Malignant tumors can evade destruction by the immune system by attracting immune-suppressive regulatory T cells (Treg) cells. The IKZF2 (Helios) transcription factor plays a crucial role in maintaining function and stability of Treg cells, and IKZF2 deficiency reduces tumor growth in mice. Here we report the discovery of NVP-DKY709, a selective molecular glue degrader of IKZF2 that spares IKZF1/3. We describe the recruitment-guided medicinal chemistry campaign leading to NVP-DKY709 that redirected the degradation selectivity of cereblon (CRBN) binders from IKZF1 toward IKZF2. Selectivity of NVP-DKY709 for IKZF2 was rationalized by analyzing the DDB1:CRBN:NVP-DKY709:IKZF2(ZF2 or ZF2-3) ternary complex X-ray structures. Exposure to NVP-DKY709 reduced the suppressive activity of human Treg cells and rescued cytokine production in exhausted T-effector cells. In vivo, treatment with NVP-DKY709 delayed tumor growth in mice with a humanized immune system and enhanced immunization responses in cynomolgus monkeys. NVP-DKY709 is being investigated in the clinic as an immune-enhancing agent for cancer immunotherapy.

Figure 1: Oxygen consumption rate of prostate cancer cell lines with different concentrations of metformin. Error bars depict the standard deviation. Standard deviation and p-values are calculated from three biological replicates. Figure 2: Glucose (upper panel) and reductive glutamine (lower panel) contribution to fatty acids in prostate cancer cell lines treated with metformin fitted from the measured incorporation of U-13C labeled glucose or 5-13C labeled glutamine (reductive glutamine contribution (red)) into palmitate. Error bars depict the 95 % confidence interval. Confidence intervals and p-values are calculated from two biological replicates. Figure 3: Comparison of glutamine contribution to tricarboxylic acid cycle in prostate cancer cell lines treated with metformin or rotenone measured by the incorporation of U-13C labeled glutamine into alpha-ketoglutarate (upper panel) and reductive glutamine contribution to palmitate using 5-13C labeled glutamine (lower panel). Confidence intervals and p-values are calculated from two biological replicates. Figure 4: (A) Relative cell count of prostate cancer cell lines treated with a combination of metformin and the glutaminase inhibitor BPTES. Cell counts were normalized to the condition with no metformin and no BPTES added. (B) Relative cell count of Huh7 liver cancer cells, which can grow without glutamine in the presence or absence of metformin. Cell counts were normalized to the corresponding condition with no metformin added. Error bars depict the standard deviation. Standard deviation and p-values are calculated from three biological replicates. Figure 5: (A) TSC2 expression in TSC2 knockdown cells and control. Standard diviation is calculated from three technical replicates. p-values are < 0.005.(B) Metformin sensitivity (2.5mM) in LNCaP cells with and without dimethyl alpha-ketoglutarate given by cell counts normalized to the corresponding condition with no metformin. Standard deviation and p-values are calculated from at least three biological replicates. p-value is < 0.05. All error bars depict the standard deviation.

Abstract Growing malignant tumors must evade destruction by the immune system, a hurdle some malignancies overcome by attracting immune-suppressive regulatory T-cells (Tregs)1. The IKZF2 (Helios) transcription factor plays a crucial role in maintaining function and stability of Tregs, and IKZF2 deficiency enhances immune responses to tumors in mice2, suggesting IKZF2 may be an attractive target for cancer immunotherapy. Here we describe the discovery and characterization of DKY709, the first molecular glue degrader of IKZF2/4 which spares IKZF1/3. DKY709 was identified through a recruitment-guided medicinal chemistry campaign that redirected the degradation selectivity of CRBN binders towards IKZF2. The IKZF transcription factor selectivity of DKY709 was rationalized by the X-ray structure of the CRBN-DKY709-IKZF2(ZF2) ternary complex. Upon exposure to DKY709, human Tregs showed reduced suppressive activity and exhausted T-effector cells recovered IFNγ production. In vivo, oral treatment with DKY709 drove a rapid and sustained degradation of IKZF2 including in humans and led to delayed tumor growth in mice with humanized immune systems and enhanced immunization responses in monkeys. DKY709 is a first-in-class, potent and selective oral IKZF2/4 degrader currently being investigated in a phase 1 clinical trial as an immune-enhancing agent for cancer immunotherapy.

