Abstract 422: Cell intrinsic determinants of response to mTOR based therapy

Lung cancer is a leading cause of cancer death with estimated 135,000 deaths in 2021. Recent developments in the immunotherapy field have expanded treatment options available to lung cancer patients, with most patients now receiving checkpoint inhibitors as part of the first line therapy. However, while durable responses have been achieved in 20-30% of patients, the majority of patients inevitably progress on immunotherapy, chemo-immunotherapy or targeted therapy regiments. With five year survival at ~10% there is an urgent need for novel strategies for the treatment of lung cancer. Lung squamous cell carcinoma (LUSC) is an aggressive subtype of non-small cell lung cancer characterized by poor prognosis. LUSC are highly metabolically active, with uptake of high levels of glucose and glutamine supporting their growth and proliferation. In addition to fueling tumor cell growth, high levels of glycolysis and glutaminolysis help create unfavorable tumor microenvironment, contributing to the poor response to immunotherapy. The Cancer Genome Atlas (TCGA) revealed that LUSC have a high mutational burden but few mutations in oncogenes that can be targeted with selective inhibitors. This lack of clear genetic drivers in LUSC has resulted in a lack of targeted therapies for these patients. We have demonstrated that catalytic mTOR kinase inhibitor TAK228 inhibits glycolysis in LUSC cell lines, in xenografts, in patient derived xenografts and genetically engineered mouse models. However, despite inhibiting active mTOR pathway and lowering glucose uptake, LUSC tumors were able to maintain high levels of proliferation. Our work showed that tumors were able to adapt to prolonged treatment with TAK228 by relying on glutaminolysis. Inhibiting both mTOR and GLS, a key enzyme in glutaminolysis, resulted in reduced proliferation index and lower tumor volume. However, while combination therapy halted tumor growth, there was a lack of tumor regression. Therefore, tumors are poised to further adapt to combination therapy. Here we show that upregulation of lysosomal function supports adaptation to TAK228 therapy in LUSC by supporting macropinocytosis, a form of endocytosis that allows cancer cells to uptake extracellular fluids and further process solutes and macromolecules in lysosomes, leading to the release of amino acids inside the cytoplasm. This suggests that macropinocytosis might be a mechanism that is utilized by LUSC in order to escape mTORi therapy, where upon treatment with mTOR inhibitors, lysosomal catabolism of macropinocytosed proteins increases, allowing tumor cells to increase their proliferation.Resistance to targeted therapies is a major hurdle to achieving effective therapies in multiple cancer types. Identifying ways to overcome resistance to targeted therapies would allow for longer and more efficient therapeutic response for larger number of patients, ultimately leading to longer survival and better quality of life.

Citation Format: Milica Momcilovic, David Shackelford. Cell intrinsic determinants of response to mTOR based therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 422.

Spatial mapping of mitochondrial networks and bioenergetics in lung cancer

Mitochondria are critical to the governance of metabolism and bioenergetics in cancer cells1. The mitochondria form highly organized networks, in which their outer and inner membrane structures define their bioenergetic capacity2,3. However, in vivo studies delineating the relationship between the structural organization of mitochondrial networks and their bioenergetic activity have been limited. Here we present an in vivo structural and functional analysis of mitochondrial networks and bioenergetic phenotypes in non-small cell lung cancer (NSCLC) using an integrated platform consisting of positron emission tomography imaging, respirometry and three-dimensional scanning block-face electron microscopy. The diverse bioenergetic phenotypes and metabolic dependencies we identified in NSCLC tumours align with distinct structural organization of mitochondrial networks present. Further, we discovered that mitochondrial networks are organized into distinct compartments within tumour cells. In tumours with high rates of oxidative phosphorylation (OXPHOSHI) and fatty acid oxidation, we identified peri-droplet mitochondrial networks wherein mitochondria contact and surround lipid droplets. By contrast, we discovered that in tumours with low rates of OXPHOS (OXPHOSLO), high glucose flux regulated perinuclear localization of mitochondria, structural remodelling of cristae and mitochondrial respiratory capacity. Our findings suggest that in NSCLC, mitochondrial networks are compartmentalized into distinct subpopulations that govern the bioenergetic capacity of tumours.

Abstract 1089: Targeting amino acid uptake in lung squamous cell carcinomas to improve response to targeted therapies

Lung squamous cell carcinomas (LUSC) are a subtype of non-small cell lung cancer characterized by poor overall survival. LUSC are highly aggressive in part due to their high metabolic activity, with uptake of high levels of glucose supporting their growth and proliferation. The main driver of high rate of glycolysis in LUSC is elevated expression of glucose transporter GLUT1, whose levels and membrane localization are regulated by activated PI3K-AKT-mTOR pathway. The Cancer Genome Atlas revealed that LUSC have high tumor mutational burden with varied genetic profile that includes amplification of receptor tyrosine kinases (RTKs), PI3KCA, and a loss of PTEN. These alterations lead to increased activity of mTOR pathway, one of the major pathways in cancer cells that drives cell proliferation and metabolism. We have recently demonstrated that catalytic mTOR kinase inhibitor TAK228 (MLN128) inhibits glycolysis in LUSC cell lines in vitro, in xenografts of human LUSC lines, in patient derived xenografts (PDXs) and genetically engineered mouse models. However, despite lowered glucose uptake measured by 18F-FDG signal LUSC tumors were able to maintain high levels of proliferation. Tumors were able to adapt to prolonged treatment with TAK228 by relying on glutaminolysis. Increased glutaminolysis was due to increased uptake of glutamine as well as increased levels of glutaminase (GLS), a key enzyme that converts glutamine to glutamate. Inhibiting both mTOR (with TAK228) and GLS (with CB-839) resulted in reduced proliferation index and lower tumor volume. However, while combination therapy halted tumor growth, there was a lack of tumor regression in xenografts and PDXs of LUSC. Therefore, tumors are poised to further adapt to combination therapy through metabolism of additional amino acids beyond glutamine. Here we show that macropinocytosis, a form of endocytosis that allows cancer cells to uptake extracellular fluids and further process solutes and macromolecules in lysosomes leading to the release of amino acids inside the cytoplasm, is upregulated in LUSC tumors that are resistant to TAK228. Macropinocytosis is induced by active RTKs, PI3KCA, Ras, loss of PTEN, and active NRF2 pathway - oncogenic alterations commonly found in LUSC tumors. This suggests that macropinocytosis might be a mechanism that supports amino acid metabolism utilized by LUSC in order to escape mTOR therapy. Basal levels of macropinocytosis in LUSC appear low, however, upon treatment with mTOR inhibitors, lysosomal catabolism of macropinocytosed proteins increases, allowing tumor cells to increase their proliferation. Resistance to targeted therapies is a major hurdle to achieving effective therapies in multiple cancer types. Identifying ways to overcome resistance to targeted therapies would allow for longer therapeutic response for larger number of patients, ultimately leading to longer survival and better quality of life.

Citation Format: Milica Momcilovic, David Shackelford. Targeting amino acid uptake in lung squamous cell carcinomas to improve response to targeted therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1089.

