AUTHOR'S VIEW Molecular & Cellular Oncology 3:2, e1008307; March 2016; © 2016 Taylor & Francis Group, LLC
Vascular endothelial growth factor blockade elicits a stable metabolic shift in tumor cells: therapeutic implications Stefano Indraccolo* Immunology and Molecular Oncology Unit; Istituto Oncologico Veneto-IRCCS; Padova, Italy
Keywords: cancer, metabolism, antiangiogenic therapy, VEGF, glycolysis
The metabolism of tumors differs remarkably from that of normal tissues, but whether this is a stable feature of tumor cells is largely unknown. Recent findings by independent teams indicate that antiangiogenic drugs cause a metabolic shift in tumor cells that is associated with increased malignancy. These results suggest therapy-driven evolutionary dynamics of tumor metabolism that could be therapeutically targeted.
Malignant growths are endowed with distinct metabolic features that distinguish them from the normal cells of the tissue they arise from. Major metabolic alterations in tumors include enhanced glucose uptake and lactate production, increased glutamine utilization and de novo fatty acid synthesis, and aberrant choline and serine metabolism.1 Tumor heterogeneity at the genetic level has been illustrated by a multitude of studies on the genomics of cancer, but whether tumors can also be heterogeneous at the metabolic level (including both intertumor and intratumor heterogeneity) is an issue that has not received much attention to date. An intriguing related question is whether the metabolic features of tumors are stable or can change following either natural tumor progression (i.e., in primary tumors versus metastasis) or therapeutic interventions. In our recent paper, we reported that vascular endothelial growth factor (VEGF)-targeted therapy of experimental tumors using the monoclonal anti-VEGF antibody bevacizumab is associated with selection of stable metabolic changes in tumor cells that involve their glycolytic phenotype.2 This key finding was supported by a variety of metabolic studies using various techniques, but was probably best shown by results of metabolic flux analysis performed with ex vivo cultures established from bevacizumab-treated
tumors. Previously, other groups noticed increased expression of glycolysis-associated markers in tumors treated with antiangiogenic therapy,3 but this metabolic change was attributed to the hypoxic tumor microenvironment and resulting accumulation of hypoxia inducible factor 1a (HIF-1a), a powerful transcriptional factor that coordinates metabolic adaptation to hypoxia. Similar metabolic changes were recently reported by other groups. Fack et al. uncovered adaptation toward anaerobic metabolism following bevacizumab administration in glioblastomas,4 whereas Hudson et al. found that resistance to the antiangiogenic tyrosine kinase inhibitor (TKI) axitinib is associated with increased glucose metabolism in pancreatic adenocarcinoma.5 Moreover, Sounni et al. provided evidence for a metabolic shift toward carbohydrate metabolism in tumors treated with the antiangiogenic TKIs sunitinib and sorafenib, followed by increased lipid synthesis upon treatment withdrawal.6 In line with these results, Bensaad et al. found that fatty acid uptake is upregulated by bevacizumab treatment in a HIF-1a–dependent manner, leading to lipid droplet accumulation in hypoxic conditions followed by increased b-oxidation when reoxygenation occurs.7 Together, these findings indicate that antiangiogenic drugs—including bevacizumab
and TKIs—can cause dramatic changes in tumor metabolism. It remains to be established whether some of the reported changes in lipid metabolism are stable, or whether they are transient and associated with intermittent hypoxia. In future studies it will be important to investigate whether anti-VEGF therapy causes perturbations in other metabolites, including amino acids (especially glutamine and serine), oxidative stress-related metabolites, and acetyl-coenzyme A, levels of which decrease rapidly in cells and organs subjected to starvation leading to the deacetylation of cellular proteins and stimulation of autophagy.8 As many metabolic processes are regulated at the post-transcriptional level, it might be appropriate to interrogate tumor samples at the protein level, for example by exploiting primary antibodies specific for key regulators of the various metabolic processes. This metabolic panel could also be used for investigation of clinical samples, provided that pre- and post-therapy samples are available for immunohistochemistry studies. A more comprehensive understanding of metabolic perturbations caused by antiangiogenic drugs in tumors might represent a first step toward improvement of therapeutic efficacy. In the long term, stable metabolic changes caused by antiVEGF therapy could indeed represent an
