Paclitaxel-loaded polyphosphate nanoparticles: a potential strategy for bone cancer treatment.

While it has been shown that phosphates can target molecules and nanocarriers to bone we herein demonstrate the preparation of polyphosphate nanoparticles loaded with paclitaxel using a simple miniemulsion/solvent-evaporation technique as a model for chemotherapeutic delivery. Polyphosphates exhibit much higher structural versatility, relying on the pentavalence of the phosphorus center compared to conventional polyesters. This versatility allows for the development of new degradable polymeric carriers with inherent bone adhesion ability by the interaction of the nanoparticles with a calcium phosphate material used for bone regeneration. The novel polyphosphate nanoparticles were investigated in detail with respect to their size distribution, zeta-potential, thermal and morphological properties and were further proven to be efficiently loaded with a hydrophobic drug (up to 15 wt%). The in vitro cytotoxicity was assessed against human cancer cell lines (HeLa and Saos-2), and the paclitaxel-loaded nanoparticles showed a similar cytotoxicity profile similar to the commercially available formulation Taxomedac® and the pure paclitaxel for loading ratios of 10 wt% but additionally proved efficient adhesion on calcium phosphate granules allowing drug delivery to bone. This first report demonstrates that polyphosphate nanoparticles are promising materials for the development of systemic or local bone cancer treatment, even by direct application or by formation of composites with calcium phosphate cements.