Metformin prevents tobacco carcinogen--induced lung tumorigenesis

Metformin and cancer: Quo vadis et cui bono?

How many lives have already been saved by the anti-cancer drug metformin? Inadvertently perhaps, among the millions of type 2 diabetics with occult or known cancers and who have been prescribed metformin since the 1950s, thousands may have benefited from the anticancer properties of this first-line pharmacotherapy. Quo vadis? Now, researchers aim to move metformin from a non-targeted stage of cancer therapy that has been mostly developed retrospectively and empirically into a targeted therapy by following a biological rationale and a predefined mechanism of action. But, who might benefit from metformin? Cui bono? Because metformin is on the leading edge of a new generation of cancer metabolism-targeted therapies, perhaps it is the right time to provide solutions to the challenges that metformin and other onco-biguanides will face in the coming years before becoming incorporated into the therapeutic armamentarium against cancer.

Metformin Addition to Chemotherapy in Stage IV Non-Small Cell Lung Cancer: an Open Label Randomized Controlled Study

PURPOSE

To evaluate effects of metformin on clinical outcome of non-diabetic patients with stage IV NSCLC.

MATERIALS AND METHODS

A prospective, randomized, open-label, controlled pilot study was conducted on patients with stage IV NSCLC with an Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0-2, excluding patients with diabetes and lactic acidosis. Thirty chemo-naive, non-diabetic patients with stage IV NSCLC were enrolled. Fifteen patients received intravenous gemcitabine/cisplatin regimen alone (arm B) while fifteen patients received the same regimen plus daily oral metformin 500 mg (arm A). The effect of metformin on chemotherapy-response rates, survival, and adverse events in these patients was evaluated.

RESULTS

Objective response rate (ORR) and median overall survival (OS) in arms A and B were 46.7% versus 13.3% respectively, p=0.109 and 12 months versus 6.5 months, respectively, p=0.119. Median progression free survival (PFS) in arms A and B was 5.5 months versus 5 months, p=0.062. No significant increase in toxicity was observed in arm A versus arm B. Percentage of patients who experienced nausea was significantly lower in arm A versus arm B, at 26.7% versus 66.7% respectively, p=0.028.

CONCLUSIONS

Metformin administration reduced occurrence of chemotherapy induced-nausea. Non-statistically significant improvements in the ORR or OS were observed. Metformin had no effect on PFS.

Metformin requires 4E-BPs to induce apoptosis and repress translation of Mcl-1 in hepatocellular carcinoma cells

Metformin inhibits the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway, which is frequently upregulated in hepatocellular carcinoma (HCC). Metformin has also been shown to induce apoptosis in this cancer. Here, we investigate whether metformin-induced apoptosis in HCC is mediated by the downstream mTORC1 effectors eukaryotic initiation factor 4E and (eIF4E)-binding proteins (4E-BPs). Further, we ask whether changes in 4E-BPs activity during metformin treatment negatively regulate translation of the anti-apoptotic myeloid cell leukemia 1 (Mcl-1) mRNA. A genetic HCC mouse model was employed to assess the ability of metformin to reduce tumor formation, induce apoptosis, and control 4E-BP1 activation and Mcl-1 protein expression. In parallel, the HCC cell line Huh7 was transduced with scrambled shRNA (control) or shRNAs targeting 4E-BP1 and 4E-BP2 (4E-BP knock-down (KD)) to measure differences in mRNA translation, apoptosis, and Mcl-1 protein expression after metformin treatment. In addition, immunohistochemical staining of eIF4E and 4E-BP1 protein levels was addressed in a HCC patient tissue microarray. We found that metformin decreased HCC tumor burden, and tumor tissues showed elevated apoptosis with reduced Mcl-1 and phosphorylated 4E-BP1 protein levels. In control but not 4E-BP KD Huh7 cells, metformin induced apoptosis and repressed Mcl-1 mRNA translation and protein levels. Immunostaining of HCC patient tumor tissues revealed a varying ratio of eIF4E/4E-BP1 expression. Our results propose that metformin induces apoptosis in mouse and cellular models of HCC through activation of 4E-BPs, thus tumors with elevated expression of 4E-BPs may display improved clinical chemopreventive benefit of metformin.

Repurposing metformin for cancer treatment: current clinical studies

In recent years, several studies have presented evidence suggesting a potential role for metformin in anti-cancer therapy. Preclinical studies have demonstrated several anticancer molecular mechanisms of metformin including mTOR inhibition, cytotoxic effects, and immunomodulation. Epidemiologic data have demonstrated decreased cancer incidence and mortality in patients taking metformin. Several clinical trials, focused on evaluation of metformin as an anti-cancer agent are presently underway. Data published from a small number of completed trials has put forth intriguing results. Clinical trials in pre-surgical endometrial cancer patients exhibited a significant decrease in Ki67 with metformin monotherapy. Another interesting observation was made in patients with breast cancer, wherein a trend towards improvement in cancer proliferation markers was noted in patients without insulin resistance. Data on survival outcomes with the use of metformin as an anti-cancer agent is awaited. This manuscript will critically review the role of metformin as a potential cancer treatment.

ROS homeostasis and metabolism: a dangerous liason in cancer cells

Tumor cells harbor genetic alterations that promote a continuous and elevated production of reactive oxygen species. Whereas such oxidative stress conditions would be harmful to normal cells, they facilitate tumor growth in multiple ways by causing DNA damage and genomic instability, and ultimately, by reprogramming cancer cell metabolism. This review outlines the metabolic-dependent mechanisms that tumors engage in when faced with oxidative stress conditions that are critical for cancer progression by producing redox cofactors. In particular, we describe how the mitochondria has a key role in regulating the interplay between redox homeostasis and metabolism within tumor cells. Last, we will discuss the potential therapeutic use of agents that directly or indirectly block metabolism.

Molecular targets of metformin antitumor action

Epidemiological studies have shown that metformin, a first line therapeutic agent for diabetes mellitus, reduced the risk of developing various malignancies. Several preclinical studies established some possible mechanisms of its anticancer effects. The primary effect of metformin action is a decrease in cell energy status, which activates AMP-activated kinase (AMPK), a cellular metabolic sensor. This event is followed by a decrease in serum concentrations of insulin and insulin growth factor I (IGF-I), the potent mitogens for cancer cells. In addition to the indirect mode of action, metformin may exhibit direct inhibitory effect on cancer cells by targeting mammalian target of rapamycin (mTOR) signaling and anabolic processes. This review gathers information on mechanisms of metformin antitumor activity, with special attention given to the impact of this antidiabetic drug on insulin/PI3K/mTOR and AMPK signaling. Furthermore, the factors required for this novel activity of metformin are discussed.