*Correspondence to: Stefano Indraccolo; Email: [email protected] Submitted: 01/09/2015; Revised: 01/12/2015; Accepted: 01/13/2015 http://dx.doi.org/10.1080/23723556.2015.1008307
www.tandfonline.com
Molecular & Cellular Oncology
e1008307-1
opportunity for new metabolism-targeting drugs. In this regard, our studies2,9 showed that tumor xenografts formed by different tumor cell lines have marked metabolic differences, which would likely confer limited therapeutic response to glycolysis inhibitors. In contrast, after antiangiogenic therapy tumors become homogeneously highly glycolytic, which might render them more responsive to glycolysis-targeting drugs. In a related study, Sounni et al. demonstrated that breast tumors treated with VEGF blockers undergo a metabolic shift involving increased lipid synthesis and have improved response to the lipogenesis inhibitor orlistat.6 These observations suggest that sequential combination of antiangiogenic drugs and certain metabolismtargeting drugs might represent a new therapeutic concept (Fig. 1), although the plasticity of tumor metabolism could also enable rapid adaptations to these new drugs. Because bevacizumab is usually combined with chemotherapy, an intriguing question is whether the metabolic shift
described by Curtarello et al. has any effects on the response of tumors to chemotherapy. So far there is only scattered information in the literature about the relationship between glycolytic metabolism and response to chemotherapy, mainly relying on in vitro studies suggesting that upregulated glycolysis confers resistance to certain drugs.10 Moreover, some consequences of an increased Warburg effect, including acidification of the tumor microenvironment, could modify the therapeutic activity of certain pHdependent cytotoxic drugs such as doxorubicin. Intriguingly, clinical studies have shown that anti-VEGF therapy with bevacizumab and other antiangiogenic drugs prolongs progression-free survival with less clear effects on overall survival, which indirectly suggests that once resistance to anti-VEGF therapy arises the tumor becomes aggressive and resistant to any subsequent line of chemotherapy. In preclinical studies, we also observed a more aggressive behavior of secondary tumors established from bevacizumab-treated
tumors compared with control tumors,2 but we did not investigate response to chemotherapy. Clearly, additional experimental work is required to fully elucidate the connections between the Warburg effect, aggressive tumor behavior, and resistance to chemotherapy. Finally, the mechanism behind this metabolic shift remains largely unexplored. Based on our findings, Darwinian selection of highly glycolytic cells seems to occur. This would imply the presence of tumor cells that have heterogeneous metabolic features prior to treatment, but this has not been formally demonstrated so far. On the other hand, in the study by Fack et al. metabolic adaptation of glioblastoma cells to bevacizumab was not mediated by clonal selection mechanisms, but rather represented an adaptive response to therapy.4 However, the identity of these epigenetic changes remains unidentified. In conclusion, the observations by Curtarello et al.,2 together with those of other groups,4,6,7 revealed for the first time that the metabolic phenotype of tumors can be shaped by antiangiogenic therapy, thus stimulating the search for the underlying mechanisms and prompting validation in clinical samples. Disclosure of Potential Conflicts of Interest
No potential conflicts of interest were disclosed. Funding
SI’s work is supported by grant IG14295 from AIRC. References
Figure 1. Antiangiogenic therapy and response to metabolism-targeted drugs. (A, B) As a result of intra- and intertumor metabolic heterogeneity, tumors show variable responses to drugs that block one specific metabolic pathway, such as glycolysis or lipid synthesis. (C) Metabolic evolution associated with antiangiogenic therapy is predicted to sensitize tumors to drugs targeting dysregulated metabolic pathways. In this diagram, the pink area indicates necrosis; gray and blue circles represent tumor cells with different metabolic phenotypes; and the red segments represent blood vessels. Metabolism-targeted therapy would selectively kill some tumor cells (blue circles).
