Denosumab and Zoledronic acid (ZOL) are two antiresorptive drugs currently in use for treating osteoporosis. They have different mechanisms of action but both have been shown to delay the onset of skeletal-related events in patients with giant cell tumor of bone (GCT). However, the anti-tumor mechanisms of denosumab on the neoplastic GCT stromal cells remain unknown. In this study, we focused on the direct effects of denosumab on the neoplastic GCT stromal cells and compared with ZOL. The microscopic view demonstrated a reduced cell growth in ZOL-treated but not in denosumab-treated GCT stromal cells. ZOL was found to exhibit a dose-dependent inhibition in cell growth in all GCT stromal cell lines tested and cause apoptosis in two out of three cell lines. In contrast, denosumab only exerted a minimal inhibitory effect in one cell line and did not induce any apoptosis. ZOL significantly inhibited the mRNA expression of receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG) in two GCT stromal cell lines whereas their protein levels remained unchanged. On the contrary, denosumab did not regulate RANKL and OPG expression at both mRNA and protein levels. Moreover, the protein expression of Macrophage Colony-Stimulating Factor (M-CSF), Alkaline Phosphatase (ALP), and Collagen α1 Type I were not regulated by denosumab and ZOL either. Our findings provide new insights in the anti-tumor effect of denosumab on GCT stromal cells and raise a concern that tumor recurrence may occur after the withdrawal of the drug.

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Bauhinia blakeana (Leguminosae subfam. Caesalpinioideae tribe Cercideae), or the Hong Kong Orchid Tree, is of great horticultural value. It is completely sterile and is shown here to be the result of hybridization between the largely sympatric species, B. purpurea and B. variegata. Although the analysis of patterns of morphological variation revealed only a few examples of phenotypic intermediacy, study of intersimple sequence repeat (ISSR) markers enabled unequivocal identification of the parental species due to the presence of additive inheritance of alleles and the absence of any bands that are unique to B. blakeana. Investigation of aspects of the reproductive biology of the taxa furthermore revealed that the parental species are largely xenogamous, have flowering periods that overlap seasonally and temporally, and share common pollinators. Evidence is provided to show that B. blakeana is not naturally stabilized and is only maintained horticulturally by artificial propagation. It is therefore recommended that the hybrid be regarded as a horticultural cultivar rather than a naturally occurring species; a new cultivar name, Bauhinia 'Blakeana', is accordingly validated.

Giant cell tumor (GCT) of bone is an aggressive non-cancerous tumor, which consists of multi-nucleated osteoclast-like giant cells, stromal cells, and monocytes. It is believed that stromal cells are the neoplastic component of this tumor. Expression of the receptor activator of nuclear factor kappa B ligand (RANKL) in the stromal cells stimulates the monocytes to form giant multi-nucleated osteoclast-like cells, causing bone over-resorption at the tumor site. Previously, our group has reported the up-regulation of RANKL in GCT of bone stromal cells, but the mechanism is unknown. Using stromal cell culture of GCT obtained from patients, we demonstrated the up-regulation of the transcriptional activator CCAAT/enhancer binding protein beta (C/EBPbeta). RANKL promoter studies revealed that C/EBPbeta over-expression induced RANKL promoter activity in a dose-dependent manner and a CCAAT-box within the region nt -357/-1 contributed to the basal transcription activity, with a possible C/EBPbeta binding element in the region nt -460/-358 leading to further induction. Furthermore, we also showed that C/EBPbeta bound to the RANKL promoter in GCT stromal cells in vivo by chromatin immunoprecipitation. To conclude, our study has shown that C/EBPbeta is a RANKL promoter activator in stromal cells of GCT of bone and we have proposed a model in which C/EBPbeta plays an important role in the osteolytic characteristics and pathological causes of GCT of bone.

