Evaluation of the covalently linked antimetabolite 5-FdU with alendronate in a preclinical breast cancer bone metastases mouse model

Patients diagnosed with breast cancer in advanced tumor stages show a high frequency of skeletal metastases. These bone lesions uncouple the balance between bone formation and resorption, resulting in severe osteolysis. These lesions often result in increased fracture risk, compression of the spine and hypercalmia, decreasing the quality of life for the patient. As a result, anti-cancer chemotherapeutics are often combined with bisphosphonates, a class of drugs with high affinity for bone mineral which inhibit bone-resorbing osteoclasts. Recently, conjugated drugs have been developed which combine the anti-tumor effects of chemotherapeutic agents with the bone-targeting abilities of these bisphosphonates. Here we present the novel drug ale-5-FdU, a conjugate between the anti-metabolite 5-FdU and the bisphosphonate alendronate. Treatment of breast cancer cells with ale-5-FdU shows cell cycle arrest consistent with treatment with 5-FdU alone. In vivo, mice treated with ale-5-FdU showed reductions in both the number of metastases per mouse, as well as in tumor size. Ale-5-FdU treatment was also found to significantly reduce osteoclast number and activity without impairing osteoblast function, resulting in improved bone health. We also demonstrate that the conjugation of 5-FdU and alendronate is stable in mice for more than 2 weeks and present at significantly greater concentrations within the bone environment in as little as 1 day after injection compared to 5-FdU alone. Overall, ale-5-FdU represents a novel anti-tumor drug with high specificity for the bone and the potential to reduce to progression and improve bone health.