Increased FoxM1 expression is a target for metformin in the suppression of EMT in prostate cancer

Metformin: A Dual-Role Player in Cancer Treatment and Prevention

Cancer continues to pose a significant global health challenge, as evidenced by the increasing incidence rates and high mortality rates, despite the advancements made in chemotherapy. The emergence of chemoresistance further complicates the effectiveness of treatment. However, there is growing interest in the potential of metformin, a commonly prescribed drug for type 2 diabetes mellitus (T2DM), as an adjuvant chemotherapy agent in cancer treatment. Although the precise mechanism of action of metformin in cancer therapy is not fully understood, it has been found to have pleiotropic effects, including the modulation of metabolic pathways, reduction in inflammation, and the regulation of cellular proliferation. This comprehensive review examines the anticancer properties of metformin, drawing insights from various studies conducted in vitro and in vivo, as well as from clinical trials and observational research. This review discusses the mechanisms of action involving both insulin-dependent and independent pathways, shedding light on the potential of metformin as a therapeutic agent for different types of cancer. Despite promising findings, there are challenges that need to be addressed, such as conflicting outcomes in clinical trials, considerations regarding dosing, and the development of resistance. These challenges highlight the importance of further research to fully harness the therapeutic potential of metformin in cancer treatment. The aims of this review are to provide a contemporary understanding of the role of metformin in cancer therapy and identify areas for future exploration in the pursuit of effective anticancer strategies.

Metformin: A promising clinical therapeutical approach for BPH treatment via inhibiting dysregulated steroid hormones-induced prostatic epithelial cells proliferation

The occurrence of benign prostate hyperplasia (BPH) was related to disrupted sex steroid hormones, and metformin (Met) had a clinical response to sex steroid hormone-related gynaecological disease. However, whether Met exerts an antiproliferative effect on BPH via sex steroid hormones remains unclear. Here, our clinical study showed that along with prostatic epithelial cell (PEC) proliferation, sex steroid hormones were dysregulated in the serum and prostate of BPH patients. As the major contributor to dysregulated sex steroid hormones, elevated dihydrotestosterone (DHT) had a significant positive relationship with the clinical characteristics of BPH patients. Activation of adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) by Met restored dysregulated sex steroid hormone homeostasis and exerted antiproliferative effects against DHT-induced proliferation by inhibiting the formation of androgen receptor (AR)-mediated Yes-associated protein (YAP1)-TEA domain transcription factor (TEAD4) heterodimers. Met's anti-proliferative effects were blocked by AMPK inhibitor or YAP1 overexpression in DHT-cultured BPH-1 cells. Our findings indicated that Met would be a promising clinical therapeutic approach for BPH by inhibiting dysregulated steroid hormone-induced PEC proliferation.

The Role of Polo-Like Kinase 1 in Regulating the Forkhead Box Family Transcription Factors

Polo-like kinase 1 (PLK1) is a serine/threonine kinase with more than 600 phosphorylation substrates through which it regulates many biological processes, including mitosis, apoptosis, metabolism, RNA processing, vesicle transport, and G₂ DNA-damage checkpoint recovery, among others. Among the many PLK1 targets are members of the FOX family of transcription factors (FOX TFs), including FOXM1, FOXO1, FOXO3, and FOXK1. FOXM1 and FOXK1 have critical oncogenic roles in cancer through their antagonism of apoptotic signals and their promotion of cell proliferation, metastasis, angiogenesis, and therapeutic resistance. In contrast, FOXO1 and FOXO3 have been identified to have broad functions in maintaining cellular homeostasis. In this review, we discuss PLK1-mediated regulation of FOX TFs, highlighting the effects of PLK1 on the activity and stability of these proteins. In addition, we review the prognostic and clinical significance of these proteins in human cancers and, more importantly, the different approaches that have been used to disrupt PLK1 and FOX TF-mediated signaling networks. Furthermore, we discuss the therapeutic potential of targeting PLK1-regulated FOX TFs in human cancers.

CKAP4-mediated activation of FOXM1 via phosphorylation pathways regulates malignant behavior of glioblastoma cells

OBJECTIVE

CKAP4 (Cytoskeleton Associated Protein 4) has been reported as an important regulator of carcinogenesis. A great deal of uncertainty still surrounds the possible molecular mechanism of CKAP4 involvement in GBM. We aimed to specifically elucidate the putative role of CKAP4 in the development of GBM.

METHODS

We identified divergent proteomics landscapes of GBM and adjacent normal tissues using mass spectrometry-based label-free quantification. Bioinformatics analysis of differentially expressed proteins (DEPs) led to the identification of CKAP4 as a hub gene. Based on the Chinese Glioma Genome Atlas data, we characterized the elevated expression of CKAP4 in GBM and developed a prognostic model. The influence of CKAP4 on malignant behavior of GBM was detected in vitro and vivo, as well as its downstream target and signaling pathways.

RESULTS

The prognosis model displayed accuracy and reliability for the probability of survival of patients with gliomas. CKAP4 knockdown remarkably reduced the malignant potential of GBM cells, whereas its overexpression reversed these effects in GBM cells and xenograft mice. Moreover, we demonstrated that overexpression of CKAP4 leads to increased FOXM1 (Forkhead Box M1) expression in conjunction with an increased level of AKT and ERK phosphorylation. Inhibition of both pathways had synergistic effects, resulting in greater effectiveness of inhibition. CKAP4 could reverse the deregulation of FOXM1 triggered by inhibition of AKT and ERK signaling.

CONCLUSIONS

This is the first study to reveal a CKAP4-FOXM1 signaling cascade that contributes to the malignant phenotype of GBMs. The CKAP4-based prognostic model would facilitate individualized treatment decisions for glioma patients.

Systematic review of antitumour efficacy and mechanism of metformin activity in prostate cancer models

Metformin, the first line pharmacotherapy for type 2 diabetes has demonstrated favourable effects in prostate cancer (PCa) across a range of studies evaluating PCa patient outcomes amongst metformin users. However, a lack of rigorously conducted prospective studies has stalled clinical use in this setting. Despite multiple studies evaluating the mechanisms underpinning antitumour effects of metformin in PCa, to date, no reviews have compared these findings. This systematic review and meta-analysis consolidates the mechanisms accounting for the antitumour effect of metformin in PCa and evaluates the antitumour efficacy of metformin in preclinical PCa studies. Data were obtained through Medline and EMBASE, extracted by two independent assessors. Risk of bias was assessed using the TOXR tool. Meta-analysis compared in vivo reductions of PCa tumour volume with metformin. In total, 447 articles were identified with 80 duplicates, and 261 articles excluded based on eligibility criteria. The remaining 106 articles were assessed and 71 excluded, with 35 articles included for systematic review, and eight included for meta-analysis. The mechanisms of action of metformin regarding tumour growth, viability, migration, invasion, cell metabolism, and activation of signalling cascades are individually discussed. The mechanisms by which metformin inhibits PCa cell growth are multimodal. Metformin regulates expression of multiple proteins/genes to inhibit cellular proliferation, cell cycle progression, and cellular invasion and migration. Published in vivo studies also conclusively demonstrate that metformin inhibits PCa growth. This highlights the potential of metformin to be repurposed as an anticancer agent, warranting further investigation of metformin in the setting of PCa.