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Molecular & Cellular Oncology
1. Dang CV. Links between metabolism and cancer. Genes Dev 2012; 26: 877-90; PMID:22549953; http://dx.doi.org/10.1101/gad.189365.112 2. Curtarello M, Zulato E, Nardo G, Valtorta S, Guzzo G, R Rossi E, Esposito G, Msaki A, Past A, Rasola A, et al. VEGF-Targeted Therapy Stably Modulates the Glycolytic Phenotype of Tumor Cells. Cancer Res 2015; 75: 120-33; PMID:25381153 3. Keunen O, Johansson M, Oudin A, Sanzey M, Rahim SA, Fack F, Thorsen F, Taxt T, Bartos M, Jirik R, et al. Anti-VEGF treatment reduces blood supply and increases tumor cell invasion in glioblastoma. Proc Natl Acad Sci USA 2011; 108: 3749-54; PMID:21321221; http://dx.doi.org/10.1073/pnas.1014480108 4. Fack F, Espedal H, Keunen O, Golebiewska A, Obad N, Harter PN, Mittelbronn M, B€ahr O, Weyerbrock A, Stuhr L, et al. Bevacizumab treatment induces metabolic adaptation toward anaerobic metabolism in
Volume 3 Issue 2
glioblastomas. Acta Neuropathol 2015; 129: 115-31; PMID:25322816; http://dx.doi.org/10.1007/s00401014-1352-5 5. Hudson CD, Hagemann T, Mather SJ, Avril N. Resistance to the tyrosine kinase inhibitor axitinib is associated with increased glucose metabolism in pancreatic adenocarcinoma. Cell Death Dis 2014; 5: e1160; PMID:24722285; http://dx.doi.org/10.1038/cddis. 2014.125 6. Sounni NE, Cimino J, Blacher S, Primac I, Truong A, Mazzucchelli G, Paye A, Calligaris D, Debois D, De Tullio P, et al. Blocking lipid synthesis overcomes tumor regrowth and metastasis after antiangiogenic therapy withdrawal. Cell Metab 2014; 20: 280-94;
www.tandfonline.com
PMID:25017943; http://dx.doi.org/10.1016/j.cmet. 2014.05.022 7. Bensaad K, Favaro E, Lewis CA, Peck B, Lord S, Collins JM, Pinnick KE, Wigfield S, Buffa FM, Li JL, et al. Fatty acid uptake and lipid storage induced by HIF1alpha contribute to cell growth and survival after hypoxia-reoxygenation. Cell Rep 2014; 9:349-65; PMID:25263561; http://dx.doi.org/10.1016/j.celrep. 2014.08.056 8. Marino G, Pietrocola F, Eisenberg T, Kong Y, Malik SA, Andryushkova A, Schroeder S, Pendl T, Harger A, Niso-Santano M, et al. Regulation of autophagy by cytosolic acetyl-coenzyme A. Mol Cell 2014; 53: 710-
Molecular & Cellular Oncology
25; PMID:24560926; http://dx.doi.org/10.1016/j. molcel.2014.01.016 9. Nardo G, Favaro E, Curtarello M, Moserle L, Zulato E, Persano L, Rossi E, Esposito G, Crescenzi M, Casanovas O, et al. Glycolytic phenotype and AMP kinase modify the pathologic response of tumor xenografts to VEGF neutralization. Cancer Res 2011; 71: 4214-25; PMID:21546569; http://dx.doi.org/10.1158/00085472.CAN-11-0242 10. Butler EB, Zhao Y, Munoz-Pinedo C, Lu J, Tan M. Stalling the engine of resistance: targeting cancer metabolism to overcome therapeutic resistance. Cancer Res 2013; 73: 2709-17; PMID:23610447; http://dx.doi. org/10.1158/0008-5472.CAN-12-3009
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Vascular endothelial growth factor blockade elicits a stable metabolic shift in tumor cells: therapeutic implications Stefano Indraccolo* Immunology and Molecular Oncology Unit; Istituto Oncologico Veneto-IRCCS; Padova, Italy
Keywords: cancer, metabolism, antiangiogenic therapy, VEGF, glycolysis
The metabolism of tumors differs remarkably from that of normal tissues, but whether this is a stable feature of tumor cells is largely unknown. Recent findings by independent teams indicate that antiangiogenic drugs cause a metabolic shift in tumor cells that is associated with increased malignancy. These results suggest therapy-driven evolutionary dynamics of tumor metabolism that could be therapeutically targeted.
