Metformin and improved treatment outcomes in radiation therapy - A review

Examining the clinical relevance of metformin as an antioxidant intervention

In physiological concentrations, reactive oxygen species play a vital role in regulating cell signaling and gene expression. Nevertheless, oxidative stress is implicated in the pathogenesis of numerous diseases and can inflict damage on diverse cell types and tissues. Thus, understanding the factors that mitigate the deleterious effects of oxidative stress is imperative for identifying new therapeutic targets. In light of the absence of direct treatment recommendations for reducing oxidative stress, there is a continuing need for fundamental research that utilizes innovative therapeutic approaches. Metformin, known for its multifaceted beneficial properties, is acknowledged for its ability to counteract the adverse effects of increased oxidative stress at both molecular and cellular levels. In this review, we delve into recent insights regarding metformin's antioxidant attributes, aiming to expand its clinical applicability. Our review proposes that metformin holds promise as a potential adjunctive therapy for various diseases, given its modulation of oxidative stress characteristics and regulation of diverse metabolic pathways. These pathways include lipid metabolism, hormone synthesis, and immunological responses, all of which may experience dysregulation in disease states, contributing to increased oxidative stress. Furthermore, our review introduces potential novel metformin-based interventions that may merit consideration in future research. Nevertheless, the necessity for clinical trials involving this drug remains imperative, as they are essential for establishing therapeutic dosages and addressing challenges associated with dose-dependent effects.

Heme Biosynthesis is Crucial for Cell Survival and Mitochondrial OXPHOS after X Irradiation

Heme is an essential component of the hemoproteins involved in the mitochondrial electron transport chain (ETC). Cancer cells have been reported to display high heme levels and increased activity of heme-containing proteins. Consistently, inhibition of heme biosynthesis by the ALAD inhibitor succinylacetone (SA) has been shown to reduce tumor cell survival. These observations indicate that heme biosynthesis is essential for cancer cell proliferation. X irradiation has been shown to increase mitochondrial mass, membrane potential, oxygen consumption, reactive oxygen species (ROS) production, and ATP synthesis. This finding suggests that radiation activates mitochondrial oxidative phosphorylation (OXPHOS). However, although heme is an essential component of the mitochondrial ETC, whether radiation influences heme biosynthesis remains unclear. In this study, we evaluated heme biosynthesis activity after X irradiation and examined the effects of heme biosynthesis inhibition by SA on cellular radiosensitivity and mitochondrial OXPHOS function. We demonstrated that X irradiation significantly increased ALAS1 mRNA levels and cellular heme content. Inhibition of heme biosynthesis by SA significantly decreased cellular heme content and sensitized cancer cells to radiation. We also showed that SA reduced cellular ATP levels, mitochondrial membrane potential, and mitochondrial ROS production, suggesting mitochondrial OXPHOS dysfunction. SA decreased the expression of mitochondrial heme-related proteins COX2 and cytochrome c but did not influence COX1 and VDAC expression. These results indicate that inhibition of heme biosynthesis decreased mitochondrial ETC protein expression and OXPHOS activity, which triggered cellular ATP depletion and radiosensitization after X irradiation. In summary, heme biosynthesis is upregulated by X irradiation and is essential for mitochondrial OXPHOS and cell survival.

Radioproteomics modeling of metformin-enhanced radiosensitivity: an animal study

PURPOSE

Metformin is considered as radiation modulator in both tumors and healthy tissues. Radiomics has the potential to decode biological mechanisms of radiotherapy response. The aim of this study was to apply radiomics analysis in metformin-induced radiosensitivity and finding radioproteomics associations of computed tomography (CT) imaging features and proteins involved in metformin radiosensitivity signaling pathways.

MATERIALS AND METHODS

A total of 32 female BALB/c mice were used in this study and were subjected to injection of breast cancer cells. When tumors reached a mean volume of 150 mm3, mice were randomly divided into the four groups including Control, Metformin, Radiation, and Radiation + Metformin. Western blot analysis was performed after treatment to measure expression of proteins including AMPK-alpha, phospho-AMPK-alpha (Thr172), mTOR, phospho-mTOR (Ser2448), phospho-4EBP1 (Thr37/46), phospho-ACC (Ser79), and β-actin. CT imaging was performed before treatment and at the end of treatment in all groups. Radiomics features extracted from segmented tumors were selected using Elastic-net regression and were assessed in terms of correlation with expression of the proteins.

RESULTS

It was observed that proteins including phospho-mTOR, phospho-4EBP1, and mTOR had positive correlations with changes in tumor volumes in days 28, 24, 20, 16, and 12, while tumor volume changes at these days had negative correlations with AMPK-alpha, phospho-AMPK-alpha, and phospho-ACC proteins. Furthermore, median feature had a positive correlation with AMPK-alpha, phospho-ACC, and phospho-AMPK-alpha proteins. Also, Cluster shade feature had positive correlations with mTOR and p-mTOR. On the other hand, LGLZE feature had negative correlations with AMPK-alpha and phospho-AMPK-alpha.

CONCLUSION

Radiomics features can decode proteins that involved in response to metformin and radiation, although further studies are warranted to investigate the optimal way to integrate radiomics into biological experiments.