Hypothesis-generating proteome perturbation to identify NEU-4438 and acoziborole modes of action in the African Trypanosome

NEU-4438 is a lead for the development of drugs against Trypanosoma brucei, which causes human African trypanosomiasis. Optimized with phenotypic screening, targets of NEU-4438 are unknown. Herein, we present a cell perturbome workflow that compares NEU-4438's molecular modes of action to those of SCYX-7158 (acoziborole). Following a 6 h perturbation of trypanosomes, NEU-4438 and acoziborole reduced steady-state amounts of 68 and 92 unique proteins, respectively. After analysis of proteomes, hypotheses formulated for modes of action were tested: Acoziborole and NEU-4438 have different modes of action. Whereas NEU-4438 prevented DNA biosynthesis and basal body maturation, acoziborole destabilized CPSF3 and other proteins, inhibited polypeptide translation, and reduced endocytosis of haptoglobin-hemoglobin. These data point to CPSF3-independent modes of action for acoziborole. In case of polypharmacology, the cell-perturbome workflow elucidates modes of action because it is target-agnostic. Finally, the workflow can be used in any cell that is amenable to proteomic and molecular biology experiments.

Forkhead Box Transcription Factors: Double-Edged Swords in Cancer

A plethora of treatment options exist for cancer therapeutics, but many are limited by side effects and either intrinsic or acquired resistance. The need for more effective targeted cancer treatment has led to the focus on forkhead box (FOX) transcription factors as possible drug targets. Forkhead factors such as FOXA1 and FOXM1 are involved in hormone regulation, immune system modulation, and disease progression through their regulation of the epithelial-mesenchymal transition. Forkhead factors can influence cancer development, progression, metastasis, and drug resistance. In this review, we discuss the various roles of forkhead factors in biological processes that support cancer as well as their function as pioneering factors and their potential as targetable transcription factors in the fight against cancer.

An Overview of siRNA Delivery Strategies for Urological Cancers

The treatment of urological cancers has been significantly improved in recent years. However, for the advanced stages of these cancers and/or for those developing resistance, novel therapeutic options need to be developed. Among the innovative strategies, the use of small interfering RNA (siRNA) seems to be of great therapeutic interest. siRNAs are double-stranded RNA molecules which can specifically target virtually any mRNA of pathological genes. For this reason, siRNAs have a great therapeutic potential for human diseases including urological cancers. However, the fragile nature of siRNAs in the biological environment imposes the development of appropriate delivery systems to protect them. Thus, ensuring siRNA reaches its deep tissue target while maintaining structural and functional integrity represents one of the major challenges. To reach this goal, siRNA-based therapies require the development of fine, tailor-made delivery systems. Polymeric nanoparticles, lipid nanoparticles, nanobubbles and magnetic nanoparticles are among nano-delivery systems studied recently to meet this demand. In this review, after an introduction about the main features of urological tumors, we describe siRNA characteristics together with representative delivery systems developed for urology applications; the examples reported are subdivided on the basis of the different delivery materials and on the different urological cancers.

Advances in PSMA-targeted therapy for prostate cancer

Prostate-specific membrane antigen (PSMA), a transmembrane glycoprotein located on the cell membrane, is specifically and highly expressed in prostate cancer (PCa). Besides, its expression level is related to tumor invasiveness. As a molecular target of PCa, PSMA has been extensively studied in the past two decades. Currently, a great deal of evidence suggests that significant progresses have been made in the PSMA-targeted therapy of PCa. Herein, different PSMA-targeted therapies for PCa are reviewed, including radioligand therapy (¹⁷⁷Lu-PSMA-RLT, ²²⁵Ac-PSMA-RLT), antibody-drug conjugates (MLN2704, PSMA-MMAE, MEDI3726), cellular immunotherapy (CAR-T, CAR/NK-92, PSMA-targeted BiTE), photodynamic therapy, imaging-guided surgery (radionuclide-guided surgery, fluorescence-guided surgery, multimodal imaging-guided surgery), and ultrasound-mediated nanobubble destruction.

Metformin and Cancer Hallmarks: Molecular Mechanisms in Thyroid, Prostate and Head and Neck Cancer Models

Metformin is the most used drug for type 2 diabetes (T2DM). Its antitumor activity has been described by clinical studies showing reduced risk of cancer development in T2DM patients, as well as management of T2DM compared with those receiving other glucose-lowering drugs. Metformin has a plethora of molecular actions in cancer cells. This review focused on in vitro data on the action mechanisms of metformin on thyroid, prostate and head and neck cancer. AMPK activation regulating specific downstream targets is a constant antineoplastic activity in different types of cancer; however, AMPK-independent mechanisms are also relevant. In vitro evidence makes it clear that depending on the type of tumor, metformin has different actions; its effects may be modulated by different cell conditions (for instance, presence of HPV infection), or it may regulate tissue-specific factors, such as the Na+/I- symporter (NIS) and androgen receptors. The hallmarks of cancer are a set of functional features acquired by the cell during malignant development. In vitro studies show that metformin regulates almost all the hallmarks of cancer. Interestingly, metformin is one of these therapeutic agents with the potential to synergize with other chemotherapeutic agents, with low cost, low side effects and high positive consequences. Some questions are still challenging: Are metformin in vitro data able to translate from bench to bedside? Does metformin affect drug resistance? Can metformin be used as a generic anticancer drug for all types of tumors? Which are the specific actions of metformin on the peculiarities of each type of cancer? Several clinical trials are in progress or have been concluded for repurposing metformin as an anticancer drug. The continuous efforts in the field and future in vitro studies will be essential to corroborate clinical trials results and to elucidate the raised questions.

A narrative review of research progress on FoxM1 in breast cancer carcinogenesis and therapeutics

OBJECTIVE

The purpose of this review is to clarify the potential roles of forkhead box transcription factor M1 (FoxM1) in the occurrence and progression of breast cancer, as well as the predictive value of FoxM1 as a prognostic biomarker and potential therapeutic target for breast cancer.

