Targeting the DKK1/CSF1 signaling axis to reprogram M2 macrophages and reverse chemoresistance in head and neck squamous cell carcinoma.

Understanding the mechanisms underlying drug resistance in head and neck squamous cell carcinoma (HNSCC) is critical for the development of effective therapeutic strategies. M2-type tumor-associated macrophages (M2-TAMs), activated by colony-stimulating factor 1 (CSF1), play a pivotal role in promoting chemoresistance and metastasis through immunosuppressive signaling and tumor-immune crosstalk. However, the precise mechanisms of CSF1-driven tumor support and macrophage activation remain incompletely understood. We employed humanized patient-derived xenograft (PDX) models of drug-resistant HNSCC to examine the functional roles of CSF1 and its downstream effectors. Drug-tolerant persister (DTP) cells derived from these models were subjected to transcriptomic profiling. In vitro, both direct and indirect co-culture systems were used to assess the impact of CSF1 modulation on tumor cell viability and M2 macrophage activity. The therapeutic potential of the CSF1R inhibitor pexidartinib (PLX3397), alone and in combination with cisplatin, was evaluated in vivo. Our findings revealed that CSF1 silencing in M2 macrophages reduced the viability of cisplatin-resistant SCC9-P and HSC3-P cells in an indirect co-culture system, indicating a paracrine survival signal. In contrast, CSF1 overexpression enhanced tumor cell proliferation. In direct co-culture, CSF1 silencing inhibited M2 macrophage activation, whereas CSF1 overexpression promoted M2 proliferation and immunosuppressive activity. In vivo, pexidartinib effectively disrupted CSF1-mediated resistance and reduced the expression of key tumor-promoting factors, including DKK1, IL10, CXCL12, and AKT1. Clinically, high DKK1 and CSF1 expression correlated with cisplatin resistance and poor prognosis. This study underscores the dual role of CSF1 in regulating both tumor survival and M2 macrophage activation in HNSCC. Targeting the DKK1/CSF1 axis may represent a promising strategy to overcome chemoresistance by disrupting tumor-macrophage crosstalk and reprogramming the immunosuppressive microenvironment.