Contributions of AMPK and p53 dependent signaling to radiation response in the presence of metformin

Efficacy of Metformin as Adjuvant Therapy in Metastatic Breast Cancer Treatment

Background: Metformin has been reported to have an anti-tumorigenic impact against metastatic breast cancer (MBC) cells through several mechanisms. Its effect can be evaluated by using many variables such as the response rate (RR) as well as the progression-free survival (PFS). Materials and methods: A prospective study was conducted to investigate and estimate the metformin effect on MBC. About 107 subjects were included in the study and were divided into two groups: Group A included non-diabetic MBC patients treated with metformin in conjunction with chemotherapy and group B included those treated with chemotherapy alone. Both PFS and RR were used as a criteria to evaluate the treatment outcome. Associated adverse effects of metformin were also assessed. Results: The average age of the participants in group A and group B was 50 vs. 47.5, respectively. No significant differences were detected between both cohorts concerning RR levels (regression disease (RD) 27.8% vs. 12.5%, stationary disease (SD) 44.4% vs. 41.7%, progression disease (PD) 27.8% vs. 45.8%, respectively, p = 0.074). Moreover, PFS showed no significant difference between both groups (p = 0.753). There was no significant correlation between metformin concentration and their adverse effects on the study participants. Conclusion: Metformin as an adjuvant therapy to MBC undergoing chemotherapy showed no significant survival benefit as determined by RR and PFS.

Phosphoproteomics Reveals the AMPK Substrate Network in Response to DNA Damage and Histone Acetylation

AMP-activated protein kinase (AMPK) is a conserved energy sensor that plays roles in diverse biological processes via phosphorylating various substrates. Emerging studies have demonstrated the regulatory roles of AMPK in DNA repair, but the underlying mechanisms remain to be fully understood. Herein, using mass spectrometry-based proteomic technologies, we systematically investigate the regulatory network of AMPK in DNA damage response (DDR). Our system-wide phosphoproteome study uncovers a variety of newly-identified potential substrates involved in diverse biological processes, whereas our system-wide histone modification analysis reveals a link between AMPK and histone acetylation. Together with these findings, we discover that AMPK promotes apoptosis by phosphorylating apoptosis-stimulating of p53 protein 2 (ASPP2) in an irradiation (IR)-dependent manner and regulates histone acetylation by phosphorylating histone deacetylase 9 (HDAC9) in an IR-independent manner. Besides, we reveal that disrupting the histone acetylation by the bromodomain BRD4 inhibitor JQ-1 enhances the sensitivity of AMPK-deficient cells to IR. Therefore, our study has provided a resource to investigate the interplay between phosphorylation and histone acetylation underlying the regulatory network of AMPK, which could be beneficial to understand the exact role of AMPK in DDR.

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.

Links between Thyroid Disorders and Glucose Homeostasis

Thyroid disorders and diabetes mellitus often coexist and are closely related. Several studies have shown a higher prevalence of thyroid disorders in patients with diabetes mellitus and vice versa. Thyroid hormone affects glucose homeostasis by impacting pancreatic β-cell development and glucose metabolism through several organs such as the liver, gastrointestinal tract, pancreas, adipose tissue, skeletal muscles, and the central nervous system. The present review discusses the effect of thyroid hormone on glucose homeostasis. We also review the relationship between thyroid disease and diabetes mellitus: type 1, type 2, and gestational diabetes, as well as guidelines for screening thyroid function with each disorder. Finally, we provide an overview of the effects of antidiabetic drugs on thyroid hormone and thyroid disorders.

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.

Metformin as a radiosensitiser for pelvic malignancy: A systematic review of the literature

BACKGROUND

The treatment of pelvic malignancies has continued to improve over recent years, with neoadjuvant radiotherapy often considered the gold standard to downstage disease. Radiosensitisers are routinely employed in an attempt to improve response of cancers to radiotherapy. Previous preclinical evidence has suggested a role for metformin, a commonly used drug for type 2 diabetes.

METHOD

A literature search was performed for published full text articles using the PubMed, Cochrane and Scopus databases using the search criteria string 'Metformin' AND ('Radiosensitivity' OR 'radiosensitising' OR 'radiosensitising'). Additional papers were detected by scanning the references of relevant papers. Data were extracted from each study by two authors onto a dedicated proforma. The review was registered on the PROSPERO database (ID: CRD42020199066).

