Antioxidants inhibit TNFalpha-induced motility and invasion of human osteosarcoma cells: possible involvement of NFkappaB activation. Osteosarcoma is the most frequent malignant bone tumor in children. It is highly invasive, however, the mechanisms behind osteosarcoma cell invasion are as yet still unknown. In the present study, treatment with TNFalpha enhanced the invasiveness of two human osteosarcoma cell lines, OST and MNNG. TNFalpha treatment also induced tumor cell motility, adhesion to laminin, the expression of matrix metalloproteinase 9 (MMP9), and the nuclear translocation of nuclear factor kappaB (NFkappaB) in the osteosarcoma cells. Moreover, antioxidants inhibited TNFalpha-induced osteosarcoma cell invasion, motility and NFkappaB nuclear translocation, but not adhesion to laminin or MMP9 expression. NFkappaB decoy, another NFkappaB inhibitor, also inhibited TNFalpha-induced osteosarcoma cell invasion and motility. Therefore, motility and NFkappaB activation were possibly related to TNFalpha-induced osteosarcoma cell invasion. However, adhesion to laminin or MMP did not demonstrate any correlation with TNFalpha-induced osteosarcoma cell invasion. Although NFkappaB is known to regulate TNFalpha-induced phenotypes, it may influence only motility and invasion, but not the MMP or laminin-mediated adhesion of these osteosarcoma cells.