Metformin efficacy and safety for colorectal polyps: a double-blind randomized controlled trial

Metformin Induces Apoptosis in Human Pancreatic Cancer (PC) Cells Accompanied by Changes in the Levels of Histone Acetyltransferases (Particularly, p300/CBP-Associated Factor (PCAF) Protein Levels)

Accumulating evidence (mainly from experimental research) suggests that metformin possesses anticancer properties through the induction of apoptosis and inhibition of the growth and proliferation of cancer cells. However, its effect on the enzymes responsible for histone acetylation status, which plays a key role in carcinogenesis, remains unclear. Therefore, the aim of our study was to evaluate the impact of metformin on histone acetyltransferases (HATs) (i.e., p300/CBP-associated factor (PCAF), p300, and CBP) and on histone deacetylases (HDACs) (i.e., SIRT-1 in human pancreatic cancer (PC) cell lines, 1.2B4, and PANC-1). The cells were exposed to metformin, an HAT inhibitor (HATi), or a combination of an HATi with metformin for 24, 48, or 72 h. Cell viability was determined using an MTT assay, and the percentage of early apoptotic cells was determined with an Annexin V-Cy3 Apoptosis Detection Assay Kit. Caspase-9 activity was also assessed. SIRT-1, PCAF, p300, and CBP expression were determined at the mRNA and protein levels using RT-PCR and Western blotting methods, respectively. Our results reveal an increase in caspase-9 in response to the metformin, indicating that it induced the apoptotic death of both 1.2B4 and PANC-1 cells. The number of cells in early apoptosis and the activity of caspase-9 decreased when treated with an HATi alone or a combination of an HATi with metformin, as compared to metformin alone. Moreover, metformin, an HATi, and a combination of an HATi with metformin also modified the mRNA expression of SIRT-1, PCAF, CBP, and p300. However, metformin did not change the expression of the studied genes in 1.2B4 cells. The results of the Western blot analysis showed that metformin diminished the protein expression of PCAF in both the 1.2B4 and PANC-1 cells. Hence, it appears possible that PCAF may be involved in the metformin-mediated apoptosis of PC cells.

Drug Repurposing Strategies for Non-Cancer to Cancer Therapeutics

Global efforts invested for the prevention and treatment of cancer need to be repositioned to develop safe, effective, and economic anticancer therapeutics by adopting rational approaches of drug discovery. Drug repurposing is one of the established approaches to reposition old, clinically approved off patent noncancer drugs with known targets into newer indications. The literature review suggests key role of drug repurposing in the development of drugs intended for cancer as well as noncancer therapeutics. A wide category of noncancer drugs namely, drugs acting on CNS, anthelmintics, cardiovascular drugs, antimalarial drugs, anti-inflammatory drugs have come out with interesting outcomes during preclinical and clinical phases. In the present article a comprehensive overview of the current scenario of drug repurposing for the treatment of cancer has been focused. The details of some successful studies along with examples have been included followed by associated challenges.

Diabetes and Colorectal Cancer Risk: A New Look at Molecular Mechanisms and Potential Role of Novel Antidiabetic Agents

Epidemiological data have demonstrated a significant association between the presence of type 2 diabetes mellitus (T2DM) and the development of colorectal cancer (CRC). Chronic hyperglycemia, insulin resistance, oxidative stress, and inflammation, the processes inherent to T2DM, also play active roles in the onset and progression of CRC. Recently, small dense low-density lipoprotein (LDL) particles, a typical characteristic of diabetic dyslipidemia, emerged as another possible underlying link between T2DM and CRC. Growing evidence suggests that antidiabetic medications may have beneficial effects in CRC prevention. According to findings from a limited number of preclinical and clinical studies, glucagon-like peptide-1 receptor agonists (GLP-1RAs) could be a promising strategy in reducing the incidence of CRC in patients with diabetes. However, available findings are inconclusive, and further studies are required. In this review, novel evidence on molecular mechanisms linking T2DM with CRC development, progression, and survival will be discussed. In addition, the potential role of GLP-1RAs therapies in CRC prevention will also be evaluated.

How far along are we in revealing the connection between metformin and colorectal cancer?

Colorectal cancer (CRC) is among the most prevalent cancers worldwide, and its prevention and reduction of incidence is imperative. The presence of diabetes has been associated with a 30% increased risk of CRC, likely through the mechanism of hyperinsulinemia, which promotes tumorigenesis via the insulin receptor in the epithelium or by insulin-like growth factor pathways, inflammation, or adipokines, inducing cancer cell proliferation and cancer spread. Metformin, the first-line agent in treating type 2 diabetes, has a chemopreventive role in CRC development. Additionally, preclinical studies suggest synergistic effects of metformin with oxaliplatin in inhibiting in vitro models of colon cancer. Although preclinical studies on the post diagnostic use of metformin were promising and suggested its synergistic effects with chemotherapy, the data on the possible effects of metformin after surgery and other CRC treatment in the clinical setting are less conclusive, and randomized controlled trials are still lacking.

Cancer Biology and Prevention in Diabetes

The available evidence suggests a complex relationship between diabetes and cancer. Epidemiological data suggest a positive correlation, however, in certain types of cancer, a more complex picture emerges, such as in some site-specific cancers being specific to type I diabetes but not to type II diabetes. Reports share common and differential mechanisms which affect the relationship between diabetes and cancer. We discuss the use of antidiabetic drugs in a wide range of cancer therapy and cancer therapeutics in the development of hyperglycemia, especially antineoplastic drugs which often induce hyperglycemia by targeting insulin/IGF-1 signaling. Similarly, dipeptidyl peptidase 4 (DPP-4), a well-known target in type II diabetes mellitus, has differential effects on cancer types. Past studies suggest a protective role of DPP-4 inhibitors, but recent studies show that DPP-4 inhibition induces cancer metastasis. Moreover, molecular pathological mechanisms of cancer in diabetes are currently largely unclear. The cancer-causing mechanisms in diabetes have been shown to be complex, including excessive ROS-formation, destruction of essential biomolecules, chronic inflammation, and impaired healing phenomena, collectively leading to carcinogenesis in diabetic conditions. Diabetes-associated epithelial-to-mesenchymal transition (EMT) and endothelial-to-mesenchymal transition (EndMT) contribute to cancer-associated fibroblast (CAF) formation in tumors, allowing the epithelium and endothelium to enable tumor cell extravasation. In this review, we discuss the risk of cancer associated with anti-diabetic therapies, including DPP-4 inhibitors and SGLT2 inhibitors, and the role of catechol-o-methyltransferase (COMT), AMPK, and cell-specific glucocorticoid receptors in cancer biology. We explore possible mechanistic links between diabetes and cancer biology and discuss new therapeutic approaches.