RESULTS

A total of 242 papers were identified, 11 of which were included in this review; an additional 5 papers were obtained from reference searches. Metformin has been demonstrated to reduce cell-viability post-radiotherapy in both rectal and prostate cancer cell lines, with an enhanced effect in tumours with a p53 mutation and increased apoptosis post-radiotherapy for cervical cancer. Clinical trials demonstrate improved tumour and nodal downstaging and pCR rates for rectal cancer using metformin as a radiosensitiser.

CONCLUSION

With an increasing understanding of the underlying mechanism of the effects on metformin prospective studies are required to assess the effect of routine use on cancer related outcomes. Progressive future studies may be better served by the use of predictive biomarker guided treatment to enable identification of the appropriate cohort to target.

Recent Research on Methods to Improve Tumor Hypoxia Environment

Cancer is a major disease burden worldwide. In recent years, in addition to surgical resection, radiotherapy and chemotherapy are recognized as the most effective methods for treating solid tumors. These methods have been introduced to treat tumors of different origins and stages clinically. However, due to insufficient blood flow and oxygen (O2) supply in solid tumors, hypoxia is caused, leading to decreased sensitivity of tumor cells and poor therapeutic effects. In addition, hypoxia will also lead to resistance to most anticancer drugs, accelerate malignant progress, and increase metastasis. In solid tumors, adequate O2 supply and adequate delivery of anticancer drugs are essential to improve radiotherapy and chemotherapy sensitivity. In recent decades, the researches on relieving tumor hypoxia have attracted researchers' extensive attention and achieved good results. However, as far as we know, there is no detailed review of the researches on alleviating tumor hypoxia. Therefore, in this contribution, we hope to give an overview of the researches on methods to improve tumor hypoxia environment and summarize their effect and application in tumor therapy, to provide a methodological reference for the research and development of new antitumor agents.

Metformin mitigates gastrointestinal radiotoxicity and radiosensitises P53 mutation colorectal tumours via optimising autophagy

BACKGROUND AND PURPOSE

There is an urgent but unmet need for mitigating radiation-induced intestinal toxicity while radio sensitising tumours for abdominal radiotherapy. We aimed to investigate the effects of metformin on radiation-induced intestinal toxicity and radiosensitivity of colorectal tumours.

EXPERIMENTAL APPROACH

Acute and chronic histological injuries of the intestine from mice were used to assess radioprotection and IEC-6 cell line was used to investigate the mechanisms in vitro. The fractionated abdominal radiation model of HCT116 and HT29 tumour grafts was used to determine the effects on colorectal cancer.

KEY RESULTS

Metformin alleviated radiation-induced acute and chronic intestinal toxicity by optimising mitophagy which was AMPK-dependent. In addition, our data indicated that metformin increased the radiosensitivity of colorectal tumours with P53 mutation both in vitro and in vivo.

CONCLUSION AND IMPLICATIONS

Metformin may be a radiotherapy adjuvant agent for colorectal cancers especially those carrying P53 mutation. Our findings provide a new strategy for further precise clinical trials for metformin on radiotherapy.

Metformin: (future) best friend of the radiation oncologist?

Several molecules are being investigated for their ability to enhance the anti-tumor effect of radiotherapy. The widely prescribed antidiabetic drug metformin has been suggested to possess anti-cancer activity; data indicate that metformin could also enhance radiation sensitivity. The purpose of this review is to summarize current knowledge on the specific effect of metformin in the field of RT, while also discussing the many unknowns that persist. Preclinical models point to multiple mechanisms involved in the radiosensitizing effects of metformin that are mainly linked to mitochondrial complex I inhibition and AMP-activated protein kinase. Transposition of results from bench to bedside will be discussed through the lens of the drug concentration, its potential limits in human settings, and possible alternatives. Clinical data suggest metformin improves progression-free and overall survival in patients for many different cancers treated with RT; nevertheless, the results are not always consistent. The main limitations of the reviewed literature are the retrospective nature of studies, and most of the time, a lack of information on MTF treatment duration and the administered dosages. Despite these limitations, the possible mechanisms of the role of metformin and its utility in enhancing radiotherapy treatments are analyzed. Ongoing clinical trials are also discussed.

