Metformin Induces Growth Inhibition and Cell Cycle Arrest by Upregulating MicroRNA34a in Renal Cancer Cells

Renal functional outcomes after nephrectomy in patients with localized renal cell carcinoma and diabetes mellitus: a systematic review and meta-analysis

INTRODUCTION AND OBJECTIVE

Diabetes mellitus (DM), one of the most common comorbidities in patients with renal cell carcinoma (RCC), was proven to be an important prognostic factor of overall survival for these patients. Regarding the influence on renal function after nephrectomy, evidence is still scant. This systematic review and meta-analysis was conducted to provide a more reliable analysis of the association between DM and long-term renal functional outcomes after nephrectomy.

METHODS

The PubMed, Web of Science, Embase and Cochrane Library (CENTRAL) databases were searched for eligible studies from inception to January 2023. Hazard ratios (HRs) with 95% confidence intervals (CIs) were extracted to evaluate the association between DM and renal functional outcomes using a random effects model. Stata 17.0 software was used for statistical analysis.

RESULTS

The meta-analysis included thirteen studies consisting of 8562 RCC patients who underwent nephrectomy. Preoperative comorbidity of DM was significantly associated with poor renal functional outcomes (HR = 1.91, 95% CI 1.48-2.48, p < 0.0001), regardless of ethnicity, follow-up time, body mass index (BMI) and age. However, in the radical nephrectomy subgroup, DM was not significantly associated with renal function decline (HR = 1.91, 95% CI 0.93-3.90, p = 0.0781).

CONCLUSIONS

The aggregate evidence indicated that preexisting DM may be associated with poor renal functional outcomes in patients with RCC after nephrectomy, especially in patients receiving partial nephrectomy. Urologists should focus more on the glycemic management of these patients after nephrectomy. More high-quality studies are needed to explore the influence of DM on renal function outcomes in postoperative patients.

Advanced nano-therapeutic delivery of metformin: potential anti-cancer effect against human colon cancer cells through inhibition of GPR75 expression

The high incidence rate coupled with significant mortality makes colorectal cancer one of the most prevalent and devastating cancers worldwide. Research is currently underway to explore new forms of treatment that could potentially maximize treatment outcomes while minimizing the side effects associated with conventional chemotherapy. Metformin, a natural biguanide drug, has anti-cancer properties that can inhibit the growth and proliferation of cancer cells. However, due to its short half-life and low bioavailability, the efficacy of Metf as an anti-cancer agent is limited. The purpose of this research is to assess the potency of PEGylated niosomes as a nano-delivery system for Metf, with the aim of increasing its anti-cancer effects on CaCo2 colorectal cancer cells through the effect on the expression of genes, including GPR75, hTERT, Bax, Bcl2, and Cyclin D1. Metf-loaded niosomal NPs (N-Metf) were synthesized using the thin-film hydration method and then characterized using SEM, FTIR, AFM, and DLS techniques. The release pattern of the drug from the nanoparticles (NPS) was determined using the dialysis membrane method. Furthermore, the cytotoxic effect of the metformin-loaded PEGylated niosome on the CaCo2 cell line was evaluated by the MTT test. Additionally, an apoptosis assay was conducted to assess the effect of free Metf and Metf-loaded NPS on the programmed death of the CaCo2 cells, and the impact on the cell cycle was studied through a cell cycle test. Finally, the expression levels of hTERT, Cyclin D1, BCL2, GPR75, and BAX genes were assessed in the presence of free Metf and Metf-loaded NPs by RT-PCR. Characterization experiments showed successful loading of metformin into PEGylated niosomes. The results of cytotoxicity evaluation showed that Metf-NPs had more cytotoxicity than free Metf in a dose-dependent manner. Furthermore, nuclear fragmentation and the percentage of apoptotic cells induced by Metf-NPs were significantly higher than those induced by free Metf. Additionally, Metf-NPs were found to induce more cell cycle arrest at the sub-G1 checkpoint than free Metf did. Compared with Metf-treated cells, the mRNA expression levels of GPR75, Cyclin D1, and hTERT were significantly changed in cells treated with Metf-NPs. Ultimately, it is hypothesized the nano-encapsulation of Metf into PEGylated niosomal NPs could be a worthwhile drug delivery system to enhance its effectiveness in treating colorectal cancer cells.

Metformin and cancer hallmarks: shedding new lights on therapeutic repurposing

Metformin is a well-known anti-diabetic drug that has been repurposed for several emerging applications, including as an anti-cancer agent. It boasts the distinct advantages of an excellent safety and tolerability profile and high cost-effectiveness at less than one US dollar per daily dose. Epidemiological evidence reveals that metformin reduces the risk of cancer and decreases cancer-related mortality in patients with diabetes; however, the exact mechanisms are not well understood. Energy metabolism may be central to the mechanism of action. Based on altering whole-body energy metabolism or cellular state, metformin's modes of action can be divided into two broad, non-mutually exclusive categories: "direct effects", which induce a direct effect on cancer cells, independent of blood glucose and insulin levels, and "indirect effects" that arise from systemic metabolic changes depending on blood glucose and insulin levels. In this review, we summarize an updated account of the current knowledge on metformin antitumor action, elaborate on the underlying mechanisms in terms of the hallmarks of cancer, and propose potential applications for repurposing metformin for cancer therapeutics.

