Metformin prevents tobacco carcinogen--induced lung tumorigenesis

Immune-mediated antitumor effect by type 2 diabetes drug, metformin

Metformin, a prescribed drug for type 2 diabetes, has been reported to have anti-cancer effects; however, the underlying mechanism is poorly understood. Here we show that this mechanism may be immune-mediated. Metformin enabled normal but not T-cell-deficient SCID mice to reject solid tumors. In addition, it increased the number of CD8(+) tumor-infiltrating lymphocytes (TILs) and protected them from apoptosis and exhaustion characterized by decreased production of IL-2, TNFα, and IFNγ. CD8(+) TILs capable of producing multiple cytokines were mainly PD-1(-)Tim-3(+), an effector memory subset responsible for tumor rejection. Combined use of metformin and cancer vaccine improved CD8(+) TIL multifunctionality. The adoptive transfer of antigen-specific CD8(+) T cells treated with metformin concentrations as low as 10 μM showed efficient migration into tumors while maintaining multifunctionality in a manner sensitive to the AMP-activated protein kinase (AMPK) inhibitor compound C. Therefore, a direct effect of metformin on CD8(+) T cells is critical for protection against the inevitable functional exhaustion in the tumor microenvironment.

Metformin Induced AMPK Activation, G0/G1 Phase Cell Cycle Arrest and the Inhibition of Growth of Esophageal Squamous Cell Carcinomas In Vitro and In Vivo

Esophageal squamous cell carcinomas (ESCC) have become a severe threat to health and the current treatments for ESCC are frequently not effective. Recent epidemiological studies suggest that the anti-hyperglycemic agent metformin may reduce the risk of developing cancer, including ESCC, among diabetic patients. However, the antitumor effects of metformin on ESCC and the mechanisms underlying its cell cycle regulation remain elusive. The findings reported herein show that the anti-proliferative action of metformin on ESCC cell lines is partially mediated by AMPK. Moreover, we observed that metformin induced G0/G1 phase arrest accompanied by the up-regulation of p21CIP1 and p27KIP1. In vivo experiments further showed that metformin inhibited tumor growth in a ESCC xenograft model. Most importantly, the up-regulation of AMPK, p53, p21CIP1, p27KIP1 and the down-regulation of cyclinD1 are involved in the anti-tumor action of metformin in vivo. In conclusion, metformin inhibits the growth of ESCC cells both in cell cultures and in an animal model. AMPK, p53, p21CIP1, p27KIP1 and cyclinD1 are involved in the inhibition of tumor growth that is induced by metformin and cell cycle arrest in ESCC. These findings indicate that metformin has the potential for use in the treatment of ESCC.

Inhibition of the GTPase Rac1 mediates the antimigratory effects of metformin in prostate cancer cells

Cell migration is a critical step in the progression of prostate cancer to the metastatic state, the lethal form of the disease. The antidiabetic drug metformin has been shown to display antitumoral properties in prostate cancer cell and animal models; however, its role in the formation of metastases remains poorly documented. Here, we show that metformin reduces the formation of metastases to fewer solid organs in an orthotopic metastatic prostate cancer cell model established in nude mice. As predicted, metformin hampers cell motility in PC3 and DU145 prostate cancer cells and triggers a radical reorganization of the cell cytoskeleton. The small GTPase Rac1 is a master regulator of cytoskeleton organization and cell migration. We report that metformin leads to a major inhibition of Rac1 GTPase activity by interfering with some of its multiple upstream signaling pathways, namely P-Rex1 (a Guanine nucleotide exchange factor and activator of Rac1), cAMP, and CXCL12/CXCR4, resulting in decreased migration of prostate cancer cells. Importantly, overexpression of a constitutively active form of Rac1, or P-Rex, as well as the inhibition of the adenylate cyclase, was able to reverse the antimigratory effects of metformin. These results establish a novel mechanism of action for metformin and highlight its potential antimetastatic properties in prostate cancer.

Koschei the immortal and anti-aging drugs

In Slavic folklore, Koschei the Immortal was bony, thin and lean. Was his condition caused by severe calorie restriction (CR)? CR deactivates the target of rapamycin pathway and slows down aging. But the life-extending effect of severe CR is limited by starvation. What if Koschei's anti-aging formula included rapamycin? And was rapamycin (or another rapalog) combined with commonly available drugs such as metformin, aspirin, propranolol, angiotensin II receptor blockers and angiotensin-converting enzyme inhibitors.

Metformin: from mechanisms of action to therapies

Metformin is currently the first-line drug treatment for type 2 diabetes. Besides its glucose-lowering effect, there is interest in actions of the drug of potential relevance to cardiovascular diseases and cancer. However, the underlying mechanisms of action remain elusive. Convincing data place energy metabolism at the center of metformin's mechanism of action in diabetes and may also be of importance in cardiovascular diseases and cancer. Metformin-induced activation of the energy-sensor AMPK is well documented, but may not account for all actions of the drug. Here, we summarize current knowledge about the different AMPK-dependent and AMPK-independent mechanisms underlying metformin action.

Exposure of mouse embryonic pancreas to metformin enhances the number of pancreatic progenitors

AIMS/HYPOTHESIS

Developing beta cells are vulnerable to nutrient environmental signals. Early developmental processes that alter the number of pancreatic progenitors can determine the number of beta cells present at birth. Metformin, the most widely used oral agent for treating diabetes, alters intracellular energy status in part by increasing AMP-activated protein kinase (AMPK) signalling. This study examined the effect of metformin on developing pancreas and beta cells.

METHODS

Pancreatic rudiments from CD-1 mice at embryonic day 13.0 (E13.0) were cultured with metformin, 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR, an AMPK activator) or vehicle control in vitro. In another set of studies, pregnant C57BL/6 mice were treated with metformin throughout gestation. Embryonic (E14.0) and neonatal pancreases were then analysed for their morphometry.

