Metformin sensitizes the response of oral squamous cell carcinoma to cisplatin treatment through inhibition of NF-κB/HIF-1α signal axis

Metformin as an immunomodulatory agent in enhancing head and neck squamous cell carcinoma therapies

Head and neck squamous cell carcinoma (HNSCC) remains a significant clinical challenge due to its aggressive behavior and poor prognosis, making the development of novel therapeutics with enhanced efficacy and minimal side effects critical. Metformin, a widely used antidiabetic agent, has recently emerged as a potential adjunctive therapy for HNSCC, exhibiting both direct anti-tumor and immunomodulatory effects. This review comprehensively explores the multifaceted role of metformin in shaping the tumor immune microenvironment within HNSCC. We emphasize its pivotal role in modulating immune cell populations and its potential for synergistic action with immunotherapeutic strategies. Furthermore, we address the current challenges associated with optimizing dosing regimens, identifying predictive biomarkers, and integrating metformin with immunotherapy. By dissecting these aspects, this review aims to pave the way for the development of personalized HNSCC treatment strategies that fully exploit the therapeutic potential of metformin.

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

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

The mechanisms of action of metformin on head and neck cancer in the pre-clinical setting: a scoping review

This scoping review identifies the mechanistic pathways of metformin when used to treat head and neck cancer cells, in the pre-clinical setting. Understanding the underlying mechanisms will inform future experimental designs exploring metformin as a potential adjuvant for head and neck cancer. This scoping review was conducted according to the Joanna-Briggs Institute framework. A structured search identified 1288 studies, of which 52 studies fulfilled the eligibility screen. The studies are presented in themes addressing hallmarks of cancer. Most of the studies demonstrated encouraging anti-proliferative effects in vitro and reduced tumor weight and volume in animal models. However, a few studies have cautioned the use of metformin which supported cancer cell growth under certain conditions.

Multitarget, multiagent PLGA nanoparticles for simultaneous tumor eradication and TME remodeling in a melanoma mouse model

Despite the fact that chemoimmunotherapy has emerged as a key component in the era of cancer immunotherapy, it is challenged by the complex tumor microenvironment (TME) that is jam-packed with cellular and non-cellular immunosuppressive components. The aim of this study was to design a nanoparticulate system capable of sufficiently accumulating in the tumor and spleen to mediate local and systemic immune responses, respectively. The study also aimed to remodel the immunosuppressive TME. For such reasons, multi-functional polylactic-co-glycolic acid (PLGA) nanoparticles (NPs) were engineered to simultaneously eradicate the cancer cells, silence the tumor-associated fibroblasts (TAFs), and re-educate the tumor-associated macrophages (TAMs) using doxorubicin, losartan, and metformin, respectively. These agents were also selected for their ability to tip the balance of the splenic immune cells towards immunostimulatory phenotypes. To establish TAM and TAF cultures, normal macrophages and fibroblasts were incubated with B16F10 melanoma cell (Mel)-derived secretome. Drug-loaded PLGA NPs were prepared, characterized, and tested in the target cell types. Organ distribution of fluorescein-loaded PLGA NPs was evaluated in a mouse model of melanoma. Finally, the local and systemic effects of different combination therapy programs were portrayed. The in vitro studies showed that the drug-loaded PLGA NPs could significantly ablate the immunosuppressive nature of Mel and skew TAMs and TAFs towards more favorable phenotypes. While in vivo, PLGA NPs were proven to exhibit long blood circulation time and to localize preferentially in the tumor and the spleen. The combination of either metformin or losartan with doxorubicin was superior to the monotherapy, both locally and systemically. However, the three-agent combo produced detrimental effects in the form of compromised well-being, immune depletion, and metastasis. These findings indicate the potential of TME remodeling as means to prime the tumors for successful chemoimmunotherapy. In addition, they shed light on the importance of the careful use of combination therapies and the necessity of employing dose-reduction strategies. D-NPs doxorubicin-loaded NPs, M-NPs metformin-loaded NPs, L-NPs losartan-loaded NPs, TAMs tumor-associated macrophages, TAFs tumor-associated fibroblasts, PD-L1 programmed death ligand 1, TNF-α tumor necrosis factor alpha, TGF-β transforming growth factor beta, CD206/40/86 cluster of differentiation 206/40/86, α-SMA alpha-smooth muscle actin, MMPs matrix metalloproteases.

Radiosensitising Effects of Metformin Added to Concomitant Chemoradiotherapy with Cisplatin in Cervical Cancer

AIMS

The role of metformin on the radiosensitising effect of cisplatin is not clear. Here we investigated the radiosensitising effect of metformin alone and combined with cisplatin in HeLa cells, as well as the implications of the adenosine monophosphate-activated protein kinase (AMPK) pathway on the radiosensitising effect.

MATERIALS AND METHODS

HeLa cells were treated with ionising radiation, metformin, cisplatin, A769662 (AMPK activator) and dorsomorphin (AMPK inhibitor) or in combination. A cell proliferation assay, Western blot and flow cytometry were carried out.

RESULTS

Metformin potentiated cisplatin cytotoxicity when administered 4 h before ionising radiation. Although the radiosensitising effects of metformin and cisplatin alone were observed, which is more apparent at high ionising radiation doses, the metformin-cisplatin combination did not increase the radiosensitivity of cisplatin at any ionising radiation dose. Dorsomorphin alone significantly decreased cell proliferation and potentiated the radiosensitising effects of cisplatin with ionising radiation. Administration of A769662 24 h prior to cisplatin treatment resulted in an increased AMPK level that yielded resistance to cisplatin, but this effect was not observed in HeLa cells concomitantly treated with A769662 and cisplatin.

CONCLUSIONS

Modulation of AMPK may have a role in cervical cancer treatment. Increased AMPK levels result in higher sensitivity to ionising radiation but causes resistance to cisplatin. Dorsomorphin is proven to be a potent radiosensitising agent. The use of metformin alone may be an option as a radiosensitiser during high-dose ionising radiation (e.g. intracavitary brachytherapy).

Novel cancer treatment paradigm targeting hypoxia-induced factor in conjunction with current therapies to overcome resistance

Chemotherapy, radiotherapy, targeted therapy, and immunotherapy are established cancer treatment modalities that are widely used due to their demonstrated efficacy against tumors and favorable safety profiles or tolerability. Nevertheless, treatment resistance continues to be one of the most pressing unsolved conundrums in cancer treatment. Hypoxia-inducible factors (HIFs) are a family of transcription factors that regulate cellular responses to hypoxia by activating genes involved in various adaptations, including erythropoiesis, glucose metabolism, angiogenesis, cell proliferation, and apoptosis. Despite this critical function, overexpression of HIFs has been observed in numerous cancers, leading to resistance to therapy and disease progression. In recent years, much effort has been poured into developing innovative cancer treatments that target the HIF pathway. Combining HIF inhibitors with current cancer therapies to increase anti-tumor activity and diminish treatment resistance is one strategy for combating therapeutic resistance. This review focuses on how HIF inhibitors could be applied in conjunction with current cancer treatments, including those now being evaluated in clinical trials, to usher in a new era of cancer therapy.