BACKGROUND

Breast cancer, well-known as a molecularly heterogeneous cancer, is still one of the most frequently diagnosed malignant tumors among females worldwide. Tumor recurrence and metastasis are the central causes of high mortality in breast cancer patients. Many factors contribute to the occurrence and progression of breast cancer, including FoxM1. FoxM1, widely regarded as a classic proliferation-related transcription factor, plays pivotal roles in the occurrence, proliferation, invasion, migration, drug resistance, and epithelial-mesenchymal transition (EMT) processes of multiple human tumors including breast cancer.

METHODS

The PubMed database was searched for articles published in English from February 2008 to May 2021 using related keywords such as "forkhead box transcription factor M1", "human breast cancer", "FoxM1", and "human tumor". About 90 research papers and reports written in English were identified, most of which were published after 2015. These papers mainly concentrated on the functions of FoxM1 in the occurrence, development, drug resistance, and treatment of human breast cancer.

CONCLUSIONS

Considering that the abnormal expression of FoxM1 plays a significant role in the proliferation, invasion, metastasis, and chemotherapy drug resistance of breast cancer, and its overexpression is closely correlated with the unfavorable clinicopathological characteristics of breast tumor patients, it is considerably important to comprehend the regulatory mechanism of FoxM1 in breast cancer. This will provide strong evidence for FoxM1 as a potential biomarker for the targeted treatment and prognostic evaluation of breast cancer patients.

How Physiologic Targets Can Be Distinguished from Drug-Binding Proteins

In clinical trials, some drugs owe their effectiveness to off-target activity. This and other observations raise a possibility that many studies identifying targets of drugs are incomplete. If off-target proteins are pharmacologically important, it will be worthwhile to identify them early in the development process to gain a better understanding of the molecular basis of drug action. Herein, we outline a multidisciplinary strategy for systematic identification of physiologic targets of drugs in cells. A drug-binding protein whose genetic disruption yields very similar molecular effects as treatment of cells with the drug may be defined as a physiologic target of the drug. For a drug developed with a rational approach, it is desirable to verify experimentally that a protein used for hit optimization in vitro remains the sole polypeptide recognized by the drug in a cell. SIGNIFICANCE STATEMENT: A body of evidence indicates that inactivation of many drug-binding proteins may not cause the pharmacological effects triggered by the drugs. A multidisciplinary cell-based approach can be of great value in identifying the physiologic targets of drugs, including those developed with target-based strategies.

The Effect of Metformin on Male Reproductive Function and Prostate: An Updated Review

Metformin is the first-line oral antidiabetic drug that shows multiple pleiotropic effects of anti-inflamation, anti-cancer, anti-aging, anti-microbia, anti-atherosclerosis, and immune modulation. Metformin's effects on men's related health are reviewed here, focusing on reproductive health under subtitles of erectile dysfunction (ED), steroidogenesis and spermatogenesis; and on prostate-related health under subtitles of prostate specific antigen (PSA), prostatitis, benign prostate hyperplasia (BPH), and prostate cancer (PCa). Updated literature suggests a potential role of metformin on arteriogenic ED but controversial and contradictory effects (either protective or harmful) on testicular functions of testosterone synthesis and spermatogenesis. With regards to prostate-related health, metformin use may be associated with lower levels of PSA in humans, but its clinical implications require more research. Although there is a lack of research on metform's effect on prostatitis, it may have potential benefits through its anti-microbial and anti-inflammatory properties. Metformin may reduce the risk of BPH by inhibiting the insulin-like growth factor 1 pathway and some but not all studies suggest a protective role of metformin on the risk of PCa. Many clinical trials are being conducted to investigate the use of metformin as an adjuvant therapy for PCa but results currently available are not conclusive. While some trials suggest a benefit in reducing the metastasis and recurrence of PCa, others do not show any benefit. More research works are warranted to illuminate the potential usefulness of metformin in the promotion of men's health.

Metformin modulates oncogenic expression of HOTAIR gene via promoter methylation and reverses epithelial-mesenchymal transition in MDA-MB-231 cells

Epithelial-mesenchymal transition (EMT) is a biological event, which critically regulates migration and invasion of cancer cells. EMT is regulated by several protein and nonprotein factors (such as noncoding RNAs). HOTAIR is an oncogenic long noncoding RNA that stimulates EMT in cancers. In the current study, we investigated the effect of metformin on EMT behavior and HOTAIR expression in MDA-MB-231 breast cancer cells. The minimal effective concentrations of metformin (10 and 20 mM) were obtained by the MTT test. Cell migration and invasion in the metformin-containing medium were assayed in the scratch assay and transwell test. Meaningful decreases in both cell migration and invasion were observed in the presence of metformin. Vimentin, snail, β-catenin, and HOTAIR transcripts were quantified by real-time polymerase chain reaction (PCR). Reduction in the expression of vimentin, β-catenin, and HOTAIR was detected as the result of metformin treatment, but the snail showed a constant expression. Western blottingrevealed the downregulation of vimentin and β-catenin proteins. HOTAIR promoter methylation pattern was also investigated in metformin-exposed cells using bisulfite sequencing PCR which the result showed differences in the methylation profile of CpG islands between the treated and untreated cells. In conclusion, metformin modulated oncogenic expression of the HOTAIR gene in the MDA-MB-231 cells. This downregulation was associated with the modification of promoter methylation patterns. Since HOTAIR induces EMT in breast cancer, HOTAIR decline might be one of the mechanisms by which metformin reverses EMT.

Glucose-Dependent FOXM1 Promotes Epithelial-to-Mesenchymal Transition Via Cellular Metabolism and Targeting Snail in Human Pancreatic Cancer

OBJECTIVES

Transcription factor Forkhead box protein M1 (FOXM1) plays critical roles in the progression of cancer including epithelial-to-mesenchymal transition (EMT). The aim of this study is to characterize the regulatory mechanisms of FOXM1 in EMT via pancreatic cancer metabolism.

METHODS

We investigated the regulation of EMT via mitochondrial respiration by FOXM1 using pancreatic cancer cell lines HPAC and PANC-1 and normal human pancreatic duct epithelial cells.

RESULTS

Forkhead box protein M1 and Snail were strongly expressed in HPAC and PANC-1. Epithelial-to-mesenchymal transition-modulated claudin-1 level was lower in PANC-1 than in HPAC. In both cell lines in low-glucose medium, FOXM1 and Snail were decreased and claudin-1 was increased. Knockdown of FOXM1 increased claudin-1 and decreased Snail in both cell lines. Low-glucose medium and downregulation of FOXM1 inhibited the cell migration in both cell lines. In both cell lines, mitochondrial respiration was at higher levels in low-glucose medium than in high-glucose medium. Downregulation of FOXM1 induced mitochondrial respiration in high-glucose medium. In normal human pancreatic duct epithelial cells, FOXM1 and Snail were low and claudin-1 was highly expressed, whereas overexpression of FOXM1 decreased claudin-1.

