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 (FDR0. 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 Suppl₂): Abstract nr PR-15.