Kamiya Mehla

The ability of tumour cells to thrive in harsh microenvironments depends on the utilization of nutrients available in the milieu. Here we show that pancreatic cancer-associated fibroblasts (CAFs) regulate tumour cell metabolism through the secretion of acetate, which can be blocked by silencing ATP citrate lyase (ACLY) in CAFs. We further show that acetyl-CoA synthetase short-chain family member 2 (ACSS2) channels the exogenous acetate to regulate the dynamic cancer epigenome and transcriptome, thereby facilitating cancer cell survival in an acidic microenvironment. Comparative H3K27ac ChIP-seq and RNA-seq analyses revealed alterations in polyamine homeostasis through regulation of SAT1 gene expression and enrichment of the SP1-responsive signature. We identified acetate/ACSS2-mediated acetylation of SP1 at the lysine 19 residue that increased SP1 protein stability and transcriptional activity. Genetic or pharmacologic inhibition of the ACSS2-SP1-SAT1 axis diminished the tumour burden in mouse models. These results reveal that the metabolic flexibility imparted by the stroma-derived acetate enabled cancer cell survival under acidosis via the ACSS2-SP1-SAT1 axis.

Nutritional factors play crucial roles in immune responses. The tumor-caused nutritional deficiencies are known to affect antitumor immunity. Here, we demonstrate that pancreatic ductal adenocarcinoma (PDAC) cells can suppress NK-cell cytotoxicity by restricting the accessibility of vitamin B6 (VB6). PDAC cells actively consume VB6 to support one-carbon metabolism, and thus tumor cell growth, causing VB6 deprivation in the tumor microenvironment. In comparison, NK cells require VB6 for intracellular glycogen breakdown, which serves as a critical energy source for NK-cell activation. VB6 supplementation in combination with one-carbon metabolism blockage effectively diminishes tumor burden in vivo. Our results expand the understanding of the critical role of micronutrients in regulating cancer progression and antitumor immunity, and open new avenues for developing novel therapeutic strategies against PDAC. SIGNIFICANCE: The nutrient competition among the different tumor microenvironment components drives tumor growth, immune tolerance, and therapeutic resistance. PDAC cells demand a high amount of VB6, thus competitively causing NK-cell dysfunction. Supplying VB6 with blocking VB6-dependent one-carbon metabolism amplifies the NK-cell antitumor immunity and inhibits tumor growth in PDAC models. This article is featured in Selected Articles from This Issue, p. 5.

