Title: Fatty acid synthesis and scavenging contribute to pancreatic cancer growth and maintenance
Description: Similar to many cancers, pancreatic cancer (PDA) assumes an altered metabolic state that is designed to support the manufacture of macromolecules necessary for cell division. For example, membrane synthesis from lipid precursors is dependent on de novo fatty acid synthesis (dnFAS), a pathway that is upregulated in many cancers. The rate-limiting enzyme of dnFAS is fatty acid synthase (FASN), an enzyme that is overexpressed in cancer but found at very low levels in normal tissues. Here we demonstrate that fatty acid synthase (FASN) inhibition using novel small molecule inhibitor IPI-9119 induces apoptosis in FASN overexpressing epithelial cells of a pre-clinical pancreatic cancer mouse model (KPC). We also provide evidence that FASN inhibition insensitivity in PDA cells is due to flux through scavenging pathways, particularly macropinocytosis. We initially hypothesized that FASN overexpression is a survival strategy for PDA epithelial cells through which they acclimate to a low nutrient microenvironment.

Indeed, K-ras driven metabolic reprograming has been shown to increase flux through the dnFAS pathway indicating that PDA cells should rely heavily on FASN activity. Surprisingly we found that PDA cell lines are minimally affected by FASN inhibition and rely chiefly on scavenging pathways. In vitro cells displayed a dependency on lysosomal function, determined using lysosomal inhibitor chloroquine (CQ). Dual therapy with FASN inhibitor, IPI-9119, and lysosomal inhibitor, CQ, increased apoptosis and decreased cell viability in human PDA cell lines and in bulk KPfl/flC PDA tumors. Our findings suggest that mutated epithelial tumor cells overexpress FASN and that these oncogenic cells can be specifically targeted using FASN inhibition. Our findings in regards to scavenging pathways demonstrate that PDA is reliant on lysosomal activity and may utilize both autophagy and macropinocytosis to maintain lipid levels in addition to dnFAS. Dual therapy with a FASN inhibitor and a lysosomal inhibitor induces apoptosis in PDA cell lines regardless of their sensitivity to FASN inhibition alone indicating that this therapeutic strategy, dual treatment with lysosomal inhibitors and FASN inhibitors, should be further developed.

Our major conclusions from this work are: (1) that PDA is not solely dependent on FASN activity for lipid maintenance but short-term inhibition results in targeted apoptosis in FASN expressing cells, in vivo. (2) Lipid scavenging pathway macropinocytosis accounts for primary resistance to FASN inhibition in vitro, although autophagy may also contribute. (3) Dual inhibition of FASN and lysosomal function induces apoptosis and decreases proliferation in PDA cell lines and tumors.