Pancreatic ductal adenocarcinoma (PDAC) is non-resectable in the majority of patients and highly resistant to chemotherapy, resulting in a poor survival. The tumor microenvironment and hypoxia are important modifiers of cancer progression in PDAC. Understanding the metabolic vulnerabilities of PDAC in the harsh tumor microenvironment may lead to novel therapeutic approaches with improved clinical efficacy. First, we found that PDAC cells showed beneficial effects of co-cultured stroma cells, but only under lipid-free serum conditions. To study the metabolic crosstalk between cancer cells and stroma in more detail, we performed an untargeted metabolomic screen of PDAC cells and fibroblasts co-cultured in normoxia and hypoxia, and performed RNA-seq profiling in parallel. We found that stromal cells are metabolically more responsive to co-culture than cancer cells. PDAC cells induce catabolic carbohydrate and protein metabolism in stromal cells, particularly in hypoxia. In contrast, 13C-based metabolic flux assays demonstrated that stromal cells display enhanced anabolic lipid metabolism in co-culture with PDAC cells. Furthermore, de novo synthesized 13C-labeled fatty acids in stromal cells were taken up by PDAC cells. In particular, PDAC cells showed extensive scavenging of lysophospholipids (lyso-PLs) from the culture medium, which was increased in co-culture under hypoxic conditions. These data were confirmed by analyzing portal vein plasma samples isolated from pancreatic cancer patients before and after surgery. In addition, we found metabolites and expression levels of metabolic enzymes from the glycerophospholipid pathway to be enriched in PDAC cells in co-culture and hypoxia. By using fibroblasts, human pancreatic stellate cells and patient-derived cancer-associated fibroblasts (CAFs), we demonstrate direct transfer of lyso-PLs from stromal to PDAC cells via lipid droplets. The transfer of lyso-PLs was abrogated by pharmacological inhibitors of autophagy, or by siRNA-mediated knockdown of autophagy genes in stromal and tumor cells. These data suggest that PDAC cells cause stroma cells to undergo autophagy, and reprogram stroma metabolism to obtain complex lipid species for their metabolic needs in the lipid-starved tumor microenvironment.
Citation Format: Petrus R. De Jong, Sean-Luc Shanahan, Morgan A. Brand, Alejandro D. Campos, Anagha Srirangam, Nikolas Marino, Claudia P. Miller, Olga Zagnitko, Adam D. Richardson, David A. Scott, Brian P. James, Andrew P. Hodges, Ally Perlina, Alexey M. Eroshin, Randall French, Malene Hansen, Sally A. Litherland, Andrew M. Lowy, J. Pablo Arnoletti, Garth Powis. Pancreatic cancer cell growth requires lipids released by tumor-induced stroma autophagy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2967. doi:10.1158/1538-7445.AM2017-2967