Inhibition of glucose transport synergizes with chemical or genetic disruption of mitochondrial metabolism and suppresses TCA cycle-deficient tumors

Efforts to target glucose metabolism in cancer have been limited by the poor potency and specificity of existing anti-glycolytic agents and a poor understanding of the glucose dependence of cancer subtypes in vivo. Here, we present an extensively characterized series of potent, orally bioavailable inhibitors of the class I glucose transporters (GLUTs). The representative compound KL-11743 specifically blocks glucose metabolism, triggering an acute collapse in NADH pools and a striking accumulation of aspartate, indicating a dramatic shift toward oxidative phosphorylation in the mitochondria. Disrupting mitochondrial metabolism via chemical inhibition of electron transport, deletion of the malate-aspartate shuttle component GOT1, or endogenous mutations in tricarboxylic acid cycle enzymes, causes synthetic lethality with KL-11743. Patient-derived xenograft models of succinate dehydrogenase A (SDHA)-deficient cancers are specifically sensitive to KL-11743, providing direct evidence that TCA cycle-mutant tumors are vulnerable to GLUT inhibitors in vivo.

Abstract 2818: In vivo imaging of mitochondrial bioenergetics in lung cancer

Non-small cell lung cancer (NSCLC) is a histologically, genetically and metabolically heterogeneous disease. The mitochondria are essential regulators of cellular energy and metabolism and they play a critical role in sustaining growth and survival of lung tumor cells. However, our understanding of mitochondrial metabolism in cancer at an in vivo level has been limited thus leaving a large gap in our knowledge of how mitochondrial bioenergetics support tumor growth. To better study mitochondrial bioenergetics in lung tumors, we recently developed and validated a voltage sensitive, positron emission tomography (PET) tracer known as 4-[18F]fluorobenzyl triphenylphosphonium (18FBnTP) that we used to profile mitochondrial bioenergetics in autochthonous K-Ras driven mouse models of lung cancer (Momcilovic et al., (2019) Nature). The use of 18FBnTP PET imaging enabled us to functionally profile mitochondrial bioenergetics in live tumors and discover distinct functional mitochondrial heterogeneity conserved across different NSCLC tumor subtypes. In order to study mitochondria at the level of ultrastructure we coupled 18FBnTP PET with 3D serial block-face scanning electron microscopy (3D SBEM). By coupling these two techniques we are able to image and quantify mitochondria heterogeneity from whole tumors down to the ultrastructures of individual mitochondria within tumor cells. Our study reveals distinct organization of mitochondrial structure and function as lung tumors adapt during tumorigenesis. We anticipate that coupling 18FBnTP PET imaging with 3D SBEM will have dynamic applications beyond that of lung cancer and enrich our understanding how mitochondria impact human disease.

Citation Format: Mingqi Han, Milica Momcilovic, Eric Bushong, Linsey Stiles, Orian Shirihai, Carla Koehler, Saman Sadeghi, Mark Ellisman, David B. Shackelford. In vivo imaging of mitochondrial bioenergetics in lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2818.

Inhibition of Granulocytic Myeloid-Derived Suppressor Cells Overcomes Resistance to Immune Checkpoint Inhibition in LKB1-Deficient Non-Small Cell Lung Cancer

LKB1 inactivating mutations are commonly observed in patients with KRAS-mutant non-small cell lung cancer (NSCLC). Although treatment of NSCLC with immune checkpoint inhibitors (ICI) has resulted in improved overall survival in a subset of patients, studies have revealed that co-occurring KRAS/LKB1 mutations drive primary resistance to ICIs in NSCLC. Effective therapeutic options that overcome ICI resistance in LKB1-mutant NSCLC are limited. Here, we report that loss of LKB1 results in increased secretion of the C-X-C motif (CXC) chemokines with an NH2-terminal Glu-Leu-Arg (ELR) motif in premalignant and cancerous cells, as well as in genetically engineered murine models (GEMM) of NSCLC. Heightened levels of ELR⁺ CXC chemokines in LKB1-deficient murine models of NSCLC positively correlated with increased abundance of granulocytic myeloid-derived suppressor cells (G-MDSC) locally within the tumor microenvironment and systemically in peripheral blood and spleen. Depletion of G-MDSCs with antibody or functional inhibition via all-trans-retinoic acid (ATRA) led to enhanced antitumor T-cell responses and sensitized LKB1-deficent murine tumors to PD-1 blockade. Combination therapy with anti-PD-1 and ATRA improved local and systemic T-cell proliferation and generated tumor-specific immunity. Our findings implicate ELR⁺ CXC chemokine-mediated enrichment of G-MDSCs as a potential mediator of immunosuppression in LKB1-deficient NSCLC and provide a rationale for using ATRA in combination with anti-PD-1 therapy in patients with LKB1-deficient NSCLC refractory to ICIs. SIGNIFICANCE: These findings show that accumulation of myeloid-derived suppressor cells in LKB1-deficient non-small cell lung cancer can be overcome via treatment with all-trans-retinoic acid, sensitizing tumors to immunotherapy.

Asparagine couples mitochondrial respiration to ATF4 activity and tumor growth

Mitochondrial respiration is critical for cell proliferation. In addition to producing ATP, respiration generates biosynthetic precursors, such as aspartate, an essential substrate for nucleotide synthesis. Here, we show that in addition to depleting intracellular aspartate, electron transport chain (ETC) inhibition depletes aspartate-derived asparagine, increases ATF4 levels, and impairs mTOR complex I (mTORC1) activity. Exogenous asparagine restores proliferation, ATF4 and mTORC1 activities, and mTORC1-dependent nucleotide synthesis in the context of ETC inhibition, suggesting that asparagine communicates active respiration to ATF4 and mTORC1. Finally, we show that combination of the ETC inhibitor metformin, which limits tumor asparagine synthesis, and either asparaginase or dietary asparagine restriction, which limit tumor asparagine consumption, effectively impairs tumor growth in multiple mouse models of cancer. Because environmental asparagine is sufficient to restore tumor growth in the context of respiration impairment, our findings suggest that asparagine synthesis is a fundamental purpose of tumor mitochondrial respiration, which can be harnessed for therapeutic benefit to cancer patients.

SARS-CoV-2 infection rewires host cell metabolism and is potentially susceptible to mTORC1 inhibition

Viruses hijack host cell metabolism to acquire the building blocks required for replication. Understanding how SARS-CoV-2 alters host cell metabolism may lead to potential treatments for COVID-19. Here we profile metabolic changes conferred by SARS-CoV-2 infection in kidney epithelial cells and lung air-liquid interface (ALI) cultures, and show that SARS-CoV-2 infection increases glucose carbon entry into the TCA cycle via increased pyruvate carboxylase expression. SARS-CoV-2 also reduces oxidative glutamine metabolism while maintaining reductive carboxylation. Consistent with these changes, SARS-CoV-2 infection increases the activity of mTORC1 in cell lines and lung ALI cultures. Lastly, we show evidence of mTORC1 activation in COVID-19 patient lung tissue, and that mTORC1 inhibitors reduce viral replication in kidney epithelial cells and lung ALI cultures. Our results suggest that targeting mTORC1 may be a feasible treatment strategy for COVID-19 patients, although further studies are required to determine the mechanism of inhibition and potential efficacy in patients.