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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AMPK activation by AICAR sensitizes prostate cancer cells to radiotherapy

Although radiotherapy is often used to treat localized disease and for palliative care in prostate cancer patients, novel methods are required to improve the sensitivity of aggressive disease to ionizing radiation. AMP-activated protein kinase (AMPK) is an energy sensor which regulates proliferation, aggressiveness and survival of cancer cells. We assessed the ability of the AMPK activator 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) to sensitize prostate cancer cells to radiation. Prostate cancer cell lines LNCaP and PC3 were treated with X-rays and AICAR then assessed for clonogenic survival, spheroid growth delay, cell cycle progression, and AMPK and p53 activity. AICAR synergistically enhanced the clonogenic killing capacity, spheroid growth inhibition and pro-apoptotic effect of X-rays. The mechanism of radiosensitization appeared to involve cell cycle regulation, but not oxidative stress. Moreover, it was not dependent on p53 status. Treatment of PC3 cells with a fatty acid synthase inhibitor further enhanced clonogenic killing of the combination of X-rays and AICAR, whereas mTOR inhibition caused no additional enhancement. These results indicate that interference with metabolic signalling pathways which protect cells against irradiation have the potential to enhance radiotherapy. Activation of AMPK in combination with radiotherapy has the potential to target metabolically active and aggressive tumors which are currently untreatable.

Metformin as a Radiation Modifier; Implications to Normal Tissue Protection and Tumor Sensitization

BACKGROUND

Nowadays, ionizing radiation is used for several applications in medicine, industry, agriculture, and nuclear power generation. Besides the beneficial roles of ionizing radiation, there are some concerns about accidental exposure to radioactive sources. The threat posed by its use in terrorism is of global concern. Furthermore, there are several side effects to normal organs for patients who had undergone radiation treatment for cancer. Hence, the modulation of radiation response in normal tissues was one of the most important aims of radiobiology. Although, so far, several agents have been investigated for protection and mitigation of radiation injury. Agents such as amifostine may lead to severe toxicity, while others may interfere with radiation therapy outcomes as a result of tumor protection. Metformin is a natural agent that is well known as an antidiabetic drug. It has shown some antioxidant effects and enhances DNA repair capacity, thereby ameliorating cell death following exposure to radiation. Moreover, through targeting endogenous ROS production within cells, it can mitigate radiation injury. This could potentially make it an effective radiation countermeasure. In contrast to other radioprotectors, metformin has shown modulatory effects through induction of several genes such as AMPK, which suppresses reduction/ oxidation (redox) reactions, protects cells from accumulation of unrepaired DNA, and attenuates initiation of inflammation as well as fibrotic pathways. Interestingly, these properties of metformin can sensitize cancer cells to radiotherapy.

CONCLUSION

In this article, we aimed to review the interesting properties of metformin such as radioprotection, radiomitigation and radiosensitization, which could make it an interesting adjuvant for clinical radiotherapy, as well as an interesting candidate for mitigation of radiation injury after a radiation disaster.

Association of Metformin Use and Survival Outcome in Women With Cervical Cancer

OBJECTIVE

Although preclinical studies suggest possible antitumor effects of metformin against cervical cancer, there is currently a lack of clinical data examining the association of metformin use and survival in women with cervical cancer. The aim of this study was to examine survival of women with cervical cancer who were receiving metformin.

METHODS

This is a retrospective study examining consecutive cases of stages I to IV cervical cancer between 2000 and 2014. Patient demographics, medication use, tumor characteristics, treatment patterns, and survival outcomes were correlated to metformin use.

RESULTS

There were 70 (8.9%; 95% confidence interval [CI], 6.9-10.9) metformin users and 715 nonusers identified for the analysis. Median follow-up time was 22.6 months. Recurrence/progression of disease and death due to cervical cancer were observed in 236 and 163 cases, respectively. Metformin users were more likely to be older, hypertensive, diabetic, and dyslipidemic compared with nonusers (all, P < 0.05). On univariate analysis, metformin users and nonusers had similar progression-free survival (PFS) (5-year rates; 57.3% vs 61.8%; P = 0.82) and cervical cancer-specific overall survival (71.7% vs 70.7%; P = 0.86). After adjusting for patient demographics and tumor characteristics, metformin use was not associated with PFS (adjusted hazards ratio, 1.11; 95% CI, 0.70-1.74; P = 0.67) or cervical cancer-specific overall survival (adjusted hazards ratio, 0.91; 95% CI, 0.52-1.60; P = 0.75). Among 478 women who received whole pelvic radiotherapy, metformin use was not associated with PFS (P = 0.93) or cervical cancer-specific overall survival (P = 0.32).