RESULTS

In vitro metformin treatment led to an increase in the proliferation and number of pancreatic duodenal homeobox 1-positive (PDX1(+)) progenitors. These results were reproduced by in vitro culture of embryonic pancreas rudiments with AICAR, suggesting that AMPK activation was involved. Similarly, metformin administration to pregnant dams induced an increase in both PDX1(+) and neurogenin 3-positive progenitors in the embryonic pancreas at E14.0 and these changes resulted in an increased beta cell fraction in neonates.

CONCLUSIONS/INTERPRETATION

These results indicate that exposure to metformin during gestation modulates the early steps of beta cell development (prior to E14.0) towards an increase in the number of pancreatic and endocrine progenitors. These changes ultimately result in a higher beta cell fraction at birth. These findings are of clinical importance given that metformin is currently used for the treatment of gestational diabetes.

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.

Do metformin a real anticarcinogen? A critical reappraisal of experimental data

Evidence has emerged that antidiabetic biguanides [phenformin (PF), buformin (BF) and metformin (MF)] are promising candidates for prevention of cancer. It was shown that antidiabetic biguanides postpone spontaneous carcinogenesis as well as inhibit carcinogenesis induced by chemical, radiation and biological factors (virus, transgene, genetic modifications, special diet, etc.) in a number of organs and tissues in various strains of mice and rats. The present review focused on some details of experiments such as design of studies, dose and route of administration of biguanide, and age of animals at start of treatment etc. Conclusion may be done that there are rather sufficient evidence of cancer-preventive activity of antidiabetic biguanides in experimental animals.

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

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

Metformin 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.

A multicenter, open-label phase II study of metformin with erlotinib in second-line therapy of stage IV non-small-cell lung cancer patients: treatment rationale and protocol dynamics of the METAL trial

We present the rationale and study design of the METAL (METformin in Advanced Lung cancer) trial (EudraCT number: 2014-000349-59), a multicenter, open label phase II study, designed to evaluate the safety and activity of metformin combined with erlotinib as second-line therapy in patients with stage IV non-small-cell lung cancer. This is a 2-part trial, consisting of a safety run-in part followed by a phase II part. The primary end point for the first part is the maximum tolerated dose and the identification of the recommended phase II dose of metformin in combination with erlotinib. Secondary end points are the study of pharmacokinetics and the antitumor activity evaluation of the experimental combination. The primary end point of part II is the time to disease progression with the combination, and antitumor activity as a secondary end point. Based on the statistical design, we plan to enroll approximately 60 patients.

Dietary restriction-resistant human tumors harboring the PIK3CA-activating mutation H1047R are sensitive to metformin

Cancer cells expressing constitutively active phosphatidylinositol-3 kinase (PI3K) are proliferative regardless of the absence of insulin, and they form dietary restriction (DR)-resistant tumors in vivo. Because the binding of insulin to its receptors activates the PI3K/AKT/mammalian target of rapamycin (mTOR) signaling cascade, activating mutations in the PIK3CA oncogene may determine tumor response to DR-like pharmacological strategies targeting the insulin and mTOR pathways. The anti-diabetic drug metformin is a stereotypical DR mimetic that exerts its anti-cancer activity through a dual mechanism involving insulin-related (systemic) and mTOR-related (cell-autonomous) effects. However, it remains unclear whether PIK3CA-activating mutations might preclude the anti-cancer activity of metformin in vivo. To model the oncogenic PIK3CA-driven early stages of cancer, we used the clonal breast cancer cell line MCF10DCIS.com, which harbors the gain-of-function H1047R hot-spot mutation in the catalytic domain of the PI3KCA gene and has been shown to form DR-refractory xenotumors. To model PIK3CA-activating mutations in late stages of cancer, we took advantage of the isogenic conversion of a PIK3CA-wild-type tumor into a PIK3CA H1047R-mutated tumor using the highly metastatic colorectal cancer cell line SW48. MCF10DCIS.com xenotumors, although only modestly affected by treatment with oral metformin (approximately 40% tumor growth inhibition), were highly sensitive to the intraperitoneal (i.p.) administration of metformin, the anti-cancer activity of which increased in a time-dependent manner and reached >80% tumor growth inhibition by the end of the treatment. Metformin treatment via the i.p. route significantly reduced the proliferation factor mitotic activity index (MAI) and decreased tumor cellularity in MCF10DCIS.com cancer tissues. Whereas SW48-wild-type (PIK3CA+/+) cells rapidly formed metformin-refractory xenotumors in mice, ad libitum access to water containing metformin significantly reduced the growth of SW48-mutated (PIK3CAH1047R/+) xenotumors by approximately 50%. Thus, metformin can no longer be considered as a bona fide DR mimetic, at least in terms of anti-cancer activity, because tumors harboring the insulin-unresponsive, DR-resistant, PIK3CA-activating mutation H1047R remain sensitive to the anti-tumoral effects of the drug. Given the high prevalence of PIK3CA mutations in human carcinomas and the emerging role of PIK3CA mutation status in the treatment selection process, these findings might have a significant impact on the design of future trials evaluating the potential of combining metformin with targeted therapy.

Metformin inhibition of neuroblastoma cell proliferation is differently modulated by cell differentiation induced by retinoic acid or overexpression of NDM29 non-coding RNA

BACKGROUND

Metformin is a widely used oral hypoglycemizing agent recently proposed as potential anti-cancer drug. In this study we report the antiproliferative effect of metformin treatment in a high risk neuroblastoma cell model, focusing on possible effects associated to different levels of differentiation and/or tumor initiating potential.

METHODS

Antiproliferative and cytotoxic effects of metformin were tested in human SKNBE2 and SH-SY5Y neuroblastoma cell lines and in SKNBE2 cells in which differentiation is induced by retinoic acid treatment or stable overexpression of NDM29 non-coding RNA, both conditions characterized by a neuron-like differentiated phenotype.