Abstract 1016: Inhibition of chemokine-induced myeloid cells potentiates the anti-PD-1 response in KRAS/LKB1 mutant non-small cell lung cancer

Dysregulated inflammation dictated by oncogene/tumor suppressor mutations can often lead to an immune suppressive tumor microenvironment (TME). Lung tumors with LKB1 mutations account for 30% of KRAS-mutant non-small cell lung cancer (NSCLC). These tumors are particularly aggressive and resistant to immunotherapy despite a high mutational burden (TMB). The mechanisms of this impaired immunogenicity remain obscure. Here, we report that LKB1 loss leads to a heightened secretion of the ELR(+) CXC chemokines, including CXCL1, CXCL2, CXCL3, CXCL5, and CXCL8, in premalignant and cancerous cells in vitro. Among multiple NSCLC cell lines, cancer cells with both KRAS and LKB1 mutations tend to express higher levels of these ELR(+) CXC chemokines. Consistently, ectopic expression of LKB1 in LKB1-null cancer cells decreases the chemokine production. In a genetically-engineered mouse model, an elevation of these chemokines is also observed in KrasG12D;Lkb1-/- (KL) tumors compared to their KrasG12D (K) or KrasG12D;Tp53-/- (KP) counterparts. Mechanistic studies reveal that the LKB1-MARK axis regulates these chemokines in the premalignant cells. Immune phenotyping of KL or KrasG12D;Tp53+/-;Lkb1-/- (KPL) tumors in vivo demonstrates significantly increased granulocytic myeloid-derived suppressor cells (G-MDSCs), which harbor high levels of reactive oxygen species (ROS). Utilizing a syngeneic murine lung cancer model with a high TMB, we demonstrate that KPL tumors have a minimal response to anti-PD-1 therapy compared to KP tumors. Therefore, we hypothesize that G-MDSCs may cause resistance to anti-PD-1 monotherapy in KPL tumors. We find that inhibition of the G-MDSCs either by depletion or by reduction of ROS can potentiate the anti-PD-1 response and subsequently eliminate the KPL tumors. Investigation of the TME reveals that G-MDSC depletion primes tumor-infiltrating lymphocytes (TILs) for activation: there is an increased percentage of TILs with high Ki67 and PD-1 expression and an increased percentage of antigen presenting cells (macrophages and dendritic cells) with high PD-L1 expression. Combination with anti-PD-1 therapy enhances the function of these TILs, evidenced by IFN-γ and TNF-α secretion. Re-challenge of these mice three months after the initial combination therapy leads to a rapid tumor rejection, suggesting a durable systemic anti-tumor immune response. In conclusion, we find that LKB1 deficiency leads to an increased ELR(+) CXC chemokine production and tumor infiltration of G-MDSCs. Inhibition of G-MDSC enhances the efficacy of anti-PD-1 blockade in LKB1-deficient tumors bearing a high TMB.

Citation Format: Rui Li, Ramin Salehi-Rad, Milica Momcilovic, Stephanie Ong, Raymond Lim, Zi Ling Huang, Linh Tran, Zhe Jing, Manash Paul, Michael Teitell, John Minna, David Shackelford, Krysan Kostyantyn, Bin Liu, Steven Dubinett. Inhibition of chemokine-induced myeloid cells potentiates the anti-PD-1 response in KRAS/LKB1 mutant non-small cell lung cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1016.

Publisher Correction: In vivo imaging of mitochondrial membrane potential in non-small-cell lung cancer

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

In vivo imaging of mitochondrial membrane potential in non-small-cell lung cancer

Mitochondria are essential regulators of cellular energy and metabolism, and have a crucial role in sustaining the growth and survival of cancer cells. A central function of mitochondria is the synthesis of ATP by oxidative phosphorylation, known as mitochondrial bioenergetics. Mitochondria maintain oxidative phosphorylation by creating a membrane potential gradient that is generated by the electron transport chain to drive the synthesis of ATP¹. Mitochondria are essential for tumour initiation and maintaining tumour cell growth in cell culture and xenografts^2,3. However, our understanding of oxidative mitochondrial metabolism in cancer is limited because most studies have been performed in vitro in cell culture models. This highlights a need for in vivo studies to better understand how oxidative metabolism supports tumour growth. Here we measure mitochondrial membrane potential in non-small-cell lung cancer in vivo using a voltage-sensitive, positron emission tomography (PET) radiotracer known as 4-[¹⁸F]fluorobenzyl-triphenylphosphonium (¹⁸F-BnTP)⁴. By using PET imaging of ¹⁸F-BnTP, we profile mitochondrial membrane potential in autochthonous mouse models of lung cancer, and find distinct functional mitochondrial heterogeneity within subtypes of lung tumours. The use of ¹⁸F-BnTP PET imaging enabled us to functionally profile mitochondrial membrane potential in live tumours.

Abstract 2710: Depletion of CXCR2-dependent myeloid-derived suppressor cells (MDSCs) overcomes anti-PD-1 resistance in a murine model of LKB1-deficient non-small cell lung cancer (NSCLC) with high mutational load

Checkpoint inhibitors such as PD-L1/PD-1 blockade have rapidly integrated into the paradigm of NSCLC treatment. However, a majority of patients do not benefit from monotherapy with checkpoint inhibitors. High tumor mutational burden (TMB), along with pre-existing intratumoral T cell infiltration and baseline high PD-L1 expression, predicts response to checkpoint blockade. Furthermore, a recent retrospective study identified LKB1 alterations as the most prevalent genomic driver of resistance to PD-1 axis inhibitors in KRAS-mutant lung adenocarcinoma. In this study, we investigate the mechanisms underlying LKB1-mediated immunosuppression in NSCLC. We show that loss of LKB1 in human bronchial epithelial cells (HBECs) and NSCLC cells leads to increased secretion of CXCR2 ligands, including CXCL1, CXCL2, CXCL3, CXCL5 and CXCL8. These CXCR2 ligands are also elevated in LKB1-deficient tumors from patient-derived xenografts and genetically-engineered murine models. We find abundant tumor infiltrating MDSCs in murine Lkb1-deficient NSCLC, consistent with the capacity for CXCR2 ligands to recruit MDSCs. MDSCs mediate potent immune suppressive activities at multiple levels including release of immunosuppressive cytokines, recruitment of regulatory T cells (Tregs), inhibition of CD8 T cell tumor infiltration and upregulation of PD-L1 expression. Although MDSC depletion activates interferon gamma signaling and decreases systemic Tregs in murine KrasK12D;Tp53-/-;Lkb1-/- (KPL) tumors, it does not sensitize KPL tumors to anti-PD-1 therapy. One of the major challenges in the preclinical assessment of lung cancer immunotherapy is that the commonly utilized murine models lack the mutational burden of human NSCLC. To assess this combination therapy in the context of a mutational burden that more accurately reflects the clinical disease, we generated tumors with high TMB by exposing KPL cells in vitroto the tobacco carcinogen N-methyl-N-nitrosourea. In the context of high TMB, MDSC depletion demonstrates remarkable anti-tumor effects in combination with anti-PD-1 therapy. Finally, we delineate the regulation of CXCR2 ligands by LKB1 which is dependent on the MARK-mediated NF-κB pathway. In conclusion, we find that LKB1 deficiency leads to increased CXCR2 ligand production and tumor infiltrating MDSCs. MDSC depletion enhances the efficacy of anti-PD-1 blockade in LKB1-deficient tumors bearing high TMB.

