Abstract
Giant cell tumor of bone (GCTB) is a benign but locally aggressive tumor, which can cause significant bone destruction at the epiphysis of long bones. Recent studies have demonstrated that norcantharidin (NCTD) can inhibit the proliferation and migration of various human cancer cells, but the role of NCTD in GCTB has not previously been evaluated. The aim of this study was to explore the nature of the anti-cancer effects of NCTD in GCTB and to elucidate the biomolecular mechanisms responsible for these effects. Primary stromal cell cultures, representing the main neoplastic component of GCTB, were used for cell-based experiments. Firstly, the anti-cancer effects of NCTD on GCTB stromal tumor cells were investigated by CCK-8 assay, flow cytometry and transwell invasion assay. Next, microRNA (miRNA) microarray and quantitative reverse transcription PCR (qRT-PCR) analyses were performed to examine and verify altered expression of miRNAs associated with NCTD treatment. Subsequently, the GCTB stromal cells were transfected with miR-30a inhibitor to confirm its involvement in the observed anti-cancer effects of NCTD. Luciferase reporter assays were carried out to identify the target gene of miR-30a. Moreover, changes in the expression of protein markers of AKT signaling were measured by Western Blot analysis. The results demonstrated that NCTD treatment could inhibit cell proliferation, block the cell cycle process and induce cell apoptosis in GCTB stromal cells. An inhibitory effect of NCTD on GCTB stromal cell invasion through inhibition of epithelial mesenchymal transition (EMT) was also observed. Expression of miR-30a was significantly upregulated by NCTD treatment and miR-30a knockdown significantly reversed the anti-tumor effects of NCTD against GCTB stromal cells. Of note, metadherin (MTDH), a novel oncogene which modulates the AKT pathway, was identified as a direct target of miR-30a in GCTB stromal cells. Further data showed that miR-30a could negatively regulate the expression of MTDH and the AKT pathway in GCTB stromal cells. Importantly, MTDH expression was found to be inversely correlated with miR-30a expression in clinical GCTB specimens. Moreover, NCTD treatment effectively suppressed the AKT signaling pathway as demonstrated by downregulation of phosphorylated-Akt S473 (p-Akt S473), p-Akt (T308), phosphorylated-glycogen synthase kinase (GSK)3β (p-GSK3β) and c-Myc, whilst miR-30a inhibition re-activated the AKT signaling pathway in GCTB stromal cells. Our findings demonstrate that NCTD can inhibit cell proliferation and metastasis of GCTB stromal cells in vitro, via modulating the miR-30a/MTDH/AKT signaling axis. This suggests that NCTD has potential as a novel therapeutic treatment for GCTB.