Targeting oral tumor microenvironment for effective therapy

Oral cancers are among the common head and neck malignancies. Different anticancer therapy modalities such as chemotherapy, immunotherapy, radiation therapy, and also targeted molecular therapy may be prescribed for targeting oral malignancies. Traditionally, it has been assumed that targeting malignant cells alone by anticancer modalities such as chemotherapy and radiotherapy suppresses tumor growth. In the last decade, a large number of experiments have confirmed the pivotal role of other cells and secreted molecules in the tumor microenvironment (TME) on tumor progression. Extracellular matrix and immunosuppressive cells such as tumor-associated macrophages, myeloid-derived suppressor cells (MDSCs), cancer-associated fibroblasts (CAFs), and regulatory T cells (Tregs) play key roles in the progression of tumors like oral cancers and resistance to therapy. On the other hand, infiltrated CD4 + and CD8 + T lymphocytes, and natural killer (NK) cells are key anti-tumor cells that suppress the proliferation of malignant cells. Modulation of extracellular matrix and immunosuppressive cells, and also stimulation of anticancer immunity have been suggested to treat oral malignancies more effectively. Furthermore, the administration of some adjuvants or combination therapy modalities may suppress oral malignancies more effectively. In this review, we discuss various interactions between oral cancer cells and TME. Furthermore, we also review the basic mechanisms within oral TME that may cause resistance to therapy. Potential targets and approaches for overcoming the resistance of oral cancers to various anticancer modalities will also be reviewed. The findings for targeting cells and potential therapeutic targets in clinical studies will also be reviewed.

Tumour microenvironment and aberrant signaling pathways in cisplatin resistance and strategies to overcome in oral cancer

OBJECTIVE

Oral cancer is the sixteenth most prevalent cancer in the world and the third-most in India. Despite of several treatment modalities, the cure rate of oral cancer is still low due to drug resistance mechanisms, which are caused by many reasons. It is necessary to improve the existing treatment strategies and discover neoteric therapy to kill cancer cells, which will give oral cancer's cure rate more success. So this review aims to delineate the molecular mechanisms behind cisplatin resistance, specifically the role of the tumor microenvironment, extracellular vesicles, and altered signaling pathways and its overcoming strategies in oral cancer.

DESIGN

This review was designed by searching words like cancer, oral cancer, cisplatin-resistance, tumor microenvironment, aberrant signalings, and extracellular vesicles, overcoming strategies for cisplatin resistance in databases like PubMed, Google Scholar, web science, and Scopus. Data available in this review is from 2017 to 2021.

RESULTS

After searching too much data, we found these 98 data appropriate for our review. From these data, we found that tumor microenvironment, extracellular vesicles, and altered signaling pathways like PI3K/AKT, EGFR, NOTCH, Ras, PTEN, Nf-κβ, and Wnt signaling have a crucial role in resistance development towards cisplatin in oral cancer.

CONCLUSIONS

Lastly, this review explores the alternative strategies to overcome cisplatin resistance likely, the combination therapy and targeted therapy by combining more than one chemotherapeutic drug or inhibitors of signaling pathways and also by using nanoparticle loaded drugs that will reduce the drug efflux, which gives new treatment strategies.

Friend or Foe: Regulation, Downstream Effectors of RRAD in Cancer

Ras-related associated with diabetes (RRAD), a member of the Ras-related GTPase superfamily, is primarily a cytosolic protein that actives in the plasma membrane. RRAD is highly expressed in type 2 diabetes patients and as a biomarker of congestive heart failure. Mounting evidence showed that RRAD is important for the progression and metastasis of tumor cells, which play opposite roles as an oncogene or tumor suppressor gene depending on cancer and cell type. These findings are of great significance, especially given that relevant molecular mechanisms are being discovered. Being regulated in various pathways, RRAD plays wide spectrum cellular activity including tumor cell division, motility, apoptosis, and energy metabolism by modulating tumor-related gene expression and interacting with multiple downstream effectors. Additionally, RRAD in senescence may contribute to its role in cancer. Despite the twofold characters of RRAD, targeted therapies are becoming a potential therapeutic strategy to combat cancers. This review will discuss the dual identity of RRAD in specific cancer type, provides an overview of the regulation and downstream effectors of RRAD to offer valuable insights for readers, explore the intracellular role of RRAD in cancer, and give a reference for future mechanistic studies.

Integrative analyses of biomarkers and pathways for metformin reversing cisplatin resistance in head and neck squamous cell carcinoma cells

OBJECTIVES

In this study, transcriptome sequencing were performed to elucidate the molecular mechanism by which metformin inhibits head and neck squamous cell carcinoma (HNSCC) cells progression and sensitizes HNSCC cells to chemotherapy. We aimed to propose a novel chemotherapeutic approach with high efficacy and few side effects and provide a new strategy for HNSCC treatment.

DESIGN

The effects of metformin on the biological behaviors of HNSCC cells were validated by CCK8 cell proliferation assays, would healing assays and flow cytometric apoptosis assays. The appropriate metformin concentrations for the experimental pretreatment of HNSCC cells were selected based on experimental results, and the treated cells were subjected to transcriptome sequencing. After bioinformatics analysis and intersection with a post-chemotherapy resistance dataset from the GEO database numbered GSE102787, the genes were identified and used to predict potential metformin targets after functional enrichment analysis.

RESULTS

Metformin significantly inhibited the proliferation and migration and induced the apoptosis of Cal27 and FaDu cells. A total of 284 genes that are potentially targeted by metformin during HNSCC cell sensitization were identified by bioinformatics, and ten hub genes with high connectivity were selected. In particular, Fen1 overexpression was associated with poor prognosis in HNSCC patients.

CONCLUSIONS

Our study demonstrates that Fen1 is overexpressed in HNSCC tissues compared with normal tissues and that Fen1 overexpression is a poor prognostic factor in HNSCC patients. Metformin enhances the ability of cisplatin to inhibit HNSCC progression. Further studies are needed to explore the therapeutic value of Fen1 in HNSCC.

