PDGFRA mediates the PI3K/AKT signaling pathway to regulate the growth and phenotype of GCTB tumor cells.

PURPOSE: The nature of true neoplastic cells of giant cell tumor of bone (GCTB) remains unverified. As the effect of denosumab on true neoplastic cells needs to be clarified, direct targeting of these cells remains unclear. METHODS: In this study, we obtained 32 formalin-fixed paraffin-embedded (FFPE) GCTB tissue blocks, performing H&E staining and immunohistochemistry staining of CD68. Multinucleated giant cells, monocytes, and CD68-negative mononuclear spindle cells were accurately captured by laser capture microdissection. The DNA of these cells was extracted, digested with HpaII and subjected to nested PCR amplification. We isolated and cultured GCTB primary tumor cells. The primary tumor cells were treated with denosumab and PDGFRA inhibitors. CCK8 assays and RT-qPCR were performed to reveal the effect of the inhibitors. RESULTS: In HUMARA-heterozygous samples, CD68 negative mononuclear spindle cells appeared as only one main peak after digestion, which suggests that the CD68 negative mononuclear spindle cells are monoclonal. Denosumab had no direct effect on the growth of GCTB primary tumor cells. PDGFRA inhibitor Avapritinib had a direct inhibitory effect on the growth of the tumor cells and altered the tumor cell phenotype. AKT inhibitors had a similar inhibitory effect as Avapritinib. Avapritinib altered the expression of AKT-related genes, and down-regulated pGSK3β. The downregulation of pAKT and pGSK3β was partially reversed by co-treatment with the AKT agonist SC79, suggesting PI3K/AKT as a downstream pathway of PDGFRA. CONCLUSION: CD68 negative mononuclear spindle cells are the true neoplastic cells of GCTB. PDGFRA inhibition may be a novel targeted therapy for GCTB.