ABSTRACT
Cancer types with lower mutational load and a non-permissive tumor microenvironment are intrinsically resistant to immune checkpoint blockade. While the combination of cytostatic drugs and immunostimulatory antibodies constitutes an attractive concept for overcoming this refractoriness, suppression of immune cell function by cytostatic drugs may limit therapeutic efficacy. Here we show that targeted inhibition of mitogen-activated protein kinase (MAPK) kinase (MEK) does not impair dendritic cell-mediated T cell priming and activation. Accordingly, combining MEK inhibitors (MEKi) with agonist antibodies (Abs) targeting the immunostimulatory CD40 receptor results in potent synergistic antitumor efficacy. Detailed analysis of the mechanism of action of MEKi shows that this drug exerts multiple pro-immunogenic effects, including the suppression of M2-type macrophages, myeloid derived suppressor cells and T-regulatory cells. The combination of MEK inhibition with agonist anti-CD40 Ab is therefore a promising therapeutic concept, especially for the treatment of mutant Kras-driven tumors such as pancreatic ductal adenocarcinoma.
Subject(s)
Adenocarcinoma/drug therapy , Antibodies, Monoclonal/pharmacology , Antineoplastic Combined Chemotherapy Protocols/pharmacology , CD40 Antigens/agonists , Carcinoma, Pancreatic Ductal/drug therapy , Mitogen-Activated Protein Kinase Kinases/antagonists & inhibitors , Protein Kinase Inhibitors/pharmacology , Animals , Antibodies, Monoclonal/therapeutic use , Antineoplastic Combined Chemotherapy Protocols/chemistry , Antineoplastic Combined Chemotherapy Protocols/therapeutic use , Biomarkers, Pharmacological/metabolism , CD40 Antigens/immunology , Cell Line, Tumor , Cell Proliferation/drug effects , Cell Survival/drug effects , Dendritic Cells/immunology , Dendritic Cells/metabolism , Drug Synergism , Gene Expression Profiling , Humans , Macrophages/drug effects , Macrophages/immunology , Male , Mice , Mice, Inbred C57BL , Protein Kinase Inhibitors/chemistry , Protein Kinase Inhibitors/therapeutic use , T-Lymphocytes/drug effects , T-Lymphocytes/immunology , T-Lymphocytes/metabolism , Transcriptome/geneticsABSTRACT
We recently described a positive feedback loop connecting c-MYC, NAMPT, DBC1 and SIRT1 that contributes to unrestricted cancer cell proliferation. Here we determine the relevance of the loop for serrated route intestinal tumorigenesis using genetically well-defined BrafV600E and K-rasG12D mouse models. In both models we show that c-MYC and SIRT1 protein expression increased through progression from hyperplasia to invasive carcinomas and metastases. It correlated with high NAMPT expression and was directly associated to activation of the oncogenic drivers. Assessing functional and molecular consequences of pharmacological interference with factors of the loop, we found that inhibition of NAMPT resulted in apoptosis and reduced clonogenic growth in human BRAF-mutant colorectal cancer cell lines and patient-derived tumoroids. Blocking SIRT1 activity was only effective when combined with a PI3K inhibitor, whereas the latter antagonized the effects of NAMPT inhibition. Interfering with the positive feedback loop was associated with down-regulation of c-MYC and temporary de-repression of TP53, explaining the anti-proliferative and pro-apoptotic effects. In conclusion we show that the c-MYC-NAMPT-DBC1-SIRT1 positive feedback loop contributes to murine serrated tumor progression. Targeting the feedback loop exerted a unique, dual therapeutic effect of oncoprotein inhibition and tumor suppressor activation. It may therefore represent a promissing target for serrated colorectal cancer, and presumably for other cancer types with deregulated c-MYC.
Subject(s)
Cell Transformation, Neoplastic , Cytokines/metabolism , Intestinal Neoplasms/etiology , Intestinal Neoplasms/metabolism , Nicotinamide Phosphoribosyltransferase/metabolism , Oncogenes , Proto-Oncogene Proteins c-myc/metabolism , Sirtuin 1/metabolism , Animals , Apoptosis/genetics , Biomarkers , Biopsy , Cell Line, Tumor , Cell Proliferation , Drug Resistance, Neoplasm/genetics , Immunohistochemistry , Intestinal Neoplasms/drug therapy , Intestinal Neoplasms/pathology , Mice , Mutation , Neoplasm Metastasis , Phosphatidylinositol 3-Kinases/metabolism , Phosphoinositide-3 Kinase Inhibitors/pharmacology , Proto-Oncogene Proteins B-raf/genetics , Signal Transduction , Sirtuin 1/antagonists & inhibitorsABSTRACT
Fluid-phase endocytosis is a homeostatic process with an unknown role in tumor initiation. The driver mutation in pancreatic ductal adenocarcinoma (PDAC) is constitutively active KRasG12D, which induces neoplastic transformation of acinar cells through acinar-to-ductal metaplasia (ADM). We have previously shown that KRasG12D-induced ADM is dependent on RAC1 and EGF receptor (EGFR) by a not fully clarified mechanism. Using three-dimensional mouse and human acinar tissue cultures and genetically engineered mouse models, we provide evidence that (i) KRasG12D leads to EGFR-dependent sustained fluid-phase endocytosis (FPE) during acinar metaplasia; (ii) variations in plasma membrane tension increase FPE and lead to ADM in vitro independently of EGFR; and (iii) that RAC1 regulates ADM formation partially through actin-dependent regulation of FPE. In addition, mice with a pancreas-specific deletion of the Neural-Wiskott-Aldrich syndrome protein (N-WASP), a regulator of F-actin, have reduced FPE and impaired ADM emphasizing the in vivo relevance of our findings. This work defines a new role of FPE as a tumor initiating mechanism.