Role of the tumor microenvironment in the lymphatic metastasis of cervical cancer (Review)

Lymphatic metastasis is the primary type of cervical cancer metastasis and is associated with an extremely poor prognosis in patients. The tumor microenvironment primarily includes cancer-associated fibroblasts, tumor-associated macrophages, myeloid-derived suppressor cells, immune and inflammatory cells, and blood and lymphatic vascular networks, which can promote the establishment of lymphatic metastatic sites within immunosuppressive microenvironments or promote lymphatic metastasis by stimulating lymphangiogenesis and epithelial-mesenchymal transformation. As the most important feature of the tumor microenvironment, hypoxia plays an essential role in lymph node metastasis. In this review, the known mechanisms of hypoxia, and the involvement of stromal components and immune inflammatory cells in the tumor microenvironment of lymphatic metastasis of cervical cancer are discussed. Additionally, a summary of the clinical trials targeting the tumor microenvironment for the treatment of cervical cancer is provided, emphasizing the potential and challenges of immunotherapy.

Metformin is a metabolic modulator and radiosensitiser in rectal cancer

Resistance to neoadjuvant chemoradiation therapy, is a major challenge in the management of rectal cancer. Increasing evidence supports a role for altered energy metabolism in the resistance of tumours to anti-cancer therapy, suggesting that targeting tumour metabolism may have potential as a novel therapeutic strategy to boost treatment response. In this study, the impact of metformin on the radiosensitivity of colorectal cancer cells, and the potential mechanisms of action of metformin-mediated radiosensitisation were investigated. Metformin treatment was demonstrated to significantly radiosensitise both radiosensitive and radioresistant colorectal cancer cells in vitro. Transcriptomic and functional analysis demonstrated metformin-mediated alterations to energy metabolism, mitochondrial function, cell cycle distribution and progression, cell death and antioxidant levels in colorectal cancer cells. Using ex vivo models, metformin treatment significantly inhibited oxidative phosphorylation and glycolysis in treatment naïve rectal cancer biopsies, without affecting the real-time metabolic profile of non-cancer rectal tissue. Importantly, metformin treatment differentially altered the protein secretome of rectal cancer tissue when compared to non-cancer rectal tissue. Together these data highlight the potential utility of metformin as an anti-metabolic radiosensitiser in rectal cancer.

Metformin counters oxidative stress and mitigates adverse effects of radiation exposure: An overview

Metformin (1,1-dimethylbiguanidine hydrochloride) (MF) is a drug that has long been in use for the treatment of type 2 diabetes mellitus and recently is coming into use in the radiation therapy of cancer and other conditions. Exposure to ionizing radiation disturbs the redox homeostasis of cells and causes damage to proteins, membranes, and mitochondria, destroying a number of biological processes. After irradiation, MF activates cellular antioxidant and repair systems by signaling to eliminate the harmful consequences of disruption of redox homeostasis. The use of MF in the treatment of the negative effects of irradiation has great potential in medical patients after radiotherapy and in victims of nuclear accidents or radiologic terrorism.

Metformin combined with local irradiation provokes abscopal effects in a murine rectal cancer model

Although preoperative chemoradiation therapy can down-stage locally advanced rectal cancer (LARC), it has little effect on distant metastases. Metformin exerts an anti-cancer effect partly through the activation of host immunity. LuM1, a highly lung metastatic subclone of colon 26, was injected subcutaneously (sc) in BALB/c mice and treated with metformin and/or local radiation (RT). Lung metastases and the primary tumors were evaluated and the phenotypes of immune cells in the spleen and lung metastases were examined with flow cytometry and immunohistochemistry. Local RT, but not metformin, partially delayed the growth of sc tumor which was augmented with metformin. Lung metastases were unchanged in metformin or RT alone, but significantly reduced in the combined therapy. The ratios of splenic T cells tended to be low in the RT group, which were increased by the addition of metformin. IFN-γ production of the splenic CD4(+) and CD8(+) T cells was enhanced and CD49b (+) CD335(+) activated NK cells was increased after combined treatment group. Density of NK cells infiltrating in lung metastases was increased after combination treatment. Metformin effectively enhances local and abscopal effects of RT though the activation of cell-mediated immunity and might be clinically useful for LARC.

Is Metformin Use Associated with Prolonged Overall Survival in Patients with Soft Tissue Sarcoma? A SEER-Medicare Study

BACKGROUND

Metformin, an oral drug used to treat patients with diabetes, has been associated with prolonged survival in patients with various visceral carcinomas. Although the exact mechanisms are unknown, preclinical translational studies demonstrate that metformin may impair tumor cellular metabolism, alter matrix turnover, and suppress oncogenic signaling pathways. Currently used chemotherapeutic agents have not been very successful in the adjuvant setting or for treating patients with metastatic sarcomas. We wanted to know whether metformin might be associated with improved survival in patients with a soft tissue sarcoma.

QUESTIONS/PURPOSES

In patients treated for a soft tissue sarcoma, we asked: (1) Is there an association between metformin use and longer survival? (2) How does this association differ, if at all, among patients with and without the diagnosis of diabetes?

METHODS

The Surveillance, Epidemiology, and End Results-Medicare (SEER-Medicare) database was used to identify patients with a diagnosis of soft tissue sarcoma from 2007 to 2016. Concomitant medication use was identified using National Drug Codes using the Medicare Part D event files. This database was chosen because of the large number of captured sarcoma patients, availability of tumor characteristics, and longitudinal linkage of Medicare data. A total of 14,650 patients were screened for inclusion. Patients with multiple malignancies, diagnosis at autopsy, or discrepant linkage to the Medicare database were excluded. Overall, 4606 patients were eligible for the study: 598 patients taking metformin and 4008 patients not taking metformin. A hazard of mortality (hazard ratio) was analyzed comparing patients taking metformin with those patient groups not taking metformin and expressed in terms of a 95% confidence interval. Cox regression analysis was used to control for patient-specific, disease-specific, and treatment-specific covariates.