Metformin restrains ZIKV replication and alleviates virus-induced inflammatory responses in microglia

The re-emergence of Zika virus (ZIKV) remains a major public health threat that has raised worldwide attention. Accumulating evidence suggests that ZIKV can cause serious pathological changes to the human nervous system, including microcephaly in newborns. Recent studies suggest that metformin, an established treatment for diabetes may play a role in viral infection; however, little is known about the interactions between ZIKV infection and metformin administration. Using fluorescent ZIKV by flow cytometry and immunofluorescence imaging, we found that ZIKV can infect microglia in a dose-dependent manner. Metformin diminished ZIKV replication without the alteration of viral entry and phagocytosis. Our study demonstrated that metformin downregulated ZIKV-induced inflammatory response in microglia in a time- and dose-dependent manner. Our RNA-Seq and qRT-PCR analysis found that type I and III interferons (IFN), such as IFNα2, IFNβ1 and IFNλ3 were upregulated in ZIKV-infected cells by metformin treatment, accompanied with the downregulation of GBP4, OAS1, MX1 and ISG15. Together, our results suggest that metformin-mediated modulation in multiple pathways may attribute to restraining ZIKV infection in microglia, which may provide a potential tool to consider for use in unique clinical circumstances.

Natural Products for the Prevention, Treatment and Progression of Breast Cancer

In this review, we summarize the most used natural products as useful adjuvants in BC by clarifying how these products may play a critical role in the prevention, treatment and progression of this disease. BC is the leading cancer, in terms of incidence, that affects women. The epidemiology and pathophysiology of BC were widely reported. Inflammation and cancer are known to influence each other in several tumors. In the case of BC, the inflammatory component precedes the development of the neoplasm through a slowly increasing and prolonged inflammation that also favors its growth. BC therapy involves a multidisciplinary approach comprising surgery, radiotherapy and chemotherapy. There are numerous observations that showed that the effects of some natural substances, which, in integration with the classic protocols, can be used not only for prevention or integration in order to prevent recurrences and induce a state of chemoquiescence but also as chemo- and radiosensitizers during classic therapy.

Effects of metformin on Sonic hedgehog subgroup medulloblastoma progression: In vitro and in vivo studies

Metformin is a first-line drug for type 2 diabetes, and its anticancer effects have also been widely studied in recent years. The Sonic hedgehog (Shh) signaling pathway is involved in the initiation and progression of medulloblastoma. In order to develop a new treatment strategy for medulloblastoma (MB), this study investigated the inhibitory effect of metformin on MB and the underlying mechanism of metformin on the Shh signaling pathway. The effect of metformin on proliferation was evaluated by the cell counting kit-8 (CCK-8) test and colony formation experiment. The effect of metformin on metastasis was assessed by the scratch-wound assay and transwell invasion assay. Cell cycle and apoptosis were evaluated by flow cytometry, and the associated proteins were examined by western blotting. The mRNA and protein expression levels related to the Shh pathway were measured by quantitative PCR, western blotting, and immunofluorescence staining. The xenograft murine model was carried out to evaluate the anticancer effect of metformin on medulloblastoma in vivo. Metformin inhibited proliferation and metastasis of the Shh subgroup MB cell line, and the inhibitory effect on proliferation was related to apoptosis and the block of the cell cycle at the G0/G1 phase. Animal experiments showed that metformin inhibits medulloblastoma growth in vivo. Moreover, metformin decreased mRNA and protein expression levels of the Shh pathway, and this effect was reversed by the AMP-activated protein kinase (AMPK) siRNA. Furthermore, the pro-apoptotic and cell cycle arrest effects of metformin on Daoy cells could be reversed by the Shh pathway activators. Our findings demonstrated that metformin could inhibit medulloblastoma progression in vitro and in vivo, and this effect was associated with AMPK-mediated inhibition of the Shh signaling pathway in vitro studies.

Synergic Effect of Metformin and Everolimus on Mitochondrial Dynamics of Renal Cell Carcinoma

Renal cell carcinoma (RCC) frequently recurs or metastasizes after surgical resection. Everolimus, an mTOR inhibitor, is used as a second-line treatment, but the response of RCC to everolimus is insufficient. Metformin is an antidiabetic drug; recent reports have indicated its anti-cancer effects in various cancers, and it is known to have synergistic effects with other drugs. We investigated the possibility of coadministering everolimus and metformin as an effective treatment for RCC. RCC cells treated with a combination of the two drugs showed significantly inhibited cell viability, cell migration, and invasion, and increased apoptosis compared to those treated with each drug alone. An anti-cancer synergistic effect was also confirmed in the xenograft model. Transcriptome analysis for identifying the underlying mechanism of the combined treatment showed the downregulation of mitochondrial fusion genes and upregulation of mitochondrial fission genes by the combination treatment. Changes in mitochondrial dynamics following the combination treatment were observed using LysoTracker, LysoSensor, and JC-1 staining. In conclusion, the combination of everolimus and metformin inhibited RCC growth by disrupting mitochondrial dynamics. Therefore, we suggest that a treatment combining metformin and everolimus disrupts mitochondrial dynamics in RCC, and may be a novel strategy for RCC treatment.

The role of MicroRNA networks in tissue-specific direct and indirect effects of metformin and its application

Metformin is a first-line oral antidiabetic agent that results in clear benefits in relation to glucose metabolism and diabetes-related complications. The specific regulatory details and mechanisms underlying these benefits are still unclear and require further investigation. There is recent mounting evidence that metformin has pleiotropic effects on the target tissue development in metabolic organs, including adipose tissue, the gastrointestinal tract and the liver. The mechanism of actions of metformin are divided into direct effects on target tissues and indirect effects via non-targeted tissues. MicroRNAs (miRNAs) are a class of endogenous, noncoding, negative gene regulators that have emerged as important regulators of a number of diseases, including type 2 diabetes mellitus (T2DM). Metformin is involved in many aspects of miRNA regulation, and metformin treatment in T2DM should be associated with other miRNA targets. A large number of miRNAs regulation by metformin in target tissues with either direct or indirect effects has gradually been revealed in the context of numerous diseases and has gradually received increasing attention. This paper thoroughly reviews the current knowledge about the role of miRNA networks in the tissue-specific direct and indirect effects of metformin. Furthermore, this knowledge provides a novel theoretical basis and suggests therapeutic targets for the clinical treatment of metformin and miRNA regulators in the prevention and treatment of cancer, cardiovascular disorders, diabetes and its complications.

