Leveraging autophagy and pyrimidine metabolism to target pancreatic cancer.

Autophagy inhibitors are promising compounds to treat pancreatic ductal adenocarcinoma (PDA) but their efficacy in patients is unclear, highlighting a need to understand mechanisms of resistance. We used a novel approach to uncover metabolic adaptations that bypass autophagy inhibition. Utilizing PDA cells with acquired resistance to different autophagy inhibitors, we found that severe autophagy depletion induces metabolic rewiring to sustain TCA intermediates and nucleotides for biosynthesis. Long-term autophagy inhibition results in altered pyruvate metabolism likely regulated by lower pyrimidine pools. Cells adapting to loss of autophagy preferentially salvage pyrimidines to replenish these pools instead of synthesizing them de novo. Exploiting this metabolic vulnerability, we found that acquired resistance to autophagy inhibition promotes increased salvage and therefore sensitivity to pyrimidine analogues, including gemcitabine and trifluridine/tipiracil leading to combinatory effects with autophagy inhibitors and pyrimidine analogs. These studies provide mechanistic insight defining how autophagy inhibition can be leveraged to treat pancreatic cancer.