Abstract Signal transducer and activator of transcription 3 (STAT3) has been implicated in multiple aspects of tumorigenesis. In addition to increasing cancer cell proliferation and survival, constitutively activated STAT3 is proposed to regulate cross-talk between tumor, stroma and immune cells to promote immune-evasion. STAT3 activity in tumors promotes the production of immune-suppressive factors that activate STAT3 in diverse immune-cell subsets. Mechanistically, genetic studies support a direct role of activated STAT3 in regulating myeloid cell differentiation to contribute to an immune-suppressed tumor microenvironment (TME) (Kortylewski et al.; Nat. Med. 2005 and Curr. Opin. Immunol. 2008) Therefore, STAT3 is a highly attractive target for immune-oncology. Here, we demonstrate that the degradation of STAT3 with a potent and selective STAT3 degrader reverses immune suppression in preclinical models. KYM-003 is a heterobifunctional molecule that hijacks the ubiquitin-proteasome system (UPS) for rapid STAT3 degradation. KYM-003 robustly degraded STAT3 in both human peripheral blood mononuclear cells (hPBMC)-derived monocytes and lymphocytes with DC50 < 100 nM. Degradation in hPBMCs was highly selective for STAT3 vs >10,000 other detected proteins (including all other STAT family members) as evaluated by deep tandem mass tag proteomics. IL-6 treatment of hPBMCs upregulates STAT3 phosphorylation, resulting in transcription of genes involved in myeloid cell-mediated immune suppression, such as IL-10 and CD163, a marker of M2 macrophage differentiation. Treatment of cells with KYM-003 at DC90 for 6 hours abrogated the IL-6 induced up-regulation of immune-suppressive gene signatures consistent with a role of STAT3 in mediating an immune suppressive environment by regulating macrophages and other myeloid cells. In several tumor cell lines, degradation of STAT3 by KYM-003 led to strong downregulation of PD-L1. Importantly, in the BioMap StroNSCLC (DiscoverRx), a co-culture system composed of NCI-H1299 lung cancer cells, hPBMCs and primary human fibroblasts that models immune-suppressed TME biology, KYM-003 treatment decreased angiogenic and immune-suppressive cytokines, including VEGF and IL-10, and promoted the pro-inflammatory anti-tumor cytokines IL-2, IFNg and TNFa. Lastly, administration of KYM-003 to mice bearing syngeneic tumors exhibited anti-tumor activity as monotherapy in the CT26 syngeneic model. We have shown that targeting STAT3 for degradation may have a role in restoring an immune-permissive environment in tumors by both rescuing the suppressed immunologic microenvironment and directly downregulating immune checkpoint signals in tumor cells. These data support STAT3 degraders as a promising new therapeutic modality as immune-oncology agents.Citations: Kortylewski et al (2005) Nat. Med, 11(12):1314-21. Kortylewski et al (2008) Curr. Opin. Immunol, 20(2):228-33 Citation Format: Alfredo Csibi, Bin Yang, Yogesh Chutake, Karen Yuan, Michele Mayo, Veronica Campbell, Alice McDonald, Scott Rusin, Kirti Sharma, Hari Kamadurai, Henry Li, Mike Sintchak, Sean Zhu, Sharon Townson, Anthony Slavin, Haojing Rong, Phillip Liu, Chris De Savi, Jared Gollob, Duncan Walker, Nan Ji, Nello Mainolfi. A STAT3 selective targeted protein degrader decreases the immunesuppressive tumor microenvironment and drives antitumor activity in preclinical models [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 LB-088.