Role of Nrf2 Signaling Cascade in Breast Cancer: Strategies and Treatment

Breast cancer is the second leading cancer among all types of cancers. It accounts for 12% of the total cases of cancers. The complex and heterogeneous nature of breast cancer makes it difficult to treat in advanced stages. The expression of various enzymes and proteins is regulated by several molecular pathways. Oxidative stress plays a vital role in cellular events that are generally regulated by nuclear factor erythroid 2-related factor 2 (Nrf2). The exact mechanism of Nrf2 behind cytoprotective and antioxidative properties is still under investigation. In healthy cells, Nrf2 expression is lower, which maintains antioxidative stress; however, cancerous cells overexpress Nrf2, which is associated with various phenomena, such as the development of drug resistance, angiogenesis, development of cancer stem cells, and metastasis. Aberrant Nrf2 expression diminishes the toxicity and potency of therapeutic anticancer drugs and provides cytoprotection to cancerous cells. In this article, we have discussed the attributes associated with Nrf2 in the development of drug resistance, angiogenesis, cancer stem cell generation, and metastasis in the specific context of breast cancer. We also discussed the therapeutic strategies employed against breast cancer exploiting Nrf2 signaling cascades.

Metformin inhibits the proliferation of canine mammary gland tumor cells through the AMPK/AKT/mTOR signaling pathway in vitro

As an anti-diabetic drug, metformin has been demonstrated to exhibit antitumor effects. However, the mechanisms involved in decreasing tumor formation, including canine mammary gland tumors (CMGTs), are not well elucidated. The aim of the present study was to evaluate the ability of metformin to induce apoptosis and cell cycle arrest in CMGT cells, as well as identifying the pathways underlying these effects. Cell viability was assessed by Cell Counting Kit-8 analysis following treating with metformin. Subsequently, apoptosis and cell cycle progression were assessed by flow cytometry, and the expression of associated proteins was examined. Expression levels of classical AMP-activated protein kinase (AMPK), protein kinase B (AKT), mechanistic target of rapamycin (mTOR) and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) were then investigated using western blot analysis. Metformin inhibited the proliferation of CHMm cells in a concentration-dependent manner. Specifically, metformin induced cell cycle arrest in the G₀/G₁ phases, accompanied by increased expression of p21 and p27, and decreased expression of cyclin D1 and cyclin-dependent kinase 4. Marked levels of apoptosis were observed in CHMm cells alongside the activation of caspase-3 and cleavage of poly(ADP-ribose) polymerase. Also, the level of Bcl-2 was decreased, and that of Bax was increased. The expression of associated signaling molecules revealed that metformin markedly increased the phosphorylation of AMPK in CHMm cells, and decreased the levels of phosphorylated (p-)AKT, p-mTOR and p-4E-BP1, while Compound C reversed these changes. These findings demonstrated that metformin may be a potential therapeutic agent for CMGTs, acting via the AMPK/AKT/mTOR signaling pathway.

Cardioprotective effects of melatonin and metformin against doxorubicin-induced cardiotoxicity in rats are through preserving mitochondrial function and dynamics

Doxorubicin (Dox) is widely used in chemotherapy regimens for several malignant conditions. Unfortunately, cumulative and irreversible cardiotoxicity of Dox is the most prominent adverse effect which limits its use. Several pharmacological interventions which exert antioxidant properties, including melatonin and metformin, have demonstrated beneficial effects against various cardiac pathological conditions. However, the exact molecular mechanisms underlying their cardioprotective effects are not completely understood. We hypothesized that treatment with either melatonin or metformin provides cardioprotection against Dox-induced cardiotoxicity through mitochondrial protection. Thirty-two male Wistar rats received 6 doses of either 0.9% normal saline solution (0.9% NSS, n = 8) or Dox (3 mg/kg, i.p., n = 24). The Dox-treated rats (n = 8/group) were co-treated with: 1) Vehicle (0.9% NSS), 2) Melatonin (10 mg/kg/day), and 3) Metformin (250 mg/kg/day) for 30 consecutive days via oral gavage. Following the treatment, left ventricular (LV) function, oxidative stress, inflammation, mitochondrial function, dynamics, biogenesis and bioenergetics, mitophagy, autophagy, and apoptosis were determined. Dox induced excessive oxidative stress, inflammation, autophagy, apoptosis, reduced mitochondrial function, dynamics balance, biogenesis, and bioenergetics leading to LV dysfunction. Treatment with either melatonin or metformin exerted equal measures of cardioprotection via reducing oxidative stress, inflammation, autophagy, apoptosis, and improved mitochondrial function, dynamics balance, biogenesis, and bioenergetics in the Dox-treated rats. Melatonin and metformin exerted both anti-cancer and cardioprotective properties, suggesting they have potential roles in concomitant therapy in cancer patients receiving Dox treatment.

