Metformin inhibits mammalian target of rapamycin-dependent translation initiation in breast cancer cells

The acetyl-CoA carboxylase enzyme: a target for cancer therapy?

As a rate-limiting enzyme, the acetyl-CoA carboxylase (ACC) is essential for fatty acid synthesis. Traditionally, the ACC has been a target of metabolic syndrome and obesity. Recent research has demonstrated that malignant tumors have a high energy flow, thus having a great ability to synthesize fatty acids. ACCs are occasionally found to be overexpressed in cancer cells, and using chemical or RNA interference to inhibit ACC can lead to cancer cell cycle arrest and apoptosis. This suggests that ACC and relative fatty acids may be critical for the survival of cancer cells. In this review, we summarize the role of ACC in tumor development. We also discuss the signaling pathways possibly affected by ACC, which may give insight into future research for cancer therapy.

Crosstalk with insulin and dependence on PI3K/Akt/mTOR rather than MAPK pathways in upregulation of basal growth following long-term oestrogen deprivation in three human breast cancer cell lines

BACKGROUND

MCF-7, T-47-D, ZR-75-1 human breast cancer cell lines are dependent on oestrogen for growth but can adapt to grow during long-term oestrogen deprivation. This serves as a model for identification of therapeutic targets in endocrine-resistant breast cancer.

METHODS

An overlooked complication of this model is that it involves more than non-addition of oestrogen, and inadequate attention has been given to separating molecular events associated with each of the culture manipulations.

RESULTS

Insulin and oestradiol were shown to protect MCF-7 cells against upregulation of basal growth, demonstrating a crosstalk in the growth adaptation process. Increased phosphorylation of p44/42MAPK and c-Raf reflected removal of insulin from the medium and proliferation of all three cell lines was inhibited to a lesser extent by PD98059 and U0126 following long-term oestrogen/insulin withdrawal, demonstrating a reduced dependence on the MAPK pathway. By contrast, long-term oestrogen/insulin deprivation did not alter levels of phosphorylated Akt and did not alter the dose-response of growth inhibition with LY294002 in any of the three cell lines. The IGF1R inhibitor picropodophyllin inhibited growth of all MCF-7 cells but only in the long-term oestrogen/insulin-deprived cells was this paralleled by reduction in phosphorylated p70S6K, a downstream target of mTOR. Long-term oestrogen/insulin-deprived MCF-7 cells had higher levels of phosphorylated p70S6K and developed increased sensitivity to growth inhibition by rapamycin.

CONCLUSIONS

The greater sensitivity to growth inhibition by rapamycin in all three cell lines following long-term oestrogen/insulin deprivation suggests rapamycin-based therapies might be more effective in breast cancers with acquired oestrogen resistance.

Impact of metformin use on survival in locally-advanced, inoperable non-small cell lung cancer treated with definitive chemoradiation

BACKGROUND

We investigated survival outcomes in diabetic patients with non-small cell lung cancer (NSCLC) treated with concurrent metformin and definitive chemoradiation.

METHODS

This single-institution, retrospective cohort study included 166 patients with NSCLC who were treated definitively with chemoradiation between 1999 and 2013. Of 40 patients who had type II diabetes, 20 (50%) were on metformin, and 20 (50%) were not on metformin. The primary outcome was overall survival (OS), and secondary outcomes included progression-free survival (PFS), locoregional recurrence-free survival (LRRFS) and distant metastasis-free survival (DMFS). Kaplan Meier method and log-rank test were performed in survival analysis. Cox regression was utilized in univariate analysis of potential confounders.

RESULTS

Median follow-up was 17.0 months. Compared with non-diabetic patients, diabetic patients on metformin demonstrated similar OS (16.3 vs. 14.3 mo, P=0.23), PFS (11.6 vs. 9.7 mo, P=0.26), LRRFS (14.1 vs. 11.9 mo, P=0.78), and DMFS (13.4 vs. 10.0 mo, P=0.69). Compared with diabetic patients not on metformin, diabetic patients on metformin also exhibited similar OS (14.3 vs. 19.2 mo, P=0.18), PFS (19.7 vs. 10.1 mo, P=0.38), LRRFS (11.9 vs. 15.5 mo, P=0.69), and DMFS (10.0 vs. 17.4 mo, P=0.12). Identified negative prognostic factors on included squamous cell histology, lower performance status, higher T stage, and non-caucasian ethnicity.

CONCLUSIONS

No statistically significant differences in survival or patterns of failure were found among the three cohorts in this small set of patients. No statistically significant differences in survival or patterns of failure were found between the three cohorts in this small set of patients. Though it is possible that metformin use may in fact have no effect on survival in NSCLC patients treated with definitive RT, larger-scale retrospective and prospective studies are implicated for clarification.

Anti-tumour effect of metformin in canine mammary gland tumour cells

Metformin is an oral hypoglycaemic drug used in type 2 diabetes. Its pharmacological activity reportedly involves mitochondrial respiratory complex I, and mitochondrial respiratory complex inhibitors have a strong inhibitory effect on the growth of metastatic canine mammary gland tumour (CMGT) cell lines. It is hypothesised that metformin has selective anti-tumour effects on metastatic CMGT cells. The aim of this study was to investigate the in vitro effect of metformin on cell growth, production of ATP and reactive oxygen species (ROS), and the AMP-activated protein kinase (AMPK) mammalian target of rapamycin (mTOR) pathway in two CMGT clonal cell lines with different metastatic potential. In addition, transcriptome analysis was used to determine cellular processes disrupted by metformin and in vivo anti-tumour effects were examined in a mouse xenograft model. Metformin inhibited CMGT cell growth in vitro, with the metastatic clone (CHMp-5b) displaying greater sensitivity. ATP depletion and ROS elevation were observed to a similar extent in the metastatic and non-metastatic (CHMp-13a) cell lines after metformin exposure. However, subsequent AMPK activation and mTOR pathway inhibition were prominent only in metformin-insensitive non-metastatic cells. Microarray analysis revealed inhibition of cell cycle progression by metformin treatment in CHMp-5b cells, which was further confirmed by Western blotting and cell cycle analysis. Additionally, metformin significantly suppressed tumour growth in xenografted metastatic CMGT cells. In conclusion, metformin exhibited an anti-tumour effect in metastatic CMGT cells through AMPK-independent cell cycle arrest. Its mechanism of action differed in the non-metastatic clone, where AMPK activation and mTOR inhibition were observed.

Metformin Treatment for the Prevention and/or Treatment of Breast/Mammary Tumorigenesis

There is increasing interest in metformin's effects on the development, treatment and/or progression of breast cancer. This emerges from observational studies that diabetic women treated with metformin in comparison to other antidiabetic compounds had lower breast cancer incidence and/or mortality rates. The mechanism of action is considered to be activation of hepatic AMPK resulting in reduced gluconeogenesis. Calorie restriction, which consistently reduces mammary tumorigenesis in rodents, is also thought to act through this pathway leading to the hypothesis that metformin's anticancer effects are mediated in a similar fashion. Here we review the literature evaluating metformin's anticancer effects in relation to breast/mammary tumorigenesis. We include clinical observations, as well as studies utilizing rodent models and mammary cell lines. In addition to the anticancer effect of metformin mediated through the AMPK pathway, additional mechanisms of action that directly target tissues have been identified including effects on stem cells, apoptosis, STAT3 and HER2.