RESULTS

We found that metformin significantly inhibits the proliferation of NB cells, an effect that correlates with the inhibition of Akt, while AMPK activity resulted unchanged. Notably, metformin effects were modulated in a different ways by differentiating stimuli, being abolished after retinoic acid treatment but potentiated by overexpression of NDM29.

CONCLUSION

These data suggest the efficacy of metformin as neuroblastoma anticancer agent, and support the requirement of further studies on the possible role of the differentiation status on the antiproliferative effects of this drug.

AMPK Activators as a Drug for Diabetes, Cancer and Cardiovascular Disease

The cellular mechanisms of AMP-Activated Protein Kinase (AMPK) activators in the treatment and prevention of diabetes, cancer, and cardiovascular disease.

Reduced risk of lung cancer with metformin therapy in diabetic patients: a systematic review and meta-analysis

Emerging evidence from epidemiologic studies and basic science suggests an inverse association between metformin use and cancer risk in diabetic patients. However, the association with lung cancer is not consistent. We summarized the evidence currently available (2009-2013) and explored sources of heterogeneity. Metformin therapy was associated with significantly lower risks of cancers of the lung (4 studies; pooled relative risk = 0.71, 95% confidence interval (CI): 0.55, 0.95; P = 0.02) and respiratory system (6 studies; pooled relative risk = 0.85, 95% CI: 0.75, 0.96; P = 0.01). There was evidence of moderate heterogeneity (I(2) > 50%). The major sources of heterogeneity were smoking adjustment status and cancer site. The relative risk from studies that adjusted for smoking was 1.16-fold (95% CI: 1.00, 1.35) closer to the null than that from studies not adjusting for smoking. The relative risk of respiratory cancer was 1.23-fold (95% CI: 1.02, 1.49) closer to the null than that for lung cancer. In conclusion, metformin use appears to be associated with lower risks of lung and respiratory cancer in diabetic patients. However, caution regarding overestimation is needed, since adjustment for smoking attenuates the association.

Metformin and Not Diabetes Influences the Survival of Resected Early Stage NSCLC Patients

BACKGROUND

Published data suggest that diabetes influences survival of patients with lung cancer. The anti-cancer effect of metformin confounds this association. We sought to study the association of diabetes and metformin with survival in patients undergoing resection of stage I non-small cell lung cancer (NSCLC).

METHODS

Pathologic stage I NSCLC patients undergoing anatomic resection from 2002 to 2011 were studied. A diagnosis of diabetes and diabetic medication use were identified through records. Univariate and multivariate analyses examined the association of diabetes and metformin usage with overall survival (OS).

RESULTS

409 eligible patients were included in the analysis - excluding patients with neoadjuvant therapy, more than one lung cancer, or resection less than lobectomy. 71 (17.4%) patients were diabetics and 41 (10.0%) used metformin. With a median follow up of 44 months, univariate analysis demonstrates that diabetes had no effect on OS (P=0.75); however, metformin use was associated with improved OS (median survival not reached vs. 60 months; P=0.02). Metformin use remained an important predictor of good survival in multivariate analysis (HR=3.08; P<0.01) after adjusting for age, gender, pathologic stage, histology and smoking status.

CONCLUSION

Metformin use rather than diabetes is associated with improved long-term survival in Stage I NSCLC patients.

Role of metformin in suppressing 1,2-dimethylhydrazine-induced colon cancer in diabetic and non-diabetic mice: effect on tumor angiogenesis and cell proliferation

Several studies indicated that type 2 diabetes mellitus and insulin resistance are associated with increased colon cancer risk. Recently, studies suggest that metformin can reduce cancer risk in diabetic or non-diabetic patients with unclear mechanisms. This work aimed to determine the effect of metformin on chemically-induced colon cancer in mice. Colon cancer was induced using 1,2-dimethylhydrazine (DMH, 20 mg/kg/week, s.c.) for fifteen weeks. Experiment I: healthy mice were fed with basal diet for four weeks and then allocated into seven groups, (i) saline, (ii) DMH, (iii) oxaliplatin, (iv-v): metformin (100 or 200 mg/kg) and (vi-vii): oxaliplatin+metformin (100 or 200 mg/kg), respectively. Experiment II: type 2 diabetes mellitus was induced by injection of STZ (30 mg/kg) after four weeks of high-fat feeding and then mice were allocated into seven groups similar to those reported in experiment I. Examination of the colonic tissue at the end of the experiment highlighted an increase in angiogenic markers and cell proliferation and showed a greater immunostaining for insulin growth factor I receptors and CD34 in the colon of diabetic mice compared to non-diabetics. In general, metformin downregulated tumor angiogenesis and augmented the antitumor effect of oxaliplatin. Overall, the current results showed that metformin protected against DMH-induced colon cancer in non-diabetic and diabetic mice. This therapeutic effect was, at least in part, attributed to its anti-angiogenic and anti-proliferative mechanisms.

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.

Latest insights into the risk of cancer in diabetes

A growing body of evidence from observational studies and meta‐analyses of the data suggest that diabetes mellitus is associated with an increased risk of cancer. Meta‐analyses have shown that diabetes increases the risks of total cancer, and of site‐specific cancers of the breast, endometrium, bladder, liver, colorectum and pancreas, and that it decreases the risk of prostate cancer. Insulin resistance and secondary hyperinsulinemia is the most frequently proposed hypothesis, and hyperglycemia itself might promote carcinogenesis. In addition to several facets of lifestyle including obesity, smoking and lack of exercise, treatment for diabetes might affect the risk of cancer. For instance, metformin, an insulin sensitizer, reportedly has a potential anticancer effect. In light of the exploding global epidemic of diabetes, even a modest increase in the cancer risk will translate into a substantial socioeconomic burden. The current insights underscore the need for clinical attention and better‐designed studies of the complex interactions between diabetes and cancer.