CONCLUSIONS

In this study population, metformin use was not associated with survival of women with cervical cancer.

Metformin for non-small cell lung cancer patients: Opportunities and pitfalls

Despite exciting advances of the anticancer armamentarium in the recent years, mortality of non-small cell lung cancer (NSCLC) remains high and novel treatments are requisite. Therapy intensification is explored with promising, but expensive and potentially toxic new compounds. Repositioning already existing drugs for cancer treatment could save money and improve patient outcomes in specific contexts. Observational data suggest that use of the standard antidiabetic agent metformin decreases lung cancer incidence and mortality. Several basic researches have shown various anticancer effects of metformin, acting both on the glycolytic metabolism and on the tumoral immune microenvironment. Synergistic actions of metformin with antitumoral agents in preclinical NSCLC models have then been highlighted. Recent retrospective studies advocated improved outcomes in NSCLC diabetic patients receiving metformin with chemoradiotherapy or systemic compounds (including conventional platinum-based chemotherapy and EGFR tyrosine kinase inhibitors). Several prospective randomized trials are therefore currently assessing the addition of metformin to standard therapy in non-diabetic lung cancer patients. This article reviews promises and possible limitations of concurrent metformin used as an anticancer agent in NSCLC patients.

Role of metformin on base excision repair pathway in p53 wild-type H2009 and HepG2 cancer cells

The antidiabetic agent metformin was shown to further possess chemopreventive and chemotherapeutic effects against cancer. Despite the advances, the underlying molecular mechanisms involved in decreasing tumor formation are still unclear. The understanding of the participation of oxidative stress in the action mechanism of metformin and its related effects on p53 and on DNA base excision repair (BER) system can help us to get closer to solve metformin puzzle in cancer. We investigated the effects of metformin in HepG2 and H2009 cells, verifying cytotoxicity, oxidative stress, antioxidant status, and DNA BER system. Our results showed metformin induced oxidative stress and reduced antioxidant capacity. Also, metformin treatment with hydrogen peroxide (H2O2) enhanced these effects. Although DNA BER enzyme activities were not changed accordantly together by metformin as a single agent or in combination with H2O2, activated p53 was decreased with increased oxidative stress in H2009 cells. Our study on the relationship between metformin/reactive oxygen species and DNA BER system in cancer cells would be helpful to understand the anticancer effects of metformin through cellular signal transduction pathways. These findings can be a model of the changes on oxidative stress that reflects p53’s regulatory role on DNA repair systems in cancer for the future studies.

Altered expression of a metformin-mediated radiation response in SA-NH and FSa tumor cells treated under in vitro and in vivo growth conditions

PURPOSE

To assess the radiosensitizing effect of the biguanide drug metformin used alone or in combination with reactive oxygen species (ROS) modifying agents N-acetyl-L-cysteine (NAC) or emodin, and contrasted to the mitochondrial complex 1 inhibitor rotenone in altering the radiation responses of the p53 wild-type SA-NH and p53 mutant FSa mouse tumor lines grown either in vitro or in vivo.

MATERIALS AND METHODS

Tumor cells were grown to confluence in vitro and exposed to a single 4 Gy dose in the presence or absence of metformin (5 mM) and ROS modifiers or to 10 Gy with or without metformin as tumors in the flanks of C3H mice using a tumor growth delay assay.

RESULTS

Both metformin and rotenone protected SA-NH (p < .001) while sensitizing FSa (p < .001) to 4 Gy. Neither NAC nor emodin altered metformin's action. Metformin was also directly toxic to FSa cells (p = .002). In contrast, in vivo metformin (250 mg/kg) sensitized both SA-NH (9-day growth delay, p < .05) and FSa (4-day growth delay, p < .05) tumors if administered 1 h before irradiation.

CONCLUSION

Metformin effects on tumor cells measured under in vitro conditions may differ from those determined in vivo due to p53 and heterogeneous environmental factors.

