Macrophage Syk-PI3Kγ-HIF axis controls tumor immune suppression

Macrophages (MΘs) play a critical role in tumor growth, immunosuppression and inhibition of adaptive immune responses in cancer. Hence, targeting signaling pathways in MΘs that promote tumor immunosuppression will provide therapeutic benefit. PI3Kγ has been recently established by our group and others as a novel immuno-oncology target. Herein, we report that macrophage Syk drives polarization of immunosuppressive macrophages which establish an immunosuppressive tumor microenvironment in in vivo syngeneic tumor models. Genetic or pharmacological blockade of Syk in MΘs promotes a pro-inflammatory MΘ phenotype, restores CD8+ T cell activity, destabilizes HIF under hypoxia, and stimulates antitumor immune response. Moreover, we have developed in silico the “first in class” dual Syk/PI3K inhibitor, SRX3207, for the combinatorial inhibition of Syk and PI3K in one small molecule to activate anti-tumor immunity in vivo. This chemotype shows great efficacy in various tumor models and represents a new therapeutic approach to treat devastating cancers. Significance: Our data indicate a central role of Syk in macrophage transcriptional programming leading to inhibition of adaptive immune responses. Furthermore, SRX3207 blocks macrophage expression of immunosuppressive factors and activates anti-tumor immune responses, validating the concept of combined Syk and PI3K inhibition as an effective approach to treat macrophage driven cancers. Examination of effects of SykKO and a dual Syk/PI3K inhibitor on tumor progression, immune cell populations, protein levels and gene expression.