RESULTS

Having adjusted for disease-, treatment-, and patient-specific characteristics, patients taking metformin experienced prolonged survival compared with all patients not taking metformin (HR 0.76 [95% CI 0.66 to 0.87]). Associated prolonged survival was also seen when patients taking metformin were compared with those patients not on metformin irrespective of a diabetes diagnosis (HR 0.79 [95% CI 0.66 to 0.94] compared with patients with a diagnosis of diabetes and HR 0.77 [95% CI 0.67 to 0.89] compared with patients who did not have a diagnosis of diabetes).

CONCLUSION

Without suggesting causation, we found that even after controlling for confounding variables such as Charlson comorbidity index, tumor grade, size, stage, and surgical/radiation treatment modalities, there was an association between metformin use and increased survival in patients with soft tissue sarcoma. When considered separately, this association persisted in patients not on metformin with and without a diabetes diagnosis. Although metformin is not normally prescribed to patients who do not have a diabetes diagnosis, these data support further study, and if these findings are substantiated, it might lead to the performance of multicenter, prospective clinical trials about the use of metformin as an adjuvant therapy for the treatment of soft tissue sarcoma in patients with and without a preexisting diabetes diagnosis.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Metformin Intervention—A Panacea for Cancer Treatment?

The molecular mechanism of action and the individual influence of various metabolic pathways related to metformin intervention are under current investigation. The available data suggest that metformin provides many advantages, exhibiting anti-inflammatory, anti-cancer, hepatoprotective, cardioprotective, otoprotective, radioprotective, and radio-sensitizing properties depending on cellular context. This literature review was undertaken to provide novel evidence concerning metformin intervention, with a particular emphasis on cancer treatment and prevention. Undoubtedly, the pleiotropic actions associated with metformin include inhibiting inflammatory processes, increasing antioxidant capacity, and improving glycemic and lipid metabolism. Consequently, these characteristics make metformin an attractive medicament to translate to human trials, the promising results of which were also summarized in this review.

Metformin exerts anti-tumor effects via Sonic hedgehog signaling pathway by targeting AMPK in HepG2 cells

Metformin, a traditional first-line pharmacologic treatment for type 2 diabetes, has recently been shown to impart anti-cancer effects on hepatocellular carcinoma (HCC). However, the molecular mechanism of metformin on its antitumor activity is still not completely clear. The Sonic hedgehog (Shh) signaling pathway is closely associated with the initiation and progression of HCC. Therefore, the aim of the current study was to investigate the effects of metformin on the biological behavior of HCC and the underlying functional mechanism of metformin on the Shh pathway. The HCC cellular was induced in HepG2 cells by recombinant human Shh (rhShh). The effects of metformin on proliferation and metastasis were evaluated by proliferation, wound healing and invasion assays in vitro. The mRNA and protein expression levels of proteins related to the Shh pathway were measured by western blotting, quantitative PCR and immunofluorescence staining. Metformin inhibited rhShh-induced proliferation and metastasis. Furthermore, metformin decreased mRNA and protein expression of components of the Shh pathway including Shh, Ptch, Smo and Gli-1. Silencing of AMPK in the presence of metformin revealed that metformin could exert its inhibitory effect via AMPK. Our findings demonstrate that metformin can suppress the migration and invasion of HepG2 cells via AMPK-mediated inhibition of the Shh pathway.

Frontiers in Anti-Cancer Drug Discovery: Challenges and Perspectives of Metformin as Anti-Angiogenic Add-On Therapy in Glioblastoma

Simple Summary

Glioblastoma is the most aggressive primary brain tumor, with the highest incidence and the worst prognosis. Life expectancy from diagnosis remains dismal, at around 15 months, despite surgical resection and treatment with radiotherapy and chemotherapy. Given the aggressiveness of the tumor and the inefficiency of the treatments adopted to date, the scientific research investigates innovative therapeutic approaches. Importantly, angiogenesis represents one of the main features of glioblastoma, becoming in the last few years a major candidate for target therapy. Metformin, a well-established therapy for type 2 diabetes, offered excellent results in preventing and fighting tumor progression, particularly against angiogenic mechanisms. Therefore, the purpose of this review is to summarize and discuss experimental evidence of metformin anti-cancer efficacy, with the aim of proposing this totally safe and tolerable drug as add-on therapy against glioblastoma.

Abstract

Glioblastoma is the most common primitive tumor in adult central nervous system (CNS), classified as grade IV according to WHO 2016 classification. Glioblastoma shows a poor prognosis with an average survival of approximately 15 months, representing an extreme therapeutic challenge. One of its distinctive and aggressive features is aberrant angiogenesis, which drives tumor neovascularization, representing a promising candidate for molecular target therapy. Although several pre-clinical studies and clinical trials have shown promising results, anti-angiogenic drugs have not led to a significant improvement in overall survival (OS), suggesting the necessity of identifying novel therapeutic strategies. Metformin, an anti-hyperglycemic drug of the Biguanides family, used as first line treatment in Type 2 Diabetes Mellitus (T2DM), has demonstrated in vitro and in vivo antitumoral efficacy in many different tumors, including glioblastoma. From this evidence, a process of repurposing of the drug has begun, leading to the demonstration of inhibition of various oncopromoter mechanisms and, consequently, to the identification of the molecular pathways involved. Here, we review and discuss metformin’s potential antitumoral effects on glioblastoma, inspecting if it could properly act as an anti-angiogenic compound to be considered as a safely add-on therapy in the treatment and management of glioblastoma patients.

