Abstract B017: Loss of UXS1 selectively kills KEAP1 mutant cancer cell lines by depleting pyrimidines and inducing replication stress

Kelch-like ECH Associated-Protein 1 (KEAP1) is the third most mutated gene in non-small cell lung cancer and is associated with poor prognosis. KEAP1 targets nuclear factor erythroid 2-related factor 2 (Nrf2) for degradation, hence KEAP1-mutated tumors have elevated Nrf2 levels and constitutive expression of its transcriptional targets. To identify potential therapeutic targets for KEAP1 mutated tumors, we interrogated the cancer Dependency Map (DepMap) database and identified UDP Xylose Synthase 1 (UXS1) as a synthetic lethal interaction gene in KEAP1 mutated cancer cell lines. UXS1 is a critical protein for the glycosaminoglycan (GAG) synthesis on proteoglycans, converting UDP-glucuronic acid (UDPGA) to UDP-xylose. UDP glucose dehydrogenase (UGDH) is a transcriptional target of Nrf2 highly expressed in KEAP1-mutant tumors, which converts UDP-glucose to UDPGA. Upon UXS1 knock-down, depletion of UDP-xylose is seen in both KEAP1-mutant and wildtype cells, as expected, whereas rapid accumulation of UDPGA is only seen in the KEAP1-mutant setting. This metabolic roadblock causes a shortage of available UDP and other pyrimidines, resulting in slowed S-phase progression, stalled DNA replication fork marks, subsequent DNA damage, and significant loss in cell viability. Notably, dependency on UXS1 can be rescued by either knocking out UGDH to prevent UDPGA accumulation or by supplementation of cells with uridine or cytidine to restore the pyrimidine nucleotide pools by boosting pyrimidine salvage pathway. Finally, we show that DNA replication stress in UXS1-depleted cells renders them sensitive to clinical cell-cycle checkpoint inhibitors, opening a further window of therapeutically exploitable vulnerability. Citation Format: Timothy Hoffman, Melat Gebru, Aaron Boudreau, Fei Han, Kelly Foster-Duke, Jessica Gajda, Ngoc Vu, Bryson Bennett, Michael Kort, Brad Shotwell, Jonathan Hickson, Noel Wilsomn, David Stokoe. Loss of UXS1 selectively kills KEAP1 mutant cancer cell lines by depleting pyrimidines and inducing replication stress [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Expanding and Translating Cancer Synthetic Vulnerabilities; 2024 Jun 10-13; Montreal, Quebec, Canada. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(6 Suppl):Abstract nr B017.