CONCLUSIONS

Glucose-dependent FOXM1 promoted EMT via Snail and pancreatic cancer metabolism.

Metformin and statins: a possible role in high-risk prostate cancer

Aim and background

There is increasing evidence that statins and oral anti-diabetic drugs, such as metformin, can have a favorable role in advanced prostate cancer treatment.Metformin has been shown to inhibit proliferation of tumor cells in vitro and statins inhibit carcinogenesis by suppressing angiogenesis/invasion mechanisms. However, clinical evidence on the protective effect of these drugs is still weak.The purpose of this study is to analyze if these drugs have an impact on Biochemical-Failure-Free-Survival (BFFS) and on Distant-Failure-Free-Survival (DFFS) in localized high-risk prostate cancer.

Material and Methods

From 2002-2016, 447 patients with histologically confirmed high-risk prostate cancer were retrospectively evaluated. All patients received radiotherapy and androgen deprivation therapy. Biochemical recurrence was determined by the Phoenix criteria and metastatic patients were defined by the presence of radiological metastasis. Survival analysis was performed using the Kaplan-Meier method.

Results

175 patients were treated with statins (65.3 % with a dose ≤ 20 mg/day) and 70 with metformin (75.7 % with a dose ≤ 1700 mg/day). Median follow-up was 88 months (1-194) with no differences in BFFS and DFFS between metformin and non-metformin patients (77.4 % versus 80 %, p = 0.91 and 89.4 % versus 88.7 %, p = 0.56, respectively). We did not find a statistical difference in BFFS and DFFS in patients taking higher doses of those drugs.

Conclusion

Metformin and statins were not associated with BFFS or DFFS improvement in our analysis. However, the small number of patients treated with these drugs limits the reliability of the results and prospective studies are needed.

OCT4B1 Promoted EMT and Regulated the Self-Renewal of CSCs in CRC: Effects Associated with the Balance of miR-8064/PLK1

Cancer stem cells (CSCs) are the main cause of tumor generation, recurrence, metastasis, and therapy failure in various malignancies including colorectal cancer (CRC). Accumulating evidence suggests that tumor cells can acquire CSC characteristics through the epithelial-mesenchymal transition (EMT) process. However, the molecular mechanism of CSCs remains unclear. OCT4B1 is a transcript of OCT4, which is initially expressed in embryonic stem and carcinoma cells, and is involved in the regulation and maintenance of an undifferentiated state of stem cells. In this study, three-dimensional (3D) microspheres were confirmed as CRC stem cells. Compared with that of parental cells, their self-renewal ability was significantly increased, and OCT4B1 expression was increased and promoted the EMT process. The knockdown of OCT4B1 decreased the self-renewal of CSCs and reversed EMT. Moreover, OCT4B1 induced the expression of Polo-like kinase 1 (PLK1), which is a key regulator of EMT in tumor cells. Further examination showed that OCT4B1 regulated the miR-8064/PLK1 balance to exert its function. Taken together, our data suggest that OCT4B1 may be involved in regulating the self-renewal of colorectal CSCs through EMT, which is at least partially due to the miR-8064/PLK1 balance. This study indicates that OCT4B1 is a potential therapeutic target for CRC by targeting CSCs.

Dual Roles of the AMP-Activated Protein Kinase Pathway in Angiogenesis

Angiogenesis plays important roles in development, stress response, wound healing, tumorigenesis and cancer progression, diabetic retinopathy, and age-related macular degeneration. It is a complex event engaging many signaling pathways including vascular endothelial growth factor (VEGF), Notch, transforming growth factor-beta/bone morphogenetic proteins (TGF-β/BMPs), and other cytokines and growth factors. Almost all of them eventually funnel to two crucial molecules, VEGF and hypoxia-inducing factor-1 alpha (HIF-1α) whose expressions could change under both physiological and pathological conditions. Hypoxic conditions stabilize HIF-1α, while it is upregulated by many oncogenic factors under normaxia. HIF-1α is a critical transcription activator for VEGF. Recent studies have shown that intracellular metabolic state participates in regulation of sprouting angiogenesis, which may involve AMP-activated protein kinase (AMPK). Indeed, AMPK has been shown to exert both positive and negative effects on angiogenesis. On the one hand, activation of AMPK mediates stress responses to facilitate autophagy which stabilizes HIF-1α, leading to increased expression of VEGF. On the other hand, AMPK could attenuate angiogenesis induced by tumor-promoting and pro-metastatic factors, such as the phosphoinositide 3-kinase /protein kinase B (Akt)/mammalian target of rapamycin (PI3K/Akt/mTOR), hepatic growth factor (HGF), and TGF-β/BMP signaling pathways. Thus, this review will summarize research progresses on these two opposite effects and discuss the mechanisms behind the discrepant findings.

Non-canonical cMet regulation by vimentin mediates Plk1 inhibitor-induced apoptosis

To address the need for improved systemic therapy for non-small-cell lung cancer (NSCLC), we previously demonstrated that mesenchymal NSCLC was sensitive to polo-like kinase (Plk1) inhibitors, but the mechanisms of resistance in epithelial NSCLC remain unknown. Here, we show that cMet was differentially regulated in isogenic pairs of epithelial and mesenchymal cell lines. Plk1 inhibition inhibits cMet phosphorylation only in mesenchymal cells. Constitutively active cMet abrogates Plk1 inhibitor-induced apoptosis. Likewise, cMet silencing or inhibition enhances Plk1 inhibitor-induced apoptosis. Cells with acquired resistance to Plk1 inhibitors are more epithelial than their parental cells and maintain cMet activation after Plk1 inhibition. In four animal NSCLC models, mesenchymal tumors were more sensitive to Plk1 inhibition alone than were epithelial tumors. The combination of cMet and Plk1 inhibition led to regression of tumors that did not regrow when drug treatment was stopped. Plk1 inhibition did not affect HGF levels but did decrease vimentin phosphorylation, which regulates cMet phosphorylation via β1-integrin. This research defines a heretofore unknown mechanism of ligand-independent activation of cMet downstream of Plk1 and an effective combination therapy.