Impact of Pelvic Radiation Therapy for Prostate Cancer on Global Metabolic Profiles and Microbiota-Driven Gastrointestinal Late Side Effects: A Longitudinal Observational Study

PURPOSE

Radiation therapy to the prostate and pelvic lymph nodes (PLNRT) is part of the curative treatment of high-risk prostate cancer. Yet, the broader influence of radiation therapy on patient physiology is poorly understood. We conducted comprehensive global metabolomic profiling of urine, plasma, and stools sampled from patients undergoing PLNRT for high-risk prostate cancer.

METHODS AND MATERIALS

Samples were taken from 32 patients at 6 timepoints: baseline, 2 to 3 and 4 to 5 weeks of PLNRT; and 3, 6, and 12 months after PLNRT. We characterized the global metabolome of urine and plasma using 1H nuclear magnetic resonance spectroscopy and ultraperformance liquid chromatography-mass spectrometry, and of stools with nuclear magnetic resonance. Linear mixed-effects modeling was used to investigate metabolic changes between timepoints for each biofluid and assay and determine metabolites of interest.

RESULTS

Metabolites in urine, plasma and stools changed significantly after PLNRT initiation. Metabolic profiles did not return to baseline up to 1 year post-PLNRT in any biofluid. Molecules associated with cardiovascular risk were increased in plasma. Pre-PLNRT fecal butyrate levels directly associated with increasing gastrointestinal side effects, as did a sharper fall in those levels during and up to 1 year postradiation therapy, mirroring our previous results with metataxonomics.

CONCLUSIONS

We showed for the first time that an overall metabolic effect is observed in patients undergoing PLNRT up to 1 year posttreatment. These metabolic changes may effect on long-term morbidity after treatment, which warrants further investigation.

Impact of hypoxia on cervical cancer outcomes

The annual global incidence of cervical cancer is approximately 604 000 cases/342 000 deaths, making it the fourth most common cancer in women. Cervical cancer is a major healthcare problem in low and middle income countries where 85% of new cases and deaths occur. Secondary prevention measures have reduced incidence and mortality in developed countries over the past 30 years, but cervical cancer remains a major cause of cancer deaths in women. For women who present with Fédération Internationale de Gynécologie et d'Obstétrique (FIGO 2018) stages IB3 or upwards, chemoradiation is the established treatment. Despite high rates of local control, overall survival is less than 50%, largely due to distant relapse. Reducing the health burden of cervical cancer requires greater individualization of treatment, identifying those at risk of relapse and progression for modified or intensified treatment. Hypoxia is a well known feature of solid tumors and an established therapeutic target. Low tumorous oxygenation increases the risk of local invasion, metastasis and treatment failure. While meta-analyses show benefit, many individual trials targeting hypoxia failed in part due to not selecting patients most likely to benefit. This review summarizes the available hypoxia-targeted strategies and identifies further research and new treatment paradigms needed to improve patient outcomes. The applications and limitations of hypoxia biomarkers for treatment selection and response monitoring are discussed. Finally, areas of greatest unmet clinical need are identified to measure and target hypoxia and therefore improve cervical cancer outcomes.

Metformin preferentially enhances the radio-sensitivity of cancer stem-like cells with highly mitochondrial respiration ability in HMPOS

Metformin has many anti-cancer effects, alone or in combination with radiation. However, the mechanism underlying its radio-sensitized effect is still unclear, especially for cancer stem-like cells (CSCs). Here, the radio-sensitized effect of metformin was investigated, and its mechanism was revealed in CSCs derived from canine osteosarcoma cell line (HMPOS), a canine osteosarcoma cell line. Spheroid cells (SCs) were used as CSCs-rich cells derived from sphere formation, and SCs were compared with normal adherent culture cells (ACs). The radio-sensitizing effect of metformin using clonogenic assay and tumor growth in mice xenograft model were evaluated, and the mechanism of its radio-sensitization focusing on mitochondrial function was revealed. Metformin significantly enhanced radio-sensitivity of SCs through its inhibition of the mitochondrial function, as shown by decreased oxygen consumption, decreased mitochondrial membrane potential, and decreased ATP production. Additionally, SCs had a higher ability of mitochondrial respiration than ACs, which may have caused difference of their sensitivity of metformin and irradiation. In conclusion, mitochondrial function might play an important role in the sensitivity of metformin and irradiation, and drugs that target mitochondrial respiration, such as metformin, are promising radio-sensitizers to target CSCs.

Improved Tumor Response in Patients on Metformin Undergoing Yttrium-90 Radioembolization Segmentectomy for Hepatocellular Carcinoma

PURPOSE

Metformin is associated with improved outcomes after external radiation and chemotherapy but has not been studied for Y-90 radiation segmentectomy (RS). This study evaluates the effect of metformin on tumor response after Y-90 RS in patients with hepatocellular carcinoma (HCC).

METHODS AND MATERIALS

A retrospective analysis of patients with HCC who underwent Y-90 RS between 2014-2018 was performed. Comparisons were made between all patients taking and not taking metformin, and diabetic patients taking and not taking metformin. Tumor response was analyzed with logistic regression to compare absolute and percent change in total tumor diameter (TTD) and modified Response Evaluation Criteria in Solid Tumors (mRECIST). Overall survival (OS) was evaluated using Kaplan-Meier estimation and log-rank analysis.

RESULTS

A total of 106 patients underwent 112 Y-90 RS, of which 40 were diabetic (38.8%) and 19 (18.4%) were on metformin. At baseline, the two groups of patients on metformin and not on metformin had no significant difference in age, Child-Pugh score, MELD score, ALBI grade, total tumor diameter, and size of dominant tumor. The only significant baseline difference was ECOG status. Uni- and multivariate analysis demonstrated a larger reduction in TTD and objective response by mRECIST criteria for patients undergoing Y-90 RS on metformin compared to those not on metformin. OS was similar between patients taking and not taking metformin (p = 0.912).

