Zoledronic acid modulates human osteosarcoma cells proliferation via GSK-3β activation

Zoledronate is clinically used for preventing skeletal complications of osteoporosis and specific types of cancer associated with bone metastasis. Zoledronate inhibits osteoclast development and induces osteoclast apoptosis, thereby reducing bone lysis. Zoledronic acid (ZOL) plays a key role in treating osteosarcoma (OS) and improving the prognosis of patients with OS; however, its mechanism remains unclear. The effect of zoledronic acid on osteosarcoma cells was examined, and MTT was performed to determine the effect of ZOL on osteosarcoma cell proliferation. Cells were treated with 0, 25, 50, 100 or 200 μM ZOL for 24 h, 48 h and 72 h. p-AKT/AKT and p-GSK-3β/GSK-3β expression levels were checked by western blotting. Further study compared 100 μM ZOL alone for 48 h, Li2CO3 (1mM) alone and ZOL (100 μM) plus Li2CO3 (1 mM) with no treatment (control). The effects of GSK-3β on ZOL-induced apoptosis among these groups were characterized by flow cytometry, MTT assay, transmission electron microscopy (TEM) and western blot. In this study, we found that the proliferation of MG-63 cells was significantly decreased after treatment with 25, 50, 100 or 200 μM ZOL for 48 and 72 h compared to untreated control cells. The expression levels of p-AKT/AKT and p-GSK-3β/GSK-3β in MG-63 cells and U-2 OS cells were inhibited by ZOL in both a dose- and time-dependent manner. Significant decreases in the expression of Cyclin D1, β-Catenin, and c-Myc were observed in the groups that underwent ZOL treatment. Additionally, compared to ZOL (100 μM) treatment alone, co-treatment with ZOL (100 μM) and Li2CO3 (1 mM) rescued cell proliferation and restored a significant percentage of apoptotic cells. Our study suggests that the specific mechanism by which ZOL affects apoptosis of osteosarcoma cells is through the AKT/GSK-3β/β-Catenin signaling pathway.