Faculty Bibliography

Oncogenic KRAS is the key driver of pancreatic ductal adenocarcinoma (PDAC). We previously described a role for KRAS in PDAC tumor maintenance through rewiring of cellular metabolism to support proliferation. Understanding the details of this metabolic reprogramming in human PDAC may provide novel therapeutic opportunities. Here we show that the dependence on oncogenic KRAS correlates with specific metabolic profiles that involve maintenance of nucleotide pools as key mediators of KRAS-dependence. KRAS promotes these effects by activating a MAPK-dependent signaling pathway leading to MYC upregulation and transcription of the non-oxidative pentose phosphate pathway (PPP) gene RPIA, which results in nucleotide biosynthesis. The use of MEK inhibitors recapitulates the KRAS-dependence pattern and the expected metabolic changes. Antagonizing the PPP or pyrimidine biosynthesis inhibits the growth of KRAS-resistant cells. Together, these data reveal differential metabolic rewiring between KRAS-resistant and sensitive cells, and demonstrate that targeting nucleotide metabolism can overcome resistance to KRAS/MEK inhibition.

Pancreatic cancer cells are characterized by deregulated metabolic programs that facilitate growth and resistance to oxidative stress. Among these programs, pancreatic cancers preferentially utilize a metabolic pathway through the enzyme aspartate aminotransferase 1 (also known as glutamate oxaloacetate transaminase 1, GOT1) to support cellular redox homeostasis. As such, small molecule inhibitors that target GOT1 could serve as starting points for the development of new therapies for pancreatic cancer. We ran a high-throughput screen for inhibitors of GOT1 and identified a small molecule, iGOT1-01, with in vitro GOT1 inhibitor activity. Application in pancreatic cancer cells revealed metabolic and growth inhibitory activity reflecting a promiscuous inhibitory profile. We then performed an in silico docking analysis to study inhibitor-GOT1 interactions with iGOT1-01 analogs that possess improved solubility and potency properties. These results suggested that the GOT1 inhibitor competed for binding to the pyridoxal 5-phosphate (PLP) cofactor site of GOT1. To analyze how the GOT1 inhibitor bound to GOT1, a series of GOT1 mutant enzymes that abolished PLP binding were generated. Application of the mutants in X-ray crystallography and thermal shift assays again suggested but were unable to formally conclude that the GOT1 inhibitor bound to the PLP site. Mutational studies revealed the relationship between PLP binding and thermal stability of GOT1, while highlighting the essential nature of several residues for GOT1 catalytic activity. Insight into the mode of action of GOT1 inhibitors may provide leads to the development of drugs that target redox balance in pancreatic cancer.

While the majority of phosphatidylinositol-4, 5-bisphosphate (PI-4, 5-P₂) in mammalian cells is generated by the conversion of phosphatidylinositol-4-phosphate (PI-4-P) to PI-4, 5-P₂, a small fraction can be made by phosphorylating phosphatidylinositol-5-phosphate (PI-5-P). The physiological relevance of this second pathway is not clear. Here, we show that deletion of the genes encoding the two most active enzymes in this pathway, Pip4k2a and Pip4k2b, in the liver of mice causes a large enrichment in lipid droplets and in autophagic vesicles during fasting. These changes are due to a defect in the clearance of autophagosomes that halts autophagy and reduces the supply of nutrients salvaged through this pathway. Similar defects in autophagy are seen in nutrient-starved Pip4k2a^-/-Pip4k2b^-/- mouse embryonic fibroblasts and in C. elegans lacking the PI5P4K ortholog. These results suggest that this alternative pathway for PI-4, 5-P₂ synthesis evolved, in part, to enhance the ability of multicellular organisms to survive starvation.

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy that is extremely refractory to the therapeutic approaches that have been evaluated to date. Recently, it has been demonstrated that PDAC tumors are dependent upon a metabolic pathway involving aspartate aminotransferase 1, also known as glutamate-oxaloacetate transaminase 1 (GOT1), for the maintenance of redox homeostasis and sustained proliferation. As such, small molecule inhibitors targeting this metabolic pathway may provide a novel therapeutic approach for the treatment of this devastating disease. To this end, from a high throughput screen of ∼800,000 molecules, 4-(1H-indol-4-yl)-N-phenylpiperazine-1-carboxamide was identified as an inhibitor of GOT1. Mouse pharmacokinetic studies revealed that potency, rather than inherent metabolic instability, would limit immediate cell- and rodent xenograft-based experiments aimed at validating this potential cancer metabolism-related target. Medicinal chemistry-based optimization resulted in the identification of multiple derivatives with >10-fold improvements in potency, as well as the identification of a tryptamine-based series of GOT1 inhibitors.