CONCLUSION

Metformin may be associated with increased tumor response after Y-90 RS in patients with HCC.

LEVEL OF EVIDENCE

III, Retrospective Study.

Metformin with neoadjuvant chemoradiation to improve pathologic response in rectal cancer: A pilot phase I/II trial

•

A prospective pilot phase I/II study on metformin given concurrently with neoadjuvant chemoradiation (CRT) in non-diabetic rectal cancer patients.

•

Three patients had a clinical complete response (cCR) and did not have surgical resection.

•

Of the 12 patients who underwent surgery, there were two pCRs. For the combined pCR/cCR rate of 33% (95% CI 19–47%), a total of 85 patients will be required to yield a 95% CI with a 10% margin of error.

•

These pilot results are encouraging, and will serve to refine the design and conduct of a future phase 2 trial to determine whether adding metformin to CRT improves pCR/cCR rates.

Purpose

Neoadjuvant radiotherapy with or without chemotherapy decreases the risk of local recurrence after surgery for rectal cancer. Emerging data suggest that diabetic patients on metformin may have improved cancer outcome after radiotherapy. A single institutional pilot study was performed to determine if metformin given concurrently with long course chemoradiation (CRT) may improve pathologic complete response (pCR) in non-diabetic rectal cancer patients. The study was designed to construct a confidence interval (CI) for the pCR rate to determine the sample size for a phase 2 trial.

Methods

Non-diabetic patients with biopsy confirmed rectal cancer deemed candidates for long course neoadjuvant CRT were invited to participate. Radiation consisted of 50.4 Gy in 28 daily fractions with concurrent daily capecitabine (825 mg/m² twice daily). Participants self-administered metformin (500 mg of twice daily) 2 weeks prior to, during and for 4 weeks after CRT.

Results

A total of 16 patients were accrued. One patient withdrew from the study. Only grade 1 or 2 adverse events were observed. Three patients had a clinical complete response (cCR) and did not undergo surgery. Of the 12 patients who underwent surgery, there were two pCRs. For the combined pCR/cCR rate of 33% (95% CI 19–47%), a total of 85 patients will be required to yield a 95% CI with a 10% margin of error.

Conclusions

Adding metformin to neoadjuvant CRT for rectal cancer does not appear to enhance toxicities. These results will be used to refine the design and conduct of a future phase 2 trial to determine whether adding metformin to CRT improves pCR/cCR rates.

Incorporation of Sulfonamide Moiety into Biguanide Scaffold Results in Apoptosis Induction and Cell Cycle Arrest in MCF-7 Breast Cancer Cells

Metformin, apart from its glucose-lowering properties, has also been found to demonstrate anti-cancer properties. Anti-cancer efficacy of metformin depends on its uptake in cancer cells, which is mediated by plasma membrane monoamine transporters (PMAT) and organic cation transporters (OCTs). This study presents an analysis of transporter mediated cellular uptake of ten sulfonamide-based derivatives of metformin in two breast cancer cell lines (MCF-7 and MDA-MB-231). Effects of these compounds on cancer cell growth inhibition were also determined. All examined sulfonamide-based analogues of metformin were characterized by greater cellular uptake in both MCF-7 and MDA-MB-231 cells, and stronger cytotoxic properties than those of metformin. Effective intracellular transport of the examined compounds in MCF-7 cells was accompanied by high cytotoxic activity. For instance, compound 2 with meta-methyl group in the benzene ring inhibited MCF-7 growth at micromolar range (IC₅₀ = 87.7 ± 1.18 µmol/L). Further studies showed that cytotoxicity of sulfonamide-based derivatives of metformin partially results from their ability to induce apoptosis in MCF-7 and MDA-MB-231 cells and arrest cell cycle in the G0/G1 phase. In addition, these compounds were found to inhibit cellular migration in wound healing assay. Importantly, the tested biguanides are more effective in MCF-7 cells at relatively lower concentrations than in MDA-MB-231 cells, which proves that the effectiveness of transporter-mediated accumulation in MCF-7 cells is related to biological effects, including MCF-7 cell growth inhibition, apoptosis induction and cell cycle arrest. In summary, this study supports the hypothesis that effective transporter-mediated cellular uptake of a chemical molecule determines its cytotoxic properties. These results warrant a further investigation of biguanides as putative anti-cancer agents.

Metformin: A Possible Option in Cancer Chemotherapy

Metformin has been used for a long time as an antidiabetic medication for type 2 diabetes. It is used either as a monotherapy or in combination with other antidiabetic medications. The drug came into prominence in diabetes and other conditions with cardiovascular risk after the landmark study of 1995 by the United Kingdom Prospective Diabetes Study which emphasized its importance. However, the drug has been used in experimental trials in various aspects of medicine and pharmacology such as in reproductive medicine, cancer chemotherapy, metabolic diseases, and neurodegenerative diseases. It has been in use in the treatment of polycystic ovarian disease and obesity and is being considered in type 1 diabetes. This study seeks to evaluate the relevance of metformin in cancer management. Different mechanisms have been proposed for its antitumor action which involves the following: (a) the activation of adenosine monophosphate kinase, (b) modulation of adenosine A1 receptor (ADORA), (c) reduction in insulin/insulin growth factors, and (d) the role of metformin in the inhibition of endogenous reactive oxygen species (ROS); and its resultant damage to deoxyribonucleic acid (DNA) molecule is another paramount antitumor mechanism.