High FOXM1 expression is a prognostic marker for poor clinical outcomes in prostate cancer

Purpose: We aimed to investigate the expression of FOXM1 and to determine the relationships between FOXM1 expression and clinicopathologic characteristics in patients with PCa. Furthermore, we reconfirmed the prognostic impact of FOXM1 in different cohorts using already published data. Patients and Methods: Formalin-fixed, paraffin-embedded tissues were collected from patients with low- (n=17), intermediate- (n=36), and high-risk (n=29) disease, from patients with CRPC (n=2) and from patients with BPH (n=28). To analyze FOXM1 expression, we performed IHC analyses. Also, we analyzed gene expression data from cBioPortal to evaluate the associations between FOXM1 alteration and prognosis of PCa. Results: FOXM1 expression measured using Allred score differed between patients with BPH, and low-, intermediate-, and high-risk PCa (0.3, 1.5, 4.8, and 6.2, respectively; p<0.001). Patients with high FOXM1 expression had higher preoperative PSA levels (p=0.023), more advanced tumor stages (p=0.047), and higher pathologic Gleason score (p<0.001) than those with low FOXM1 expression. ROC curve analysis indicated that FOXM1 expression was a useful marker for discriminating PCa from BPH (AUC 0.851, 95% CI 0.783-0.920) and for discriminating high-risk PCa from low- and intermediate-risk PCa (AUC 0.807, 95% CI 0.719-0.894). In multivariate analyses, high FOXM1 expression was an independent predictor of BCR. Finally, in the TCGA dataset, FOXM1 alteration was associated with poor overall (p=4.521e-4) and disease-free survival (p=0.0108). Conclusions: In patients with PCa, high FOXM1 expression was associated with advanced tumor stages, high Gleason score, and poor prognosis. These data suggest a role of FOXM1 in biologically and clinically aggressive PCa.

Three May Be Better Than Two: A Proposal for Metformin Addition to PI3K/Akt Inhibitor-antiandrogen Combination in Castration-resistant Prostate Cancer

Prostate cancer is a prevalent malignant disease. Castration-resistant prostate cancer (CRPC) is a poor prognosis form that develops upon resistance to first-line androgen deprivation therapy. Intensive research is ongoing to find efficient therapeutics for this refractory state. Actually, the combination of PI3K/Akt inhibitors with new-generation antiandrogens is among the most promising therapeutic schemes, although not yet at the optimal level. Metformin effects on prostate cancer, notably its therapeutic targets shared with antiandrogens and/or PI3K/Akt inhibitors, are reviewed in this article. From that, the hypothesis of PI3K/Akt-antiandrogens dual blockade optimization by metformin addition in CRPC will be deduced.

Ultrasound-mediated nanobubble destruction (UMND) facilitates the delivery of A10-3.2 aptamer targeted and siRNA-loaded cationic nanobubbles for therapy of prostate cancer

The Forkhead box M1 (FoxM1) transcription factor is an important anti-tumor target. A novel targeted ultrasound (US)-sensitive nanobubble that is likely to make use of the physical energy of US exposure for the improvement of delivery efficacy to target tumors and specifically silence FoxM1 expression appears as among the most potential nanocarriers in respect of drug delivery. In this study, we synthesized a promising anti-tumor targeted FoxM1 siRNA-loaded cationic nanobubbles (CNBs) conjugated with an A10-3.2 aptamer (siFoxM1-Apt-CNBs), which demonstrate high specificity when binding to prostate-specific membrane antigen (PSMA) positive LNCaP cells. Uniform nanoscaled siFoxM1-Apt-CNBs were developed using a thin-film hydration sonication, carbodiimide chemistry approaches, and electrostatic adsorption methods. Fluorescence imaging as well as flow cytometry evidenced the fact that the siFoxM1-Apt-CNBs were productively developed and that they specifically bound to PSMA-positive LNCaP cells. siFoxM1-Apt-CNBs combined with ultrasound-mediated nanobubble destruction (UMND) significantly improved transfection efficiency, cell apoptosis, and cell cycle arrest in vitro while reducing FoxM1 expression. In vivo xenografts tumors in nude-mouse model results showed that siFoxM1-Apt-CNBs combined with UMND led to significant inhibition of tumor growth and prolonged the survival of the mice, with low toxicity, an obvious reduction in FoxM1 expression, and a higher apoptosis index. Our study suggests that siFoxM1-Apt-CNBs combined with UMND might be a promising targeted gene delivery strategy for therapy of prostate cancer.

Vimentin immunohistochemical expression as a prognostic factor in gastric cancer: A meta-analysis

OBJECTIVE

The prognostic value of vimentin expression in Gastric Cancer (GC) has been assessed for years while the results are still in dispute. Thus, we performed a meta-analysis to determine the effect of vimentin immunohistochemical (IHC) expression on the prognosis of GC.

METHODS

Literature searches were performed in PubMed and Embase. The meta-analysis examined the association of vimentin IHC expression with prognosis and clinicopathological characteristics of GC patients.

RESULTS

In total, ten studies involving 1598 cases were enrolled in this meta-analysis. Vimentin positive expression was significantly correlated with poor overall survival (OS) in GC patients (HR = 2.05, 95% CI: 1.29-3.24) but there was a significant degree of heterogeneity (I² = 77%, P = 0.0006). Subgroup analysis indicated that vimentin expression had an unfavorable impact on OS in Chinese patients (HR = 2.43, 95% CI: 1.30-4.55). Moreover, vimentin positive expression rates was significantly associated with age, tumor location, TNM stage and lymph node metastasis. However, vimentin positive expression rates did not correlate with gender, grade of differentiation, vascular invasion, the depth of invasion, hepatic metastasis or peritoneal metastasis.

CONCLUSIONS

Positive vimentin expression could serve as a poor prognostic marker in GC.

SIRT4 acts as a tumor suppressor in gastric cancer by inhibiting cell proliferation, migration, and invasion

Background

Previous study has proven that SIRT4 is downregulated in gastric cancer (GC), but the role of SIRT4 has not been clearly understood. The aim of our work was to explore in detail the function and mechanism of SIRT4 in GC.

Methods

A total of 86 pairs of GC tumor tissues and adjacent normal tissues were collected, and quantitative real-time polymerase chain reaction and Western blotting analyses were used to determine the expression of SIRT4.

Results

Our study revealed that the expression of SIRT4 was downregulated in GC tissues and cells. In addition, the low expression of SIRT4 was negatively correlated with tumor size, pathological grade, and lymph node metastasis, which predicted a poor prognosis. Multiple functional experiments, including Cell Counting Kit-8 assay as well as colony formation assay, demonstrated SIRT4 suppressed cell proliferation. Moreover, we found epithelial-mesenchymal transition was regulated by SIRT4, thereby regulating cell migration and invasion.

Conclusion

Overall, our findings show that SIRT4 serves as a tumor suppressor in GC and might act as a novel biomarker and a therapeutic target of GC.

