252 Letter to the Editor
Letter to the Editor European Journal of Cancer Prevention 2016, 25:252–253
AMP-activated protein kinase activators, cancer regression, and survival Salvatore Chirumbolo, Laboratory of Physiopathology of Obesity, Department of Medicine, University of Verona, Verona, Italy Correspondence to Salvatore Chirumbolo, PhD, Laboratory of Physiopathology of Obesity, Department of Medicine, University of Verona, LURM Est, Policlinico GB Rossi, Piazzale AL Scuro 10, 37134 Verona, Italy Tel: + 39 045 812 8456; fax: + 39 045 802 7403; e-mail: [email protected] Received 31 March 2015 Accepted 10 April 2015
The recent paper by Lee et al. (2015) showed that isocaloric carbohydrate restriction in combination with a mixture of natural AMP-activated protein kinase (AMPK)-activating substances, such as phytochemical extracts including quercetin, curcumin, resveratrol, and catechins, produced survival benefits in mice models. Although neither simple polyphenols (MPs), lowcarbohydrate diet (LCD) or medium-carbohydrate diet (MCD) yielded significant survival trends using the Kaplan–Meier approach, intake of phytochemicals associated with calorie restriction significantly improved the survival of mice undergoing a subcutaneous injection (xenografts) of B16F10 melanoma cells (Lee et al., 2015). Phytochemicals were selected for their potential as stimulators of AMPK and actually the role of AMPK in chemoprevention has been reviewed recently as a function closely related to tumor suppression (Kim and He, 2013). Except for some reports on quercetin, which may enhance hypoxia-induced apoptosis in HCT116 colon cancer (xenograft model) by directly inhibiting AMPK (Kim et al., 2012), curcumin, catechins, and resveratrol are promising anticancer molecules via activating AMPK (Hwang et al., 2007; Beevers et al., 2009; Murase et al., 2009; Shehzad and Lee, 2013; Widlund et al., 2013; Xu et al., 2014). The critical cancer suppression mechanisms outlined by the authors included, besides the activation of AMPK/SIRT1/LKB1 signaling, the suppression of NF-κB and of the IGF1/PI3K/Akt/mTOR pathway (Lee et al., 2015). Interestingly, neither polyphenols alone nor the simple LCD elicited AMPK activation and improved survival curves, despite possible expectations, but a suggestion would come from the complex role exerted by calorie restriction and phytochemicals on these molecular systems. Yet, the synergistic activity claimed by the authors should be better studied. Resveratrol and catechins may synergize with leucine and its metabolite β-hydroxy-β-methylbutyrate to 0959-8278 Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved.
activate the AMPK/SIRT1 pathway in muscle and adipose tissue (Bruckbauer and Zemel, 2014). The role of leucine is fundamental as it exerts a direct effect on SIRT1 kinetics and modulates mitochondrial biogenesis (Liang et al., 2014), and therefore this might be a possible mechanism of AMPK activation in the condition investigated by the authors, leading to stress response and survival. However, this suggested mechanism depends on the bioavailable polyphenols dose, and in this paper, the detailed composition of flavonoids and phenolic acids in the polyphenol mixture has not been provided. Although the authors analyzed only the survival parameters in animals with xenograft tumors, the overall representation of the complex AMPK-mediated pathway involved in the reported evidence might be radically different in a tumor subjected to chemotherapy. Both the levels of carbohydrates, such as glucose, and aminoacids, such as leucine, play a major role in the regulation of some cell-cycle repressor proteins, such as p27 (Kip1). At least in breast cancer, 4-hydroxytamoxifen upregulates p27 using a molecular pathway that includes mTORC1, which, interestingly, is inhibited by curcumin (Beevers et al., 2009). Depending on the dietary intake and metabolism homeostasis, the above-reported mechanism involving AMPK for cancer may be markedly different, with apparently controversial evidence. Deficiency in D(+ )-glucose, as well as L(− )-leucine starvation, promotes the expression of p27 through a pathway involving AMPK activation and the downstream recruitment of mTORC1 (Eto, 2011). The therapeutic activity of 4-hydroxytamoxifen, at least on human MDA-MB-231 breast cancer cells in vitro, requires the activation of PI3K/Akt/mTOR, a pathway that is inhibited in the reported evidence (Lee et al., 2015). Therefore, a LCD should activate cell-cycle repressor proteins, particularly fundamental in cancer control, and moreover glucose starvation can eradicate cancer cells by apoptosis (Mendivil-Perez et al., 2013). Dietary panels used by the authors could not eradicate xenograft tumors, unless polyphenols were introduced. The activation of AMPK by flavonoids leads to the inhibition of inflammation, through NF-κB, and to a better lifespan through the activation of SIRT1, and yet polyphenols alone cannot fight tumors successfully (Lee et al., 2015). These appear as the main hallmarks of longevity and the antiaging mechanism, more than antitumoral signals, which may elucidate better survival curves observed by the authors. Flavonoids increased notably the ability of mice to respond to stressors, particularly those arising from DOI: 10.1097/CEJ.0000000000000170
Copyright r 2016 Wolters Kluwer Health, Inc. All rights reserved.