Dysregulation of polyamine metabolism has been implicated in cancer initiation and progression; however, the mechanism of polyamine dysregulation in cancer is not fully understood. In this study, we investigated the role of MUC1, a mucin protein overexpressed in pancreatic cancer, in regulating polyamine metabolism. Utilizing pancreatic cancer patient data, we noted a positive correlation between MUC1 expression and the expression of key polyamine metabolism pathway genes. Functional studies revealed that knockdown of spermidine/spermine N1-acetyltransferase 1 ( SAT1 ), a key enzyme involved in polyamine catabolism, attenuated the oncogenic functions of MUC1, including cell survival and proliferation. We further identified a regulatory axis whereby MUC1 stabilized hypoxia-inducible factor (HIF-1α), leading to increased SAT1 expression, which in turn induced carbon flux into the tricarboxylic acid cycle. MUC1-mediated stabilization of HIF-1α enhanced the promoter occupancy of the latter on SAT1 promoter and corresponding transcriptional activation of SAT1 , which could be abrogated by pharmacological inhibition of HIF-1α or CRISPR/Cas9-mediated knockout of HIF1A . MUC1 knockdown caused a significant reduction in the levels of SAT1-generated metabolites, N1-acetylspermidine and N8-acetylspermidine. Given the known role of MUC1 in therapy resistance, we also investigated whether inhibiting SAT1 would enhance the efficacy of FOLFIRINOX chemotherapy. By utilizing organoid and orthotopic pancreatic cancer mouse models, we observed that targeting SAT1 with pentamidine improved the efficacy of FOLFIRINOX, suggesting that the combination may represent a promising therapeutic strategy against pancreatic cancer. This study provides insights into the interplay between MUC1 and polyamine metabolism, offering potential avenues for the development of treatments against pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignancy with a dire prognosis.Standard-of-care chemotherapy regimens offer marginal survival benefit and carry risk of severe toxicity, while immunotherapy approaches have uniformly failed in clinical trials.Extensive desmoplasia in the PDAC tumor microenvironment (TME) disrupts blood flow to and from the tumor, thereby creating a nutrient-depleted, hypoxic, and acidic milieu that suppresses the function of antitumor immune cells and imparts chemotherapy resistance.Additionally, recent seminal studies have demonstrated crucial roles for metabolic crosstalkthe exchange of metabolites between PDAC cells and stromal cell populations in the TMEin establishing and maintaining core malignant behaviors of PDAC: tumor growth, metastasis, immune evasion, and therapy resistance.In this review, we provide a conceptual overview of metabolic crosstalk and how it evolves under various selection pressures in the TME, analyze the landscape of proposed tumorigenic metabolic crosstalk pathways, and highlight potentially druggable nodes. Pancreatic cancer remodels the TME to favor tumor progressionPDAC is a deadly malignancy that carries a dismal prognosis.The extreme mortality is due to late diagnosis, early metastasis, recurrence, and poor response to existing therapies.A compelling body of emerging evidence suggests that the aggressive clinical behavior of PDAC is in significant part attributable to the ability of PDAC cells to cause changes in the TME that support its malignant capabilities (Box 1) [1][2][3][4][5].A variety of stromal cells in the TME, including cancer-associated fibroblasts (CAFs), tumor-associated macrophages (TAMs), myeloid-derived suppressor cells (MDSCs), T regulatory cells (Tregs), and others, facilitate PDAC progression by various mechanisms [2,6].Deranged cancer cell metabolism has been recognized as a driver of malignant tumor behavior since at least the 1920s [7].Metabolic changes are initiated early in the preneoplastic lesions [8].More recently, major technological advances in experimental biology have facilitated the discovery of metabolite exchange networks involving cancer cells and various stromal cell types in the TME, which has been termed 'metabolic crosstalk'.Seminal studies have since proposed essential roles for metabolic crosstalk across disparate domains of PDAC biology, including tumor growth, survival of tumor cells under harsh microenvironments, immune evasion, metastasis, and chemothe rapy resistance.In this review, we provide a conceptual overview of metabolic crosstalk and analyze an illustrative cross-section of proposed mechanisms by which it enables PDAC disease progression, with an emphasis on metabolic crosstalk pathways that may represent tractable and efficacious targets suitable for clinical testing. Metabolic symbiosis enables tumor growth in the nutrient-poor PDAC TMEThe term 'metabolic symbiosis' refers to the mutually fitness-enhancing exchange of metabolites between malignant epithelial cells (hereafter referred to as 'PDAC cells') and other cell types in the

Cathepsins, a group of lysosomal peptidases, have traditionally been recognized as tumor facilitators. Recent research, however, highlights their critical role in orchestrating cancer and the tumor microenvironment (TME). Primality, cathepsins degrade extracellular matrix, enabling cancer cells to invade and metastasize, while also promoting vascular endothelial infiltration and subsequent angiogenesis. Additionally, cathepsins boost fibroblast growth, thereby supporting tumor progression. More importantly, cathepsins are pivotal in modulating immune cells within the TME by regulating their recruitment, antigen processing and presentation, differentiation, and cell death, primarily contributing to immune suppression. Given their overexpression in tumors and elevated levels in the circulation of cancer patients, it is crucial to consider the systemic effects of cathepsins. Although the comprehensive role of cathepsins in cancer patients' bodies remains underexplored, they likely influence systemic immunity and inflammation, cellular metabolism, muscle wasting, and distant metastasis through their unique proteolytic functions. Notably, cathepsins also confer resistance to chemoradiotherapy by rewriting the cellular profile within the TME. In this context, promising results are emerging from studies combining cathepsin inhibitors with conventional therapies to suppress tumor development effectively. This review aims to decipher the cathepsin-driven networks within cancer cells and the TME, detailing their contribution to chemoradioresistance by reshaping both micro- and macroenvironments. Furthermore, we explore current and future perspectives on therapies targeting cathepsins' interactions, offering insights into innovative treatment strategies.