Metformin targets multiple signaling pathways in cancer

Metformin, an inexpensive and well-tolerated oral agent commonly used in the first-line treatment of type 2 diabetes, has become the focus of intense research as a candidate anticancer agent. Here, we discuss the potential of metformin in cancer therapeutics, particularly its functions in multiple signaling pathways, including AMP-activated protein kinase, mammalian target of rapamycin, insulin-like growth factor, c-Jun N-terminal kinase/mitogen-activated protein kinase (p38 MAPK), human epidermal growth factor receptor-2, and nuclear factor kappaB pathways. In addition, cutting-edge targeting of cancer stem cells by metformin is summarized.

MATE2 Expression Is Associated with Cancer Cell Response to Metformin

BACKGROUND

There is great interest in repurposing the commonly prescribed anti-diabetic drug metformin for cancer therapy. Intracellular uptake and retention of metformin is affected by the expression of organic cation transporters (OCT) 1-3 and by multidrug and toxic compound extrusion (MATE) 1-2. Inside cells, metformin inhibits mitochondrial function, which leads to reduced oxygen consumption and inhibition of proliferation. Reduced oxygen consumption can lead to improved tumor oxygenation and radiation response.

PURPOSE

Here we sought to determine if there is an association between the effects of metformin on inhibiting oxygen consumption, proliferation and expression of OCTs and MATEs in a panel of 19 cancer cell lines.

RESULTS

There was relatively large variability in the anti-proliferative response of different cell lines to metformin, with a subset of cell lines being very resistant. In contrast, all cell lines demonstrated sensitivity to the inhibition of oxygen consumption by metformin, with relatively small variation. The expression of OCT1 correlated with expression of both OCT2 and OCT3. OCT1 and OCT2 were relatively uniformly expressed, whereas expression of OCT3, MATE1 and MATE2 showed substantial variation across lines. There were statistically significant associations between resistance to inhibition of proliferation and MATE2 expression, as well as between sensitivity to inhibition of oxygen consumption and OCT3 expression. One cell line (LNCaP) with high OCT3 and low MATE2 expression in concert, had substantially higher intracellular metformin concentration than other cell lines, and was exquisitely sensitive to both anti-proliferative and anti-respiratory effects. In all other cell lines, the concentration of metformin required to inhibit oxygen consumption acutely in vitro was substantially higher than that achieved in the plasma of diabetic patients. However, administering anti-diabetic doses of metformin to tumor-bearing mice resulted in intratumoral accumulation of metformin and reduced hypoxic tumor fractions.

CONCLUSIONS

All cancer cells are susceptible to inhibition of oxygen consumption by metformin, which results in reduced hypoxic tumor fractions beneficial for the response to radiotherapy. High MATE2 expression may result in resistance to the anti-proliferative effect of metformin and should be considered as a negative predictive biomarker in clinical trials.

Metformin displays in vitro and in vivo antitumor effect against osteosarcoma

Purpose

Patients with unresectable, relapsed, or refractory osteosarcoma need a novel therapeutic agent. Metformin is a biguanide derivative used in the treatment of type II diabetes, and is recently gaining attention in cancer research.

Methods

We evaluated the effect of metformin against human osteosarcoma. Four osteosarcoma cell lines (KHOS/NP, HOS, MG-63, U-2 OS) were treated with metformin and cell proliferation was evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Cell cycle progression and apoptosis were evaluated using flow cytometric analysis, and migration and wound healing assay were performed. Fourteen female Balb/c-nude mice received KHOS/NP cell grafts in their thigh, and were allowed access to metformin containing water (2 mg/mL) ad libitum. Tumor volume was measured every 3–4 days for a period of 4 weeks.

Results

Metformin had a significant antiproliferative effect on human osteosarcoma cells. In particular, metformin inhibited the proliferation and migration of KHOS/NP cells by activation of AMP-activated protein kinase and consequent inhibition of the mammalian target of rapamycin pathway. It also inhibited the proliferation of cisplatin-resistant KHOS/NP clone cells. Analysis of KHOS/NP xenograft Balb/c-nude models indicated that metformin displayed potent in vivo antitumor effects.

Conclusion

Further studies are necessary to explore metformin's therapeutic potential and the possibilities for its use as an adjuvant agent for osteosarcoma.