Therapeutic targeting of autophagy in cancer. Part II: pharmacological modulation of treatment-induced autophagy

Autophagy, the catabolic pathway in which cells recycle organelles and other parts of their own cytoplasm, is increasingly recognised as an important cytoprotective mechanism in cancer cells. Several cancer treatments stimulate the autophagic process and when autophagy is inhibited, cancer cells show an enhanced response to multiple treatments. These findings have nourished the theory that autophagy provides cancer cells with a survival advantage during stressful conditions, including exposure to therapeutics. Therefore, interference with the autophagic response can potentially enhance the efficacy of cancer therapy. In this review we examine two approaches to modulate autophagy as complementary cancer treatment: inhibition and induction. Inhibition of autophagy during cancer treatment eliminates its cytoprotective effects. Conversely, induction of autophagy combined with conventional cancer therapy exerts severe cytoplasmic degradation that can ultimately lead to cell death. We will discuss how autophagy can be therapeutically manipulated in cancer cells and how interactions between the conventional cancer therapies and autophagy modulation influence treatment outcome.

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.

microRNAs and cancer metabolism reprogramming: the paradigm of metformin

Increasing evidence witnesses that cancer metabolism alterations represent a critical hallmark for many types of human tumors. There is a strong need to understand and dissect the molecular mechanisms underlying cancer metabolism to envisage specific biomarkers and underpin critical molecular components that might represent novel therapeutic targets. One challenge, that is the focus of this review, is the reprogramming of the altered metabolism of a cancer cell toward that of un-transformed cell. The anti-hyperglicemic agent, metformin has proven to be effective in reprogramming the metabolism of cancer cells even from those subpopulations endowed with cancer stem like features and very high chemoresistenace to conventional anticancer treatments. A functional interplay involving selective modulation of microRNAs (miRNAs) takes place along the anticancer metabolic effects exerted by metformin. The implications of this interplay will be also discussed in this review.

The peroxisome proliferator-activated receptor (PPAR) α agonist fenofibrate suppresses chemically induced lung alveolar proliferative lesions in male obese hyperlipidemic mice

Activation of peroxisome proliferator-activated receptor (PPAR) α disrupts growth-related activities in a variety of human cancers. This study was designed to determine whether fenofibrate, a PPARα agonist, can suppress 4-nitroquinoline 1-oxide (4-NQO)-induced proliferative lesions in the lung of obese hyperlipidemic mice. Male Tsumura Suzuki Obese Diabetic mice were subcutaneously injected with 4-NQO to induce lung proliferative lesions, including adenocarcinomas. They were then fed a diet containing 0.01% or 0.05% fenofibrate for 29 weeks, starting 1 week after 4-NQO administration. At week 30, the incidence and multiplicity (number of lesions/mouse) of pulmonary proliferative lesions were lower in mice treated with 4-NQO and both doses of fenofibrate compared with those in mice treated with 4-NQO alone. The incidence and multiplicity of lesions were significantly lower in mice treated with 4-NQO and 0.05% fenofibrate compared with those in mice treated with 4-NQO alone (p<0.05). Both doses of fenofibrate significantly reduced the proliferative activity of the lesions in 4-NQO-treated mice (p<0.05). Fenofibrate also significantly reduced the serum insulin and insulin-like growth factor (IGF)-1 levels, and decreased the immunohistochemical expression of IGF-1 receptor (IGF-1R), phosphorylated Akt, and phosphorylated Erk1/2 in lung adenocarcinomas. Our results indicate that fenofibrate can prevent the development of 4-NQO-induced proliferative lesions in the lung by modulating the insulin-IGF axis.

Metformin sensitizes prostate cancer cells to radiation through EGFR/p-DNA-PKCS in vitro and in vivo

Although neo-adjuvant radiotherapy is generally successful in treatment of advanced prostate cancer, radioresistance is still a major therapeutic problem in many patients. In the current study, we investigated the effects of metformin (1,1-dimethylbiguanide hydrochloride), a widely used antidiabetic drug, on tumor cell radiosensitivity in prostate cancer. Through clonogenic survival assays, we found that metformin treatment enhanced radiosensitivity of prostate cancer cells with a dose enhancement factor. Moreover, irradiation of subcutaneous C4-2 tumors in mice treated with metformin resulted in an increase in radiation-induced tumor growth delay (17.3 days to 29.5 days, P < 0.01), which indicates that the tumor radiosensitivity increased by metformin in vivo. We also measured the sublethal damage repair and analyzed double-strand breaks (DSBs) in X-irradiated cells. γ-H2AX, as an indicator of DSBs, had significantly more foci per cell in the group treated with metformin and radiation compared to groups treated with metformin or irradiation, respectively. Moreover, mice with subcutaneous tumor implants lived longer after a combined treatment of metformin and radiation. In addition, the reduced phosphorylation of DNA-PKcs caused by EGFR/PI3K/Akt down-regulation is essential for metformin to induce radiosensitivity in prostate cancer cells. Our results indicate that metformin enhances prostate cancer cell radiosensitivity in vitro and in vivo. Exposure to metformin before radiation therapy could be a beneficial option for the treatment of prostate cancer.

Metformin inhibits mitochondrial complex I of cancer cells to reduce tumorigenesis

Recent epidemiological and laboratory-based studies suggest that the anti-diabetic drug metformin prevents cancer progression. How metformin diminishes tumor growth is not fully understood. In this study, we report that in human cancer cells, metformin inhibits mitochondrial complex I (NADH dehydrogenase) activity and cellular respiration. Metformin inhibited cellular proliferation in the presence of glucose, but induced cell death upon glucose deprivation, indicating that cancer cells rely exclusively on glycolysis for survival in the presence of metformin. Metformin also reduced hypoxic activation of hypoxia-inducible factor 1 (HIF-1). All of these effects of metformin were reversed when the metformin-resistant Saccharomyces cerevisiae NADH dehydrogenase NDI1 was overexpressed. In vivo, the administration of metformin to mice inhibited the growth of control human cancer cells but not those expressing NDI1. Thus, we have demonstrated that metformin's inhibitory effects on cancer progression are cancer cell autonomous and depend on its ability to inhibit mitochondrial complex I.DOI: http://dx.doi.org/10.7554/eLife.02242.001.

