LAUSR

Introduction: Pancreatic ductal adenocarcinomas are one of the deadliest cancer types with limited response to current therapies. Thus, this study examined changes in the proteome of epithelial cells in pancreatic cancer after neoadjuvant chemotherapy with gemcitabine, to identify new therapeutic targets. Methods: Upon receiving patient consent, fresh pancreatic cancer tissue was received from surgical tumor resections at the University Hospital of Bonn. We mechanically and enzymatically digested and purified the tissue to create single-cell suspensions. After staining the cells against CD45 und CD326, we purified epithelial cells, blood cells, and stroma through FACS. To analyze their proteome, the sorted cells were lysed in TEAB buffer and the protein lysates were measured by the mass spectrometry core facility at the University of Bonn. We then analyzed the data using DAVID and Shiny GO. Results: Gene enrichment analyses showed a significantly reduced expression of calreticulin after neoadjuvant chemotherapy in epithelial cells. A direct comparison between untreated and treated epithelium cancer cells using a heat map showed a decreased expression of actin and enzymes of glycolysis in treated cancer cells. Moreover, untreated epithelial cells showed an increase of proteins related to MHC class Ib protein complex assembly and antigen processing and presentation of endogenous peptide antigen via MHC class. In contrast, treated cells showed a higher presence of proteins for nutrient supply from the blood. Furthermore, untreated stroma cells exhibited an increased number of proteins responsible for mesenchymal migration and for actin filament fragmentation. Conclusion: This study shows that neoadjuvant chemotherapy with gemcitabine leads to distinct changes in the proteome of tumor cells in pancreatic cancers. In particular, a decreased expression of the “eat-me-signal” calreticulin impairs macrophage-mediated cancer cell phagocytosis, thereby indicating a mechanism by which cancer cells protect themselves after chemotherapy. Citation Format: Michael C. Stoffel, Elisabeth BH Dingendorf, Dahlia L. Kittel, Glen Kristiansen, Tristan Lerbs. Mass spectrometry reveals a downregulation of calreticulin after neoadjuvant chemotherapy in pancreatic cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3963.