Metformin Attenuates Hyperglycaemia-Stimulated Pro-Fibrotic Gene Expression in Adventitial Fibroblasts via Inhibition of Discoidin Domain Receptor 2

Molecular mechanisms underlying the diverse therapeutic effects of anti-diabetic metformin, beyond its anti-hyperglycaemic effects, remain largely unclear. Metformin is reported to reduce the long-term complications of diabetes, including cardiovascular fibrosis and remodelling. Our recent investigations show that Discoidin Domain Receptor 2 (DDR2), a Collagen receptor tyrosine kinase, has an obligate regulatory role in Collagen type I gene expression in cardiac and vascular adventitial fibroblasts, and that it may be a molecular link between arterial fibrosis and metabolic syndrome in rhesus monkeys. Using gene knockdown and overexpression approaches, the present study examined whether DDR2 is a target of metformin and whether, by targeting DDR2, it inhibits Fibronectin and Collagen type I expression in rat aortic adventitial fibroblasts exposed to hyperglycaemic conditions. Metformin was found to attenuate hyperglycaemia-induced increase in DDR2 mRNA and protein expression by inhibiting TGF-β1/SMAD2/3 signalling that mediates the stimulatory effect of hyperglycaemia on DDR2 expression. Metformin also inhibited DDR2-dependent expression of Fibronectin and Collagen type I, indicating that it regulates these matrix proteins via DDR2 inhibition. The findings identify DDR2, a mediator of cardiovascular remodelling, as a molecular target of metformin, thereby uncovering the molecular basis of its protective role in vascular fibrosis and possibly cardiac fibrosis associated with diabetic cardiomyopathy.

The Mechanism of Action of Biguanides: New Answers to a Complex Question

Biguanides are a family of antidiabetic drugs with documented anticancer properties in preclinical and clinical settings. Despite intensive investigation, how they exert their therapeutic effects is still debated. Many studies support the hypothesis that biguanides inhibit mitochondrial complex I, inducing energy stress and activating compensatory responses mediated by energy sensors. However, a major concern related to this “complex” model is that the therapeutic concentrations of biguanides found in the blood and tissues are much lower than the doses required to inhibit complex I, suggesting the involvement of additional mechanisms. This comprehensive review illustrates the current knowledge of pharmacokinetics, receptors, sensors, intracellular alterations, and the mechanism of action of biguanides in diabetes and cancer. The conditions of usage and variables affecting the response to these drugs, the effect on the immune system and microbiota, as well as the results from the most relevant clinical trials in cancer are also discussed.

Combined regimens of cisplatin and metformin in cancer therapy: A systematic review and meta-analysis

INTRODUCTION

Cancer cell resistance to chemotherapy agents is a challenging issue in treating patients with cancer. Findings suggest that a combination of drugs may have synergistic or additive effects. in the present study, we systematically reviewed the combined regimens of metformin with cisplatin in various treating cancers.

METHODS

A comprehensive systematic search was performed in PubMed, Scopus, Embase, and other relevant databases with the following keyword "metformin", "cisplatin", "combination", "using all their equivalents and similar terms. Pooled odds ratio (OR) and 95% confidence intervals of cell viability and tumor volume as primary outcomes were calculated using Der-Simonian and Laird method while random effects meta-analysis was used, taking into account clinical and statistical heterogeneity.

RESULTS

Overall, 44 studies were retrieved, Findings of the present meta-analysis showed that combined regimens of metformin plus cisplatin was significantly associated with decreased odds of tumor volume and cell viability for all cancers compared with cisplatin alone (pooled OR: 0.40; 95% CI: 0.27, 0.58) and (pooled OR: 0.49; 95% CI: 0.42, 0.58) respectively. The result was same for cell viability in lung cancer (pooled OR: 0.59; 95% CI: 0.49, 0.70). The tumor size reduction and the response rate were evident in the animal xenografts model.

CONCLUSION

Findings indicated that combining metformin with cisplatin is a practical therapeutic approach to increase treatment efficacy in the case of cell viability and tumor volume and minimize side effects. A combination of metformin with cisplatin could enhance treatment efficacy through synergistic inhibitory effects on the growth of cancer cells.

Metformin overcomes metabolic reprogramming-induced resistance of skin squamous cell carcinoma to photodynamic therapy

Objective

Cancer metabolic reprogramming promotes resistance to therapies. In this study, we addressed the role of the Warburg effect in the resistance to photodynamic therapy (PDT) in skin squamous cell carcinoma (sSCC). Furthermore, we assessed the effect of metformin treatment, an antidiabetic type II drug that modulates metabolism, as adjuvant to PDT.

Methods

For that, we have used two human SCC cell lines: SCC13 and A431, called parental (P) and from these cell lines we have generated the corresponding PDT resistant cells (10GT).

Results

Here, we show that 10GT cells induced metabolic reprogramming to an enhanced aerobic glycolysis and reduced activity of oxidative phosphorylation, which could influence the response to PDT. This result was also confirmed in P and 10GT SCC13 tumors developed in mice. The treatment with metformin caused a reduction in aerobic glycolysis and an increase in oxidative phosphorylation in 10GT sSCC cells. Finally, the combination of metformin with PDT improved the cytotoxic effects on P and 10GT cells. The combined treatment induced an increase in the protoporphyrin IX production, in the reactive oxygen species generation and in the AMPK expression and produced the inhibition of AKT/mTOR pathway. The greater efficacy of combined treatments was also seen in vivo, in xenografts of P and 10GT SCC13 cells.

Conclusions

Altogether, our results reveal that PDT resistance implies, at least partially, a metabolic reprogramming towards aerobic glycolysis that is prevented by metformin treatment. Therefore, metformin may constitute an excellent adjuvant for PDT in sSCC.

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Cell resistant to Photodynamic therapy (PDT) is due to the metabolic reprogramming.

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Metformin modulates energetic metabolism in PDT-resistant cells, sensitizing to PDT.

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Metformin increases protoporphyrin IX and reactive oxygen species generation.

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Metformin+PDT is proposed as potential therapy against skin squamous cell carcinoma.

Synthesis and Validation of a Bioinspired Catechol-Functionalized Pt(IV) Prodrug for Preclinical Intranasal Glioblastoma Treatment

Simple Summary

Glioblastoma (GB) is a type of brain cancer with a poor prognosis and few improvements in its treatment. One of the greatest difficulties in GB therapy lies in the fact that most of the drugs with high anticancer potential do not reach the brain and exert high therapeutic activity while minimizing side effects. To overcome these limitations, we focused on a catechol-based Pt(IV) prodrug (able to reverse cisplatin in a cellular environment) with the intention of repurposing Pt-based drugs as GB chemotherapeutic agents. Our in vitro results have corroborated the therapeutic effect of the synthesized complexes as comparable to cisplatin, and in vivo studies have demonstrated the potential of nose-to-brain delivery of this Pt(IV) prodrug for GB treatment.