Metformin inhibits mitochondrial complex I of cancer cells to reduce tumorigenesis

Recent epidemiological and laboratory-based studies suggest that the anti-diabetic drug metformin prevents cancer progression. How metformin diminishes tumor growth is not fully understood. In this study, we report that in human cancer cells, metformin inhibits mitochondrial complex I (NADH dehydrogenase) activity and cellular respiration. Metformin inhibited cellular proliferation in the presence of glucose, but induced cell death upon glucose deprivation, indicating that cancer cells rely exclusively on glycolysis for survival in the presence of metformin. Metformin also reduced hypoxic activation of hypoxia-inducible factor 1 (HIF-1). All of these effects of metformin were reversed when the metformin-resistant Saccharomyces cerevisiae NADH dehydrogenase NDI1 was overexpressed. In vivo, the administration of metformin to mice inhibited the growth of control human cancer cells but not those expressing NDI1. Thus, we have demonstrated that metformin's inhibitory effects on cancer progression are cancer cell autonomous and depend on its ability to inhibit mitochondrial complex I.DOI: http://dx.doi.org/10.7554/eLife.02242.001.

Oral and intraperitoneal administration of quercetin decreased lymphocyte DNA damage and plasma lipid peroxidation induced by TSA in vivo

Our previous study showed that quercetin enhances the anticancer effect of trichostatin A (TSA) in xenograft mice given quercetin intraperitoneally (10 mg/kg, 3 times/week). Herein, we investigate whether quercetin administered orally exerts such an effect and prevents the cytotoxic side effects of TSA. We found that quercetin given orally (20 and 100 mg/kg, 3 times/week) failed to enhance the antitumor effect of TSA although it increased the total quercetin concentration more than quercetin administered intraperitoneally in the plasma. The compound quercetin-3-glucuronide (Q3G) increased the most. However, quercetin administered intraperitoneally increased the total quercetin level in tumor tissues more than oral quercetin. Oral and intraperitoneal administration of quercetin similarly decreased lymphocyte DNA damage and plasma lipid peroxidation level induced by TSA. Furthermore, we found that the enhancing effect of Q3G on the antitumor effect of TSA and the incorporation of Q3G was less than that of quercetin in A549 cells. However, we found that A549 cells possessed the ability to convert Q3G to quercetin. In conclusion, different from quercetin administered intraperitoneally, quercetin administered orally failed to enhance the antitumor effect of TSA because of its metabolic conversion. However, it prevented TSA-induced DNA damage and lipid peroxidation.

Modulation by metformin of molecular and histopathological alterations in the lung of cigarette smoke-exposed mice

The anti-diabetic drug metformin is endowed with anti-cancer properties. Epidemiological and experimental studies, however, did not provide univocal results regarding its role in pulmonary carcinogenesis. We used Swiss H mice of both genders in order to detect early molecular alterations and tumors induced by mainstream cigarette smoke. Based on a subchronic toxicity study, oral metformin was used at a dose of 800 mg/kg diet, which is 3.2 times higher than the therapeutic dose in humans. Exposure of mice to smoke for 4 months, starting at birth, induced a systemic clastogenic damage, formation of DNA adducts, oxidative DNA damage, and extensive downregulation of microRNAs in lung after 10 weeks. Preneoplastic lesions were detectable after 7.5 months in both lung and urinary tract along with lung tumors, both benign and malignant. Modulation by metformin of 42 of 1281 pulmonary microRNAs in smoke-free mice highlighted a variety of mechanisms, including modulation of AMPK, stress response, inflammation, NFκB, Tlr9, Tgf, p53, cell cycle, apoptosis, antioxidant pathways, Ras, Myc, Dicer, angiogenesis, stem cell recruitment, and angiogenesis. In smoke-exposed mice, metformin considerably decreased DNA adduct levels and oxidative DNA damage, and normalized the expression of several microRNAs. It did not prevent smoke-induced lung tumors but inhibited preneoplastic lesions in both lung and kidney. In conclusion, metformin was able to protect the mouse lung from smoke-induced DNA and microRNA alterations and to inhibit preneoplastic lesions in lung and kidney but failed to prevent lung adenomas and malignant tumors induced by this complex mixture.

Managing lipid metabolism in proliferating cells: new perspective for metformin usage in cancer therapy

Cancer cells metabolically adapt to undergo cellular proliferation. Lipids, besides their well-known role as energy storage, represent the major building blocks for the synthesis of neo-generated membranes. There is increasing evidence that cancer cells show specific alterations in different aspects of lipid metabolism. The changes of expression and activity of lipid metabolising enzymes are directly regulated by the activity of oncogenic signals. The dependence of tumour cells on the deregulated lipid metabolism suggests that proteins involved in this process could be excellent chemotherapeutic targets for cancer treatment. Due to its rare side effects in non-cancerous cells, metformin has been recently revaluated as a potential anti-tumourigenic drug, which negatively affects lipid biosynthetic pathways. In this review we summarised the emerging molecular events linking the anti-proliferative effect of metformin with lipid metabolism in cancer cells.

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

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

[New promises for metformin: advances in the understanding of its mechanisms of action]

Metformin is currently the drug of first choice for the treatment of type 2 diabetes. However, although prescribed since the end of the 1950s, the mechanism of action of metformin remains as yet incompletely understood but recent work has unveiled novel and surprising properties. Epidemiological reports have suggested that metformin protects against heart failure and has antitumor properties independent of its anti-hyperglycemic effect. Here, we review the proposed mechanisms for metformin action in diabetes, cardiovacular diseases and cancer.

