Abstract 3198: Therapeutic potential of MET inhibitor combined with immune checkpoint blockade in pancreatic cancer

Abstract

Abstract Novel Combination Therapeutic Targeting of the Immune Checkpoint PD-1 and c-MET in Pancreatic Cancer Introduction: Therapeutic regimens incorporating immune checkpoint inhibitors (ICIs) have improved survival in many cancers, but have had little impact in pancreatic ductal adenocarcinoma (PDAC). We previously discovered that these ICIs directly target autonomously expressed and functional PD-1 on PDAC cells. We sought to investigate downstream effectors of PD-1 signaling in PDAC cells as potential novel therapeutic targets. Methods: We performed a Phospho Explorer Array, which measures the levels of over 200 phospho-specific antibodies and their corresponding total proteins, to determine activated signaling pathways following exposure of PDAC cells to PD-L1 (the ligand for PD-1). Upon detecting upregulation of PD-1 mediated MET signaling, we verified MET pathway activation by exposing PDAC cells (MIAPaCa-2 and PANC-1) to PD-L1 and measuring levels of phosphorylated MET by immunoblotting. Then, we tested whether the MET small molecule inhibitor blocked PD-1 mediated MET signaling. Finally, PDAC patient-derived organoids (PDOs) were utilized to test the cytotoxicity of ICIs alone or in combination with cabozantinib. Results: The phospho-protein array revealed 10-fold upregulation of MET activity followed exposure of PDAC cells to PD-L1. Western blot assay verified increased levels of MET phosphorylation that varied in a time-dependent manner following PD-L1 treatment in both PANC-1 and MIAPaCa-2 cell lines. Pre-treatment of PDAC cells with cabozantinib completely blocked PD-1/PD-L1 mediated MET phosphorylation. By CellTiter-Glo assay the IC50 of cabozantinib was calculated in MIAPaCa-2 and PANC-1 cells as 9.5 µM and 8.6 µM, respectively. Combining cabozantinib with clinical grade anti-PD-1 monoclonal antibodies nivolumab and pembrolizumab revealed synergistic cytotoxicity in PDAC cells and PDOs. Conclusion: In these preliminary studies, we report PD-1 activation of the MET pathway and synergy killing of PDAC cancer models with novel combination therapy of cabozantinib and ICIs in PDAC. This positive data warrants further exploration of the interaction of MET with the PD-1/PD-L1 axis and its role in PDAC progression. Note: This abstract was not presented at the meeting. Citation Format: Mei Gao, Miranda Lin, Yachao Yang, Joseph Kim. Therapeutic potential of MET inhibitor combined with immune checkpoint blockade in pancreatic cancer [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 3198.