Letter to the Editor 253
oxidative stress, endoplasmic reticulum stress, mitochondria dysfunction, and inflammation. Their ability to inhibit downstream (mTOR, FOXO3) or upstream (PI3K/Akt) signals of the AMPK pathway should not match the role played by these signaling mechanisms in the activation either of cell-cycle repressors or tumor suppressors, such as p53, as the role of AMPK in cancer still remains elusive (Saito and Nakada, 2014). Particularly interesting would be a comparison of tumor size regression in MP-treated, LCD-treated, and MCDtreated mice compared with LCDmp and MCDmp (Lee et al., 2015) to better highlight the role of any dietary components in AMPK/SIRT-1-mediated survival and tumor development (cell cycle, apoptosis). For example, the deregulation (inhibition) of NF-κB in cancer, which may be performed by miRNAs, negatively regulates cellcycle progression in breast cancer (Shukla et al., 2015). The reported synergism might finally shed light on the role of NF-κB, the inhibition of which increases longevity and reduces tumor masses (Chirumbolo, 2012; Shukla et al., 2015). Furthermore, an antagonistic crosstalk between SIRT1 and NF-κB should be taken into account; a reduction in inflammation (NF-κB) correlates with an increase in longevity (SIRT1) (Kauppinen et al., 2013). The homeostatic dynamics relating stress response/survival to cancer progression is particularly puzzling and the complex activity and pleiotropism of different biochemical plant-derived molecules may hamper a full understanding of why the survival of mice increased with a synergistic association of isocaloric carbohydrate restriction and flavonoids. Which factor actually synergizes with calorie restriction in inducing tumor regression is yet to be elucidated.
Acknowledgements Conflicts of interest
There are no conflicts of interest.
References Beevers CS, Chen L, Liu L, Luo Y, Webster NJ, Huang S (2009). Curcumin disrupts the mammalian target of rapamycin-raptor complex. Cancer Res 69:1000–1008. Bruckbauer A, Zemel MB (2014). Synergistic effects of polyphenols and methylxanthines with leucine on AMPK/sirtuin-mediated metabolism in muscle cells and adipocytes. PLoS One 9:e89166. Chirumbolo S (2012). Possible role of NF-κB in hormesis during ageing. Biogerontology 13:637–646. Eto I (2011). Upstream molecular signaling pathways of p27(Kip1) expression in human breast cancer cells in vitro: differential effects of 4-hydroxytamoxifen and deficiency of either D-(+ )-glucose or L-leucine. Cancer Cell Int 11:31. Hwang JT, Kwak DW, Lin SK, Kim HM, Kim YM, Park OJ (2007). Resveratrol induces apoptosis in chemoresistant cancer cells via modulation of AMPK signaling pathway. Ann N Y Acad Sci 1095:441–448. Kauppinen A, Suuronen T, Ojala J, Kaarniranta K, Salminen A (2013). Antagonistic crosstalk between NF-κB and SIRT1 in the regulation of inflammation and metabolic disorders. Cell Signal 25:1939–1948. Kim I, He YY (2013). Targeting the AMP-activated protein kinase for cancer prevention and therapy. Front Oncol 3:175. Kim HS, Wannatung T, Lee S, Yang WK, Chung SH, Lim JS, et al. (2012). Quercetin enhances hypoxia-mediated apoptosis via direct inhibition of AMPK activity in HCT116 colon cancer. Apoptosis 17:938–949. Lee JD, Choi MA, Ro SW, Yang WI, Cho AE, Ju HL, et al. (2015). Synergic chemoprevention with dietary carbohydrate restriction and supplementation of AMPK-activating phytochemicals: the role of SIRT1. Eur J Cancer Prev [Epub ahead of print]. Liang C, Curry BJ, Brown PL, Zemel MB (2014). Leucine modulates mitochondrial biogenesis and SIRT1-AMPK signaling in C2C12 myotubes. J Nutr Metab 2014:239750. Mendivil-Perez M, Jimenez-Del-Rio M, Velez-Pardo C (2013). Glucose starvation induces apoptosis in a model of acute T leukemia dependent on caspase-3 and apoptosis-inducing factor: a therapeutic strategy. Nutr Cancer 65:99–109. Murase T, Misawa K, Haramizu S, Hase T (2009). Catechin-induced activation of the LKB1/AMP-activated protein kinase pathway. Biochem Pharmacol 78:78–84. Saito Y, Nakada D (2014). The role of the Lkb1/AMPK pathway in hematopoietic stem cells and leukemia. Crit Rev Oncog 19:383–397. Shehzad A, Lee YS (2013). Molecular mechanisms of curcumin action: signal transduction. Biofactors 39:27–36. Shukla K, Sharma AK, Ward A, Will R, Hielscher T, Balwierz A, et al. (2015). MicroRNA-30c-2–3p negatively regulates NF-κB signaling and cell cycle progression through downregulation of TRADD and CCNE1 in breast cancer. Mol Oncol [Epub ahead of print]. Widlund AL, Baur JA, Vang O (2013). mTOR: more targets of resveratrol? Expert Rev Mol Med 15:e10. Xu K, Liu P, Wei W (2014). mTOR signaling in tumorigenesis. Biochim Biophys Acta 1846:638–654.
Copyright r 2016 Wolters Kluwer Health, Inc. All rights reserved.
Letter to the Editor European Journal of Cancer Prevention 2016, 25:252–253
AMP-activated protein kinase activators, cancer regression, and survival Salvatore Chirumbolo, Laboratory of Physiopathology of Obesity, Department of Medicine, University of Verona, Verona, Italy Correspondence to Salvatore Chirumbolo, PhD, Laboratory of Physiopathology of Obesity, Department of Medicine, University of Verona, LURM Est, Policlinico GB Rossi, Piazzale AL Scuro 10, 37134 Verona, Italy Tel: + 39 045 812 8456; fax: + 39 045 802 7403; e-mail: [email protected] Received 31 March 2015 Accepted 10 April 2015
The recent paper by Lee et al. (2015) showed that isocaloric carbohydrate restriction in combination with a mixture of natural AMP-activated protein kinase (AMPK)-activating substances, such as phytochemical extracts including quercetin, curcumin, resveratrol, and catechins, produced survival benefits in mice models. Although neither simple polyphenols (MPs), lowcarbohydrate diet (LCD) or medium-carbohydrate diet (MCD) yielded significant survival trends using the Kaplan–Meier approach, intake of phytochemicals associated with calorie restriction significantly improved the survival of mice undergoing a subcutaneous injection (xenografts) of B16F10 melanoma cells (Lee et al., 2015). Phytochemicals were selected for their potential as stimulators of AMPK and actually the role of AMPK in chemoprevention has been reviewed recently as a function closely related to tumor suppression (Kim and He, 2013). Except for some reports on quercetin, which may enhance hypoxia-induced apoptosis in HCT116 colon cancer (xenograft model) by directly inhibiting AMPK (Kim et al., 2012), curcumin, catechins, and resveratrol are promising anticancer molecules via activating AMPK (Hwang et al., 2007; Beevers et al., 2009; Murase et al., 2009; Shehzad and Lee, 2013; Widlund et al., 2013; Xu et al., 2014). The critical cancer suppression mechanisms outlined by the authors included, besides the activation of AMPK/SIRT1/LKB1 signaling, the suppression of NF-κB and of the IGF1/PI3K/Akt/mTOR pathway (Lee et al., 2015). Interestingly, neither polyphenols alone nor the simple LCD elicited AMPK activation and improved survival curves, despite possible expectations, but a suggestion would come from the complex role exerted by calorie restriction and phytochemicals on these molecular systems. Yet, the synergistic activity claimed by the authors should be better studied. Resveratrol and catechins may synergize with leucine and its metabolite β-hydroxy-β-methylbutyrate to 0959-8278 Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved.