Malignant growths are endowed with distinct metabolic features that distinguish them from the normal cells of the tissue they arise from. Major metabolic alterations in tumors include enhanced glucose uptake and lactate production, increased glutamine utilization and de novo fatty acid synthesis, and aberrant choline and serine metabolism.1 Tumor heterogeneity at the genetic level has been illustrated by a multitude of studies on the genomics of cancer, but whether tumors can also be heterogeneous at the metabolic level (including both intertumor and intratumor heterogeneity) is an issue that has not received much attention to date. An intriguing related question is whether the metabolic features of tumors are stable or can change following either natural tumor progression (i.e., in primary tumors versus metastasis) or therapeutic interventions. In our recent paper, we reported that vascular endothelial growth factor (VEGF)-targeted therapy of experimental tumors using the monoclonal anti-VEGF antibody bevacizumab is associated with selection of stable metabolic changes in tumor cells that involve their glycolytic phenotype.2 This key finding was supported by a variety of metabolic studies using various techniques, but was probably best shown by results of metabolic flux analysis performed with ex vivo cultures established from bevacizumab-treated
tumors. Previously, other groups noticed increased expression of glycolysis-associated markers in tumors treated with antiangiogenic therapy,3 but this metabolic change was attributed to the hypoxic tumor microenvironment and resulting accumulation of hypoxia inducible factor 1a (HIF-1a), a powerful transcriptional factor that coordinates metabolic adaptation to hypoxia. Similar metabolic changes were recently reported by other groups. Fack et al. uncovered adaptation toward anaerobic metabolism following bevacizumab administration in glioblastomas,4 whereas Hudson et al. found that resistance to the antiangiogenic tyrosine kinase inhibitor (TKI) axitinib is associated with increased glucose metabolism in pancreatic adenocarcinoma.5 Moreover, Sounni et al. provided evidence for a metabolic shift toward carbohydrate metabolism in tumors treated with the antiangiogenic TKIs sunitinib and sorafenib, followed by increased lipid synthesis upon treatment withdrawal.6 In line with these results, Bensaad et al. found that fatty acid uptake is upregulated by bevacizumab treatment in a HIF-1a–dependent manner, leading to lipid droplet accumulation in hypoxic conditions followed by increased b-oxidation when reoxygenation occurs.7 Together, these findings indicate that antiangiogenic drugs—including bevacizumab
and TKIs—can cause dramatic changes in tumor metabolism. It remains to be established whether some of the reported changes in lipid metabolism are stable, or whether they are transient and associated with intermittent hypoxia. In future studies it will be important to investigate whether anti-VEGF therapy causes perturbations in other metabolites, including amino acids (especially glutamine and serine), oxidative stress-related metabolites, and acetyl-coenzyme A, levels of which decrease rapidly in cells and organs subjected to starvation leading to the deacetylation of cellular proteins and stimulation of autophagy.8 As many metabolic processes are regulated at the post-transcriptional level, it might be appropriate to interrogate tumor samples at the protein level, for example by exploiting primary antibodies specific for key regulators of the various metabolic processes. This metabolic panel could also be used for investigation of clinical samples, provided that pre- and post-therapy samples are available for immunohistochemistry studies. A more comprehensive understanding of metabolic perturbations caused by antiangiogenic drugs in tumors might represent a first step toward improvement of therapeutic efficacy. In the long term, stable metabolic changes caused by antiVEGF therapy could indeed represent an
*Correspondence to: Stefano Indraccolo; Email: [email protected] Submitted: 01/09/2015; Revised: 01/12/2015; Accepted: 01/13/2015 http://dx.doi.org/10.1080/23723556.2015.1008307