Metformin suppresses diethylnitrosamine-induced liver tumorigenesis in obese and diabetic C57BL/KsJ-+Leprdb/+Leprdb mice

Obesity and related metabolic disorders, such as diabetes mellitus, raise the risk of liver carcinogenesis. Metformin, which is widely used in the treatment of diabetes, ameliorates insulin sensitivity. Metformin is also thought to have antineoplastic activities and to reduce cancer risk. The present study examined the preventive effect of metformin on the development of diethylnitrosamine (DEN)-induced liver tumorigenesis in C57BL/KsJ-+Lepr^db/+Lepr^db (db/db) obese and diabetic mice. The mice were given a single injection of DEN at 2 weeks of age and subsequently received drinking water containing metformin for 20 weeks. Metformin administration significantly reduced the multiplicity of hepatic premalignant lesions and inhibited liver cell neoplasms. Metformin also markedly decreased serum levels of insulin and reduced insulin resistance, and inhibited phosphorylation of Akt, mammalian target of rapamycin (mTOR), and p70S6 in the liver. Furthermore, serum levels of leptin were decreased, while those of adiponectin were increased by metformin. These findings suggest that metformin prevents liver tumorigenesis by ameliorating insulin sensitivity, inhibiting the activation of Akt/mTOR/p70S6 signaling, and improving adipokine imbalance. Therefore, metformin may be a potent candidate for chemoprevention of liver tumorigenesis in patients with obesity or diabetes.

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.

DEPTOR-related mTOR suppression is involved in metformin's anti-cancer action in human liver cancer cells

Metformin, one of the most commonly used drugs for patients with type 2 diabetes, recently has received much attention regarding its anti-cancer action. It is thought that the suppression of mTOR signaling is involved in metformin's anti-cancer action. Although liver cancer is one of the most responsive types of cancer for reduction of incidence by metformin, the molecular mechanism of the suppression of mTOR in liver remains unknown. In this study, we investigated the mechanism of the suppressing effect of metformin on mTOR signaling and cell proliferation using human liver cancer cells. Metformin suppressed phosphorylation of p70-S6 kinase, and ribosome protein S6, downstream targets of mTOR, and suppressed cell proliferation. We found that DEPTOR, an endogenous substrate of mTOR suppression, is involved in the suppressing effect of metformin on mTOR signaling and cell proliferation in human liver cancer cells. Metformin increases the protein levels of DEPTOR, intensifies binding to mTOR, and exerts a suppressing effect on mTOR signaling. This increasing effect of DEPTOR by metformin is regulated by the proteasome degradation system; the suppressing effect of metformin on mTOR signaling and cell proliferation is in a DEPTOR-dependent manner. Furthermore, metformin exerts a suppressing effect on proteasome activity, DEPTOR-related mTOR signaling, and cell proliferation in an AMPK-dependent manner. We conclude that DEPTOR-related mTOR suppression is involved in metformin's anti-cancer action in liver, and could be a novel target for anti-cancer therapy.

Recent advances in the use of metformin: can treating diabetes prevent breast cancer?

There is substantial epidemiological evidence pointing to an increased incidence of breast cancer and morbidity in obese, prediabetic, and diabetic patients. In vitro studies strongly support metformin, a diabetic medication, in breast cancer therapy. Although metformin has been heralded as an exciting new breast cancer treatment, the principal consideration is whether metformin can be used as a generic treatment for all breast cancer types. Importantly, will metformin be useful as an inexpensive therapy for patients with comorbidity of diabetes and breast cancer? In general, meta-analyses of clinical trial data from retrospective studies in which metformin treatment has been used for patients with diabetes and breast cancer have a positive trend; nevertheless, the supporting clinical data outcomes remain inconclusive. The heterogeneity of breast cancer, confounded by comorbidity of disease in the elderly population, makes it difficult to determine the actual benefits of metformin therapy. Despite the questionable evidence available from observational clinical studies and meta-analyses, randomized phases I-III clinical trials are ongoing to test the efficacy of metformin for breast cancer. This special issue review will focus on recent research, highlighting in vitro research and retrospective observational clinical studies and current clinical trials on metformin action in breast cancer.

The association between type 2 diabetes mellitus and women cancer: the epidemiological evidences and putative mechanisms

Type 2 diabetes mellitus (T2DM), a chronic disease increasing rapidly worldwide, is well established as an important risk factor for various types of cancer. Although many factors impact the development of T2DM and cancer including sex, age, ethnicity, obesity, diet, physical activity levels, and environmental exposure, many epidemiological and experimental studies are gradually contributing to knowledge regarding the interrelationship between DM and cancer. The insulin resistance, hyperinsulinemia, and chronic inflammation associated with diabetes mellitus are all associated strongly with cancer. The changes in bioavailable ovarian steroid hormone that occur in diabetes mellitus (the increasing levels of estrogen and androgen and the decreasing level of progesterone) are also considered potentially carcinogenic conditions for the breast, endometrium, and ovaries in women. In addition, the interaction among insulin, insulin-like growth factors (IGFs), and ovarian steroid hormones, such as estrogen and progesterone, could act synergistically during cancer development. Here, we review the cancer-related mechanisms in T2DM, the epidemiological evidence linking T2DM and cancers in women, and the role of antidiabetic medication in these cancers.

The association between glucose-lowering drug use and mortality among breast cancer patients with type 2 diabetes

This study assessed the association between glucose-lowering drug (GLD) use, including metformin, sulphonylurea derivatives and insulin, after breast cancer diagnosis and breast cancer-specific and all-cause mortality. 1763 breast cancer patients, diagnosed between 1998 and 2010, with type 2 diabetes were included. Cancer information was retrieved from English cancer registries, prescription data from the UK Clinical Practice Research Datalink and mortality data from the Office of National Statistics (up to January 2012). Time-varying Cox regression models were used to calculate HRs and 95 % CIs for the association between GLD use and breast cancer-specific and all-cause mortality. In 1057 patients with diabetes before breast cancer, there was some evidence that breast cancer-specific mortality decreased with each year of metformin use (adjusted HR 0.88; 95 % CI 0.75-1.04), with a strong association seen with over 2 years of use (adjusted HR 0.47; 95 % CI 0.26-0.82). Sulphonylurea derivative use for less than 2 years was associated with increased breast cancer-specific mortality (adjusted HR 1.70; 95 % CI 1.18-2.46), but longer use was not (adjusted HR 0.94; 95 % CI 0.54-1.66). In 706 patients who developed diabetes after breast cancer, similar patterns were seen for metformin, but sulphonylurea derivative use was strongly associated with cancer-specific mortality (adjusted HR 3.64; 95 % CI 2.16-6.16), with similar estimates for short- and long-term users. This study provides some support for an inverse association between, mainly long-term, metformin use and (breast cancer-specific) mortality. In addition, sulphonylurea derivative use was associated with increased breast cancer-specific mortality, but this should be interpreted cautiously, as it could reflect selective prescribing in advanced cancer patients.

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.

