CaMKK2 deletion increases antitumor potential through enhanced MHC-II expression in Macrophages

Abstract Objective: Glioblastoma is the most common and aggressive primary brain tumor with a 5 year prognosis of less than 5% survival. Efforts to extend this survival through therapeutic advancement have only led to modest improvements. Immunotherapy has shown promise in other cancers but only has limited effect in GBM, partially due to the dense infiltration of pro-tumor myeloid cells. Calmodulin-dependent Kinase Kinase 2 (CaMKK2) is highly expressed in myeloid cells and high expression is associated with a more severe tumor grade and worse survival in GBM. Preliminary studies show that CaMKK2 KO mice display extended median survival and tumor clearance. We hypothesize that CaMKK2 may drive myeloid cells’ pro-tumor function. Methods: To investigate this, immune cells were isolated from tumor-bearing CaMKK2 KO, LysMcre x CaMKK2fl/fl and CaMKK2-eGFP reporter mice. Multi-parameter flow was used to detect CaMKK2 and phenotype the tumor microenvironment (TME). The presence of CaMKK2 expressing myeloid cells in the TME was confirmed by confocal microscopy. Results/Conclusions: CaMKK2 is preferentially expressed in myeloid cells in naïve and tumorous mice. CaMKK2 deletion upregulated MHC-II in macrophages which is expected to promote an antitumor response. Upregulation was not seen in naive CaMKK2 KO mice suggesting it is a product of tumor-exposure. Conditional deletion of CaMKK2 in bone-marrow derived macrophages (BMDM) did not lead to this MHC-II upregulation suggesting that it is not a BMDM-intrinsic phenotype but results from CaMKK2 deletion in another cell-type. In summary, CaMKK2 deletion induced macrophages to a more immunostimulatory phenotype with expected anti-tumor effect, making CaMKK2 a promising therapeutic target for GBM.