Effect of metformin on the mortality of colorectal cancer patients with T2DM: meta-analysis of sex differences

PURPOSE

To evaluate the effect of metformin as a treatment for the mortality of colorectal cancer (CRC) patients with type 2 diabetes mellitus (T2DM).

METHODS

We searched Medline, PubMed, EMBASE, Clinical Trials.gov (http://www.clinicaltrials.gov), and the Cochrane Collaboration Library from inception to November 2019. To analyze the relationship between metformin and the overall mortality, specific mortality, and sex differences in CRC patients with T2DM, hazard ratios (HRs) with 95% confidence intervals (CIs) were used. Egger's test and Begg's test were used to assess publication bias.

RESULTS

We included 8 cohort studies in our meta-analysis. CRC patients with T2DM treated with metformin had a lower overall mortality than CRC patients with T2DM who did not receive metformin (HR = 0.80, 95% CI 0.67-0.95). There was no significant difference in CRC-specific mortality between CRC patients with T2DM who used metformin and those who did not (HR = 0.84, 95% CI 0.65-1.08). However, females had a lower CRC-specific mortality among CRC patients with T2DM than males (HR = 0.63, 95% CI 0.41-0.97).

CONCLUSION

Metformin reduced the overall mortality of CRC patients with T2DM. Moreover, female CRC patients with T2DM using metformin had lower CRC-specific mortality than male CRC patients with T2DM.

Drug repurposing in oncology: Compounds, pathways, phenotypes and computational approaches for colorectal cancer

The strategy of using existing drugs originally developed for one disease to treat other indications has found success across medical fields. Such drug repurposing promises faster access of drugs to patients while reducing costs in the long and difficult process of drug development. However, the number of existing drugs and diseases, together with the heterogeneity of patients and diseases, notably including cancers, can make repurposing time consuming and inefficient. The key question we address is how to efficiently repurpose an existing drug to treat a given indication. As drug efficacy remains the main bottleneck for overall success, we discuss the need for machine-learning computational methods in combination with specific phenotypic studies along with mechanistic studies, chemical genetics and omics assays to successfully predict disease-drug pairs. Such a pipeline could be particularly important to cancer patients who face heterogeneous, recurrent and metastatic disease and need fast and personalized treatments. Here we focus on drug repurposing for colorectal cancer and describe selected therapeutics already repositioned for its prevention and/or treatment as well as potential candidates. We consider this review as a selective compilation of approaches and methodologies, and argue how, taken together, they could bring drug repurposing to the next level.

Metformin inhibits lithocholic acid-induced interleukin 8 upregulation in colorectal cancer cells by suppressing ROS production and NF-kB activity

Metformin, an inexpensive, well-tolerated oral agent that is a commonly used first-line treatment for type 2 diabetes, has become the focus of intense research as a potential anticancer agent. In this study, we describe the inhibitory effect of metformin in interleukin 8 (IL-8) upregulation by lithocholic acid (LCA) in HCT116 colorectal cancer (CRC) cells. Pharmacological inhibition studies indicated that reactive oxygen species (ROS) were involved in LCA-induced IL-8 upregulation through activation of the transcription factor NF-κB. Metformin was demonstrated to block LCA-stimulated ROS production, in turn suppressing NF-κB signaling that was critical for IL-8 upregulation. An NADPH oxidase assay proved that the inhibitory effect of metformin on ROS production was derived from its strong suppression of NADPH oxidase, a key producer of ROS in cells. Compared with conditioned media (CM) derived from HCT116 cells treated with LCA, CM derived from HCT116 cells pretreated with metformin and then treated with LCA lost all stimulatory effect on endothelial cell proliferation and tubelike formation. In conclusion, metformin inhibited NADPH oxidase, which in turn suppressed ROS production and NF-κB activation to prevent IL-8 upregulation stimulated by LCA; this prevention thus obstructed endothelial cell proliferation and tubelike formation.

Drug Repurposing Using Deep Embeddings of Gene Expression Profiles

Computational drug repositioning requires assessment of the functional similarities among compounds. Here, we report a new method for measuring compound functional similarity based on gene expression data. This approach takes advantage of deep neural networks to learn an embedding that substantially denoises expression data, making replicates of the same compound more similar. Our method uses unlabeled data in the sense that it only requires compounds to be labeled by identity rather than detailed pharmacological information, which is often unavailable and costly to obtain. Similarity in the learned embedding space accurately predicted pharmacological similarities despite the lack of any such labels during training and achieved substantially improved performance in comparison with previous similarity measures applied to gene expression measurements. Our method could identify drugs with shared therapeutic and biological targets even when the compounds were structurally dissimilar, thereby revealing previously unreported functional relationships between compounds. Thus, our approach provides an improved engine for drug repurposing based on expression data, which we have made available through the online tool DeepCodex ( http://deepcodex.org ).

