Patients with pancreatic ductal adenocarcinoma (PDAC) have a poor prognosis, and more effective systemic treatments for patients with local progression or metastasis (85% of cases) are needed. The pancreatic tumor microenvironment provides a rich source for novel drug targets. We aimed to identify and validate novel metabolic drug targets that are unique to hypoxic PDAC cells. Using bulk RNA sequencing in combination with metabolomics analyses in vitro, we previously found that PDAC cells negate the loss of intracellular unsaturated fatty acids in hypoxia by orchestrating the release of lysophospholipids (lyso-PLs) by cancer-associated fibroblasts, which are then taken up and stored in intracellular lipid droplets in hypoxic cancer cells. To confirm the relevance of these findings in vivo, we performed 3' droplet based single-cell RNA sequencing (scRNA-seq) combined with metabolomics analyses of intracellular and extracellular (tumor interstitial fluid) metabolites of MIAPaCa2 and patient-derived xenografts (PDX). Identification of cell lineages and subpopulations with hypoxic gene signatures was performed to correlate changes in metabolite levels with metabolic gene expression in vivo. This approach confirmed differential expression of lipid droplet-associated enzymes in hypoxic areas of the tumor, including lyso-PL acyl transferases (LPCAT1, LPCAT3), and phospholipases (LYPLA1, PLA2G15). We found that resistance of PDAC cell lines to pharmacologic treatment with inhibitors of fatty acid desaturases (FADS), reminiscent of hypoxia and nutrient starvation in vivo, was mediated by uptake of lyso-PLs from the medium. Importantly, genetic knockdown of LPCAT and LYPLA isoforms reversed the resistance to FADS inhibitors in culture in vitro and in vivo. Clinical relevance was demonstrated by mRNA expression analysis of PDAC patients from The Cancer Genome Atlas (TCGA) database, which showed that the expression of lyso-PL metabolizing genes is correlated with a significant worse prognosis (log-rank test, P=0.008). We are currently developing pharmacologic approaches to target LPCAT and LYPLA enzymes in hypoxic cancer cells as a novel approach for PDAC patients with unresectable disease.
Citation Format: Petrus R. de Jong, Marco Maruggi, Alejandro D. Campos, Morgan A. Brand, Robert Lemos, David A. Scott, Sally A. Litherland, J. Pablo Arnoletti, Brian P. James, Garth Powis. Targeting lysophospholipid metabolism inhibits pancreatic cancer cell proliferation under nutrient-limiting conditions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2916.