell line. HLF cells were treated with fucoidan (10, 50, or 100 µg/ml; n=4) or phosphate buffered saline (control; n=4) for 96 h. Proliferation was evaluated by counting cells every 24 h. AMPK, TSC2, mTOR, GSK3β, acetyl-CoA carboxylase (ACC), ATP-citrate lyase, p53, cyclin D1, cyclin-dependent kinase (CDK) 4, and CDK6 expression and/or phosphorylation were examined by immunoblotting 24 h after treatment with 100 µg/ml fucoidan. Cell cycle progression was analyzed by fluorescence-activated cell sorter 48 h after treatment. Treatment with 50 or 100 µg/ml fucoidan significantly and dose- and time-dependently suppressed HLF cell proliferation (P<0.0001). Fucoidan induced AMPK phosphorylation on Ser172 24 h after treatment. Although no differences were seen in expression and phosphorylation levels of TSC2, mTOR, GSK3β, ATP-citrate lyase, and p53 between the control and fucoidan-treated HLF cells, fucoidan induced ACC phosphorylation on Ser79. Moreover, fucoidan decreased cyclin D1, CDK4 and CDK6 expression 24 h after treatment. Furthermore, HLF cells were arrested in the G1/S phase 48 h after fucoidan treatment. We demonstrated that fucoidan suppressed HLF cell proliferation with AMPK phosphorylation. We showed that fucoidan phosphorylated ACC and downregulated cyclin D1, CDK4 and CDK6 expression. Our findings suggest that fucoidan inhibits proliferation through AMPK-associated suppression of fatty acid synthesis and G1/S transition in HLF cells.

Metformin inhibits the proliferation of A431 cells by modulating the PI3K/Akt signaling pathway

The ability of metformin, an antidiabetic drug with wide applications, to inhibit tumor cell growth has recently been discovered. The PI3K/Akt signaling pathway has been found to play an important role in the survival, proliferation and apoptosis of tumor cells. The aim of the present study was to explore the effect of metformin on the proliferation of A431 human squamous cell carcinoma cells and the underlying molecular mechanisms. A431 cells in the logarithmic growth phase were treated with 0, 15, 30, 45 and 60 mM metformin for 12, 24 and 36 h, respectively. Cell morphology with 45 mM metformin treatment for 24 h was observed under a microscope. The proliferation of A431 cells was detected by the Cell Counting kit-8 colorimetric method. The mRNA expression levels of PI3K and Akt were detected by reverse transcription-polymerase chain reaction (RT-PCR). The protein expression levels of PI3K, Akt and phosphorylated (p)-Akt were detected by western blot analysis. Metformin treatment caused morphological change in A431 cells and inhibited their proliferation in a significant time- and dose-dependent manner. RT-PCR results showed that the mRNA expression of PI3K was inhibited by metformin in a time- and dose-dependent manner (P<0.05). However, there was no significant change in the mRNA expression of Akt following metformin treatment (P>0.05). Western blotting results showed that the protein expression levels of PI3K and p-Akt were inhibited by metformin in a time- and dose-dependent manner (P<0.05). In conclusion, metformin significantly inhibited the proliferation of A431 cells in the current study, which may be strongly associated with the inhibition of the PI3K/Akt signaling pathway.

Metformin-clinical pharmacology in PCOs

Oligo-anovulation, hyperandrogenism and insulin resistance characterizes polycystic ovary syndrome (PCOs). Metformin is the oldest insulin sensitizer used in the management of type 2 diabetes mellitus. In PCOs, metformin decreases the serum lipids, androgen and insulin; induces ovulation and regular menstrual cycle; increases the pregnancy rate.

Sucrose non-fermenting related kinase enzyme is essential for cardiac metabolism

In this study, we have identified a novel member of the AMPK family, namely Sucrose non-fermenting related kinase (Snrk), that is responsible for maintaining cardiac metabolism in mammals. SNRK is expressed in the heart, and brain, and in cell types such as endothelial cells, smooth muscle cells and cardiomyocytes (CMs). Snrk knockout (KO) mice display enlarged hearts, and die at postnatal day 0. Microarray analysis of embryonic day 17.5 Snrk hearts, and blood profile of neonates display defect in lipid metabolic pathways. SNRK knockdown CMs showed altered phospho-acetyl-coA carboxylase and phospho-AMPK levels similar to global and endothelial conditional KO mouse. Finally, adult cardiac conditional KO mouse displays severe cardiac functional defects and lethality. Our results suggest that Snrk is essential for maintaining cardiac metabolic homeostasis, and shows an autonomous role for SNRK during mammalian development.

Adenosine monophosphate-activated kinase and its key role in catabolism: structure, regulation, biological activity, and pharmacological activation

Adenosine monophosphate-activated protein kinase (AMPK) is a cellular energy sensor, which once activated, plays a role in several processes within the cell to restore energy homeostasis. The protein enhances catabolic pathways, such as β-oxidation and autophagy, to generate ATP, and inhibits anabolic processes that require energy, including fatty acid, cholesterol, and protein synthesis. Due to its key role in the regulation of critical cellular pathways, deregulation of AMPK is associated with the pathology of many diseases, including cancer, Wolff-Parkinson-White syndrome, neurodegenerative disorders, diabetes, and metabolic syndrome. In fact, AMPK is a target of some pharmacological agents implemented in the treatment of diabetes (metformin and thiazolidinediones) as well as other naturally derived products, such as berberine, which is used in traditional medicine. Due to its critical role in the cell and the pathology of several disorders, research into developing AMPK as a therapeutic target is becoming a burgeoning and exciting field of pharmacological research. A profound understanding of the regulation and activity of AMPK would enhance its development as a promising therapeutic target.

Diet quality and survival after ovarian cancer: results from the Women's Health Initiative

BACKGROUND

Survival after an ovarian cancer diagnosis is poor. Given the high mortality in these patients, efforts to identify modifiable lifestyle behaviors that could influence survival are needed. Earlier evidence suggests a protective role for vegetables, but no prior studies have evaluated overall dietary quality and ovarian cancer survival. The purpose of this analysis was to evaluate the role of prediagnosis diet quality in ovarian cancer survival.

METHODS

We identified 636 centrally adjudicated cases of ovarian cancer within the Women's Health Initiative Observational Study or Clinical Trials of 161808 postmenopausal women followed from 1995 to 2012. Dietary quality was assessed for the Healthy Eating Index (2005) using a food frequency questionnaire, covariables were obtained from standardized questionnaires, and adiposity was measured by clinic-based measurements of height, weight, and waist circumference. The association between diet quality and mortality was analyzed using Cox proportional hazards regression, adjusted for potential confounders, and stratified by waist circumference, physical activity level, and diabetes status. Tests of statistical significance were two-sided.

RESULTS

Overall, higher diet quality was associated with lower all-cause mortality after ovarian cancer (hazard ratio [HR] for highest vs lowest tertile = 0.73; 95% confidence interval [CI] = 0.55 to 0.97, P(trend) = .03). The effect was strongest among women with waist circumference of 88 cm or less and with no history of diabetes (HR = 0.73, 95% CI = 0.54 to 0.98). Physical activity level did not modify the association between diet quality and survival.

CONCLUSION

Our results suggest that overall higher prediagnosis diet quality may protect against mortality after ovarian cancer.

Old drug, new trick: repurposing metformin for gynecologic cancers?

OBJECTIVE

There is increasing pre-clinical and clinical evidence that metformin, a commonly used diabetes medication, has a protective effect in cancer. The aim of this review is to discuss metformin's anti-cancer molecular mechanisms of action and to summarize the current literature demonstrating metformin's potential in gynecologic cancer prevention and treatment.