MnTE-2-PyP, a manganese porphyrin, reduces cytotoxicity caused by irradiation in a diabetic environment through the induction of endogenous antioxidant defenses

Radiation is a common anticancer therapy for many cancer patients, including prostate cancer. Diabetic prostate cancer patients suffer from increased lymph node metastasis, tumor recurrence and decreased survival as compared to non-diabetic prostate cancer patients. These patients are also at increased risk for enhanced radiation-induced normal tissue damage such as proctitis. Diabetics are oxidatively stressed and radiation causes additional oxidative damage. We and others have reported that, MnTE-2-PyP, a manganese porphyrin, protects normal prostate tissue from radiation damage. We have also reported that, in an in vivo mouse model of prostate cancer, MnTE-2-PyP decreases tumor volume and increases survival of the mice. In addition, MnTE-2-PyP has also been shown to reduce blood glucose and inhibits pro-fibrotic signaling in a diabetic model. Therefore, to investigate the role of MnTE-2-PyP in normal tissue protection in an irradiated diabetic environment, we have treated human prostate fibroblast cells with MnTE-2-PyP in an irradiated hyperglycemic environment. This study revealed that hyperglycemia causes increased cell death after radiation as compared to normo-glycemia. MnTE-2-PyP protects against hyperglycemia-induced cell death after radiation. MnTE-2-PyP decreases expression of NOX4 and α-SMA, one of the major oxidative enzymes and pro-fibrotic molecules respectively. MnTE-2-PyP obstructs NF-κB activity by decreasing DNA binding of the p50-p50 homodimer in the irradiated hyperglycemic environment. MnTE-2-PyP increases NRF2 mediated cytoprotection by increasing NRF2 protein expression and DNA binding. Therefore, we are proposing that, MnTE-2-PyP protects fibroblasts from irradiation and hyperglycemia damage by enhancing the NRF2- mediated pathway in diabetic prostate cancer patients, undergoing radiotherapy.

Metformin as Potential Therapy for High-Grade Glioma

Metformin (MET), 1,1-dimethylbiguanide hydrochloride, is a biguanide drug used as the first-line medication in the treatment of type 2 diabetes. The recent years have brought many observations showing metformin in its new role. The drug, commonly used in the therapy of diabetes, may also find application in the therapy of a vast variety of tumors. Its effectiveness has been demonstrated in colon, breast, prostate, pancreatic cancer, leukemia, melanoma, lung and endometrial carcinoma, as well as in gliomas. This is especially important in light of the poor options offered to patients in the case of high-grade gliomas, which include glioblastoma (GBM). A thorough understanding of the mechanism of action of metformin can make it possible to discover new drugs that could be used in neoplasm therapy.

Effects of metformin on tumor hypoxia and radiotherapy efficacy: a [18F]HX4 PET imaging study in colorectal cancer xenografts

Background

In a colorectal cancer xenograft model, we investigated the therapeutic effect of metformin on tumor hypoxia with [¹⁸F]flortanidazole ([¹⁸F]HX4) small-animal positron emission tomography (μPET). We also assessed the additive effect of metformin on long-term radiotherapy outcome and we studied the potential of [¹⁸F]HX4 as a predictive and/or prognostic biomarker within this setup.

Methods

Colo205-bearing mice (n = 40) underwent a baseline [¹⁸F]HX4 hypoxia μPET/computed tomography (CT) scan. The next day, mice received 100 mg/kg metformin or saline intravenously (n = 20/group) and [¹⁸F]HX4 was administered intravenously 30 min later, whereupon a second μPET/CT scan was performed to assess changes in tumor hypoxia. Two days later, mice were further divided into four therapy groups (n = 10/group): control (1), metformin (2), radiotherapy (3), and metformin + radiotherapy, i.e., combination (4). Then, they received a second dose of metformin (groups 2 and 4) or saline (groups 1 and 3), followed by a single radiotherapy dose of 15 Gy (groups 3 and 4) or sham irradiation (groups 1 and 2) 30 min later. Tumor growth was followed three times a week by caliper measurements to assess the therapeutic outcome.

Results

[¹⁸F]HX4 uptake decreased in metformin-treated tumors with a mean intratumoral reduction in [¹⁸F]HX4 tumor-to-background ratio (TBR) from 2.53 ± 0.30 to 2.28 ± 0.26 (p = 0.04), as opposed to saline treatment (2.56 ± 0.39 to 3.08 ± 0.39; p = 0.2). The median tumor doubling time (TDT) was 6, 8, 41, and 43 days in the control, metformin, radiotherapy and combination group, respectively (log-rank p < 0.0001), but no metformin-specific therapy effects could be detected. Baseline [¹⁸F]HX4 TBR was a negative prognostic biomarker for TDT (hazard ratio, 2.39; p = 0.02).

Conclusions

Metformin decreased [¹⁸F]HX4 uptake of Colo205-tumors, but had no additive effect on radiotherapy efficacy. Nevertheless, [¹⁸F]HX4 holds promise as a prognostic imaging biomarker.