Mitochondria-targeted drugs stimulate mitophagy and abrogate colon cancer cell proliferation

Mutations in the KRAS proto-oncogene are present in 50% of all colorectal cancers and are increasingly associated with chemotherapeutic resistance to frontline biologic drugs. Accumulating evidence indicates key roles for overactive KRAS mutations in the metabolic reprogramming from oxidative phosphorylation to aerobic glycolysis in cancer cells. Here, we sought to exploit the more negative membrane potential of cancer cell mitochondria as an untapped avenue for interfering with energy metabolism in KRAS variant-containing and KRAS WT colorectal cancer cells. Mitochondrial function, intracellular ATP levels, cellular uptake, energy sensor signaling, and functional effects on cancer cell proliferation were assayed. 3-Carboxyl proxyl nitroxide (Mito-CP) and Mito-Metformin, two mitochondria-targeted compounds, depleted intracellular ATP levels and persistently inhibited ATP-linked oxygen consumption in both KRAS WT and KRAS variant-containing colon cancer cells and had only limited effects on nontransformed intestinal epithelial cells. These anti-proliferative effects reflected the activation of AMP-activated protein kinase (AMPK) and the phosphorylation-mediated suppression of the mTOR target ribosomal protein S6 kinase B1 (RPS6KB1 or p70S6K). Moreover, Mito-CP and Mito-Metformin released Unc-51-like autophagy-activating kinase 1 (ULK1) from mTOR-mediated inhibition, affected mitochondrial morphology, and decreased mitochondrial membrane potential, all indicators of mitophagy. Pharmacological inhibition of the AMPK signaling cascade mitigated the anti-proliferative effects of Mito-CP and Mito-Metformin. This is the first demonstration that drugs selectively targeting mitochondria induce mitophagy in cancer cells. Targeting bioenergetic metabolism with mitochondria-targeted drugs to stimulate mitophagy provides an attractive approach for therapeutic intervention in KRAS WT and overactive mutant-expressing colon cancer.

Suppressed Helicobacter pylori-associated gastric tumorigenesis in Fat-1 transgenic mice producing endogenous ω-3 polyunsaturated fatty acids

Dietary approaches to preventing Helicobacter pylori (H. pylori)-associated gastric carcinogenesis are widely accepted because surrounding break-up mechanisms are mandatory for cancer prevention, however, eradication alone has been proven to be insufficient. Among these dietary interventions, omega-3-polyunsaturated-fatty acids (ω-3 PUFAs) are often the first candidate selected. However, there was no trial of fatty acids in preventing H. pylori-associated carcinogenesis and inconclusive results have been reported, likely based on inconsistent dietary administration. In this study, we developed an H. pylori initiated-, high salt diet promoted-gastric tumorigenesis model and conducted a comparison between wild-type (WT) and Fat-1-transgenic (TG)-mice. Gross and pathological lesions in mouse stomachs were evaluated at 16, 24, 32, and 45 weeks after H. pylori infection, and the underlying molecular changes to explain the cancer preventive effects were investigated. Significant changes in: i) ameliorated gastric inflammations at 16 weeks of H. pylori infection, ii) decreased angiogenic growth factors at 24 weeks, iii) attenuated atrophic gastritis and tumorigenesis at 32 weeks, and iv) decreased gastric cancer at 45 weeks were all noted in Fat-1-TG-mice compared to WT-mice. While an increase in the expression of Cyclooxygenase (COX)-2, and reduced expression of the tumor suppressive 15-PGDH were observed in WT-mice throughout the experimental periods, the expression of Hydroxyprostaglandin dehydrogenase (15-PGDH) was preserved in Fat-1-TG-mice. Using a comparative protein array, attenuated expressions of proteins implicated in proliferation and inflammation were observed in Fat-1-TG-mice compared to WT-mice. Conclusively, long-term administration of ω-3 PUFAs can suppress H. pylori-induced gastric tumorigenesis through a dampening of inflammation and reduced proliferation in accordance with afforded rejuvenation.

Metformin and Colorectal Cancer

Colorectal Cancer (CRC) is one of the most frequently encountered neoplasms in humans. The incidence of CRC has been increasing and new strategies for prevention, including chemoprevention, are required to lower its incidence and associated mortality. Metformin is a biguanide compound commonly used for the treatment of diabetes mellitus. Many recent basic research, epidemiological and clinical trial studies have indicated that metformin has benefits not only in diabetes treatment, but also in lowering the risk of developing cancer (including CRC). These studies indicate that metformin may be a candidate chemoprevention agent for CRC. This review article shall discuss the present evidence of metformin treatment and CRC, as well as outline our challenge in the investigation of metformin use in chemoprevention therapy for colorectal tumors.

Chemopreventive Potential of 2,3,5,4'-Tetrahydroxystilbene-2-O-β-D-glucoside on the Formation of Aberrant Crypt Foci in Azoxymethane-Induced Colorectal Cancer in Rats

2,3,5,4′-Tetrahydroxystilbene-2-O-β-D-glucoside (THSG) has been shown to have antioxidative and anti-inflammatory effects. Oxidative and inflammatory reactions are related to the development of colorectal carcinoma (CRC). In the present study, we characterized the preventive activities of THSG on colon carcinogenesis using the azoxymethane- (AOM-) mediated rat colon carcinogenesis model. F344 male rats were randomly divided into 5 groups (untreated and AOM model rats treated with or without THSG at 30, 150, or 250 mg/kg) after which the numbers of aberrant crypt foci (ACF) were assessed in the colon tissues of all rats. The expressions of nuclear factor-κB (NF-κB), cyclooxygenase-2 (COX-2), matrix metalloproteinase proteins (MMPs), and carcinoembryonic antigen (CEA) were measured as effective early predictors of CRC using western blot analysis. Treatment with THSG (150 or 250 mg/kg) induced a 50% reduction in total colonic ACF formation (P < 0.05). Furthermore, our results revealed a downregulation of CEA and NF-κB protein levels in the reduced number of ACF elicited by treatment with THSG, whereas levels of COX-2 and MMPs proteins were not changed. Collectively, THSG may be a promising natural lead compound or drug candidate for treating early phases of CRC.

Population and allelic variation of A-to-I RNA editing in human transcriptomes

Background

A-to-I RNA editing is an important step in RNA processing in which specific adenosines in some RNA molecules are post-transcriptionally modified to inosines. RNA editing has emerged as a widespread mechanism for generating transcriptome diversity. However, there remain significant knowledge gaps about the variation and function of RNA editing.

Results

In order to determine the influence of genetic variation on A-to-I RNA editing, we integrate genomic and transcriptomic data from 445 human lymphoblastoid cell lines by combining an RNA editing QTL (edQTL) analysis with an allele-specific RNA editing (ASED) analysis. We identify 1054 RNA editing events associated with cis genetic polymorphisms. Additionally, we find that a subset of these polymorphisms is linked to genome-wide association study signals of complex traits or diseases. Finally, compared to random cis polymorphisms, polymorphisms associated with RNA editing variation are located closer spatially to their respective editing sites and have a more pronounced impact on RNA secondary structure.