activate the AMPK/SIRT1 pathway in muscle and adipose tissue (Bruckbauer and Zemel, 2014). The role of leucine is fundamental as it exerts a direct effect on SIRT1 kinetics and modulates mitochondrial biogenesis (Liang et al., 2014), and therefore this might be a possible mechanism of AMPK activation in the condition investigated by the authors, leading to stress response and survival. However, this suggested mechanism depends on the bioavailable polyphenols dose, and in this paper, the detailed composition of flavonoids and phenolic acids in the polyphenol mixture has not been provided. Although the authors analyzed only the survival parameters in animals with xenograft tumors, the overall representation of the complex AMPK-mediated pathway involved in the reported evidence might be radically different in a tumor subjected to chemotherapy. Both the levels of carbohydrates, such as glucose, and aminoacids, such as leucine, play a major role in the regulation of some cell-cycle repressor proteins, such as p27 (Kip1). At least in breast cancer, 4-hydroxytamoxifen upregulates p27 using a molecular pathway that includes mTORC1, which, interestingly, is inhibited by curcumin (Beevers et al., 2009). Depending on the dietary intake and metabolism homeostasis, the above-reported mechanism involving AMPK for cancer may be markedly different, with apparently controversial evidence. Deficiency in D(+ )-glucose, as well as L(− )-leucine starvation, promotes the expression of p27 through a pathway involving AMPK activation and the downstream recruitment of mTORC1 (Eto, 2011). The therapeutic activity of 4-hydroxytamoxifen, at least on human MDA-MB-231 breast cancer cells in vitro, requires the activation of PI3K/Akt/mTOR, a pathway that is inhibited in the reported evidence (Lee et al., 2015). Therefore, a LCD should activate cell-cycle repressor proteins, particularly fundamental in cancer control, and moreover glucose starvation can eradicate cancer cells by apoptosis (Mendivil-Perez et al., 2013). Dietary panels used by the authors could not eradicate xenograft tumors, unless polyphenols were introduced. The activation of AMPK by flavonoids leads to the inhibition of inflammation, through NF-κB, and to a better lifespan through the activation of SIRT1, and yet polyphenols alone cannot fight tumors successfully (Lee et al., 2015). These appear as the main hallmarks of longevity and the antiaging mechanism, more than antitumoral signals, which may elucidate better survival curves observed by the authors. Flavonoids increased notably the ability of mice to respond to stressors, particularly those arising from DOI: 10.1097/CEJ.0000000000000170
Copyright r 2016 Wolters Kluwer Health, Inc. All rights reserved.
Letter to the Editor 253
oxidative stress, endoplasmic reticulum stress, mitochondria dysfunction, and inflammation. Their ability to inhibit downstream (mTOR, FOXO3) or upstream (PI3K/Akt) signals of the AMPK pathway should not match the role played by these signaling mechanisms in the activation either of cell-cycle repressors or tumor suppressors, such as p53, as the role of AMPK in cancer still remains elusive (Saito and Nakada, 2014). Particularly interesting would be a comparison of tumor size regression in MP-treated, LCD-treated, and MCDtreated mice compared with LCDmp and MCDmp (Lee et al., 2015) to better highlight the role of any dietary components in AMPK/SIRT-1-mediated survival and tumor development (cell cycle, apoptosis). For example, the deregulation (inhibition) of NF-κB in cancer, which may be performed by miRNAs, negatively regulates cellcycle progression in breast cancer (Shukla et al., 2015). The reported synergism might finally shed light on the role of NF-κB, the inhibition of which increases longevity and reduces tumor masses (Chirumbolo, 2012; Shukla et al., 2015). Furthermore, an antagonistic crosstalk between SIRT1 and NF-κB should be taken into account; a reduction in inflammation (NF-κB) correlates with an increase in longevity (SIRT1) (Kauppinen et al., 2013). The homeostatic dynamics relating stress response/survival to cancer progression is particularly puzzling and the complex activity and pleiotropism of different biochemical plant-derived molecules may hamper a full understanding of why the survival of mice increased with a synergistic association of isocaloric carbohydrate restriction and flavonoids. Which factor actually synergizes with calorie restriction in inducing tumor regression is yet to be elucidated.