How metformin affects various malignancies by means of microRNAs: a brief review

Metformin known as the first-line orally prescribed drug for lowering blood glucose in type II diabetes (T2DM) has recently found various therapeutic applications including in cancer. Metformin has been studied for its influences in prevention and treatment of cancer through multiple mechanisms such as microRNA (miR) regulation. Alteration in the expression of miRs by metformin may play an important role in the treatment of various cancers. MiRs are single-stranded RNAs that are involved in gene regulation. By binding to the 3'UTR of target mRNAs, miRs influence protein levels. Irregularities in the expression of miRs that control the expression of oncogenes and tumor suppressor genes are associated with the onset and progression of cancer. Metformin may possess an effect on tumor prevention and progression by modifying miR expression and downstream pathways. Here, we summarize the effect of metformin on different types of cancer by regulating the expression of various miRs and the associated downstream molecules.

Metformin impairs cisplatin resistance effects in A549 lung cancer cells through mTOR signaling and other metabolic pathways

Lung cancer is the leading cause of cancer‑associated death worldwide and exhibits intrinsic and acquired therapeutic resistance to cisplatin (CIS). The present study investigated the role of mTOR signaling and other signaling pathways after metformin (MET) treatment in control and cisplatin‑resistant A549 cells, mapping pathways and possible targets involved in CIS sensitivity. MTT, flow cytometry, clonogenic assay, western blotting, proteomic analysis using the Stable Isotope Labeling by Amino acids in Cell culture (SILAC) approach and reverse transcription‑quantitative PCR were performed. The results revealed that CIS treatment induced mTOR signaling pathway overactivation, and the mTOR status was restored by MET. MET and the mTOR inhibitor rapamycin (RAPA) decreased the viability in control and resistant cells, and decreased the cell size increase induced by CIS. In control cells, MET and RAPA decreased colony formation after 72 h and decreased IC₅₀ values, potentiating the effects of CIS. Proteomics analysis revealed important pathways regulated by MET, including transcription, RNA processing and IL‑12‑mediated signaling. In CIS‑resistant cells, MET regulated the apoptotic process, oxidative stress and G₂/M transition. Annexin 4 (ANXA4) and superoxide dismutase 2 (SOD2), involved in apoptosis and oxidative stress, respectively, were chosen to validate the SILAC analysis and may represent potential therapeutic targets for lung cancer treatment. In conclusion, the chemosensitizing and antiproliferative effects of MET were associated with mTOR signaling and with potential novel targets, such as ANXA4 and SOD2, in human lung cancer cells.

Mechanism and application of metformin in kidney diseases: An update

Metformin is an oral antihyperglycemic drug widely used to treat type 2 diabetes mellitus (T2DM), acting via indirect activation of 5' Adenosine monophosphate-activated Protein Kinase (AMPK). Beyond the anti-diabetic effect, accumulative pieces of evidence have revealed that metformin also everts a beneficial effect in diverse kidney diseases. In various acute kidney diseases (AKI) animal models, metformin protects renal tubular cells from inflammation, apoptosis, reactive oxygen stress (ROS), endoplasmic reticulum (ER) stress, epithelial-mesenchymal transition (EMT) via AMPK activation. In diabetic kidney disease (DKD), metformin also alleviates podocyte loss, mesangial cells apoptosis, and tubular cells senescence through AMPK-mediated signaling pathways. Besides, metformin inhibits cystic fibrosis transmembrane conductance regulator (CFTR)-mediated fluids secretion and the mammalian target of rapamycin (mTOR)-involved cyst formation negatively regulated by AMPK in autosomal dominant polycystic kidney disease (APDKD). Furthermore, metformin also contributes to the alleviation of urolithiasis and renal cell carcinoma (RCC). As the common pathway for chronic kidney disease (CKD) progressing towards end-stage renal disease (ESRD), renal fibrosis is ameliorated by metformin, to a great extent dependent on AMPK activation. However, clinical data are not always consistent with preclinical data, some clinical investigations showed the unmeaningful even detrimental effect of metformin on T2DM patients with kidney diseases. Most importantly, metformin-associated lactic acidosis (MALA) is a vital issue restricting the application of metformin. Thus, we conclude the application of metformin in kidney diseases and uncover the underlying molecular mechanisms in this review.

Metformin Reduces NGF-Induced Tumour Promoter Effects in Epithelial Ovarian Cancer Cells

Epithelial ovarian cancer (EOC) is a lethal gynaecological neoplasm characterized by rapid growth and angiogenesis. Nerve growth factor (NGF) and its high affinity receptor tropomyosin receptor kinase A (TRKA) contribute to EOC progression by increasing the expression of c-MYC, survivin and vascular endothelial growth factor (VEGF) along with a decrease in microRNAs (miR) 23b and 145. We previously reported that metformin prevents NGF-induced proliferation and angiogenic potential of EOC cells. In this study, we sought to obtain a better understanding of the mechanism(s) by which metformin blocks these NGF-induced effects in EOC cells. Human ovarian surface epithelial (HOSE) and EOC (A2780/SKOV3) cells were stimulated with NGF and/or metformin to assess the expression of c-MYC, β-catenin, survivin and VEGF and the abundance of the tumor suppressor miRs 23b and 145. Metformin decreased the NGF-induced transcriptional activity of MYC and β-catenin/T-cell factor/lymphoid enhancer-binding factor (TCF-Lef), as well as the expression of c-MYC, survivin and VEGF in EOC cells, while it increased miR-23b and miR-145 levels. The preliminary analysis of ovarian biopsies from women users or non-users of metformin was consistent with these in vitro results. Our observations shed light on the mechanisms by which metformin may suppress tumour growth in EOC and suggest that metformin should be considered as a possible complementary therapy in EOC treatment.

