Inhibition of Breast Cancer Metastasis and Angiogenesis by Antiosteopontin Single-Chain Fv-Fc Fusion Protein

Abstract Osteopontin (OPN) is associated with many diseases, and its role in tumor growth and metastasis has been studied in breast cancers. Previous studies have described anti-OPN antibodies that could inhibit tumor cell adhesion and invasion in vitro , but until now, there are no systematic studies on antitumor effects of anti-OPN antibodies in vivo . In the present study, we have raised several anti-OPN single-chain variable fragments from phage antibody library and expressed them as single-chain variable fragment-constant region fragment fusion proteins in Chinese hamster ovary cells. Of them, two antibodies (1A12 and 2H8) were able to inhibit MDA-MB-435s breast cancer cell attachment, invasion, migration, and colony formation in soft agar. Furthermore, 1A12 and 2H8 inhibited the anti-apoptotic and prosurvival functions of OPN in human umbilical vein endothelial cell. In human umbilical vein endothelial cell capillary tube formation, chicken chorioallantoic membrane assay, and rabbit corneal micropocket assay, the two antibodies showed markedly inhibitory effects toward angiogenesis. We investigated antitumor effects of anti-OPN antibodies in nude mice by assessing xenograft tumor growth and lung metastasis potential. The results showed that the two antibodies were capable of delaying primary tumor growth and reducing spontaneous lung metastasis. Epitope mappings of these two anti-OPN antibodies were performed, and a new binding site of 1A12 was revealed. In summary, the present study has demonstrated the roles of anti-OPN antibodies in blocking the function of OPN, suggesting that they may have the potential to be developed for future clinical use.