METHODS

A PubMed search was conducted combining the keywords "metformin" with "neoplasm", "uterine neoplasms", "ovarian neoplasms", and "uterine cervical neoplasms". Studies published in English between 1994 and 2014 were included.

RESULTS

Pre-clinical studies in endometrial, ovarian, and cervical cancer suggest that metformin inhibits the growth of cancer cells. The primary molecular mechanism mediating this effect appears to be the activation of AMP-activated protein kinase (AMPK) and the subsequent inhibition of mammalian targets of rapamycin (mTOR). The pre-clinical findings are augmented by clinical studies indicating that metformin use is associated with a reduced risk of cancer and improved survival in diabetic women with ovarian and endometrial cancers. No clinical analyses have evaluated metformin use and cervical cancer. Overall, the data showing a favorable effect of metformin is strongest for endometrial and ovarian cancer and prospective clinical testing is ongoing in these two malignancies.

CONCLUSIONS

Numerous clinical studies have reported an association between metformin use by diabetic patients and improved outcomes in gynecologic cancers. In addition, pre-clinical reports have identified plausible biological mechanisms to explain the molecular mechanism of action of metformin in cancer. However, the most important question remains unanswered: Will metformin be effective against cancer in patients without diabetes? Until this question is answered with prospective clinical testing, the role of metformin in the treatment or prevention of gynecologic malignancies remains theoretical and the clinical use of metformin as a cancer therapeutic is experimental.

Impact of metformin on reproductive tissues: an overview from gametogenesis to gestation

Metformin is an oral anti-hyperglycemic drug that acts as an insulin sensitizer in the treatment of diabetes mellitus type 2. It has also been widely used in the treatment of polycystic ovary syndrome (PCOS) and gestational diabetes. This drug has been shown to activate a protein kinase called 5' AMP-activated protein kinase or AMPK. AMPK is present in many tissues making metformin's effect multi factorial. However as metformin crosses the placenta, its use during pregnancy raises concerns regarding potential adverse effects on the mother and fetus. The majority of reports suggest no significant adverse effects or teratogenicity. However, disconcerting reports of male mouse offspring that were exposed to metformin in utero that present with a reduction in testis size, seminiferous tubule size and in Sertoli cell number suggest that we do not understand the full suite of effects of metformin. In addition, recent molecular evidence is suggesting an epigenetic effect of metformin which could explain some of the long-term effects reported. Nevertheless, the data are still insufficient to completely confirm or disprove negative effects of metformin. The aims of this review are to provide a summary of the safety of metformin in various aspects of sexual reproduction, the use of metformin by gestating mothers, and its possible side-effects on offspring from women who are administered metformin during pregnancy.

Metformin displays anti-myeloma activity and synergistic effect with dexamethasone in in vitro and in vivo xenograft models

Epidemiologic studies and meta-analyses have suggested that patients with type 2 diabetes mellitus (T2DM) have a higher incidence of malignancies, including myeloma. Metformin is a widely prescribed antidiabetic drug. Recently, researchers have shown that metformin has direct anticancer activity against many tumor cell lines, mainly through activating AMP-activated protein kinase (AMPK) or reducing the blood insulin level. In the present study, we investigated whether metformin exerts an anti-myeloma effect in in vitro and in vivo xenograft models and explored the underlying mechanism. We found that metformin can inhibit proliferation of MM cells by inducing apoptosis and cell cycle arrest in the G0/G1 phase. Western blot showed that metformin activated caspase 3, caspase 9, PARP-1, Bak, and p21 and inactivated Mcl-1, HIAP-1, cyclin D1, CDK4, and CDK6. Metformin inhibited the expression of insulin growth factor-I receptor (IGF-IR), and phosphatidyl inositol 3-kinase (PI3K), protein kinase B (PKB/AKT) and the downstream mammalian target of rapamycin (mTOR). IGF-I blocked metformin-induced MM cell apoptosis and reactivation of the PI3K/AKT/mTOR signaling pathway. Metformin also demonstrated synergistic activity with dexamethasone but not bortezomib to eradicate MM cells in vitro and in vivo, especially in MM.1S cells. We conclude that metformin inhibits MM cell proliferation through the IGF-1R/PI3K/AKT/mTOR signaling pathway. Metformin and dexamethasone combination therapy may be an option for MM treatment.

Metformin combined with p38 MAPK inhibitor improves cisplatin sensitivity in cisplatin‑resistant ovarian cancer

The aim of the present study was to determine the effects of metformin, combined with a p38 mitogen‑activated protein kinase (MAPK) inhibitor, on the sensitivity of cisplatin‑resistant ovarian cancer to cisplatin. The expression and distribution of phosphorylated p38 MAPK (P‑p38 MAPK) was confirmed in drug‑resistant and primary ovarian cancer tissues by immunohistochemistry and western blotting. A bromodeoxyuridine ELISA kit was used to analyze the effects of metformin, SB203580, a p38 MAPK inhibitor, and metformin combined with SB203580, on the cell proliferation of SKOV3/DDP cisplatin‑resistant ovarian cancer cells. The protein expression of P‑p38 MAPK was significantly higher in cisplatin‑resistant ovarian cancer, as compared with the primary ovarian cancer tissues. Metformin combined with SB203580 significantly enhanced the sensitivity of SKOV3/DDP cells to cisplatin. In conclusion, the p38 MAPK signaling pathway may be associated with cisplatin‑resistant ovarian cancer. Metformin, combined with the p38 MAPK inhibitor, significantly increased the sensitivity of SKOV3/DDP cells to cisplatin treatment.

Is it time to test biguanide metformin in the treatment of melanoma?

Metformin is the most widely used antidiabetic drug that belongs to the biguanide class. It is very well tolerated and has the major clinical advantage of not inducing hypoglycemia. Metformin decreases hepatic glucose production via a mechanism requiring liver kinase B1, which controls the metabolic checkpoint, AMP-activated protein kinase-mammalian target of rapamycin and neoglucogenic genes. The effects of metformin on this pathway results in reduced protein synthesis and cell proliferation. These observations have given the impetus for many investigations on the role of metformin in the regulation of tumor cell proliferation, cell-cycle regulation, apoptosis, and autophagy. Encouraging results from these studies have shown that metformin could potentially be used as an efficient anticancer drug in various neoplasms such as prostate, breast, lung, pancreas cancers, and melanoma. These findings are strengthened by retrospective epidemiological studies that have found a decrease in cancer risk in diabetic patients treated with metformin. In this review, we have focused our discussion on recent molecular mechanisms of metformin that have been described in various solid tumors in general and in melanoma in particular.

Metformin against cancer stem cells through the modulation of energy metabolism: special considerations on ovarian cancer

Ovarian cancer is the most lethal gynecologic malignancy among women worldwide and is presumed to result from the presence of ovarian cancer stem cells. To overcome the limitation of current anticancer agents, another anticancer strategy is necessary to effectively target cancer stem cells in ovarian cancer. In many types of malignancies, including ovarian cancer, metformin, one of the most popular antidiabetic drugs, has been demonstrated to exhibit chemopreventive and anticancer efficacy with respect to incidence and overall survival rates. Thus, the metabolic reprogramming of cancer and cancer stem cells driven by genetic alterations during carcinogenesis and cancer progression could be therapeutically targeted. In this review, the potential efficacy and anticancer mechanisms of metformin against ovarian cancer stem cells will be discussed.

