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Sunitinib treat ment did not significantly decrease the size of osteolytic lesions compared to the control group. To determine the effect of treatment on osteoclast number, bone sections of the hind legs were stained for TRAP to determine presence of osteoclasts at the tumor bone interface. selleck chemical MLN8237 Histological examination showed lower TRAP positive osteoclasts in the metastatic hind legs of mice treated with Sunitinib but this difference was not significant. Histological appearances of representative sections stained for TRAP are shown in Figure 2B. growth to the boundary of the periosteum. Statistical analyses Two tailed unpaired Students t tests were used to assess differences between treated and control groups. P values less than 0. 05 were considered statistically significant.

Sunitinib as a monotherapy inhibits tumor growth The effect of Sunitinib on tumor growth as a single agent was evaluated. Fluorescent tumor area was deter mined as this parameter has been reported to have a better correlation with micro CT based osteolytic lesion grade than fluorescent intensity. The fluorescent area of metastatic tumors was measured when tumors were first detected at 4 weeks following tumor cell inoculation and again one week later. Mice treated with Sunitinib alone had significantly lower tumor fluorescent area at 4 weeks than mice in the control group. Further more, imaging at 5 weeks also revealed significantly smaller tumors. Therefore Sunitinib preventive treatment results in inhibition of growth of smaller tumors in bone and is also effective in inhibiting tumor growth of estab lished tumors in the bone microenvironment.

Histo logical measurement of cross sectional tumor area from the epiphyseal line of the distal femur and extending into the diaphysis confirmed a decrease in size of tumor in the bone with Sunitinib treatment. Furthermore, histological evaluation of tumor angiogen esis revealed that Sunitinib significantly inhibited tumor neovascularization. The mean vessel density of hind legs with bone metastases was 63 17 with Sunitinib treatment compared to 139 11 for control mice. The data suggest that Sunitinib is effective in inhibiting growth of bone metastases through inhibition of new blood vessel formation. Histological appearances of representative sections stained for CD34 are shown in Figure 4B.

Discussion In this study we evaluated whether preventive dose admin istration of the multi tyrosine kinase Sunitinib is effective in inhibiting bone metastases arising from disseminated tumor cells. We show that Sunitinib used in the prophylac tic setting does not decrease the number of metastatic colonized sites or inhibit subsequent progression of osteo lytic lesions. There is however a reduction in tumor growth which is associated with a significant decrease in tumor blood vessels.