Targeting AMPK for cancer prevention and treatment

AMP-activated protein kinase (AMPK) is an important mediator in maintaining cellular energy homeostasis. AMPK is activated in response to a shortage of energy. Once activated, AMPK can promote ATP production and regulate metabolic energy. AMPK is a known target for treating metabolic syndrome and type-2 diabetes; however, recently AMPK is emerging as a possible metabolic tumor suppressor and target for cancer prevention and treatment. Recent epidemiological studies indicate that treatment with metformin, an AMPK activator reduces the incidence of cancer. In this article we review the role of AMPK in regulating inflammation, metabolism, and other regulatory processes with an emphasis on cancer, as well as, discuss the potential for targeting AMPK to treat various types of cancer. Activation of AMPK has been found to oppose tumor progression in several cancer types and offers a promising cancer therapy. This review evaluates the evidence linking AMPK with tumor suppressor function and analyzes the molecular mechanisms involved. AMPK activity opposes tumor development and progression in part by regulating inflammation and metabolism.

Fundamentals of cancer metabolism

Tumors reprogram pathways of nutrient acquisition and metabolism to meet the bioenergetic, biosynthetic, and redox demands of malignant cells. These reprogrammed activities are now recognized as hallmarks of cancer, and recent work has uncovered remarkable flexibility in the specific pathways activated by tumor cells to support these key functions. In this perspective, we provide a conceptual framework to understand how and why metabolic reprogramming occurs in tumor cells, and the mechanisms linking altered metabolism to tumorigenesis and metastasis. Understanding these concepts will progressively support the development of new strategies to treat human cancer.

Metformin-induced energy deficiency leads to the inhibition of lipogenesis in prostate cancer cells

The deregulation of lipid metabolism is a hallmark of tumor cells, and elevated lipogenesis has been reported in prostate cancer. Metformin, a drug commonly prescribed for type II diabetes, displays antitumor properties. Here, we show that metformin inhibits lipogenesis in several prostate cancer cell lines. In LNCaP cells, this effect parallels the decrease of key lipogenic proteins: ACC (acetyl-CoA carboxylase), FASN (fatty acid synthase) and SREBP1c (sterol regulatory element binding protein-1c), whereas there is no modification in DU145 and PC3 cells. Despite the relatively high level of lipogenic proteins induced by the overexpression of a constitutively active form of SREBP1c or treatment with androgens, metformin is still able to inhibit lipogenesis. Metformin does not alter the concentration of malonyl-CoA (the fatty acid precursor), and it only slightly decreases the NADPH levels, which is a co-factor required for lipogenesis, in LNCaP. Finally, we show that the inhibitory effect of metformin on lipogenesis is primarily due to a cellular energy deficit. Metformin decreases ATP in a dose-dependent manner, and this diminution is significantly correlated with the inhibition of lipogenesis in LNCaP and DU145. Indeed, the effect of metformin is linked to changes in the ATP content rather than the regulation of protein expression. Our results describe a new mechanism of action for metformin on prostate cancer metabolism.

Molecular chaperone GRP78 enhances aggresome delivery to autophagosomes to promote drug resistance in multiple myeloma

Despite the clinical benefit of the proteasome inhibitor bortezomib, multiple myeloma (MM) patients invariably relapse through poorly defined mechanisms. Myeloma cells inevitably develop chemoresistance that leads to disease relapse and patient-related deaths. Studies in tumor cell lines and biopsies obtained from patients refractory to therapy have revealed that myeloma cells adapt to stress by inducing expression of glucose-regulated protein 78 (GRP78), an endoplasmic reticulum (ER) chaperone with anti-apoptotic properties. Treatment of myeloma cells with bortezomib increased GRP78 levels and activated GRP78-dependent autophagy. Expression profiling indicated that GRP78-encoding HSPA5 was significantly upregulated in bortezomib-resistant cells. Co-treatment with the anti-diabetic agent metformin suppressed GRP78 and enhanced the anti-proliferative effect of bortezomib. Bortezomib treatment led to GRP78 co-localization with proteotoxic protein aggregates, known as aggresomes. Pharmacologic suppression, genetic ablation or mutational inactivation of GRP78 followed by bortezomib treatment led to the accumulation of aggresomes but impaired autophagy and enhanced anti-myeloma effect of bortezomib. GRP78 was co-immunoprecipitated with the KDEL receptor, an ER quality control regulator that binds proteins bearing the KDEL motif to mediate their retrieval from the Golgi complex back to the ER. Taken together, we demonstrate that inhibition of GRP78 functional activity disrupts autophagy and enhances the anti-myeloma effect of bortezomib.

Tristetraprolin mediates the anti-proliferative effects of metformin in breast cancer cells

Metformin, which is a drug commonly prescribed to treat type 2 diabetes, has anti-proliferative effects in cancer cells; however, the molecular mechanisms underlying this effect remain largely unknown. The aim is to investigate the role of tristetraprolin (TTP), an AU-rich element-binding protein, in anti-proliferative effects of metformin in cancer cells. p53 wild-type and p53 mutant breast cancer cells were treated with metformin, and expression of TTP and c-Myc was analyzed by semi-quantitative RT-PCR, Western blots, and promoter activity assay. Breast cancer cells were transfected with siRNA against TTP to inhibit TTP expression or c-Myc and, after metformin treatment, analyzed for cell proliferation by MTS assay. Metformin induces the expression of tristetraprolin (TTP) in breast cancer cells in a p53-independent manner. Importantly, inhibition of TTP abrogated the anti-proliferation effect of metformin. We observed that metformin decreased c-Myc levels, and ectopic expression of c-Myc blocked the effect of metformin on TTP expression and cell proliferation. Our data indicate that metformin induces TTP expression by reducing the expression of c-Myc, suggesting a new model whereby TTP acts as a mediator of metformin’s anti-proliferative activity in cancer cells.

Targeting AMPK for the Alleviation of Pathological Pain

Chronic pain is a major clinical problem that is poorly treated with available therapeutics. Adenosine monophosphate-activated protein kinase (AMPK) has recently emerged as a novel target for the treatment of pain with the exciting potential for disease modification. AMPK activators inhibit signaling pathways that are known to promote changes in the function and phenotype of peripheral nociceptive neurons and promote chronic pain. AMPK activators also reduce the excitability of these cells suggesting that AMPK activators may be efficacious for the treatment of chronic pain disorders, like neuropathic pain, where changes in the excitability of nociceptors is thought to be an underlying cause. In agreement with this, AMPK activators have now been shown to alleviate pain in a broad variety of preclinical pain models indicating that this mechanism might be engaged for the treatment of many types of pain in the clinic. A key feature of the effect of AMPK activators in these models is that they can lead to a long-lasting reversal of pain hypersensitivity even long after treatment cessation, indicative of disease modification. Here, we review the evidence supporting AMPK as a novel pain target pointing out opportunities for further discovery that are likely to have an impact on drug discovery efforts centered around potent and specific allosteric activators of AMPK for chronic pain treatment.