Dual effect of metformin on growth inhibition and oestradiol production in breast cancer cells

Evidence has been accumulating for a role for metformin in reducing breast cancer risk in post-menopausal women. It inhibits growth of breast cancer cells via several mechanisms, primarily the AMPK/mTOR signalling pathway. Another possible protective mechanism may be the ability of metformin to inhibit aromatase activity. In the present study, we investigated the effects of metformin on the basal growth of MCF-7 cells, after oestradiol (E2) stimulation and after the inhibition of mTOR by rapamycin. Secondly, we investigated the effects of metformin on the activity of a number of steroidogenic enzymes and the mRNA expression of aromatase and steroid sulphatase (STS). High doses of metformin significantly inhibited both basal and oestrogen-stimulated cell division. Low-dose rapamycin (10-10 M) did not inhibit growth, but the addition of metformin induced a significant reduction in growth. High-dose rapamycin (10-8 M) inhibited growth, and this was further attenuated by the addition of metformin. Exposure to low (10-7 M) and high (10-4 M) doses of metformin for 7-10 days significantly reduced the conversion of androstenedione (ANDRO) and testosterone (TESTO) (both requiring aromatase), but not the conversion of oestrone or oestrone sulphate (ES) via 17β-hydroxysteroid dehydrogenase/sulphatase to E2. This attenuation was via a downregulation in the expression of total aromatase mRNA and promoter II, whilst the expression of sulphatase was unaffected by metformin. In conclusion, plasma levels of metformin have a dual therapeutic action, first by directly inhibiting cell proliferation which can be augmented by rapamycin analogues, and secondly, by inhibiting aromatase activity and reducing the local conversion of androgens to E2.

Drug radiotherapy combinations: review of previous failures and reasons for future optimism

Combining chemotherapy with radiotherapy has resulted in significant clinical improvements in many different tumour types. However, the non-specific mechanisms by which these drugs exert their effects mean that this is often at the expense of increased side effects. Previous attempts at using targeted drugs to induce more tumour specific radiosensitisation have been generally disappointing. Although cetuximab, an EGFR monoclonal antibody, resulted in improved overall survival in HNSCC when combined with radiotherapy, it has failed to show benefit when added to chemo-radiotherapy. In addition, our inability to successfully use drug treatments to reverse tumour hypoxia is underlined by the fact that no such treatment is currently in widespread clinical use. The reasons for these failures include the lack of robust biomarkers, and the previous use of drugs with unacceptable side-effect profiles. Despite these disappointments, there is reason for optimism. Our improved understanding of key signal transduction pathways and of tumour specific DNA repair deficiencies has produced new opportunities to specifically radiosensitise tumours. Novel strategies to reduce tumour hypoxia include the use of drugs that cause vascular normalisation and drugs that reduce tumour oxygen consumption. These new strategies, combined with better compounds at our disposal, and an ability to learn from our previous mistakes, mean that there is great promise for future drug-radiotherapy combinations to result in significant clinical benefits.

Inhibition of polo-like kinase 1 (Plk1) enhances the antineoplastic activity of metformin in prostate cancer

The widely used anti-diabetic drug metformin has been shown to exert strong antineoplastic actions in numerous tumor types, including prostate cancer (PCa). In this study, we show that BI2536, a specific Plk1 inhibitor, acted synergistically with metformin in inhibiting PCa cell proliferation. Furthermore, we also provide evidence that Plk1 inhibition makes PCa cells carrying WT p53 much more sensitive to low-dose metformin treatment. Mechanistically, we found that co-treatment with BI2536 and metformin induced p53-dependent apoptosis and further activated the p53/Redd-1 pathway. Moreover, we also show that BI2536 treatment inhibited metformin-induced glycolysis and glutamine anaplerosis, both of which are survival responses of cells against mitochondrial poisons. Finally, we confirmed the cell-based observations using both cultured cell-derived and patient-derived xenograft studies. Collectively, our findings support another promising therapeutic strategy by combining two well tolerated drugs against PCa proliferation and the progression of androgen-dependent PCa to the castration-resistant stage.

NQO1-induced activation of AMPK contributes to cancer cell death by oxygen-glucose deprivation

Oxygen and glucose deprivation (OGD) due to insufficient blood circulation can decrease cancer cell survival and proliferation in solid tumors. OGD increases the intracellular [AMP]/[ATP] ratio, thereby activating the AMPK. In this study, we have investigated the involvement of NQO1 in OGD-mediated AMPK activation and cancer cell death. We found that OGD activates AMPK in an NQO1-dependent manner, suppressing the mTOR/S6K/4E-BP1 pathway, which is known to control cell survival. Thus, the depletion of NQO1 prevents AMPK-induced cancer cell death in OGD. When we blocked OGD-induced Ca²⁺/CaMKII signaling, the NQO1-induced activation of AMPK was attenuated. In addition, when we blocked the RyR signaling, the accumulation of intracellular Ca²⁺ and subsequent activation of CaMKII/AMPK signaling was decreased in NQO1-expressing cells under OGD. Finally, siRNA-mediated knockdown of CD38 abrogated the OGD-induced activation of Ca²⁺/CaMKII/AMPK signaling. Taken together, we conclude that NQO1 plays a key role in the AMPK-induced cancer cell death in OGD through the CD38/cADPR/RyR/Ca²⁺/CaMKII signaling pathway.

mTOR: a pharmacologic target for autophagy regulation

mTOR, a serine/threonine kinase, is a master regulator of cellular metabolism. mTOR regulates cell growth and proliferation in response to a wide range of cues, and its signaling pathway is deregulated in many human diseases. mTOR also plays a crucial role in regulating autophagy. This Review provides an overview of the mTOR signaling pathway, the mechanisms of mTOR in autophagy regulation, and the clinical implications of mTOR inhibitors in disease treatment.

Promoting autophagic clearance: viable therapeutic targets in Alzheimer's disease

Many neurodegenerative disorders are characterized by the aberrant accumulation of aggregate-prone proteins. Alzheimer's disease (AD) is associated with the buildup of β-amyloid peptides and tau, which aggregate into extracellular plaques and neurofibrillary tangles, respectively. Multiple studies have linked dysfunctional intracellular degradation mechanisms with AD pathogenesis. One such pathway is the autophagy-lysosomal system, which involves the delivery of large protein aggregates/inclusions and organelles to lysosomes through the formation, trafficking, and degradation of double-membrane structures known as autophagosomes. Converging data suggest that promoting autophagic degradation, either by inducing autophagosome formation or enhancing lysosomal digestion, provides viable therapeutic strategies. In this review, we discuss compounds that can augment autophagic clearance and may ameliorate disease-related pathology in cell and mouse models of AD. Canonical autophagy induction is associated with multiple signaling cascades; on the one hand, the best characterized is mammalian target of rapamycin (mTOR). Accordingly, multiple mTOR-dependent and mTOR-independent drugs that stimulate autophagy have been tested in preclinical models. On the other hand, there is a growing list of drugs that can enhance the later stages of autophagic flux by stabilizing microtubule-mediated trafficking, promoting lysosomal fusion, or bolstering lysosomal enzyme function. Although altering the different stages of autophagy provides many potential targets for AD therapeutic interventions, it is important to consider how autophagy drugs might also disturb the delicate balance between autophagosome formation and lysosomal degradation.