Effect of metformin on cell proliferation, apoptosis, migration and invasion in A172 glioma cells and its mechanisms

The purpose of the present study was to determine the effects of metformin on the inhibition of proliferation, apoptosis, invasion and migration of A172 human glioma cells in vitro and determine the underlying mechanism. The effects of metformin at different concentrations (0, 0.1, 1 and 10 mmol/l) on the inhibition of A172 cell proliferation were detected using a 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide assay. Cell apoptosis was detected by flow cytometry. Caspase‑3 activity was analyzed by spectrophotometry. The invasion and migration of cells were detected by Transwell assays. The levels of Bcl‑2‑associated X protein (Bax), B‑cell lymphoma 2 (Bcl‑2), AMP‑activated protein kinase (AMPK), phosphorylated‑(p)AMPK and mechanistic target of rapamycin (mTOR) protein expression were detected by western blot analysis, and changes in the malondialdehyde (MDA) content and activity of superoxide dismutase (SOD) were determined. Compared with the control group, metformin significantly increased the inhibition of proliferation and apoptosis, and significantly reduced the invasion and migration of A172 cells in dose‑ and time‑dependent manners (P<0.05). In addition, compared with the control group, metformin significantly enhanced the activity of caspase‑3, increased the expression of AMPK/pAMPK/Bax proteins and reduced the expression of mTOR/Bcl‑2 proteins (P<0.05). Metformin increased the MDA content and reduced the activity of SOD in a dose‑dependent manner (P<0.05). Metformin may inhibit glioma cell proliferation, migration and invasion, and promote its apoptosis; the effects may be associated with the AMPK/mTOR signaling pathway and oxidative stress.

The beneficial effects of metformin on cancer prevention and therapy: a comprehensive review of recent advances

Metformin is a widely used drug in today’s prescriptions by physicians due to its specific effects in treating and curing type II diabetes. Diabetes is a common disease that may occur throughout human life, and can increase the likelihood of the occurrence of various types of cancer, such as colon, rectum, pancreas and liver cancers, compared to non-diabetic patients. Metformin inhibits mTOR activity by activating ATM (ataxia telangiectasia mutated) and LKB1 (liver kinase B1) and then adenosine monophosphate-activated kinase (AMPK), and thus prevents protein synthesis and cell growth. Metformin can activate p53 by activating AMPK and thereby ultimately stop the cell cycle. Given the potential of metformin in the treatment of cancer, it can be used in radiotherapy, chemotherapy and to improve the response to treatment in androgen derivatives (ADT), and also, according to available evidence, metformin can also be used to prevent various types of cancers. Generally, metformin can: 1) reduce the incidence of cancers, 2) reduce the mortality from cancers, 3) increase the response to treatment in cancer cells when using radiotherapy and chemotherapy, 4) optimize tumor movement and reduce the malignancy, 5) reduce the likelihood of relapse, and 6) reduce the damaging effects of ADT. Therefore, this drug can be used as a complementary therapeutic agent for cancer treatment and prevention. In this review, we have summarized the data from various experimental and clinical studies and highlight the possible potential effects of metformin on cancer therapeutic responses.

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Effects of metformin treatment on radiotherapy efficacy in patients with cancer and diabetes: a systematic review and meta-analysis

Purpose

Metformin is a key pharmaceutical for patients with diabetes mellitus (DM). Metformin also can enhance tumor radiosensitivity in vitro and in vivo. Some retrospective cohort studies have indicated that metformin can improve the efficacy of radiotherapy in patients with cancer and DM. The aim of this systematic review was to evaluate the radiotherapy efficacy of metformin in patients with cancer and DM.

Methods

Multiple databases were queried for studies that address the efficacy of metformin in radiotherapy of patients with cancer and DM. Studies were included that involved comparisons of the short-term tumor responses and long-term survival outcomes of these patients who were managed with or without metformin as well as of nondiabetic patients without metformin. The OR and HR with accompanying 95% CI were assessed in a random effects model. The main endpoints were 2-year and 5-year overall survival (2y-OS and 5y-OS, respectively).

Results

The database search yielded 17 cohort studies that met the inclusion criteria. The results indicated that the tumor response was higher in patients who also were treated with metformin than in those who were not (OR, 0.48; 95% CI, 0.22-1.07; P=0.07) and nondiabetic (OR, 0.27; 95% CI, 0.07-0.98; P=0.05). Moreover, patients who received metformin had survival benefits compared with patients not treated with metformin (2y-OS: OR, 0.48; 95% CI, 0.29-0.80; P=0.005; 5y-OS: OR, 0.38; 95% CI, 0.25-0.56; P<0.00001). The metformin-related HRs of OS values were not significantly different.

Conclusion

Metformin appears to improve the tumor response to radiotherapy in patients with cancer and DM and partly yield survival benefits. Despite the apparent advantages provided by metformin treatment on 2y-OS and 5y-OS, these retrospective data are at risk of bias and should be interpreted with caution.

Metformin Protects Against Radiation-Induced Heart Injury and Attenuates the Upregulation of Dual Oxidase Genes Following Rat's Chest Irradiation

Radiation-induced heart toxicity is one of the serious side effects after a radiation disaster or radiotherapy for patients with chest cancers, leading to a reduction in the quality of life of the patients. Evidence has shown that infiltration of inflammatory cells plays a key role in the development of functional damages to the heart via chronic upregulation of some pro-fibrotic and pro-inflammatory cytokines. These changes are associated with continuous free radical production and increased stiffness of heart muscle. IL-4 and IL-13 are two important pro-fibrotic cytokines which contribute to the side effects of ionizing radiation exposure. Recent studies have proposed that IL-4 through upregulation of DUOX2, and IL-13 via stimulation of DUOX1 gene expression, are involved in the development of radiation late effects. In the present study, we aimed to detect changes in the expression of these pathways following irradiation of rat’s heart. Furthermore, we evaluated the possible protective effect of metformin on the development of these abnormal changes. 20 male rats were divided into 4 groups (control, radiation, metformin treated, metformin + radiation). These rats were irradiated with 15 Gy ⁶⁰Co gamma rays, and sacrificed after 10 weeks for evaluation of the changes in the expression of IL4R1, IL-13R2a, DUOX1 and DUOX2. In addition, the levels of IL-4 and IL-13 cytokines, as well as infiltration of macrophages and lymphocytes were detected. Results showed an upregulation of both DUOX1 and DUOX2 pathways in the presence of metformin, while the level of IL-13 did not show any significant change. This was associated with infiltration of macrophages and lymphocytes. Also, treatment with metformin could significantly attenuate accumulation of inflammatory cells, and upregulate these pathways. Therefore, suppression of dual oxidase genes by metformin may be a contributory factor to its protective effect.