Obesity and cancer, a case for insulin signaling

Obesity is a worldwide epidemic, with the number of overweight and obese individuals climbing from just over 500 million in 2008 to 1.9 billion in 2014. Type 2 diabetes (T2D), cardiovascular disease and non-alcoholic fatty liver disease have long been associated with the obese state, whereas cancer is quickly emerging as another pathological consequence of this disease. Globally, at least 2.8 million people die each year from being overweight or obese. It is estimated that by 2020 being overweight or obese will surpass the health burden of tobacco consumption. Increase in the body mass index (BMI) in overweight (BMI>25 kg/m²) and obese (BMI>30 kg/m²) individuals is a result of adipose tissue (AT) expansion, which can lead to fat comprising >50% of the body weight in the morbidly obese. Extensive research over the last several years has painted a very complex picture of AT biology. One clear link between AT expansion and etiology of diseases like T2D and cancer is the development of insulin resistance (IR) and hyperinsulinemia. This review focuses on defining the link between obesity, IR and cancer.

Pharmacological Modulation of Lung Carcinogenesis in Smokers: Preclinical and Clinical Evidence

Many drugs in common use possess pleiotropic properties that make them capable of interfering with carcinogenesis mechanisms. We discuss here the ability of pharmacological agents to mitigate the pulmonary carcinogenicity of mainstream cigarette smoke. The evaluated agents include anti-inflammatory drugs (budesonide, celecoxib, aspirin, naproxen, licofelone), antidiabetic drugs (metformin, pioglitazone), antineoplastic agents (lapatinib, bexarotene, vorinostat), and other drugs and supplements (phenethyl isothiocyanate, myo-inositol, N-acetylcysteine, ascorbic acid, berry extracts). These drugs have been evaluated in mouse models mimicking interventions either in current smokers or in ex-smokers, or in prenatal chemoprevention. They display a broad spectrum of activities by attenuating either smoke-induced preneoplastic lesions or benign tumors and/or malignant tumors. Together with epidemiological data, these findings provide useful information to predict the potential effects of pharmacological agents in smokers.

Evolving Lessons on the Complex Role of AMPK in Normal Physiology and Cancer

AMP kinase (AMPK) is an evolutionarily conserved enzyme required for adaptive responses to various physiological and pathological conditions. AMPK executes numerous cellular functions, some of which are often perceived at odds with each other. While AMPK is essential for embryonic growth and development, its full impact in adult tissues is revealed under stressful situations that organisms face in the real world. Conflicting reports about its cellular functions, particularly in cancer, are intriguing and a growing number of AMPK activators are being developed to treat human diseases such as cancer and diabetes. Whether these drugs will have only context-specific benefits or detrimental effects in the treatment of human cancer will be a subject of intense research. Here we review the current state of AMPK research with an emphasis on cancer and discuss the yet unresolved context-dependent functions of AMPK in human cancer.

Control of PD-L1 Expression by Oncogenic Activation of the AKT-mTOR Pathway in Non-Small Cell Lung Cancer

Alterations in EGFR, KRAS, and ALK are oncogenic drivers in lung cancer, but how oncogenic signaling influences immunity in the tumor microenvironment is just beginning to be understood. Immunosuppression likely contributes to lung cancer, because drugs that inhibit immune checkpoints like PD-1 and PD-L1 have clinical benefit. Here, we show that activation of the AKT-mTOR pathway tightly regulates PD-L1 expression in vitro and in vivo. Both oncogenic and IFNγ-mediated induction of PD-L1 was dependent on mTOR. In human lung adenocarcinomas and squamous cell carcinomas, membranous expression of PD-L1 was significantly associated with mTOR activation. These data suggest that oncogenic activation of the AKT-mTOR pathway promotes immune escape by driving expression of PD-L1, which was confirmed in syngeneic and genetically engineered mouse models of lung cancer where an mTOR inhibitor combined with a PD-1 antibody decreased tumor growth, increased tumor-infiltrating T cells, and decreased regulatory T cells.

Sustained proliferation in cancer: Mechanisms and novel therapeutic targets

Proliferation is an important part of cancer development and progression. This is manifest by altered expression and/or activity of cell cycle related proteins. Constitutive activation of many signal transduction pathways also stimulates cell growth. Early steps in tumor development are associated with a fibrogenic response and the development of a hypoxic environment which favors the survival and proliferation of cancer stem cells. Part of the survival strategy of cancer stem cells may manifested by alterations in cell metabolism. Once tumors appear, growth and metastasis may be supported by overproduction of appropriate hormones (in hormonally dependent cancers), by promoting angiogenesis, by undergoing epithelial to mesenchymal transition, by triggering autophagy, and by taking cues from surrounding stromal cells. A number of natural compounds (e.g., curcumin, resveratrol, indole-3-carbinol, brassinin, sulforaphane, epigallocatechin-3-gallate, genistein, ellagitannins, lycopene and quercetin) have been found to inhibit one or more pathways that contribute to proliferation (e.g., hypoxia inducible factor 1, nuclear factor kappa B, phosphoinositide 3 kinase/Akt, insulin-like growth factor receptor 1, Wnt, cell cycle associated proteins, as well as androgen and estrogen receptor signaling). These data, in combination with bioinformatics analyses, will be very important for identifying signaling pathways and molecular targets that may provide early diagnostic markers and/or critical targets for the development of new drugs or drug combinations that block tumor formation and progression.

Metformin and trametinib have synergistic effects on cell viability and tumor growth in NRAS mutant cancer

Attempts to directly block the mutant neuroblastoma rat sarcoma oncogene (NRAS) protein, a driving mutation in many cancer types, have been unsuccessful. Current treatments focus on inhibition of different components of NRAS' two main downstream cascades: PI3K/AKT/mTOR and MAPK. Here we test a novel dual therapy combination of metformin and trametinib on a panel of 16 NRAS mutant cell lines, including melanoma cells, melanoma cells with acquired trametinib resistance, lung cancer and neuroblastoma cells. We show that both of the main downstream cascades of NRAS can be blocked by this combination: metformin indirectly inhibits the PI3K/AKT/mTOR pathway and trametinib directly impedes the MAPK pathway. This dual therapy synergistically reduced cell viability in vitro and xenograft tumor growth in vivo. We conclude that metformin and trametinib combinations are effective in preclinical models and may be a possible option for treatment of NRAS mutant cancers.