The small molecule H3B-8800 selectively modulates RNA splicing to preferentially kill tumor cells bearing mutations in genes encoding spliceosome components. Genomic analyses of cancer have identified recurrent point mutations in the RNA splicing factor–encoding genes SF3B1, U2AF1, and SRSF2 that confer an alteration of function1,2,3,4,5,6. Cancer cells bearing these mutations are preferentially dependent on wild-type (WT) spliceosome function7,8,9,10,11, but clinically relevant means to therapeutically target the spliceosome do not currently exist. Here we describe an orally available modulator of the SF3b complex, H3B-8800, which potently and preferentially kills spliceosome-mutant epithelial and hematologic tumor cells. These killing effects of H3B-8800 are due to its direct interaction with the SF3b complex, as evidenced by loss of H3B-8800 activity in drug-resistant cells bearing mutations in genes encoding SF3b components. Although H3B-8800 modulates WT and mutant spliceosome activity, the preferential killing of spliceosome-mutant cells is due to retention of short, GC-rich introns, which are enriched for genes encoding spliceosome components. These data demonstrate the therapeutic potential of splicing modulation in spliceosome-mutant cancers.

A hallmark of prostate cancer progression is dysregulation of lipid metabolism via overexpression of fatty acid synthase (FASN), a key enzyme in de novo fatty acid synthesis. Metastatic castration-resistant prostate cancer (mCRPC) develops resistance to inhibitors of androgen receptor (AR) signaling through a variety of mechanisms, including the emergence of the constitutively active AR variant V7 (AR-V7). Here, we developed an FASN inhibitor (IPI-9119) and demonstrated that selective FASN inhibition antagonizes CRPC growth through metabolic reprogramming and results in reduced protein expression and transcriptional activity of both full-length AR (AR-FL) and AR-V7. Activation of the reticulum endoplasmic stress response resulting in reduced protein synthesis was involved in IPI-9119-mediated inhibition of the AR pathway. In vivo, IPI-9119 reduced growth of AR-V7-driven CRPC xenografts and human mCRPC-derived organoids and enhanced the efficacy of enzalutamide in CRPC cells. In human mCRPC, both FASN and AR-FL were detected in 87% of metastases. AR-V7 was found in 39% of bone metastases and consistently coexpressed with FASN. In patients treated with enzalutamide and/or abiraterone FASN/AR-V7 double-positive metastases were found in 77% of cases. These findings provide a compelling rationale for the use of FASN inhibitors in mCRPCs, including those overexpressing AR-V7.

The mammalian target of rapamycin complex 1 (mTORC1) integrates multiple signals from growth factors, nutrients, and cellular energy status to control a wide range of metabolic processes, including mRNA biogenesis; protein, nucleotide, and lipid synthesis; and autophagy. Deregulation of the mTORC1 pathway is found in cancer as well as genetic disorders such as tuberous sclerosis complex (TSC) and sporadic lymphangioleiomyomatosis. Recent studies have shown that the mTORC1 inhibitor rapamycin and its analogs generally suppress proliferation rather than induce apoptosis. Therefore, it is critical to use alternative strategies to induce death of cells with activated mTORC1. In this study, a small-molecule screen has revealed that the combination of glutaminase (GLS) and heat shock protein 90 (Hsp90) inhibitors selectively triggers death of TSC2-deficient cells. At a mechanistic level, high mTORC1-driven translation rates in TSC1/2-deficient cells, unlike wild-type cells, sensitizes these cells to endoplasmic reticulum (ER) stress. Thus, Hsp90 inhibition drives accumulation of unfolded protein and ER stress. When combining proteotoxic stress with oxidative stress by depletion of the intracellular antioxidant glutathione by GLS inhibition, acute cell death is observed in cells with activated mTORC1 signaling. This study suggests that this combination strategy may have the potential to be developed into a therapeutic use for the treatment of mTORC1-driven tumors.

