Targeting pancreatic cancer metabolic dependencies through glutamine antagonism.

Pancreatic ductal adenocarcinoma (PDAC) cells use glutamine (Gln) to support proliferation and redox balance. Early attempts to inhibit Gln metabolism using glutaminase inhibitors resulted in rapid metabolic reprogramming and therapeutic resistance. Here, we demonstrated that treating PDAC cells with a Gln antagonist, 6-diazo-5-oxo-L-norleucine (DON), led to a metabolic crisis in vitro. In addition, we observed a profound decrease in tumor growth in several in vivo models using sirpiglenastat (DRP-104), a pro-drug version of DON that was designed to circumvent DON-associated toxicity. We found that extracellular signal-regulated kinase (ERK) signaling is increased as a compensatory mechanism. Combinatorial treatment with DRP-104 and trametinib led to a significant increase in survival in a syngeneic model of PDAC. These proof-of-concept studies suggested that broadly targeting Gln metabolism could provide a therapeutic avenue for PDAC. The combination with an ERK signaling pathway inhibitor could further improve the therapeutic outcome.

Autophagy fuels mitochondrial function through regulation of iron metabolism in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) has one of the lowest 5-year survival rates of any cancer in the United States. Our previous work has shown that autophagy can promote PDAC progression. We recently established the importance of autophagy in regulating bioavailable iron to control mitochondrial metabolism in PDAC. We found that inhibition of autophagy in PDAC leads to mitochondrial dysfunction due to abrogation of succinate dehydrogenase complex iron sulfur subunit B (SDHB) expression. Additionally, we observed that cancer-associated fibroblasts (CAFs) can provide iron to autophagy-inhibited PDAC tumor cells, thereby increasing their resistance to autophagy inhibition. To impede such metabolic compensation, we used a low iron diet together with autophagy inhibition and demonstrated a significant improvement of tumor response in syngeneic PDAC models.Abbreviations: PDAC: Pancreatic ductal adenocarcinoma; CAFs: cancer-associated fibroblasts; SDHB: succinate dehydrogenase complex iron sulfur subunit B; ISCA1: iron sulfur cluster assembly protein 1; FPN: ferroportin; LIP: labile iron pool; FAC: ferric ammonium chloride; OCR: oxygen consumption rate; OXPHOS: oxidative phosphorylation, IL6: interleukin 6; Fe-S: iron sulfur; ATP: adenosine triphosphate.

Autophagy supports mitochondrial metabolism through the regulation of iron homeostasis in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) cells maintain a high level of autophagy, allowing them to thrive in an austere microenvironment. However, the processes through which autophagy promotes PDAC growth and survival are still not fully understood. Here, we show that autophagy inhibition in PDAC alters mitochondrial function by losing succinate dehydrogenase complex iron sulfur subunit B expression by limiting the availability of the labile iron pool. PDAC uses autophagy to maintain iron homeostasis, while other tumor types assessed require macropinocytosis, with autophagy being dispensable. We observed that cancer-associated fibroblasts can provide bioavailable iron to PDAC cells, promoting resistance to autophagy ablation. To overcome this cross-talk, we used a low-iron diet and demonstrated that this augmented the response to autophagy inhibition therapy in PDAC-bearing mice. Our work highlights a critical link between autophagy, iron metabolism, and mitochondrial function that may have implications for PDAC progression.

Seeing is believing.

The lack of culturally relevant role models for trainees and diverse voices in the biomedical workforce is a significant challenge for innovation. Diversity, inclusion, and scientific progress are not distinct issues to be pursued separately. Here I highlight a student-led initiative that aims to highlight diverse voices in biomedical sciences.

Harnessing metabolic dependencies in pancreatic cancers.

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive disease with a 5-year survival rate of <10%. The tumour microenvironment (TME) of PDAC is characterized by excessive fibrosis and deposition of extracellular matrix, termed desmoplasia. This unique TME leads to high interstitial pressure, vascular collapse and low nutrient and oxygen diffusion. Together, these factors contribute to the unique biology and therapeutic resistance of this deadly tumour. To thrive in this hostile environment, PDAC cells adapt by using non-canonical metabolic pathways and rely on metabolic scavenging pathways such as autophagy and macropinocytosis. Here, we review the metabolic pathways that PDAC use to support their growth in the setting of an austere TME. Understanding how PDAC tumours rewire their metabolism and use scavenging pathways under environmental stressors might enable the identification of novel therapeutic approaches.

Spontaneous hydrolysis and spurious metabolic properties of α-ketoglutarate esters.

α-ketoglutarate (KG), also referred to as 2-oxoglutarate, is a key intermediate of cellular metabolism with pleiotropic functions. Cell-permeable esterified analogs are widely used to study how KG fuels bioenergetic and amino acid metabolism and DNA, RNA, and protein hydroxylation reactions, as cellular membranes are thought to be impermeable to KG. Here we show that esterified KG analogs rapidly hydrolyze in aqueous media, yielding KG that, in contrast to prevailing assumptions, imports into many cell lines. Esterified KG analogs exhibit spurious KG-independent effects on cellular metabolism, including extracellular acidification, arising from rapid hydrolysis and de-protonation of α-ketoesters, and significant analog-specific inhibitory effects on glycolysis or mitochondrial respiration. We observe that imported KG decarboxylates to succinate in the cytosol and contributes minimally to mitochondrial metabolism in many cell lines cultured in normal conditions. These findings demonstrate that nuclear and cytosolic KG-dependent reactions may derive KG from functionally distinct subcellular pools and sources.

