Hydroxyapatite (HAp) nanoparticles: Promises in cancer diagnosis and therapy

Hydroxyapatite (HAp) nanoparticles have recently achieved a unique position in cancer diagnosis and therapy (theranostics). In vitro experiments have shown that HAp nanoparticles can enter tumor cells and cause programmed cell death (apoptosis). To improve the anticancer effects of HAp nanoparticles, bioengineers and biomedical scientists incorporate particular elements (e.g., iron (Fe)) into theranostic HAp nanoparticles. Accordingly, HAp nanoparticles can be employed in different cancer therapy approaches like photothermal therapy and photodynamic therapy, either alone or in combination with other materials (e.g., biopolymers). Moreover, HAp nanoparticles can serve as suitable vectors for targeted delivery of anticancer chemicals and drugs. Adding some elements, such as gadolinium and europium, to the HAp composition makes it a suitable imaging agent for bio-imaging applications like magnetic resonance imaging. Various surface modifications can be applied to improve the biocompatibility of HAp nanoparticles and prevent their aggregation. In addition, targeted therapy seems possible with HAp nanoparticles having the surface modified with specific ligands (e.g., anti-Herceptin antibody). In conclusion, HAp nanoparticles are showing great promise in cancer theranostic strategies; however, doing animal and clinical trials is suggested as a key step forward to take benefit from these stunning materials.