Abstract

Glioblastoma is the most malignant and frequently occurring type of brain tumors in adults. Its treatment has been greatly hampered by the difficulty to achieve effective therapeutic concentration in the tumor sites due to its location and the blood–brain barrier. Intranasal administration has emerged as an alternative for drug delivery into the brain though mucopenetration, and rapid mucociliary clearance still remains an issue to be solved before its implementation. To address these issues, based on the intriguing properties of proteins secreted by mussels, polyphenol and catechol functionalization has already been used to promote mucopenetration, intranasal delivery and transport across the blood–brain barrier. Thus, herein we report the synthesis and study of complex 1, a Pt(IV) prodrug functionalized with catecholic moieties. This complex considerably augmented solubility in contrast to cisplatin and showed a comparable cytotoxic effect on cisplatin in HeLa, 1Br3G and GL261 cells. Furthermore, preclinical in vivo therapy using the intranasal administration route suggested that it can reach the brain and inhibit the growth of orthotopic GL261 glioblastoma. These results open new opportunities for catechol-bearing anticancer prodrugs in the treatment for brain tumors via intranasal administration.

Prognostic value and non-neuroendocrine role of INSM1 in small cell lung cancer

BACKGROUND

Small cell lung cancer (SCLC) is a malignant lung neuroendocrine tumor with early metastasis, rapid progression, and poor outcomes. Insulinoma-associated protein 1 (INSM1) has been an excellent marker for neuroendocrine (NE) differentiation and widely used in the diagnosis of NE neoplasms, including SCLC. However, its role beyond NE diagnostic marker remained little reported.

METHODS

We examined immunohistochemical expression of INSM1 in 73 surgically resected SCLC, analyzed its prognostic value by Kaplan-Meier method, and investigated clinical-pathological features of INSM1 high SCLC. In vitro, We assessed INSM1 function on glucose intake, tumor migration, and Cisplatin resistance by 2-NBDG glucose uptake fluorescent assay, transwell assay, and ANNEXIN V/PI assay, respectively. In vivo, we evaluated the therapeutic value of metformin on reversing INSM1 induced chemoresistance by BALB/c nude mice xenograft tumor model.

RESULTS

High INSM1 expression was correlated with lymph node metastasis (LNM) (p = 0.0005), later TNM stages (p = 0.0003), and predicted poor survival (Log-rank p = 0.038). Multivariate Cox analysis confirmed INSM1 as an independent prognostic factor in SCLC (p = 0.012, HR:3.195, 95%CI:1.288-7.927). Interestingly, LNM was correlated with worse prognosis only in patients received chemotherapy (Log-rank p = 0.027) rather than the others (Log-rank p = 0.40). In patients having LNM and treated with chemotherapy, high INSM1 was correlated with worse clinic outcome (Log-rank p = 0.009). In vitro, overexpression of INSM1 decreased AMPK-α expression as well as glucose intake, promoted tumor cell migration, and limited the apoptosis induced by Cisplatin, which all could be reversed by Metformin. In vivo, INSM1 overexpression also contributed to tumor growth beyond inducing Cisplatin resistance.

CONCLUSION

Our finding suggested INSM1 played more role than a NE marker, partly through down-regulating AMPK signal. INSM1 may serve as a novel prognostic marker and therapeutic target in SCLC.

The Molecular Basis and Therapeutic Aspects of Cisplatin Resistance in Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) is a kind of malignant tumors with low survival rate and prone to have early metastasis and recurrence. Cisplatin is an alkylating agent which induces DNA damage through the formation of cisplatin-DNA adducts, leading to cell cycle arrest and apoptosis. In the management of advanced OSCC, cisplatin-based chemotherapy or chemoradiotherapy has been considered as the first-line treatment. Unfortunately, only a portion of OSCC patients can benefit from cisplatin treatment, both inherent resistance and acquired resistance greatly limit the efficacy of cisplatin and even cause treatment failure. Herein, this review outline the underlying mechanisms of cisplatin resistance in OSCC from the aspects of DNA damage and repair, epigenetic regulation, transport processes, programmed cell death and tumor microenvironment. In addition, this review summarizes the strategies applicable to overcome cisplatin resistance, which can provide new ideas to improve the clinical therapeutic outcome of OSCC.

Metformin pretreatment reduces effect to dacarbazine and suppresses melanoma cell resistance

Oxidative stress role on metformin process of dacarbazine (DTIC) inducing resistance of B16F10 melanoma murine cells are investigated. To induce resistance to DTIC, murine melanoma cells were exposed to increasing concentrations of dacarabazine (DTIC-res group). Metformin was administered before and during the induction of resistance to DTIC (MET-DTIC). The oxidative stress parameters of the DTIC-res group showed increased levels of malondialdehyde (MDA), thiol, and reduced nuclear p53, 8-hydroxy-2'-deoxyguanosine (8-OH-DG), nuclear factor kappa B (NF-ĸB), and Nrf2. In presence of metformin in the resistant induction process to DTIC, (MET-DTIC) cells had increased antioxidant thiols, MDA, nuclear p53, 8-OH-DG, Nrf2, and reducing NF-ĸB, weakening the DTIC-resistant phenotype. The exclusive administration of metformin (MET group) also induced the cellular resistance to DTIC. The MET group presented high levels of total thiols, MDA, and reduced percentage of nuclear p53. It also presented reduced nuclear 8-OH-DG, NF-ĸB, and Nrf2 when compared with the control. Oxidative stress and the studied biomarkers seem to be part of the alterations evidenced in DTIC-resistant B16F10 cells. In addition, metformin administration is able to play a dual role according to the experimental protocol, preventing or inducing a DTIC-resistant phenotype. These findings should help future research with the aim of investigating DTIC resistance in melanoma.

Cancer-associated fibroblasts secrete hypoxia-induced serglycin to promote head and neck squamous cell carcinoma tumor cell growth in vitro and in vivo by activating the Wnt/β-catenin pathway

BACKGROUND

The tumor microenvironment (TME) is known to play a prominent role in the pathology of head and neck squamous cell carcinoma (HNSCC). Cancer-associated fibroblasts (CAFs) have been reported to regulate tumor progression, and serglycin (SRGN), one of the paracrine cytokines of CAFs, has been reported to play an important role in various signaling pathways. Hypoxia is a distinct feature of the HNSCC TME. Here, we investigated the mechanism underlying CAF-secreted SRGN leading to HNSCC progression under hypoxia.

METHODS

Immunohistochemical staining was used to detect SRGN expression in clinical HNSCC samples, after which its relation with patient survival was assessed. CAFs were isolated and SRGN expression and secretion by CAFs under normoxia and hypoxia were confirmed using qRT-PCR and ELISA assays, respectively. HNSCC sphere-forming abilities, stemness-related gene expression, and chemoresistance were assessed with or without SRGN treatment. A Wnt/β-catenin pathway inhibitor (PNU-75,654) was used to block its activation, after which nuclear translocation of β-catenin in the presence of SRGN with or without PNU-75,654 was evaluated. shRNAs were used to stably knock down SRGN expression in CAFs. HNSCC tumor cells with or without (SRGN silenced) CAFs were inoculated submucosally in nude mice after which tumor weights and sizes were determined to assess the effects of CAFs and SRGN on tumor growth.

