B-Raf(V600E) cells in which either B-Raf(V600E) or TSP-1 were knocked down were implanted orthotopically into the thyroids of immunocompromised mice, resulting in significant reduction in tumor size and fewer pulmonary metastases from the primary carcinoma as compared with the control cells.
To confirm that lack of cleavage of TSP1 ablated its antiangiogenic function in the lung, we generated colon cancer cells stably secreting only the 3TSR domain and found that they inhibited formation of both liver and lung metastases.
In this study, we exploited S. choleraesuis carrying thrombospondin-1 (TSP-1) gene for treating primary melanoma and experimental pulmonary metastasis in the syngeneic murine B16F10 melanoma model.
In the present study, we found that epidermal growth factor (EGF) up-regulated TSP-1 expression in FTC-133 (primary tumor) but not in FTC-238 (lung metastasis) thyroid cancer cells.
Our laboratory previously showed that the CSVTCG (cys-ser-val-thr-cys-gly) sequence of TSP-1 functioned as a tumor cell adhesion domain and CSVTCG peptides as well as an anti-peptide antibody possessed anti-metastatic activity in a murine model of lung metastasis.
Injection of transfected clones that overexpressed TSP1 into the mammary fat pad of nude mice resulted in a dose-dependent inhibition of primary tumor size and an inhibition of spontaneous pulmonary metastases, which occurred in 21-30% of THBS-1 transfectants compared to 44-49% of controls (P = 0.007).