Metformin: a metabolic disruptor and anti-diabetic drug to target human leukemia

There is a global and urgent need for expanding our current therapeutical arsenal against leukemia in order to improve their actual cure rates and fight relapse. Targeting the reprogrammed, altered cancer metabolism is an emerging strategy which should profoundly affect cancer cells in their intimate and irrepressible needs and addictions for nutrients uptake and incorporation into the biomass during malignant proliferation. We present here how metformin, an anti-diabetic drug that has attracted a strong interest for its recently discovered anti-cancer properties, can be envisioned as a new adjuvant approach to treat leukemia. Metformin may have a double-edged sword effect (i) by acting on the organism to decrease hyperglycaemia and hyperinsulinemia in diabetic patients and (ii) at the cellular level, by inhibiting the mTORC1-cancer supporting pathway through AMPK-dependent and independent mechanisms.

Metformin: a potential therapeutic agent for recurrent colon cancer

Accumulating evidence suggests that metformin, a biguanide class of anti-diabetic drugs, possesses anti-cancer properties. However, most of the studies to evaluate therapeutic efficacy of metformin have been on primary cancer. No information is available whether metformin could be effectively used for recurrent cancer, specifically colorectal cancer (CRC) that affects up to 50% of patients treated by conventional chemotherapies. Although the reasons for recurrence are not fully understood, it is thought to be due to re-emergence of chemotherapy-resistant cancer stem/stem-like cells (CSCs/CSLCs). Therefore, development of non-toxic treatment strategies targeting CSCs would be of significant therapeutic benefit. In the current investigation, we have examined the effectiveness of metformin, in combination with 5-fluorouracil and oxaliplatin (FuOx), the mainstay of colon cancer therapeutics, on survival of chemo-resistant colon cancer cells that are highly enriched in CSCs/CSLCs. Our data show that metformin acts synergistically with FuOx to (a) induce cell death in chemo resistant (CR) HT-29 and HCT-116 colon cancer cells, (b) inhibit colonospheres formation and (c) enhance colonospheres disintegration. In vitro cell culture studies have further demonstrated that the combinatorial treatment inhibits migration of CR colon cancer cells. These changes were associated with increased miRNA 145 and reduction in miRNA 21. Wnt/β-catenin signaling pathway was also down-regulated indicating its pivotal role in regulating the growth of CR colon cancer cells. Data from SCID mice xenograft model of CR HCT-116 and CR HT-29 cells show that the combination of metformin and FuOX is highly effective in inhibiting the growth of colon tumors as evidenced by ∼ 50% inhibition in growth following 5 weeks of combination treatment, when compared with the vehicle treated controls. Our current data suggest that metformin together with conventional chemotherapy could be an effective treatment regimen for recurring colorectal cancer (CRC).

Discrete mechanisms of mTOR and cell cycle regulation by AMPK agonists independent of AMPK

The multifunctional AMPK-activated protein kinase (AMPK) is an evolutionarily conserved energy sensor that plays an important role in cell proliferation, growth, and survival. It remains unclear whether AMPK functions as a tumor suppressor or a contextual oncogene. This is because although on one hand active AMPK inhibits mammalian target of rapamycin (mTOR) and lipogenesis--two crucial arms of cancer growth--AMPK also ensures viability by metabolic reprogramming in cancer cells. AMPK activation by two indirect AMPK agonists AICAR and metformin (now in over 50 clinical trials on cancer) has been correlated with reduced cancer cell proliferation and viability. Surprisingly, we found that compared with normal tissue, AMPK is constitutively activated in both human and mouse gliomas. Therefore, we questioned whether the antiproliferative actions of AICAR and metformin are AMPK independent. Both AMPK agonists inhibited proliferation, but through unique AMPK-independent mechanisms and both reduced tumor growth in vivo independent of AMPK. Importantly, A769662, a direct AMPK activator, had no effect on proliferation, uncoupling high AMPK activity from inhibition of proliferation. Metformin directly inhibited mTOR by enhancing PRAS40's association with RAPTOR, whereas AICAR blocked the cell cycle through proteasomal degradation of the G2M phosphatase cdc25c. Together, our results suggest that although AICAR and metformin are potent AMPK-independent antiproliferative agents, physiological AMPK activation in glioma may be a response mechanism to metabolic stress and anticancer agents.

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

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

New perspective for an old antidiabetic drug: metformin as anticancer agent

Metformin, an inexpensive, well-tolerated oral agent that is commonly used in the first-line treatment for type 2 diabetes, has become the focus of intense research as a potential anticancer agent. This research reflects a convergence of epidemiologic, clinical, and preclinical evidence, suggesting that metformin may lower cancer risk in diabetics and improve outcomes of many common cancers. Notably, metformin mediates an approximately 30 % reduction in the lifetime risk of cancer in diabetic patients. There is growing recognition that metformin may act (1) directly on cancer cells, primarily by impacting mitochondrial respiration leading to the activation of the AMP-activated protein kinase (AMPK), which controls energy homeostasis in cells, but also through other mechanisms or (2) indirectly on the host metabolism, largely through AMPK-mediated reduction in hepatic gluconeogenesis, leading to reduced circulating insulin levels and decreased insulin/IGF-1 receptor-mediated activation of the PI3K pathway. Support for this comes from the observation that metformin inhibits cancer cell growth in vitro and delays the onset of tobacco carcinogen-induced lung cancer in mice and that metformin and its analog phenformin delay spontaneous tumor development cancer-prone transgenic mice. The potential for both direct antitumor effects and indirect host-mediated effects has sparked enormous interest, but has led to added challenges in translating preclinical findings to the clinical setting. Nonetheless, the accumulation of evidence has been sufficient to justify initiation of clinical trials of metformin as an anticancer agent in the clinical setting, including a large-scale adjuvant study in breast cancer, with additional studies planned.