Lymphangioleiomyomatosis LAM is a female predominant and devastating pulmonary disease, characterized by diffusely infiltrated smooth muscle like cells that carry mutations in the tuberous sclerosis complex (TSC) genes. TSC1, TSC2 and TBC1D7 interact and inhibit the mammalian target of rapamycin complex 1 (mTORC1). The reasons that LAM exclusively affects women and how TSC1 or TSC2 deficiency contributes to the pathogenesis of LAM are not yet fully understood. We previously discovered that estrogen promotes the survival and lung metastases of tuberin-deficient rat uterine leiomyoma-derived ELT3 cells in a xenograft tumor model (PNAS 2009). Recently, we reported that estrogen and mTORC2 coordinate to enhance prostaglandin biosynthesis and tumorigenesis in LAM (J. Expt. Med. 2013). Prostaglandins are lipid mediators that participate in tumor survival, growth, invasion, and inflammation. Phospholipase A2 (PLA2), Cyclooxygenase-2 (COX-2) and prostacyclin synthase (PTGIS) are critical enzymes responsible for the production of prostaglandins. Prostaglandin receptors (EPs) mediate the biological function of prostaglandins. This study is to determine whether suppression of prostaglandin biosynthesis pathway potentially leads to tumor regression LAM in both cell culture and preclinical models of LAM. To identify additional pathways activated by TSC loss, we performed bioinformatics analysis of public expression arrays and found a rapamycin-insensitive upregulation of prostaglandin biosynthesis genes including (PLA2), cyclooxygenase-2 (COX-2), prostacyclin synthase (PTGIS), and prostaglandin E2 (PGE2) receptor 3 (EP3), in TSC2-deficient LAM patient-derived cells compared to TSC2-addback cells. Real-time RT-PCR assays validated the enhanced expression of PLA2, COX-2, PTGIS and EP3 in TSC2-deficient cells. Immunoblotting analysis showed the increased levels of PLA2, COX-2, PTGIS and EP3 in TSC2-deficient cells compared to TSC2-addback cells. Immunohistochemistry demonstrated abundant accumulation of PLA2, COX-2 and EP3 in LAM lung lesions compared to adjacent normal tissues. Interestingly, PGE2 specifically stimulated the growth of TSC2-deficient LAM patient-derived cells compared to TSC2-addback cells. Importantly, treatment of TSC2-deficient LAM patient-derived cells with PLA2 inhibitor or EP3 inhibitor more potently reduced cell proliferation in dose-dependent manner compared to TSC2-addback cells. Our data documents that loss of TSC2 leads to the aberrant expression and accumulation of prostaglandin biosynthesis regulators PLA2, COX-2, PTGIS and EP3, thereby enhancing prostaglandin production and promoting TSC-related cell growth and tumor development. Our data supports the potential application of prostaglandin metabolites as biomarkers of disease severity and the development of prostaglandin biosynthesis inhibitors as alternative therapeutic options for lesions occurring in LAM patients and in other gender-specific neoplasm. Citation Format: Chenggang Li, Po-Shun Lee, Yang Sun, Erik Zhang, Xiaoxiao Gu, Jing Li, Kai-Feng Xu, Alfredo Csibi, John Blenis, Elizabeth Petri Henske, Bruce Levy, David Kwiatkowski, Jane J. Yu. Estradiol and mTORC2 cooperate to enhance prostaglandin biosynthesis and tumorigenesis in tuberous sclerosis complex. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr B10.

Alfredo Csibi,1,6,7 Gina Lee,1,6 Sang-Oh Yoon,1 Haoxuan Tong,2 Didem Ilter,1,3 Ilaria Elia,4,5 Sarah-Maria Fendt,4,5 Thomas M. Roberts,2 and John Blenis1,3,* 1Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA 2Department of Cancer Biology, Dana Farber Cancer Institute and Harvard Medical School, Boston, MA 02115, USA 3Department of Pharmacology, Meyer Cancer Center, Weill Cornell Medical College, New York, NY 10065, USA 4Flemish Institute of Biotechnology (VIB), Vesalius Research Center, Herestraat 49, 3000 Leuven, Belgium 5Department of Oncology, KU Leuven–University of Leuven, Herestraat 49, 3000 Leuven, Belgium

Growth-promoting signaling molecules, including the mammalian target of rapamycin complex 1 (mTORC1), drive the metabolic reprogramming of cancer cells required to support their biosynthetic needs for rapid growth and proliferation. Glutamine is catabolyzed to α-ketoglutarate (αKG), a tricarboxylic acid (TCA) cycle intermediate, through two deamination reactions, the first requiring glutaminase (GLS) to generate glutamate and the second occurring via glutamate dehydrogenase (GDH) or transaminases. Activation of the mTORC1 pathway has been shown previously to promote the anaplerotic entry of glutamine to the TCA cycle via GDH. Moreover, mTORC1 activation also stimulates the uptake of glutamine, but the mechanism is unknown. It is generally thought that rates of glutamine utilization are limited by mitochondrial uptake via GLS, suggesting that, in addition to GDH, mTORC1 could regulate GLS. Here we demonstrate that mTORC1 positively regulates GLS and glutamine flux through this enzyme. We show that mTORC1 controls GLS levels through the S6K1-dependent regulation of c-Myc (Myc). Molecularly, S6K1 enhances Myc translation efficiency by modulating the phosphorylation of eukaryotic initiation factor eIF4B, which is critical to unwind its structured 5' untranslated region (5'UTR). Finally, our data show that the pharmacological inhibition of GLS is a promising target in pancreatic cancers expressing low levels of PTEN.