Metformin for cancer and aging prevention: is it a time to make the long story short?

During the last decade, the burst of interest is observed to antidiabetic biguanide metformin as candidate drug for cancer chemoprevention. The analysis of the available data have shown that the efficacy of cancer preventive effect of metformin (MF) and another biguanides, buformin (BF) and phenformin (PF), has been studied in relation to total tumor incidence and to 17 target organs, in 21 various strains of mice, 4 strains of rats and 1 strain of hamsters (inbred, outbred, transgenic, mutant), spontaneous (non- exposed to any carcinogenic agent) or induced by 16 chemical carcinogens of different classes (polycycIic aromatic hydrocarbons, nitroso compounds, estrogen, etc.), direct or indirect (need metabolic transformation into proximal carcinogen), by total body X-rays and γ- irradiation, viruses, genetic modifications or special high fat diet, using one stage and two-stage protocols of carcinogenesis, 5 routes of the administration of antidiabetic biguanides (oral gavage, intraperitoneal or subcutaneous injections, with drinking water or with diet) in a wide ranks of doses and treatment regimens. In the majority of cases (86%) the treatment with biguanides leads to inhibition of carcinogenesis. In 14% of the cases inhibitory effect of the drugs was not observed. Very important that there was no any case of stimulation of carcinogenesis by antidiabetic biguanides. It was conclude that there is sufficient experimental evidence of anti-carcinogenic effect of antidiabetic biguanides.

Metformin inhibits salivary adenocarcinoma growth through cell cycle arrest and apoptosis

The inhibitory effects of metformin have been observed in many types of cancer. However, its effect on human salivary gland carcinoma is unknown. The effect of metformin alone or in combination with pp242 (an mTOR inhibitor) on salivary adenocarcinoma cells growth were determined in vitro and in vivo. We found that metformin suppressed HSY cell growth in vitro in a time and dose dependent manner associated with a reduced expression of MYC onco-protein, and the same inhibitory effect of metformin was also confirmed in HSG cells. In association with the reduction of MYC onco-protein, metformin significantly restored p53 tumor suppressor gene expression. The distinctive effects of metformin and PP242 on MYC reduction and P53 restoration suggested that metformin inhibited cell growth through a different pathway from PP242 in salivary carcinoma cells. Furthermore, the anti-tumor efficacy of metformin was confirmed in vivo as indicated by the increases of tumor necrosis and reduced proliferation in xenograft tumors from metformin treated group. For the first time, the inhibitory effect of metformin on human salivary gland tumor cells was documented. Moreover, metformin inhibitory effects were enhanced by mTOR inhibitor suggesting that metformin and mTOR inhibitor utilize distinctive signaling pathways to suppress salivary tumor growth.

Lasting glycolytic stress governs susceptibility to urethane-induced lung carcinogenesis in vivo and in vitro

Urethane is a recognized genotoxic carcinogen in fermented foods and beverages. This study is to compare susceptibility of ICR mice, BALB/c mice and C57BL/6 mice to urethane-induced lung carcinogenesis. The mice were injected intraperitoneally with 600 mg/kg of urethane for three times or ten times at 7-day intervals. At week 26, lung carcinogenic incidence was found in 40% ICR mice, 20% BALB/c mice and 10% C57BL/6 mice of the 3× injection group, respectively, whereas 100% lung tumor incidence took place in three mouse strains of the 10× injection group. In the 10× injection group, urethane induced lasting glycolytic stress of lung with an increase in lactate, monocarboxylate transporter 1 (MCT-1), reactive oxygen species(ROS) and 7,8-dihydro-8-oxo-29-deoxyguanosine (8-OHdG) and a decrease in pyruvate dehydrogenase (PDH) and cytochrome C oxidase (COX). In the 3× injection group, urethane also promoted lung glycolytic stress at the end of urethane injection but it lasted no more than 7 days besides in lung tumor-bearing mice. Metformin as a glycolytic enhancer promoted urethane carcinogenic efficacy in the 3× injection group, whereas 2-deoxy-glucose (2-DG) as a glycolytic inhibitor decreased urethane carcinogenic efficacy in the 10× injection group. Further, urethane promoted tumor survival in A549 cells by inducing cancer stem-like cellular state. These data suggest that lasting glycolytic stress is sufficient for urethane-induced lung tumorigenesis, and that urethane 10× injection-induced lung cancer can serve as a valuable model for lung tumor biology and tumor prevention.

Effects of metformin on clinical outcome in diabetic patients with advanced HCC receiving sorafenib

BACKGROUND AND OBJECTIVE

Several studies have reported an association between type 2 diabetes mellitus and hepatocellular carcinoma (HCC). Data from several retrospective studies and meta-analyses have highlighted a reduction of about 50% in the risk of developing HCC in cirrhotic patients treated with metformin for diabetes. The aim of this study was to evaluate the different outcomes of patients who received or did not receive metformin during treatment with sorafenib.

METHODS

We analyzed 93 patients consecutively treated with sorafenib. Forty-two (45.2%) patients were diabetic, of whom 31 were on metformin. Progression-free survival (PFS) and overall survival (OS) were estimated with the Kaplan-Meier method and compared with the log-rank test.

RESULTS

The concomitant use of sorafenib and metformin was associated with a median PFS of 2.6 months (95% CI 1.9-3.3) compared to 5.0 months (95% CI 2.5-8.2) for patients receiving sorafenib alone (p = 0.029). The median OS of patients treated with the combination was 10.4 months (95% CI 3.9-14.4) compared to 15.1 months (95% CI 11.7-17.8) for those who were not given metformin (p = 0.014).

CONCLUSIONS

Our findings could be the result of increased tumor aggressiveness and resistance to sorafenib in metformin-treated patients.

Metformin use and lung cancer risk in patients with diabetes

Methodologic biases may explain why observational studies examining metformin use in relation to lung cancer risk have produced inconsistent results. We conducted a cohort study to further investigate this relationship, accounting for potential biases. For 47,351 patients with diabetes ages ≥40 years, who completed a health-related survey administered between 1994 and 1996, data on prescribed diabetes medications were obtained from electronic pharmacy records. Follow-up for incident lung cancer occurred from January 1, 1997, until June 30, 2012. Using Cox regression, we estimated lung cancer risk associated with new use of metformin, along with total duration, recency, and cumulative dose (all modeled as time-dependent covariates), adjusting for potential confounding factors. During 428,557 person-years of follow-up, 747 patients were diagnosed with lung cancer. No association was found with duration, dose, or recency of metformin use and overall lung cancer risk. Among never smokers, however, ever use was inversely associated with lung cancer risk [HR, 0.57; 95% confidence interval (CI), 0.33-0.99], and risk appeared to decrease monotonically with longer use (≥5 years: HR, 0.48; 95% CI, 0.21-1.09). Among current smokers, corresponding risk estimates were >1.0, although not statistically significant. Consistent with this variation in effect by smoking history, longer use was suggestively associated with lower adenocarcinoma risk (HR, 0.69; 95% CI, 0.40-1.17), but higher small cell carcinoma risk (HR, 1.82; 95% CI, 0.85-3.91). In this population, we found no evidence that metformin use affects overall lung cancer risk. The observed variation in association by smoking history and histology requires further confirmation.

