title: Metformin represses glucose starvation induced autophagic response in microvascular endothelial cells and promotes cell death.
abstract: Metformin, the most frequently administered drug for the treatment of type 2 diabetes, is being investigated for its potential in the treatment of various types of cancer; however, the cellular basis for this putative anti-cancer action remains controversial. In the current study we examined the effect of metformin on endoplasmic reticulum (ER) stress and autophagy in glucose-starved micro-vascular endothelial cells (MECs). The rationale for our experimental protocol is that in a growing tumor MECs are subjected to hypoxia and nutrient/glucose starvation that results from the reduced supply and relatively high consumption of glucose. Mouse MECs (MMECs) were glucose-starved for up to 48h in the absence or presence of metformin (50μM and 2mM) and the status of ER stress, autophagic, cell survival and apoptotic markers were assessed. Activation of ER stress and autophagy was observed in glucose starved MECs as evidenced by the significant increase in the levels of ER stress and autophagic markers while accumulation of LC3B stained punctae in the MECs confirmed autophagic activation. Treatment with 2mM metformin, independent of AMPK, significantly reversed glucose starvation induced ER stress and autophagy in MECs, but, at 24h, did not decrease cell viability; however, at 48h, persistent ER stress and metformin associated inhibition of autophagy decreased cell viability, caused cell cycle arrest in G2/M and increased the number of cells in the sub-G0/G1 phase of cell cycle. Treatment with metformin reduced phosphorylation of Akt and mTOR and inhibited downstream targets of mTOR. Our findings support the argument that treatment with metformin when used in combination with glycolytic inhibitors will inhibit pro-survival autophagy and promote cell death and potentially prove to be the basis for an effective anti-cancer strategy.
authors.affiliation: Department of Pharmacology, Weill Cornell Medicine-Qatar, Education City, Qatar Foundation, P.O. Box No. 24144, Doha, Qatar.
authors.forename: Samson Mathews
authors.initials: SM
authors.lastname: Samuel
authors.affiliation: Department of Pharmacology, Weill Cornell Medicine-Qatar, Education City, Qatar Foundation, P.O. Box No. 24144, Doha, Qatar.
authors.forename: Suparna
authors.initials: S
authors.lastname: Ghosh
authors.affiliation: Department of Pharmacology, Weill Cornell Medicine-Qatar, Education City, Qatar Foundation, P.O. Box No. 24144, Doha, Qatar.
authors.forename: Yasser
authors.initials: Y
authors.lastname: Majeed
authors.affiliation: Department of Pharmacology, Weill Cornell Medicine-Qatar, Education City, Qatar Foundation, P.O. Box No. 24144, Doha, Qatar.
authors.forename: Gnanapragasam
authors.initials: G
authors.lastname: Arunachalam
authors.affiliation: Neurological Disorders Research Center, Qatar Biomedical Research Institute (QBRI), Hamad Bin Khalifa University (HBKU), Qatar Foundation, P.O. Box No. 5825, Doha, Qatar.
authors.forename: Mohamed M
authors.initials: MM
authors.lastname: Emara
authors.affiliation: Department of Pharmacology, Weill Cornell Medicine-Qatar, Education City, Qatar Foundation, P.O. Box No. 24144, Doha, Qatar; Department of Medical Education, Weill Cornell Medicine-Qatar, Education City, Qatar Foundation, P.O. Box No. 24144, Doha, Qatar.
authors.forename: Hong
authors.initials: H
authors.lastname: Ding
authors.affiliation: Department of Pharmacology, Weill Cornell Medicine-Qatar, Education City, Qatar Foundation, P.O. Box No. 24144, Doha, Qatar; Department of Medical Education, Weill Cornell Medicine-Qatar, Education City, Qatar Foundation, P.O. Box No. 24144, Doha, Qatar. Electronic address: cht2011@qatar-med.cornell.edu.
authors.forename: Chris R
authors.initials: CR
authors.lastname: Triggle
mesh_terms: D000818:Animals; D001343:Autophagy / Q000187:drug effects*; D016923:Cell Death / Q000187:drug effects*; D002478:Cells, Cultured; D003470:Culture Media; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects*; D005947:Glucose / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D008687:Metformin / Q000494:pharmacology*; D051379:Mice; D055806:Microvessels / Q000166:cytology / Q000187:drug effects
chemical_list: D003470:Culture Media; D007004:Hypoglycemic Agents; D008687:Metformin; D005947:Glucose
keywords: Autophagy; Cancer; ER stress; Endothelium; Metformin