Abstract 1936: KEAP1-NRF2 mediated resistance against KRASG12D inhibitor in pancreatic ductal adenocarcinoma

Abstract Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer deaths in the US. Mutational activation of the KRAS oncogene is associated with 95% of PDAC and is essential for maintaining PDAC tumorigenic growth. Although inhibitors (sotorasib and adagrasib) targeting one KRAS mutation (G12C) have been approved for the treatment of KRASG12C-mutant lung cancer, the G12C mutation comprises less than 2% of KRAS mutations in PDAC. Recently, the clinical candidate KRASG12D-selective inhibitor MRTX1133 (G12Di) has been shown to potently suppress both activation of the RAF-MEK-ERK signaling pathway downstream of KRAS and tumorigenic growth of KRASG12D-mutant PDAC in vitro and in vivo. Since KRASG12D represents 40% of KRAS-mutant PDAC, G12D-selective inhibitors hold promise as an effective therapy for a significant fraction of PDAC patients. However, the efficacy of these inhibitors is hindered by persistent challenges related to both primary (innate) and acquired treatment-associated resistance, which curtails the long-term effectiveness of likely all KRAS inhibitors. Here, our studies focus on unraveling the mechanism of primary and acquired resistance to G12Di treatment in PDAC. We applied a loss-of-function CRISPR screen targeting the druggable genome on KRASG12D-mutant PDAC cells treated with a sublethal concentration of G12Di to identify genes that modulate G12Di sensitivity. We identified loss of genes (e.g., CBL, RB1, and PTEN) found previously in patients who relapsed on G12Ci treatment, providing validation of the screen. One gene also identified was KEAP1. KEAP1 is known as a substrate-specific adapter of an E3 ubiquitin ligase complex that promotes the degradation of NRF2, and the loss of KEAP1 is commonly associated with increased stability of NRF2, a transcription factor that promotes the transcription of many anti-oxidative stress and pro-cell survival genes. We found that knockout of KEAP1 significantly compromised the ability of G12Di to inhibit PDAC cell proliferation in vitro. KEAP1 loss was associated with upregulated expression of NRF2, and concurrent CRISPR knockout of NRF2 restored sensitivity of G12Di in PDAC. Interestingly, we determined that G12Di-resistant KEAP1-deficient PDAC cells exhibited high dependence on glutaminase (GLS), which converts glutamine to glutamate. We further discovered that combination treatment with a glutaminase inhibitor (CB-839) synergistically enhanced G12Di growth suppression not only of KEAP1-knockout but also of parental PDAC cells. In summary, our study establishes a role for KEAP1 loss as a mechanism that drives PDAC resistance to KRAS inhibitors and identifies GLS inhibition as a possible approach to overcome NRF2-driven resistance. Citation Format: Wen-Hsuan Chang, Addison G. Stamey, Andrew M. Waters, Kirsten L. Bryant, Adrienne D. Cox, Channing J. Der. KEAP1-NRF2 mediated resistance against KRASG12D inhibitor in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1936.