Elevated de novo protein synthesis in FMRP-deficient human neurons and its correction by metformin treatment

FXS is the most common genetic cause of intellectual (ID) and autism spectrum disorders (ASD). FXS is caused by loss of FMRP, an RNA-binding protein involved in the translational regulation of a large number of neuronal mRNAs. Absence of FMRP has been shown to lead to elevated protein synthesis and is thought to be a major cause of the synaptic plasticity and behavioural deficits in FXS. The increase in protein synthesis results in part from abnormal activation of key protein translation pathways downstream of ERK1/2 and mTOR signalling. Pharmacological and genetic interventions that attenuate hyperactivation of these pathways can normalize levels of protein synthesis and improve phenotypic outcomes in animal models of FXS. Several efforts are currently underway to trial this strategy in patients with FXS. To date, elevated global protein synthesis as a result of FMRP loss has not been validated in the context of human neurons. Here, using an isogenic human stem cell-based model, we show that de novo protein synthesis is elevated in FMRP-deficient neural cells. We further show that this increase is associated with elevated ERK1/2 and Akt signalling and can be rescued by metformin treatment. Finally, we examined the effect of normalizing protein synthesis on phenotypic abnormalities in FMRP-deficient neural cells. We find that treatment with metformin attenuates the increase in proliferation of FMRP-deficient neural progenitor cells but not the neuronal deficits in neurite outgrowth. The elevated level of protein synthesis and the normalization of neural progenitor proliferation by metformin treatment were validated in additional control and FXS patient-derived hiPSC lines. Overall, our results validate that loss of FMRP results in elevated de novo protein synthesis in human neurons and suggest that approaches targeting this abnormality are likely to be of partial therapeutic benefit in FXS.

Metformin: the updated protective property in kidney disease

Metformin is a frontline hypoglycemic agent, which is mainly prescribed to manage type 2 diabetes mellitus with obesity. Emerging evidence suggests that metformin also exerts protective effects against various kidney diseases. Some postulate that kidney disease is actually a metabolic disease, accompanied by nonresolving pathophysiologic pathways controlling oxidative stress, endoplasmic reticulum stress, inflammation, lipotoxicity, fibrosis, and senescence, as well as insufficient host defense mechanisms such as AMP-activated protein kinase (AMPK) signaling and autophagy. Metformin may interfere with these pathways by orchestrating AMPK signaling and AMPK-independent pathways to protect the kidneys from injury. Furthermore, the United States Food and Drug Administration declared metformin is safe for patients with mild or moderate kidney impairment in 2016, assuaging some conservative attitudes about metformin management in patients with renal insufficiency and broadening the scope of research on the renal protective effects of metformin. This review focuses on the molecular mechanisms by which metformin imparts renal protection and its potential in the treatment of various kidney diseases.

Anticancer mechanisms of metformin: A review of the current evidence

Metformin, a US Food and Drug Administration-approved "star" drug used for diabetes mellitus type 2, has become a topic of increasing interest to researchers due to its anti-neoplastic effects. Growing evidence has demonstrated that metformin may be a promising chemotherapeutic agent, and several clinical trials of metformin use in cancer treatment are ongoing. However, the anti-neoplastic effects of metformin and its underlying mechanisms have not been fully elucidated. In this review, we present the newest findings on the anticancer activities of metformin, and highlight its diverse anticancer mechanisms. Several clinical trials, as well as the limitations of the current evidence are also demonstrated. This review explores the crucial roles of metformin and provides supporting evidence for the repurposing of metformin as a treatment of cancer.

Activation of AMP-activated protein kinase during sepsis/inflammation improves survival by preserving cellular metabolic fitness

The purpose was to determine the role of AMPK activation in the renal metabolic response to sepsis, the development of sepsis-induced acute kidney injury (AKI) and on survival. In a prospective experimental study, 167 10- to 12-week-old C57BL/6 mice underwent cecal ligation and puncture (CLP) and human proximal tubule epithelial cells (TEC; HK2) were exposed to inflammatory mix (IM), a combination of lipopolysaccharide (LPS) and high mobility group box 1 (HMGB1). Renal/TEC metabolic fitness was assessed by monitoring the expression of drivers of oxidative phosphorylation (OXPHOS), the rates of utilization of OXPHOS/glycolysis in response to metabolic stress, and mitochondrial function by measuring O₂ consumption rates (OCR) and the membrane potential (Δψ_m ). Sepsis/IM resulted in AKI, increased mortality, and in renal AMPK activation 6-24 hours after CLP/IM. Pharmacologic activation of AMPK with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) or metformin during sepsis improved the survival, while AMPK inhibition with Compound C increased mortality, impaired mitochondrial respiration, decreased OCR, and disrupted TEC metabolic fitness. AMPK-driven protection was associated with increased Sirt 3 expression and restoration of metabolic fitness. Renal AMPK activation in response to sepsis/IM is an adaptive mechanism that protects TEC, organs, and the host by preserving mitochondrial function and metabolic fitness likely through Sirt3 signaling.

MicroRNAs in Tumor Cell Metabolism: Roles and Therapeutic Opportunities

Dysregulated metabolism is a common feature of cancer cells and is considered a hallmark of cancer. Altered tumor-metabolism confers an adaptive advantage to cancer cells to fulfill the high energetic requirements for the maintenance of high proliferation rates, similarly, reprogramming metabolism confers the ability to grow at low oxygen concentrations and to use alternative carbon sources. These phenomena result from the dysregulated expression of diverse genes, including those encoding microRNAs (miRNAs) which are involved in several metabolic and tumorigenic pathways through its post-transcriptional-regulatory activity. Further, the identification of key actionable altered miRNA has allowed to propose novel targeted therapies to modulated tumor-metabolism. In this review, we discussed the different roles of miRNAs in cancer cell metabolism and novel miRNA-based strategies designed to target the metabolic machinery in human cancer.

