Faculty Bibliography

Pancreatic ductal adenocarcinoma (PDA) is an aggressive cancer that frequently presents with disseminated disease. The PDA metastatic microenvironment imposes distinct metabolic stressors, potentially generating context-dependent vulnerabilities. Therefore, we employed CRISPR-based genetic screening in a model of PDA liver metastasis to identify novel and possibly targetable liabilities. Remarkably, ferritin heavy chain (FTH1) emerged as the most prominent liver-specific dependency - loss of FTH1 suppressed tumor growth specifically in the liver microenvironment. FTH1 deletion and subsequent disruption of iron handling triggers mitochondrial dysfunction and ionic imbalance, including cytosolic calcium overload. These perturbations result in the activation of a transcriptional program that triggers anti-tumor immunity mediated by immunostimulatory cytokine IL36G. Mechanistically, FTH1 deletion and subsequent ionic imbalance causes decreased protein levels of the tumor suppressor Stk11 (LKB1) which we propose to be mediated by an RNA G-quadruplex located in the 5'-UTR of LKB1. The loss of LKB1 protein levels alters signaling cascades resulting in reduced SIK signaling and inhibition of nonsense mediated decay, ultimately leading to Il36g mRNA stabilization. Taken together, this work elucidates novel ionic disruptions that regulate the translation of LKB1 through a previously undescribed quadruplex in the 5'UTR, altering signaling axes that can be targeted to generate an anti-tumor immune response in PDA.

Breast cancer remains the second leading cause of cancer-related mortality among women, with triple-negative breast cancer (TNBC) exhibiting a particularly poor five-year prognosis. Here, we demonstrated that, among genetic and pharmacological perturbations targeting DNA replication, suppression of DNA polymerase epsilon (POLE) induced a potent, TNBC-specific gene expression signature enriched in inflammatory cytokines that are transcriptional targets of NF-κB. TNBC cells exhibited markedly higher levels of DNA damage and canonical NF-κB activation compared to luminal breast cancer cells. Notably, NF-κB activation in this context depended on the canonical component RELA but not the non-canonical component RELB. Mechanistically, ATM, STING, and RIG-I each contributed to NF-κB activation following POLE suppression. POLE suppression in an in vivo murine TNBC model led to cancer cell-intrinsic elimination of tumor burden and increased immune cell infiltration. Together, these findings support a model in which replication stress from POLE inhibition triggers robust NF-κB-mediated inflammation and immune microenvironment remodeling in TNBC and can independently trigger tumor eradication. These results suggest a potential therapeutic avenue for targeting POLE in TNBC.

Iron-sulfur clusters (ISCs) are redox active cofactors for essential proteins with diverse functions. We demonstrate that Tempol, a redox cycling nitroxide, limits iron bioavailability in a manner distinct from iron chelators, mainly via its effect on ascorbate and iron redox balance. This non-canonical iron limitation triggers upregulation of IRP2 and HIF1α, proteins whose degradation is ferrous iron-dependent, while disrupting ISC synthesis only in a subset of cell lines. Suppression of ISC synthesis inhibits ISC-dependent enzymes, destabilizes ISC proteins, and reduces cell viability, particularly in cells dependent on ISC protein ACO2. These effects are reversed by the reducing agent ascorbate, a cofactor required for multiple enzymes, such as the HIF1α prolyl hydroxylases. Tempol treatment also inhibits ferroptosis, an oxidative form of cell death catalyzed by reduced iron. These results demonstrate ascorbate and cellular iron redox state are essential in iron homeostasis, which is proposed to underlie pathological conditions from neurodegeneration to cancer.

Iron is a critical nutrient, especially to power mitochondrial iron-sulfur cofactor synthesis. In this issue of Molecular Cell, Liu et al.¹ engineer a fluorescent iron sensor, enabling them to define a critical function of the mitochondrial translocase, TIM22, in powering mitochondrial iron use by proper targeting of the mitochondrial iron importers, the mitoferrins.

UNLABELLED:Cancer cells require substantial metabolic adaptations to metastasize to distant organs, but the metabolites essential for successful colonization remain poorly defined. In this study, we used a mitochondrial metabolomics approach to compare primary and metastatic breast cancer cells. This analysis revealed accumulation of mitochondrial glutathione (GSH) during lung metastasis, driven by elevated expression of SLC25A39, a mitochondrial GSH transporter. Loss of SLC25A39 impairs metastatic colonization in genetic screens, cell line models, and patient-derived xenografts, without affecting primary tumor growth. Mitochondrial GSH import is specifically required during early colonization and functions independently of its canonical antioxidant role. CRISPR activation screens identified ATF4, a stress-induced transcription factor, as a bypass mechanism that restores metastatic potential in SLC25A39-deficient cells. Mechanistically, SLC25A39 is required for optimal ATF4 activation during metastasis and under hypoxia, linking mitochondrial GSH availability to integrated stress response signaling. These findings identify mitochondrial GSH as a necessary and limiting metabolite for metastatic progression. SIGNIFICANCE/UNASSIGNED:Mitochondrial GSH import via SLC25A39 is essential for early metastatic colonization in breast cancer, linking metabolic adaptation to stress response signaling. Targeting this pathway may uncover a therapeutic vulnerability specific to metastasis without affecting primary tumor growth.