RESULTS

We found that SRGN was expressed in both HNSCC tumor and stroma cells, and that high SRGN expression in the stroma cells, but not in the tumor cells, was significantly related to a poor patient survival. After the extraction of CAFs and normal fibroblasts (NFs) from paired tumor samples and adjacent normal tissues, respectively, we found that the expression of CAF-specific genes, including fibroblast activation protein (FAP) and alpha-smooth muscle actin (α-SMA), was clearly upregulated compared to the expression in NFs. The hypoxia marker HIF-1α was found to be expressed in tumor stroma cells. Hypoxyprobe immunofluorescence staining confirmed stromal hypoxia in an orthotopic tongue cancer mouse model. Using qRT-PCR and ELISA we found that a hypoxic TME upregulated SRGN expression and secretion by CAFs. SRGN markedly enhanced the sphere-forming ability, stemness-related gene expression and chemoresistance of HNSCC tumor cells. SRGN activated the Wnt/β-catenin pathway and promoted β-catenin nuclear translocation. An in vivo study confirmed that CAFs can accelerate HNSCC tumor growth, and that this effect can be counteracted by SRGN silencing.

CONCLUSIONS

Our data indicate that a hypoxic tumor stroma can lead to upregulation of SRGN expression. SRGN secreted by CAFs can promote β-catenin nuclear translocation to activate downstream signaling pathways, leading to enhanced HNSCC cell stemness, chemoresistance and accelerated tumor growth.

The Chemosensitizing Role of Metformin in Anti-Cancer Therapy

Chemoresistance, which leads to the failure of chemotherapy and further tumor recurrence, presents the largest hurdle for the success of anti-cancer therapy. In recent years, metformin, a widely used first-line antidiabetic drug, has attracted increasing attention for its anti-cancer effects. A growing body of evidence indicates that metformin can sensitize tumor responses to different chemotherapeutic drugs, such as hormone modulating drugs, anti-metabolite drugs, antibiotics, and DNA-damaging drugs via selective targeting of Cancer Stem Cells (CSCs), improving the hypoxic microenvironment, and by suppressing tumor metastasis and inflammation. In addition, metformin may regulate metabolic programming, induce apoptosis, reverse Epithelial to Mesenchymal Transition (EMT), and Multidrug Resistance (MDR). In this review, we summarize the chemosensitization effects of metformin and focus primarily on its molecular mechanisms in enhancing the sensitivity of multiple chemotherapeutic drugs, through targeting of mTOR, ERK/P70S6K, NF-κB/HIF-1 α, and Mitogen- Activated Protein Kinase (MAPK) signaling pathways, as well as by down-regulating the expression of CSC genes and Pyruvate Kinase isoenzyme M2 (PKM2). Through a comprehensive understanding of the molecular mechanisms of chemosensitization provided in this review, the rationale for the use of metformin in clinical combination medications can be more systematically and thoroughly explored for wider adoption against numerous cancer types.>.

Self-enforcing HMGB1/NF-κB/HIF-1α Feedback Loop Promotes Cisplatin Resistance in Hepatocellular Carcinoma Cells

Hepatocellular carcinoma (HCC) is ranked the sixth most common cancer and the fourth leading cause of cancer-related death worldwide, and its incidence is expected to increase in the future. Cisplatin has been widely used in chemotherapy and transarterial chemoembolization in treatment for HCC. However, the main obstacle to the clinical use of cisplatin is the development of resistance, the mechanisms of which are poorly defined. Therefore, it is imperative to investigate the cellular mechanisms mediating cisplatin resistance in HCC. Here, we demonstrated that high mobility group box 1 (HMGB1) is upregulated in patients with cancer, and implicated in a tumor-supportive role. Further, we showed that HMGB1 has an important role in mediating cisplatin resistance via an HMGB1/ nuclear factor kappa-B (NF-κB)/ hypoxia inducible factor-1α (HIF-1α) feedback loop. The study findings reveal an unappreciated molecular mechanism of HMGB1-mediated cisplatin resistance and may provide a new clue in cancer therapy.

HPV 16 E6/E7 up-regulate the expression of both HIF-1α and GLUT1 by inhibition of RRAD and activation of NF-κB in lung cancer cells

Chronic infection of HPV16 E6/E7 is frequently associated with lung cancers, especially in non-smokers and in Asians. In our previous studies, we found that HPV16 E6/E7 up-regulated HIF-1α at protein level and further up-regulated GLUT1 at both protein and mRNA levels in well-established lung cancer cell lines. In one of our further mechanism study, the results demonstrated that HPV16 E6/E7 up-regulated the expression of GLUT1 through HPV-LKB1-HIF-1α-GLUT1 axis. However, there are multiple pathways involved in HPV16 E6/E7 regulation of HIF-1α expression. In current study, using double directional genetic manipulation in well-established lung cancer cell lines, we showed that both E6 and E7 down-regulated the expression of RRAD at both protein and mRNA levels. Like LKB1, RRAD is one of the cancer suppressor genes. The loss of RRAD further activated NF-κB by promoted cytoplasmic p65 translocated to nucleus, and up-regulated the expression level of the p-p65 in nucleus. Furthermore, p-p65 up regulated HIF-1α and GLUT1 at both protein and mRNA levels. Thus, we proposed HPV16 E6/E7 up-regulated the expression of GLUT1 through HPV-RRAD-p65- HIF-1α- GLUT1 axis. In conclusion, we demonstrated for the first time that E6 and E7 promoted the expression of HIF-1α and GLUT1 by relieving the inhibitory effect of RRAD which resulted in the activation of NF-κB by promoting cytoplasmic p65 translocated to nucleus, and up-regulated the expression of the p-p65 in nucleus in lung cancer cells. Our findings provided new evidence to support the critical role of RRAD in the pathogenesis of HPV-related lung cancer, and suggested novel therapeutic targets.

Metformin overcomes resistance to cisplatin in triple-negative breast cancer (TNBC) cells by targeting RAD51

BACKGROUND

Chemotherapy is a standard therapeutic regimen to treat triple-negative breast cancer (TNBC); however, chemotherapy alone does not result in significant improvement and often leads to drug resistance in patients. In contrast, combination therapy has proven to be an effective strategy for TNBC treatment. Whether metformin enhances the anticancer effects of cisplatin and prevents cisplatin resistance in TNBC cells has not been reported.

METHODS

Cell viability, wounding healing, and invasion assays were performed on Hs 578T and MDA-MB-231 human TNBC cell lines to demonstrate the anticancer effects of combined cisplatin and metformin treatment compared to treatment with cisplatin alone. Western blotting and immunofluorescence were used to determine the expression of RAD51 and gamma-H2AX. In an in vivo 4T1 murine breast cancer model, a synergistic anticancer effect of metformin and cisplatin was observed.