Metformin: risk-benefit profile with a focus on cancer

INTRODUCTION

Epidemiological evidence suggests an increased incidence of cancer in obese, prediabetic, and diabetic patients and a reduced risk of cancer incidence and mortality in diabetic patients on metformin compared with other antidiabetic drugs. In vitro studies support the efficacy of metformin in cancer therapy and prevention. Although metformin seems to be promising as a cancer chemopreventive or therapeutic drug, the principal consideration is whether metformin will be effective in cancer clinical trials for nondiabetic subjects or only in diabetics or subjects with insulin resistance. Safety of metformin is even more important in treating nondiabetic patients.

AREAS COVERED

The present review focuses on epidemiological data and clinical trials testing the efficacy of metformin on cancer, the safety in nondiabetic patients and the future development of this promising drug.

EXPERT OPINION

Meta-analyses of epidemiological in which metformin treatment has been used for diabetic patients show a positive trend for benefit; nevertheless, clinical data outcomes are preliminary and the results of ongoing trials are awaited. The different types of cancer, heterogeneity of populations and presence of comorbidity make it difficult to determine the benefits of metformin in cancer prevention and treatment.

Repurposing old drugs to chemoprevention: the case of metformin

Multiple epidemiologic studies have documented an association between the anti-diabetic agent metformin and reduced cancer incidence and mortality. However, this effect has not been consistently demonstrated in animal models or more recent epidemiological studies. The purpose of this paper is to examine metformin's chemopreventive potential by reviewing relevant mechanisms of action, preclinical evidence of efficacy, updated epidemiologic evidence after correction for potential biases and confounders, and recently completed and ongoing clinical trials. Although repurposing drugs with well described mechanisms of action and safety profiles is an appealing strategy for cancer prevention, there is no substitute for well executed late phase clinical trials to define efficacy and populations that are most likely to benefit from an intervention.

Metformin and erlotinib synergize to inhibit basal breast cancer

Basal-like breast cancers (BBCs) are enriched for increased EGFR expression and decreased expression of PTEN. We found that treatment with metformin and erlotinib synergistically induced apoptosis in a subset of BBC cell lines. The drug combination led to enhanced reduction of EGFR, AKT, S6 and 4EBP1 phosphorylation, as well as prevented colony formation and inhibited mammosphere outgrowth. Our data with other compounds suggested that biguanides combined with EGFR inhibitors have the potential to outperform other targeted drug combinations and could be employed in other breast cancer subtypes, as well as other tumor types, with activated EGFR and PI3K signaling. Analysis of BBC cell line alterations led to the hypothesis that loss of PTEN sensitized cells to the drug combination which was confirmed using isogenic cell line models with and without PTEN expression. Combined metformin and erlotinib led to partial regression of PTEN-null and EGFR-amplified xenografted MDA-MB-468 BBC tumors with evidence of significant apoptosis, reduction of EGFR and AKT signaling, and lack of altered plasma insulin levels. Combined treatment also inhibited xenografted PTEN null HCC-70 BBC cells. Measurement of trough plasma drug levels in xenografted mice and a separately performed pharmacokinetics modeling study support possible clinical translation.

Metformin repositioning as antitumoral agent: selective antiproliferative effects in human glioblastoma stem cells, via inhibition of CLIC1-mediated ion current

Epidemiological and preclinical studies propose that metformin, a first-line drug for type-2 diabetes, exerts direct antitumor activity. Although several clinical trials are ongoing, the molecular mechanisms of this effect are unknown.

Here we show that chloride intracellular channel-1 (CLIC1) is a direct target of metformin in human glioblastoma cells. Metformin exposure induces antiproliferative effects in cancer stem cell-enriched cultures, isolated from three individual WHO grade IV human glioblastomas. These effects phenocopy metformin-mediated inhibition of a chloride current specifically dependent on CLIC1 functional activity. CLIC1 ion channel is preferentially active during the G1-S transition via transient membrane insertion. Metformin inhibition of CLIC1 activity induces G1 arrest of glioblastoma stem cells. This effect was time-dependent, and prolonged treatments caused antiproliferative effects also for low, clinically significant, metformin concentrations. Furthermore, substitution of Arg29 in the putative CLIC1 pore region impairs metformin modulation of channel activity.

The lack of drugs affecting cancer stem cell viability is the main cause of therapy failure and tumor relapse. We identified CLIC1 not only as a modulator of cell cycle progression in human glioblastoma stem cells but also as the main target of metformin's antiproliferative activity, paving the way for novel and needed pharmacological approaches to glioblastoma treatment.

Metformin and cancer: Between the bioenergetic disturbances and the antifolate activity

For decades, metformin has been the first-line drug for the treatment of type II diabetes mellitus, and it thus is the most widely prescribed antihyperglycemic drug. Retrospective studies associate the use of metformin with a reduction in cancer incidence and cancer-related death. However, despite extensive research about the molecular effects of metformin in cancer cells, its mode of action remains controversial. In this review, we summarize the current molecular evidence in an effort to elucidate metformin's mode of action against cancer cells. Some authors describe that metformin acts directly on mitochondria, inhibiting complex I and restricting the cell's ability to cope with energetic stress. Furthermore, as the drug interrupts the tricarboxylic acid cycle, metformin-induced alteration of mitochondrial function leads to a compensatory increase in lactate and glycolytic ATP. It has also been reported that cell cycle arrest, autophagy, apoptosis and cell death induction is mediated by the activation of AMPK and Redd1 proteins, thus inhibiting the mTOR pathway. Additionally, unbiased metabolomics studies have provided strong evidence to support that metformin alters the methionine and folate cycles, with a concomitant decrease in nucleotide synthesis. Indeed, purines such as thymidine or hypoxanthine restore the proliferation of tumor cells treated with metformin in vitro. Consequently, some authors prefer to refer to metformin as an "antimetabolite drug" rather than a "mitochondrial toxin". Finally, we also review the current controversy concerning the relationship between the experimental conditions of in vitro-reported effects and the plasma concentrations achieved by chronic treatment with metformin.

