Bone is a common site of osteolytic and richly vascularized metastases of renal cell carcinoma (RCC) and Interferon (IFN)-α based therapies have been considered for the treatment of patients affected by this disease. The effects of IFN-α on metastatic RCC patients have been related to its immunomodulatory, and cytotoxic activity on tumor cells, but there could be an effect also on tumor induced osteoclast differentiation and bone angiogenesis. When osteoclasts obtained from human peripheral blood mononuclear cells, cultured in the presence of receptor activator of nuclear factor-kB (RANKL) and macrophage-colony stimulating factor (M-CSF), were treated with IFN-α, the expression of bone tartrate resistant acid phosphatase (TRACP) type 5b was reduced, as well as calcium-phosphate resorption activity and expression of pro-osteoclatic transcription factor c-Fos. IFN-α modulation of angiogenesis was studied by analysis of proliferation, survival, and migration of a bone endothelial cell line (BBE), and by the analysis of pro-angiogenic factor expression in RCC cell lines. IFN-α inhibited bone endothelial cell proliferation and the expression of FGF-2, while the vascular endothelial growth (VEGF) did not show any significant variation. Moreover, IFN-α inhibited the migration induced by the RCC through the impairment of fibroblast growth factor-2 (FGF-2) secretion. These data demonstrate multiple activities of IFN-α on renal cancer-induced bone disease, in addition to its recognized role as a cytotoxic and immunomodulatory agent, because they indicate its ability to reduce bone resorption and to impair tumor-associated angiogenesis, and they also suggest the use of IFN-α to treat skeletal metastases of other carcinomas.

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