Conclusions

Our study reveals widespread cis variation in RNA editing among genetically distinct individuals and sheds light on possible phenotypic consequences of such variation on complex traits and diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-017-1270-7) contains supplementary material, which is available to authorized users.

Metformin suppresses cancer initiation and progression in genetic mouse models of pancreatic cancer

Background

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-associated mortality worldwide with an overall five-year survival rate less than 7%. Accumulating evidence has revealed the cancer preventive and therapeutic effects of metformin, one of the most widely prescribed medications for type 2 diabetes mellitus. However, its role in pancreatic cancer is not fully elucidated. Herein, we aimed to further study the preventive and therapeutic effects of metformin in genetically engineered mouse models of pancreatic cancer.

Methods

LSL-Kras^G12D/+; Pdx1-Cre (KC) mouse model was established to investigate the effect of metformin in pancreatic tumorigenesis suppression; LSL-Kras^G12D/+; Trp53^fl/+; Pdx1-Cre (KPC) mouse model was used to evaluate the therapeutic efficiency of metformin in PDAC. Chronic pancreatitis was induced in KC mice by peritoneal injection of cerulein.

Results

Following metformin treatment, pancreatic acinar-to-ductal metaplasia (ADM) and mouse pancreatic intraepithelial neoplasia (mPanIN) were decreased in KC mice. Chronic pancreatitis induced a stroma-rich and duct-like structure and increased the formation of ADM and mPanIN lesions, in line with an increased cytokeratin 19 (CK19)-stained area. Metformin treatment diminished chronic pancreatitis-mediated ADM and mPanIN formation. In addition, it alleviated the percent area of Masson’s trichrome staining, and decreased the number of Ki67-positive cells. In KPC mice, metformin inhibited tumor growth and the incidence of abdominal invasion. More importantly, it prolonged the overall survival.

Conclusions

Metformin inhibited pancreatic cancer initiation, suppressed chronic pancreatitis-induced tumorigenesis, and showed promising therapeutic effect in PDAC.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-017-0701-0) contains supplementary material, which is available to authorized users.

The association between metformin use and colorectal cancer survival among patients with diabetes mellitus: An updated meta-analysis

OBJECTIVE

Recent studies have reported conflicting results on the correlation between metformin use and outcomes in patients with colorectal cancer (CRC). A meta-analysis was performed to evaluate the efficacy of metformin therapy on the prognosis of CRC patients with type 2 diabetes mellitus (T2DM).

METHODS

We conducted a systematic search of PubMed, EMBASE, the Cochrane Library, and the Web of Science for related articles up to August 2016. Two investigators independently identified and extracted information. Pooled risk estimates [hazard ratios (HRs)] and 95% confidence intervals (CIs) were calculated using fixed-effects models. The risk of publication bias was assessed by examining funnel plot asymmetry as well as Egger's test and Begg's test.

RESULTS

Of 81 articles identified, 8 retrospective cohort studies, representing 6098 cases of CRC patients with T2DM who used metformin and 4954 cases of CRC patients with T2DM who did not use metformin, were included in this meta-analysis. There was no significant heterogeneity and quality difference between studies. Metformin users had significantly improved overall survival (OS) (HR = 0.82, 95% CI: 0.77-0.87, P = 0.000). However, Metformin use cannot affect CRC-specific survival (HR = 0.84, 95% CI: 0.69-1.02, P = 0.079) compared to non-users.

CONCLUSION

This meta-analysis suggests that metformin use may improve survival among CRC patients with T2DM. However, prospective controlled studies are still needed to rigorously evaluate the efficacy of metformin as an anti-tumor agent.

Effect of Insulin and Metformin Combination Treatment on Colon Adenoma and Advanced Adenoma Among DM II

BACKGROUND

The risk for colorectal adenoma and advanced adenoma among diabetes mellitus II (DM II) has been debated to differ with the type of anti-diabetic therapy. Insulin increases whereas metformin decreases the risk for colon adenoma (Ad) and advanced Ad (AAd). There have been no studies to evaluate the effect of combination treatment with insulin and metformin on colon Ad and AAd.

METHODS

The retrospective study included DM II patients undergoing screening colonoscopy. Subjects with incomplete colonoscopy, poor bowel preparation, personal history of colorectal cancer (CRC)/inflammatory bowel disease/hereditary nonpolyposis colorectal cancer/familial adenomatosis polyposis/colectomy or family history of CRC were excluded. Subjects were categorized into group 1 (insulin only), group 2 (metformin only), group 3 (combination of insulin and metformin) and group 4 (miscellaneous). Group 4 was excluded from data analysis. Ad detection rate (ADR) and advanced ADR (AADR) were calculated for each group.

RESULTS

Three hundred thirty-nine subjects composed the study group, with a mean age of 60.0 years and male to female ratio of 1:1.4. Composite ADR and AADR for study population was 35.1 and 15.3 %, respectively. Groups 1, 2 and 3 were composed of 88 (26.0 %), 211 (62.2 %) and 40 (11.8 %) subjects, respectively. ADR for groups 1, 2 and 3 was 40.9, 33.2 and 32.5 %, respectively (p value = 0.413). AADR for groups 1, 2 and 3 was 18.2, 15.2 and 10.0 %, respectively (p value = 0.489).

CONCLUSION

A decremental trend was observed in ADR and AADR across group 1, group 2 and group 3 (p value >0.05).

Metformin prevents hormonal and metabolic disturbances and 1,2-dimethylhydrazine-induced colon carcinogenesis in non-diabetic rats

Effects of two doses of the anti-diabetic drug, metformin (MF), on hormonal and metabolic levels of serum of non-diabetic male Wistar rats with 1,2-dimethylhydrazine (DMH)-induced colon tumor adenocarcinomas were studied. Carcinogenesis in the animals was also observed. Rats with DMH-induced colon adenocarcinomas had elevated levels of serum glucose, insulin, insulin-like growth factor-1, total cholesterol, triglycerides, catalase, malonic dialdehyde, glycated hemoglobin, aspartate aminotransferase, and alanine aminotransferase and decreased hemoglobin. Treatment with two doses of MF normalized majority of these changes in DMH-treated rats, whereas the drug was ineffective in rats without DMH treatment. The only exception was the decreased triglyceride levels in MF-treated rats. A 100 mg/kg dose of MF increased DMH-induced exophytic colon carcinomas and decreased endophytic tumors compared with untreated rats. Moreover, both MF doses increased DMH-induced and highly differentiated tumors and decreased the invasiveness of colon carcinomas compared with rats provided with DMH and water. Therefore, effects of MF on metabolic homeostasis are critical for preventing colon cancer.