Metformin represses androgen-dependent and androgen-independent prostate cancers by targeting androgen receptor

BACKGROUND

Metformin has been reported to inhibit the growth of different types of cancers, including prostate cancer. We were interested to understand if the effect of metformin on prostate cancer is AR-dependent and, if so, whether metformin could act synergistically with the other anti-AR agents to serve as a therapeutic regimen with high efficacy and low toxicity.

METHODS

Cell viabilities and apoptosis were determined by MTT assay and annexin V-FITC staining, respectively, when the two human prostate cancer cell lines, the androgen-dependent LNCaP and the androgen-independent 22RV1 were treated with metformin alone or in combination with bicalutamide. Quantitative RT-PCR and western blotting assays were conducted to examine metformin effects on AR mRNA and protein levels, respectively. Chromatin immunoprecipitation (ChIP) assays were conducted to confirm the recruitment of AR to the ARE(s) located on the promoter region of the AR target gene PSA.

RESULTS

Metformin treatment reduced cell viability and enhanced apoptosis for both cell lines and additive effects were observed when LNCaP cells were treated with combined metformin and bicalutamide. Metformin down-regulated full-length AR protein in LNCaP cells. Both full-length and the truncated AR (AR-v7) were down-regulated by metformin in CWR22Rv1 cells. In both LNCaP and CWR22Rv1 cells, metformin repressed AR signaling pathway not by affecting AR protein degradation/stability, but rather through down-regulating the levels of AR mRNAs.

CONCLUSIONS

Metformin represses prostate cancer cell viability and enhances apoptosis by targeting the AR signaling pathway. Combinations of metformin and other anti-AR agents pose a potentially promising therapeutic approach for treatment of prostate cancers, especially the castrate-resistant prostate cancer, with high efficacy and low toxicity.

Treatment Strategies that Enhance the Efficacy and Selectivity of Mitochondria-Targeted Anticancer Agents

Nearly a century has passed since Otto Warburg first observed high rates of aerobic glycolysis in a variety of tumor cell types and suggested that this phenomenon might be due to an impaired mitochondrial respiratory capacity in these cells. Subsequently, much has been written about the role of mitochondria in the initiation and/or progression of various forms of cancer, and the possibility of exploiting differences in mitochondrial structure and function between normal and malignant cells as targets for cancer chemotherapy. A number of mitochondria-targeted compounds have shown efficacy in selective cancer cell killing in pre-clinical and early clinical testing, including those that induce mitochondria permeability transition and apoptosis, metabolic inhibitors, and ROS regulators. To date, however, none has exhibited the standards for high selectivity and efficacy and low toxicity necessary to progress beyond phase III clinical trials and be used as a viable, single modality treatment option for human cancers. This review explores alternative treatment strategies that have been shown to enhance the efficacy and selectivity of mitochondria-targeted anticancer agents in vitro and in vivo, and may yet fulfill the clinical promise of exploiting the mitochondrion as a target for cancer chemotherapy.

Therapeutic Effects of Repurposed Therapies in Non-Small Cell Lung Cancer: What Is Old Is New Again

The recent emergence of targeted and immunotherapeutic agents has dramatically changed the management for patients with non-small cell lung cancer (NSCLC). Despite these advances, lung cancer is not exempt from the challenges facing oncology drug development, including the huge financial cost and the time required for drug implementation. Repositioning noncancer therapies with potential antineoplastic properties into new therapeutic niches is an alternative treatment strategy offering the possibility of saving money and time and improving outcomes. The goal of such a strategy is to deliver an effective drug with a favorable toxicity profile at a reduced cost. Preclinical models and observational data have demonstrated promising activity for many of these agents, and they are now being studied in prospective trials. We review the relevant published data regarding the therapeutic effects of metformin, statins, nonsteroidal anti-inflammatory drugs, β-blockers, and itraconazole in NSCLC, with a focus on the putative mechanisms of action and clinical data. As these drugs are increasingly being tested in clinical trials, we aim to highlight the salient challenges and future strategies to optimize this approach.

Tobacco carcinogen NNK-induced lung cancer animal models and associated carcinogenic mechanisms

Tobacco usage is a major risk factor in the development, progression, and outcomes for lung cancer. Of the carcinogens associated with lung cancer, tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is among the most potent ones. The oncogenic mechanisms of NNK are not entirely understood, hindering the development of effective strategies for preventing and treating smoking-associated lung cancers. Here, we introduce the NNK-induced lung cancer animal models in different species and its potential mechanisms. Finally, we summarize several chemopreventive agents developed from these animal models.

Prognosis of small cell lung cancer patients with diabetes treated with metformin

BACKGROUNDS

It has been reported that metformin has an anticancer impact in various solid tumors, but its role in small cell lung cancer (SCLC) remains unclear. This study aimed to investigate the effect of metformin on survival in diabetic SCLC patients.

METHODS

A total of 79 SCLC patients with diabetes treated in our hospital between 2000 and 2010 were enrolled. The clinicopathological data and survival time were collected and evaluated. Univariate and multivariate analyses were used to investigate the association between metformin use and the survival of SCLC.

RESULTS

Among the 79 diabetic patients, 36 patients took metformin. The median OS and DFS were significantly better in the metformin group compared to non-metformin group (OS 18.0 vs 11.5 months, p < 0.001; DFS 10.8 vs 6.5 months, p < 0.001). Multivariate Cox analysis indicated that metformin use was an independent prognostic factor for long-term outcome (HR = 0.549, 95 % CI 0.198-0.978, p = 0.001).

CONCLUSIONS

The prognosis of SCLC patients with diabetes treated with metformin was improved, which might be considered a potential useful anticancer drug in treating SCLC patients.

Antidiabetic drugs and risk of cancer

Antidiabetic drugs are an important group of medications used worldwide. They differ from each other in the mechanisms of lowering blood glucose as well as in adverse effects that may affect the course of the treatment and its efficacy. In recent years, new drugs have been discovered in order to improve the maintenance of proper blood glucose level and to reduce unwanted effects of these drugs. Their growing administration is related to the increasing incidence of diabetes observed in all countries in the world. Epidemiological data indicate that diabetes increases the risk of cancer, as well as the risk of death linked with neoplasms. It is still unknown whether this is an effect of antidiabetic drugs or just the effect of diabetes itself. In recent years there have been numerous investigations and meta-analyzes, based on both comparative and cohort studies trying to establish the relationship between antidiabetic pharmacotherapy and the incidence and mortality due to cancer. According to their findings, most of antidiabetic drugs increase the risk of cancer while only few of them show antitumor properties. Different mechanisms of action of glucose-lowering drugs may be responsible for these effects. However, most of the published studies concerning the influence of these drugs on cancer incidence were designed with some limitations and differed from each other in the approach. In this review, we discuss the association between antidiabetic drugs used in monotherapy or polytherapy and cancer risk, and consider potential mechanisms responsible for the observed effects.