Negative regulation of TGF-β by AMPK and implications in the treatment of associated disorders

Transforming growth factor beta (TGF-β) regulates a large number of biological processes, including proliferation, differentiation, immune response, and development. In addition, TGF-β plays important roles in some pathological processes, for instance, it is upregulated and activated in fibrosis and advanced cancer. Adenosine monophosphate-activated protein kinase (AMPK) acts as a fuel gauge that is activated when cells sense shortage of ATP and increase in AMP or AMP:ATP ratio. Activation of AMPK slows down anabolic processes and stimulates catabolic processes, leading to increased production of ATP. Furthermore, the functions of AMPK have been extended beyond energy homeostasis. In fact, AMPK has been shown to exert a tumor suppressive effect. Recent studies have demonstrated negative impacts of AMPK on TGF-β function. Therefore, in this review, we will discuss the differences in the biological functions of TGF-β and AMPK, and some pathological processes such as fibrosis, epithelial-mesenchymal transition (EMT) and cancer metastasis, as well as angiogenesis and heterotopic ossifications where TGF-β and AMPK exert opposite effects.

p66Shc regulates migration of castration-resistant prostate cancer cells

Metastatic castration-resistant (CR) prostate cancer (PCa) is a lethal disease for which no effective treatment is currently available. p66Shc is an oxidase previously shown to promote androgen-independent cell growth through generation of reactive oxygen species (ROS) and is elevated in clinical PCa and multiple CR PCa cell lines. We hypothesize p66Shc also increases the migratory activity of PCa cells through ROS and investigate the associated mechanism. Using the transwell assay, our study reveals that the level of p66Shc protein correlates with cell migratory ability across several PCa cell lines. Furthermore, we show hydrogen peroxide treatment induces migration of PCa cells that express low levels of p66Shc in a dose-dependent manner, while antioxidants inhibit migration. Conversely, PCa cells that express high levels of endogenous p66Shc or by cDNA transfection possess increased cell migration which is mitigated upon p66Shc shRNA transfection or expression of oxidase-deficient dominant-negative p66Shc W134F mutant. Protein microarray and immunoblot analyses reveal multiple proteins, including ErbB-2, AKT, mTOR, ERK, FOXM1, PYK2 and Rac1, are activated in p66Shc-elevated cells. Their involvement in PCa migration was examined using respective small-molecule inhibitors. The role of Rac1 was further validated using cDNA transfection and, significantly, p66Shc is found to promote lamellipodia formation through Rac1 activation. In summary, the results of our current studies clearly indicate p66Shc also regulates PCa cell migration through ROS-mediated activation of migration-associated proteins, notably Rac1.

Unravelling the role of fatty acid metabolism in cancer through the FOXO3-FOXM1 axis

Obesity and cachexia represent divergent states of nutritional and metabolic imbalance but both are intimately linked to cancer. There is an extensive overlap in their signalling pathways and molecular components involved such as fatty acids (FAs), which likely play a crucial role in cancer. Forkhead box (FOX) proteins are responsible of a wide range of transcriptional programmes during normal development, and the FOXO3-FOXM1 axis is associated with cancer initiation, progression and drug resistance. Free fatty acids (FFAs), FA synthesis and β-oxidation are associated with cancer development and progression. Meanwhile, insulin and some adipokines, that are up-regulated by FAs, are also involved in cancer development and poor prognosis. In this review, we discuss the role of FA metabolism in cancer and how FA metabolism integrates with the FOXO3-FOXM1 axis. These new insights may provide leads to better cancer diagnostics as well as strategies for tackling cancer development, progression and drug resistance.

Metformin Increases E-cadherin in Tumors of Diabetic Patients With Endometrial Cancer and Suppresses Epithelial-Mesenchymal Transition in Endometrial Cancer Cell Lines

PURPOSE

Epithelial-mesenchymal transition (EMT) is a critical process for cancer metastasis and recurrence. Metformin, an effective oral antidiabetic drug, has been associated with decreased cancer risk and mortality. In this pilot study, we started to evaluate the effect of metformin on EMT in vivo and in vitro in endometrial cancer (EC).

METHODS

Endometrial cancer cell lines and freshly isolated EC tumor specimens were used to assess EMT after metformin treatment. Cell lines were subjected to wound healing and AlamarBlue assays to determine cell migration and cell proliferation; messenger RNA levels were measured by real-time reverse transcriptase (RT) quantitative polymerase chain reaction (PCR), and protein levels were measured by Western blots to detect EMT marker expression.

RESULTS

Protein expression and messenger RNA of E-cadherin was found to be increased (P = 0.02 and 0.04, respectively) in 30 EC tumor specimens of diabetic patients treated with metformin compared with 20 EC tumor specimens of diabetic patients treated with other antidiabetic agents. In vitro, metformin reduced cell migration at 5 mM for 48 hours, as determined by the wound healing assay in EC cell lines (Ishikawa, 45% reduction; HEC50, 40% reduction), whereas more than 90% of the cells remained viable on the AlamarBlue assay. Metformin reduced EMT in the cell lines and regulated the expression of the EMT-related epithelial markers, E-cadherin and Pan-keratin; the mesenchymal markers, N-cadherin, fibronectin, and vimentin; and the EMT drivers, Twist-1, snail-1, and ZEB-1.

CONCLUSIONS

Tumors of patients on metformin have increased E-cadherin expression, and metformin decreases EMT in EC cell lines in vitro, suggesting clinical biological relevance of metformin in women with EC.

FoxM1 is a promising candidate target in the treatment of breast cancer

Forkhead box protein M1(FoxM1) is a member of forkhead superfamily transcription factors. Emerging evidences have progressively contributed to our understanding on a central role of FoxM1 in human cancers. However, perspectives on the function of FoxM1 in breast cancer (BC) remain conflicting, and mostly were from basic research. Here, we explored the expression profile and prognostic values of FoxM1 based on analysis of pooled clinical datasets derived from online accessible databases, including ONCOMINE, Breast Cancer Gene-Expression Miner v4.0, and Kaplan-Meier plotter. It was found that, FoxM1 mRNA expression was significantly higher in breast tumor versus normal control. FoxM1expression profile presented a distinct pattern in different molecular subtypes of BC patients. Higher expression of FoxM1 was correlated to low mRNA expression of estrogen receptor 1 (ESR1), erb-B2 receptor tyrosine kinase 2 (ERBB2), and was inversely associated with the expression of classical luminal regulators forkhead box protein A1 (FoxA1) and GATA binding protein 3 (GATA3). Elevated FoxM1 expression predicted shorter distance metastasis free survival (DMFS) in BC patients, particularly with estrogen receptor (ER) positive and Luminal A, Luminal B subtypes of BC. More interestingly, elevated FoxM1 expression predicted poor survival in breast cancer patients, especially in the ER (+), progesterone receptor (PR) (+) subgroups and BC patients received adjuvant chemotherapy only or treated with tamoxifen only. These results implied that FoxM1 is an essential prognostic factor and promising candidate target in the treatment of breast cancer.