Metformin impairs growth of endometrial cancer cells via cell cycle arrest and concomitant autophagy and apoptosis

Background

Effective therapies for early endometrial cancer usually involve surgical excision and consequent infertility Therefore, new treatment approaches that preserve fertility should be developed. Metformin, a well-tolerated anti-diabetic drug, can inhibit cancer cell growth. However, the mechanism of metformin action is not well understood. Here we investigate the roles of autophagy and apoptosis in the anti-cancer effects of metformin on endometrial cancer cells.

Methods

Ishikawa endometrial cancer cells were treated with metformin. WST-8 assays, colony formation assays, flow cytometry, caspase luminescence measurement, immunofluorescence, and western blots were used to assess the effects of metformin on cell viability, proliferation, cell cycle progression, apoptosis, and autophagy.

Results

Metformin-treated cells exhibited significantly lower viability and proliferation and significantly more cell cycle arrest in G1 and G2/M than control cells. These cells also exhibited significantly more apoptosis via both intrinsic and extrinsic pathways. In addition, metformin treatment induced autophagy. Inhibition of autophagy, either by Beclin1 knockdown or by 3-methyladenine-mediated inhibition of caspase-3/7, suppressed the anti-proliferative effects of metformin on endometrial cancer cells. These findings indicate that the anti-proliferative effects and apoptosis caused by metformin are partially or completely dependent on autophagy.

Conclusions

We showed that metformin suppresses endometrial cancer cell growth via cell cycle arrest and concomitant autophagy and apoptosis.

Preclinical therapeutic potential of a nitrosylating agent in the treatment of ovarian cancer

This study examines the role of s-nitrosylation in the growth of ovarian cancer using cell culture based and in vivo approaches. Using the nitrosylating agent, S-nitrosoglutathione (GSNO), a physiological nitric oxide molecule, we show that GSNO treatment inhibited proliferation of chemoresponsive and chemoresistant ovarian cancer cell lines (A2780, C200, SKVO3, ID8, OVCAR3, OVCAR4, OVCAR5, OVCAR7, OVCAR8, OVCAR10, PE01 and PE04) in a dose dependent manner. GSNO treatment abrogated growth factor (HB-EGF) induced signal transduction including phosphorylation of Akt, p42/44 and STAT3, which are known to play critical roles in ovarian cancer growth and progression. To examine the therapeutic potential of GSNO in vivo, nude mice bearing intra-peritoneal xenografts of human A2780 ovarian carcinoma cell line (2×10⁶) were orally administered GSNO at the dose of 1 mg/kg body weight. Daily oral administration of GSNO significantly attenuated tumor mass (p<0.001) in the peritoneal cavity compared to vehicle (phosphate buffered saline) treated group at 4 weeks. GSNO also potentiated cisplatin mediated tumor toxicity in an A2780 ovarian carcinoma nude mouse model. GSNO’s nitrosylating ability was reflected in the induced nitrosylation of various known proteins including NFκB p65, Akt and EGFR. As a novel finding, we observed that GSNO also induced nitrosylation with inverse relationship at tyrosine 705 phosphorylation of STAT3, an established player in chemoresistance and cell proliferation in ovarian cancer and in cancer in general. Overall, our study underlines the significance of S-nitrosylation of key cancer promoting proteins in modulating ovarian cancer and proposes the therapeutic potential of nitrosylating agents (like GSNO) for the treatment of ovarian cancer alone or in combination with chemotherapeutic drugs.

Bioenergetic analysis of ovarian cancer cell lines: profiling of histological subtypes and identification of a mitochondria-defective cell line

Epithelial ovarian cancer (EOC) is the most lethal of all gynecological cancers, and encompasses distinct histological subtypes that have specific genetic and tissues-of-origin differences. Ovarian clear cell carcinoma (OCCC) represents approximately 10% of cases and has been termed a stress responsive cancer. OCCC is characterized by increased expression of oxidative stress and glycolysis-related genes. In the present study, we hypothesized that bioenergetic profiling might uniquely distinguish OCCC from other EOC histological subtypes. Using an extracellular flux analyzer, OCCC lines (ES-2, TOV-21-G) were shown to be highly metabolically active, with high oxygen consumption rate (OCR) and high extracellular acidification rate (ECAR), indicative of enhanced mitochondrial oxidative phosphorylation and glycolytic rate, respectively. A high bioenergetics profile was associated with the cell lines' ability to form anchorage independent spheroids. Given their high glycolytic and mitochondrial activity, OCCC cells displayed strong sensitivity to 2-deoxy-D-glucose and Rotenone growth inhibition, although this chemosensitivity profile was not specific to only OCCC cells. Bioenergetic profiling also identified a non-OCCC cell line, OVCA420, to have severely compromised mitochondrial function, based on low OCR and a lack of stimulation of maximal respiration following application of the uncoupler FCCP. This was accompanied by mitochondrial morphology changes indicative of enhanced fission, increased expression of the mitochondrial fission protein Drp1, a loss of mitochondrial membrane potential and dependence on glycolysis. Importantly, this loss of mitochondrial function was accompanied by the inability of OVCA420 cells to cope with hypoxic stress, and a compromised ability to stabilize HIF-1α in response to 1% O₂ hypoxia. This knowledge may be imperative for researchers planning to utilize this cell line for further studies of metabolism and hypoxia, and suggests that altered mitochondrial fission dynamics represents a phenotype of a subpopulation of EOCs.

Association between phosphorylated AMP-activated protein kinase and acetyl-CoA carboxylase expression and outcome in patients with squamous cell carcinoma of the head and neck

Background

Epidemiological studies have indicated that impaired glucose metabolism may increase the risk of squamous cell carcinoma of the head and neck (SCCHN). AMP-activated protein kinase (AMPK) regulates glucose and lipid metabolism via the phosphorylation and subsequent inactivation of its downstream target acetyl-CoA carboxylase (ACC).Thus, we analyzed the expression of pAMPK and its downstream target phosphorylated acetyl-CoA carboxylase (pACC), as well as their impact on the survival of patients with resected SCCHN.

Methods

One hundred eighteen patients with surgically resected SCCHN were enrolled. Immunohistochemical (IHC) staining for pAMPK and pACC was performed using tissue microarrays of operative specimens of SCCHN. The expression was divided into two or three groups according to the IHC score [pAMPK: negative (0), positive (1–3); pACC: negative (0), low expression (1, 2), and high expression (3)]. Statistical analysis was performed to determine the association of pAMPK expression with clinicopathological features and pACC and pErk expression.

Results

The positive rates of pAMPK and pACC expression were 64.4% (76/118) and 68.6% (81/118), respectively. pAMPK was significantly higher in patients aged younger than 60 years (P = 0.024; χ²test) and those with early-stage (T1/T2; P = 0.02; χ² test) and oral cavity (P = 0.026; Fisher’s exact test) tumors. In multivariate analysis, pAMPK expression was not significantly correlated with overall survival (OS) (adjusted hazard ratio [HR]: 0.66; 95% confidence interval [CI]: 0.35–1.23), whereas high pACC expression was independently associated with worse OS in node-positive patients (adjusted HR: 17.58; 95% CI: 3.50–88.18).

Conclusions

Strong expression of pACC was found to be an independent prognostic marker for patients with node-positive SCCHN. Our results suggest that pACC may play a role in tumor progression of SCCHN and may help to identify patient subgroups at high risk for poor disease outcome.