Acknowledgements Conflicts of interest
There are no conflicts of interest.
References Beevers CS, Chen L, Liu L, Luo Y, Webster NJ, Huang S (2009). Curcumin disrupts the mammalian target of rapamycin-raptor complex. Cancer Res 69:1000–1008. Bruckbauer A, Zemel MB (2014). Synergistic effects of polyphenols and methylxanthines with leucine on AMPK/sirtuin-mediated metabolism in muscle cells and adipocytes. PLoS One 9:e89166. Chirumbolo S (2012). Possible role of NF-κB in hormesis during ageing. Biogerontology 13:637–646. Eto I (2011). Upstream molecular signaling pathways of p27(Kip1) expression in human breast cancer cells in vitro: differential effects of 4-hydroxytamoxifen and deficiency of either D-(+ )-glucose or L-leucine. Cancer Cell Int 11:31. Hwang JT, Kwak DW, Lin SK, Kim HM, Kim YM, Park OJ (2007). Resveratrol induces apoptosis in chemoresistant cancer cells via modulation of AMPK signaling pathway. Ann N Y Acad Sci 1095:441–448. Kauppinen A, Suuronen T, Ojala J, Kaarniranta K, Salminen A (2013). Antagonistic crosstalk between NF-κB and SIRT1 in the regulation of inflammation and metabolic disorders. Cell Signal 25:1939–1948. Kim I, He YY (2013). Targeting the AMP-activated protein kinase for cancer prevention and therapy. Front Oncol 3:175. Kim HS, Wannatung T, Lee S, Yang WK, Chung SH, Lim JS, et al. (2012). Quercetin enhances hypoxia-mediated apoptosis via direct inhibition of AMPK activity in HCT116 colon cancer. Apoptosis 17:938–949. Lee JD, Choi MA, Ro SW, Yang WI, Cho AE, Ju HL, et al. (2015). Synergic chemoprevention with dietary carbohydrate restriction and supplementation of AMPK-activating phytochemicals: the role of SIRT1. Eur J Cancer Prev [Epub ahead of print]. Liang C, Curry BJ, Brown PL, Zemel MB (2014). Leucine modulates mitochondrial biogenesis and SIRT1-AMPK signaling in C2C12 myotubes. J Nutr Metab 2014:239750. Mendivil-Perez M, Jimenez-Del-Rio M, Velez-Pardo C (2013). Glucose starvation induces apoptosis in a model of acute T leukemia dependent on caspase-3 and apoptosis-inducing factor: a therapeutic strategy. Nutr Cancer 65:99–109. Murase T, Misawa K, Haramizu S, Hase T (2009). Catechin-induced activation of the LKB1/AMP-activated protein kinase pathway. Biochem Pharmacol 78:78–84. Saito Y, Nakada D (2014). The role of the Lkb1/AMPK pathway in hematopoietic stem cells and leukemia. Crit Rev Oncog 19:383–397. Shehzad A, Lee YS (2013). Molecular mechanisms of curcumin action: signal transduction. Biofactors 39:27–36. Shukla K, Sharma AK, Ward A, Will R, Hielscher T, Balwierz A, et al. (2015). MicroRNA-30c-2–3p negatively regulates NF-κB signaling and cell cycle progression through downregulation of TRADD and CCNE1 in breast cancer. Mol Oncol [Epub ahead of print]. Widlund AL, Baur JA, Vang O (2013). mTOR: more targets of resveratrol? Expert Rev Mol Med 15:e10. Xu K, Liu P, Wei W (2014). mTOR signaling in tumorigenesis. Biochim Biophys Acta 1846:638–654.
Copyright r 2016 Wolters Kluwer Health, Inc. All rights reserved.