Potential Benefit of Metformin as Treatment for Colon Cancer: the Evidence so Far

Metformin is known as a hypoglycaemic agent that regulates glucose homeostasis by inhibiting liver glucose production and increasing muscle glucose uptake. Colorectal cancer (CRC) is one of the most common cancers worldwide, with about a million new cases diagnosed each year. The risk factors for CRC include advanced age, smoking, black race, obesity, low fibre diet, insulin resistance, and the metabolic syndrome. We have searched Medline for the metabolic syndrome and its relation to CRC, and metformin as a potential treatment of colorectal cancer. Administration of metformin alone or in combination with chemotherapy has been shown to suppress CRC. The mechanism that explains how insulin resistance is associated with CRC is complex and not fully understood. In this review we have summarised studies which showed an association with the metabolic syndrome as well as studies which tackled metformin as a potential treatment of CRC. In addition, we have also provided a summary of how metformin at the cellular level can induce changes that suppress the activity of cancer cells.

Functional characterization of AMP-activated protein kinase signaling in tumorigenesis

AMP-activated protein kinase (AMPK) is a ubiquitously expressed metabolic sensor among various species. Specifically, cellular AMPK is phosphorylated and activated under certain stressful conditions, such as energy deprivation, in turn to activate diversified downstream substrates to modulate the adaptive changes and maintain metabolic homeostasis. Recently, emerging evidences have implicated the potential roles of AMPK signaling in tumor initiation and progression. Nevertheless, a comprehensive description on such topic is still in scarcity, especially in combination of its biochemical features with mouse modeling results to elucidate the physiological role of AMPK signaling in tumorigenesis. Hence, we performed this thorough review by summarizing the tumorigenic role of each component along the AMPK signaling, comprising of both its upstream and downstream effectors. Moreover, their functional interplay with the AMPK heterotrimer and exclusive efficacies in carcinogenesis were chiefly explained among genetically altered mice models. Importantly, the pharmaceutical investigations of AMPK relevant medications have also been highlighted. In summary, in this review, we not only elucidate the potential functions of AMPK signaling pathway in governing tumorigenesis, but also potentiate the future targeted strategy aiming for better treatment of aberrant metabolism-associated diseases, including cancer.

Metformin, Diabetes, and Survival among U.S. Veterans with Colorectal Cancer

BACKGROUND

Metformin has been associated with improved colorectal cancer survival, but investigations are limited by small numbers of patients and confounding by diabetic severity. We examined the association between metformin use and overall survival (OS) in patients with diabetes and colorectal cancer in a large population of U.S. veterans, while adjusting for measures of diabetic severity.

METHODS

Patients diagnosed with colorectal cancer from January 2001 to December 2008 were identified from the Veterans Affairs Central Cancer Registry. Multivariable models were used to examine the adjusted association of OS with diabetes and use of antidiabetic medications.

RESULTS

There were 21,352 patients diagnosed with colorectal cancer identified (n = 16,355 nondiabetic patients, n = 2,038 diabetic patients on metformin, n = 2,136 diabetic patients on medications other than metformin, n = 823 diabetic patients not on antidiabetic medication). Diabetic patients had a significantly worse OS than nondiabetic patients, but metformin users had only a 10% increase in death (HR_adj 1.10; 95% CI, 1.03-1.17, P = 0.004), as compared with 22% for users of other antidiabetic medications (HR_adj 1.22; 95% CI, 1.15-1.29, P < 0.0001). Among colorectal cancer patients with diabetes, metformin users had a 13% improved OS versus patients taking other antidiabetic medications (HR_adj 0.87; 95% CI, 0.79-0.95, P = 0.003), while diabetic patients not on any antidiabetic medications did not differ with respect to OS (HR_adj 1.02; 95% CI, 0.90-1.15, P = 0.76).

CONCLUSIONS

Among diabetics with colorectal cancer, metformin use is associated with improved survival, despite adjustments for diabetes severity and other risk factors.

IMPACT

These data lend further support to the conduct of randomized studies of possible anticancer effects of metformin among patients with colorectal cancer. Cancer Epidemiol Biomarkers Prev; 25(10); 1418-25. ©2016 AACR.

Metformin for chemoprevention of metachronous colorectal adenoma or polyps in post-polypectomy patients without diabetes: a multicentre double-blind, placebo-controlled, randomised phase 3 trial

BACKGROUND

The prevalence of, and mortality from, colorectal cancer is increasing worldwide, and new strategies for prevention are needed to reduce the burden of this disease. The oral diabetes medicine metformin might have chemopreventive effects against cancer, including colorectal cancer. However, no clinical trial data exist for the use of metformin for colorectal cancer chemoprevention. Therefore, we devised a 1-year clinical trial to assess the safety and chemopreventive effects of metformin on sporadic colorectal cancer (assessed by adenoma and polyp recurrence) in patients with a high risk of adenoma recurrence.

METHODS

This trial was a multicentre, double-blind, placebo-controlled, randomised phase 3 trial. Non-diabetic adult patients who had previously had single or multiple colorectal adenomas or polyps resected by endoscopy were enrolled into the study from five hospitals in Japan. Eligible patients were randomly assigned (1:1) to receive oral metformin (250 mg daily) or identical placebo tablets by a stratified computer-based randomisation method, with stratification by institute, age, sex, and body-mass index. All patients, endoscopists, doctors, and investigators were masked to drug allocation until the end of the trial. After 1 year of administration of metformin or placebo, colonoscopies were done to assess the co-primary endpoints: the number and prevalence of adenomas or polyps. Our analysis included all participants who underwent random allocation, according to the intention-to-treat principle. This trial is registered with University Hospital Medical Information Network (UMIN), number UMIN000006254.

