Anti-tumor activity of metformin: from metabolic and epigenetic perspectives

Metformin is associated with decreased skin cancer risk in Taiwanese patients with type 2 diabetes

BACKGROUND

Metformin, an antidiabetic drug, is associated with decreased cancer risk, but its effect on skin cancer is unknown.

OBJECTIVE

To evaluate skin cancer risk associated with metformin use.

METHODS

In total, 16,237 matched pairs of ever and never metformin users with new-onset type 2 diabetes diagnosed during 1999-2005 were retrospectively enrolled and followed until December 31, 2011, using Taiwan's National Health Insurance database. Hazard ratios (HRs) were estimated using Cox regression weighted for propensity scores.

RESULTS

Skin cancer incidence was 45.59 and 83.90 per 100,000 person-years among ever and never users, respectively (HR 0.540, 95% confidence interval [CI] 0.357-0.819). Among ever users, the HRs (95% CIs) for the first (<21.00 months), second (21.00-45.83 months), and third (>45.83 months) cumulative duration tertiles were 0.817 (0.448-1.489), 0.844 (0.504-1.412), and 0.114 (0.036-0.364), respectively, and the HRs (95% CIs) for the first, second, and third cumulative dose tertiles were 1.006 (0.579-1.748), 0.578 (0.317-1.051), and 0.229 (0.099-0.530), respectively. HRs (95% CIs) were 0.523 (0.175-1.562) for melanoma and 0.496 (0.319-0.772) for nonmelanoma skin cancer.

LIMITATIONS

Few patients had skin cancer and information on ultraviolet light exposure and tumor histopathology was lacking.

CONCLUSION

Metformin use is associated with a decreased skin cancer risk.

Metformin sensitizes lung cancer cells to treatment by the tyrosine kinase inhibitor erlotinib

Lung cancer is one of the deadliest malignant tumors with limited treatment options. Although targeted therapy, using tyrosine-kinase inhibitors such as erlotinib (Erlo), has shown therapeutic benefit, only 15 % patients with mutated epidermal growth factor receptor (EGFR) in lung cancer cells are sensitive. Therefore, additional therapeutic strategy should be developed. In this study, we found that metformin (Met), which is widely used for the treatment of type 2 diabetes (T2D), sensitized lung cancer cells bearing wild-type EGFR to Erlo treatment by enriching cancer cells expressing higher levels of EGFR with persistent phosphorylation. As a consequence, combination of Met and Erlo more efficiently inhibited the growth of lung cancer cells both in vitro and in mice with xenografted tumors. Our results suggest a novel approach to treating lung cancer cases which are originally resistant to Erlo.

Demographic Characteristics, Survival and Prognostic Factors of Early Breast Cancer Patients with Type 2 Diabetes Mellitus: A Hospital-Based Cohort Study

Objective: With increasing prevalence of type 2 diabetes mellitus and breast cancer in Iran, we aimed to search hospital registries of breast cancer patients to investigate type 2 diabetes mellitus association with survival outcomes of early breast cancer after adjustment of confounding factors. Methods: In a retrospective cohort study conducted from July 2003 to Feb 2014 and followed up until death or December 2016, female patients with early breast cancer who have been treated for the first time at the Cancer Institute of Iran, were divided to diabetic and non-diabetic groups. Primary and secondary outcomes were relapse free survival (RFS) and overall survival (OS). SPSS version 23 was used for analysis of data. Other variables included age, tumor stage, hormone receptor status, tumor subtype, and patient’s body mass index (BMI). Result: From a total of 1021 patients, 218 (21.4%) had type 2 diabetes mellitus. Diabetic patients had a higher mean age (53.31 vs 47.00), higher mean BMI (31.13 vs 29.15), lower HER2 expression (20.8% vs 32.1%) and higher frequency of luminal A subtype (61.1% vs 51.0). Overall, after adjustment of other variables, diabetes status did not affect RFS or OS independently. However, in luminal A subgroup, patients with diabetes mellitus had significantly lower survival outcomes of OS (135.277 vs 154.701) and RFS (114.107 vs 133.612) as well as OS higher hazard ratio of 1.830 and RFS hazard ratio of 1.663 compared to non-diabetic patients. BMI, hormone receptor status and tumor stage significantly affected the survival of the patients. Conclusion: In the present study, in addition to known breast cancer risk factors, BMI and type 2 diabetes mellitus had an independent impact on survival of the patients, highlighting the importance of health issues such as obesity and diabetes suboptimal performance in the treatment outcomes of early breast cancer patients in Iran.

