Alexander Muir

Nutrient limitation is a characteristic feature of poorly perfused tumors. In contrast to well-perfused tissues, nutrient deficits in tumors impose metabolic constraints on cancer cells. The metabolic constraints created by the tumor microenvironment can lead to vulnerabilities in cancers. Identifying the metabolic constraints of the tumor microenvironment and the vulnerabilities that arise in cancers can provide new insight into tumor biology and identify promising anti-neoplastic targets. To identify how the microenvironment constrains the metabolism of pancreatic tumors, we challenged pancreatic cancer cells with microenvironmental nutrient levels and analyzed changes in cellular metabolism. We found that arginine limitation in pancreatic tumors perturbs saturated and monounsaturated fatty acid synthesis by suppressing the lipogenic transcription factor SREBP1, in part via activation of the amino acid sensor GCN2. Synthesis of these fatty acids is critical for maintaining a balance of saturated, monounsaturated, and polyunsaturated fatty acids (PUFAs) in cellular membranes. Because of microenvironmental constraints on fatty acid synthesis, pancreatic cancer cells and tumors are unable to maintain lipid homeostasis when exposed to PUFAs, leading to cell death by ferroptosis. In sum, arginine restriction in the tumor microenvironment constrains lipid metabolism in pancreatic cancers, which renders these tumors vulnerable to polyunsaturated-enriched fats.

Nutrient limitation is a characteristic feature of poorly perfused tumors. In contrast to well-perfused tissues, nutrient deficits in tumors impose metabolic constraints on cancer cells. The metabolic constraints created by the tumor microenvironment can lead to vulnerabilities in cancers. Identifying the metabolic constraints of the tumor microenvironment and the vulnerabilities that arise in cancers can provide new insight into tumor biology and identify promising antineoplastic targets. To identify how the microenvironment constrains the metabolism of pancreatic tumors, we challenged pancreatic cancer cells with microenvironmental nutrient levels and analyzed changes in cellular metabolism. We found that arginine limitation in pancreatic tumors perturbs saturated and monounsaturated fatty acid synthesis by suppressing the lipogenic transcription factor SREBP1, in part via activation of the amino acid sensor GCN2. Synthesis of these fatty acids is critical for maintaining a balance of saturated, monounsaturated, and polyunsaturated fatty acids in cellular membranes. Because of microenvironmental constraints on fatty acid synthesis, pancreatic cancer cells and tumors are unable to maintain lipid homeostasis when exposed to polyunsaturated fatty acids, leading to cell death by ferroptosis. In sum, arginine restriction in the tumor microenvironment constrains lipid metabolism in pancreatic cancers, which renders these tumors vulnerable to polyunsaturated-enriched fats.

Here authors report intraoperative sampling of blood entering and leaving the lung allowing direct assessment of nutrient use by lung cancer.

TGF-β-dependent activation of lung fibroblasts is a hallmark of Idiopathic Pulmonary Fibrosis (IPF) which results in excessive collagen deposition and progressive scarring. Collagen production by lung fibroblasts is supported by de novo synthesis of glycine, the most abundant amino acid in collagen protein. SHMT2 produces glycine by transferring a one-carbon (1 C) unit from serine to tetrahydrofolate (THF), producing 5,10-methylene-THF (meTHF). meTHF is then converted back to THF in the mitochondrial 1 C pathway. It is unknown how 1 C metabolism contributes to collagen protein production and fibrosis. Here, we demonstrate that TGF-β induces the expression of mitochondrial 1 C pathway enzymes, including MTHFD2, in human lung fibroblasts. MTHFD2 was required for TGF-β-induced cellular glycine accumulation and collagen protein production in lung fibroblasts. Pharmacologic inhibition of MTHFD2 ameliorated fibrotic responses after intratracheal bleomycin instillation in vivo. Our findings suggest that mitochondrial 1 C metabolism is a therapeutic target for IPF and other fibrotic diseases.

Systemic therapies are the standard of care for most pancreatic ductal adenocarcinoma (PDAC) patients but provide limited benefit due to pervasive resistance. The fibrotic tumor microenvironment (TME) is thought to drive resistance by restricting perfusion and drug delivery. Here, we show that therapeutically relevant drug concentrations are achieved even in poorly perfused, therapy-resistant murine PDAC tumors, indicating that impaired delivery alone does not explain drug resistance. Instead, we find TME exposure imprints a therapy-resistant state upon PDAC cells. These observations raised the question of how the TME imposes this state. Poor perfusion alters nutrient availability in the TME. To model this, we developed Tumor Interstitial Fluid Medium (TIFM), which recapitulates TME nutrient conditions. TIFM cultured PDAC cells acquire a therapy-resistant phenotype that mirrors resistance observed in the TME. In this state, cytotoxic and targeted therapies retain on-target activity but fail to trigger cell death, resulting in therapeutic tolerance. Mechanistically, drug tolerance is driven by suppression of apoptotic priming and can be reversed by inhibition of the anti-apoptotic regulator BCL-XL. These results identify TME-driven reprogramming of cell death as a key mechanism of therapy resistance in PDAC and establish TIFM as a physiologically relevant model for studying microenvironment-induced drug resistance.