The radioprotective effect of metformin against cytotoxicity and genotoxicity induced by ionizing radiation in cultured human blood lymphocytes

Metformin is a widely prescribed drug used in the treatment of patients with type 2 diabetes. In this study, the radioprotective effect of metformin was investigated against cytotoxicity and genotoxicity induced by ionizing radiation (IR) in human peripheral blood lymphocytes. Human lymphocytes were treated with metformin at concentrations 10 and 50μM for 2h and irradiated with 6MV X-rays. The radiation antagonistic potential of metformin was assessed by MTT [3-(4,5-dimethyl-2-thiaozolyl)-2,5-diphenyl-2H tetrazolium bromide] assay, chromosomal aberration (CA) analysis, cytokinesis blocked micronucleus (CBMN) assay, and flow cytometry. Observations demonstrated a radiation-dose-dependent decrease in the percentage of cell viability after 24h. It was found that pretreatment with metformin (10 and 50μM) increased the percentage of cell viability. A highly significant dose modifying factor (DMF) 1.35 and 1.42 was observed for 10 and 50μM metformin, respectively. Metformin (10 and 50μM) pretreatment significantly decreased the frequency of dicentrics (DCs), acentric fragments (AFs), rings (RIs), micronuclei (MN), and nucleoplasmic bridges (NPBs) in irradiated human peripheral blood lymphocytes. Also, treatment with metformin (10 and 50μM) without irradiation did not increase the number of MN, NPBs, DCs, AFs, RIs, and did not show a cytostatic effect in the human peripheral blood lymphocytes. On the other hand, metformin treatment (10 and 50μM) 2h prior to irradiation significantly reduced X-radiation-induced apoptotic incidence in human lymphocytes. The present study demonstrates metformin to be an effective radioprotector against DNA damage and apoptosis induced by IR in human lymphocytes. These data have an important application for the protection of lymphocytes from the genetic damage and side-effects induced by radiotherapy in cancer patients.

Metformin enhances the response to radiotherapy in diabetic patients with rectal cancer

PURPOSE

Metformin may have anticancer effects and could improve response to radiotherapy in several malignancies. We aimed to investigate the effect of metformin on response to radiotherapy in rectal cancer.

METHODS

A total of 543 rectal cancer patients who were treated with neoadjuvant chemoradiotherapy followed by radical surgery from January 2007 to December 2011 were reviewed. Patients were divided into three groups: diabetics taking metformin (n = 42), diabetics not taking metformin (n = 29), and non-diabetics (n = 472). Tumor response and survival were compared between groups.

RESULTS

The rates of N downstaging and tumor regression grades (TRG) 3-4 were significantly higher in diabetics taking metformin (p = 0.006 and p = 0.029, respectively). There were no significant differences between groups in terms of T downstaging and pathologic complete response. On multivariate analysis, metformin use was associated with increased rates of N downstaging and TRG 3-4 (p = 0.003 and p = 0.019, respectively). Recurrence-free survival, disease-free survival, and overall survival rates were not significantly different between groups.

CONCLUSIONS

Metformin is associated with higher tumor response rates to radiotherapy in rectal cancer, especially in patients with diabetes.

Improved progression free survival for patients with diabetes and locally advanced non-small cell lung cancer (NSCLC) using metformin during concurrent chemoradiotherapy

BACKGROUND AND PURPOSE

The aim was to investigate whether the use of metformin during concurrent chemoradiotherapy (cCRT) for locally advanced non-small cell lung cancer (NSCLC) improved treatment outcome.

MATERIAL AND METHODS

A total of 682 patients were included in this retrospective cohort study (59 metformin users, 623 control patients). All received cCRT in one of three participating radiation oncology departments in the Netherlands between January 2008 and January 2013. Primary endpoint was locoregional recurrence free survival (LRFS), secondary endpoints were overall survival (OS), progression-free survival (PFS) and distant metastasis free survival (DMFS).

RESULTS

No significant differences in LRFS or OS were found. Metformin use was associated with an improved DMFS (74% versus 53% at 2 years; p=0.01) and PFS (58% versus 37% at 2 years and a median PFS of 41 months versus 15 months; p=0.01). In a multivariate cox-regression analysis, the use of metformin was a statistically significant independent variable for DMFS and PFS (p=0.02 and 0.03).

