Targeting Myeloid Cells in Head and Neck Squamous Cell Carcinoma: A Kinase Inhibitor Library Screening Approach

Head and neck squamous cell carcinoma (HNSCC) is highly enriched with tumor-infiltrating myeloid cells, including tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs). However, effective therapeutic agents targeting tumor-associated myeloid cells in HNSCC are currently lacking. Here, we employed a unique co-culture system to investigate how HNSCC cells affect tumor-associated myeloid cells. We found that the presence of cancer cells significantly enhances myeloid cell proliferation and promotes TAM differentiation. To identify potential therapeutic agents, we screened a custom library of 70 kinase inhibitors to assess their effects on distinct subsets of tumor-associated myeloid cells. We discovered specific inhibitors that differentially suppressed the populations of TAMs, monocytic MDSCs (M-MDSCs), or polymorphonuclear MDSCs (PMN-MDSCs), suggesting that inhibiting different targets could reduce distinct subsets of tumor-associated myeloid cells. Conversely, some inhibitors were found to increase the population of CD11b⁺Ly6G^-Ly6C^- myeloid cells. Among the promising inhibitors tested, vatalanib, a VEGF-R inhibitor, demonstrated significant in vivo efficacy at inhibiting tumor growth and reducing tumor-associated myeloid cells, thereby underscoring its potential as a therapeutic agent. Our findings highlight specific kinase inhibitors with differential modulatory effects on HNSCC-associated myeloid subsets and caution the application of some as anti-cancer drugs. This experimental system may provide a robust platform for identifying new agents targeting tumor-associated myeloid cells in HNSCC and beyond, and for elucidating mechanistic insights into tumor-myeloid cell interaction.