Abstract 4969: Autophagy modulates lipid metabolism to support Liver Kinase B1 (LKB1) - deficient lung tumor growth
Authors: Bhatt Vrushank D. , Hu Zhixian , Su Xiaoyang , Guo Jessie Yanxiang 
Published: August 2018

Autophagy degrades and recycles macromolecules for cells to survive starvation. In genetically engineered mouse models (GEMMs) for human non-small cell lung cancer (NSCLC), autophagy supports Kras-driven lung tumor growth with or without Trp53. Tumor suppressor liver kinase B1 (LKB1) activates 5'-adenosine monophosphate protein kinase (AMPK) to maintain energy homeostasis. LKB1 mutations are detected in 20-30% of NSCLC, causing aggressive tumor growth and resistance to chemotherapy. Identifying novel target to improve LKB1-deficient tumor treatment is urgently needed. Using GEMMs for NSCLC with oncogenic Kras and LKB1 loss (KL), we found that autophagy deficiency increased the survival of the mice bearing Atg7-/- tumors compared to mice bearing wild-type (WT) tumors. To determine the mechanism of autophagy in supporting LKB1-deficient Kras-driven lung tumor growth, tumor derived cell lines (TDCLs) were generated from the lung tumors of these mice. We found that Atg7 null TDCLs were more sensitive to glucose and glutamine deprivation-induced cell death compared to Atg7 WT TDCLs. Atg7 null TDCLs were also more sensitive to starvation-induced cell death than Atg7 WT TDCLs, which can be rescued by glucose, glutamine, pyruvate, lactate and nucleotide supplementation. Thus, autophagy is required for KL TDCLs to tolerate metabolic stress. Furthermore, we observed that palmitate supplementation successfully rescued starvation-induced Atg7 null TDCLs death, indicating that autophagy is required to maintain free fatty acid level for cells to survive starvation. We further performed metabolomics in TDCLs in normal and starvation conditions and found that level of amino acids and intermediates for glycolysis and TCA cycle metabolism were significantly lower in Atg7 null TDCLs compared to Atg7 WT TDCLs during HBSS starvation. Surprisingly, we observed a significant increase in the levels of biotin, a precursor for fatty acid synthesis, in Atg7 null TDCLs than that in WT TDCLs, indicating that accumulation of biotin in autophagy deficient cells might be due to defective fatty acid synthesis. In support of this, we found that the lipid droplets accumulation is significantly lower in Atg7 null KL TDCLs than that in Atg7 WT cells. To further evaluate the functional consequences of autophagy-mediated lipid metabolism in supporting KL tumor growth, we treated Atg7 null and WT cells with etomoxir, an irreversible inhibitor of carnitine palmitoyltransferase-1 (CPT-1) to inhibit fatty acid oxidation, in normal and starvation conditions. We found that Atg7 null TDCLs are much more sensitive to etomoxir treatment than WT cells. Taken together, autophagy plays a critical role in supporting lipid metabolism for cells to survive metabolic stress. Thus, a combination of autophagy inhibition with interruption of lipid metabolism could be a novel therapeutic strategy to treat LKB1-deficient lung tumor.

Citation Format: Vrushank D. Bhatt, Zhixian Hu, Xiaoyang Su, Jessie Yanxiang Guo. Autophagy modulates lipid metabolism to support Liver Kinase B1 (LKB1) - deficient lung tumor growth [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 4969.