Respiratory Supercomplexes Promote Mitochondrial Efficiency and Growth in Severely Hypoxic Pancreatic Cancer.

Pancreatic ductal adenocarcinoma (PDAC) is characterized by extensive fibrosis and hypovascularization, resulting in significant intratumoral hypoxia (low oxygen) that contributes to its aggressiveness, therapeutic resistance, and high mortality. Despite oxygen being a fundamental requirement for many cellular and metabolic processes, and the severity of hypoxia in PDAC, the impact of oxygen deprivation on PDAC biology is poorly understood. Investigating how PDAC cells survive in the near absence of oxygen, we find that PDAC cell lines grow robustly in oxygen tensions down to 0.1%, maintaining mitochondrial morphology, membrane potential, and the oxidative metabolic activity required for the synthesis of key metabolites for proliferation. Disrupting electron transfer efficiency by targeting mitochondrial respiratory supercomplex assembly specifically affects hypoxic PDAC proliferation, metabolism, and in vivo tumor growth. Collectively, our results identify a mechanism that enables PDAC cells to thrive in severe, oxygen-limited microenvironments.

Selective Alanine Transporter Utilization Creates a Targetable Metabolic Niche in Pancreatic Cancer.

Pancreatic ductal adenocarcinoma (PDAC) evolves a complex microenvironment comprised of multiple cell types, including pancreatic stellate cells (PSC). Previous studies have demonstrated that stromal supply of alanine, lipids, and nucleotides supports the metabolism, growth, and therapeutic resistance of PDAC. Here we demonstrate that alanine cross-talk between PSCs and PDAC is orchestrated by the utilization of specific transporters. PSCs utilize SLC1A4 and other transporters to rapidly exchange and maintain environmental alanine concentrations. Moreover, PDAC cells upregulate SLC38A2 to supply their increased alanine demand. Cells lacking SLC38A2 fail to concentrate intracellular alanine and undergo a profound metabolic crisis resulting in markedly impaired tumor growth. Our results demonstrate that stromal-cancer metabolic niches can form through differential transporter expression, creating unique therapeutic opportunities to target metabolic demands of cancer. SIGNIFICANCE: This work identifies critical neutral amino acid transporters involved in channeling alanine between pancreatic stellate and PDAC cells. Targeting PDAC-specific alanine uptake results in a metabolic crisis impairing metabolism, proliferation, and tumor growth. PDAC cells specifically activate and require SLC38A2 to fuel their alanine demands that may be exploited therapeutically.This article is highlighted in the In This Issue feature, p. 890.

Targeting miR-21-3p inhibits proliferation and invasion of ovarian cancer cells.

MicroRNA-21 is overexpressed in most cancers and has been implicated in tumorigenesis. Accumulating evidence supports a central role for the miR-21 guide strand (miR-21-5p) in ovarian cancer initiation, progression, and chemoresistance. However, there is limited information regarding the biological role of the miR-21 passenger strand (miR-21-3p) in ovarian cancer cells. The aim of this study was to investigate the role of miR-21-3p and its target genes in cisplatin-resistant ovarian cancer cells. Expression profiling of miR-21-5p and miR-21-3p was performed in a panel of cancer cells by qPCR. Colony formation and invasion assays were carried out on ovarian and prostate cancer cells transfected with miR-21-5p and miR-21-3p inhibitors. Dual luciferase reporter assays were used to identify the miR-21-3p target genes in ovarian cancer cells. Our results show that miR-21-5p had higher expression levels compared to miR-21-3p on a panel of cancer cells. Moreover, inhibition of miR-21-5p or miR-21-3p resulted in a significant decrease in ovarian and prostate cancer cell proliferation and invasion. Luciferase reporter assays identify RNA Binding Protein with Multiple Splicing (RBPMS), Regulator of Chromosome Condensation and POZ Domain Containing Protein 1 (RCBTB1), and Zinc Finger protein 608 (ZNF608) as miR-21-3p target genes. SiRNA-induced RBPMS silencing reduced the sensitivity of ovarian cancer cells to cisplatin treatment. Immunohistochemical analyses of serous ovarian cancer patient samples suggest a significant decrease of RBMPS levels when compared to normal ovarian epithelium. Taken together, the data generated in this study suggests a functional role for miR-21-3p in ovarian cancer and other solid tumors.

Improving cytotoxicity against cancer cells by chemo-photodynamic combined modalities using silver-graphene quantum dots nanocomposites.

The combination of chemotherapy and photodynamic therapy has emerged as a promising strategy for cancer therapy due to its synergistic effects. In this work, PEGylated silver nanoparticles decorated with graphene quantum dots (Ag-GQDs) were tested as a platform to deliver a chemotherapy drug and a photosensitizer, simultaneously, in chemo-photodynamic therapy against HeLa and DU145 cancer cells in vitro. Ag-GQDs have displayed high efficiency in delivering doxorubicin as a model chemotherapy drug to both cancer cells. The Ag-GQDs exhibited a strong antitumor activity by inducing apoptosis in cancer cells without affecting the viability of normal cells. Moreover, the Ag-GQDs exhibited a cytotoxic effect due to the generation of the reactive singlet oxygen upon 425 nm irradiation, indicating their applicability in photodynamic therapy. In comparison with chemo or photodynamic treatment alone, the combined treatment of Ag-GQDs conjugated with doxorubicin under irradiation with a 425 nm lamp significantly increased the death in DU145 and HeLa. This study suggests Ag-GQDs as a multifunctional and efficient therapeutic system for chemo-photodynamic modalities in cancer therapy.