Adenovirus-mediated ING4 Gene Transfer in Osteosarcoma Suppresses Tumor Growth via Induction of Apoptosis and Inhibition of Tumor Angiogenesis

The inhibitor of growth (ING) family proteins have been defined as candidate tumor suppressors. ING4 as a novel member of ING family has potential tumor-suppressive effects via multiple pathways. However, the therapeutic effect of adenovirus-mediated ING4 (Ad-ING4) gene transfer in human osteosarcoma is still unknown. In this study, we explored the in vitro and in vivo antitumor activity of Ad-ING4 in human osteosarcoma and its potential mechanism using a MG-63 human osteosarcoma cell line. We demonstrated that Ad-ING4 induced significant growth inhibition and apoptosis, upregulated the expression of P21, P27 and Bax, downregulated the Bcl-2 expression and activated Caspase-3 in MG-63 human osteosarcoma cells. Moreover, intratumoral injections of Ad-ING4 in athymic nude mice bearing MG-63 human osteosarcoma tumors significantly suppressed osteosarcoma xenografted tumor growth, increased the expression of P21, P27 and Bax, reduced the Bcl-2 and CD34 expression and microvessel density (MVD) in tumors. This retarded MG-63 osteosarcoma growth in vitro and in vivo in an athymic nude mouse model elicited by Ad-ING4 was closely associated with the increase in the expression of cell cycle-related molecules P21 and P27, decrease in the ratio of anti- to pro-apoptotic molecules Bcl-2/Bax followed by the activation of Caspase-3 leading to apoptosis via intrinsic apoptotic pathways, and the inhibition of tumor angiogenesis. Thus, our results indicate that Ad-ING4 is a potential candidate for human osteosarcoma gene therapy.