Targeting integrin α6 stimulates curative-type bone metastasis lesions in a xenograft model.

Laminin binding integrin receptors are key mediators of epithelial cell migration and tumor metastasis. Recent studies have demonstrated a role for the alpha 6 integrin (ITGA6/CD49f) in maintaining stem cell compartments within normal bone marrow and in residency of tumors metastatic to bone. In this study, we tested a function-blocking antibody specific for ITGA6, called J8H, to determine if pre-existing cancer lesions in bone could be slowed and/or animal survival improved. Human prostate tumors were established by intracardiac injection into male severe combined immunodeficient (SCID) mice and treatment with J8H antibody was initiated after one week. Tumor progression was monitored by micro computed tomography (CT) imaging of skeletal lesions. Animals that received weekly injections of the anti-ITGA6 antibody showed radiographic progression in only 40% of osseous tumors (femur or tibia), compared to control animals, where 80% of the lesions (femur or tibia) showed progression at 5 weeks. Kaplan-Meier survival analysis demonstrated a significant survival advantage for J8H-treated animals. Unexpectedly, CT image analysis revealed an increased proportion of bone lesions displaying a sclerotic rim of new bone formation, encapsulating the arrested lytic lesions in animals that received the anti-ITGA6 antibody treatment. Histopathology of the sclerotic lesions demonstrated well-circumscribed tumor within bone, surrounded by fibrosis. These data suggest that systemic targeting of the ITGA6-dependent function of established tumors in bone may offer a non-cytotoxic approach to arrest the osteolytic progression of metastatic prostate cancer, thereby providing a new therapeutic strategy for advanced disease.