Metformin increases peroxisome proliferator-activated receptor γ Co-activator-1α and utrophin a expression in dystrophic skeletal muscle

INTRODUCTION

Metformin (MET) stimulates skeletal muscle AMP-activated protein kinase (AMPK), a key phenotype remodeling protein with emerging therapeutic relevance for Duchenne muscular dystrophy (DMD). Our aim was to identify the mechanism of impact of MET on dystrophic muscle.

METHODS

We investigated the effects of MET in cultured C2 C12 muscle cells and mdx mouse skeletal muscle. Expression of potent phenotypic modifiers was assessed, including peroxisome proliferator-activated receptor (PPAR)γ coactivator-1α (PGC-1α), PPARδ, and receptor-interacting protein 140 (RIP140), as well as that of the dystrophin-homolog, utrophin A.

RESULTS

In C2 C12 cells, MET augmented expression of PGC-1α, PPARδ, and utrophin A, whereas RIP140 content was reciprocally downregulated. MET treatment of mdx mice increased PGC-1α and utrophin A and normalized RIP140 levels.

CONCLUSIONS

In this study we identify the impact of MET on skeletal muscle and underscore the timeliness and importance of investigating MET and other AMPK activators as relevant therapeutics for DMD.

Metformin suppresses pancreatic tumor growth with inhibition of NFκB/STAT3 inflammatory signaling

OBJECTIVES

To further elucidate the anticancer mechanisms of metformin against pancreatic cancer, we evaluated the inhibitory effects of metformin on pancreatic tumorigenesis in a genetically engineered mouse model and investigated its possible anti-inflammatory and antiangiogenesis effects.

METHODS

Six-week-old LSL-Kras;Trp53 mice (10 per group) were administered once daily intraperitoneally with saline (control) for 1 week or metformin (125 mg/kg) for 1 week (Met_1wk) or 3 weeks (Met_3wk) before tumor initiation. All mice continued with their respective injections for 6 weeks after tumor initiation. Molecular changes were evaluated through quantitative polymerase chain reaction, immunohistochemistry, and Western blotting.

RESULTS

At euthanasia, pancreatic tumor volume in the Met_1wk (median, 181.8 mm) and Met_3wk (median, 137.9 mm) groups was significantly lower than those in the control group (median, 481.1 mm; P = 0.001 and 0.0009, respectively). No significant difference was observed between the Met_1wk and Met_3wk groups (P = 0.51). These results were further confirmed using tumor weight and tumor burden measurements. Furthermore, metformin treatment decreased the phosphorylation of nuclear factor κB and signal transducer and activator of transcription 3 as well as the expression of specificity protein 1 transcription factor and several nuclear factor κB-regulated genes.

CONCLUSIONS

Metformin may inhibit pancreatic tumorigenesis by modulating multiple molecular targets in inflammatory pathways.

Survival of patients with stage IV lung cancer with diabetes treated with metformin

RATIONALE

Prior studies have shown an anticancer effect of metformin in patients with breast and colorectal cancer. It is unclear, however, whether metformin has a mortality benefit in lung cancer.

OBJECTIVES

To compare overall survival of patients with diabetes with stage IV non-small cell lung cancer (NSCLC) taking metformin versus those not on metformin.

METHODS

Using data from the Surveillance, Epidemiology, and End Results registry linked to Medicare claims, we identified 750 patients with diabetes 65-80 years of age diagnosed with stage IV NSCLC between 2007 and 2009. We used propensity score methods to assess the association of metformin use with overall survival while controlling for potential confounders.

MEASUREMENTS AND MAIN RESULTS

Overall, 61% of patients were on metformin at the time of lung cancer diagnosis. Median survival in the metformin group was 5 months, compared with 3 months in patients not treated with metformin (P < 0.001). Propensity score analyses showed that metformin use was associated with a statistically significant improvement in survival (hazard ratio, 0.80; 95% confidence interval, 0.71-0.89), after controlling for sociodemographics, diabetes severity, other diabetes medications, cancer characteristics, and treatment.

CONCLUSIONS

Metformin is associated with improved survival among patients with diabetes with stage IV NSCLC, suggesting a potential anticancer effect. Further research should evaluate plausible biologic mechanisms and test the effect of metformin in prospective clinical trials.

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.

Targeting the translation machinery in cancer

Dysregulation of mRNA translation is a frequent feature of neoplasia. Many oncogenes and tumour suppressors affect the translation machinery, making aberrant translation a widespread characteristic of tumour cells, independent of the genetic make-up of the cancer. Therefore, therapeutic agents that target components of the protein synthesis apparatus hold promise as novel anticancer drugs that can overcome intra-tumour heterogeneity. In this Review, we discuss the role of translation in cancer, with a particular focus on the eIF4F (eukaryotic translation initiation factor 4F) complex, and provide an overview of recent efforts aiming to 'translate' these results to the clinic.

Changes in insulin receptor signaling underlie neoadjuvant metformin administration in breast cancer: a prospective window of opportunity neoadjuvant study

INTRODUCTION

The antidiabetic drug metformin exhibits potential anticancer properties that are believed to involve both direct (insulin-independent) and indirect (insulin-dependent) actions. Direct effects are linked to activation of AMP-activated protein kinase (AMPK) and an inhibition of mammalian target of rapamycin mTOR signaling, and indirect effects are mediated by reductions in circulating insulin, leading to reduced insulin receptor (IR)-mediated signaling. However, the in vivo impact of metformin on cancer cell signaling and the factors governing sensitivity in patients remain unknown.

METHODS

We conducted a neoadjuvant, single-arm, "window of opportunity" trial to examine the clinical and biological effects of metformin on patients with breast cancer. Women with untreated breast cancer who did not have diabetes were given 500 mg of metformin three times daily for ≥2 weeks after diagnostic biopsy until surgery. Fasting blood and tumor samples were collected at diagnosis and surgery. Blood glucose and insulin were assayed to assess the physiologic effects of metformin, and immunohistochemical analysis of tumors was used to characterize cellular markers before and after treatment.

RESULTS

Levels of IR expression decreased significantly in tumors (P = 0.04), as did the phosphorylation status of protein kinase B (PKB)/Akt (S473), extracellular signal-regulated kinase 1/2 (ERK1/2, T202/Y204), AMPK (T172) and acetyl coenzyme A carboxylase (S79) (P = 0.0001, P < 0.0001, P < 0.005 and P = 0.02, respectively). All tumors expressed organic cation transporter 1, with 90% (35 of 39) exhibiting an Allred score of 5 or higher.