Metformin Induces Different Responses in Clear Cell Renal Cell Carcinoma Caki Cell Lines

Clear cell renal cell carcinoma (ccRCC) is the most common and lethal form of urological cancer diagnosed globally. Mutations of the von Hippel-Lindau (VHL) tumor-suppressor gene and the resultant overexpression of hypoxia-inducible factor (HIF)-1α protein are considered hallmarks of ccRCC. Persistently activated HIF-1α is associated with increased cell proliferation, angiogenesis, and epithelial–mesenchymal transition (EMT), consequently leading to ccRCC progression and metastasis to other organs. However, the VHL status alone cannot predict the differential sensitivity of ccRCC to cancer treatments, which suggests that other molecular differences may contribute to the differential response of ccRCC cells to drug therapies. In this study, we investigated the response to metformin (an antidiabetic drug) of two human ccRCC cell lines Caki-1 and Caki-2, which express wild-type VHL. Our findings demonstrate a differential response between the two ccRCC cell lines studied, with Caki-2 cells being more sensitive to metformin compared to Caki-1 cells, which could be linked to the differential expression of HIF-1α despite both cell lines carrying a wild-type VHL. Our study unveils the therapeutic potential of metformin to inhibit the progression of ccRCC in vitro. Additional preclinical and clinical studies are required to ascertain the therapeutic efficacy of metformin against ccRCC.

Metformin alters H2A.Z dynamics and regulates androgen dependent prostate cancer progression

Epigenetic mechanisms involved in prostate cancer include hypermethylation of tumor suppressor genes, general hypomethylation of the genome, and alterations in histone posttranslational modifications (PTMs). In addition, over expression of the histone variant H2A.Z as well as deregulated expression of Polycomb group proteins including EZH2 have been well-documented. Recent evidence supports a role for metformin in prostate cancer (PCa) treatment. However, the mechanism of action of metformin in PCa is poorly understood. We provide data showing that metformin epigenetically targets PCa by altering the levels and gene binding dynamics of histone variant H2A.Z. Moreover, we show that the increase in H2A.Z upon metformin treatment occurs preferentially due to H2A.Z.1 isoform. Chromatin immunoprecipitation (ChIP)-RT PCR analysis indicates that metformin treatment results in an increased H2A.Z occupancy on the androgen receptor (AR) and AR-regulated genes that is more prominent in the androgen dependent AR positive LNCaP cells. Repression of H2A.Z.1 gene by siRNA-mediated knock down identified this H2A.Z isoform to be responsible. Based on preliminary data with an EZH2-specific inhibitor, we suggest that the effects of metformin on the early stages of PCa may involve both EZH2 and H2A.Z through the alteration of different molecular pathways.

Astrocyte Elevated Gene 1 (AEG-1) Acts as a Promoter Gene in Clear Cell Renal Cell Carcinoma Cell Growth and Metastasis

Background

Clear cell renal cell carcinoma (ccRCC) is usually incurable once it progresses to metastatic stage. Hence, in-depth investigations to reveal the precise molecular mechanisms behind the metastasis of ccRCC are required to improve the therapeutic outcome of ccRCC.

Material/Methods

The level of astrocyte elevated gene 1 (AEG-1) in ccRCC tissues and cell lines was determined by quantitative real-time PCR (qRT-PCR) assay. The MTS, colony formation, wound-healing, and Transwell invasion assays were used to assess the role of AEG-1 in ccRCC cells growth, migration, and invasion in vitro, respectively. Xenograft model and lung metastasis models were constructed to analyze the functions of AEG-1 in ccRCC cells growth and metastasis in vivo.

Result

We found that AEG-1 was overexpressed in ccRCC and was associated with the progression of ccRCC. Knocked-down AEG-1 impaired the migration and invasion of ccRCC cells in vitro. Furthermore, under-expression of AEG-1 caused complete inhibition of ccRCC cells growth and metastasis in vivo. In contrast, overexpression of AEG-1 significantly increased the migration and invasion ability of ccRCC cells in vitro. Finally, we revealed that AEG-1 boosted the metastatic ability of ccRCC cells via regulating Notch homolog 1 (Notch1).

Conclusions

The AEG-1/Notch1 signaling axis plays a vital role in ccRCC cell growth and metastasis.

Efficacy of metformin in mediating cellular uptake and inducing apoptosis activity of doxorubicin

The clinical use of doxorubicin (DOX) is limited due to its systemic side effects and drug resistance. Recent evidence suggests that metformin prevents and controls certain but not all types of cancer. The beneficial use of metformin in combination with some chemotherapeutic agents has been reported. The aim of this study is to investigate the influence of metformin on DOX-induced effects in human prostate DU145 cancer cells and clarify its molecular mechanisms. For this purpose, DU145 cells were treated with DOX or metformin, either alone or in combination with each other. The proliferation of DU145 cells was inhibited by DOX-alone and metformin-alone treatment in a time and dose-dependent manner. Metformin could enhance the cytotoxicity of DOX by increasing DOX cellular uptake and cell cycle arrest at G1/S checkpoint which is associated with the enhancement of p21 protein expression. Moreover, metformin could elevate DOX-induced apoptosis in DU145 cells in a concentration-dependent manner and DOX-induced caspase-3 activity. These findings suggest that the combined treatment of metformin with DOX potentiates the anticancer efficacy of DOX in DU145 cells via inhibiting ABCB1 function, cell cycle arrest at G1/S transition and apoptosis induction.