Fatty acid synthase (FASN) as a therapeutic target in breast cancer

INTRODUCTION

Ten years ago, we put forward the metabolo-oncogenic nature of fatty acid synthase (FASN) in breast cancer. Since the conception of this hypothesis, which provided a model to explain how FASN is intertwined with various signaling networks to cell-autonomously regulate breast cancer initiation and progression, FASN has received considerable attention as a therapeutic target. However, despite the ever-growing evidence demonstrating the involvement of FASN as part of the cancer-associated metabolic reprogramming, translation of the basic science-discovery aspects of FASN blockade to the clinical arena remains a challenge. Areas covered: Ten years later, we herein review the preclinical lessons learned from the pharmaceutical liabilities of the first generation of FASN inhibitors. We provide an updated view of the current development and clinical testing of next generation FASN-targeted drugs. We also discuss new clinico-molecular approaches that should help us to convert roadblocks into roadways that will propel forward our therapeutic understanding of FASN. Expert opinion: With the recent demonstration of target engagement and early signs of clinical activity with the first orally available, selective, potent and reversible FASN inhibitor, we can expect Big pharma to revitalize their interest in lipogenic enzymes as well-credentialed targets for oncology drug development in breast cancer.

Metformin Inhibits Tumorigenesis and Tumor Growth of Breast Cancer Cells by Upregulating miR-200c but Downregulating AKT2 Expression

Background: Metformin has been reported to inhibit the growth of various types of cancers, including breast cancer. Yet the mechanisms underlying the anticancer effects of metformin are not fully understood. Growing evidence suggests that metformin's anticancer effects are mediated at least in part by modulating microRNAs, including miR-200c, which has a tumor suppressive role in breast cancer. We hypothesized that miR-200c has a role in the antitumorigenic effects of metformin on breast cancer cells.

Methods: To delineate the role of miR-200c in the effects of metformin on breast cancer, plasmids containing pre-miR-200c or miR-200c inhibitor were transfected into breast cancer cell lines. The MDA-MB-231, BT549, MCF-7, and T-47-D cells' proliferation, apoptosis, migration, and invasion were assessed. The antitumor role of metformin in vivo was investigated in a MDA-MB-231 xenograft tumor model in SCID mice.

Results: Metformin significantly inhibited the growth, migration, and invasion of breast cancer cells, and induced their apoptosis; these effects were dependent on both dose and time. Metformin also suppressed MDA-MB-231 tumor growth in SCID mice in vivo. Metformin treatment was associated with increased miR-200c expression and decreased c-Myc and AKT2 protein expression in both breast cancer cells and tumor tissues. Overexpression of miR-200c exhibited effects on breast cancer cells similar to those of metformin treatment. In contrast, inhibiting the expression of miR-200c increased the growth, migration, and invasion of MCF-7 and MDA-MB-231 cells.

Conclusion: Metformin inhibits the growth and invasiveness of breast cancer cells by upregulation of miR-200c expression by targeting AKT2. These findings provide novel insight into the molecular functions of metformin that suggest its potential as an anticancer agent.

Regulation of SESAME-mediated H3T11 phosphorylation by glycolytic enzymes and metabolites

Cancer cells prefer aerobic glycolysis, but little is known about the underlying mechanism. Recent studies showed that the rate-limiting glycolytic enzymes, pyruvate kinase M2 (PKM2) directly phosphorylates H3 at threonine 11 (H3T11) to regulate gene expression and cell proliferation, revealing its non-metabolic functions in connecting glycolysis and histone modifications. We have reported that the yeast homolog of PKM2, Pyk1 phosphorylates H3T11 to regulate gene expression and oxidative stress resistance. But how glycolysis regulates H3T11 phosphorylation remains unclear. Here, using a series of glycolytic enzyme mutants and commercial available metabolites, we investigated the role of glycolytic enzymes and metabolites on H3T11 phosphorylation. Mutation of glycolytic genes including phosphoglucose isomerase (PGI1), enolase (ENO2), triosephosphate isomerase (TPI1), or folate biosynthesis enzyme (FOL3) significantly reduced H3T11 phosphorylation. Further study demonstrated that glycolysis regulates H3T11 phosphorylation by fueling the substrate, phosphoenonylpyruvate and the coactivator, FBP to Pyk1. Thus, our results provide a comprehensive view of how glycolysis modulates H3T11 phosphorylation.