CONCLUSIONS

Metformin use during cCRT is associated with an improved DMFS and PFS for locally advanced NSCLC patients, suggesting that metformin may be a valuable treatment addition in these patients. Evidently, our results merit to be verified in a prospective trial.

Metformin Radiosensitizes p53-Deficient Colorectal Cancer Cells through Induction of G2/M Arrest and Inhibition of DNA Repair Proteins

The present study addressed whether the combination of metformin and ionizing radiation (IR) would show enhanced antitumor effects in radioresistant p53-deficient colorectal cancer cells, focusing on repair pathways for IR-induced DNA damage. Metformin caused a higher reduction in clonogenic survival as well as greater radiosensitization and inhibition of tumor growth of p53^-/- than of p53^+/+ colorectal cancer cells and xenografts. Metformin combined with IR induced accumulation of tumor cells in the G2/M phase and delayed the repair of IR-induced DNA damage. In addition, this combination significantly decreased levels of p53-related homologous recombination (HR) repair compared with IR alone, especially in p53^-/- colorectal cancer cells and tumors. In conclusion, metformin enhanced radiosensitivity by inducing G2/M arrest and reducing the expression of DNA repair proteins even in radioresistant HCT116 p53^-/- colorectal cancer cells and tumors. Our study provides a scientific rationale for the clinical use of metformin as a radiosensitizer in patients with p53-deficient colorectal tumors, which are often resistant to radiotherapy.

Hypofractionated radiotherapy induces miR-34a expression and enhances apoptosis in human nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma (NPC) is a relatively radiosensitive disease. However, the therapeutic effects of radiotherapy are not always satisfactory due to radioresistance. The hypofractionated schema is currently widely used in clinical practice. In the present study, we investigated the effects of hypofractionated radiotherapy on NPC cells and explored the mechanisms involved. In addition, we aimed to determine the role of miR-34a in the effects of hypofractionated radiotherapy and whether these effects occur in a p53-dependent manner. For this purpose, we used CNE1 and CNE2 NPC cells which were subjected to hyperfractionated and hypofractionated radiotherapy. The viability of the cells was measured by MTT assay and acridine orange (AO) and ethidium bromide (EB) staining was used to observe morphological changes. In addition, Annexin V-propidium iodide (PI) staining and flow cytometry were used to determine the number of apoptotic cells and mRNA and protein expression was measured by qPCR and western blot analysis, respectively. The results revealed that hypofractionated radiotherapy enhanced apoptosis and increased the expression of miR-34a and p53 in the NPC cells. In addition, it stimulated p53 promoter activity and downregulated the protein expression of c-Myc in the human NPC cells. Furthermore, the knockdown of miR-34a suppressed the growth inhibitory effects induced by hypofractionated radiotherapy. Thus, our results suggest that the enhanced apoptosis of NPC cells may be associated with the miR-34a-mediated suppression of c-Myc in a p53-dependent manner.

Molecular radiobiology: the state of the art

Traditional cytotoxic agents used in cancer therapy were initially discovered based on their ability to kill rapidly dividing cells. The targets of these early-generation agents were typically one or more aspects of DNA synthesis or mitosis. Thus, dose-limiting toxicities commonly associated with these agents include GI dysfunction, immunosuppression, and other consequences of injury to normal tissues in which cells are replicating under normal physiologic conditions. Although many of these agents still play an important role in cancer therapy when given concurrently with radiation therapy, the major thrust of radiobiology research in the last two decades has focused on discovering tumor-specific traits that might be exploited for more selective targeting that would enhance the efficacy of radiotherapy with less normal tissue toxicity. These newer generation molecular targeted therapies interfere with the growth of tumor cells by inhibiting genes and their protein products that are needed specifically by the tumor for survival and expansion. These agents can be complementary to radiotherapy, a spatially targeted agent. Although there have been extraordinary technical advances in radiotherapy in recent years, we are reaching the limits of improvements that radiotherapy delivery technology can bring and need different approaches. This review will highlight promising new tumor biology-based targets and other novel strategies to reduce normal tissue injury, increase tumor control, and expand the use of radiotherapy to treat widespread metastatic disease.