Metformin, cancer and glucose metabolism

Metformin is the first-line treatment for type 2 diabetes. Results from several clinical studies have indicated that type 2 diabetic patients treated with metformin might have a lower cancer risk. One of the primary metabolic changes observed in malignant cell transformation is an increased catabolic glucose metabolism. In this context, once it has entered the cell through organic cation transporters, metformin decreases mitochondrial respiration chain activity and ATP production that, in turn, activates AMP-activated protein kinase, which regulates energy homeostasis. In addition, metformin reduces cellular energy availability and glucose entrapment by inhibiting hexokinase-II, which catalyses the glucose phosphorylation reaction. In this review, we discuss recent findings on molecular mechanisms that sustain the anticancer effect of metformin through regulation of glucose metabolism. In particular, we have focused on the emerging action of metformin on glycolysis in normal and cancer cells, with a drug discovery perspective.

Effects of metformin on cell proliferation and apoptosis in human esophageal squamous cancer cell line Eca109

AIM: To investigate the effects of metformin on cell proliferation, apoptosis and cell cycle progression in human esophageal cancer cell line Eca109 in vitro, to explore the possible mechanisms, and to observe whether there is a synergistic effect between metformin and 5-fluorouracil (5-FU).

METHODS: MTT assay was used to detect cell inhibition rate after treatment with metformin alone or in combination with 5-FU. Morphological changes of cells were observed by Hoechest33258 staining. The changes in cell cycle progression were examined by flow cytometry (FCM). The expression of p27 and cyclin D1 mRNAs in Eca109 cells was detected by reverse transcription-PCR.

RESULTS: Apoptotic features including nuclear pyknosis, chromatin margination and apoptotic bodies were observed in Eca109 cells after treatment with metformin by inverted phase contrast microscopy and Hoechest33258 staining. Metformin significantly inhibited the proliferation of Eca109 cells in a dose- (r = 0.968, P < 0.05 ) and time-dependent (r = 0.914, P < 0.05) manner. Metformin treatment enhanced 5-Fu-mediated cell growth inhibition (24 h: t = 6.943, P < 0.05; 48 h: t = 7.764, P < 0.05; 72 h: t = 14.554, P < 0.05 vs metformin alone). However, metformin and 5-FU had no synergistic anti-proliferative effect in esophageal cells. Flow cytometry analysis showed that metformin increased the percentage of cells in G₀/G₁ phase in a dose-dependent manner. The expression of cyclin D1 mRNA was down-regulated, while the expression of p27 mRNA was up-regulated after metformin treatment.

CONCLUSION: Metformin inhibits cell proliferation, promotes apoptosis and blocks the cell cycle at G₀/G₁ phase, which may be attributable to down-regulation of cyclin D1 and up-regulation of p27. Metformin and 5-FU have no synergistic anti-proliferative effect in Eca109 cells.

Metformin selectively targets tumor-initiating cells in ErbB2-overexpressing breast cancer models

Metformin is an oral biguanide used for type II diabetes. Epidemiologic studies suggest a link between metformin use and reduced risk of breast and other types of cancers. ErbB2-expressing breast cancer is a subgroup of tumors with poor prognosis. Previous studies demonstrated that metformin is a potent inhibitor of ErbB2-overexpressing breast cancer cells; metformin treatment extends the life span and impedes mammary tumor development in ErbB2 transgenic mice in vivo. However, the mechanisms of metformin associated antitumor activity, especially in prevention models, remain unclear. We report here for the first time that systemic administration of metformin selectively inhibits CD61(high)/CD49f(high) subpopulation, a group of tumor-initiating cells (TIC) of mouse mammary tumor virus (MMTV)-ErbB2 mammary tumors, in preneoplastic mammary glands. Metformin also inhibited CD61(high)/CD49f(high) subpopulation in MMTV-ErbB2 tumor-derived cells, which was correlated with their compromised tumor initiation/development in a syngeneic tumor graft model. Molecular analysis indicated that metformin induced downregulation of ErbB2 and EGFR expression and inhibited the phosphorylation of ErbB family members, insulin-like growth factor-1R, AKT, mTOR, and STAT3 in vivo. In vitro data indicate that low doses of metformin inhibited the self-renewal/proliferation of cancer stem cells (CSC)/TICs in ErbB2-overexpressing breast cancer cells. We further demonstrated that the expression and activation of ErbB2 were preferentially increased in CSC/TIC-enriched tumorsphere cells, which promoted their self-renewal/proliferation and rendered them more sensitive to metformin. Our results, especially the in vivo data, provide fundamental support for developing metformin-mediated preventive strategies targeting ErbB2-associated carcinogenesis.

Metformin: On Ongoing Journey across Diabetes, Cancer Therapy and Prevention

Cancer metabolism is the focus of intense research, which witnesses its key role in human tumors. Diabetic patients treated with metformin exhibit a reduced incidence of cancer and cancer-related mortality. This highlights the possibility that the tackling of metabolic alterations might also hold promising value for treating cancer patients. Here, we review the emerging role of metformin as a paradigmatic example of an old drug used worldwide to treat patients with type II diabetes which to date is gaining strong in vitro and in vivo anticancer activities to be included in clinical trials. Metformin is also becoming the focus of intense basic and clinical research on chemoprevention, thus suggesting that metabolic alteration is an early lesion along cancer transformation. Metabolic reprogramming might be a very efficient prevention strategy with a profound impact on public health worldwide.