www.tandfonline.com
Molecular & Cellular Oncology
e1008307-1
opportunity for new metabolism-targeting drugs. In this regard, our studies2,9 showed that tumor xenografts formed by different tumor cell lines have marked metabolic differences, which would likely confer limited therapeutic response to glycolysis inhibitors. In contrast, after antiangiogenic therapy tumors become homogeneously highly glycolytic, which might render them more responsive to glycolysis-targeting drugs. In a related study, Sounni et al. demonstrated that breast tumors treated with VEGF blockers undergo a metabolic shift involving increased lipid synthesis and have improved response to the lipogenesis inhibitor orlistat.6 These observations suggest that sequential combination of antiangiogenic drugs and certain metabolismtargeting drugs might represent a new therapeutic concept (Fig. 1), although the plasticity of tumor metabolism could also enable rapid adaptations to these new drugs. Because bevacizumab is usually combined with chemotherapy, an intriguing question is whether the metabolic shift
described by Curtarello et al. has any effects on the response of tumors to chemotherapy. So far there is only scattered information in the literature about the relationship between glycolytic metabolism and response to chemotherapy, mainly relying on in vitro studies suggesting that upregulated glycolysis confers resistance to certain drugs.10 Moreover, some consequences of an increased Warburg effect, including acidification of the tumor microenvironment, could modify the therapeutic activity of certain pHdependent cytotoxic drugs such as doxorubicin. Intriguingly, clinical studies have shown that anti-VEGF therapy with bevacizumab and other antiangiogenic drugs prolongs progression-free survival with less clear effects on overall survival, which indirectly suggests that once resistance to anti-VEGF therapy arises the tumor becomes aggressive and resistant to any subsequent line of chemotherapy. In preclinical studies, we also observed a more aggressive behavior of secondary tumors established from bevacizumab-treated
tumors compared with control tumors,2 but we did not investigate response to chemotherapy. Clearly, additional experimental work is required to fully elucidate the connections between the Warburg effect, aggressive tumor behavior, and resistance to chemotherapy. Finally, the mechanism behind this metabolic shift remains largely unexplored. Based on our findings, Darwinian selection of highly glycolytic cells seems to occur. This would imply the presence of tumor cells that have heterogeneous metabolic features prior to treatment, but this has not been formally demonstrated so far. On the other hand, in the study by Fack et al. metabolic adaptation of glioblastoma cells to bevacizumab was not mediated by clonal selection mechanisms, but rather represented an adaptive response to therapy.4 However, the identity of these epigenetic changes remains unidentified. In conclusion, the observations by Curtarello et al.,2 together with those of other groups,4,6,7 revealed for the first time that the metabolic phenotype of tumors can be shaped by antiangiogenic therapy, thus stimulating the search for the underlying mechanisms and prompting validation in clinical samples. Disclosure of Potential Conflicts of Interest
No potential conflicts of interest were disclosed. Funding
SI’s work is supported by grant IG14295 from AIRC. References
Figure 1. Antiangiogenic therapy and response to metabolism-targeted drugs. (A, B) As a result of intra- and intertumor metabolic heterogeneity, tumors show variable responses to drugs that block one specific metabolic pathway, such as glycolysis or lipid synthesis. (C) Metabolic evolution associated with antiangiogenic therapy is predicted to sensitize tumors to drugs targeting dysregulated metabolic pathways. In this diagram, the pink area indicates necrosis; gray and blue circles represent tumor cells with different metabolic phenotypes; and the red segments represent blood vessels. Metabolism-targeted therapy would selectively kill some tumor cells (blue circles).