FINDINGS

Between Sept 1, 2011, and Dec 30, 2014, 498 patients who had had single or multiple colorectal adenomas resected by endoscopy were enrolled into the study. After exclusions for ineligibility, 151 patients underwent randomisation: 79 were assigned to the metformin group and 72 to the placebo group. 71 patients in the metformin group and 62 in the placebo group underwent 1-year follow-up colonoscopy. The prevalence of total polyps (hyperplastic polyps plus adenomas) and of adenomas in the metformin group was significantly lower than that in the placebo group (total polyps: metformin group 27 [38·0%; 95% CI 26·7-49·3] of 71 patients, placebo group 35 [56·5%; 95% CI 44·1-68·8] of 62; p=0·034, risk ratio [RR] 0·67 [95% CI 0·47-0·97]; adenomas: metformin group 22 [30·6%; 95% CI 19·9-41·2] of 71 patients, placebo group 32 [51·6%; 95% CI 39·2-64·1] of 62; p=0·016, RR 0·60 [95% CI 0·39-0·92]). The median number of polyps was zero (IQR 0-1) in the metformin group and one (0-1) in the placebo group (p=0·041). The median number of adenomas was zero (0-1) in the metformin group and zero (0-1) in the placebo group (p=0·037). 15 (11%) of patients had adverse events, all of which were grade 1. We recorded no serious adverse events during the 1-year trial.

INTERPRETATION

The administration of low-dose metformin for 1 year to patients without diabetes was safe. Low-dose metformin reduced the prevalence and number of metachronous adenomas or polyps after polypectomy. Metformin has a potential role in the chemoprevention of colorectal cancer. However, further large, long-term trials are needed to provide definitive conclusions.

FUNDING

Ministry of Health, Labour and Welfare, Japan.

Inhibitory effect of metformin therapy on the incidence of colorectal advanced adenomas in patients with diabetes

BACKGROUND/AIMS

Metformin use has been associated with decreased colorectal cancer risk and mortality among diabetic patients. Recent research suggests that metformin use may decrease the incidence of colorectal adenomas in diabetic patients with previous colorectal cancer. This study aimed to assess the clinical effect of metformin use on the development of colorectal adenomas in diabetic patients without previous colorectal cancer.

METHODS

Among 604 consecutive diabetic patients who underwent colonoscopic surveillance after initial colonoscopy between January 2002 and June 2012, 240 patients without previous colorectal cancer were enrolled in this study and were divided in two groups: 151 patients receiving metformin and 89 patients not receiving metformin. Patient demographics and clinical characteristics as well as the colorectal adenoma incidence rate were retrospectively analyzed.

RESULTS

The incidence rate of total colorectal adenomas was not different according to metformin use (P=0.349). However, the advanced adenoma incidence rate was significantly lower in the metformin group compared with the non-metformin group (relative risk [RR], 0.09; P=0.011). Metformin use was independently associated with a decreased incidence of advanced colorectal adenomas after adjustment for clinically relevant factors (RR, 0.072; P=0.016). In addition, the cumulative development rate of advanced adenomas during follow-up was significantly lower in the metformin group compared with the non-metformin group (P=0.007).

CONCLUSIONS

Metformin use in diabetic patients without previous colorectal cancer is associated with a lower risk of advanced colorectal adenomas.

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

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

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

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.

Metformin in cancer treatment and prevention

Patients with diabetes mellitus are at increased risk of cancer development. Metformin is a well-established, effective agent for the management of type 2 diabetes mellitus. Epidemiological studies have identified an association between metformin use and a beneficial effect on cancer prevention and treatment, which has led to increasing interest in the potential use of metformin as an anticancer agent. Basic science has provided a better understanding of the mechanism of action of metformin and the potential for metformin to modulate molecular pathways involved in cancer cell signaling and metabolism. This article outlines the link between metformin and cancer, the potential for metformin in oncology, and limitations of currently available evidence.

From genotype to functional phenotype: unraveling the metabolomic features of colorectal cancer

Much effort in recent years has been expended in defining the genomic and epigenetic alterations that characterize colorectal adenocarcinoma and its subtypes. However, little is known about the functional ramifications related to various subtypes. Metabolomics, the study of small molecule intermediates in disease, provides a snapshot of the functional phenotype of colorectal cancer. Data, thus far, have characterized some of the metabolic perturbations that accompany colorectal cancer. However, further studies will be required to identify biologically meaningful metabolic subsets, including those corresponding to specific genetic aberrations. Moreover, further studies are necessary to distinguish changes due to tumor and the host response to tumor.

Cancer biology in diabetes

Diabetes is a serious metabolic disease that causes multiple organ dysfunctions. Recent evidence suggests that diabetes could contribute to the initiation and progression of certain cancers in addition to the classic diabetic complications. Furthermore, some of the drugs used clinically to treat patients with diabetes might affect cancer initiation, progression and mortality. The recent discovery of the possible anticancer effects of metformin, a classic antidiabetic drug, has led physicians and scientists to reconsider the interaction between diabetes and cancer. In the present review, we analyze recent reports in this field, and explore possible mechanistic links between diabetes and cancer biology.

Targeting mTOR network in colorectal cancer therapy

The mechanistic target of rapamycin (mTOR) integrates growth factor signals with cellular nutrient and energy levels and coordinates cell growth, proliferation and survival. A regulatory network with multiple feedback loops has evolved to ensure the exquisite regulation of cell growth and division. Colorectal cancer is the most intensively studied cancer because of its high incidence and mortality rate. Multiple genetic alterations are involved in colorectal carcinogenesis, including oncogenic Ras activation, phosphatidylinositol 3-kinase pathway hyperactivation, p53 mutation, and dysregulation of wnt pathway. Many oncogenic pathways activate the mTOR pathway. mTOR has emerged as an effective target for colorectal cancer therapy. In vitro and preclinical studies targeting the mTOR pathway for colorectal cancer chemotherapy have provided promising perspectives. However, the overall objective response rates in major solid tumors achieved with single-agent rapalog therapy have been modest, especially in advanced metastatic colorectal cancer. Combination regimens of mTOR inhibitor with agents such as cytotoxic chemotherapy, inhibitors of vascular endothelial growth factor, epidermal growth factor receptor and Mitogen-activated protein kinase kinase (MEK) inhibitors are being intensively studied and appear to be promising. Further understanding of the molecular mechanism in mTOR signaling network is needed to develop optimized therapeutic regimens. In this paper, oncogenic gene alterations in colorectal cancer, as well as their interaction with the mTOR pathway, are systematically summarized. The most recent preclinical and clinical anticancer therapeutic endeavors are reviewed. New players in mTOR signaling pathway, such as non-steroidal anti-inflammatory drug and metformin with therapeutic potentials are also discussed here.