MicroRNA-937 inhibits cell proliferation and metastasis in gastric cancer cells by downregulating FOXL2

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Metformin: A Bridge between Diabetes and Prostate Cancer

Prostate cancer (PCa) has become the most frequent type of cancer in men. Recent data suggest that diabetic patients taking metformin have a lower incidence of certain cancer, including PCa. Metformin is the most common drug used in type II diabetes mellitus; its use has been shown to lower the incidence of several cancers, although there are ambiguous data about the anticancer activity of metformin. A large number of studies examined the potential antineoplastic mechanism of metformin although it is not still completely understood. This review summarizes the literature concerning the effects of metformin on PCa cells, highlighting its numerous mechanisms of action through which it can act. We analyze the possible causes of the discordances regarding the impact of metformin on risk of PCa; we discuss the latest findings in this field, suggesting that metformin may have a future role in the management of PCa both as monotherapy and in combination with other drugs.

The Emerging Role of Polo-Like Kinase 1 in Epithelial-Mesenchymal Transition and Tumor Metastasis

Polo-like kinase 1 (PLK1) is a serine/threonine kinase that plays a key role in the regulation of the cell cycle. PLK1 is overexpressed in a variety of human tumors, and its expression level often correlates with increased cellular proliferation and poor prognosis in cancer patients. It has been suggested that PLK1 controls cancer development through multiple mechanisms that include canonical regulation of mitosis and cytokinesis, modulation of DNA replication, and cell survival. However, emerging evidence suggests novel and previously unanticipated roles for PLK1 during tumor development. In this review, we will summarize the recent advancements in our understanding of the oncogenic functions of PLK1, with a focus on its role in epithelial-mesenchymal transition and tumor invasion. We will further discuss the therapeutic potential of these functions.

Epithelial-Mesenchymal Transition Phenotype, Metformin, and Survival for Colorectal Cancer Patients with Diabetes Mellitus II

OBJECTIVES

We aimed to explore the association between metformin treatment and epithelial-mesenchymal transition (EMT) phenotype and further appraise the prognostic values of metformin and EMT markers E-cadherin and vimentin for colorectal cancer (CRC) in clinical practice.

METHODS

We collected specimens and evaluated clinicopathological parameters of 102 stage I to III CRC patients with prediagnosed type 2 diabetes mellitus (DM II). Expression of E-cadherin and vimentin in tumors was detected by immunohistochemistry (IHC), and statistical analysis was performed using SPSS 19.0.

RESULTS

In correlation tests, we found a lower tumor cell EMT degree (more E-cadherin (P = 0.014) and less vimentin (P = 0.011) expression in patients who used metformin, and the expression of E-cadherin and vimentin was associated with serum CA19-9 (P = 0.048, P = 0.009), tumor invasive depth (T) (P < 0.001, P = 0.045), and lymph invasion (N) (P = 0.013, P = 0.001). In Cox multivariate regression analysis, E-cadherin was identified as a prognostic factor for disease-free survival (DFS) (P = 0.038) and metformin use (P = 0.015P = 0.044) and lymph invasion (P = 0.016P = 0.023) were considered as the prognostic factors for both DFS and overall survival (OS).

CONCLUSION

Our study suggested that metformin may impede the EMT process and improve survival for stage I-III CRC patients with DM II.

Blocking epithelial-to-mesenchymal transition in glioblastoma with a sextet of repurposed drugs: the EIS regimen

This paper outlines a treatment protocol to run alongside of standard current treatment of glioblastoma- resection, temozolomide and radiation. The epithelial to mesenchymal transition (EMT) inhibiting sextet, EIS Regimen, uses the ancillary attributes of six older medicines to impede EMT during glioblastoma. EMT is an actively motile, therapy-resisting, low proliferation, transient state that is an integral feature of cancers’ lethality generally and of glioblastoma specifically. It is believed to be during the EMT state that glioblastoma’s centrifugal migration occurs. EMT is also a feature of untreated glioblastoma but is enhanced by chemotherapy, by radiation and by surgical trauma. EIS Regimen uses the antifungal drug itraconazole to block Hedgehog signaling, the antidiabetes drug metformin to block AMP kinase (AMPK), the analgesic drug naproxen to block Rac1, the anti-fibrosis drug pirfenidone to block transforming growth factor-beta (TGF-beta), the psychiatric drug quetiapine to block receptor activator NFkB ligand (RANKL) and the antibiotic rifampin to block Wnt- all by their previously established ancillary attributes. All these systems have been identified as triggers of EMT and worthy targets to inhibit. The EIS Regimen drugs have a good safety profile when used individually. They are not expected to have any new side effects when combined. Further studies of the EIS Regimen are needed.

Metformin inhibits gastric cancer cells metastatic traits through suppression of epithelial-mesenchymal transition in a glucose-independent manner

Epithelial-mesenchymal transition (EMT), which is mainly recognized by upregulation of mesenchymal markers and movement of cells, is a critical stage occurred during embryo development and spreading cancerous cells. Metformin is an antidiabetic drug used in treatment of type 2 diabetes. EMT inhibitory effect of metformin has been studied in several cancers; however, it remains unknown in gastric cancer. The aim of the present study was to investigate the metformin effects on inhibition of EMT-related genes as well as migration and invasion of AGS gastric cancer cell line. Moreover, to study the effect of glucose on metformin-mediated EMT inhibition, all experiments were performed in two glucose levels, similar to non-fasting blood sugar (7.8 mM) and hyperglycemic (17.5 mM) conditions. The results showed reduction of mesenchymal markers, including vimentin and β-catenin, and induction of epithelial marker, E-cadherin, by metformin in both glucose concentrations. Furthermore, wound-healing and invasion assays showed a significant decrease in cell migration and invasion after metformin treatment in both glucose levels. In conclusion, our results indicated that metformin strongly inhibited EMT of gastric cancer cells in conditions mimicking normo and hyperglycemic blood sugar.