Pancreatic ductal adenocarcinoma (PDA) is an aggressive cancer that is highly refractory to the current standards of care. The difficulty in treating this disease is due to a number of different factors, including altered metabolism. In PDA, the metabolic rewiring favors anabolic reactions which supply the cancer cell with necessary cellular building blocks for unconstrained growth. Furthermore, PDA cells display high levels of basal autophagy and macropinocytosis. KRAS is the driving oncogene in PDA and many of the metabolic changes are downstream of its activation. Together, these unique pathways for nutrient utilization and acquisition result in metabolic plasticity enabling cells to rapidly adapt to nutrient and oxygen fluctuations. This remarkable adaptability has been implicated as a cause of the intense therapeutic resistance. In this review, we discuss metabolic pathways in PDA tumors and highlight and how they contribute to the pathogenesis and treatment of the disease.

Autophagy has been shown to be elevated in pancreatic adenocarcinoma (PDAC) and its role in promoting established tumor growth has made it a promising therapeutic target. However, due to limitations of prior mouse models as well as the lack of potent and selective autophagy inhibitors, the ability to fully assess the mechanistic basis of how autophagy supports pancreatic cancer has been limited. To test the feasibility of treating PDAC using autophagy inhibition and further our understanding of the mechanisms of pro-tumor effects of autophagy, we developed a novel mouse model that allowed the acute and reversible inhibition of autophagy. We observed that autophagy inhibition causes significant tumor regression in an autochthonous mouse model of PDAC. A detailed analysis of these effects indicated that the tumor regression was likely multifactorial, involving both tumor cell intrinsic as well as host effects. Thus, our study supports autophagy inhibition in PDAC may have future utility in the treatment of pancreatic cancer and illustrates the importance of assessing complex biological processes in relevant autochthonous models.

Innovation and progress in radiation oncology depend on discovery and insights realized through research in radiation biology. Radiobiology research has led to fundamental scientific insights, from the discovery of stem/progenitor cells to the definition of signal transduction pathways activated by ionizing radiation that are now recognized as integral to the DNA damage response (DDR). Radiobiological discoveries are guiding clinical trials that test radiation therapy combined with inhibitors of the DDR kinases DNA-dependent protein kinase (DNA-PK), ataxia telangiectasia mutated (ATM), ataxia telangiectasia related (ATR), and immune or cell cycle checkpoint inhibitors. To maintain scientific and clinical relevance, the field of radiation biology must overcome challenges in research workforce, training, and funding. The National Cancer Institute convened a workshop to discuss the role of radiobiology research and radiation biologists in the future scientific enterprise. Here, we review the discussions of current radiation oncology research approaches and areas of scientific focus considered important for rapid progress in radiation sciences and the continued contribution of radiobiology to radiation oncology and the broader biomedical research community.

Autophagy is a highly conserved and regulated process that targets proteins and damaged organelles for lysosomal degradation to maintain cell metabolism, genomic integrity, and cell survival. The role of autophagy in cancer is dynamic and depends, in part, on tumor type and stage. Although autophagy constrains tumor initiation in normal tissue, some tumors rely on autophagy for tumor promotion and maintenance. Studies in genetically engineered mouse models support the idea that autophagy can constrain tumor initiation by regulating DNA damage and oxidative stress. In established tumors, autophagy can also be required for tumor maintenance, allowing tumors to survive environmental stress and providing intermediates for cell metabolism. Autophagy can also be induced in response to chemotherapeutics, acting as a drug-resistance mechanism. Therefore, targeting autophagy is an attractive cancer therapeutic option currently undergoing validation in clinical trials.

Pancreatic ductal adenocarcinoma (PDAC) is an extremely aggressive disease with poor prognosis. Therefore, novel treatment options are essential to combat this highly refractory disease. Oncogenic Kras can promote a metabolic rewiring of pancreatic cancers, including the non-canonical use of glutamine to support growth and proliferation through redox homeostasis. Indeed, inhibition of downstream components of glutamine metabolism leads to a decrease in tumor growth. The first step in glutamine metabolism is mediated by the enzyme glutaminase (GLS) which catalyzes the conversion of glutamine to glutamate in the mitochondria where, in PDAC, glutamine-derived glutamate is metabolized ultimately resulting in increased reducing potential in the form of increased NADPH and GSH. An outstanding question in pancreatic cancer is whether GLS inhibition is a viable therapeutic strategy given it is the most proximal enzyme in the PDAC-specific glutamine metabolism pathway, and how this may differ from targeting distal parts of the pathway. Using a combination of in vitro and in vivo models of pancreatic cancer, we tested whether recently developed highly potent inhibitors of GLS are an effective therapy for PDAC. We demonstrate that despite dramatic early effects on in vitro proliferation caused by GLS inhibition, pancreatic cancer cells have adaptive metabolic networks that allow them to sustain proliferation in vitro and in vivo. Through an integrated proteomic and metabolomic analysis, we identify multiple compensatory pathways that may explain the resistance to GLS inhibition and show as proof of concept that combining inhibitors to these pathways with GLS inhibitors may have therapeutic utility