Bone-induced expression of integrin b3 enables targeted nanotherapy of breast cancer metastases

Bone metastases occur in approximately 70% of metastatic breast cancer patients, often leading to skeletal injuries. Current treatments are mainly palliative and underscore the unmet clinical need for improved therapies. In this study, we provide preclinical evidence for an antimetastatic therapy based on targeting integrin b3 (b3), which is selectively induced on breast cancer cells in bone by the local bone microenvironment. In a preclinical model of breast cancer, b3 was strongly expressed on bone metastatic cancer cells, but not primary mammary tumors or visceral metastases. In tumor tissue from breast cancer patients, b3 was significantly elevated on bone metastases relative to primary tumors from the same patient (n ¼ 42). Mechanistic investigations revealed that TGFb signaling through SMAD2/ SMAD3 was necessary for breast cancer induction of b3 within the bone. Using a micelle-based nanoparticle therapy that recognizes integrin avb3 (avb3-MPs of 12.5 nm), we demonstrated specific localization to breast cancer bone metastases in mice. Using this system for targeted delivery of the chemotherapeutic docetaxel, we showed that bone tumor burden could be reduced significantly with less bone destruction and less hepatotoxicity compared with equimolar doses of free docetaxel. Furthermore, mice treated with avb3-MP-docetaxel exhibited a significant decrease in bone-residing tumor cell proliferation compared with free docetaxel. Taken together, our results offer preclinical proof of concept for a method to enhance delivery of chemother-apeutics to breast cancer cells within the bone by exploiting their selective expression of integrin avb3 at that metastatic site.