Decoding and targeting saccharopine pathway in cancer metastasis

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Growing evidence suggests that cancer cells undergo significant metabolic alterations during metastasis. Recent studies show that functional mitochondria are essential for the tumor cell development. However, we largely do not know how mitochondrial factors contribute to metastatic progression. To identify a novel mitochondrial factor critical for cancer metastasis, we performed an unbiased RNAi-based screen using a customized RNAi library targeting 120 mitochondrial enzymes. Screen using various types of cancer cells reveled that aminoadipate- semialdehyde synthase (AASS) in the saccharopine pathway is a common critical factor for the invasion. In vitro and in vivo study using AASS variants demonstrated that the activity of AASS is required for cancer cell invasion and metastasis. Targeting each of the enzymes in the saccharopine pathway revealed 2-aminoadipate (2-AAA), a metabolic intermediate, as a key factor for cell invasion. Metabolic, genomic, and transcriptomics approaches were made to gain mechanistic insight into AASS in cancer metastasis. Through a series of metabolic assays, we found that AASS promotes invasion by managing redox homeostasis in lung and head/neck cancers. Genomic profiling and GSEA showed that AASS loss results in decrease of peroxisomal genes and a redox protein TXNDC5. Moreover, spliced form of XBP1, an activated transcription factor of TXNDC5, was reduced in cells that lack AASS, suggesting a potential link among AASS, sXBP1, and TXNDC5. In addition, through a kinase inhibitor profiling and comprehensive transcription factor profiling, we identified upstream regulators of AASS. In particular, we found HGF/c-MET as a kinase and an activator of AASS, and SATB1 as a potential transcription factor of AASS. Furthermore, our preliminary data showed that AASS upregulation positively correlates with metastatic progression in tumor tissues from cancer patients, suggesting AASS as a promising prognostic marker and a therapeutic target to treat metastatic cancers. Therefore, we screened and identified a US FDA approved compound tannic acid as a potent AASS inhibitor and an anti-metastasis agent. Our central hypothesis is that AASS and its metabolic intermediate 2-AAA provide metastastic signals through their potential regulators and effectors in cancer cells. Thus, AASS signaling represents a promising anti-metastasis target in human cancers. We will use lung cancer and head and neck cancer as a research platform to validate AASS signaling as a common metastasis driver. Three specific aims are proposed: (1) To decipher the molecular mechanism underlying AASS-XBP1 activation, which manages redox signaling and confers metastatic potential in human cancer; (2) To determine how AASS is activated and induced by HGF/c- MET and SATB1 to mediate metastasis; (3) To validate AASS as a therapeutic target in treatment of metastatic cancers using the novel AASS inhibitor tannic acid.