Effects Of Bortezomib On Osteoblast In Myeloma Bone Disease

[Background] Multiple myeloma is the disease with the highest incidence of bone involvement among the malignant diseases. It has a severe impact on patients' quality of life. Complex interactions between myeloma cells and bone marrow stroma cells promote osteoclastic bone resorption and suppress osteoblast activity, there is uncoupled or severely imbalanced bone remodeling with increased bone resorption and decreased or absent bone formation. Bisphosphonates are specific inhibitors of osteoclast activity and are the current mainstay of therapy for myeloma bone disease. They reduce skeletal damage but do not restore bone formation. Clinical data indicate that Bortezomib has potential to regulate bone turnover, it could increased serum concentrations of alkaline phosphatase and osteocalcin. But lytic lesions have not been reported to heal in patients receiving Bortezomib. Mechanism of Bortezomib effecting on osteoblast is uncleared. We compared the effect between Bortezomib and Dexamethasone on osteoblast in different culture condition to explore the mechanism of the effecting on osteoblasts in myeloma bone disease by Bortezomib.[Objectives] The proliferation and apoptosis of MC-3T3E1 cells by Bortezomib and Dexamethasone were observed to evaluate the clinical significance on Bortezomib in myeloma bone disease.[Methods] The proliferation and apoptosis of osteoblast were observed in different culture condition in vitro. Cell growth index were evaluated by MTT assay. The numbers of mineralized nodules were counted after alizarin red staining. Annexin V/PI staining was performed to detect apoptosis rate. RT-PCR and Wstern blot were used to detect mRNA and protein of osteoblast markers Runx2/cbfa1, osteocalcin (OCN) and osterix(OSX).[Rusults] Bortezomib inhibited proliferation of MC-3T3E1 cells in a dose-dependent manner, and the 48h IC50 was 38.1nM. Bortezomib in low concentration (5nM) did not have effect on osteoblast cell proliferation (P>0.10). But at this concentration the decrease of early opoptosis rates was 49.6% and 61.7% for MC-3T3E1 at myeloma cell cocultured and conditioned medium. After the treatment of low does Bortezomib, the mRNA and protein level of osteoblast marker OCN and OSX but not Runx2/cbfa1 were increased, while no significant change was observed in activity of Alkaline phosphatase and the number of mineralized nodules.[Conclusion] Proteasome inhibitor bortezomib in low concentration could prevent the apoptosis of osteoblasts induced by myeloma cells and up-regulat osteoblast markers related to Runx2/cbfa1 pathway. The internal mechanisms of osteoblast were activated by Bortezomib might directly protect osteoblasts from apoptosis induced by MM cells.