Targeting MYC Dependence by Metabolic Inhibitors in Cancer

MYC is a critical growth regulatory gene that is commonly overexpressed in a wide range of cancers. Therapeutic targeting of MYC transcriptional activity has long been a goal, but it has been difficult to achieve with drugs that directly block its DNA-binding ability. Additional approaches that exploit oncogene addiction are promising strategies against MYC-driven cancers. Also, drugs that target metabolic regulatory pathways and enzymes have potential for indirectly reducing MYC levels. Glucose metabolism and oxidative phosphorylation, which can be targeted by multiple agents, promote cell growth and MYC expression. Likewise, modulation of the signaling pathways and protein synthesis regulated by adenosine monophosphate-activated protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) can also be an effective route for suppressing MYC translation. Furthermore, recent data suggest that metabolism of nucleotides, fatty acids and glutamine are exploited to alter MYC levels. Combination therapies offer potential new approaches to overcome metabolic plasticity caused by single agents. Although potential toxicities must be carefully controlled, new inhibitors currently being tested in clinical trials offer significant promise. Therefore, as both a downstream target of metabolism and an upstream regulator, MYC is a prominent central regulator of cancer metabolism. Exploiting metabolic vulnerabilities of MYC-driven cancers is an emerging research area with translational potential.

Downregulation of mitochondrial cyclooxygenase-2 inhibits the stemness of nasopharyngeal carcinoma by decreasing the activity of dynamin-related protein 1

Cancer stem cells (CSCs) are a small subset of malignant cells, possessing stemness, with strong tumorigenic capability, conferring resistance to therapy and leading to the relapse of nasopharyngeal carcinoma (NPC). Our previous study suggested that cyclooxygenase-2 (COX-2) would be a novel target for the CSCs-like side population (SP) cells in NPC. In the present study, we further found that COX-2 maintained the stemness of NPC by enhancing the activity of mitochondrial dynamin-related protein 1 (Drp1), a mitochondrial fission mediator, by studying both sorted SP cells from NPC cell lines and gene expression analyses in NPC tissues. Using both overexpression and knockdown of COX-2, we demonstrated that the localization of COX-2 at mitochondria promotes the stemness of NPC by recruiting the mitochondrial translocation of p53, increasing the activity of Drp1 and inducing mitochondrial fisson. Inhibition of the expression or the activity of Drp1 by siRNA or Mdivi-1 downregulates the stemness of NPC. The present study also found that inhibition of mitochondrial COX-2 with resveratrol (RSV), a natural phytochemical, increased the sensitivity of NPC to 5-fluorouracil (5-FU), a classical chemotherapy drug for NPC. The underlying mechanism is that RSV suppresses mitochondrial COX-2, thereby reducing NPC stemness by inhibiting Drp1 activity as demonstrated in both the in vitro and the in vivo studies. Taken together, the results of this study suggest that mitochondrial COX-2 is a potential theranostic target for the CSCs in NPC. Inhibition of mitochondrial COX-2 could be an attractive therapeutic option for the effective clinical treatment of therapy-resistant NPC.

Metformin Use Is Associated with Reduced Incidence and Improved Survival of Endometrial Cancer: A Meta-Analysis

Studies have suggested that metformin can potentially decrease the incidence of cancer and improve survival outcomes. However, the association between metformin use and the incidence and survival of endometrial cancer (EC) remains controversial. So, a meta-analysis was performed. An electronic search was conducted using PubMed, EMBASE, and Web of Science. The outcome measures were relative risks (RRs) or hazard ratios (HRs) with 95% confidence intervals (CIs) comparing the EC incidence and survival in patients treated with and without metformin. Eleven studies involving 766,926 participants were included in this study. In the pooled analysis of five studies which evaluated the association of metformin use with the incidence of EC, we found that metformin use was associated with a 13% reduction in EC risk among patients with diabetes (RR = 0.87, 95% CI: 0.80–0.95; p = 0.006). In the pooled analysis of six retrospective cohort studies evaluating the effect of metformin on the survival of EC patients, we found that, relative to nonuse, metformin use significantly improved the survival of EC patients (HR = 0.63, 95% CI: 0.45–0.87; p = 0.006). This study showed that metformin use was significantly associated with a decreased incidence of EC in diabetes and a favorable survival outcome of EC patients.