Co-targeting BET Bromodomain Proteins and MNK Kinases in Pancreatic Cancer

A growing body of research has now demonstrated that inhibitors targeting bromodomain and extra-terminal domain (BET) proteins, which mediate mRNA transcription, have anti-tumor effects against pancreatic ductal adenocarcinoma (PDAC). BET inhibitors can also normalize the PDAC stroma by suppressing the activation of cancer-associated fibroblasts (CAFs). However, BET inhibitors induce Rac1-mediated activation of MNK kinases, which mediate mRNA translation. Importantly, targeting MNK kinases and the MNK effector hnRNPA1 enhances the efficacy of BET inhibitors. Significantly, MNK inhibitors induce CD8+ T cell infiltration, but their effector function is suppressed by the tumor-associated macrophages (TAMs). Notably, BET inhibitors can decrease the infiltration of TAMs. The objective in this application is to elucidate the mechanisms by which the combination of BET and MNK inhibitors demonstrates anti-tumor responses against PDAC. The central hypothesis is that the combination effectively targets the cancer cells, modulates the tumor immune microenvironment, and normalizes the pancreatic stroma to suppress PDAC growth. Three specific aims are proposed: 1) Define and target negative feedback loops to enhance the anti-tumor effects of BET inhibitors in vivo; 2) Evaluate the effects of the combination of BET and MNK inhibitors on CD8+ T cell infiltration and activation; 3) Determine the effects of the combination of BET and MNK inhibitors on the pancreatic stroma. Under the first aim, the mechanisms by which MNK effectors hnRNPA1 and CYFIP1, which can function downstream of Rac1, limit the efficacy of BET inhibitors will be evaluated. Further, the efficacy of co-treatment with BET and MNK inhibitors will be evaluated in organoid and transgenic mouse models of PDAC. For the second aim, the effects of the combination therapy on CD8+ T cell infiltration and activation and macrophage abundance and polarization will be evaluated. In addition, the contribution of MNK kinases and the MNK effectors hnRNPA1 and CYFIP1 in macrophages to limiting the efficacy of BET inhibitors will be evaluated. In the third aim, the effects of the combination therapy on the stromal reaction will be characterized in the transgenic mouse model. The contribution of MNK kinases, CYFIP1, and hnRNPA1 in pancreatic CAFs to limiting the efficacy of BET inhibitors will also be evaluated. In addition, the relationship between BET and MNK kinase activity, MNK effectors, and stromal reaction will be evaluated in human PDAC tumor specimens. There are several innovative elements in this proposal, including the novel therapeutic approach to enhance anti-tumor responses in PDAC patients; novel concepts on how the combination therapy of BET and MNK inhibitors modulates the tumor immune microenvironment and the stromal reaction for synergistic anti-tumor responses; and the unique combination of complex models of PDAC, including in vivo orthotopic, organoid, and transgenic mouse models. This proposed research is significant because it will have important clinical-translational implications and should result in the development of novel combination therapies for PDAC patients.