Response of breast cancer cells and cancer stem cells to metformin and hyperthermia alone or combined

Metformin, the most widely prescribed drug for treatment of type 2 diabetes, has been shown to exert significant anticancer effects. Hyperthermia has been known to kill cancer cells and enhance the efficacy of various anti-cancer drugs and radiotherapy. We investigated the combined effects of metformin and hyperthermia against MCF-7 and MDA-MB-231 human breast cancer cell, and MIA PaCa-2 human pancreatic cancer cells. Incubation of breast cancer cells with 0.5-10 mM metformin for 48 h caused significant clonogenic cell death. Culturing breast cancer cells with 30 µM metformin, clinically relevant plasma concentration of metformin, significantly reduced the survival of cancer cells. Importantly, metformin was preferentially cytotoxic to CD44(high)/CD24(low) cells of MCF-7 cells and, CD44(high)/CD24(high) cells of MIA PaCa-2 cells, which are known to be cancer stem cells (CSCs) of MCF-7 cells and MIA PaCa-2 cells, respectively. Heating at 42°C for 1 h was slightly toxic to both cancer cells and CSCs, and it markedly enhanced the efficacy of metformin to kill cancer cells and CSCs. Metformin has been reported to activate AMPK, thereby suppressing mTOR, which plays an important role for protein synthesis, cell cycle progression, and cell survival. For the first time, we show that hyperthermia activates AMPK and inactivates mTOR and its downstream effector S6K. Furthermore, hyperthermia potentiated the effect of metformin to activate AMPK and inactivate mTOR and S6K. Cell proliferation was markedly suppressed by metformin or combination of metformin and hyperthermia, which could be attributed to activation of AMPK leading to inactivation of mTOR. It is conclude that the effects of metformin against cancer cells including CSCs can be markedly enhanced by hyperthermia.

New molecules and old drugs as emerging approaches to selectively target human glioblastoma cancer stem cells

Despite relevant progress obtained by multimodal treatment, glioblastoma (GBM), the most aggressive primary brain tumor, is still incurable. The most encouraging advancement of GBM drug research derives from the identification of cancer stem cells (CSCs), since these cells appear to represent the determinants of resistance to current standard therapies. The goal of most ongoing studies is to identify drugs able to affect CSCs biology, either inducing selective toxicity or differentiating this tumor cell population into nontumorigenic cells. Moreover, the therapeutic approach for GBM could be improved interfering with chemo- or radioresistance mechanisms, microenvironment signals, and the neoangiogenic process. During the last years, molecular targeted compounds such as sorafenib and old drugs, like metformin, displayed interesting efficacy in preclinical studies towards several tumors, including GBM, preferentially affecting CSC viability. In this review, the latest experimental results, controversies, and prospective application concerning these promising anticancer drugs will be discussed.

The antidiabetic drug metformin inhibits the proliferation of bladder cancer cells in vitro and in vivo

Recent studies suggest that metformin, a widely used antidiabetic agent, may reduce cancer risk and improve prognosis of certain malignancies. However, the mechanisms for the anti-cancer effects of metformin remain uncertain. In this study, we investigated the effects of metformin on human bladder cancer cells and the underlying mechanisms. Metformin significantly inhibited the proliferation and colony formation of 5637 and T24 cells in vitro; specifically, metformin induced an apparent cell cycle arrest in G0/G1 phases, accompanied by a strong decrease of cyclin D1, cyclin-dependent kinase 4 (CDK4), E2F1 and an increase of p21^waf-1. Further experiments revealed that metformin activated AMP-activated protein kinase (AMPK) and suppressed mammalian target of rapamycin (mTOR), the central regulator of protein synthesis and cell growth. Moreover, daily treatment of metformin led to a substantial inhibition of tumor growth in a xenograft model with concomitant decrease in the expression of proliferating cell nuclear antigen (PCNA), cyclin D1 and p-mTOR. The in vitro and in vivo results demonstrate that metformin efficiently suppresses the proliferation of bladder cancer cells and suggest that metformin may be a potential therapeutic agent for the treatment of bladder cancer.

Adiponectin and metformin additively attenuate IL1β-induced malignant potential of colon cancer

Both adiponectin (AD) and metformin (Met) have been proposed to downregulate cell proliferation of colon cancer cells, but whether their effect might be additive has not been studied to date. Genetic studies in humans have suggested an important role for interleukin 1β (IL1β) in cancer pathogenesis. Direct evidence that IL1β contributes to the development of colon cancer has not yet been fully confirmed and no previous studies have evaluated how IL1β may interact with AD and/or Met to regulate malignant potential and intracellular signaling pathways in human and mouse colon cancer cells. We conducted in vitro studies using human (LoVo) and mouse (MCA38) colon cancer cell lines to evaluate whether AD and Met alone or in combination may antagonize IL1β-regulated malignant potential in human and mouse colon cancer cell lines. IL1β increased malignant potential and regulated the expression of tumor suppressor (p53) and cell cycle regulatory genes (p21, p27, and cyclin E2) in human and mouse colon cancer cell lines. These effects were reversed by co-administration of AD and/or Met and were additively altered by AD and Met in combination in a STAT3- and AMPK/LKB1-dependent manner. We also observed using fluorescence activated cell sorter analysis that IL1β-regulated cell cycle progression is altered by AD and Met alone or in combination. Our novel mechanistic studies provide evidence for an important role for IL1β in colon cancer and suggest that AD and/or Met might be useful agents in the management or chemoprevention of IL1β-induced colon carcinogenesis.

Metformin inhibits proliferation of human keratinocytes through a mechanism associated with activation of the MAPK signaling pathway

In the present study, the effects of metformin on the proliferation of human immortalized keratinocytes (HaCaTs) and the underlying mechanisms were investigated. HaCaT cells in the logarithmic growth phase were treated with 50 mM metformin for 24, 48 and 72 h. Cell morphology after 24 h of treatment was observed under a microscope. Cell proliferation was detected using a colorimetric cell proliferation and cytotoxicity assay kit. Western blot analyses were performed to detect the protein phosphorylation levels of adenosine monophosphate-activated protein kinase (AMPK) and extracellular signal-related kinase 1/2 (ERK1/2). Metformin treatment resulted in morphological changes of the HaCaT cells. The survival rates of HaCaT cells treated with metformin were 36.18, 12.70 and 10.12% at 24, 48 and 72 h, respectively. As the treatment time extended, the survival rates of HaCaT cells decreased. Western blot analysis results showed that the mean level of phosphorylated (p)-AMPK in the HaCaT cells without metformin treatment was 2.856±0.323. However, the mean p-AMPK level following metformin treatment for 24 h increased to 5.198±0.625, indicating a significant difference between these two groups (P<0.05). The mean absorbance ratio of p-ERK1/2 was 7.550±1.087 for the untreated cells, but the levels in cells following metformin treatment for 24 h increased to 10.430±1.217, indicating a significant difference between the two groups (P<0.05). In conclusion, metformin treatment upregulated the levels of p-AMPK and p-ERK1/2 in HaCaT cells, and significantly inhibited HaCaT cell proliferation in vitro by a mechanism associated with activation of the mitogen-activated protein kinase signaling pathway.