Citation Format: Rui Li, Ramin Salehi-Rad, Stephanie Ong, Milica Momcilovic, Bin Liu, Raymond Lim, Linh Tran, Ziling Huang, Zhe Jing, Manash Paul, Kostyantyn Krysan, Stacy Park, John Minna, Michael Teitell, David Shackelford, Steven Dubinett. Depletion of CXCR2-dependent myeloid-derived suppressor cells (MDSCs) overcomes anti-PD-1 resistance in a murine model of LKB1-deficient non-small cell lung cancer (NSCLC) with high mutational load [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2710.

Teaching an Old Drug New Tricks

In this issue of Cancer Cell, Elgendy et al. describe the use of intermittent fasting as a strategy to reduce tumor glucose levels and sensitize otherwise resistant tumor cells to metformin. The authors demonstrate that intermittent fasting before metformin treatment sensitized tumors to metformin and significantly reduced tumor growth.

Extracellular Matrix Remodeling Regulates Glucose Metabolism through TXNIP Destabilization

The metabolic state of a cell is influenced by cell-extrinsic factors, including nutrient availability and growth factor signaling. Here, we present extracellular matrix (ECM) remodeling as another fundamental node of cell-extrinsic metabolic regulation. Unbiased analysis of glycolytic drivers identified the hyaluronan-mediated motility receptor as being among the most highly correlated with glycolysis in cancer. Confirming a mechanistic link between the ECM component hyaluronan and metabolism, treatment of cells and xenografts with hyaluronidase triggers a robust increase in glycolysis. This is largely achieved through rapid receptor tyrosine kinase-mediated induction of the mRNA decay factor ZFP36, which targets TXNIP transcripts for degradation. Because TXNIP promotes internalization of the glucose transporter GLUT1, its acute decline enriches GLUT1 at the plasma membrane. Functionally, induction of glycolysis by hyaluronidase is required for concomitant acceleration of cell migration. This interconnection between ECM remodeling and metabolism is exhibited in dynamic tissue states, including tumorigenesis and embryogenesis.

Abstract B28: Targeted inhibition of EGFR and glutaminase induces metabolic crisis in EGFR-mutant lung cancer

Cancer cells exhibit increased use of nutrients, including glucose and glutamine, to support the bioenergetic and biosynthetic demands of proliferation. We tested the small-molecule inhibitor of glutaminase CB-839 in combination with erlotinib on epidermal growth factor receptor (EGFR)-mutant non-small cell lung cancer (NSCLC) as a therapeutic strategy to simultaneously impair cancer glucose and glutamine utilization and thereby suppress tumor growth. Here, we show that CB-839 cooperates with erlotinib to drive energetic stress and activate the AMP-activated protein kinase (AMPK) pathway in EGFR (del19) lung tumors. Tumor cells undergo metabolic crisis and cell death, resulting in rapid tumor regression in vivo in mouse NSCLC xenografts. Consistently, positron emission tomography (PET) imaging with 18F-fluoro-2-deoxyglucose (18F-FDG) and 11C-glutamine (11C-Gln) of xenografts indicated reduced glucose and glutamine uptake in tumors following treatment with CB-839 + erlotinib. Therefore, PET imaging with 18F-FDG and 11C-Gln tracers can be used to noninvasively measure metabolic response to CB-839 and erlotinib combination therapy.

Citation Format: Milica Momcilovic, Sean T. Bailey, Jason T. Lee, Clara Magyar, Daniel Braas, Thomas Graeber, Francesco Parlati, Susan Demo, Konstyantyn Krysan, Tonya C. Walser, Steven M. Dubinett, Saman Sadeghi, Heather R. Christofk, David B. Shackelford. Targeted inhibition of EGFR and glutaminase induces metabolic crisis in EGFR-mutant lung cancer [abstract]. In: Proceedings of the Fifth AACR-IASLC International Joint Conference: Lung Cancer Translational Science from the Bench to the Clinic; Jan 8-11, 2018; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(17_Suppl):Abstract nr B28.

Abstract PR10: Multimodality imaging of human lung squamous cell carcinoma reveals unique metabolic dependencies that are effectively targeted with metabolic-based therapies

Altered metabolism is known to commonly contribute to cancer growth, forming the conceptual basis for the development of metabolic therapies as cancer treatments. However, the specific metabolic characteristics of individual cancer types in vivo are still largely unknown, limiting the translatability of metabolic therapies in the clinic. In this study we used a multimodality imaging approach to identify metabolic dependencies in lung squamous cell carcinomas (SCC) in order to guide precise treatments with metabolic therapies. We performed in vivo metabolic profiling and molecular analysis of lung SCC using positron emission tomography (PET) imaging, liquid chromatography mass spectrometry (LC-MS), and immunohistochemistry (IHC). PET imaging lung SCC tumors with 18F-fluoro-2-deoxyglucose (18F-FDG) and 11C-Glutamine PET tracers identifed a conserved metabolic reliance on both glucose and glutamine that we confirmed with LC-MS based metabolomics and quantitative IHC. The mTOR kinase is a central regulator of growth and metabolism and is readily inhibited using allosteric and catalytic kinase inhibitors. Using the mTOR catalytic kinase inhibitor MLN128, we successfully inhibited glycolysis in lung SCC. However, lung SCC tumors were able to metabolically adapt to chronic mTOR inhibition through upregulation of glutamine metabolism. We discovered that chronic mTOR inhibition induced phosphorylation and inactivation of GSK3a/b resulting in upregulation and activation of cMYC and cJUN—both central regulators of the glutaminase (GLS) enzyme and glutaminolysis. Importantly, phospho-GSK3α/β and phospho-cJUN proteins serve as functional biomarkers that predict MLN128 resistance and upregulation of glutaminolysis. To overcome MLN128 resistance we treated lung SCC tumors with the glutaminase inhibitor CB-839. The combination of MLN128 and CB-839 effectively overcame therapy resistance in genetically engineered mouse models (GEMMs) and patient-derived xenografts (PDXs) of lung SCC. Lastly, data mining from The Lung Cancer Genome Atlas coupled to our PET imaging and IHC biomarkers analysis allowed us to construct a metabolic signature that is conserved in human lung SCC as well as a broad spectrum of hypermetabolic human tumors. These tumors include lung SCC, head and neck squamous cell carcinoma (HNSCC), osteosarcomas (OS), and triple-negative breast cancer (TNBC). Importantly, this metabolic signature is predictive of patient outcome and response to combined metabolic therapies targeting mTOR and glutaminase. We therefore propose a clinically translatable treatment strategy for lung SCC patients that is driven by PET imaging and IHC to first stratify patients by their metabolic signature, which is then used to guide the delivery of precise metabolic-based therapies that target key metabolic nodes such as mTOR and GLS.

This abstract is also being presented as Poster B11.

