Pexidartinib modulates pro-inflammatory cytokines in a co-culture model of stromal-immune cell crosstalk in tenosynovial giant cell tumor

Tenosynovial giant cell tumor (TGCT) is driven by CSF1 translocation, leading to chronic inflammation within the joint microenvironment dominated by CSF1R-expressing macrophages. Although pexidartinib successfully achieves tumor-volume reduction, its role in modulating the inflammatory component and stromal-immune cell crosstalk remains poorly characterized. We utilized a model where TGCT synoviocytes were stimulated with TNF + IL-17 or co-cultured with activated peripheral blood mononuclear cells (PBMCs). Cultures were treated with varying pexidartinib doses (0–50 µM). Cytokine profiles were analyzed via ELISA, and PBMC aggregate formation was qualitatively assessed by light microscopy. In isolated synoviocytes, pexidartinib showed minimal cytotoxicity in the localized subtype, whereas higher doses selectively reduced the viability of diffuse TGCT synoviocytes. The treatment significantly suppressed IL-6 and IL-8 secretion across both subtypes. In co-cultures, IFNγ was the most sensitive cytokine to pexidartinib, showing significant reduction starting at 10 µM, whereas higher doses (25–50 µM) were required to suppress IL-6, IL-17, and IL-1β release. Conversely, TNF levels increased significantly at 25 µM and failed to decline at 50 µM. Additionally, microscopic examination revealed a qualitative reduction in PBMC aggregation at higher pexidartinib doses, though formal image quantification and underlying mechanisms remain to be established. Pexidartinib modulates the TGCT secretory profile and requires high concentrations to effectively inhibit synovial-immune crosstalk. The unexpected elevation in TNF raises the hypothesis that pexidartinib may trigger immune reprogramming with possible consequences for long-term joint integrity.