Metformin inhibits skin tumor promotion in overweight and obese mice

In the present study, the ability of metformin to inhibit skin tumor promotion by 12-O-tetradecanoylphorbol-13-acetate (TPA) was analyzed in mice maintained on either an overweight control diet or an obesity-inducing diet. Rapamycin was included for comparison, and a combination of metformin and rapamycin was also evaluated. Metformin (given in the drinking water) and rapamycin (given topically) inhibited development of both papillomas and squamous cell carcinomas in overweight and obese mice in a dose-dependent manner. A low-dose combination of these two compounds displayed an additive inhibitory effect on tumor development. Metformin treatment also reduced the size of papillomas. Interestingly, all treatments seemed to be at least as effective for inhibiting tumor formation in obese mice, and both metformin and rapamycin were more effective at reducing tumor size in obese mice compared with overweight control mice. The effect of metformin on skin tumor development was associated with a significant reduction in TPA-induced epidermal hyperproliferation. Furthermore, treatment with metformin led to activation of epidermal AMP-activated protein kinase (AMPK) and attenuated signaling through mTOR complex (mTORC)-1 and p70S6K. Combinations of metformin and rapamycin were more effective at blocking epidermal mTORC1 signaling induced by TPA consistent with the greater inhibitory effect on skin tumor promotion. Collectively, the current data demonstrate that metformin given in the drinking water effectively inhibited skin tumor promotion in both overweight and obese mice and that the mechanism involves activation of epidermal AMPK and attenuated signaling downstream of mTORC1.

The Effects of Metformin on Ovarian Cancer: A Systematic Review

Objective

The potential therapeutic effects of metformin on several cancers were reported. However, the evidence of the effects of metformin on ovarian cancer is still limited and inconclusive. This systematic review and meta-analysis study aims to summarize the existing evidence of the therapeutic effects of metformin on ovarian cancer.

Methods

We performed systematic searches using electronic databases including PubMed and EMBASE until December 2012. Key words included “metformin” AND (“ovarian cancer” OR “ovary tumor”). All human studies assessing the effects of metformin on ovarian cancer were eligible for inclusion. All articles were reviewed independently by 2 authors with a standardized approach for the purpose of study, study design, patient characteristics, exposure, and outcomes. The data were pooled using a random-effects model.

Results

Of 190 studies retrieved, only 3 observational studies and 1 report of 2 randomized controlled trials were included. Among those studies, 2 reported the effects of metformin on survival outcomes of ovarian cancer, whereas the other 2 reported the effects of metformin on ovarian cancer prevention. The findings of studies reporting the effects on survival outcomes indicated that metformin may prolong overall, disease-specific, and progression-free survival in ovarian cancer patients. The results of studies reporting the effects of metformin on ovarian cancer prevention were meta-analyzed. It indicated that metformin tended to decrease occurrence of ovarian cancer among diabetic patients with the pooled odds ratio of 0.57 (95% confidence interval, 0.16–1.99).

Conclusions

Our findings showed the potential therapeutic effects of metformin on survival outcomes of ovarian cancer and ovarian cancer prevention. However, most of the evidence was observational studies. There is a call for further well-conducted controlled clinical trials to confirm the effects of metformin on ovarian cancer survival and ovarian cancer prevention.

Exploring the effects of isothiocyanates on chemotherapeutic drugs

INTRODUCTION

Chemoprevention has emerged as a promising strategy to reduce the risk and to control cancer. In this context, isothiocyanates (ITCs), found in abundance in the form of glucosinolates in cruciferous vegetables, have gained increasing consideration for their chemopreventive activity. ITCs exert their effects mainly by inducing carcinogen metabolism or by inhibiting tumor cell proliferation.

AREAS COVERED

In recent years, novel combination treatments, by coupling chemopreventive agents and typical chemotherapeutics, have been exploited to increase the antitumor activities. The aim of this article is to examine the foremost studies carried out, so far, on the effects of dietary and synthetic ITCs on different signaling pathways involved in the pharmacokinetics and pharmacodynamics of chemotherapeutic agents, in order to enhance their effectiveness.

EXPERT OPINION

Undoubtedly, the beneficial anticarcinogenic potential of ITCs, both singly and in combination, has emerged in in vitro and in vivo studies. However, only a few clinical trials have been carried out so far with ITCs, which try to better define both the pharmacokinetic and pharmacodynamic impacts in humans. More toxicological evaluations after long-term administration of ITCs in different species are required for the clinical development of ITCs as anticarcinogenic agents.

Effect of metformin on residual cells after chemotherapy in a human lung adenocarcinoma cell line

Cancer chemotherapy, including molecular targeted therapy, has major limitations because it does not kill all the cancer cells; the residual cells survive until they acquire chemoresistance. In the present study, the combined effects of metformin and gefitinib were examined in vivo in a mouse xenograft model, inoculated with a human lung adenocarcinoma cell line that possesses an activating epidermal growth factor receptor mutation. The mechanism of the interaction was further elucidated in vitro. Metformin did not suppress the growth of already established tumors, nor did metformin augment tumor shrinkage by gefitinib. However, metformin significantly suppressed the regrowth of the tumor after effective treatment with gefitinib, suggesting the specific effect of metformin on the residual cells. Cytotoxicity of metformin was characterized by the absence of apoptosis induction and unremarkable cell cycle shift in vitro. The residual cell population after treatment with gefitinib was characterized by enriched cells with high expression of CD133 and CD24. Metformin was still effective on this specific cell population. Targeting residual cells after chemotherapy may represent an effective novel strategy for the treatment of cancer. Elucidating the mechanism of metformin cytotoxicity provides insights into future development of anticancer therapeutics.

AMP-Activated Protein Kinase α 2 Isoform Suppression in Primary Breast Cancer Alters AMPK Growth Control and Apoptotic Signaling

Adenosine monophosphate-activated protein kinase (AMPK) is a metabolic regulator that promotes energy conservation and restoration when cells are exposed to nutrient stress. Given the high metabolic requirement of cancer cells, AMPK activation has been suggested as a potential preventative and therapeutic target. However, previous findings have shown that AMPK activity is diminished in some cancers. Expression of the 2 catalytic isoforms, AMPKα1 and AMPKα2, was evaluated in primary breast cancer and matched nontumor-adjacent tissue samples using immunohistochemistry. AMPK-dependent growth signaling events were examined in primary human mammary epithelial cells (HMECs) using RNAi to understand the importance of AMPKα2 in normal growth regulation. To test whether AMPKα2 would reinstate growth control and apoptotic mechanisms in breast cancer cells, metabolic stress assays and tumor xenografts were performed in MCF-7 cells, expressing low levels of AMPKα2, with stable transfection of either green fluorescent protein (GFP) or AMPKα2 expression constructs. AMPKα2 was found to be significantly suppressed in breast cancer tissue samples, whereas AMPKα1 was not. In normal HMECs, low glucose stress resulted in AMPK-driven growth inhibition. Interestingly, this response was ablated when AMPKα2 was silenced. Metabolic stress assays in MCF-7 cells indicated that AMPKα2 expression reduced both mTOR signaling and cyclin D1 expression, contributing to G1-phase cell cycle arrest. Cells expressing AMPKα2 underwent apoptosis more readily than GFP control cells. Xenograft studies demonstrated that MCF-7 tumors expressing AMPKα2 display reduced proliferation and increased apoptotic events. Furthermore, AMPKα2 xenografts exhibited diminished cyclin D1 levels along with an increased amount of nuclear p53, thereby implicating the AMPKα2-p53 signaling axis as a mediator of cell apoptosis. Together, these results highlight the significance of reduced AMPK activity contributing to human carcinogenesis and, specifically, the role of AMPKα2 with respect to its control of normal mammary epithelial cell growth and its reduced expression in breast cancer.

Activation of AMPK inhibits cervical cancer cell growth through AKT/FOXO3a/FOXM1 signaling cascade

BACKGROUND

Although advanced-stage cervical cancer can benefit from current treatments, approximately 30% patients may fail after definitive treatment eventually. Therefore, exploring alternative molecular therapeutic approaches is imperatively needed for this disease. We have recently shown that activation of AMP-activated protein kinase (AMPK), a metabolic sensor, hampers cervical cancer cell growth through blocking the Wnt/β-catenin signaling activity. Here, we report that activated AMPK (p-AMPK) also inhibits cervical cancer cell growth by counteracting FOXM1 function.

