Abstract PR-15: Identifying synergistic combinations with KRAS inhibition in PDAC

Abstract Background: To date, targeted therapies have largely failed in eliciting sustained responses in advanced pancreatic ductal adenocarcinoma (PDAC). KRAS-targeted therapies have the potential to drastically transform clinical management. Emerging data indicate that only a subset of patients respond, and that acquired resistance is common. Here, we used a combination of in vivo CRISPR activation (CRISPRa) screening and in vitro/preclinical models to identify synergistic combinations with KRAS inhibition (KRASi) in pancreatic and lung cancer. Material and Methods: We used our CRISPRa-competent PPKS (P53(F/F), Kras(LSL-G12D/+), R26(LSL-SAM)) model of adenocarcinoma to conduct targeted screening for drivers of resistance to MRTX133. Our library consisted of ∼450 frequently mutated and amplified putative oncogenes across human adenocarcinoma based on TCGA data. Mice were treated with 1e8 TU of lentiviral library through nasal instillation. After 6 weeks, treatment was initiated with 3 mg/kg MRTX1133 daily, 5 days/week (i.p.). Mice were sacrificed after 4 weeks of treatment and the guide distribution determined through bioinformatic analysis. Genes statistically significantly enriched (FDR<0.05) in the treatment group were determined. Cell lines with acquired resistance to MRTX1133 derived from the KPC PDAC model and the KPP lung adenocarcinoma (LUAD) model were generated using long-term, low-dose treatment. Resistance was confirmed with MTT drug response assays. In vitro combinatorial drug response was determined using a 72h, 96-well MTT assay, and clonogenic response using a 2 week, 384-well FACS assay. Mice were treated with 20 mg/kg MRTX1133 and/or 20mg/kg Temuterkib once daily, 7 days/week (i.p.) for 2 weeks. Results: We performed targeted in vivo CRISPRa screening for drivers of resistance to KRASi in an autochthons model of lung adenocarcinoma (LUAD) using a library targeting 452 genes commonly amplified or mutated in cancer. We identified a set of genes that were specifically enriched in at least 50% of tumors treated with MRTX1133, including MAPK1/ERK2. We also generated 16 cell lines with acquired resistance to MRTX1133, derived from KPC PDAC or KPP LUAD tumors. Transcriptomic analysis identified a large set of genes differentially expressed in cell with acquired resistance relative to controls. GSEA indicated that reactivation of the MAPK cascade as a common trait in resistant cells. To test if ERK inhibition synergizes with KRASi, we quantified the combinatorial response to MRTX1133 and Temuterkib, a specific inhibitor of ERK1 and ERK2, in a set of KPC and KPP derived cell lines, revealing significant synergy and reduced clonogenic potential in a majority of cell lines. A majority of cell lines with acquired resistance to MRTX1133 remained sensitive to Temuterkib. Finally, we tested combinatorial treatment of MRTX1133 and Temuterkib in a syngenetic subcutaneous model of PDAC, which showed at minimum additive effect. In conclusion we have identified ERK inhibition as a promising combination with KRAS inhibition in KRAS-mutant PDAC and LUAD. Citation Format: Fredrik I Thege, Amber Hoskins, Sonja M Woermann, Anirban Maitra. Identifying synergistic combinations with KRAS inhibition in PDAC [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr PR-15.