Lack of metformin effects on different molecular subtypes of breast cancer under normoglycemic conditions: an in vitro study

BACKGROUND

In the past few years, a considerable number of preclinical studies have been proposed metformin as a potential anticancer agent, but some of these studies suffer from a number of methodological limitations such as assessment of cytotoxicity in the presence of supraphysiological glucose concentrations or applying suprapharmacological levels of the drug. These objections have limited the translation of published preclinical data to the clinical setting. The present study aimed to investigate direct anticancer effects of metformin on different molecular subtypes of breast cancer with pharmacological concentrations and under normoglycemic conditions in vitro.

MATERIALS AND METHODS

Breast cancer cell lines from luminal A, luminal B, ErbB2 and triple-negative molecular subtypes were treated with a pharmacological concentration of metformin (2mM) at a glucose concentration of 5.5mM. Time-dependant cell viability was assessed by dye exclusion assay. MTT- based cytotoxicity assays were also performed with metformin alone or in combination with paclitaxel.

RESULTS

Metformin did not show any growth inhibitory effects or time-dependant cytotoxicity on breast cancer cell lines in the presence of normal glucose concentrations at the therapeutic plasma level. No augmentation of the anti- neoplastic properties of paclitaxel was apparent under the tested conditions.

CONCLUSIONS

Metformin is probably unable to exert cytotoxic or cytostatic effects on breast cancer subtypes at pharmacological concentrations and normal plasma glucose levels. These results highlight the importance of establishing a higher steady-state plasma concentration of metformin in the clinical setting for assessment of anticancer effects in normoglycemic patients.

Metformin induces PGC-1α expression and selectively affects hepatic PGC-1α functions

BACKGROUND AND PURPOSE

The objective of this study was to determine how the AMPK activating antidiabetic drug metformin affects the major activator of hepatic gluconeogenesis, PPARγ coactivator 1α (PGC-1α) and liver functions regulated by PGC-1α.

EXPERIMENTAL APPROACH

Mouse and human primary hepatocytes and mice in vivo were treated with metformin. Adenoviral overexpression, siRNA and reporter gene constructs were used for mechanistic studies.

KEY RESULTS

Metformin increased PGC-1α mRNA and protein expression in mouse primary hepatocytes. 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) (another AMPK activator) had the opposite effect. Metformin also increased PGC-1α in human primary hepatocytes; this effect of metformin was abolished by AMPK inhibitor compound C and sirtuin 1 siRNA. AMPK overexpression by AMPK-Ad also increased PGC-1α. Whereas metformin increased PGC-1α, it down-regulated gluconeogenic genes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase). Furthermore, metformin attenuated the increase in PEPCK and G6Pase mRNAs induced by PGC-1α overexpression, but did not affect PGC-1α-mediated induction of mitochondrial genes. Metformin down-regulated several key transcription factors that mediate the effect of PGC-1α on gluconeogenic genes including Krüppel-like factor 15, forkhead box protein O1 and hepatocyte NF 4α, whereas it increased nuclear respiratory factor 1, which is involved in PGC-1α-mediated regulation of mitochondrial proteins.

CONCLUSIONS AND IMPLICATIONS

Down-regulation of PGC-1α is not necessary for suppression of gluconeogenic genes by metformin. Importantly, metformin selectively affects hepatic PGC-1α-mediated gene regulation and prevents activation of gluconeogenesis, but does not influence its regulation of mitochondrial genes. These results identify selective modulation of hepatic PGC-1α functions as a novel mechanism involved in the therapeutic action of metformin.

Metformin protects skeletal muscle from cardiotoxin induced degeneration

The skeletal muscle tissue has a remarkable capacity to regenerate upon injury. Recent studies have suggested that this regenerative process is improved when AMPK is activated. In the muscle of young and old mice a low calorie diet, which activates AMPK, markedly enhances muscle regeneration. Remarkably, intraperitoneal injection of AICAR, an AMPK agonist, improves the structural integrity of muscles of dystrophin-deficient mdx mice. Building on these observations we asked whether metformin, a powerful anti-hyperglycemic drug, which indirectly activates AMPK, affects the response of skeletal muscle to damage. In our conditions, metformin treatment did not significantly influence muscle regeneration. On the other hand we observed that the muscles of metformin treated mice are more resilient to cardiotoxin injury displaying lesser muscle damage. Accordingly myotubes, originated in vitro from differentiated C2C12 myoblast cell line, become more resistant to cardiotoxin damage after pre-incubation with metformin. Our results indicate that metformin limits cardiotoxin damage by protecting myotubes from necrosis. Although the details of the molecular mechanisms underlying the protective effect remain to be elucidated, we report a correlation between the ability of metformin to promote resistance to damage and its capacity to counteract the increment of intracellular calcium levels induced by cardiotoxin treatment. Since increased cytoplasmic calcium concentrations characterize additional muscle pathological conditions, including dystrophies, metformin treatment could prove a valuable strategy to ameliorate the conditions of patients affected by dystrophies.

Suppression of the HSF1-mediated proteotoxic stress response by the metabolic stress sensor AMPK

Numerous extrinsic and intrinsic insults trigger the HSF1-mediated proteotoxic stress response (PSR), an ancient transcriptional program that is essential to proteostasis and survival under such conditions. In contrast to its well-recognized mobilization by proteotoxic stress, little is known about how this powerful adaptive mechanism reacts to other stresses. Surprisingly, we discovered that metabolic stress suppresses the PSR. This suppression is largely mediated through the central metabolic sensor AMPK, which physically interacts with and phosphorylates HSF1 at Ser121. Through AMPK activation, metabolic stress represses HSF1, rendering cells vulnerable to proteotoxic stress. Conversely, proteotoxic stress inactivates AMPK and thereby interferes with the metabolic stress response. Importantly, metformin, a metabolic stressor and popular anti-diabetic drug, inactivates HSF1 and provokes proteotoxic stress within tumor cells, thereby impeding tumor growth. Thus, these findings uncover a novel interplay between the metabolic stress sensor AMPK and the proteotoxic stress sensor HSF1 that profoundly impacts stress resistance, proteostasis, and malignant growth.

Combined use of vitamin D3 and metformin exhibits synergistic chemopreventive effects on colorectal neoplasia in rats and mice

Vitamin D3 and metformin are widely used in humans for regulating mineral metabolism and as an antidiabetic drug, respectively; and both of them have been shown to have chemopreventive effects against various tumors. This study was designed to investigate the potential synergistic chemopreventive effects of vitamin D3 and metformin against the development of early colon neoplasia in two models. The first model was a 1,2-dimethylhydrazine dihydrochloride (DMH)-induced colon cancer rat model and the second, a DMH-dextran sodium sulfate (DSS)-induced colitis-associated colon neoplasia mouse model. Compared with either vitamin D3 or metformin alone, combined use of vitamin D3 and metformin showed more pronounced effect in reducing the numbers of aberrant crypt foci (ACF) and tumor in the colon. The most prominent inhibitory effects were observed in the vitamin D3 medium dose (100 IU/kg/d) and metformin medium dose (120 mg/kg/d) combination group. Furthermore, our results showed that enhancement of metformin's chemopreventive effects by vitamin D3 was associated with downregulation of S6P expression, via the AMPK (IGFI)/mTOR pathway. In addition, enhancement of vitamin D3's chemopreventive effects by metformin was associated with inhibition of the protein expressions of c-Myc and Cyclin D1, via the vitamin D receptor/β-catenin pathway. These findings show that the combined use of vitamin D3 and metformin exhibits synergistic effects against the development of early colon neoplasia. They suggest that the combined use of vitamin D3 and metformin may represent a novel strategy for chemoprevention of colorectal cancer.