Valproic acid sensitizes metformin-resistant human renal cell carcinoma cells by upregulating H3 acetylation and EMT reversal

BACKGROUND

Metformin (Met) is a widely available diabetic drug and shows suppressed effects on renal cell carcinoma (RCC) metabolism and proliferation. Laboratory studies in RCC suggested that metformin has remarkable antitumor activities and seems to be a potential antitumor drug. But the facts that metformin may be not effective in reducing the risk of RCC in cancer clinical trials made it difficult to determine the benefits of metformin in RCC prevention and treatment. The mechanisms underlying the different conclusions between laboratory experiments and clinical analysis remains unclear. The goal of the present study was to determine whether long-term metformin use can induce resistance in RCC, whether metformin resistance could be used to explain the disaccord in laboratory and clinical studies, and whether the drug valproic acid (VPA), which inhibits histone deacetylase, exhibits synergistic cytotoxicity with metformin and can counteract the resistance of metformin in RCC.

METHODS

We performed CCK8, transwell, wound healing assay, flow cytometry and western blotting to detect the regulations of proliferation, migration, cell cycle and apoptosis in 786-O, ACHN and metformin resistance 786-O (786-M-R) cells treated with VPA, metformin or a combination of two drugs. We used TGF-β, SC79, LY294002, Rapamycin, protein kinase B (AKT) inhibitor to treat the 786-O or 786-M-R cells and detected the regulations in TGF-β /pSMAD3 and AMPK/AKT pathways.

RESULTS

786-M-R was refractory to metformin-induced antitumor effects on proliferation, migration, cell cycle and cell apoptosis. AMPK/AKT pathways and TGF-β/SMAD3 pathways showed low sensibilities in 786-M-R. The histone H3 acetylation diminished in the 786-M-R cells. However, the addition of VPA dramatically upregulated histone H3 acetylation, increased the sensibility of AKT and inhibited pSMAD3/SMAD4, letting the combination of VPA and metformin remarkably reappear the anti-tumour effects of metformin in 786-M-R cells.

CONCLUSIONS

VPA not only exhibits synergistic cytotoxicity with metformin but also counteracts resistance to metformin in renal cell carcinoma cell. The re-sensitization to metformin induced by VPA in metformin-resistant cells may help treat renal cell carcinoma patients.

Long Noncoding RNA Metastasis-Associated Lung Adenocarcinoma Transcript 1 (MALAT1) Promotes Renal Cell Carcinoma Progression via Sponging miRNA-429

Background

It is well known that long noncoding RNA (lncRNA) metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) is closely correlated with the tumorigenesis of multiple cancers, including renal cell carcinoma (RCC). However, the potential functional mechanism is still elusive.

Material/Methods

In our present research, quantitative real-time polymerase chain reaction (qRT-PCR) was performed for the measurement of MALAT1 and miR-429. CCK-8 assay and Transwell assay were performed for the proliferation, migration, and invasion abilities of RCC cells. Dual-luciferase reporter assay was performed to validate the interaction within MALAT1 and miR-429.

Results

Data found that MALAT1 was overexpressed in RCC clinical samples and cell lines. Moreover, loss-of-functional experiments showed that MALAT1 knockdown suppress the proliferation, migration, and invasion abilities of RCC cells. RT-PCR showed that miR-429 expression was downregulated in RCC cell lines, which was negatively correlated with that of MALAT1. Bioinformatics analysis suggested that miR-429 had complementary binding sequences with MALAT1, which was confirmed by dual-luciferase reporter assay.

Conclusions

In summary, our results concluded that MALAT1 functioned as an oncogene in RCC by sponging miR-429, acting as its competing endogenous RNA (ceRNA).

Metformin as an anti-cancer agent: actions and mechanisms targeting cancer stem cells

Metformin, a first line medication for type II diabetes, initially entered the spotlight as a promising anti-cancer agent due to epidemiologic reports that found reduced cancer risk and improved clinical outcomes in diabetic patients taking metformin. To uncover the anti-cancer mechanisms of metformin, preclinical studies determined that metformin impairs cellular metabolism and suppresses oncogenic signaling pathways, including receptor tyrosine kinase, PI3K/Akt, and mTOR pathways. Recently, the anti-cancer potential of metformin has gained increasing interest due to its inhibitory effects on cancer stem cells (CSCs), which are associated with tumor metastasis, drug resistance, and relapse. Studies using various cancer models, including breast, pancreatic, prostate, and colon, have demonstrated the potency of metformin in attenuating CSCs through the targeting of specific pathways involved in cell differentiation, renewal, metastasis, and metabolism. In this review, we provide a comprehensive overview of the anti-cancer actions and mechanisms of metformin, including the regulation of CSCs and related pathways. We also discuss the potential anti-cancer applications of metformin as mono- or combination therapies.

Metformin: Focus on Melanoma

Metformin is the most common biguanide used in the treatment of diabetes, with 120 million treated patients worldwide. Metformin decreases hyperglycemia without inducing hypoglycemia in diabetic patients and is very well tolerated. The principal effects of metformin are to decrease hepatic gluconeogenesis and increase glucose absorption by skeletal muscles. These effects are primarily due to metformin's action on mitochondria, which requires the activation of metabolic checkpoint AMP-activated protein kinase (AMPK). AMPK is implicated in several pathways, and following metformin activation, it decreases protein synthesis and cell proliferation. Many studies have examined the role of metformin in the regulation of cancer cells, particularly its effects on cancer cell proliferation and cell death. Encouraging results have been obtained in different types of cancers, including prostate, breast, lung, and skin cancers (melanoma). Furthermore, many retrospective epidemiological studies in diabetes patients have shown that metformin treatment decreased the risk of cancers compared with other antidiabetic treatments. In this review, we will discuss the effects of metformin on melanoma cells. Together, our novel data demonstrate the importance of developing metformin and new biguanide-derived compounds as potential treatments against a number of different cancers, particularly melanoma.