METHODS

Effect of the activation of AMPK on FOXM1 expression was examined by hypoxia and glucose deprivation, as well as pharmacological AMPK activators such as A23187, AICAR and metformin. RT Q-PCR and Western blot analysis were employed to investigate the activities of AMPK, FOXM1 and AKT/FOXO3a signaling.

RESULTS

Consistent with our previous findings, the activation of AMPK by either AMPK activators such as AICAR, A23187, metformin, glucose deprivation or hypoxia significantly inhibited the cervical cancer cell growth. Importantly, we found that activated AMPK activity was concomitantly associated with the reduction of both the mRNA and protein levels of FOXM1. Mechanistically, we showed that activated AMPK was able to reduce AKT mediated phosphorylation of p-FOXO3a (Ser253). Interestingly, activated AMPK could not cause any significant changes in FOXM1 in cervical cancer cells in which endogenous FOXO3a levels were knocked down using siRNAs, suggesting that FOXO3a is involved in the suppression of FOXM1.

CONCLUSION

Taken together, our results suggest the activated AMPK impedes cervical cancer cell growth through reducing the expression of FOXM1.

Metformin blocks melanoma invasion and metastasis development in AMPK/p53-dependent manner

Metformin was reported to inhibit the proliferation of many cancer cells, including melanoma cells. In this report, we investigated the effect of metformin on melanoma invasion and metastasis development. Using different in vitro approaches, we found that metformin inhibits cell invasion without affecting cell migration and independently of antiproliferation action. This inhibition is correlated with modulation of expression of proteins involved in epithelial-mesenchymal transition such as Slug, Snail, SPARC, fibronectin, and N-cadherin and with inhibition of MMP-2 and MMP-9 activation. Furthermore, our data indicate that this process is dependent on activation of AMPK and tumor suppressor protein p53. Finally, we showed that metformin inhibits melanoma metastasis development in mice using extravasation and metastasis models. The presented data reinforce the fact that metformin might be a good candidate for clinical trial in melanoma treatment.

ABT-263 enhances sensitivity to metformin and 2-deoxyglucose in pediatric glioma by promoting apoptotic cell death

Pediatric high grade glioma is refractory to conventional multimodal treatment, highlighting a need to develop novel efficacious therapies. We investigated tumor metabolism as a potential therapeutic target in a panel of diverse pediatric glioma cell lines (SF188, KNS42, UW479 and RES186) using metformin and 2-deoxyglucose. As a single agent, metformin had little effect on cell viability overall. SF188 cells were highly sensitive to 2-deoxyglucose however, combination of metformin with 2-deoxyglucose significantly reduced cell proliferation compared to either drug alone in all cell lines tested. In addition, the combination of the two agents was associated with a rapid decrease in cellular ATP and subsequent AMPK activation. However, increased cell death was only observed in select cell lines after prolonged exposure to the drug combination and was caspase independent. Anti-apoptotic BCL-2 family proteins have been indicated as mediators of resistance against metabolic stress. Therefore we sought to determine whether pharmacological inhibition of BCL-2/BCL-xL with ABT-263 could potentiate apoptosis in response to these agents. We found that ABT-263 increased sensitivity to 2-deoxyglucose and promoted rapid and extensive cell death in response to the combination of 2-deoxyglucose and metformin. Furthermore, cell death was inhibited by the pan-caspase inhibitor, z-VAD-FMK suggesting that ABT-263 potentiated caspase-dependent cell death in response to 2-deoxyglucose or its combination with metformin. Overall, these data provide support for the concept that targeting metabolic and anti-apoptotic pathways may be an effective therapeutic strategy in pediatric glioma.

Metformin, at concentrations corresponding to the treatment of diabetes, potentiates the cytotoxic effects of carboplatin in cultures of ovarian cancer cells

The use of the type 2 diabetics drug metformin has been correlated with enhanced progression-free survival in ovarian cancer. The literature has speculated that this enhancement is due to the high concentration of metformin directly causing cancer cell death. However, this explanation does not fit with clinical data reporting that the women exposed to constant micromolar concentrations of metformin, as present in the treatment of diabetes, respond better to chemotherapy. Herein, our aim was to examine whether micromolar concentrations of metformin alone could bring about cancer cell death and whether micromolar metformin could increase the cytotoxic effect of commonly used chemotherapies in A2780 and SKOV3 cell lines and primary cultured cancer cells isolated from the peritoneal fluid of patients with advanced ovarian cancer. Our results in cell lines demonstrate that no significant loss of viability or change in cell cycle was observed with micromolar metformin alone; however, we observed cytotoxicity with micromolar metformin in combination with chemotherapy at concentrations where the chemotherapy alone produced no loss in viability. We demonstrate that previous exposure and maintenance of metformin in conjunction with carboplatin produces a synergistic enhancement in cytotoxicity of A2780 and SKOV3 cells (55% and 43%, respectively). Furthermore, in 5 (44%) of the 11 ovarian cancer primary cultures, micromolar metformin improved the cytotoxic response to carboplatin but not paclitaxel or doxorubicin. In conclusion, we present data that support the need for a clinical study to evaluate the adjuvant maintenance or prescription of currently approved doses of metformin during the chemotherapeutic treatment of ovarian cancer.

Reversing the Warburg effect as a treatment for glioblastoma

Glioblastoma multiforme (GBM), like most cancers, possesses a unique bioenergetic state of aerobic glycolysis known as the Warburg effect. Here, we documented that methylene blue (MB) reverses the Warburg effect evidenced by the increasing of oxygen consumption and reduction of lactate production in GBM cell lines. MB decreases GBM cell proliferation and halts the cell cycle in S phase. Through activation of AMP-activated protein kinase, MB inactivates downstream acetyl-CoA carboxylase and decreases cyclin expression. Structure-activity relationship analysis demonstrated that toluidine blue O, an MB derivative with similar bioenergetic actions, exerts similar action in GBM cell proliferation. In contrast, two other MB derivatives, 2-chlorophenothiazine and promethazine, exert no effect on cellular bioenergetics and do not inhibit GBM cell proliferation. MB inhibits cell proliferation in both temozolomide-sensitive and -insensitive GBM cell lines. In a human GBM xenograft model, a single daily dosage of MB does not activate AMP-activated protein kinase signaling, and no tumor regression was observed. In summary, the current study provides the first in vitro proof of concept that reversal of Warburg effect might be a novel therapy for GBM.

Nanoceria: a rare-earth nanoparticle as a novel anti-angiogenic therapeutic agent in ovarian cancer

Ovarian cancer (OvCa) is the fifth most common cause of death from all cancers among women in United Sates and the leading cause of death from gynecological malignancies. While most OvCa patients initially respond to surgical debulking and chemotherapy, 75% of patients later succumb to the disease. Thus, there is an urgent need to test novel therapeutic agents to counteract the high mortality rate associated with OvCa. In this context, we have developed and engineered Nanoceria (NCe), nanoparticles of cerium oxide, possessing anti-oxidant properties, to be used as a therapeutic agent in OvCa. We show for the first time that NCe significantly inhibited production of reactive oxygen species (ROS) in A2780 cells, attenuated growth factor (SDF1, HB-EGF, VEGF₁₆₅ and HGF) mediated cell migration and invasion of SKOV3 cells, without affecting the cell proliferation. NCe treatment also inhibited VEGF₁₆₅ induced proliferation, capillary tube formation, activation of VEGFR2 and MMP2 in human umbilical vascular endothelial cells (HUVEC). NCe (0.1 mg/kg body weigh) treatment of A2780 ovarian cancer cells injected intra-peritoneally in nude mice showed significant reduction (p<0.002) in tumor growth accompanied by decreased tumor cell proliferation as evident from reduced tumor size and Ki67 staining. Accumulation of NCe was found in tumors isolated from treated group using transmission electron microscopy (TEM) and inductively coupled plasma mass spectroscopy (ICP-MS). Reduction of the tumor mass was accompanied by attenuation of angiogenesis, as observed by reduced CD31 staining and specific apoptosis of vascular endothelial cells. Collectively, these results indicate that cerium oxide based NCe is a novel nanoparticle that can potentially be used as an anti-angiogenic therapeutic agent in ovarian cancer.