18F-Flortanidazole Hypoxia PET Holds Promise as a Prognostic and Predictive Imaging Biomarker in a Lung Cancer Xenograft Model Treated with Metformin and Radiotherapy

Metformin may improve tumor oxygenation and thus radiotherapy response, but imaging biomarkers for selection of suitable patients are still under investigation. First, we assessed the effect of acute metformin administration on non-small cell lung cancer xenograft tumor hypoxia using PET imaging with the hypoxia tracer ¹⁸F-flortanidazole. Second, we verified the effect of a single dose of metformin before radiotherapy on long-term treatment outcome. Third, we examined the potential of baseline ¹⁸F-flortanidazole as a prognostic or predictive biomarker for treatment response. Methods: A549 tumor-bearing mice underwent a ¹⁸F-flortanidazole PET/CT scan to determine baseline tumor hypoxia. The next day, mice received a 100 mg/kg intravenous injection of metformin. ¹⁸F-flortanidazole was administered intravenously 30 min later, and a second PET/CT scan was performed to assess changes in tumor hypoxia. Two days later, the mice were divided into 3 therapy groups: controls (group 1), radiotherapy (group 2), and metformin + radiotherapy (group 3). Animals received saline (groups 1-2) or metformin (100 mg/kg; group 3) intravenously, followed by a single radiotherapy dose of 10 Gy (groups 2-3) or sham irradiation (group 1) 30 min later. Tumor growth was monitored triweekly by caliper measurement, and tumor volume relative to baseline was calculated. The tumor doubling time (TDT), that is, the time to reach twice the preirradiation tumor volume, was defined as the endpoint. Results: Thirty minutes after metformin treatment, ¹⁸F-flortanidazole demonstrated a significant change in tumor hypoxia, with a mean intratumoral reduction in ¹⁸F-flortanidazole tumor-to-background ratio (TBR) from 3.21 ± 0.13 to 2.87 ± 0.13 (P = 0.0001). Overall, relative tumor volume over time differed across treatment groups (P < 0.0001). Similarly, the median TDT was 19, 34, and 52 d in controls, the radiotherapy group, and the metformin + radiotherapy group, respectively (log-rank P < 0.0001). Both baseline ¹⁸F-flortanidazole TBR (hazard ratio, 2.0; P = 0.0004) and change from baseline TBR (hazard ratio, 0.39; P = 0.04) were prognostic biomarkers for TDT irrespective of treatment, and baseline TBR predicted metformin-specific treatment effects that were dependent on baseline tumor hypoxia. Conclusion: Using ¹⁸F-flortanidazole PET imaging in a non-small cell lung cancer xenograft model, we showed that metformin may act as a radiosensitizer by increasing tumor oxygenation and that baseline ¹⁸F-flortanidazole shows promise as an imaging biomarker.

Cancer cell specific inhibition of Wnt/β-catenin signaling by forced intracellular acidification

Use of the diabetes type II drug Metformin is associated with a moderately lowered risk of cancer incidence in numerous tumor entities. Studying the molecular changes associated with the tumor-suppressive action of Metformin we found that the oncogene SOX4, which is upregulated in solid tumors and associated with poor prognosis, was induced by Wnt/β-catenin signaling and blocked by Metformin. Wnt signaling inhibition by Metformin was surprisingly specific for cancer cells. Unraveling the underlying specificity, we identified Metformin and other Mitochondrial Complex I (MCI) inhibitors as inducers of intracellular acidification in cancer cells. We demonstrated that acidification triggers the unfolded protein response to induce the global transcriptional repressor DDIT3, known to block Wnt signaling. Moreover, our results suggest that intracellular acidification universally inhibits Wnt signaling. Based on these findings, we combined MCI inhibitors with H⁺ ionophores, to escalate cancer cells into intracellular hyper-acidification and ATP depletion. This treatment lowered intracellular pH both in vitro and in a mouse xenograft tumor model, depleted cellular ATP, blocked Wnt signaling, downregulated SOX4, and strongly decreased stemness and viability of cancer cells. Importantly, the inhibition of Wnt signaling occurred downstream of β-catenin, encouraging applications in treatment of cancers caused by APC and β-catenin mutations.

Pushing the Limits of Cancer Therapy: The Nutrient Game

The standard cancer treatments include chemotherapy, radiotherapy, or their combination, which are generally associated with a multitude of side effects ranging from discomfort to the development of secondary tumors and severe toxicity to multiple systems including immune system. Mounting evidence has highlighted that the fine-tuning of nutrients may selectively sensitize cancer cells to conventional cancer therapies, while simultaneously protecting normal cells from their side effects. Nutrient modulation through diet also improves cancer immunesurveillance in a way that severe immunosuppression could be avoided or even the immune response or immune-based cancer therapies be potentiated also through patient microbiota remodeling. Here, we review recent advances in cancer therapy focusing on the effects of adjuvant dietary interventions (e.g., ketogenic diets, fasting) on the metabolic pathways within cancer cells and tumor environment (e.g., microbiota, immune system, tumor microenvironment) that are involved in cancer progression and resistance as well as cancer cell death. Finally, based on the overall literature data, we designed a nutritional intervention consisting in a plant-based moderate ketogenic diet that could be exploited for future preclinical research in cancer therapy.