In vitro and in vivo cytotoxicity of an anti-osteosarcoma immunotoxin containing pokeweed antiviral protein.

Abstract

Successful treatment of many patients with osteosarcoma requires more effective chemotherapy. Since new agents are needed, we have developed an immunotoxin using TP-3, an IgG2b mAb which recognizes human and canine osteosarcomas and budding capillaries of tumors. The plant hemitoxin, pokeweed antiviral protein (PAP), was conjugated to TP-3 to produce an immunotoxin highly active against osteosarcoma. After 48 h no viable human OHS osteosarcoma cells were present in cultures containing TP-3-PAP as demonstrated by the absence of [3H]thymidine uptake into DNA. Furthermore, clonogenic assays indicated > 3.9 log kill of OHS at 18 h. The IC50 of TP-3-PAP against OHS was 3.5 +/- 1.0 (SD) x 10(-12) M. TP-3 mAb without PAP had no effect on OHS proliferation; PAP alone had no effect on OHS growth unless concentrations > 1000 pM were used. When TP-3-PAP (1.25 micrograms-10.0 micrograms) was given i.p. q.d. on days 3-5 after tumor inoculation, a dose-dependent reduction of the number of lung metastases was observed (P < 0.001). These results indicate that the TP-3-PAP immunotoxin may be useful in the treatment of osteosarcoma and some soft tissue sarcomas.