Therapeutic strategies targeting cancer stem cells

Increasing studies have demonstrated a small proportion of cancer stem cells (CSCs) exist in the cancer cell population. CSCs have powerful self-renewal capacity and tumor-initiating ability and are resistant to chemotherapy and radiation. Conventional anticancer therapies kill the rapidly proliferating bulk cancer cells but spare the relatively quiescent CSCs, which cause cancer recurrence. So it is necessary to develop therapeutic strategies acting specifically on CSCs. In recent years, studies have shown that therapeutic agents such as metformin, salinomycin, DECA-14, rapamycin, oncostatin M (OSM), some natural compounds, oncolytic viruses, microRNAs, cell signaling pathway inhibitors, TNF-related apoptosis inducing ligand (TRAIL), interferon (IFN), telomerase inhibitors, all-trans retinoic acid (ATRA) and monoclonal antibodies can suppress the self-renewal of CSCs in vitro and in vivo. A combination of these agents and conventional chemotherapy drugs can significantly inhibit tumor growth, metastasis and recurrence. These strategies targeting CSCs may bring new hopes to cancer therapy.

Targeting LKB1 signaling in cancer

The serine/threonine kinase LKB1 is a master kinase involved in cellular responses such as energy metabolism, cell polarity and cell growth. LKB1 regulates these crucial cellular responses mainly via AMPK/mTOR signaling. Germ-line mutations in LKB1 are associated with the predisposition of the Peutz-Jeghers syndrome in which patients develop gastrointestinal hamartomas and have an enormously increased risk for developing gastrointestinal, breast and gynecological cancers. In addition, somatic inactivation of LKB1 has been associated with sporadic cancers such as lung cancer. The exact mechanisms of LKB1-mediated tumor suppression remain so far unidentified; however, the inability to activate AMPK and the resulting mTOR hyperactivation has been detected in PJS-associated lesions. Therefore, targeting LKB1 in cancer is now mainly focusing on the activation of AMPK and inactivation of mTOR. Preclinical in vitro and in vivo studies show encouraging results regarding these approaches, which have even progressed to the initiation of a few clinical trials. In this review, we describe the functions, regulation and downstream signaling of LKB1, and its role in hereditary and sporadic cancers. In addition, we provide an overview of several AMPK activators, mTOR inhibitors and additional mechanisms to target LKB1 signaling, and describe the effect of these compounds on cancer cells. Overall, we will explain the current strategies attempting to find a way of treating LKB1-associated cancer.

Role of the microenvironment in ovarian cancer stem cell maintenance

Despite recent progresses in cancer therapy and increased knowledge in cancer biology, ovarian cancer remains a challenging condition. Among the latest concepts developed in cancer biology, cancer stem cells and the role of microenvironment in tumor progression seem to be related. Indeed, cancer stem cells have been described in several solid tumors including ovarian cancers. These particular cells have the ability to self-renew and reconstitute a heterogeneous tumor. They are characterized by specific surface markers and display resistance to therapeutic regimens. During development, specific molecular cues from the tumor microenvironment can play a role in maintaining and expanding stemness of cancer cells. The tumor stroma contains several compartments: cellular component, cytokine network, and extracellular matrix. These different compartments interact to form a permissive niche for the cancer stem cells. Understanding the molecular cues underlying this crosstalk will allow the design of new therapeutic regimens targeting the niche. In this paper, we will discuss the mechanisms implicated in the interaction between ovarian cancer stem cells and their microenvironment.

Metformin intake is associated with better survival in ovarian cancer: a case-control study

BACKGROUND

The objective of this case-control study was to identify any association of metformin intake with the survival of patients with ovarian cancer.

METHODS

In this retrospective case-control study, women with ovarian cancer who received metformin (cases) were compared with women with ovarian cancer who did not receive metformin (controls). A 2-layered analysis was conducted. In preliminary analysis, all cases (the OC cohort) were compared with controls at a 1:2 ratio. Subsequently, in definitive analysis, only patients who had epithelial ovarian cancer (the EOC cohort) were compared with controls at a 1:3 ratio. In the EOC cohort, cases were matched with controls for age (±5 years), International Federation of Gynecology and Obstetrics stage, and residual disease. Prognostic variables and disease specific survival were compared using chi-square tests, the Kaplan-Meier (log-rank) method, and Cox proportional hazards analysis.

RESULTS

In a preliminary analysis of the OC cohort (72 cases and 143 controls), cases had better survival (5-year disease-specific survival for cases vs controls, 73% vs 44%; P = .0002). In the definitive analysis of the EOC cohort (61 cases and 178 controls), the distribution of age, disease stage, optimal cytoreduction, serous histology, and platinum chemotherapy remained similar between cases and controls (P > .05). Despite these similarities, cases had significantly better survival (5-year disease-specific survival for cases vs controls, 67% vs 47%; P = .007). On multivariate analysis, metformin remained an independent predictor of survival (hazard ratio, 2.2; 95% confidence interval, 1.2-3.8; P = .007) after controlling for disease stage, grade, histology, chemotherapy, body mass index, and surgical cytoreduction.

CONCLUSIONS

The results of this study indicated an association of metformin intake with survival in patients with ovarian cancer. The receipt of metformin was associated with better survival, and the authors concluded that metformin is worthy of clinical trials in ovarian cancer.

Obesity, type 2 diabetes, and cancer: the insulin and IGF connection

Epidemiological studies suggest a positive association between obesity and type 2 diabetes mellitus (T2D) with the risk of cancer and cancer-related mortality. Insulin resistance, hyperinsulinemia, increased levels of IGF, elevated levels of steroid and peptide hormones, and inflammatory markers appear to play a role in the connection between these different diseases. Medications, such as metformin and exogenous insulin, used to treat T2D may affect the risk of cancer and cancer-related mortality. Newer therapies targeting the insulin and IGF1 systems are being developed for use in cancer therapy.

Over-expressions of AMPK subunits in ovarian carcinomas with significant clinical implications

Background

AMP-activated protein kinase (AMPK) has recently been considered as a potential target for cancer therapy. However, the expression status of various subunits of the heterotrimeric AMPK in human cancers is rarely reported. We decided to determine their expressions in ovarian carcinomas and their relationships with the disease.

Methods

Expressions and locations of the AMPK-α1, -α2, -β1, -β2, -γ1 and -γ2 were detected by quantitative PCR (Q-PCR) and immunohistochemical staining (IHC). Their expression levels in ovarian tumors were compared with normal controls and also correlated with clinicopathological parameters.

