SUMMARY Treating KRAS mutant lung adenocarcinoma (LUAD) remains a major challenge for clinical oncology. Approximately 20% of KRAS mutant LUAD tumors carry loss-of-function mutations in KEAP1, a negative regulator of NRF2, which is the master transcriptional regulator of the endogenous antioxidant response. Using CRISPR/Cas9-based somatic editing in a genetically engineered mouse model of KRAS-driven LUAD we demonstrated that loss of KEAP1 hyper-activates NRF2 and dramatically accelerates KRAS-driven LUAD. Our data are in line with mounting evidence demonstrating that, contrary to popular belief, antioxidants can promote cancer progression. Combining CRISPR/Cas9-based genetic screening and metabolic analyses, we have identified novel synthetic lethal interactions in KEAP1 mutant cells. We observe that the ability of KEAP1 mutant tumors to divert their metabolism towards antioxidant production comes with a cost, creating metabolic vulnerabilities that may be targeted by novel therapeutic strategies. In preliminary studies, we observed a dependency of KEAP1 mutant tumors on the amino acid serine. In this application we focus on elucidating this newly appreciated metabolic vulnerability of KRAS-driven KEAP1 mutant tumors to serine and explore the therapeutic potential of targeting serine metabolism in highly relevant pre-clinical mouse and human models. This application aims to: 1) Determine the therapeutic potential of inhibiting the serine transporter SLC1A5 and serine uptake in KRAS-driven LUAD models with KEAP1 mutations, 2) Define the metabolic mechanisms underlying serine dependency in LUAD and other KEAP1 mutant cancers, 3) Determine whether dietary serine restriction can selectively affect the growth of KEAP1 mutant tumors, 4) Dissect the metabolic crosstalk of glutamine and serine dependency in cancers with hyperactivation of the NRF2 pathway. Our studies will provide a rationale for sub-stratification of patients with hyperactivation of the NRF2 pathway as treatment responders to therapies targeting serine metabolism, which is pertinent to the goals of precision medicine.