Exploiting the high-affinity phosphonate–hydroxyapatite nanoparticle interaction for delivery of radiation and drugs

Hydroxyapatite is biocompatible and used in various biomedical applications. Here, we generated hydroxyapatite nanoparticles (HNPs) of various sizes (40–200 nm) and demonstrated that they can be stably loaded with drugs or radioisotopes by exploiting the high-affinity HA–(poly)phosphonate interaction. Clinically available phosphonates, clodronate, and Tc-99m-methylene-diphosphonate (Tc-99m-MDP), were efficiently loaded onto HNPs within 15 min. Biodistribution of radiolabeled HNP-MDP-Tc99m in mice was monitored non-invasively using microSPECT-CT. Imaging and dosimetry studies indicated that the HNPs, regardless of size, were quickly taken up by Kupffer cells in the liver after systemic administration into mice. Clodronate loaded onto HNPs remained biologically active and were able to result in selective depletion of Kupffer cells. This method of drug or isotope loading on HA is fast and easy as it eliminates the need for additional surface modifications of the nanoparticles.