Synergism between metformin and statins in modifying the risk of biochemical recurrence following radical prostatectomy in men with diabetes

BACKGROUND

To determine the effect of statins and metformin in combination on biochemical recurrence (BCR) among diabetic men undergoing radical prostatectomy (RP).

METHODS

Diabetic men undergoing RP at our institution from January 1995 to March 2012 were retrospectively reviewed. Recipients of adjuvant radiation or hormonal therapy were excluded. Statin and/or metformin use was determined through review of electronic records. BCR-free survival was plotted using Kaplan-Meier analysis, and the effect of statins and metformin on BCR was assessed via a multivariate Cox proportional hazards model.

RESULTS

Seven hundred and sixty-seven men met the inclusion criteria. Seventy-six (9.9%) were users of statins only, 56 (7.3%) were users of metformin only and 42 (5.5%) were dual users. Median follow-up time was 27 months. Dual users were less likely than nonusers or users of either medication alone to have a biopsy Gleason sum of 8-10 (P=0.033), and tended towards a lower rate of pathological T stage of pT3 or higher (P=0.064). Dual users had the highest 2-year and 5-year BCR-free survival, although this was not statistically significant (P=0.205). On multivariate regression, neither statin nor metformin use alone was significantly associated with BCR-free survival. However, their interaction led to a significantly lower BCR risk than would be expected from each medication's independent effects (hazard ratio=0.2; P=0.037).

CONCLUSIONS

The combination of statins and metformin in men undergoing RP for prostate cancer (PCa) may be associated with a lower BCR risk than would be predicted based on the independent effects of both medications. A synergism between these two agents is biologically plausible based on our current understanding of their diverse molecular pathways of action. The results of future clinical trials involving the use of either medication in men with PCa should be carefully assessed for confirmatory evidence of such a relationship.

The mTORC1 effectors S6K1 and 4E-BP play different roles in CNS axon regeneration

Using mouse optic nerve (ON) crush as a CNS injury model, we and others have found that activation of the mammalian target of rapamycin complex 1 (mTORC1) in mature retinal ganglion cells by deletion of the negative regulators, phosphatase and tensin homolog (PTEN) and tuberous sclerosis 1, promotes ON regeneration. mTORC1 activation inhibits eukaryotic translation initiation factor 4E-binding protein (4E-BP) and activates ribosomal protein S6 kinase 1 (S6K1), both of which stimulate translation. We reasoned that mTORC1’s regeneration-promoting effects might be separable from its deleterious effects by differential manipulation of its downstream effectors. Here we show that S6K1 activation, but not 4E-BP inhibition, is sufficient to promote axon regeneration. However, inhibition of 4E-BP is required for PTEN deletion-induced axon regeneration. Both activation and inhibition of S6K1 decrease the effect of PTEN deletion on axon regeneration, implicating a dual role of S6K1 in regulating axon growth.

Antihyperglycaemic therapies and cancer risk

AIMS

This review is aimed at highlighting the potential mitogenic/tumour growth-promoting or antimitogenic/tumour growth-inhibiting effects of the main antihyperglycaemic drug classes.

METHODS

We review and discuss the most current studies evaluating the association between antidiabetic medications used in clinical practice and malignancies as described so far.

RESULTS

Metformin seems to be the only antidiabetic drug to exert protective effects both on monotherapy and also when combined with other oral antidiabetic drugs or insulins in several site-specific cancers. In contrast, several other drug classes may increase cancer risk. Some reason for concern remains regarding sulphonylureas and also the incretin-based therapies regarding pancreas and thyroid cancers and the sodium glucose cotransporter-2 inhibitors as well as pioglitazone regarding bladder cancer. The majority of meta-analyses suggest that there is no evidence for a causal relationship between insulin glargine and elevated cancer risk, although the studies have been controversially discussed. For α-glucosidase inhibitors and glinides, neutral or only few data upon cancer risk exist.

CONCLUSION

Although the molecular mechanisms are not fully understood, a potential risk of mitogenicity and tumour growth promotion cannot be excluded in case of several antidiabetic drug classes. However, more large-scale, randomized, well-designed clinical studies with especially long follow-up time periods are needed to get reliable answers to these safety issues.

Metformin in cancer prevention and therapy

The prevalence of diabetes is dramatically increasing worldwide. The results of numerous epidemiological studies indicate that diabetic population is not only at increased risk of cardiovascular complications, but also at substantially higher risk of many forms of malignancies. The use of metformin, the most commonly prescribed drug for type 2 diabetes, was repeatedly associated with the decreased risk of the occurrence of various types of cancers, especially of pancreas and colon and hepatocellular carcinoma. This observation was also confirmed by the results of numerous meta-analyses. There are however, several unanswered questions regarding the exact mechanism of the anticancer effect of metformin as well as its activity against various types of cancer both in diabetic and nondiabetic populations. In the present work we discuss the proposed mechanism(s) of anticancer effect of metformin and preclinical and clinical data suggesting its anticancer effect in different populations.

Metformin may function as anti-cancer agent via targeting cancer stem cells: the potential biological significance of tumor-associated miRNAs in breast and pancreatic cancers

Metformin is one of the most used diabetic drugs for the management of type II diabetes mellitus (DM) in the world. Increased numbers of epidemiological and clinical studies have provided convincing evidence supporting the role of metformin in the development and progression of a variety of human tumors including breast and pancreatic cancer. Substantial pre-clinical evidence from in vitro and in vivo experimental studies strongly suggests that metformin has an anti-cancer activity mediated through the regulation of several cell signaling pathways including activation of AMP kinase (AMPK), and other direct and indirect mechanisms; however, the detailed mechanism(s) has not yet been fully understood. The concept of cancer stem cells (CSCs) has gained significant attention in recent years due its identification and defining its clinical implications in many different tumors including breast cancer and pancreatic cancer. In this review, we will discuss the protective role of metformin in the development of breast and pancreatic cancers. We will further discuss the role of metformin as an anti-cancer agent, which is in part mediated through targeting CSCs. Finally, we will discuss the potential role of metformin in the modulation of tumor-associated or CSC-associated microRNAs (miRNAs) as part of the novel mechanism of action of metformin in the development and progression of breast and pancreatic cancers.

