Hydroxyapatite – A trojan horse in the delivery of apatite-binding cytostatics in bone cancer

Sammanfattning: Osteosarcoma is a malignant cancer of the bone mainly affecting adolescents. Despite progress, the clinical management of osteosarcoma is still challenging. With the current chemotherapy protocol being used for more than 30 years, the number of poor responders is increasing. Although new treatments have been explored since then, no improved tumor eradication effect have been found. In the present thesis, we have developed a new treatment method for osteosarcoma, using hydroxyapatite (HA) based materials as a platform for local delivery of cytostatics. Doxorubicin (DOX), a cornerstone osteosarcoma drug, was chosen as a drug candidate, due to its binding capacity to HA. Different types of HA-based biomaterials were tested for local or targeted delivery of DOX. The efficacy of the developed system was evaluated in-vitro, in osteosarcoma cells as well as in-vivo, in mice bearing an aggressive osteosarcoma.In Study 1, a clinically approved calcium sulphate (CaS)/HA biomaterial achieved a sustained and controlled release of DOX up to 28 days, both in-vitro and in-vivo. Compared to no treatment or the clinical standard with systemic DOX administration, the local delivery of DOX using a CaS/HA biomaterial significantly hindered tumor progression by inhibiting angiogenesis and cell proliferation.In Study 2, we investigated the physicochemical interactions between DOX and different sizes of HA particles, both in-vitro and in-vivo. When delivered by HA nanoparticles, DOX is routed to the mitochondria causing insufficient ATP synthesis, less cell migration and cell apoptosis. This leads to stronger in-vivo tumor eradication compared to systemic administration of DOX. Furthermore, nHA mediated delivery of DOX may prevent further metastases in- vivo, which was indirectly verified by PET/CT data.In Study 3, HA particles (nHA, mHA or n/mHA) were labelled with carbon 14 (14C) to detect particle migration in- vivo. During the observational time of 28 days, the majority (>99.9%) of implanted HA particles, irrespective of the size, stayed in the implantation site (proximal tibia), without migrating to other vital organs. No pathological changes were detected in the vital organs.In summary, we describe a new and efficient method to supplement osteosarcoma treatment, with a possible rapid translational potential, using clinically approved constituents. By using a hydroxyapatite-based biomaterial, DOX could be routed to the tumor site, more efficiently and with less side effects compared to systemic administration. The chemical interaction between DOX and HA lead to a sustained and controlled DOX release which further improved its tumor eradication effect. When using HA nanoparticles, DOX could be directed to the mitochondria causing tumor cell starvation, reduced migration and apoptosis, jointly leading to improved tumor eradication. The local administration of HA particles, irrespective of size, was confirmed as safe without damage to vital organs. In the future, chemotherapeutics with multi-release profile potentially could be applied by using a combination of nHA and mHA.