Abstract
Targeting the colony-stimulating factor 1 receptor (CSF1R) pathway to deplete tumor-associated macrophages (TAMs) represents a promising strategy to overcome immunotherapy resistance in colorectal cancer (CRC). However, resistance to CSF1R inhibitors limits effectiveness. We find that CSF1R inhibition, while effectively reducing TAM abundance, fails to suppress tumor growth. Through imaging mass cytometry (IMC), we further reveal that the CSF1R inhibitor PLX3397 indirectly activates cancer-associated fibroblasts (CAFs), impedes T cell infiltration, and suppresses T cell function. Mechanistically, CSF1R inhibitors unexpectedly activate the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway, which promotes connective tissue growth factor (CTGF) release and subsequent CAF activation. Critically, anti-CTGF therapy rescues CSF1R inhibitor efficacy in vivo. The addition of checkpoint immunotherapy to CSF1R inhibitor and anti-CTGF in animal models leads to complete tumor regression. This combination strategy presents a potential approach to enhance the efficacy of immune checkpoint inhibitors in CRC.