Prospects on strategies for therapeutically targeting oncogenic regulatory factors by small-molecule agents

Although the Human Genome Project has raised much hope for the identification of druggable genetic targets for cancer and other diseases, this genetic target-based approach has not improved productivity in drug discovery over the traditional approach. Analyses of known human target proteins of currently marketed drugs reveal that these drugs target only a limited number of proteins as compared to the whole proteome. In contrast to genome-based targets, mechanistic targets are derived from empirical research, at cellular or molecular levels, in disease models and/or in patients, thereby enabling the exploration of a greater number of druggable targets beyond the genome and epigenome. The paradigm shift has made a tremendous headway in developing new therapeutic agents targeting different clinically relevant mechanisms/pathways in cancer cells. In this Prospects article, we provide an overview of potential drug targets related to the following four emerging areas: (1) tumor metabolism (the Warburg effect), (2) dysregulated protein turnover (E3 ubiquitin ligases), (3) protein-protein interactions, and (4) unique DNA high-order structures and protein-DNA interactions. Nonetheless, considering the genetic and phenotypic heterogeneities that characterize cancer cells, the development of drug resistance in cancer cells by adapting signaling circuitry to take advantage of redundant pathways or feedback/crosstalk systems is possible. This "phenotypic adaptation" underlies the rationale of using therapeutic combinations of these targeted agents with cytotoxic drugs.

Metformin decreases lung cancer risk in diabetic patients in a dose-dependent manner

OBJECTIVES

Higher risk of lung cancer has been noted in patients with type 2 diabetes mellitus (DM). Some observational studies have shown a reduced risk of lung cancer in DM patients taking metformin, but a dose-response relationship has never been reported. The aim of this study is to exam the association between the dose of metformin and the incidence of lung cancer in a Chinese population.

MATERIALS AND METHODS

The dataset used for this nationwide population-based study is a cohort of 1 million subjects randomly sampled from individuals enrolled in the Taiwan National Health Insurance system. We enrolled all subjects with newly diagnosed type 2 DM between 1997 and 2007. Subjects with a diagnosis of neoplasm before DM diagnosis, those using metformin before DM diagnosis, those with polycystic ovary syndrome, and those with a DM diagnosis before their 15 years of age were excluded. The demographic data and duration, cumulative dose and intensity of metformin use were compared between patients developing lung cancer and those without lung cancer.

RESULTS

Totally, 47,356 subjects were identified. After adjusting for age, gender, and modified Charlson Comorbidity Index score, the utilization of metformin was an independent protecting factor, and the risk of developing lung cancer decreased progressively with either the higher cumulative dose or the higher intensity of metformin use.

CONCLUSIONS

This study revealed that the use of metformin decreased the risk of lung cancer in a dose-dependent manner in patients with type 2 DM. The chemo-preventive effect of metformin deserves further study.

Metformin-induced killing of triple-negative breast cancer cells is mediated by reduction in fatty acid synthase via miRNA-193b

The anti-diabetic drug metformin (1,1-dimethylbiguanide hydrochloride) reduces both the incidence and mortality of several types of cancer. Metformin has been shown to selectively kill cancer stem cells, and triple-negative breast cancer (TNBC) cell lines are more sensitive to the effects of metformin as compared to luminal breast cancer. However, the mechanism underlying the enhanced susceptibility of TNBC to metformin has not been elucidated. Expression profiling of metformin-treated TNBC lines revealed fatty acid synthase (FASN) as one of the genes most significantly downregulated following 24 h of treatment, and a decrease in FASN protein was also observed. Since FASN is critical for de novo fatty acid synthesis and is important for the survival of TNBC, we hypothesized that FASN downregulation facilitates metformin-induced apoptosis. Profiling studies also exposed a rapid metformin-induced increase in miR-193 family members, and miR-193b directly targets the FASN 3'UTR. Addition of exogenous miR-193b mimic to untreated TNBC cells decreased FASN protein expression and increased apoptosis of TNBC cells, while spontaneously immortalized, non-transformed breast epithelial cells remained unaffected. Conversely, antagonizing miR-193 activity impaired the ability of metformin to decrease FASN and cause cell death. Further, the metformin-stimulated increase in miR-193 resulted in reduced mammosphere formation by TNBC lines. These studies provide mechanistic insight into metformin-induced killing of TNBC.

Screening of alternative drugs to the tumor suppressor miR-375 in esophageal squamous cell carcinoma using the connectivity map

OBJECTIVE

The aim of this study was to identify alternative compounds to the tumor suppressor miR-375 using the connectivity map (CMAP) and to validate the antitumor effects of the identified drugs in esophageal squamous cell carcinoma (ESCC).

METHODS

Gene profiling of miR-375-treated TE2 and T.Tn cells was applied in order to search the CMAP database. Among the compounds identified using the CMAP, we focused on 8 drugs [(-)-epigallocatechin-3-gallate, metformin, rosiglitazone among others], excluding 2 drugs among the top 10 compounds. We evaluated whether these compounds possess tumor-suppressive functions in ESCC.

RESULTS

A cytotoxicity assay showed that the sensitivity of TE2 and T.Tn cells treated with the 8 compounds was evaluated based on IC50 values of 42.9 µM to 3.8 mM. A cell cycle analysis revealed that the percentage of TE2 and T.Tn cells incubated with 6 compounds in the G0/G1 phase or the G2/M phase increased by approximately 40-80%. A TUNEL assay showed that the percentages of apoptotic cells treated with almost all compounds were significantly increased (p < 0.05) compared with the control cells.

CONCLUSION

The CMAP database is a useful tool for identifying compounds affecting the same molecular pathways, particularly products that are difficult to apply via practical approaches, such as microRNAs.

Functional effects of a pathogenic mutation in Cereblon (CRBN) on the regulation of protein synthesis via the AMPK-mTOR cascade

Initially identified as a protein implicated in human mental deficit, cereblon (CRBN) was recently recognized as a negative regulator of adenosine monophosphate-activated protein kinase (AMPK) in vivo and in vitro. Here, we present results showing that CRBN can effectively regulate new protein synthesis through the mammalian target of rapamycin (mTOR) signaling pathway, a downstream target of AMPK. Whereas deficiency of Crbn repressed protein translation via activation of the AMPK-mTOR cascade in Crbn-knock-out mice, ectopic expression of the wild-type CRBN increased protein synthesis by inhibiting endogenous AMPK. Unlike the wild-type CRBN, a mutant CRBN found in human patients, which lacks the last 24 amino acids, failed to rescue mTOR-dependent repression of protein synthesis in Crbn-deficient mouse fibroblasts. These results provide the first evidence that Crbn can activate the protein synthesis machinery through the mTOR signaling pathway by inhibiting AMPK. In light of the fact that protein synthesis regulated by mTOR is essential for various forms of synaptic plasticity that underlie the cognitive functions of the brain, the results of this study suggest a plausible mechanism for CRBN involvement in higher brain function in humans, and they may help explain how a specific mutation in CRBN can affect the cognitive ability of patients.

