Metformin is a widely used antidiabetic drug whose anticancer effects, mediated by the activation of AMP-activated protein kinase (AMPK) and reduction of mTOR signaling, have become noteworthy. Chemotherapy produces genotoxic stress and induces p53 activity, which can cross-talk with AMPK/mTOR pathway. Herein, we investigate whether the combination of metformin and paclitaxel has an effect in cancer cell lines.
Human tumors were xenografted into severe combined immunodeficient (SCID) mice and the cancer cell lines were treated with only paclitaxel or only metformin, or a combination of both drugs. Western blotting, flow cytometry, and immunohistochemistry were then used to characterize the effects of the different treatments.
The results presented herein show that the addition of metformin to paclitaxel leads to quantitative potentialization of molecular signaling through AMPK and a subsequent potent inhibition of the mTOR signaling pathway. Treatment with metformin and paclitaxel resulted in an increase in the number of cells arrested in the G(2)-M phase of the cell cycle, and decreased the tumor growth and increased apoptosis in tumor-bearing mice, when compared with individual drug treatments.
We have provided evidence for a convergence of metformin and paclitaxel induced signaling at the level of AMPK. This mechanism shows how different drugs may cooperate to augment antigrowth signals, and suggests that target activation of AMPK by metformin may be a compelling ally in cancer treatment.
"Metformin is commonly considered as an insulin sensitizer as it enhances signaling through the insulin receptor, resulting in an decrease in insulin resistance and subsequent reduction in circulating insulin levels (18). Recent studies have reported that metformin use is associated with a significant reduction in the incidence of cancer (18,19). A preliminary study suggested that metformin inhibits cancer cell growth by activating adenosine monophosphate protein kinase (AMPK), inactivating mTOR and eventually reducing the activity of the mTOR effector S6K1 (20). "
[Show abstract][Hide abstract] ABSTRACT: Obesity, diabetes and insulin resistance are marked risk factors that promote the development of type I endometrial cancer. Previous studies have demonstrated that insulin-like growth factor 1 (IGF-1) and IGF-2 promote cell proliferation in endometrial cancer cells, while metformin reverses this effect and inhibits cell proliferation. However, the effects of metformin on the regulation of the IGF signaling pathway are unclear. The aim of this study was to investigate the regulation of IGF signaling by metformin in endometrial cancer cells, and to determine the effects of metformin combined with IGF-1 receptor (IGF-1R) inhibitor on cell proliferation and apoptosis. Cell proliferation was assessed following exposure of Ishikawa and HEC-1B endometrial cancer cell lines to metformin and/or the IGF-1R inhibitor, PPP. Apoptosis was assessed by TdT-mediated dUTP nick end labeling assay. Metformin was observed to downregulate IGF-1R and upregulate IGF binding protein-1 (IGFBP-1) mRNA and protein expression, while compound C, an adenosine monophosphate protein kinase inhibitor, reversed this effect. Metformin administered with PPP inhibited endometrial cancer cell proliferation to a greater degree than treatment with either agent alone. At high concentrations (1 or 2 mM), metformin induced apoptosis in endometrial cancer cells. Metformin combined with IGF-1R axis inhibitors may act synergistically to kill tumor cells, as metformin was shown to delay and prevent IGF-1R feedback. In conclusion, this study supported the results of animal studies and subclinical studies, demonstrating the feasibility of metformin combined with IGF-1R axis inhibitors in the treatment of endometrial cancer.
"However, whether AMPK is pro-apoptotic or pro-survival is dependent on the type and/or severity of stresses. Severe stresses including vincristine  , taxol   and temozolomide -activated AMPK appears proapoptotic . While in conditions like starvation , hypoxia  and oxidative stress , AMPK activation could promote cell survival . "
[Show abstract][Hide abstract] ABSTRACT: In this study, we explored the cytoprotective potential of silibinin against oxygen–glucose deprivation (OGD)-induced neuronal cell damages, and studied underling mechanisms. In vitro model of ischemic stroke was created by keeping neuronal cells (SH-SY5Y cells and primary mouse cortical neurons) in an OGD condition followed by re-oxygenation. Pre-treatment of silibinin significantly inhibited OGD/re-oxygenation-induced necrosis and apoptosis of neuronal cells. OGD/re-oxygenation-induced reactive oxygen species (ROS) production and mitochondrial membrane potential (MMP) reduction were also inhibited by silibinin. At the molecular level, silibinin treatment in SH-SY5Y cells and primary cortical neurons led to significant AMP-activated protein kinase (AMPK) signaling activation, detected by phosphorylations of AMPKα1, its upstream kinase liver kinase B1 (LKB1) and the downstream target acetyl-CoA Carboxylase (ACC). Pharmacological inhibition or genetic depletion of AMPK alleviated the neuroprotective ability of silibinin against OGD/re-oxygenation. Further, ROS scavenging ability by silibinin was abolished with AMPK inhibition or silencing. While A-769662, the AMPK activator, mimicked silibinin actions and suppressed ROS production and neuronal cell death following OGD/re-oxygenation. Together, these results show that silibinin-mediated neuroprotection requires activation of AMPK signaling.
Biochemical and Biophysical Research Communications 10/2014; 454(2). DOI:10.1016/j.bbrc.2014.10.080 · 2.30 Impact Factor
"Although AMPK is generally recognized as the metabolic switcher , a number of recent papers have suggested that cellular stresses-activated AMPK also promotes cell apoptosis , such an effect by AMPK is through regulating AMPK’s downstream signals, including c-Jun N-terminal kinases (JNK) , p53  and mTOR . Meanwhile, anti-cancer chemotherapies such as taxol [18,19] and temozolomide  activate AMPK-dependent apoptosis pathways. Meanwhile, resveratrol , capsaicin  and EGCG  anti-cancer plant extracts induced cancer cell death also requires AMPK activation. "
[Show abstract][Hide abstract] ABSTRACT: Background
Hepatocellular carcinoma (HCC), the primary liver cancer, is one of the most malignant human tumors with extremely poor prognosis. The aim of this study was to investigate the anti-cancer effect of berberine in a human hepatocellular carcinoma cell line (HepG2), and to study the underlying mechanisms by focusing on the AMP-activated protein kinase (AMPK) signaling cascade.
We found that berberine induced both apoptotic and autophagic death of HepG2 cells, which was associated with a significant activation of AMPK and an increased expression of the inactive form of acetyl-CoA carboxylase (ACC). Inhibition of AMPK by RNA interference (RNAi) or by its inhibitor compound C suppressed berberine-induced caspase-3 cleavage, apoptosis and autophagy in HepG2 cells, while AICAR, the AMPK activator, possessed strong cytotoxic effects. In HepG2 cells, mammalian target of rapamycin complex 1 (mTORC1) activation was important for cell survival, and berberine inhibited mTORC1 via AMPK activation.
Together, these results suggested that berberine-induced both apoptotic and autophagic death requires AMPK activation in HepG2 cells.
Cancer Cell International 06/2014; 14(1):49. DOI:10.1186/1475-2867-14-49 · 2.77 Impact Factor
Brandon Leonard, Jennifer L McCann, Gabriel J Starrett, Leah Kosyakovsky, Elizabeth Luengas, Amy M Molan, Michael B Burns, Rebecca M McDougle, Peter J Parker, William L Brown, Reuben S Harris
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