Phenformin enhances the therapeutic benefit of BRAF(V600E) inhibition in melanoma

Biguanides, such as the diabetes therapeutics metformin and phenformin, have demonstrated antitumor activity both in vitro and in vivo. The energy-sensing AMP-activated protein kinase (AMPK) is known to be a major cellular target of biguanides. Based on our discovery of cross-talk between the AMPK and v-Raf murine sarcoma viral oncogene homolog B1 (BRAF) signaling pathways, we investigated the antitumor effects of combining phenformin with a BRAF inhibitor PLX4720 on the proliferation of BRAF-mutated melanoma cells in vitro and on BRAF-driven tumor growth in vivo. Cotreatment of BRAF-mutated melanoma cell lines with phenformin and PLX4720 resulted in synergistic inhibition of cell viability, compared with the effects of the single agent alone. Moreover, treatment with phenformin significantly delayed the development of resistance to PLX4720 in cultured melanoma cells. Biochemical analyses showed that phenformin and PLX4720 exerted cooperative effects on inhibiting mTOR signaling and inducing apoptosis. Noticeably, phenformin selectively targeted subpopulations of cells expressing JARID1B, a marker for slow cycling melanoma cells, whereas PLX4720 selectively targeted JARID1B-negative cells. Finally, in contrast to their use as single agents, the combination of phenformin and PLX4720 induced tumor regression in both nude mice bearing melanoma xenografts and in a genetically engineered BRAF(V600E)/PTEN(null)-driven mouse model of melanoma. These results strongly suggest that significant therapeutic advantage may be achieved by combining AMPK activators such as phenformin with BRAF inhbitors for the treatment of melanoma.

Asymmetric dimethylarginine attenuates serum starvation-induced apoptosis via suppression of the Fas (APO-1/CD95)/JNK (SAPK) pathway

Asymmetric dimethylarginine (ADMA) is synthesized by protein arginine methyltransferases during methylation of protein arginine residues and released into blood upon proteolysis. Higher concentrations of ADMA in blood have been observed in patients with metabolic diseases and certain cancers. However, the role of ADMA in colon cancer has not been well investigated. ADMA serum levels in human patients diagnosed with colon cancer were found to be higher than those present in healthy subjects. ADMA treatment of LoVo cells, a human colon adenocarcinoma cell line, attenuated serum starvation-induced apoptosis and suppressed the activation of the Fas (APO-1/CD95)/JNK (SAPK) (c-Jun N terminal protein kinase/stress-activated protein kinase)pathway. ADMA also suppressed the activation of JNK triggered by death receptor ligand anti-Fas mAb and exogenous C2-ceramide. Moreover, we demonstrated that ADMA pretreatment protected LoVo cells from doxorubicin hydrochloride-induced cell death and activation of the Fas/JNK pathway. In summary, our results suggest that the elevated ADMA in colon cancer patients may contribute to the blocking of apoptosis of cancer cells in response to stress and chemotherapy.

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

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

Beyond aspirin-cancer prevention with statins, metformin and bisphosphonates

Cancer risk reduction using pharmacological means is an attractive modern preventive approach that supplements the classical behavioural prevention recommendations. Medications that are commonly used by large populations to treat a variety of common, non-cancer-related, medical situations are an attractive candidate pool. This Review discusses three pharmacological agents with the most evidence for their potential as cancer chemopreventive agents: anti-hypercholesterolaemia medications (statins), an antidiabetic agent (metformin) and antiosteoporosis drugs (bisphosphonates). Data are accumulating to support a significant negative association of certain statins with cancer occurrence or survival in several major tumour sites (mostly gastrointestinal tumours and breast cancer), with an augmented combined effect with aspirin or other non-steroidal anti-inflammatory drugs. Metformin, but not other hypoglycaemic drugs, also seems to have some antitumour growth activity, but the amount of evidence in human studies, mainly in breast cancer, is still limited. Experimental and observational data have identified bisphosphonates as a pharmacological group that could have significant impact on incidence and mortality of more than one subsite of malignancy. At the current level of evidence these potential chemopreventive drugs should be considered in high-risk situations or using the personalized approach of maximizing individual benefits and minimizing the potential for adverse effects with the aid of pharmacogenetic indicators.

Randomized, double-blind, placebo-controlled, phase III chemoprevention trial of selenium supplementation in patients with resected stage I non-small-cell lung cancer: ECOG 5597

PURPOSE

Selenium has been reported to have chemopreventive benefits in lung cancer. We conducted a double-blind, placebo-controlled trial to evaluate the incidence of second primary tumors (SPTs) in patients with resected non-small-cell lung cancer (NSCLC) receiving selenium supplementation.

PATIENTS AND METHODS

Patients with completely resected stage I NSCLC were randomly assigned to take selenized yeast 200 μg versus placebo daily for 48 months. Participation was 6 to 36 months postoperatively and required a negative mediastinal node biopsy, no excessive vitamin intake, normal liver function, negative chest x-ray, and no other evidence of recurrence.

RESULTS

The first interim analysis in October 2009, with 46% of the projected end points accumulated, showed a trend in favor of the placebo group with a low likelihood that the trial would become positive; thus, the study was stopped. One thousand seven hundred seventy-two participants were enrolled, with 1,561 patients randomly assigned. Analysis was updated in June 2011 with the maturation of 54% of the planned end points. Two hundred fifty-two SPTs (from 224 patients) developed, of which 98 (from 97 patients) were lung cancer (38.9%). Lung and overall SPT incidence were 1.62 and 3.54 per 100 person-years, respectively, for selenium versus 1.30 and 3.39 per 100 person-years, respectively, for placebo (P = .294). Five-year disease-free survival was 74.4% for selenium recipients versus 79.6% for placebo recipients. Grade 1 to 2 toxicity occurred in 31% of selenium recipients and 26% of placebo recipients, and grade ≥ 3 toxicity occurred in less than 2% of selenium recipients versus 3% of placebo recipients. Compliance was excellent. No increase in diabetes mellitus or skin cancer was detected.

CONCLUSION

Selenium was safe but conferred no benefit over placebo in the prevention of SPT in patients with resected NSCLC.