Citation Format: Milica Momcilovic, David B. Shackelford. Multimodality imaging of human lung squamous cell carcinoma reveals unique metabolic dependencies that are effectively targeted with metabolic-based therapies [abstract]. In: Proceedings of the Fifth AACR-IASLC International Joint Conference: Lung Cancer Translational Science from the Bench to the Clinic; Jan 8-11, 2018; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(17_Suppl):Abstract nr PR10.

Utilizing 18F-FDG PET/CT Imaging and Quantitative Histology to Measure Dynamic Changes in the Glucose Metabolism in Mouse Models of Lung Cancer

A hallmark of advanced tumors is a switch to aerobic glycolysis that is readily measured by [¹⁸F]-2-fluoro-2-deoxy-D-glucose positron emission tomography (¹⁸F-FDG PET) imaging. Co-mutations in the KRAS proto-oncogene and the LKB1 tumor suppressor gene are frequent events in lung cancer that drive hypermetabolic, glycolytic tumor growth. A critical pathway regulating the growth and metabolism of these tumors is the mechanistic target of the rapamycin (mTOR) pathway, which can be effectively targeted using selective catalytic mTOR kinase inhibitors. The mTOR inhibitor MLN0128 suppresses glycolysis in mice bearing tumors with Kras and Lkb1 co-mutations, referred to as KL mice. The therapy response in KL mice is first measured by ¹⁸F-FDG PET and computed tomography (CT) imaging before and after the delivery of MLN0128. By utilizing ¹⁸F-FDG PET/CT, researchers are able to measure dynamic changes in the glucose metabolism in genetically engineered mouse models (GEMMs) of lung cancer following a therapeutic intervention with targeted therapies. This is followed by ex vivo autoradiography and a quantitative immunohistochemical (qIHC) analysis using morphometric software. The use of qIHC enables the detection and quantification of distinct changes in the biomarker profiles following treatment as well as the characterization of distinct tumor pathologies. The coupling of PET imaging to quantitative histology is an effective strategy to identify metabolic and therapeutic responses in vivo in mouse models of disease.

The GSK3 Signaling Axis Regulates Adaptive Glutamine Metabolism in Lung Squamous Cell Carcinoma

Altered metabolism is a hallmark of cancer growth, forming the conceptual basis for development of metabolic therapies as cancer treatments. We performed in vivo metabolic profiling and molecular analysis of lung squamous cell carcinoma (SCC) to identify metabolic nodes for therapeutic targeting. Lung SCCs adapt to chronic mTOR inhibition and suppression of glycolysis through the GSK3α/β signaling pathway, which upregulates glutaminolysis. Phospho-GSK3α/β protein levels are predictive of response to single-therapy mTOR inhibition while combinatorial treatment with the glutaminase inhibitor CB-839 effectively overcomes therapy resistance. In addition, we identified a conserved metabolic signature in a broad spectrum of hypermetabolic human tumors that may be predictive of patient outcome and response to combined metabolic therapies targeting mTOR and glutaminase.

Imaging Cancer Metabolism

It is widely accepted that altered metabolism contributes to cancer growth and has been described as a hallmark of cancer. Our view and understanding of cancer metabolism has expanded at a rapid pace, however, there remains a need to study metabolic dependencies of human cancer in vivo. Recent studies have sought to utilize multi-modality imaging (MMI) techniques in order to build a more detailed and comprehensive understanding of cancer metabolism. MMI combines several in vivo techniques that can provide complementary information related to cancer metabolism. We describe several non-invasive imaging techniques that provide both anatomical and functional information related to tumor metabolism. These imaging modalities include: positron emission tomography (PET), computed tomography (CT), magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS) that uses hyperpolarized probes and optical imaging utilizing bioluminescence and quantification of light emitted. We describe how these imaging modalities can be combined with mass spectrometry and quantitative immunochemistry to obtain more complete picture of cancer metabolism. In vivo studies of tumor metabolism are emerging in the field and represent an important component to our understanding of how metabolism shapes and defines cancer initiation, progression and response to treatment. In this review we describe in vivo based studies of cancer metabolism that have taken advantage of MMI in both pre-clinical and clinical studies. MMI promises to advance our understanding of cancer metabolism in both basic research and clinical settings with the ultimate goal of improving detection, diagnosis and treatment of cancer patients.

Targeted Inhibition of EGFR and Glutaminase Induces Metabolic Crisis in EGFR Mutant Lung Cancer

Cancer cells exhibit increased use of nutrients, including glucose and glutamine, to support the bioenergetic and biosynthetic demands of proliferation. We tested the small-molecule inhibitor of glutaminase CB-839 in combination with erlotinib on epidermal growth factor receptor (EGFR) mutant non-small cell lung cancer (NSCLC) as a therapeutic strategy to simultaneously impair cancer glucose and glutamine utilization and thereby suppress tumor growth. Here, we show that CB-839 cooperates with erlotinib to drive energetic stress and activate the AMP-activated protein kinase (AMPK) pathway in EGFR (del19) lung tumors. Tumor cells undergo metabolic crisis and cell death, resulting in rapid tumor regression in vivo in mouse NSCLC xenografts. Consistently, positron emission tomography (PET) imaging with ¹⁸F-fluoro-2-deoxyglucose (¹⁸F-FDG) and ¹¹C-glutamine (¹¹C-Gln) of xenografts indicated reduced glucose and glutamine uptake in tumors following treatment with CB-839 + erlotinib. Therefore, PET imaging with ¹⁸F-FDG and ¹¹C-Gln tracers can be used to non-invasively measure metabolic response to CB-839 and erlotinib combination therapy.

Abstract 1830: Targeted inhibition of EGFR and glutaminase induces metabolic crisis in EGFR mutant lung cancer

Cancer cells exhibit increased use of nutrients including glucose and glutamine to support the bioenergetic and biosynthetic demands of proliferation. We tested CB-839, a small molecule inhibitor of glutaminase that impairs glutamine utilization, in combination with erlotinib on EGFR mutant non- small cell lung cancer (NSCLC) as a therapeutic strategy to simultaneously impair cancer glucose and glutamine utilization and thereby suppress tumor growth. Here we show that CB-839 synergizes with erlotinib to drive energetic stress and activate the AMPK pathway in EGFR (del19) lung tumors. Tumor cells undergo metabolic crisis and cell death resulting in rapid tumor regression in vivo in mouse NSCLC xenografts. Consistently, positron emission tomography (PET) imaging with 18F- fluoro-2-deoxyglucose (18F-FDG) and 11C-Glutamine (11C-Gln) of xenografts indicated reduced glucose and glutamine uptake in tumors following CB-839 + erlotinib treatment. Therefore, PET imaging with 18F-FDG and 11C-Gln can be used to non-invasively monitor tumor metabolic and therapeutic response to CB-839 and erlotinib combination therapy.

Note: This abstract was not presented at the meeting.