CONCLUSIONS

Reduced PKB/Akt and ERK1/2 phosphorylation, coupled with decreased insulin and IR levels, suggest insulin-dependent effects are important in the clinical setting. These results are consistent with beneficial anticancer effects of metformin and highlight key factors involved in sensitivity, which could be used to identify patients with breast cancer who may be responsive to metformin-based therapies.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT00897884. Registered 8 May 2009.

Lack of effect of metformin on mammary carcinogenesis in nondiabetic rat and mouse models

Epidemiologic studies have shown that diabetics receiving the biguanide metformin, as compared with sulfonylureas or insulin, have a lower incidence of breast cancer. Metformin increases levels of activated AMPK (AMP-activated protein kinase) and decreases circulating IGF-1; encouraging its potential use in both cancer prevention and therapeutic settings. In anticipation of clinical trials in nondiabetic women, the efficacy of metformin in nondiabetic rat and mouse mammary cancer models was evaluated. Metformin was administered by gavage or in the diet, at a human equivalent dose, in standard mammary cancer models: (i) methylnitrosourea (MNU)-induced estrogen receptor-positive (ER(+)) mammary cancers in rats, and (ii) MMTV-Neu/p53KO ER(-) (estrogen receptor-negative) mammary cancers in mice. In the MNU rat model, metformin dosing (150 or 50 mg/kg BW/d, by gavage) was ineffective in decreasing mammary cancer multiplicity, latency, or weight. Pharmacokinetic studies of metformin (150 mg/kg BW/d, by gavage) yielded plasma levels (Cmax and AUC) higher than humans taking 1.5 g/d. In rats bearing small palpable mammary cancers, short-term metformin (150 mg/kg BW/d) treatment increased levels of phospho-AMPK and phospho-p53 (Ser20), but failed to reduce Ki67 labeling or expression of proliferation-related genes. In the mouse model, dietary metformin (1,500 mg/kg diet) did not alter final cancer incidence, multiplicity, or weight. Metformin did not prevent mammary carcinogenesis in two mammary cancer models, raising questions about metformin efficacy in breast cancer in nondiabetic populations.

Targeting mitochondria metabolism for cancer therapy

Mitochondria have a well-recognized role in the production of ATP and the intermediates needed for macromolecule biosynthesis, such as nucleotides. Mitochondria also participate in the activation of signaling pathways. Overall, accumulating evidence now suggests that mitochondrial bioenergetics, biosynthesis and signaling are required for tumorigenesis. Thus, emerging studies have begun to demonstrate that mitochondrial metabolism is potentially a fruitful arena for cancer therapy. In this Perspective, we highlight recent developments in targeting mitochondrial metabolism for the treatment of cancer.

AMPK as a potential anticancer target - friend or foe?

Adenosine monophosphate-activated protein kinase (AMPK) is a key player in maintaining energy homeostasis in response to metabolic stress. Beyond diabetes and metabolic syndrome, there is a growing interest in the therapeutic exploitation of the AMPK pathway in cancer treatment in light of its unique ability to regulate cancer cell proliferation through the reprogramming of cell metabolism. Although many studies support the tumor-suppressive role of AMPK, emerging evidence suggests that the metabolic checkpoint function of AMPK might be overridden by stress or oncogenic signals so that tumor cells use AMPK activation as a survival strategy to gain growth advantage. These findings underscore the complexity in the cellular function of AMPK in maintaining energy homeostasis under physiological versus pathological conditions. Thus, this review aims to provide an overview of recent findings on the functional interplay of AMPK with different cell metabolic and signaling effectors, particularly histone deacetylases, in mediating downstream tumor suppressive or promoting mechanisms in different cell systems. Although AMPK activation inhibits tumor growth by targeting multiple signaling pathways relevant to tumorigenesis, under certain cellular contexts or certain stages of tumor development, AMPK might act as a protective response to metabolic stresses, such as nutrient deprivation, low oxygen, and low pH, or as downstream effectors of oncogenic proteins, including androgen receptor, hypoxia-inducible factor-1α, c-Src, and MYC. Thus, investigations to define at which stage(s) of tumorigenesis and cancer progression or for which genetic aberrations AMPK inhibition might represent a more relevant strategy than AMPK activation for cancer treatment are clearly warranted.

Enhanced antitumor activity of 3-bromopyruvate in combination with rapamycin in vivo and in vitro

3-Bromopyruvate (3-BrPA) is an alkylating agent and a well-known inhibitor of energy metabolism. Rapamycin is an inhibitor of the serine/threonine protein kinase mTOR. Both 3-BrPA and rapamycin show chemopreventive efficacy in mouse models of lung cancer. Aerosol delivery of therapeutic drugs for lung cancer has been reported to be an effective route of delivery with little systemic distribution in humans. In this study, 3-BrPA and rapamycin were evaluated in combination for their preventive effects against lung cancer in mice by aerosol treatment, revealing a synergistic ability as measured by tumor multiplicity and tumor load compared treatment with either single-agent alone. No evidence of liver toxicity was detected by monitoring serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) enzymes. To understand the mechanism in vitro experiments were performed using human non-small cell lung cancer (NSCLC) cell lines. 3-BrPA and rapamycin also synergistically inhibited cell proliferation. Rapamycin alone blocked the mTOR signaling pathway, whereas 3-BrPA did not potentiate this effect. Given the known role of 3-BrPA as an inhibitor of glycolysis, we investigated mitochondrial bioenergetics changes in vitro in 3-BrPA-treated NSCLC cells. 3-BrPA significantly decreased glycolytic activity, which may be due to adenosine triphosphate (ATP) depletion and decreased expression of GAPDH. Our results demonstrate that rapamycin enhanced the antitumor efficacy of 3-BrPA, and that dual inhibition of mTOR signaling and glycolysis may be an effective therapeutic strategy for lung cancer chemoprevention.

Autophagy, cell death, and cancer

Autophagy is an evolutionarily conserved intracellular catabolic process that is used by all cells to degrade dysfunctional or unnecessary cytoplasmic components through delivery to the lysosome. Increasing evidence reveals that autophagic dysfunction is associated with human diseases, such as cancer. Paradoxically, although autophagy is well recognized as a cell survival process that promotes tumor development, it can also participate in a caspase-independent form of programmed cell death. Induction of autophagic cell death by some anticancer agents highlights the potential of this process as a cancer treatment modality. Here, we review our current understanding of the molecular mechanism of autophagy and the potential roles of autophagy in cell death, cancer development, and cancer treatment.