TP3-pokeweed antiviral protein (PAP) immunotoxin is directed against the p80 antigen on osteosarcoma cells. Previous studies have demonstrated that TP3-PAP kills clonogenic human osteosarcoma cells in vitro and shows significant antitumor activity in a murine soft tissue sarcoma model (P. M. Anderson, et al, Cancer Res., 55: 1321-1327, 1995.) In this study, we demonstrate that TP3-PAP elicits potent in vivo antitumor activity in a hamster cheek pouch model of human osteosarcoma. Furthermore, treatment with TP3-PAP at nontoxic dose levels significantly delayed the emergence and progression of leg tumors and markedly improved tumor-free survival in severe combined immunodeficient mice challenged with OHS human osteosarcoma cells. Thus, TP3-PAP may be useful in the treatment of poor risk osteosarcoma.

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