Lymphangioleiomyomatosis (LAM) is a progressive neoplastic disorder that leads to lung destruction and respiratory failure primarily in women. LAM is typically caused by tuberous sclerosis complex 2 (TSC2) mutations resulting in mTORC1 activation in proliferative smooth muscle-like cells in the lung. The female predominance of LAM suggests that estradiol contributes to disease development. Metabolomic profiling identified an estradiol-enhanced prostaglandin biosynthesis signature in Tsc2-deficient (TSC(-)) cells, both in vitro and in vivo. Estradiol increased the expression of cyclooxygenase-2 (COX-2), a rate-limiting enzyme in prostaglandin biosynthesis, which was also increased at baseline in TSC-deficient cells and was not affected by rapamycin treatment. However, both Torin 1 treatment and Rictor knockdown led to reduced COX-2 expression and phospho-Akt-S473. Prostaglandin production was also increased in TSC-deficient cells. In preclinical models, both Celecoxib and aspirin reduced tumor development. LAM patients had significantly higher serum prostaglandin levels than healthy women. 15-epi-lipoxin-A4 was identified in exhaled breath condensate from LAM subjects and was increased by aspirin treatment, indicative of functional COX-2 expression in the LAM airway. In vitro, 15-epi-lipoxin-A4 reduced the proliferation of LAM patient-derived cells in a dose-dependent manner. Targeting COX-2 and prostaglandin pathways may have therapeutic value in LAM and TSC-related diseases, and possibly in other conditions associated with mTOR hyperactivation.

The eukaryotic initiation factor 3 subunit f (eIF3f) is one of the 13 subunits of the translation initiation factor complex eIF3 required for several steps in the initiation of mRNA translation. In skeletal muscle, recent studies have demonstrated that eIF3f plays a central role in skeletal muscle size maintenance. Accordingly, eIF3f overexpression results in hypertrophy through modulation of protein synthesis via the mTORC1 pathway. Importantly, eIF3f was described as a target of the E3 ubiquitin ligase MAFbx/atrogin-1 for proteasome-mediated breakdown under atrophic conditions. The biological importance of the MAFbx/atrogin-1-dependent targeting of eFI3f is highlighted by the finding that expression of an eIF3f mutant insensitive to MAFbx/atrogin-1 polyubiquitination is associated with enhanced protection against starvation-induced muscle atrophy. A better understanding of the precise role of this subunit should lead to the development of new therapeutic approaches to prevent or limit muscle wasting that prevails in numerous physiological and pathological states such as immobilization, aging, denervated conditions, neuromuscular diseases, AIDS, cancer, diabetes. This article is part of a Directed Issue entitled: Molecular basis of muscle wasting.

Mutations in the TSC1 or TSC2 genes are responsible for causing Tuberous Sclerosis Complex (TSC) and Lymphangioleiomyomatosis (LAM). These mutations lead to the uncontrolled activation of the mTOR complex 1 (mTORC1), a cellular protein kinase complex that regulates metabolism, autophagy and cell growth. Cells with TSC1/2 mutations require increased energy and carbon sources to meet their high metabolic needs for cell growth. To meet this demand, we have found that activated mTORC1 uses distinct mechanisms to increase glutamine consumption (glutaminolysis) by elevating the expression of glutaminase and the activity of glutamate dehydrogenase. Furthermore, TSC mutant cells sense the increased energy production and in a positive feedback loop, promote more mTORC1 assembly via an AMP kinase (AMPK)‐dependent, and a novel AMPK‐independent mechanism. This acquired addiction to glutamine provides a novel therapeutic strategy for treating patients with activated mTORC1. Indeed, by acutely blocking the ability of TSC‐mutant cells to use glutamine, we are able to selectively kill cells with mutations in TSC1 or TSC2 without damaging normal cells. We anticipate that these studies will lead to the development of “synthetic‐lethal” drugs useful in the treatment of cancers with inappropriate regulation of mTORC1.

