Overexpression of Smad7 Blocks Primary Tumor Growth and Lung Metastasis Development in Osteosarcoma

Abstract

Purpose: Osteosarcoma is the main malignant primary bone tumor in children and adolescents for whom the prognosis remains poor, especially when metastasis is present at diagnosis. Because transforming growth factor-b (TGFb) has been shown to promote metastasis in many solid tumors, we investigated the effect of the natural TGFb/Smad signaling inhibitor Smad7 and the TbRI inhibitor SD-208 on osteosarcoma behavior.Experimental Design: By using a mouse model of osteosarcoma induced by paratibial injection of cells, we assessed the impact of Smad7 overexpression or SD-208 on tumor growth, tumor microenvironment, bone remodeling, and metastasis development.Results: First, we demonstrated that TGFb levels are higher in serum samples from patients with osteosarcoma compared with healthy volunteers and that TGFb/Smad3 signaling pathway is activated in clinical samples. Second, we showed that Smad7 slows the growth of the primary tumor and increases mice survival. We furthermore demonstrated that Smad7 expression does not affect in vitro osteosarcoma cell proliferation but affects the microarchitectural parameters of bone. In addition, Smad7-osteosarcoma bone tumors expressed lower levels of osteolytic factors such as RANKL, suggesting that Smad7 overexpression affects the "vicious cycle" established between tumor cells and bone cells by its ability to decrease osteoclast activity. Finally, we showed that Smad7 overexpression in osteosarcoma cells and the treatment of mice with SD208 inhibit the development of lung metastasis.Conclusion: Taken together, these results demonstrate that the inhibition of the TGFb/Smad signaling pathway may be a promising therapeutic strategy against tumor progression of osteosarcoma, specifically against the development of lung metastasis.

Emerging Cytokine Networks in Osteosarcoma

“…Other studies have shown that high TGFβ mRNA levels in tumour cells are associated with aggressive behaviour as well as with lung metastasis [48] . Significant increased activation of SMAD3 signalling cascades and increased amounts of TGFβ1 in the serum of patients at high risk of developing pulmonary metastasis have also been observed [46] . Furthermore, TGFβ gene polymorphism has been identified in the serum of patients with metastatic osteosarcoma [49] .…”

“…In the early stages of carcinogenesis, TGFβ acts as tumour suppressor and its functions include inhibition of cell proliferation, induction of apoptosis, and inhibition of cell immortalisation [45,46] . In later stages, TGFβ promotes metastasis by inducing epithelial-mesenchymal transition (EMT) and promoting cell adhesion, migration, invasion, and chemotaxis.…”

“…In later stages, TGFβ promotes metastasis by inducing epithelial-mesenchymal transition (EMT) and promoting cell adhesion, migration, invasion, and chemotaxis. These functions are especially observed in aggressive and invasive tumours [45,46] . As regard to osteosarcoma, an in vitro study showed that tumour cells secrete TGFβ by activation of the TGFβ/SMAD-2/-3 signalling pathway.…”

Microenvironment Signals and Mechanisms in the Regulation of Osteosarcoma

“…The TGF-β1 inhibitor SB525334 signiicantly inhibited the migration and invasion of sphere-forming stemlike cells [54]. In an OS mouse model, either overexpression of the natural TGF-β/SMAD signaling inhibitor SMAD7 in OS cells or treatment with the TGF-β receptor inhibitor SD208 afected the microarchitectural parameters of the bone and inhibited lung metastasis [55]. The natural alkaloid halofuginone, an inhibitor of the TGF-β/ Smad3 cascade, speciically hindered OS progression against lung metastatic dissemination [56].…”

Updates on the Molecular Genetics of Colorectal Cancer

“…SMAD7 is a gene located on 18q21. It is a member of the transforming growth factor-β (TGF-β) family, in the anti-inflammatory signaling pathway which also plays a role in the metastasis of solid tumors [66][67][68]. SMAD7 inhibits TAK1 by binding TAB2 and TAB3, which potentiates the effects of TGF-β [66,67].…”