Chemopreventive drugs: Mechanisms via inhibition of cancer stem cells in colorectal cancer

Recent epidemiological studies, basic research and clinical trials on colorectal cancer (CRC) prevention have helped identify candidates for effective chemopreventive drugs. However, because of the conflicting results of clinical trials or side effects, the effective use of chemopreventive drugs has not been generalized, except for patients with a high-risk for developing hereditary CRC. Advances in genetic and molecular technologies have highlighted the greater complexity of carcinogenesis, especially the heterogeneity of tumors. We need to target cells and processes that are critical to carcinogenesis for chemoprevention and treatment of advanced cancer. Recent research has shown that intestinal stem cells may serve an important role in tumor initiation and formation of cancer stem cells. Moreover, studies have shown that the tumor microenvironment may play additional roles in dedifferentiation, to enable tumor cells to take on stem cell features and promote the formation of tumorigenic stem cells. Therefore, early tumorigenic changes of stem cells and signals for dedifferentiation may be good targets for chemoprevention. In this review, I focus on cancer stem cells in colorectal carcinogenesis and the effect of major chemopreventive drugs on stem cell-related pathways.

Accumulation of aberrant DNA methylation during colorectal cancer development

Despite the recent advances in the therapeutic modalities, colorectal cancer (CRC) remains to be one of the most common causes of cancer-related death. CRC arises through accumulation of multiple genetic and epigenetic alterations that transform normal colonic epithelium into adenocarcinomas. Among crucial roles of epigenetic alterations, gene silencing by aberrant DNA methylation of promoter regions is one of the most important epigenetic mechanisms. Recent comprehensive methylation analyses on genome-wide scale revealed that sporadic CRC can be classified into distinct epigenotypes. Each epigenotype cooperates with specific genetic alterations, suggesting that they represent different molecular carcinogenic pathways. Precursor lesions of CRC, such as conventional and serrated adenomas, already show similar methylation accumulation to CRC, and can therefore be classified into those epigenotypes of CRC. In addition, specific DNA methylation already occurs in the normal colonic mucosa, which might be utilized for prediction of the personal CRC risk. DNA methylation is suggested to occur at an earlier stage than carcinoma formation, and may predict the molecular basis for future development of CRC. Here, we review DNA methylation and CRC classification, and discuss the possible clinical usefulness of DNA methylation as biomarkers for the diagnosis, prediction of the prognosis and the response to therapy of CRC.

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.

Management of colorectal cancer and diabetes

Colorectal cancer is associated with diabetes mellitus and both of these common conditions are often managed together by a surgeon. The surgical focus is usually upon cancer treatment rather than diabetes management. The relationship between colorectal cancer and diabetes is a complex one and can raise problems in both diagnosis and the management of patients with both conditions. This literature review explores the relationship between diabetes, diabetic treatment and colorectal cancer and addresses the issues that arise in diagnosing and treating this patient group. By highlighting these difficulties, this review aims to improve understanding and to provide clearer insight into both surgical and non-surgical management.

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.

Antidiabetic medications and the risk of colorectal cancer in patients with diabetes mellitus: a systematic review and meta-analysis

BACKGROUND

Antidiabetic medications (ADM) may modify colorectal cancer risk in patients with diabetes mellitus. We performed a systematic review and meta-analysis, evaluating the effect of metformin, thiazolidinediones (TZD), sulfonylureas, and insulin on colorectal cancer risk in diabetic patients.

METHODS

We conducted a systematic search of multiple bibliographic databases, up to September 2012, for articles that evaluated exposure to metformin, TZD, sulfonylureas, and insulin, reported colorectal cancer risk in patients with diabetes mellitus, and reported OR or provided data for their estimation. Summary OR estimates with 95% confidence intervals (CI) were estimated using the random-effects model.

RESULTS

Fifteen studies reporting 13,871 cases of colorectal cancer in 840,787 patients with diabetes mellitus were included. Meta-analysis of observational studies showed an 11% reduction in colorectal cancer risk associated with metformin use (n = 9 studies; OR, 0.89; 95% CI, 0.81-0.99), whereas TZD use was not associated with colorectal cancer risk (n = 5 studies; OR, 0.96; 95% CI, 0.87-1.05). Conversely, a trend toward higher colorectal cancer risk was observed with sulfonylurea (n = 7 studies; OR, 1.11; 95% CI, 0.97-1.26) and insulin (n = 9 studies; OR, 1.33; 95% CI, 0.91-1.94) use, although these associations were not statistically significant. There was considerable heterogeneity across studies, partly explained by study location and adjustment for concomitant use of other ADMs. Post-hoc analysis of randomized controlled trials did not reveal any significant association between ADM and colorectal cancer risk.

CONCLUSIONS

Meta-analysis of published studies supports a protective association between metformin use and colorectal cancer risk in patients with diabetes mellitus.

IMPACT

Clinical trials on the chemopreventive effect of metformin against colorectal cancer are warranted.

Potential targets for colorectal cancer prevention

The step-wise development of colorectal neoplasia from adenoma to carcinoma suggests that specific interventions could delay or prevent the development of invasive cancer. Several key factors involved in colorectal cancer pathogenesis have already been identified including cyclooxygenase 2 (COX-2), nuclear factor kappa B (NF-κB), survivin and insulin-like growth factor-I (IGF-I). Clinical trials of COX-2 inhibitors have provided the “proof of principle” that inhibition of this enzyme can prevent the formation of colonic adenomas and potentially carcinomas, however concerns regarding the potential toxicity of these drugs have limited their use as a chemopreventative strategy. Curcumin, resveratrol and quercetin are chemopreventive agents that are able to suppress multiple signaling pathways involved in carcinogenesis and hence are attractive candidates for further research.