Understanding mechanisms that facilitate early events in metastatic seeding is key to developing therapeutic approaches to reduce metastasis. Here we identify uracil as a metastasis-associated metabolite in genetically engineered mouse models of cancer and in patients with metastatic breast cancer. Uracil is generated by the enzyme uridine phosphorylase-1 (UPP1), and we find that neutrophils are a significant source of UPP1 in metastatic cancer. Mammary tumours increase expression of adhesion molecules on the neutrophil surface, in a UPP1-dependent manner, leading to decreased neutrophil motility in the pre-metastatic lung. UPP1-expressing neutrophils suppress T-cell proliferation, and the UPP1 product uracil increases fibronectin deposition in the extracellular microenvironment. Knockout or inhibition of UPP1 in mice with mammary tumours increases T-cell numbers and reduces fibronectin content in the lung, and decreases the proportion of mice that develop lung metastasis. These data indicate that UPP1 influences neutrophil behaviour and extracellular matrix deposition in the lung, and suggest that circulating uracil could be a marker of metastasis, and that pharmacological inhibition of UPP1 could be a strategy to reduce recurrence.

The tumor microenvironment (TME) of pancreatic ductal adenocarcinoma (PDAC) is composed of a dense stromal compartment and is poorly vascularized, resulting in limited nutrient delivery. As a result, PDAC cells must adapt to cope with the metabolic stresses brought on by TME nutrient limitation. In this article, we first review recent studies that have provided quantitative measurements of nutrient levels in the PDAC TME. These studies have provided a new understanding of the nutrient limitations and metabolic stresses that occur in PDAC. We next discuss the adaptive strategies employed by PDAC in response to TME nutrient limitation. We propose that PDAC adaptations to metabolic stress can be generalized into four categories: (a) cutting down on metabolic costs by recycling metabolites and suppressing nonessential processes, (b) upregulating biosynthetic pathways to meet TME metabolic demands, (c) supporting essential metabolic processes with alternative fuel sources, and (d) dampening antiproliferative and cell death responses that nutrient limitation normally triggers. Improving our understanding of the nutrient limitations within the TME, and the adaptations cells employ to cope with these stresses, provides a more complete picture of PDAC biology and reveals new opportunities for therapeutic targeting of this disease.

Nutrient stress represents an important barrier for anti-tumour immunity, and tumour interstitial fluid often contains metabolites that hinder immune function. However, it is difficult to isolate the effects of tumour nutrient stress from other suppressive factors. Thus, we used a chemically defined cell culture medium based on the metabolomic profile of tumour interstitial fluid: tumour interstitial fluid medium (TIFM). Culture of CD8⁺ T cells in TIFM limited cell expansion and impaired CD8⁺ T cell effector functions upon restimulation, suggesting that tumour nutrient stress alone is sufficient to drive T cell dysfunction. We identified phosphoethanolamine (pEtn), a phospholipid intermediate, as a driver of T cell dysfunction. pEtn dampened T cell receptor signalling by depleting T cells of diacylglycerol required for T cell receptor signal transduction. The reduction of pEtn accumulation in tumours improved intratumoural T cell function and tumour control, suggesting that pEtn accumulation plays a dominant role in immunosuppression in the tumour microenvironment.

Glioblastoma (GBM) is most common and aggressive primary brain tumor in adults, for which standard of care hasn’t changed in twenty years. GBM tumor associated macrophages (TAMCs), consisting of infiltrating myeloid cells from the periphery and resident microglia cells, are pro-tumorigenic, promoting tumor growth. Fructose is one of the most abundant metabolites in the GBM tumor microenvironment (TME), as well as in the healthy central nervous system (CNS). In the CNS and GBM, microglia are the predominant expressors of the fructose transporter GLUT5. Mice lacking the GLUT5 transporter (GLUT5-KO) survive significantly longer after orthotopic implantation of two glioma cell lines than wildtype mice, which is not due to dietary fructose or peripherally derived TAMCs. Investigation of the TME showed that GLUT5-KO mice have more highly activated and inflammatory innate and adaptive immune compartments. Microglia cultured in fructose have a decreased phagocytic ability and exhibit decreased inflammatory capacity due to the polyol pathway promoting redox homeostasis.

Nutrient limitation is a characteristic feature of poorly perfused tumors. In contrast to well-perfused tissues, nutrient deficits in tumors impose metabolic constraints on cancer cells. The metabolic constraints created by the tumor microenvironment can lead to vulnerabilities in cancers. Identifying the metabolic constraints of the tumor microenvironment and the vulnerabilities that arise in cancers can provide new insight into tumor biology and identify promising antineoplastic targets. To identify how the microenvironment constrains the metabolism of pancreatic tumors, we challenged pancreatic cancer cells with microenvironmental nutrient levels and analyzed changes in cellular metabolism. We found that arginine limitation in pancreatic tumors perturbs saturated and monounsaturated fatty acid synthesis by suppressing the lipogenic transcription factor SREBP1, in part via activation of the amino acid sensor GCN2. Synthesis of these fatty acids is critical for maintaining a balance of saturated, monounsaturated, and polyunsaturated fatty acids in cellular membranes. Because of microenvironmental constraints on fatty acid synthesis, pancreatic cancer cells and tumors are unable to maintain lipid homeostasis when exposed to polyunsaturated fatty acids, leading to cell death by ferroptosis. In sum, arginine restriction in the tumor microenvironment constrains lipid metabolism in pancreatic cancers, which renders these tumors vulnerable to polyunsaturated-enriched fats.