Abstract 4073: Using Patient-Derived PDAC Cells to Understand C-Myc Involvement in the Drug Resistance Mechanisms of Pancreatic Cancer

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease that is typically incurable due to acquired resistance to systemic chemotherapy. A deeper understanding of the mechanisms involving drug resistance is needed to improve patient outcomes. Commercially available PDAC cell lines are the most used model in research but do not accurately recapitulate a given patient's tumor. Using the conditional reprogrammed cell (CRC) technique, we established patient-specific cell lines and created nab-paclitaxel (nab-PTX)-resistant clones, which allowed us to better study resistance mechanisms. In many cancers, c-MYC has a known function in tumor progression, and recent studies suggest that the c-MYC pathway is involved in PDAC. However, the role of c-MYC in the mechanisms leading to nab-PTX resistance has not been extensively explored. Methods: Biopsies were collected from treatment-naive PDAC patients, and long-term cultures of PDAC CRCs were established. The PDAC origin of the cell lines was validated with genomic analysis. The IC50s for nab-PTX were calculated and used to generate drug-resistant clones. The Zebrafish model was used to verify the drug resistance in vivo, while subcutaneous injections of the parental and drug-resistant CRCs in nude mice were performed to test the cells' ability to form tumors. Exome sequencing, microarray, and Western blotting analyses were used to characterize and compare the parental lines with the drug-resistant clones and to identify key pathways involved in the evolution of drug resistance. Results: We established KRAS-mutant primary cell lines from PDAC patients' biopsies. Using 2 parental lines, we generated 5 nab-PTX-resistant clones, with IC50s up to 800 times greater than those of the matched parents; resistant profiles were verified in Zebrafish. Subcutaneous injections in nude mice showed the CRCs' ability to form tumors that recapitulate human PDAC. A greater metastatic phenotype was observed in the tumors derived from the resistant clones. RNA microarrays, comparing the parental cells with the resistant clones, identified a possible resistance mechanism involving the induction of a pro-inflammatory pathway leading to c-MYC overexpression. Western blotting, as well as immunocytochemical and immunohistochemical staining, performed on the CRCs and CRC-PDX-derived samples confirmed the role of c-MYC overexpression in the evolution of nab-PTX resistance. Conclusion: The conditional reprogrammed cell (CRC) methodology addresses the need for a reliable method for generating primary cell lines on a single patient basis. The ability to rapidly model in vitro, and verify in vivo, that the overexpression of c-MYC contributes to the development of nab-PTX resistance is a significant advancement in the field and provides a platform for discovery of more effective treatment of refractory PDAC. Citation Format: George S. Avetian, Erika M. Parasido, Jonathan Brody, Jordan Winter, Eric Londin, Michael Pishvaian, Eric Glasgow, Stephen Byers, Christopher Albanese. Using patient-derived PDAC cells to understand c-MYC involvement in the drug resistance mechanisms of pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4073.