Regulation of insulin-like growth factor signaling by metformin in endometrial cancer cells

Obesity, diabetes and insulin resistance are marked risk factors that promote the development of type I endometrial cancer. Previous studies have demonstrated that insulin-like growth factor 1 (IGF-1) and IGF-2 promote cell proliferation in endometrial cancer cells, while metformin reverses this effect and inhibits cell proliferation. However, the effects of metformin on the regulation of the IGF signaling pathway are unclear. The aim of this study was to investigate the regulation of IGF signaling by metformin in endometrial cancer cells, and to determine the effects of metformin combined with IGF-1 receptor (IGF-1R) inhibitor on cell proliferation and apoptosis. Cell proliferation was assessed following exposure of Ishikawa and HEC-1B endometrial cancer cell lines to metformin and/or the IGF-1R inhibitor, PPP. Apoptosis was assessed by TdT-mediated dUTP nick end labeling assay. Metformin was observed to downregulate IGF-1R and upregulate IGF binding protein-1 (IGFBP-1) mRNA and protein expression, while compound C, an adenosine monophosphate protein kinase inhibitor, reversed this effect. Metformin administered with PPP inhibited endometrial cancer cell proliferation to a greater degree than treatment with either agent alone. At high concentrations (1 or 2 mM), metformin induced apoptosis in endometrial cancer cells. Metformin combined with IGF-1R axis inhibitors may act synergistically to kill tumor cells, as metformin was shown to delay and prevent IGF-1R feedback. In conclusion, this study supported the results of animal studies and subclinical studies, demonstrating the feasibility of metformin combined with IGF-1R axis inhibitors in the treatment of endometrial cancer.

Use of metformin and survival of diabetic women with breast cancer

Objective: This study was set out to determine whether metformin use influences survival in breast cancer patients treated with antidiabetic drugs as compared to non-users.

Research Design and Methods: We used data from the Danish national registries (1996-2008) to identify adult female patients diagnosed with breast cancer who were prescribed antidiabetic medication. We performed multivariate Cox-proportional hazard regression to assess all-cause and breast cancer-specific mortality risks associated with metformin exposure. In a secondary analysis, we stratified use of metformin according to the cumulative number of prescriptions.

Results: Of the 1058 breast cancer patients 349 died during follow-up, with breast cancer listed as the primary cause of death for 152 cases. Compared to non-use, current metformin treatment was associated with a significant reduction in overall mortality (adjusted HR 0.74, 95% CI, 0.58-0.96). For breast cancer-specific mortality, a non-significant risk reduction (adjusted HR 0.88, 95% CI, 0.59-1.29) was observed, which became significant after stratification according to cumulative number of prescriptions. An increased risk of both overall and breast cancer-specific mortality was observed in the first 12 months after discontinuation of metformin.

Conclusions: We observed a nonsignificant reduction in breast cancer-specific mortality associated with metformin exposure among breast cancer patients treated with antidiabetic drugs. However, our findings suggest that long-term metformin use may have a beneficial effect on survival in patients with breast cancer. Further confirmation of these findings is needed.

Obesity and cancer--mechanisms underlying tumour progression and recurrence

Over the past several years, the field of cancer research has directed increased interest towards subsets of obesity-associated tumours, which include mammary, renal, oesophageal, gastrointestinal and reproductive cancers in both men and women. The increased risk of breast cancer that is associated with obesity has been widely reported; this has drawn much attention and as such, warrants investigation of the key mechanisms that link the obese state with cancer aetiology. For instance, the obese setting provides a unique adipose tissue microenvironment with concomitant systemic endocrine alterations that favour both tumour initiation and progression. Major metabolic differences exist within tumours that distinguish them from non-transformed healthy tissues. Importantly, considerable metabolic differences are induced by tumour cells in the stromal vascular fraction that surrounds them. The precise mechanisms that underlie the association of obesity with cancer and the accompanying metabolic changes that occur in the surrounding microenvironment remain elusive. Nonetheless, specific therapeutic agents designed for patients with obesity who develop tumours are clearly needed. This Review discusses recent advances in understanding the contributions of obesity to cancer and their implications for tumour treatment.

The effect of metformin on mortality following cancer among patients with diabetes

Diabetes may be a risk factor for cancer and is associated with worse cancer outcomes. Metformin may reduce cancer risk; however, its effect on mortality following cancer remains less clear. EMBASE and Medline were searched through February 10, 2014, for studies reporting an adjusted risk estimate for the effect of metformin therapy on mortality following cancer among diabetic patients. Random-effects models were used to obtain summary HR for the association between metformin and all-cause and cancer-specific mortality. Twenty-one observational studies were meta-analyzed in the primary analysis. Metformin was associated with a reduction in all-cause mortality [HR, 0.73; 95% confidence intervals (CI), 0.64-0.83] and cancer-specific mortality (HR, 0.74; 95% CI, 0.62-0.88). Subgroup analyses by cancer site showed a significant reduction in mortality for colon cancer (four studies, HR, 0.65; 95% CI, 0.56-0.76) but not for breast and prostate cancers. Observational studies indicate that metformin exposure at cancer diagnosis may be associated with a reduction in mortality. However, these findings need to be interpreted with caution as methodologic limitations of individual studies may have introduced biases in these findings. Our results emphasize the need for well-designed studies to further understand the relationship between metformin and survival following cancer.

Recent progress in metabolic signaling pathways regulating aging and life span

The NIH Summit, Advances in Geroscience: Impact on Health Span and Chronic Disease, discusses several aspects of cellular degeneration that underlie susceptibility to chronic aging-associated diseases, morbidity, and mortality. In particular, the session on Metabolism focuses on the interrelationship between signal transduction, intermediary metabolism, and metabolic products and byproducts that contribute to pathophysiologic phenotypes and detrimental effects that occur during the aging process, thus leading to susceptibility to disease. Although it is well established that many metabolic pathways (ie, oxidative phosphorylation, insulin-stimulated glucose uptake) decline with age, it often remains uncertain if these are a cause or consequence of the aging process. Moreover, the mechanisms accounting for the decline in metabolic function remain enigmatic. Several novel and unexpected concepts are emerging that will help to define the roles of altered metabolic control in the degenerative mechanisms of aging. This brief review summarizes several of the topics to be discussed in the metabolism of aging session (http://www.geron.org/About%20Us/nih-geroscience-summit).

AMPK at the nexus of energetics and aging

When energy supply is low, organisms respond by slowing aging and increasing resistance to diverse age-related pathologies. Targeting the mechanisms underpinning this response may therefore treat multiple disorders through a single intervention. Here, we discuss AMP-activated protein kinase (AMPK) as an integrator and mediator of several pathways and processes linking energetics to longevity. Activated by low energy, AMPK is both prolongevity and druggable, but its role in some pathologies may not be beneficial. As such, activating AMPK may modulate multiple longevity pathways to promote healthy aging, but unlocking its full potential may require selective targeting toward substrates involved in longevity assurance.

Improving treatment for obese women with early stage cancer of the uterus: rationale and design of the levonorgestrel intrauterine device ± metformin ± weight loss in endometrial cancer (feMME) trial

PURPOSE

Endometrial adenocarcinoma (EC) is the most common gynaecologic cancer. Up to 90% of EC patients are obese which poses a health threat to patients post-treatment. Standard treatment for EC includes hysterectomy, although this has significant side effects for obese women at high risk of surgical complications and for women of childbearing age. This trial investigates the effectiveness of non-surgical or conservative treatment options for obese women with early stage EC. The primary aim is to determine the efficacy of: levonorgestrel intrauterine device (LNG-IUD); with or without metformin (an antidiabetic drug); and with or without a weight loss intervention to achieve a pathological complete response (pCR) in EC at six months from study treatment initiation. The secondary aim is to enhance understanding of the molecular processes and to predict a treatment response by investigating EC biomarkers.