Citation Format: Milica Momcilovic, Sean T. Bailey, Jason T. Lee, Daniel Braas, Thomas G. Graeber, Melissa Works, Francesco Parlati, Susan Demo, Tonya C. Walser, Steven M. Dubinett, Saman Sadeghi, Heather Christofk, David B. Shackelford. Targeted inhibition of EGFR and glutaminase induces metabolic crisis in EGFR mutant lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1830. doi:10.1158/1538-7445.AM2017-1830

Dual targeting of EGFR and glutaminase in lung cancer

We have recently demonstrated that targeted inhibition of epidermal growth factor receptor (EGFR) signaling and glutaminase led to metabolic crisis in EGFR mutant lung adenocarcinomas and significant tumor regression in mouse xenograft models. Combining targeted therapies that restrict the metabolic activity and growth of tumors represents a therapeutic strategy that holds promise for clinical translation.

Heightening Energetic Stress Selectively Targets LKB1-Deficient Non-Small Cell Lung Cancers

Inactivation of the LKB1 tumor suppressor is a frequent event in non-small cell lung carcinoma (NSCLC) leading to the activation of mTOR complex 1 (mTORC1) and sensitivity to the metabolic stress inducer phenformin. In this study, we explored the combinatorial use of phenformin with the mTOR catalytic kinase inhibitor MLN0128 as a treatment strategy for NSCLC bearing comutations in the LKB1 and KRAS genes. NSCLC is a genetically and pathologically heterogeneous disease, giving rise to lung tumors of varying histologies that include adenocarcinomas and squamous cell carcinomas (SCC). We demonstrate that phenformin in combination with MLN0128 induced a significant therapeutic response in KRAS/LKB1-mutant human cell lines and genetically engineered mouse models of NSCLC that develop both adenocarcinomas and SCCs. Specifically, we found that KRAS/LKB1-mutant lung adenocarcinomas responded strongly to phenformin + MLN0128 treatment, but the response of SCCs to single or combined treatment with MLN0128 was more attenuated due to acquired resistance to mTOR inhibition through modulation of the AKT-GSK signaling axis. Combinatorial use of the mTOR inhibitor and AKT inhibitor MK2206 robustly inhibited the growth and viability of squamous lung tumors, thus providing an effective strategy to overcome resistance. Taken together, our findings define new personalized therapeutic strategies that may be rapidly translated into clinical use for the treatment of KRAS/LKB1-mutant adenocarcinomas and squamous cell tumors.

Targeting LKB1 in cancer - exposing and exploiting vulnerabilities

The LKB1 tumour suppressor is a serine/threonine kinase that functions as master regulator of cell growth, metabolism, survival and polarity. LKB1 is frequently mutated in human cancers and research spanning the last two decades have begun decoding the cellular pathways deregulated following LKB1 inactivation. This work has led to the identification of vulnerabilities present in LKB1-deficient tumour cells. Pre-clinical studies have now identified therapeutic strategies targeting this subset of tumours that promise to benefit this large patient population harbouring LKB1 mutations. Here, we review the current efforts that are underway to translate pre-clinical discovery of therapeutic strategies targeting LKB1 mutant cancers into clinical practice.

Abstract 2449: Identifying therapy responsive and resistant LKB1 mutant non-small cell lung tumor populations

The LKB1/STK11 tumor suppressor is mutationally inactivated in ∼30% of sporadic non-small cell lung cancers (NSCLC), and to date there are no agents targeting loss of LKB1 in lung cancer. LKB1 is the major upstream kinase activating the energy sensing kinase AMPK under conditions of low intracellular ATP. In cells defective for LKB1, metabolic stress is not appropriately sensed and energy homeostasis is not efficiently restored, providing an Achilles heel to target in tumors with this genetic lesion. Importantly, LKB1-deficient (LKB1-/-) NSCLC cells are unable to restore energy homeostasis in response to biguanide-induced energy stress and preferentially undergo apoptosis. As targeted therapy for LKB1 mutant tumors are needed, we explored the use of the metabolic stress agent phenformin as an anti- cancer drug to target the LKB1-/- NSCLC. Phenformin is a biguanide that has historically used to treat metabolic disease and we demonstrated that it potently induced apoptosis in LKB1-/- lung tumors and significantly prolonged survival in genetically engineered mouse models (GEMMs) of lung cancer in mice bearing tumors with mutated Kras and Lkb1 genes but not mice with compound mutations in Kras and p53. Our pre-clinical studies suggest phenformin may be used as a cancer metabolism-based prevention agent or therapeutic to selectively target LKB1-/- pulmonary epithelial cells and tumors. However, phenformin as a single agent therapy was not curative, highlighting the need to find additional therapies to prevent or target LKB1-/- lung tumors in combination with phenformin. We have previously shown LKB1 loss leads to mTORC1 hyperactivation therefore we explored the combinatorial use of phenformin with the mTOR kinase inhibitor MLN128. We tested phenformin and MLN128 together on our human and mouse models of lung cancer and demonstrated the two drugs cooperated together to enhance apoptosis and reduce proliferation. KrasG12D driven, Lkb1-/- mice develop both adenocarcinoma (ADC) and squamous cell carcinomas (SQCC). We performed 18FDG-PET and CT guided pre-clinical studies assessing phenformin + MLN128 as a combinatorial therapy in vivo using our Lkb1-/- GEMMs of NSCLC. We discovered that lung ADC were highly responsive to the combination therapy while the SQCC lung tumor populations appear highly resistant. These findings carry important clincal relevance as currently there are limited options for patients with LKB1-mutant tumors. Here we define the hypersensitivity of LKB1-/- lung ADC tumors to metabolic stress and mTOR inhibition while in parallel identifying a therapy resistant SQCC lung tumor population. These results suggest phenformin in combination with mTOR kinase inhibitors may find clinical utility to treat LKB1 mutant lung ADC.

Citation Format: Evan Abt, Milica Momcilovic, Atsuko Seki, Robert McMickle, David Stout, Michael C. Fishbein, David B. Shackelford. Identifying therapy responsive and resistant LKB1 mutant non-small cell lung tumor populations. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2449. doi:10.1158/1538-7445.AM2014-2449

Bradykinin type 2 receptor -9/-9 genotype is associated with triceps brachii muscle hypertrophy following strength training in young healthy men

Background

Bradykinin type 2 receptor (B2BRK) genotype was reported to be associated with changes in the left-ventricular mass as a response to aerobic training, as well as in the regulation of the skeletal muscle performance in both athletes and non-athletes. However, there are no reports on the effect of B2BRK 9-bp polymorphism on the response of the skeletal muscle to strength training, and our aim was to determine the relationship between the B2BRK SNP and triceps brachii functional and morphological adaptation to programmed physical activity in young adults.

Methods

In this 6-week pretest-posttest exercise intervention study, twenty nine healthy young men (21.5 ± 2.7 y, BMI 24.2 ± 3.5 kg/m²) were put on a 6-week exercise protocol using an isoacceleration dynamometer (5 times a week, 5 daily sets with 10 maximal elbow extensions, 1 minute rest between sets). Triceps brachii muscle volumes were assessed by using magnetic resonance imaging before and after the strength training. Bradykinin type 2 receptor 9 base pair polymorphism was determined for all participants.