Gliomas are the most common primary brain tumors and a major source of mortality and morbidity in adults and children. Recent genomic studies have identified multiple molecular subtypes; however metabolic characterization of these tumors has thus far been limited. We performed metabolic profiling of 114 adult and pediatric primary gliomas and integrated metabolomic data with transcriptomics and DNA methylation classes. We identified that pediatric tumors have higher levels of glucose and reduced lactate compared to adult tumors regardless of underlying genetics or grade, suggesting differences in availability of glucose and/or utilization of glucose for downstream pathways. Differences in glucose utilization in pediatric gliomas may be facilitated through overexpression of SLC2A4, which encodes the insulin-stimulated glucose transporter GLUT4. Transcriptomic comparison of adult and pediatric tumors suggests that adult tumors may have limited access to glucose and experience more hypoxia, which is supported by enrichment of lactate, 2-hydroxyglutarate (2-HG), even in isocitrate dehydrogenase (IDH) wild-type tumors, and 3-hydroxybutyrate, a ketone body that is produced by oxidation of fatty acids and ketogenic amino acids during periods of glucose scarcity. Our data support adult tumors relying more on fatty acid oxidation, as they have an abundance of acyl carnitines compared to pediatric tumors and have significant enrichment of transcripts needed for oxidative phosphorylation. Our findings suggest striking differences exist in the metabolism of pediatric and adult gliomas, which can provide new insight into metabolic vulnerabilities for therapy.

Cancer cells often experience nutrient-limiting conditions because of their robust proliferation and inadequate tumour vasculature, which results in metabolic adaptation to sustain proliferation. Most cancer cells rapidly consume glucose, which is severely reduced in the nutrient-scarce tumour microenvironment. In CRISPR-based genetic screens to identify metabolic pathways influenced by glucose restriction, we find that tumour-relevant glucose concentrations (low glucose) protect cancer cells from inhibition of de novo pyrimidine biosynthesis, a pathway that is frequently targeted by chemotherapy. We identify two mechanisms to explain this result, which is observed broadly across cancer types. First, low glucose limits uridine-5-diphosphate-glucose synthesis, preserving pyrimidine nucleotide availability and thereby prolonging the time to replication fork stalling. Second, low glucose directly modulates apoptosis downstream of replication fork stalling by suppressing BAK activation and subsequent cytochrome c release, key events that activate caspase-9-dependent mitochondrial apoptosis. These results indicate that the low glucose levels frequently observed in tumours may limit the efficacy of specific chemotherapeutic agents, highlighting the importance of considering the effects of the tumour nutrient environment on cancer therapy.

UNLABELLED:Iron-sulfur clusters (ISCs) are cell-essential cofactors present in ∼60 proteins including subunits of OXPHOS complexes I-III, DNA polymerases, and iron-sensing proteins. Dysfunctions in ISC biosynthesis are associated with anemias, neurodegenerative disorders, and metabolic diseases. To assess consequences of acute ISC inhibition in a whole body setting, we developed a mouse model in which key ISC biosynthetic enzyme NFS1 can be acutely and reversibly suppressed. Contrary to in vitro ISC inhibition and pharmacological OXPHOS suppression, global NFS1 inhibition rapidly enhances lipid utilization and decreases adiposity without affecting caloric intake and physical activity. ISC proteins decrease, including key proteins involved in OXPHOS (SDHB), lipoic acid synthesis (LIAS), and insulin mRNA processing (CDKAL1), causing acute metabolic inflexibility. Age-related metabolic changes decelerate loss of adiposity substantially prolonged survival of mice with NFS1 inhibition. Thus, the observation that ISC metabolism impacts organismal fuel choice will aid in understanding the mechanisms underlying ISC diseases with increased risk for diabetes. HIGHLIGHTS/UNASSIGNED:Acute ISC inhibition leads to rapid loss of adiposity in miceMulti-metabolic pathway disruption upon ISC deficiency blocks energy storageNfs1 inhibition induces glucose dyshomeostasis due to ISC deficiency in β-cellsEnergy distress caused by inhibition of ISC synthesis is attenuated in aged mice.

Cells require micronutrients for numerous basic functions. Among these, iron, copper, and selenium are particularly critical for redox metabolism, and their importance is heightened during oncogene-driven perturbations in cancer. In this review, which particularly focuses on iron, we describe how these micronutrients are carefully chaperoned about the body and made available to tissues, a process that is designed to limit the toxicity of free iron and copper or by-products of selenium metabolism. We delineate perturbations in iron metabolism and iron-dependent proteins that are observed in cancer, and describe the current approaches being used to target iron metabolism and iron-dependent processes.