Results

Except AMPK-α1, expressions of the other five AMPK subunits are significantly higher in ovarian carcinomas as determined by Q-PCR. Although IHC detection of AMPK-γ1 and -γ2 were not successful, over-expressions of AMPK-α2, -β1, and -β2 were further confirmed by IHC. Over-expressions of various AMPK subunits occurred independently and were mainly detected in the cytoplasm. Interestingly, AMPK-α2 and -β1 were also detected in the nucleus and cell membrane, respectively. Clinical correlation analyses indicate that expressions of different AMPK subunits are associated with different subtypes of carcinoma. High expression of AMPK-α2 is significantly associated with endometrioid carcinomas. On the other hand, high expressions of AMPK-β and -γ subunits are associated with mucinous and serous carcinomas, respectively. Furthermore, high expressions of AMPK-β1 and -γ2 are also associated with early and late stages of disease, respectively. Finally, patients with high expression of AMPK-α2 had better prognosis.

Conclusions

Aberrant expressions of AMPK subunits may play important roles in ovarian carcinogenesis. Each AMPK subunit may have its own function other than just a component of the AMPK molecule. Correlations with clinical parameters suggest that expressions of AMPK subunits have different clinical implications in ovarian cancer development.

Metformin targets ovarian cancer stem cells in vitro and in vivo

PURPOSE

Studies in non-gynecologic tumors indicate that metformin inhibits growth of cancer stem cells (CSC). Diabetic patients with ovarian cancer who are taking metformin have better outcomes than those not taking metformin. The purpose of this study was to directly address the impact of metformin on ovarian CSC.

METHODS

The impact of metformin on ovarian cancer cell line growth and viability was assessed with trypan blue staining. Aldehyde dehydrogenase (ALDH) expressing CSC were quantified using FACS®. Tumor sphere assays were performed to determine the impact of metformin on cell line and primary human ovarian tumor CSC growth in vitro. In vivo therapeutic efficacy and the anti-CSC effects of metformin were confirmed using both tumor cell lines and ALDH(+) CSC tumor xenografts.

RESULTS

Metformin significantly restricted the growth of ovarian cancer cell lines in vitro. This effect was additive with cisplatin. FACS analysis confirmed that metformin reduced ALDH(+) ovarian CSC. Consistent with this, metformin also inhibited the formation of CSC tumor spheres from both cell lines and patient tumors. In vivo, metformin significantly increased the ability of cisplatin to restrict whole tumor cell line xenografts. In addition, metformin significantly restricted the growth of ALDH(+) CSC xenografts. This was associated with a decrease in ALDH(+) CSC, cellular proliferation, and angiogenesis.

CONCLUSIONS

Metformin can restrict the growth and proliferation of ovarian cancer stem cells in vitro and in vivo. This was true in cell lines and in primary human CSC isolates. These results provide a rationale for using metformin to treat ovarian cancer patients.

Enhanced cytotoxic effect of low doses of metformin combined with ionizing radiation on hepatoma cells via ATP deprivation and inhibition of DNA repair

Metformin, one of the most widely used antidiabetic drugs, has recently been associated with potential antitumorigenic effects. In this study, we evaluated the possible cytotoxic impact of combined low doses of metformin and ionizing radiation (IR) on 2 human hepatoma cell lines. The cytotoxic effect of metformin combined with IR was subsequently determined by clonogenic survival and cell cycle assays, assessment of mitochondrial complex I and lactate dehydrogenase (LDH) activity, measurement of cellular adenosine triphosphate (ATP) levels, comet assay and analyses of the formation and disappearance of phosphorylated histone H2AX (γ-H2AX) protein. The combination of metformin and IR caused a much stronger cytotoxicity than the treatment with metformin or IR alone, leading to an ~80% decrease in cell viability and ~35% increase in the accumulation of cells in the G2/M phase of the cell cycle in the 2 hepatoma cell lines. In addition, a reduction in mitochondrial complex I activity (~70%) and a significant increase in LDH activity, as well as lactate production were observed in the cells exposed to metformin. Interestingly, a severe depletion in ATP, increased olive tail moment and the delayed disappearance of γ-H2AX expression were detected in the hepatoma cells treated by metformin plus IR. These findings show that the combination of a low concentration of metformin and IR results in the considerable enhancement of cytotoxic effects in human hepatoma cell lines, leading to decreased DNA repair by reducing ATP production. The data provided in this study may elucidate the remarkable efficiency of this combination treatment and suggest that metformin may be used as a potential adjunct to the radiotherapy of hepatocellular carcinoma.

Metformin and phenethyl isothiocyanate combined treatment in vitro is cytotoxic to ovarian cancer cultures

BACKGROUND

High mortality rates in ovarian cancer are largely a result of resistance to currently used chemotherapies. Expanding therapies with a variety of drugs has the potential to reduce this high mortality rate. Metformin and phenethyl isothiocyanate (PEITC) are both potentially useful in ovarian cancer, and they are particularly attractive because of their safety.

METHODS

Cell proliferation of each drug and drug combination was evaluated by hemacytometry with Trypan blue exclusion or Sytox green staining for cell death. Levels of total and cleaved PARP were measured by Western blot. General cellular and mitochondrial reactive oxygen species were measured by flow cytometry and live cell confocal microscopy with the fluorescent dyes dihydroethidine and MitoSOX.

RESULTS

Individually, metformin and PEITC each show inhibition of cell growth in multiple ovarian cancer cell lines. Alone, PEITC was also able to induce apoptosis, whereas metformin was primarily growth inhibitory. Both total cellular and mitochondrial reactive oxygen species were increased when treated with either metformin or PEITC. The growth inhibitory effects of metformin were reversed by methyl succinate supplementation, suggesting complex I plays a role in metformin's anti-cancer mechanism. PEITC's anti-cancer effect was reversed by N-acetyl-cysteine supplementation, suggesting PEITC relies on reactive oxygen species generation to induce apoptosis. Metformin and PEITC together showed a synergistic effect on ovarian cancer cell lines, including the cisplatin resistant A2780cis.

CONCLUSIONS

Here we show that when used in combination, these drugs are effective in both slowing cancer cell growth and killing ovarian cancer cells in vitro. Furthermore, the combination of these drugs remains effective in cisplatin resistant cell lines. Novel combinations such as metformin and PEITC show promise in expanding ovarian cancer therapies and overcoming the high incidence of cisplatin resistant cancers.

Relationship of type II diabetes and metformin use to ovarian cancer progression, survival, and chemosensitivity

OBJECTIVE

To estimate whether metformin use by ovarian cancer patients with type II diabetes was associated with improved survival.

METHODS

We reviewed the effect of diabetes and diabetes medications on ovarian cancer treatment and outcomes in a single-institution retrospective cohort. Inclusion criteria were International Federation of Gynecology and Obstetrics stage I-IV epithelial ovarian, fallopian, or peritoneal cancer. Exclusion criteria were noninvasive pathology or nonepithelial malignancies. The primary exposures analyzed were history of type II diabetes and diabetes medications. The primary outcomes were progression-free and overall ovarian cancer survival.

RESULTS

Of the 341 ovarian cancer patients included in the study, 297 did not have diabetes, 28 were type II diabetic patients who did not use metformin, and 16 were type II diabetic patients who used metformin. The progression-free survival at 5 years was 51% for diabetic patients who used metformin compared with 23% for the nondiabetic patients and 8% for the diabetic patients who did not use metformin (P=.03). The overall survival at 5 years was 63%, 37%, and 23% for the diabetic patients who used metformin, the nondiabetic patients, and the diabetic patients who did not use metformin, respectively (P=.03). The patients with diabetes received the same treatment for ovarian cancer as the patients without diabetes. The association of metformin use and increased progression-free survival, but not overall survival, remained significant after controlling for standard clinicopathologic parameters.

CONCLUSION

In this ovarian cancer cohort, the patients with type II diabetes who used metformin had longer progression-free survival, despite receiving similar treatment for ovarian cancer.