Giant cell tumor of bone (GCT) is a destructive neoplasm of uncertain etiology that affects the epiphyseal ends of long bones in young adults. GCT stromal cells (GCTSCs) are the primary neoplastic cells of this tumor and are the only proliferating cell component in long-term culture, which recruits osteoclast-like giant cells that eventually mediate bone destruction. The oncogenesis of GCT and factors driving the neoplastic stromal cells to proliferate extensively and pause at an early differentiation stage of pre-osteoblast lineage remain unknown. Overexpression of p63 was observed in GCTSCs and there is growing evidence that p63 is involved in oncogenesis through different mechanisms. This study aimed to understand the specific role of p63 in cell proliferation and oncogenesis of GCTSCs. We confirmed p63 expression in the mononuclear cells in GCT by immunohistochemical staining. By real-time PCR analysis, we showed a higher level (>15-fold) of TAp63 expression in GCTSCs compared to that in mesenchymal stem cells. Furthermore, we observed that knockdown of the p63 gene by siRNA transfection greatly reduced cell proliferation and induced cell cycle arrest at S phase in GCTSCs. We found that the mRNA expression of CDC2 and CDC25C was substantially suppressed by p63 knockdown at 24–72 h. Moreover, p63 was found to be recruited on the regulatory regions of CDC2 and CDC25C, which contain p53-responsive elements. In summary, our data suggest that p63 regulates GCTSC proliferation by binding to the CDC2 and CDC25C p53-REs, which may inhibit the p53 tumor suppressor activity and contribute to GCT tumorigenesis.

Giant cell tumor of bone (GCTB) is a locally aggressive destructive bone lesion. The management of pulmonary metastasis and local recurrence after the surgical treatment of GCTB remains a challenge. Pathologically, stromal cells in GCTB are known as primary neoplastic cells and are recognized as incompletely differentiated preosteoblasts. Therefore, inducing GCTB stromal cells to differentiate into cells with a mature osteoblastic phenotype may stop tumor growth and recurrence. In this study, we aimed to investigate how simvastatin, a clinically approved and commonly used statin that has been known to promote the maturation of cells of the osteogenic lineage, affects GCTB stromal cells. We found that simvastatin effectively inhibited cell viability by suppressing proliferation and by inducing apoptosis in GCTB stromal cells. Moreover, simvastatin treatment upregulated the expression of genes related to osteogenic maturation, such as runt-related transcription factor 2, osteopontin, and osteocalcin, and increased the mineralization of the extracellular matrix in GCTB stromal cells. Ingenuity pathway analysis was used to discover that the vitamin D receptor pathway was involved in the simvastatin-induced osteogenic differentiation of GCTB stromal cells by upregulating the 1,25-dihydroxyvitamin D metabolism. Taken together, this in vitro study demonstrates the antitumor and differentiation-promoting effects of simvastatin on GCTB stromal cells and suggests the possibility of using simvastatin as an adjuvant therapy for GCTB. These findings support further clinical investigation of the efficacy of using simvastatin as an adjuvant therapy for GCTB to reduce recurrence and distant metastasis after surgical treatment.

Giant cell tumor (GCT) is the most common nonmalignant primary bone tumor reported in Hong Kong. It usually affects young adults between the ages of 20 and 40. This tumor is well known for its potential to recur following treatment. To date no effective adjuvant therapy exists for GCT. Our project aimed to study the effects of pamidronate (PAM), farnesyl transferase inhibitor (FTI-277), geranylgeranyl transferase inhibitor (GGTI-298), and their combinations on GCT stromal cells (SC). Individual treatment with PAM, FTI-277, and GGTI-298, inhibited the cell viability and proliferation of GCT SC in a dose-dependent way. Combination of FTI-277 with GGTI-298 caused synergistic effects in reducing cell viability, and its combination index was 0.49, indicating a strong synergism. Moreover, the combination of FTI-277 with GGTI-298 synergistically enhanced cell apoptosis and activated caspase-3/7, -8, and -9 activities. PAM induced cell-cycle arrest at the S-phase. The combination of PAM with GGTI-298 significantly increased OPG/RANKL mRNA ratio and activated caspase-3/7 activity. Our findings support that the combination of bisphosphonates with GGTIs or FTIs with GGTIs may be used as potential adjuvants in the treatment of GCT of bone. ß