Abstract Metformin inhibits cancer cell proliferation, and epidemiology studies suggest an association with increased survival in patients with cancer taking metformin; however, the mechanism by which metformin improves cancer outcomes remains controversial. To explore how metformin might directly affect cancer cells, we analyzed how metformin altered the metabolism of prostate cancer cells and tumors. We found that metformin decreased glucose oxidation and increased dependency on reductive glutamine metabolism in both cancer cell lines and in a mouse model of prostate cancer. Inhibition of glutamine anaplerosis in the presence of metformin further attenuated proliferation, whereas increasing glutamine metabolism rescued the proliferative defect induced by metformin. These data suggest that interfering with glutamine may synergize with metformin to improve outcomes in patients with prostate cancer. Cancer Res; 73(14); 4429–38. ©2013 AACR.

Lymphangioleiomyomatosis (LAM) is a female predominant progressive and neoplastic disorder that leads to lung destruction and respiratory failure primarily in women. LAM is typically due to TSC2 mutations resulting in mTORC1 activation in proliferative smooth muscle-like cells in the lung. The female predominance of LAM suggests that estradiol contributes to disease development. Metabolomic profiling identified estradiol-enhanced prostaglandin biosynthesis signature in Tsc2-deficient cells, both in vitro and in vivo. Estradiol increased the expression of cyclooxygenase-2 (COX-2), a rate-limiting enzyme in prostaglandin biosynthesis, which was increased at baseline in TSC2-deficient cells, and was not affected by rapamycin treatment, but decreased by Torin 1 treatment and Rictor knockdown, associated with reduction of levels phospho-Akt (S473). Prostaglandin production was also increased in TSC2-deficient cells. In preclinical models, Celecoxib or aspirin treatment suppressed tumor progression. LAM patients had significantly higher serum prostaglandin levels than healthy women. 15-epi-lipoxin-A4 was identified in exhaled breath condensate from LAM subjects and was increased by aspirin treatment, indicative of functional COX-2 expression in the LAM airway. Targeting COX-2 and prostaglandin pathways may have therapeutic value in LAM and TSC-related diseases, and possibly in other conditions associated with mTOR-hyperactivation. Citation Format: Chenggang Li, Po-Shun Lee, Xiaoxiao Gu, Yang Sun, Erik Zhang, Alfredo Csibi, Jing Li, Carmen Priolo, Yanan Guo, Chin-Lee Wu, John Blenis, Kai-Feng Xu, Elizabeth Petri Henske, Bruce Levy, David Kwiatkowski, Jane J. Yu. Estradiol and mTORC2 orchestrate to enhance prostaglandin biosynthesis andtumorigenesis in tuberous sclerosis complex. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr C59.

Proliferating mammalian cells use glutamine as a source of nitrogen and as a key anaplerotic source to provide metabolites to the tricarboxylic acid cycle (TCA) for biosynthesis. Recently, mammalian target of rapamycin complex 1 (mTORC1) activation has been correlated with increased nutrient uptake and metabolism, but no molecular connection to glutaminolysis has been reported. Here, we show that mTORC1 promotes glutamine anaplerosis by activating glutamate dehydrogenase (GDH). This regulation requires transcriptional repression of SIRT4, the mitochondrial-localized sirtuin that inhibits GDH. Mechanistically, mTORC1 represses SIRT4 by promoting the proteasome-mediated destabilization of cAMP-responsive element binding 2 (CREB2). Thus, a relationship between mTORC1, SIRT4, and cancer is suggested by our findings. Indeed, SIRT4 expression is reduced in human cancer, and its overexpression reduces cell proliferation, transformation, and tumor development. Finally, our data indicate that targeting nutrient metabolism in energy-addicted cancers with high mTORC1 signaling may be an effective therapeutic approach.