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Molecular & Cellular Oncology
1. Dang CV. Links between metabolism and cancer. Genes Dev 2012; 26: 877-90; PMID:22549953; http://dx.doi.org/10.1101/gad.189365.112 2. Curtarello M, Zulato E, Nardo G, Valtorta S, Guzzo G, R Rossi E, Esposito G, Msaki A, Past A, Rasola A, et al. VEGF-Targeted Therapy Stably Modulates the Glycolytic Phenotype of Tumor Cells. Cancer Res 2015; 75: 120-33; PMID:25381153 3. Keunen O, Johansson M, Oudin A, Sanzey M, Rahim SA, Fack F, Thorsen F, Taxt T, Bartos M, Jirik R, et al. Anti-VEGF treatment reduces blood supply and increases tumor cell invasion in glioblastoma. Proc Natl Acad Sci USA 2011; 108: 3749-54; PMID:21321221; http://dx.doi.org/10.1073/pnas.1014480108 4. Fack F, Espedal H, Keunen O, Golebiewska A, Obad N, Harter PN, Mittelbronn M, B€ahr O, Weyerbrock A, Stuhr L, et al. Bevacizumab treatment induces metabolic adaptation toward anaerobic metabolism in
Volume 3 Issue 2
glioblastomas. Acta Neuropathol 2015; 129: 115-31; PMID:25322816; http://dx.doi.org/10.1007/s00401014-1352-5 5. Hudson CD, Hagemann T, Mather SJ, Avril N. Resistance to the tyrosine kinase inhibitor axitinib is associated with increased glucose metabolism in pancreatic adenocarcinoma. Cell Death Dis 2014; 5: e1160; PMID:24722285; http://dx.doi.org/10.1038/cddis. 2014.125 6. Sounni NE, Cimino J, Blacher S, Primac I, Truong A, Mazzucchelli G, Paye A, Calligaris D, Debois D, De Tullio P, et al. Blocking lipid synthesis overcomes tumor regrowth and metastasis after antiangiogenic therapy withdrawal. Cell Metab 2014; 20: 280-94;
www.tandfonline.com
PMID:25017943; http://dx.doi.org/10.1016/j.cmet. 2014.05.022 7. Bensaad K, Favaro E, Lewis CA, Peck B, Lord S, Collins JM, Pinnick KE, Wigfield S, Buffa FM, Li JL, et al. Fatty acid uptake and lipid storage induced by HIF1alpha contribute to cell growth and survival after hypoxia-reoxygenation. Cell Rep 2014; 9:349-65; PMID:25263561; http://dx.doi.org/10.1016/j.celrep. 2014.08.056 8. Marino G, Pietrocola F, Eisenberg T, Kong Y, Malik SA, Andryushkova A, Schroeder S, Pendl T, Harger A, Niso-Santano M, et al. Regulation of autophagy by cytosolic acetyl-coenzyme A. Mol Cell 2014; 53: 710-
Molecular & Cellular Oncology
25; PMID:24560926; http://dx.doi.org/10.1016/j. molcel.2014.01.016 9. Nardo G, Favaro E, Curtarello M, Moserle L, Zulato E, Persano L, Rossi E, Esposito G, Crescenzi M, Casanovas O, et al. Glycolytic phenotype and AMP kinase modify the pathologic response of tumor xenografts to VEGF neutralization. Cancer Res 2011; 71: 4214-25; PMID:21546569; http://dx.doi.org/10.1158/00085472.CAN-11-0242 10. Butler EB, Zhao Y, Munoz-Pinedo C, Lu J, Tan M. Stalling the engine of resistance: targeting cancer metabolism to overcome therapeutic resistance. Cancer Res 2013; 73: 2709-17; PMID:23610447; http://dx.doi. org/10.1158/0008-5472.CAN-12-3009
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