Bone-Specific Enhancement of Antibody Therapy for Breast Cancer Metastasis to Bone

Therapeutic antibodies have gone a long way toward realizing their clinical potential and have become very useful for treating a variety of pathologies. Despite the rapid evolution of therapeutic antibodies, their clinical efficacy in treatment of bone tumors has been hampered by the inadequate pharmacokinetics and poor bone tissue accessibility of these large macromolecules. Here, we show that engineering therapeutic antibodies to include bone-homing peptide sequences dramatically enhances their concentration in the bone metastatic niche, resulting in significantly reduced survival and progression of breast cancer bone metastases. To enhance the bone tumor-targeting ability of engineered antibodies, we introduced varying numbers of a bone-homing peptide into permissive internal sites of the anti-HER2 antibody trastuzumab. Compared to the unmodified antibody, the engineered bone-targeting antibodies have similar pharmacokinetics and in vitro cytotoxic activity against HER2-positive cancer cells, but exhibit improved bone tumor distribution in vivo. Accordingly, in xenograft models of breast cancer metastasis to bone sites, engineered antibodies with enhanced bone specificity exhibit increased inhibition of both initial bone metastases and secondary multi-organ metastases from bone lesions. Furthermore, this engineering strategy is also applied to prepare bone-targeting antibody-drug conjugates with enhanced therapeutic efficacy. These results demonstrate that adding bone-specific targeting to antibody therapy results in robust delivery of therapeutic antibodies to the bone tumor niche. This provides a powerful strategy for overcoming inadequate treatment of bone cancer and the development of potentially acquired resistance to therapy.