Abstract 1089: Targeting amino acid uptake in lung squamous cell carcinomas to improve response to targeted therapies
Authors: Momcilovic Milica , Shackelford David 
Published: June 2022

Abstract
Lung squamous cell carcinomas (LUSC) are a subtype of non-small cell lung cancer characterized by poor overall survival. LUSC are highly aggressive in part due to their high metabolic activity, with uptake of high levels of glucose supporting their growth and proliferation. The main driver of high rate of glycolysis in LUSC is elevated expression of glucose transporter GLUT1, whose levels and membrane localization are regulated by activated PI3K-AKT-mTOR pathway. The Cancer Genome Atlas revealed that LUSC have high tumor mutational burden with varied genetic profile that includes amplification of receptor tyrosine kinases (RTKs), PI3KCA, and a loss of PTEN. These alterations lead to increased activity of mTOR pathway, one of the major pathways in cancer cells that drives cell proliferation and metabolism. We have recently demonstrated that catalytic mTOR kinase inhibitor TAK228 (MLN128) inhibits glycolysis in LUSC cell lines in vitro, in xenografts of human LUSC lines, in patient derived xenografts (PDXs) and genetically engineered mouse models. However, despite lowered glucose uptake measured by 18F-FDG signal LUSC tumors were able to maintain high levels of proliferation. Tumors were able to adapt to prolonged treatment with TAK228 by relying on glutaminolysis. Increased glutaminolysis was due to increased uptake of glutamine as well as increased levels of glutaminase (GLS), a key enzyme that converts glutamine to glutamate. Inhibiting both mTOR (with TAK228) and GLS (with CB-839) resulted in reduced proliferation index and lower tumor volume. However, while combination therapy halted tumor growth, there was a lack of tumor regression in xenografts and PDXs of LUSC. Therefore, tumors are poised to further adapt to combination therapy through metabolism of additional amino acids beyond glutamine. Here we show that macropinocytosis, a form of endocytosis that allows cancer cells to uptake extracellular fluids and further process solutes and macromolecules in lysosomes leading to the release of amino acids inside the cytoplasm, is upregulated in LUSC tumors that are resistant to TAK228. Macropinocytosis is induced by active RTKs, PI3KCA, Ras, loss of PTEN, and active NRF2 pathway - oncogenic alterations commonly found in LUSC tumors. This suggests that macropinocytosis might be a mechanism that supports amino acid metabolism utilized by LUSC in order to escape mTOR therapy. Basal levels of macropinocytosis in LUSC appear low, however, upon treatment with mTOR inhibitors, lysosomal catabolism of macropinocytosed proteins increases, allowing tumor cells to increase their proliferation. Resistance to targeted therapies is a major hurdle to achieving effective therapies in multiple cancer types. Identifying ways to overcome resistance to targeted therapies would allow for longer therapeutic response for larger number of patients, ultimately leading to longer survival and better quality of life.
Citation Format: Milica Momcilovic, David Shackelford. Targeting amino acid uptake in lung squamous cell carcinomas to improve response to targeted therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1089.