The Sustained Induction of c-MYC Drives Nab-Paclitaxel Resistance in Primary Pancreatic Ductal Carcinoma Cells

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive disease with limited and, very often, ineffective medical and surgical therapeutic options. The treatment of patients with advanced unresectable PDAC is restricted to systemic chemotherapy, a therapeutic intervention to which most eventually develop resistance. Recently, nab-paclitaxel (n-PTX) has been added to the arsenal of first-line therapies, and the combination of gemcitabine and n-PTX has modestly prolonged median overall survival. However, patients almost invariably succumb to the disease, and little is known about the mechanisms underlying n-PTX resistance. Using the conditionally reprogrammed (CR) cell approach, we established and verified continuously growing cell cultures from treatment-naïve patients with PDAC. To study the mechanisms of primary drug resistance, nab-paclitaxel-resistant (n-PTX-R) cells were generated from primary cultures and drug resistance was verified in vivo, both in zebrafish and in athymic nude mouse xenograft models. Molecular analyses identified the sustained induction of c-MYC in the n-PTX-R cells. Depletion of c-MYC restored n-PTX sensitivity, as did treatment with either the MEK inhibitor, trametinib, or a small-molecule activator of protein phosphatase 2a. IMPLICATIONS: The strategies we have devised, including the patient-derived primary cells and the unique, drug-resistant isogenic cells, are rapid and easily applied in vitro and in vivo platforms to better understand the mechanisms of drug resistance and for defining effective therapeutic options on a patient by patient basis.

Abstract 1283: Targeting c-MYC and MAPK pathway to overcome pancreatic cancer drug resistance

Background: Acquired resistance to systemic chemotherapy is the main complication in pancreatic ductal adenocarcinoma (PDAC) treatment. Although there are studies focused on gemcitabine resistance mechanisms, our understanding of the mechanisms of nab-paclitaxel (n-PTX) treatment failure remains extremely limited. To enhance the use of properly powered patient-derived platforms, we adopted the conditionally reprogrammed (CR) cell culture technique in order to develop both parental and nab-PTX-resistant cells. The CR approach allowed us to identify the critical role of c-MYC and ERK in the PDAC drug response. Small molecule activators of PP2A (SMAPS) have showed activity in inhibiting lung KRAS-mutant tumor growth. We used SMAPS as new therapeutic agents in PDAC, for its ability to alter c-MYC activity through PP2A dysregulation and enhance PDAC sensitivity to n-PTX.

Methods: Long-term cultures of PDAC CRs were established from treatment-naive PDAC patients’ biopsies, and used to generate drug-resistant cells. Zebrafish and mouse model were used to test the cells’ ability to form tumors and to verify the drug resistance in vivo. Molecular analyses were used to characterize the drug-resistant cells and to identify key pathways involved in the drug resistance evolution. Genomic and chemical alterations of the key proteins were used to confirm the involvement in the drug resistance mechanism. We regulated the expression of c-MYC and ERK using SMAPS as a new targeting agent and trametenib to verify the direct correlation between c-MYC and ERK and the drug resistance mechanism.

Results: Using the credentialed KRAS-mutant CR cultures, we generated n-PTX-resistant cell lines. The parental and nab-PTX resistant cells were subjected to subcutaneous injections in nude mice, and formed tumors in 2-3 weeks. Histological evaluation showed that the CRs self-assembled into ductal structures, surrounded by a desmoplastic stromal microenvironment that faithfully recapitulates human PDAC. Resistant profiles were verified both in mouse and Zebrafish model. RNA microarrays identified a sustained induction of a pro-inflammatory pathway leading to c-MYC overexpression. c-MYC silencing and overexpression confirmed the role of c-MYCin the evolution of nab-PTX resistance. Treatment of the resistant CRs with either trametenib or with SMAPS resulted in enhanced sensitivity to nab-PTX. We furtherverified that the enhanced sensitivity was commensurate with a reduction in p-Erk and c-Myc.

Conclusion: The CR 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 n-PTX resistance is a significant advancement in the field. Our data showed that SMAPs or trametanib overcome a significant component of the n-PTX resistance providing new hope for refractory PDAC.

Citation Format: Erika Maria Parasido, George S. Avetian, Jonathan Brody, Jordan Winter, Eric Londin, Michael Pishvaian, Eric Glasgow, Stephen Byers, Goutham Narla, Christopher Albanese. Targeting c-MYC and MAPK pathway to overcome pancreatic cancer drug resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1283.