Starving Cancer from the Inside and Outside: Nutrient Stress in Combination with Autophagy Inhibition to Kill Pancreatic Ductal Adenocarcinoma (PDAC)

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  • May 15, 2019
Creator
  • Pearce, Jane
    • College of Arts and Sciences, Department of Biology
Abstract
  • Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers worldwide, with a 5- year survival rate of less than 5 percent. Given the current lack of effective therapeutic options, novel strategies for treatment of this disease are urgently required. Most PDAC tumors acquire mutations that result in constitutive activation of the GTPase KRAS, which promotes mitogen- activated protein kinase (MAPK) signaling and tumor development. Notably, KRAS-driven PDACs often exhibit increased dependence on autophagy, the process by which cells degrade internal components to mobilize energy stores. When faced with cellular stress, such as nutrient or growth factor deprivation, tumor growth may initially slow in response to decreasing supplies of growth factors and cytokines. Under these conditions, the induction of autophagy can enable continued tumor growth even in the presence of nutrient stress, and PDAC cells have been demonstrated to upregulate autophagy to maintain pro-tumorigenic growth. Therefore, we posited that nutrient restriction in combination with autophagy inhibition would synergistically disrupt aberrant metabolic pathways and more effectively stunt PDAC tumor progression. To determine the impact of transient autophagy inhibition, the aminoquinoline chloroquine (CQ, the only FDA- approved autophagy inhibitor) was selected. The combination of CQ and nutrient stress elicited a compounding effect on cellular proliferation in both murine and human-derived PDAC cells in vitro, demonstrating the potential efficacy of CQ and nutrient stress as an adjuvant therapy for PDAC. Next, the mechanistic impact of permanent autophagy inhibition was explored, in order to identify secondary metabolic alterations arising in response to autophagy ablation. Using CRISPR/Cas9 technology, a key gene in autophagic induction, autophagy related 5 (Atg5) was deleted in a murine-derived KRAS-mutant PDAC cell line (Panc02) rendering them autophagy- deficient (Atg5-/-) PDAC cell line. To understand the effect of systemic nutrient deprivation and autophagy deficiency, these Atg5 wildtype and knockout cells were used in an in vivo model in which animals were prescribed a control or calorie restricted diet. Upon intrapancreatic injection in a syngeneic C57BL/6 model, the complete loss of autophagy in Atg-/- cells resulted in reduced tumor growth relative to control (Atg5+/+) cells. However, no differences in growth were observed in vitro under standard growth conditions or in combination with nutrient stress, indicating the cells with permanent autophagy deficiency have reprogrammed to grow in an autophagy- independent manner. Thus, our findings reveal a potential synergism between autophagy inhibition and nutrient stress, and also caution against suppressing autophagy completely and/or permanently due to the potential for pro-survival cellular adaptation to occur.
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Advisor
  • Hursting, Stephen
Degree
  • Bachelor of Science
Honors level
  • Honors
Degree granting institution
  • University of North Carolina at Chapel Hill
Graduation year
  • 2016
Language
  • English
Date uploaded
  • November 21, 2018

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