RESULTS

Cisplatin combined with metformin decreased cell viability and metastatic effect more than cisplatin alone. Metformin suppressed cisplatin-mediated RAD51 upregulation by decreasing RAD51 protein stability and increasing its ubiquitination. In contrast, cisplatin increased RAD51 expression in an ERK-dependent manner. In addition, metformin also increased cisplatin-induced phosphorylation of γ-H2AX. Overexpression of RAD51 blocked the metformin-induced inhibition of cell migration and invasion, while RAD51 knockdown enhanced cisplatin activity. Moreover, the combination of metformin and cisplatin exhibited a synergistic anticancer effect in an orthotopic murine model of 4T1 breast cancer in vivo.

CONCLUSIONS

Metformin enhances anticancer effect of cisplatin by downregulating RAD51 expression, which represents a novel therapeutic target in TNBC management.

Combination of quercetin and cisplatin enhances apoptosis in OSCC cells by downregulating xIAP through the NF-κB pathway

While cisplatin is a first-line chemotherapeutic drug commonly used to treat patients with oral squamous cell carcinoma (OSCC), the cisplatin-resistance poses a major challenge for its clinical application. Recent studies have shown that quercetin, a natural flavonoid found in various plants and foods possesses an anti-cancer effect. The following study examined the combined effect of quercetin and cisplatin on OSCC apoptosis in vitro and in vivo (using a mice tumor model). We found that quercetin promotes cisplatin-induced apoptosis in human OSCC (cell lines Tca-8113 and SCC-15) by down-regulating NF-κB. Pretreatment of cancer cells with quercetin inhibited the phosphorylation Akt and IKKβ, and led to the suppression of NF-κB and anti-apoptotic protein xIAP. In addition, we observed that the pretreatment of cancer cells with quercetin improves extrinsic and intrinsic apoptosis by activating caspase-8 and caspase-9, respectively. Our in vivo data also indicated that the combination of quercetin and cisplatin may inhibit the xenograft growth in mice. To sum up, our results provide a new evidence for the application of quercetin and cisplatin in OSCC therapy.

Metformin attenuates cisplatin-induced genotoxicity and apoptosis in rat bone marrow cells

Metformin is widely used as an oral hypoglycemic drug in the management of type 2 diabetes mellitus. This study evaluated the possible protective effects of metformin against cisplatin-induced genotoxicity and apoptosis in rat bone marrow cells. Two different doses of metformin (50 and 100 mg/kg b.w.) were administered orally to experimental animals for seven consecutive days. On the seventh day, the rats were exposed to cisplatin (5 mg/kg, i.p.) 1 h after the last oral metformin administration. Rats in the control group were treated orally with 10 ml/kg PBS for 7 consecutive days and a single intraperitoneal injection of saline (0.9%) on the 7th day. The antagonistic effects of metformin against cisplatin were evaluated using micronucleus assay, reactive oxygen species (ROS) level analysis, hematological analysis, and flow cytometry. Treatment with 50 and 100 mg/kg metformin before cisplatin injection produced a significant reduction in the frequencies of micronucleated polychromatic erythrocytes (MnPCEs) and micronucleated normochromatic erythrocytes (MnNCEs) 24 h after cisplatin treatment with a corresponding increase in the PCE/(PCE + NCE) ratio. Moreover, metformin markedly elevated the levels of both red and white blood cells in peripheral blood and decreased the percentage of apoptotic cells and the ROS level in bone marrow cells of rats treated with cisplatin. The data suggest that metformin has potential chemoprotective properties in rat bone marrow after cisplatin treatment, which support its candidature as a potential chemoprotective agent for cancer patients undergoing chemotherapy.

Metformin enhances the radiosensitizing effect of cisplatin in non-small cell lung cancer cell lines with different cisplatin sensitivities

Cisplatin is an extensively used chemotherapeutic drug for lung cancer, but the development of resistance decreases its effectiveness in the treatments of non-small cell lung cancer (NSCLC). In this study, we examined the effects of metformin, a widely used antidiabetic drug, on cisplatin radiosensitization in NSCLC cell lines. Human NSCLC cell lines, A549 (cisplatin-resistant) and H460 (cisplatin-sensitive), were treated with metformin, cisplatin or a combination of both drugs before ionizing radiation. Cell proliferation, clonogenic assays, western blotting, cisplatin-DNA adduct formation and immunocytochemistry were used to characterize the treatments effects. Metformin increased the radiosensitivity of NSCLC cells. Metformin showed additive and over-additive effects in combination with cisplatin and the radiation response in the clonogenic assay in H460 and A549 cell lines (p = 0.018 for the interaction effect between cisplatin and metformin), respectively. At the molecular level, metformin led to a significant increase in cisplatin-DNA adduct formation compared with cisplatin alone (p < 0.01, ANOVA-F test). This was accompanied by a decreased expression of the excision repair cross-complementation 1 expression (ERCC1), a key enzyme in nucleotide excision repair pathway. Furthermore, compared with each treatment alone metformin in combination with cisplatin yielded the lowest level of radiation-induced Rad51 foci, an essential protein of homologous recombination repair. Ionizing radiation-induced γ-H2AX and 53BP1 foci persisted longer in both cell lines in the presence of metformin. Pharmacological inhibition of AMP-activated protein kinase (AMPK) demonstrated that metformin enhances the radiosensitizing effect of cisplatin through an AMPK-dependent pathway only in H460 but not in A549 cells. Our results suggest that metformin can enhance the effect of combined cisplatin and radiotherapy in NSCLC and can sensitize these cells to radiation that are not sensitized by cisplatin alone.

Anticancer effect of novel platinum nanocomposite beads on oral squamous cell carcinoma cells

Nanoparticles are used in industry and medicine, because of their physiochemical properties, such as size, charge, large surface area and surface reactivity. Recently, metal nanoparticles were reported to show cell toxicity on cancer cells. In this study, we focused novel platinum nanoparticles-conjugated latex beads (P2VPs), platinum nanocomposite (PtNCP) beads, and investigated the possibility to incorporate novel anti-cancer effect of these combined nanoparticles. Oral squamous cell carcinoma cell lines, HSC-3-M3 cells were injected subcutaneously into the back of nude mice to produce a xenograft model. PtNCP beads were injected locally and examined by measuring tumor volume and comparing pathological histology. PtNCP beads treatment suppressed tumor growth and identified increasing pathological necrotic areas, in vivo. PtNCP beads inhibited the cell viability of HSC-3-M3 cells in dose-dependent manner and induced the cytotoxicity with extracellular LDH value, in vitro. Furthermore, SEM images were morphologically observed in PtNCP beads-treated HSC-3-M3 cells. The aggregation of the PtNCP beads on the cell membrane, the destructions of the cell membrane and globular structures were observed in the SEM image. Our results indicated that a potential anti-cancer effect of the PtNCP beads, suggesting the possibility as a therapeutic tool for cancer cell-targeted therapy. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2281-2287, 2019.

