Abstract 1386: MAPK inhibition remodels antigen presentation in pancreatic ductal adenocarcinoma

Abstract Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignancy with a 5-year survival rate of less than 10%, highlighting the need for new therapeutic options. Hallmarks of this aggressive disease include constitutive activation of the MAPK signaling pathway via mutant KRAS (mKRAS) and an immunosuppressive tumor microenvironment (TME). Constituently-active KRAS has now been rendered targetable via clinical-stage mKRAS-specific small molecule inhibitors. While the impact of KRAS inhibition on tumor growth is well-studied, its ability to engender anti-tumor adaptive immune responses is not fully understood. Prior data generated by our group demonstrated mKRAS inhibition (mKRASi) increased expression of genes associated with antigen presentation in two models of PDAC in vitro. Additionally, proteomic analysis revealed increased expression of two tumor associated antigens (TAAs), MSLN and PSCA. To better understand the alteration of antigen presentation in response to MAPK signaling perturbation, we measured surface expression of MHC-I and PD-L1 after mKRAS and/or SHP2 inhibition via flow cytometry in a PDAC-KRASG12C model in vitro. Results demonstrate an additive increase in MHC-I surface expression following inhibition of SHP2 and in combination with mKRASi that is more pronounced in the setting of type I interferon (IFN). Inhibition of MEK in a PDAC KRASG12D model recapitulates these findings. Addition of a JAK inhibitor did not suppress the additional MHC-I expression suggesting a potential JAK/STAT-independent mechanism for this observation. To better understand the extent of alteration of presented epitopes in response to these perturbations we established an immunopeptidomics profiling workflow, using LC-MS/MS to identify peptide ligands eluted from MHC-I complexes after inhibition of mKRAS and/or SHP2. We additionally profiled epitope alterations after the addition of type I or II IFN. MAPK perturbation resulted in more unique epitopes identified, especially with dual inhibition of mKRAS and SHP2 and further potentiated by type I IFN. Furthermore, we were able to directly identify epitopes derived from MSLN and PSCA in our cell line models. This data demonstrates the potential for MAPK inhibition to render PDAC more sensitive to the adaptive immune system and synergize with immunotherapeutic treatment strategies. Additionally, direct identification of epitopes presented by cancer cells via mass spectrometry can aid in the rational design of targeted immunotherapies. Citation Format: Amanda L. Creech, Thuc M. Le, Evan R. Abt, Joseph R. Capri, Timothy R. Donahue, Caius G. Radu. MAPK inhibition remodels antigen presentation in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1386.