Metformin repositioning as antitumoral agent: selective antiproliferative effects in human glioblastoma stem cells, via inhibition of CLIC1-mediated ion current.

Marta Gritti,Paul M.G Curmi,Marta Peretti,Michele Mazzanti,Alessandra Pattarozzi,Rodolfo Sirito,Roberto Würth,Elisa Carra,Federica Barbieri,Antonio Daga,Tullio Florio,Erika Pizzi,Marina Angelini

doi:10.18632/oncotarget.2617

Marta Gritti, Paul M.G Curmi + Show 11 more

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https://doi.org/10.18632/oncotarget.2617

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Abstract

Epidemiological and preclinical studies propose that metformin, a first-line drug for type-2 diabetes, exerts direct antitumor activity. Although several clinical trials are ongoing, the molecular mechanisms of this effect are unknown. Here we show that chloride intracellular channel-1 (CLIC1) is a direct target of metformin in human glioblastoma cells. Metformin exposure induces antiproliferative effects in cancer stem cell-enriched cultures, isolated from three individual WHO grade IV human glioblastomas. These effects phenocopy metformin-mediated inhibition of a chloride current specifically dependent on CLIC1 functional activity. CLIC1 ion channel is preferentially active during the G1-S transition via transient membrane insertion. Metformin inhibition of CLIC1 activity induces G1 arrest of glioblastoma stem cells. This effect was time-dependent, and prolonged treatments caused antiproliferative effects also for low, clinically significant, metformin concentrations. Furthermore, substitution of Arg29 in the putative CLIC1 pore region impairs metformin modulation of channel activity. The lack of drugs affecting cancer stem cell viability is the main cause of therapy failure and tumor relapse. We identified CLIC1 not only as a modulator of cell cycle progression in human glioblastoma stem cells but also as the main target of metformin's antiproliferative activity, paving the way for novel and needed pharmacological approaches to glioblastoma treatment.

Highlights

Epidemiological studies reported that metformin, a first-line treatment for type-2 diabetes [1], is associated with reduced incidence and favorable prognosis in several cancers [2,3,4]
Several studies reported the in vitro and in vivo efficacy of metformin as antitumoral agent for most human tumors, including GBM [17, 18], showing its efficacy in reducing proliferation, survival, clonogenicity and in vivo tumorigenicity of cancer stem cells (CSCs) subpopulations. While these studies opened the way to ongoing clinical trials [2, 54], in most cases, they did not address two central issues: Fig. 8: Molecular characterization of chloride intracellular channel-1 (CLIC1) activity modulation by metformin A) Outside-out single channel experiments in native Chinese Hamster Ovary-K1 (CHO) cells show that anti-FLAG antibody does not inhibit CLIC1 current, differently from metformin (10mM) that closes the channel
Www.impactjournals.com/oncotarget (i) the molecular mechanism by which metformin reduces tumor development and growth, and (ii) the mechanisms for metformin selectivity towards cancer cells, a rather unique characteristic for antitumoral drugs, and demonstrated by the absence of significant toxicity of metformin when chronically used in diabetic patients

Summary

Introduction

Epidemiological studies reported that metformin, a first-line treatment for type-2 diabetes [1], is associated with reduced incidence and favorable prognosis in several cancers [2,3,4]. Metformin directly inhibits cancer cell proliferation, mainly acting on cancer stem cells (CSCs) [5,6,7,8,9,10]. On these bases, several clinical trials are underway [4, 11]. Metformin was clinically approved several decades ago, its mechanism of action has not been completely elucidated. Metformin metabolic effects www.impactjournals.com/oncotarget mainly rely on mitochondrial activity: it decreases ATP production and activates AMP-activated protein kinase (AMPK), regulating gluconeogenesis and fatty acid synthesis [12]. Since AMPK controls mammalian target of rapamycin (mTOR) activity, metformin’s regulation of AMPK could account for its antiproliferative effects [13, 14]

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