Metformin and cancer

Type 2 diabetes mellitus is a rising cause of cardiovascular morbidity and mortality. A number of studies have also identified diabetic patients as having increased risk for the development of cancer. Metformin is a widely prescribed antidiabetic drug with an established efficacy coupled with a favorable safety profile and low cost. An increasing number of studies have associated metformin treatment with a decrease of cancer risk. Moreover, metformin has also been associated with improved outcomes in cancer patients. These possible pleiotropic effects of metformin may establish metformin as a cancer prevention and treatment option. However, any favorable effects of metformin on cancer are not always corroborated by clinical trials. Larger studies are expected to better investigate the possible antineoplastic effects of metformin.

Diabetes and cancer: Could vitamin D provide the link?

Diabetes and cancer are common diseases that may co-exist in the same individual. There is significant evidence that patients with diabetes have increased risk of developing certain cancers, especially colorectal, pancreatic and primary hepatic cancer. There is also good evidence that low levels of vitamin D are associated with increased risk of diabetes and increased risk of colorectal, and possibly other, cancers. In this article we propose that low levels of vitamin D may increase the risk of cancer in people with diabetes and describe potential molecular pathways. We suggest that large scale randomised trials of vitamin D supplementation in patients at risk of diabetes, and in patients with established diabetes to examine the effect on cancer risk, are required.

Metformin and the risk of cancer: time-related biases in observational studies

OBJECTIVE

Time-related biases in observational studies of drug effects have been described extensively in different therapeutic areas but less so in diabetes. Immortal time bias, time-window bias, and time-lag bias all tend to greatly exaggerate the benefits observed with a drug.

RESEARCH DESIGN AND METHODS

These time-related biases are described and shown to be prominent in observational studies that have associated metformin with impressive reductions in the incidence of and mortality from cancer. As a consequence, metformin received much attention as a potential anticancer agent; these observational studies sparked the conduction of randomized, controlled trials of metformin as cancer treatment. However, the spectacular effects reported in these studies are compatible with time-related biases.

RESULTS

We found that 13 observational studies suffered from immortal time bias; 9 studies had not considered time-window bias, whereas other studies did not consider inherent time-lagging issues when comparing the first-line treatment metformin with second- or third-line treatments. These studies, subject to time-related biases that are avoidable with proper study design and data analysis, led to illusory extraordinarily significant effects, with reductions in cancer risk with metformin ranging from 20 to 94%. Three studies that avoided these biases reported no effect of metformin use on cancer incidence.

CONCLUSIONS

Although observational studies are important to better understand the effects of drugs, their proper design and analysis is essential to avoid major time-related biases. With respect to metformin, the scientific evidence of its potential beneficial effects on cancer would need to be reassessed critically before embarking on further long and expensive trials.

Metformin: Midlife maturity, maiden charm

Metformin is one of the most commonly prescribed drugs for management of Type 2 diabetes mellitus. It has been in use for almost five decades. Now, pharmacological properties of this agent are being exapted for use in a number of other indications. New facets of its personality are coming up, generating more interest of the scientific community in this "middle-aged" molecule. This article explores the role of metformin in cardioprotection and its hepatoprotective properties. Nephroprotective, protection against excess body fat and gonadoprotective actions, properties have also been discussed. Additionally, this manuscript briefly reviews the thyroid stimulating hormone (TSH)-lowering properties in diabetic and non-diabetic patients, besides reviewing its actions on different types of cancers. Some of these actions may become approved indications for use of metformin following generation of new evidence. Metformin still has many unexplored dimensions that deserve further exploration.

Eicosapentaenoic acid (EPA) efficacy for colorectal aberrant crypt foci (ACF): a double-blind randomized controlled trial

BACKGROUND

Colorectal cancer (CRC) is one of the most commonly occurring neoplasms and a leading cause of cancer death worldwide, and new preventive strategies are needed to lower the burden of this disease. Eicosapentaenoic acid (EPA), the omega-3 polyunsaturated fatty acid that is widely used in the treatment of hyperlipidemia and prevention of cardiovascular disease, has recently been suggested to have a suppressive effect on tumorigenesis and cancer cell growth. In CRC chemoprevention trials, in general, the incidence of polyps or of the cancer itself is set as the study endpoint. Although the incidence rate of CRC would be the most reliable endpoint, use of this endpoint would be unsuitable for chemoprevention trials, because of the relatively low occurrence rate of CRC in the general population and the long-term observation period that it would necessitate. Moreover, there is an ethical problem in conducting long-term trials to determine whether a test drug might be effective or harmful. Aberrant crypt foci (ACF), defined as lesions containing crypts that are larger in diameter and stain more darkly with methylene blue than normal crypts, are considered as a reliable surrogate biomarker of CRC. Thus, we devised a prospective randomized controlled trial as a preliminary study prior to a CRC chemoprevention trial to evaluate the chemopreventive effect of EPA against colorectal ACF formation and the safety of this drug, in patients scheduled for polypectomy.

METHODS

This study is a multicenter, double-blind, placebo-controlled, randomized controlled trial to be conducted in patients with both colorectal ACF and colorectal polyps scheduled for polypectomy. Eligible patients shall be recruited for the study and the number of ACF in the rectum counted at the baseline colonoscopy. Then, the participants shall be allocated randomly to either one of two groups, the EPA group and the placebo group. Patients in the EPA group shall receive oral 900-mg EPA capsules thrice daily (total daily dose, 2.7 g per day), and those in the placebo group shall receive oral placebo capsules thrice daily. After one month's treatment with EPA/placebo, colonoscopic examination and polypectomy will be performed to evaluate the formation of ACF, and the cell-proliferative activity and cell-apoptotic activity in normal colorectal mucosa and colorectal polyps.

DISCUSSION

This is the first study proposed to explore the effect of EPA against colorectal ACF formation in humans.This trial has been registered in the University hospital Medical Information Network (UMIN) Clinical Trials Registry as UMIN000008172.