Results

Following the elbow extensors training, an average increase in the volume of both triceps brachii was 5.4 ± 3.4% (from 929.5 ± 146.8 cm³ pre-training to 977.6 ± 140.9 cm³ after training, p<0.001). Triceps brachii volume increase was significantly larger in individuals homozygous for −9 allele compared to individuals with one or two +9 alleles (−9/-9, 8.5 ± 3.8%; vs. -9/+9 and +9/+9 combined, 4.7 ± 4.5%, p < 0.05). Mean increases in endurance strength in response to training were 48.4 ± 20.2%, but the increases were not dependent on B2BRK genotype (−9/-9, 50.2 ± 19.2%; vs. -9/+9 and +9/+9 combined, 46.8 ± 20.7%, p > 0.05).

Conclusions

We found that muscle morphological response to targeted training – hypertrophy – is related to polymorphisms of B2BRK. However, no significant influence of different B2BRK genotypes on functional muscle properties after strength training in young healthy non athletes was found. This finding could be relevant, not only in predicting individual muscle adaptation capacity to training or sarcopenia related to aging and inactivity, but also in determining new therapeutic strategies targeting genetic control of muscle function, especially for neuromuscular disorders that are characterized by progressive adverse changes in muscle quality, mass, strength and force production (e.g., muscular dystrophy, multiple sclerosis, Parkinson’s disease).

Alterations at dispersed sites cause phosphorylation and activation of SNF1 protein kinase during growth on high glucose

The SNF1/AMP-activated protein kinases are central energy regulators in eukaryotes. SNF1 of Saccharomyces cerevisiae is inhibited during growth on high levels of glucose and is activated in response to glucose depletion and other stresses. Activation entails phosphorylation of Thr(210) on the activation loop of the catalytic subunit Snf1 by Snf1-activating kinases. We have used mutational analysis to identify Snf1 residues that are important for regulation. Alteration of Tyr(106) in the αC helix or Leu(198) adjacent to the Asp-Phe-Gly motif on the activation loop relieved glucose inhibition of phosphorylation, resulting in phosphorylation of Thr(210) during growth on high levels of glucose. Substitution of Arg for Gly(53), at the N terminus of the kinase domain, increased activation on both high and low glucose. Alteration of the ubiquitin-associated domain revealed a modest autoinhibitory effect. Previous studies identified alterations of the Gal83 (β) and Snf4 (γ) subunits that relieve glucose inhibition, and we have here identified a distinct set of Gal83 residues that are required. Together, these results indicate that alterations at dispersed sites within each subunit of SNF1 cause phosphorylation of the kinase during growth on high levels of glucose. These findings suggest that the conformation of the SNF1 complex is crucial to maintenance of the inactive state during growth on high glucose and that the default state for SNF1 is one in which Thr(210) is phosphorylated and the kinase is active.

Adaptation to a high-tungsten environment: Pyrobaculum aerophilum contains an active tungsten nitrate reductase

Nitrate reductases (Nars) belong to the DMSO reductase family of molybdoenzymes. The hyperthermophilic denitrifying archaeon Pyrobaculum aerophilum exhibits nitrate reductase (Nar) activity even at WO(4)(2-) concentrations that are inhibitory to bacterial Nars. In this report, we establish that the enzyme purified from cells grown with 4.5 μM WO(4)(2-) contains W as the metal cofactor but is otherwise identical to the Mo-Nar previously purified from P. aerophilum grown at low WO(4)(2-) concentrations. W is coordinated by a bis-molybdopterin guanine dinucleotide cofactor. The W-Nar has a 2-fold lower turnover number (633 s(-1)) but the same K(m) value for nitrate (56 μM) as the Mo-Nar. Quinol reduction and nitrate oxidation experiments monitored by EPR with both pure W-Nar and mixed W- and Mo-Nar preparations suggest a monodentate ligation by the conserved Asp241 for W(V), while Asp241 acts as a bidentate ligand for Mo(V). Redox titrations of the Mo-Nar revealed a midpoint potential of 88 mV for Mo(V/IV). The E(m) for W(V/IV) of the purified W-Nar was estimated to be -8 mV. This relatively small difference in midpoint potential is consistent with comparable enzyme activities of W- and Mo-Nars. Unlike bacterial Nars, the P. aerophilum Nar contains a unique membrane anchor, NarM, with a single heme of the o(P) type (E(m) = 126 mV). In contrast to bacterial Nars, the P. aerophilum Nar faces the cell's exterior and, hence, does not contribute to the proton motive force. Formate is used as a physiological electron donor. This is the first description of an active W-containing Nar demonstrating the unique ability of hyperthermophiles to adapt to their high-WO(4)(2-) environment.

Biochemical and functional studies on the regulation of the Saccharomyces cerevisiae AMPK homolog SNF1

AMP-activated protein kinase (AMPK) is a master metabolic regulator for controlling cellular energy homeostasis. Its homolog in yeast, SNF1, is activated in response to glucose depletion and other stresses. The catalytic (alpha) subunit of AMPK/SNF1, Snf1 in yeast, contains a protein Ser/Thr kinase domain (KD), an auto-inhibitory domain (AID), and a region that mediates interactions with the two regulatory (beta and gamma) subunits. Previous studies suggested that Snf1 contains an additional segment, a regulatory sequence (RS, corresponding to residues 392-518), which may also have an important role in regulating the activity of the enzyme. The crystal structure of the heterotrimer core of Saccharomyces cerevisiae SNF1 showed interactions between a part of the RS (residues 460-498) and the gamma subunit Snf4. Here we report biochemical and functional studies on the regulation of SNF1 by the RS. GST pulldown experiments demonstrate strong and direct interactions between residues 450-500 of the RS and the heterotrimer core, and single-site mutations in the RS-Snf4 interface can greatly reduce these interactions in vitro. On the other hand, functional studies appear to show only small effects of the RS-Snf4 interactions on the activity of SNF1 in vivo. This suggests that residues 450-500 may be constitutively associated with Snf4, and the remaining segments of the RS, as well as the AID, may be involved in regulating SNF1 activity.

Roles of the glycogen-binding domain and Snf4 in glucose inhibition of SNF1 protein kinase

The SNF1/AMP-activated protein kinase (AMPK) family is required for adaptation to metabolic stress and energy homeostasis. The gamma subunit of AMPK binds AMP and ATP, and mutations that affect binding cause human disease. We have here addressed the role of the Snf4 (gamma) subunit in regulating SNF1 protein kinase in response to glucose availability in Saccharomyces cerevisiae. Previous studies of mutant cells lacking Snf4 suggested that Snf4 counteracts autoinhibition by the C-terminal sequence of the Snf1 catalytic subunit but is dispensable for glucose regulation, and AMP does not activate SNF1 in vitro. We first introduced substitutions at sites that, in AMPK, contribute to nucleotide binding and regulation. Mutations at several sites relieved glucose inhibition of SNF1, as judged by catalytic activity, phosphorylation of the activation-loop Thr-210, and growth assays, although analogs of the severe human mutations R531G/Q had little effect. We further showed that alterations of Snf4 residues that interact with the glycogen-binding domain (GBD) of the beta subunit strongly relieved glucose inhibition. Finally, substitutions in the GBD of the Gal83 beta subunit that are predicted to disrupt interactions with Snf4 and also complete deletion of the GBD similarly relieved glucose inhibition of SNF1. Analysis of mutant cells lacking glycogen synthase showed that regulation of SNF1 is normal in the absence of glycogen. These findings reveal novel roles for Snf4 and the GBD in regulation of SNF1.

