The targeted delivery of
tumor necrosis factor-α (TNF-α) with
antibodies specific to splice
isoforms of
fibronectin [e.g., F8-TNF, specific to the extra-domain A (EDA) domain of
fibronectin] has already shown efficacy against
experimental sarcomas but has not yet been investigated in orthotopic
sarcomas. Here, we investigated F8-TNF in a syngeneic K7 M2-derived orthotopic model of
osteosarcoma as a treatment against pulmonary
metastases, the most frequent cause of
osteosarcoma-related death. Immunofluorescence on human
osteosarcoma tissue confirmed the presence of EDA in primary
tumors (PTs) as well as
metastases. In mice, the efficacy of F8-TNF against PTs and early pulmonary
metastases was evaluated. Intratibial PT growth was not affected by F8-TNF, yet early
micrometastases were reduced possibly due to an F8-TNF-dependent attraction of pulmonary CD4+, CD8+, and natural killer cells. Furthermore, immunofluorescence revealed stronger expression of EDA in early pulmonary
metastases compared with PT tissue. To study progressing pulmonary
metastases, a hind limb
amputation model was established, and the efficacy of F8-TNF, alone or combined with
doxorubicin, was investigated. Despite the presence of EDA in
metastases, no inhibition of progressive metastatic growth was detected. No significant differences in numbers of CD4+ or CD8+ cells or F4/80+ and Ly6G+ myeloid-derived cells were observed, although a strong association between metastatic growth and presence of pulmonary Ly6G+ myeloid-derived cells was detected. In summary, these findings demonstrate the potential of F8-TNF in activating the immune system and reducing early metastatic growth yet suggest a lack of efficacy of F8-TNF alone or combined with
doxorubicin against progressing
osteosarcoma metastases.