Abstract The mTOR complex 1 (mTORC1) is a ser/thr protein kinase complex and critical regulator of cellular metabolism, protein synthesis, autophagy and cell growth. This signaling system is normally carefully controlled by the integration of inputs from growth factors, nutrients, cellular energy status, oxygen availability and stress. A variety of loss-of-function or gain-of-function alterations in key mTORC1 regulatory proteins, very often results in inappropriate regulation of this signaling system. Uncontrolled mTORC1 activation contributes on its own or in combination with other pathways to metabolic diseases ranging from diabetes and obesity, cardiac hypertrophy, neurodegeneration, aging, benign tumor syndromes to highly malignant cancers. Mechanistically, uncontrolled mTORC1 activation leads to a constant positive input into anabolic processes and suppression of many catabolic processes. As a result, these cells require increased energy and carbon sources to meet their high metabolic needs for cell growth. To meet this demand, we have found in cells that are PTEN or TSC1/2 null, that activated mTORC1 uses distinct mechanisms to increase glutamine consumption (glutaminolysis) by elevating the expression of glutaminase and the activity of glutamate dehydrogenase. Furthermore, under nutrient-rich conditions, these tumor cells sense the increased energy production and in a positive feedback loop, promote more mTORC1 assembly via an AMP kinase (AMPK)-dependent, and a novel AMPK-independent mechanism. This acquired addiction to glutamine provides a novel therapeutic strategy for treating patients with activated mTORC1. Indeed, by acutely blocking the ability of energetically stressed cells with hyperactive mTORC1 to metabolize glutamine, we can selectively kill some tumor cells without damaging normal cells. We anticipate that these studies will lead to the development of “synthetic-lethal” drugs useful in the treatment of patients with diseases linked to inappropriate activation of mTORC1. Research supported by NIH RO1-GM51405 and the LAM Foundation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr SY29-01. doi:1538-7445.AM2012-SY29-01

The AMP-activated protein kinase (AMPK) is a serine/threonine protein kinase that acts as a sensor of cellular energy status switch regulating several systems including glucose and lipid metabolism. Recently, AMPK has been implicated in the control of skeletal muscle mass by decreasing mTORC1 activity and increasing protein degradation through regulation of ubiquitin-proteasome and autophagy pathways. In this review, we give an overview of the central role of AMPK in the control of skeletal muscle plasticity. We detail particularly its implication in the control of the hypertrophic and atrophic signaling pathways. In the light of these cumulative and attractive results, AMPK appears as a key player in regulating muscle homeostasis and the modulation of its activity may constitute a therapeutic potential in treating muscle wasting syndromes in humans.

In skeletal muscle, protein levels are determined by relative rates of protein synthesis and breakdown. The balance between synthesis and degradation of intracellular components determines the overall muscle fiber size. AMP‐activated protein kinase (AMPK), a sensor of cellular energy status, was recently shown to increase myofibrillar protein degradation through the expression of MAFbx and MuRF1. In the present study, the effect of AMPK activation by AICAR on autophagy was investigated in muscle cells. Our results show that FoxO3a transcription factor activation by AMPK induces the expression of the autophagy‐related proteins LC3B‐II, Gabarapl1, and Beclin1 in primary mouse skeletal muscle myotubes and in the Tibialis anterior (TA) muscle. Time course studies reveal that AMPK activation by AICAR leads to a transient nuclear relocalization of FoxO3a followed by an increase of its cytosolic level. Moreover, AMPK activation leads to the inhibition of mTORC1 and its subsequent dissociation of Ulk1, Atg13, and FIP200 complex. Interestingly, we identify Ulk1 as a new interacting partner of AMPK in muscle cells and we show that Ulk1 is associated with AMPK under normal conditions and dissociates from AMPK during autophagy process. Moreover, we find that AMPK phosphorylates FoxO3a and Ulk1. In conclusion, our data show that AMPK activation stimulates autophagy in skeletal muscle cells through its effects on the transcriptional function of FoxO3a and takes part in the initiation of autophagosome formation by interacting with Ulk1. Here, we present new evidences that AMPK plays a crucial role in the fine tuning of protein expression programs that control skeletal muscle mass. J. Cell. Biochem. 113: 695–710, 2012. © 2011 Wiley Periodicals, Inc.