Interleukin-17 stimulates inducible nitric oxide synthase-dependent toxicity in mouse beta cells

The influence of the proinflammatory cytokine interleukin (IL)-17 on inducible nitric oxide (NO) synthase (iNOS)-mediated NO release was investigated in the mouse insulinoma cell line MIN6 and mouse pancreatic islets. IL-17 markedly augmented iNOS mRNA/protein expression and subsequent NO production induced in MIN6 cells or pancreatic islets by different combinations of interferon-gamma, tumor necrosis factor-alpha, and IL-1beta. The induction of iNOS by IL-17 was preceded by phosphorylation of p38 mitogen-activated protein kinase (MAPK), and inhibition of p38 MAPK activation completely abolished IL-17-stimulated NO release. IL-17 enhanced the NO-dependent toxicity of proinflammatory cytokines toward MIN6 cells, while IL-17-specific neutralizing antibody partially reduced the NO production and rescued insulinoma cells and pancreatic islets from NO-dependent damage induced by activated T cells. Finally, a significant increase in blood IL-17 levels was observed in a multiple low-dose streptozotocin model of diabetes, suggesting that T cell-derived IL-17 might be involved in NO-dependent damage of beta cells in this disease.

Mammalian TAK1 activates Snf1 protein kinase in yeast and phosphorylates AMP-activated protein kinase in vitro

The Snf1/AMP-activated protein kinase (AMPK) family is important for metabolic regulation and is highly conserved from yeast to mammals. The upstream kinases are also functionally conserved, and the AMPK kinases LKB1 and Ca2+/calmodulin-dependent protein kinase kinase activate Snf1 in mutant yeast cells lacking the native Snf1-activating kinases, Sak1, Tos3, and Elm1. Here, we exploited the yeast genetic system to identify members of the mammalian AMPK kinase family by their function as Snf1-activating kinases. A mouse embryo cDNA library in a yeast expression vector was used to transform sak1Delta tos3Delta elm1Delta yeast cells. Selection for a Snf+ growth phenotype yielded cDNA plasmids expressing LKB1, Ca2+/calmodulin-dependent protein kinase kinase, and transforming growth factor-beta-activated kinase (TAK1), a member of the mitogen-activated protein kinase kinase kinase family. We present genetic and biochemical evidence that TAK1 activates Snf1 protein kinase in vivo and in vitro. We further show that recombinant TAK1, fused to the activation domain of its binding partner TAB1, phosphorylates Thr-172 in the activation loop of the AMPK catalytic domain. Finally, expression of TAK1 and TAB1 in HeLa cells or treatment of cells with cytokines stimulated phosphorylation of Thr-172 of AMPK. These findings indicate that TAK1 is a functional member of the Snf1/AMPK kinase family and support TAK1 as a candidate for an authentic AMPK kinase in mammalian cells.

Ca2+/calmodulin-dependent protein kinase kinase-beta acts upstream of AMP-activated protein kinase in mammalian cells

AMP-activated protein kinase (AMPK) is the downstream component of a kinase cascade that plays a pivotal role in energy homeostasis. Activation of AMPK requires phosphorylation of threonine 172 (T172) within the T loop region of the catalytic alpha subunit. Recently, LKB1 was shown to activate AMPK. Here we show that AMPK is also activated by Ca(2+)/calmodulin-dependent protein kinase kinase (CaMKK). Overexpression of CaMKKbeta in mammalian cells increases AMPK activity, whereas pharmacological inhibition of CaMKK, or downregulation of CaMKKbeta using RNA interference, almost completely abolishes AMPK activation. CaMKKbeta isolated from rat brain or expressed in E. coli phosphorylates and activates AMPK in vitro. In yeast, CaMKKbeta expression rescues a mutant strain lacking the three kinases upstream of Snf1, the yeast homolog of AMPK. These results demonstrate that AMPK is regulated by at least two upstream kinases and suggest that AMPK may play a role in Ca(2+)-mediated signal transduction pathways.

Function of Mammalian LKB1 and Ca2+/Calmodulin-dependent Protein Kinase Kinase α as Snf1-activating Kinases in Yeast

The Snf1/AMP-activated protein kinase (AMPK) family is important for metabolic regulation in response to stress. In the yeast Saccharomyces cerevisiae, the Snf1 kinase cascade comprises three Snf1-activating kinases, Pak1, Tos3, and Elm1. The only established mammalian AMPK kinase is LKB1. We show that LKB1 functions heterologously in yeast. In pak1Delta tos3Delta elm1Delta cells, LKB1 activated Snf1 catalytic activity and conferred a Snf(+) growth phenotype. Coexpression of STRADalpha and MO25alpha, which form a complex with LKB1, enhanced LKB1 function. Thus, the Snf1/AMPK kinase cascade is functionally conserved between yeast and mammals. Ca(2+)/calmodulin-dependent kinase kinase (CaMKK) shows more sequence similarity to Pak1, Tos3, and Elm1 than does LKB1. When expressed in pak1Delta tos3Delta elm1Delta cells, CaMKKalpha activated Snf1 catalytic activity, restored the Snf(+) phenotype, and also phosphorylated the activation loop threonine of Snf1 in vitro. These findings indicate that CaMKKalpha is a functional member of the Snf1/AMPK kinase family and support CaMKKalpha as a likely candidate for an AMPK kinase in mammalian cells. Analysis of the function of these heterologous kinases in yeast provided insight into the regulation of Snf1. When activated by LKB1 or CaMKKalpha, Snf1 activity was significantly inhibited by glucose, suggesting that a mechanism independent of the activating kinases can mediate glucose signaling in yeast. Finally, this analysis provided evidence that Pak1 functions in another capacity, besides activating Snf1, to regulate the nuclear enrichment of Snf1 protein kinase in response to carbon stress.

Aloe-emodin prevents cytokine-induced tumor cell death: the inhibition of auto-toxic nitric oxide release as a potential mechanism

Aloe-emodin (AE) is a plant-derived hydroxyanthraquinone with potential anticancer activity. We investigated the ability of AE to modulate survival of mouse L929 fibrosarcoma and rat C6 astrocytoma cells through interference with the activation of inducible nitric oxide (NO) synthase (NOS) and subsequent production of tumoricidal free radical NO. Somewhat surprisingly, AE in a dose-dependent manner rescued interferon-gamma + interleukin-1-stimulated L929 cells from NO-dependent killing by reducing their autotoxic NO release. The observed protective effect was less pronounced in C6 cells, due to their higher sensitivity to a direct toxic action of the drug. AE-mediated inhibition of tumor cell NO release coincided with a reduction in cytokine-induced accumulation of transcription and translation products of genes encoding inducible NOS and its transcription factor IRF-1, while activation of NF-kappaB remained unaltered. These data indicate that the influence of AE on tumor growth might be more complex that previously recognized, the net effect being determined by the balance between the two opposing actions of the drug: its capacity to directly kill tumor cells, but also to protect them from NO-mediated toxicity.