Metformin exhibits radiation countermeasures efficacy when used alone or in combination with sulfhydryl containing drugs

Metformin, a biguanide drug used in the treatment of type II diabetes, was evaluated alone and in combination with amifostine, captopril, MESNA or N-acetyl-cysteine (NAC) for its ability to protect when administered 24 h after irradiation. Mouse embryo fibroblasts (MEF), human microvascular endothelial cells (HMEC) and SA-NH mouse sarcoma cells were exposed to 4 Gy in vitro. C3H mice were exposed to 7 Gy and evaluated utilizing an endogenous spleen colony assay system. Amifostine and WR1065, administered 30 min prior to irradiation, were used as positive controls. Treatment of MEF, HMEC and SA-NH cells with metformin elevated survival levels by 1.4-, 1.5- and 1.3-fold compared to 1.9-, 1.8- and 1.6-fold for these same cells treated with WR1065, respectively. Metformin (250 mg/kg) was effective in protecting splenic cells from a 7 Gy dose in vivo (protection factor = 1.8). Amifostine (400 mg/kg), administered 30 min prior to irradiation resulted in a 2.6-fold survival elevation, while metformin administered 24 h after irradiation in combination with NAC (400 mg/kg), MESNA (300 mg/kg) or captopril (200 mg/kg) enhanced survival by 2.6-, 2.8- and 2.4-fold, respectively. Each of these agents has been approved by the FDA for human use and each has a well characterized human safety profile. Metformin alone or in combination with selected sulfhydryl agents possesses radioprotective properties when administered 24 h after radiation exposure comparable to that observed for amifostine administered 30 min prior to irradiation making it a potentially useful agent for radiation countermeasures use.

Repositioning metformin in cancer: genetics, drug targets, and new ways of delivery

After sitting many years on the shelves of drug stores as a harmless antidiabetic drug, metformin comes back in the spotlight of the scientific community as a surprisingly effective antineoplastic drug. Metformin targets multiple pathways that play pivotal roles in cancer progression, impacting various cellular processes, such as proliferation, cell death, metabolism, and even the cancer stemness features. The biomolecular characteristics of tumors, such as appropriate expression of organic cation transporters or genetic alterations including p53, K-ras, LKB1, and PI3K may impact metformin's anticancer efficiency. This could indicate a need for tumor genetic profiling in order to identify patients most likely to benefit from metformin treatment. Considering that the majority of experimental models suggest that higher, supra-clinical doses of metformin should be used in order to obtain an antineoplastic effect, new ways of drug delivery could be developed, such as metformin-loaded nanoparticles or incorporation of metformin into microparticles used in transarterial chemoembolization, with the aim of obtaining higher intratumoral drug concentrations and a targeted therapy which will ultimately maximize metformin's efficacy.

Reprogramming metabolism with metformin improves tumor oxygenation and radiotherapy response

PURPOSE

Tumor hypoxia is a negative prognostic factor in multiple cancers, due in part to its role in causing resistance to radiotherapy. Hypoxia arises in tumor regions distal to blood vessels as oxygen is consumed by more proximal tumor cells. Reducing the rate of oxygen consumption is therefore a potential strategy to reduce tumor hypoxia. We hypothesized that the anti-diabetic drug metformin, which reduces oxygen consumption through inhibition of mitochondrial complex I, would improve radiation response by increasing tumor oxygenation.

EXPERIMENTAL DESIGN

Tumor hypoxia was measured in xenografts before and after metformin treatment using 2-nitroimidazole hypoxia markers quantified by immunohistochemistry (IHC), flow cytometry, and positron emission tomography (PET) imaging. Radiation response was determined by tumor growth delay and clonogenic survival in xenografts with and without administration of metformin. The impact of metformin use on outcome was assessed in 504 patients with localized prostate cancer treated with curative-intent, image-guided radiotherapy (IGRT) from 1996 to 2012. Three-year biochemical relapse-free rates were assessed using the Kaplan-Meier method.

RESULTS

Metformin treatment significantly improved tumor oxygenation in two xenograft models as measured by IHC, flow cytometry, and PET imaging. Metformin also led to improved radiotherapy responses when mice were administered metformin immediately before irradiation. Clinically, metformin use was associated with an independent and significant decrease in early biochemical relapse rates (P = 0.0106).

CONCLUSION

Our data demonstrate that metformin can improve tumor oxygenation and response to radiotherapy. Our study suggests that metformin may represent an effective and inexpensive means to improve radiotherapy outcome with an optimal therapeutic ratio.