Metformin inhibits castration-induced EMT in prostate cancer by repressing COX2/PGE2/STAT3 axis

Castration is the standard therapeutic treatment for advanced prostate cancer but with limited benefit due to the profound relapse and metastasis. Activation of inflammatory signaling pathway and initiation of epithelial-mesenchymal transition (EMT) are closely related to drug resistance, tumor relapseas well as metastasis. In this study, we demonstrated that metformin is capable of inhibiting prostate cancer cell migration and invasion by repressing EMT evidenced by downregulating the mesenchymal markers N-cadherin, Vimentin, and Twist and upregulating the epithelium E-cadherin. These effects have also been observed in our animal model as well as prostate cancer patients. In addition, we showed the effects of metformin on the expression of genes involved in EMT through repressing the levels of COX2, PGE2 and phosphorylated STAT3. Furthermore, inactivating COX2 abolishes metformin's regulatory effects and exogenously administered PGE2 is capable of enhancing STAT3 phosphorylation and expression of EMT biomarker. We propose that metformin represses prostate cancer EMT and metastasis through targeting the COX2/PGE2/STAT3 axis. These findings suggest that metformin by itself or in combination with other anticancer drugs could be used as an anti-metastasis therapy.

Expression of FoxM1 and the EMT-associated protein E-cadherin in gastric cancer and its clinical significance

The aim of the present study was to investigate the expression of forkhead box M1 (FoxM1) and E-cadherin in tissues of gastric cancer in order to reveal any correlation between FoxM1, E-cadherin and clinicopathological parameters. The association between FoxM1 and E-cadherin in the development and progression of gastric cancer was also investigated. The expression of FoxM1 and E-cadherin in gastric cancer and adjacent normal tissue on tissue microarray was detected using immunohistochemistry. The clinicopathological significance of FoxM1 and E-cadherin in gastric cancer was explored, and the association between FoxM1 and E-cadherin was further examined using statistical techniques. In gastric cancer tissues, the expression of FoxM1 and E-cadherin was strongly positive, but it was weak in normal gastric mucosa. Overexpression of FoxM1 was evident in gastric cancer, and was associated with poor tumor differentiation (P<0.05), advanced tumor state (P<0.05) and lymph node (or distant) metastasis (P<0.05), whereas E-cadherin had the opposite effects. Furthermore, the correlation between FoxM1 and E-cadherin expression in gastric cancer tissue was negative. In conclusion, the high FoxM1 expression and low E-cadherin expression in gastric cancer tissue suggests that these proteins play a critical role in the development and progression of gastric cancer.

LKB1/AMPK inhibits TGF-β1 production and the TGF-β signaling pathway in breast cancer cells

Adenosine monophosphate-activated protein kinase (AMPK) acts as a fuel gauge that maintains energy homeostasis in both normal and cancerous cells, and has emerged as a tumor suppressor. The present study aims to delineate the functional relationship between AMPK and transforming growth factor beta (TGF-β). Our results showed that expression of liver kinase B1 (LKB1), an upstream kinase of AMPK, impeded TGF-β-induced Smad phosphorylation and their transcriptional activity in breast cancer cells, whereas knockdown of LKB1 or AMPKα1 subunit by short hairpin RNA (shRNA) enhanced the effect of TGF-β. Furthermore, AMPK activation reduced the promoter activity of TGF-β1. In accordance, type 2 diabetic patients taking metformin displayed a trend of reduction of serum TGF-β1, as compared with those without metformin. A significant reduction of serum TGF-β1 was found in mice after treatment with metformin. These results suggest that AMPK inhibits the transcription of TGF-β1, leading to reduction of its concentration in serum. Finally, metformin suppressed epithelial-to-mesenchymal transition of mammary epithelial cells. Taken together, our study demonstrates that AMPK exerts multiple actions on TGF-β signaling and supports that AMPK can serve as a therapeutic drug target for breast cancer.

Expanding the therapeutic spectrum of metformin: from diabetes to cancer

INTRODUCTION

Metformin, an oral hypoglycemic agent, was introduced in the clinical practice for the treatment of type 2 diabetes mellitus more than a half-century ago. Over the years, several studies demonstrated that diabetic patients treated with metformin have a lower incidence of cancer, raising the hypothesis that the spectrum of clinical applications of the drug could be expanded also to cancer therapy. Following these initial findings, a large number of studies were performed aimed at elucidating the effects of metformin on different types of tumor, at explaining its direct and indirect anti-cancer mechanisms and at identifying the molecular pathways targeted by the drug. Several clinical trials were also performed aimed at evaluating the potential anti-cancer effect of metformin among diabetic and non-diabetic patients affected by different types of cancer. While the results of several clinical studies are encouraging, a considerable number of other investigations do not support a role of metformin as an anti-cancer agent, and highlight variables possibly accounting for discrepancies.

AIM

We hereby review the results of in vitro and in vivo studies addressing the issue of the anti-cancer effects of metformin.

CONCLUSIONS

If in vitro data appear solid, the results provided by in vivo studies are somehow controversial. In this view, larger studies are needed to fully elucidate the role of metformin on cancer development and progression, as well as the specific clinical settings in which metformin could become an anti-cancer drug.

AMPK Inhibits the Stimulatory Effects of TGF-β on Smad2/3 Activity, Cell Migration, and Epithelial-to-Mesenchymal Transition

AMP-activated protein kinase (AMPK), an important downstream effector of the tumor suppressor liver kinase 1 (LKB1) and pharmacologic target of metformin, is well known to exert a preventive and inhibitory effect on tumorigenesis; however, its role in cancer progression and metastasis has not been well characterized. The present study investigates the potential roles of AMPK in inhibiting cancer-cell migration and epithelial-to-mesenchymal transition (EMT) by regulating the canonical transforming growth factor β (TGF-β) signaling pathway, an important promoting factor for cancer progression. Our results showed that activation of AMPK by metformin inhibited TGF-β-induced Smad2/3 phosphorylation in cancer cells in a dose-dependent manner. The effect of metformin is dependent on the presence of LKB1. A similar effect was obtained by expressing a constitutive active mutant of AMPKα1 subunit, whereas the expression of a dominant negative mutant of AMPKα1 or ablation of AMPKα subunits greatly enhanced TGF-β stimulation of Smad2/3 phosphorylation. As a consequence, expression of genes downstream of Smad2/3, including plasminogen activator inhibitor-1, fibronectin, and connective tissue growth factor, was suppressed by metformin in a LKB1-dependent fashion. In addition, metformin blocked TGF-β-induced inteleukin-6 expression through both LKB1-dependent and -independent mechanisms. Our results also indicate that activation of LKB1/AMPK inhibits TGF-β-stimulated cancer cell migration. Finally, TGF-β induction of EMT was inhibited by phenformin and enhanced by knockdown of LKB1 expression with shRNA. Together, our data suggest that AMPK could be a drug target for controlling cancer progression and metastasis.