Metformin sensitizes hypoxia-induced gefitinib treatment resistance of HNSCC via cell cycle regulation and EMT reversal

Objectives

The objectives of this study were to explore the mechanisms of metformin sensitization to hypoxia-induced gefitinib treatment in resistant head and neck squamous cell carcinoma (HNSCC) and evaluate the effects of this combined treatment strategy.

Methods

The effects of gefitinib treatment on HNSCC were measured under normoxic and hypoxic conditions. The relationship between hypoxia and cell cycle and epithelial-mesenchymal transition (EMT) in tumor cells were analyzed. Palbociclib and LY294002 were used in combination with gefitinib to evaluate the effects on HNSCC cell cytotoxicity during hypoxia. Finally, metformin was used to evaluate the sensitizing effects of gefitinib treatment on HNSCC in vivo and in vitro.

Results

Cell viability and apoptosis assays demonstrated a significant difference in HNSCC cells treated with gefitinib between the normoxia and hypoxia groups. Hypoxia induced the expression of cyclin D1, decreased the percentage of cells in G1, and promoted the EMT of tumor cells. Both palbociclib and LY294002 enhanced gefitinib-induced cytotoxicity of HNSCC cells under hypoxic conditions. Encouragingly, metformin sensitized HNSCC to gefitinib treatment in vivo and in vitro.

Conclusion

Hypoxia promotes G1-S cell cycle progression and EMT in HNSCC, resulting in gefitinib treatment resistance. Metformin sensitizes HNSCC to gefitinib treatment, which might serve as a novel combined treatment strategy.

Hyperglycemia-Associated Dysregulation of O-GlcNAcylation and HIF1A Reduces Anticancer Action of Metformin in Ovarian Cancer Cells (SKOV-3)

Although cancer cells need more glucose than normal cells to maintain energy demand, chronic hyperglycemia induces metabolic alteration that may dysregulate signaling pathways, including the O-GlcNAcylation and HIF1A (Hypoxia-inducible factor 1-alpha) pathways. Metformin was demonstrated to evoke metabolic stress and induce cancer cell death. The aim of this study was to determine the cytotoxic efficiency of metformin on SKOV-3 cells cultured in hyperglycemia and normoglycemia. To identify the potential mechanism, we assessed the expression of O-linked β-N-acetlyglucosamine transferase (OGT) and glycoside hydrolase O-GlcNAcase (OGA), as well as hypoxia-inducible factor 1-alpha (HIF1A) and glucose transporters (GLUT1, GLUT3). SKOV-3 cells were cultured in normoglycaemia (NG, 5 mM) and hyperglycemia (HG, 25 mM) with and without 10 mM metformin for 24, 48, and 72 h. The proliferation rate, apoptotic and necrotic SKOV-3 cell death were evaluated. Real-Time qPCR was employed to determine mRNA expression of OGT, OGA, GLUT1, GLUT3, and HIF1A. Metformin significantly reduced the proliferation of SKOV-3 cells under normal glucose conditions. Whereas, the efficacy of metformin to induce SKOV-3 cell death was reduced in hyperglycemia. Both hyperglycemia and metformin induced changes in the expression of genes involved in the O-GlcNAcylation status and HIF1A pathway. The obtained results suggest that dysregulation of O-GlcNAcylation, and the related HIF1A pathway, via hyperglycemia, is responsible for the decreased cytotoxic efficiency of metformin in human ovarian cancer cells.

Tumor-targeted hybrid protein oxygen carrier to simultaneously enhance hypoxia-dampened chemotherapy and photodynamic therapy at a single dose

Hypoxia is a characteristic feature of solid tumors and an important causation of resistance to chemotherapy and photodynamic therapy (PDT). It is challenging to develop efficient functional nanomaterials for tumor oxygenation and therapeutic applications.

Methods: Through disulfide reconfiguration to hybridize hemoglobin and albumin, tumor-targeted hybrid protein oxygen carriers (HPOCs) were fabricated, serving as nanomedicines for precise tumor oxygenation and simultaneous enhancement of hypoxia-dampened chemotherapy and photodynamic therapy. Based on encapsulation of doxorubicin (DOX) and chlorin e6 (Ce6) into HPOCs to form ODC-HPOCs, the mechanism and therapeutic efficacy of oxygen-enhanced chemo-PDT was investigated in vitro and in vivo.

Results: The precise oxygen preservation and release of the HPOC guaranteed sufficient tumor oxygenation, which is able to break hypoxia-induced chemoresistance by downregulating the expressions of hypoxia-inducible factor-1α (HIF-1α), multidrug resistance 1 (MDR1) and P-glycoprotein (P-gp), resulting in minimized cellular efflux of chemodrug. Moreover, the oxygen supply is fully exploited for upgrading the generation of reactive oxygen species (ROS) during the photodynamic process. As a result, only a single-dose treatment of the HPOCs-based chemo-PDT exhibited superior tumor suppression. The combination therapy was guided by in vivo fluorescence/photoacoustic imaging with nanoparticle tracking and oxygen monitoring.

Conclusion: This well-defined HPOC as a versatile nanosystem is expected to pave a new way for breaking multiple hypoxia-induced therapeutic resistances to achieve highly effective treatment of solid tumors.

Metformin-Induced Reduction of CD39 and CD73 Blocks Myeloid-Derived Suppressor Cell Activity in Patients with Ovarian Cancer

Metformin is a broadly prescribed drug for type 2 diabetes that exerts antitumor activity, yet the mechanisms underlying this activity remain unclear. We show here that metformin treatment blocks the suppressive function of myeloid-derived suppressor cells (MDSC) in patients with ovarian cancer by downregulating the expression and ectoenzymatic activity of CD39 and CD73 on monocytic and polymononuclear MDSC subsets. Metformin triggered activation of AMP-activated protein kinase α and subsequently suppressed hypoxia-inducible factor α, which was critical for induction of CD39/CD73 expression in MDSC. Furthermore, metformin treatment correlated with longer overall survival in diabetic patients with ovarian cancer, which was accompanied by a metformin-induced reduction in the frequency of circulating CD39+CD73+ MDSC and a concomitant increase in the antitumor activities of circulating CD8+ T cells. Our results highlight a direct effect of metformin on MDSC and suggest that metformin may yield clinical benefit through improvement of antitumor T-cell immunity by dampening CD39/CD73-dependent MDSC immunosuppression in ovarian cancer patients.Significance: The antitumor activity of an antidiabetes drug is attributable to reduced immunosuppressive activity of myeloid-derived tumor suppressor cells. Cancer Res; 78(7); 1779-91. ©2018 AACR.