METHODS

An open label, three-armed, randomised, phase-II, multi-centre trial of LNG-IUD ± metformin ± weight loss intervention. 165 participants from 28 centres are randomly assigned in a 3:3:5 ratio to the treatment arms. Clinical, quality of life and health behavioural data will be collected at baseline, six weeks, three and six months. EC biomarkers will be assessed at baseline, three and six months.

CONCLUSIONS

There is limited prospective evidence for conservative treatment for EC. Trial results could benefit patients and reduce health system costs through a reduction in hospitalisations and through lower incidence of adverse events currently observed with standard treatment.

Effect of metformin on apoptosis induction in ovarian cancer cells

Introduction

Ovarian cancer is one of the most difficult problems in gynecologic oncology and the search for new drugs effective in the treatment of this kind of cancer, especially in cases resistant to current forms of therapy, remains a challenging priority.

The aim of the study

The aim of the study was to analyze the effect of metformin on apoptosis and the BIRC5 gene expression in ovarian cancer cell line SKOV-3. The BIRC5 gene encodes survivin protein.

Material and methods

SKOV-3 cells were treated with metformin (10 mM). Apoptotic changes in studied cells were analyzed by double staining using a mixture of fluorochromes – Hoechst 33258/propidium iodide (PI). The expression of the BIRC5 gene at the mRNA level was analyzed using the real-time PCR technique.

Results

Treatment of cells with metformin causes changes in the cell shape from oval to spindle and leads to the separation of the cells from the monolayer. Furthermore, metformin induces apoptosis and necrosis of ovarian cancer cells. A statistically significant increase in the number of apoptotic cells after 48 and 72 hours’ treatment with metformin relative to a control cells seems to be correlated with a decrease in the expression of the BIRC5 gene at the mRNA level.

Conclusions

Metformin seems to be a promising agent, whose use in ovarian cancer patients may contribute to improving the effectiveness of therapy.

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.

Nutrition and metabolism in hepatocellular carcinoma

Hepatocellular carcinoma is the fifth most common human cancer worldwide, with an overall 5-year survival in the range of 10%. In addition to the very substantial role of chronic viral hepatitis in causing hepatocellular carcinoma, nutritional status and specific nutritional factors appear to influence disease risk. This is apparent in the increased risk associated with non-alcoholic hepatic cirrhosis occurring in the context of obesity, the metabolic syndrome, and type 2 diabetes. Specific nutrients and ingested toxins, including ethanol, aflatoxin, microcystins, iron, and possibly components of red meat, also are associated with increased hepatocellular carcinoma risk. Other dietary components, including omega-3 fatty acids and branched chain amino acids, may have protective effects. Recent data further suggest that several metabolic regulatory drugs, including metformin, pioglitazone, and statins, may have the potential to decrease the risk of hepatocellular carcinoma. The available data on these nutritional and metabolic factors in causing hepatocellular carcinoma are reviewed with the goal of identifying the strength of current knowledge and directions for future investigation.

The effect of metformin on breast cancer outcomes in patients with type 2 diabetes

Observational data suggest that metformin use decreases breast cancer (BC) incidence in women with diabetes; the impact of metformin on BC outcomes in this population is less clear. The purpose of this analysis was to explore whether metformin use influences BC outcomes in women with type 2 diabetes. Prospective institutional databases were reviewed to identify patients with diabetes who received chemotherapy for stages I–III BC from 2000 to 2005. Patients diagnosed with diabetes before or within 6 months of BC diagnosis were included. Males and those with type I, gestational, or steroid-induced diabetes were excluded. Patients were stratified based on metformin use, at baseline, defined as use at time of BC diagnosis or at diabetes diagnosis if within 6 months of BC diagnosis. Kaplan–Meier methods were used to estimate rates of recurrence-free survival (RFS), overall survival (OS), and contralateral breast cancer (CBC). We identified 313 patients with diabetes who received chemotherapy for BC, 141 (45%) fulfilled inclusion criteria and 76 (54%) used metformin at baseline. There were no differences in clinical presentation or tumor characteristics between metformin users and nonusers. At a median follow-up of 87 months (range, 6.9–140.4 months), there was no difference in RFS (P = 0.61), OS (P = 0.462), or CBC (P = 0.156) based on metformin use. Five-year RFS was 90.4% (95% CI, 84–97) in metformin users and 85.4% (95% CI, 78–94) in nonusers. In this cohort of patients with type 2 diabetes receiving systemic chemotherapy for invasive BC, the use of metformin was not associated with improved outcomes.

Signalling pathways in endometrial cancer

Carcinogenesis is a multistage process, during which the activity of signalling pathways responsible for cell cycle regulation and division is disrupted which leads to inhibition of apoptosis and enhanced proliferation. Improper activation of Wnt/β-catenin and PI3K. Akt pathways play essential role in endometrial cancers (EC), mainly type I. Mutations in APC, axin or CTNBB1 may lead to β-catenin overactivation leading to excessive gene expression. PTEN inactivation, mutations in the PIK3CA or Akt result in increased transmission in the PI3K/Akt pathway, apoptosis inhibition, intensive cell division, mTOR excitation. In non-endometrioid cancers, key mutations include suppressor gene TP53 responsible for repairing damaged DNA or apoptosis initiation. Irregularities in gene P16, encoding a protein forming the p16-cyclinD/CDK-pRb have also been described. Understanding the complex relations between specific proteins taking part in signal transduction of the abovementioned pathways is key to research on drugs used in targeted therapy.

Effects of metformin on endometrial cancer cell growth in vivo: a preoperative prospective trial

BACKGROUND

Metformin, an antidiabetic drug, decreases the incidence of various cancers in diabetic patients. Metformin-induced inhibition of cancer cell proliferation has been confirmed in vitro but not in humans. Because endometrial cancer is associated with insulin resistance, the authors investigated whether a diabetes-therapeutic metformin dose inhibits cancer cell growth in patients with endometrial cancer.

METHODS

A dose of metaformin was administered (1500-2250 mg/day) to 31 patients with endometrial cancer preoperatively for 4 to 6 weeks. Cell proliferation was assessed in patient tissues using immunohistochemical and Western blot analyses and DNA synthesis was measured in serum using a thymidine uptake assay. All statistical tests were 2-sided. P values of < .05 were considered statistically significant.

RESULTS

Preoperative metformin treatment decreased DNA synthesis in sera and significantly reduced the Ki-67 (mean proportional decrease, 44.2%; 95% confidence interval [95% CI], 35.4-53.0 [P < .001]) and topoisomerase IIα (mean proportional decrease, 36.4%; 95% CI, 26.7-46.0 [P < .001]) labeling indices. Levels of phospho-ribosomal protein S6 and phospho-extracellular signal-regulated kinase 1/2 (ERK1/2) were found to be significantly decreased and phospho-adenosine monophosphate-activated protein kinase and p27 levels were significantly increased. Preoperative metformin use caused significant decreases in circulating factors, including insulin, glucose, insulin-like growth factor 1, and leptin. DNA synthesis-stimulating activity in patient sera was significantly decreased during metformin administration.

CONCLUSIONS

An antidiabetic dose of metformin inhibited endometrial cancer cell growth in vivo, an effect likely due to its effect on humoral factor(s). This translational study provides considerable rationale to initiate large clinical trials.