Metformin partially reverses the carboplatin-resistance in NSCLC by inhibiting glucose metabolism

Platinum-based chemotherapeutic drugs are irreplaceable for the treatment of advanced non-small cell lung cancer (NSCLC). However, acquired drug resistance has become a major obstacle for the clinical application of chemotherapy on NSCLC. In the present study, we established carboplatin-resistant NSCLC models on A549 and PC9 cell lines, which were named A549/R and PC9/R. Besides the low sensitivity of A549/R and PC9/R to carboplatin treatment, they exhibited higher metabolism rate of glucose compared to their parental A549 and PC9 cells, respectively. Mechanically, we confirmed that overexpression of PKM2 in A549/R and PC9/R was responsible for the high glucose metabolism and carboplatin resistance. Metformin, an antidiabetic drug, was observed to increase the sensitivity of carboplatin-resistant NSCLC cells to carboplatin treatment in vitro and in vivo. Mechanically, metformin decreased expression of PKM2 and subsequently inhibited the glucose uptake, lactate generation and ATP production in A549/R and PC9/R. Therefore, metformin promoted carboplatin-induced apoptosis through the mitochondria pathway. In addition, we demonstrated that metformin treatment also impaired the cross-resistance of A549/R and PC9/R to cisplatin, etoposide and 5-fluorouracil.

Metformin ameliorates skeletal muscle insulin resistance by inhibiting miR-21 expression in a high-fat dietary rat model

Insulin resistance (IR) plays a major role in the pathogenesis of abdominal obesity, hypertension, coronary heart disease, atherosclerosis and diabetes. miR-21 and TGF-β/smads is closely related to IR. However, it remained elusive whether metformin improved skeletal muscle insulin resistance (IRSM) by regulating miR-21 and its target signal TGF-β1/smads expression. In this study, high-fat diet rats with IR model and IR-skeletal muscle L6 cells (L6-SMCs) model were established, insulin sensitive index (ISI) and Homeostasis model assessment of IR (HOMA-IR) were applied, miR-21 and TGF-β1/smads mRNA expression were examined by RT-PCR, smad3 and smad7 protein were detected by western-blotting and laser scanning confocal microscopy (LSCM), the valid target of miR-21 was detected by luciferase reporter gene assay. Here, we found that metformin dose-dependently decreased miR-21 expression, accompanied by the decrease of HOMA-IR and the increase of HOMA-ISI. Luciferase report gene assay showed that smad7 was an effective target of miR-21. miR-21 overexpression directly downregulated smad7 and indirectly upregulated smad3 expression. Interestingly, miR-21 expression positively correlated with HOMA-IR and negatively correlated with HOMA-ISI. In conclusion, our results demonstrated that metformin improved IRSM by inhibiting miR-21 expression, and that miR-21 may be one of the therapeutic targets for IR.

Metformin Suppresses Proliferation and Viability of Rat Pheochromocytoma Cells

BACKGROUND Previous studies have clearly demonstrated that metformin inhibits cell proliferation and cell growth in many types of human cancers. Increased survival rates in patients with breast and lung cancer receiving metformin have also been observed. However, the effect of metformin on pheochromocytoma cells remains unexplored. MATERIAL AND METHODS Rat pheochromocytoma cells (PC12 cells) were cultured and treated with metformin or vehicle control. Cell proliferation, cell-cycle, apoptosis, genes expression, and the signaling pathways involved were analyzed in PC12 cells. RESULTS The metformin treatment reduced cell viability and proliferation in rat pheochromocytoma PC12 cells in a dose- and time-dependent manner. Furthermore, metformin exposure led to an increased apoptosis rate and cell-cycle arrest accompanied with downregulation of Ccna2 and Ccnb2. At the molecular level, the AMPK signaling pathway was activated, whereas the mTOR and ERK1/2 signaling pathways were inhibited by metformin. CONCLUSIONS Our data suggest an antiproliferative role of metformin in pheochromocytoma development, which may provide a novel option for future cancer therapy.

Chloride intracellular channel 1 regulates the antineoplastic effects of metformin in gallbladder cancer cells

Metformin is the most commonly used drug for type 2 diabetes and has potential benefit in treating and preventing cancer. Previous studies indicated that membrane proteins can affect the antineoplastic effects of metformin and may be crucial in the field of cancer research. However, the antineoplastic effects of metformin and its mechanism in gallbladder cancer (GBC) remain largely unknown. In this study, the effects of metformin on GBC cell proliferation and viability were evaluated using the Cell Counting Kit‐8 (CCK‐8) assay and an apoptosis assay. Western blotting was performed to investigate related signaling pathways. Of note, inhibition, knockdown and upregulation of the membrane protein Chloride intracellular channel 1 (CLIC1) can affect GBC resistance in the presence of metformin. Our data demonstrated that metformin apparently inhibits the proliferation and viability of GBC cells. Metformin promoted cell apoptosis and increased the number of early apoptotic cells. We found that metformin can exert growth‐suppressive effects on these cell lines via inhibition of p‐Akt activity and the Bcl‐2 family. Notably, either dysfunction or downregulation of CLIC1 can partially decrease the antineoplastic effects of metformin while upregulation of CLIC1 can increase drug sensitivity. Our findings provide experimental evidence for using metformin as an antitumor treatment for gallbladder carcinoma.