Antitumor effect of a Pt-loaded nanocomposite based on graphene quantum dots combats hypoxia-induced chemoresistance of oral squamous cell carcinoma

Background

Tumor microenvironment plays an important role in the chemoresistance of oral squamous cell carcinoma (OSCC). Hypoxia in the microenvironment is one of the important factors that contributes to OSCC chemoresistance; therefore overcoming hypoxia-mediated chemoresistance is one of the great challenges in clinical practice.

Methods

In this study, we developed a drug delivery system based on Pt-loaded, polyethylene glycol-modified graphene quantum dots via chemical oxidation and covalent reaction.

Results

Our results show that synthesized polyethylene glycol-graphene quantum dots-Pt (GPt) is about 5 nm in diameter. GPt sensitizes OSCC cells to its treatment in both normoxia and hypoxia conditions. Inductively coupled plasma-mass spectrometry assay shows that GPt enhances Pt accumulation in cells, which leads to a notable increase of S phase cell cycle arrest and apoptosis of OSCC cells in both normoxia and hypoxic conditions. Finally, compared with free cisplatin, GPt exhibits a strong inhibitory effect on the tumor growth with less systemic drug toxicity in an OSCC xenograft mouse tumor model.

Conclusion

Taken together, our results show that GPt demonstrates superiority in combating hypoxia-induced chemoresistance. It might serve as a novel strategy for future microenvironment-targeted cancer therapy.

Buformin suppresses proliferation and invasion via AMPK/S6 pathway in cervical cancer and synergizes with paclitaxel

Buformin is an old anti-diabetic agent and manifests potent anti-tumor activities in several malignancies. In the present study, we aimed to explore the functions of buformin in human cervical cancer. As our data shown, buformin exhibited significant anti-proliferative effects in a dose-dependent manner in 4 cervical cancer cell lines. Compared to the control, buformin notably suppressed colony formation and increased ROS production in C33A, Hcc94 and SiHa cells. Flow cytometric analysis showed that buformin induced marked cell cycle arrest but only resulted in mild apoptosis. The invasion of C33A and SiHa cells sharply declined with buformin treatment. Consistently, western blotting showed that buformin activated AMPK and suppressed S6, cyclin D1, CDK4, and MMP9. Moreover, we found that buformin enhanced glucose uptake and LDH activity, increased lactate level, while decreased ATP production in cervical cancer cells. In addition, low doses of buformin synergized with routine chemotherapeutic drugs (such as paclitaxel, cisplatin, and 5-FU) to achieve more significant anti-tumor effects. In vivo, a single use of buformin exerted moderate anti-tumor effects, and the combination with buformin and paclitaxel exhibited even greater suppressive effects. Buformin also consistently showed synergistic effects with paclitaxel in treating primary cultures of cervical cancer cells. Take together, we are the first to demonstrate that buformin suppresses cellular proliferation and invasion through the AMPK/S6 signaling pathway, which arrests cell cycle and inhibits cellular invasion. Buformin also could synergize with routine chemotherapies, producing much more powerful anti-tumor effects. With these findings, we strongly support buformin as a potent choice for treating cervical cancer, especially in combination with routine chemotherapy.

Selective cytotoxicity of the anti-diabetic drug, metformin, in glucose-deprived chicken DT40 cells

Metformin is a biguanide drug that is widely used in the treatment of diabetes. Epidemiological studies have indicated that metformin exhibits anti-cancer activity. However, the molecular mechanisms underlying this activity currently remain unclear. We hypothesized that metformin is cytotoxic in a tumor-specific environment such as glucose deprivation and/or low oxygen (O₂) tension. We herein demonstrated that metformin was highly cytotoxic under glucose-depleted, but not hypoxic (2% O₂) conditions. In order to elucidate the underlying mechanisms of this selective cytotoxicity, we treated exposed DNA repair-deficient chicken DT40 cells with metformin under glucose-depleted conditions and measured cellular sensitivity. Under glucose-depleted conditions, metformin specifically killed fancc and fancl cells that were deficient in FANCC and FANCL proteins, respectively, which are involved in DNA interstrand cross-link repair. An analysis of chromosomal aberrations in mitotic chromosome spreads revealed that a clinically relevant concentration of metformin induced DNA double-strand breaks (DSBs) in fancc and fancl cells under glucose-depleted conditions. In summary, metformin induced DNA damage under glucose-depleted conditions and selectively killed cells. This metformin-mediated selective toxicity may suppress the growth of malignant tumors that are intrinsically deprived of glucose.

Redox-dependent modulation of metformin contributes to enhanced sensitivity of esophageal squamous cell carcinoma to cisplatin

Glutathione is the major intracellular anti-oxidant against reactive oxygen species and serves as a detoxification essential. The anti-diabetic drug metformin has been showed to exert anti-tumor activity via modulation of redox homeostasis. In this study, we provided evidence that metformin inhibits proliferation and induces apoptosis of esophageal squamous cancer cells. Importantly, we found that metformin acts as pro-oxidant via depletion of intracellular glutathione. Co-treatment with metformin reversed the elevated intracellular glutathione induced by cisplatin and therefore enhanced the sensitivity to cisplatin in vitro and in vivo. Taken together, our data indicate that combination of metformin with cisplatin may represent a novel therapeutic strategy for esophageal squamous cell carcinoma treatment.

Metformin and caffeic acid regulate metabolic reprogramming in human cervical carcinoma SiHa/HTB-35 cells and augment anticancer activity of Cisplatin via cell cycle regulation

Metformin shows benefits in anticancer prevention in humans. In this study, normal human fibroblasts (FB) and metastatic cervical cancer cells (SiHa) were exposed to 10 mM Metformin (Met), 100 μM Caffeic Acid (trans-3,4-dihydroxycinnamic acid, CA) or combination of the compounds. Both drugs were selectively toxic towards cancer cells, but neither Met nor CA treatment suppressed growth of normal cells. Met and CA regulated metabolic reprogramming in SiHa tumor cells through different mechanisms: Met suppressed regulatory enzymes Glurtaminase (GLS) and Malic Enzyme 1 (ME1) and enhanced pyruvate oxidation via tricarboxylic acids (TCA) cycle, while CA acted as glycolytic inhibitor. Met/CA treatment impaired expression of Sterol Regulatory Element-Binding Protein 1 (SREBP1c) which resulted in alleviation of de novo synthesis of unsaturated fatty acid. The toxic action of CisPt was supported by Met and CA not only in tumor cells, but also during co-culture of SiHa GFP+ cells with fibroblasts. Furthermore, Met and CA augmented Cisplatin (CisPt) action against quiescent tumor cells involving reprogramming of cell cycle. Our findings provide new insights into specific targeting of mitochondrial metabolism in neoplastic cells and into designing new cisplatin-based selective strategies for treating cervical cancer in humans with regard to the role of tumor microenvironment.