Towards more efficient inhalable chemotherapy: Fabrication of nanodiamonds-releasing microspheres

Nanodiamonds (NDs) are among the most promising chemotherapy vectors, however, they tend to aggregate upon storage, or when exposed to mild changes in pH or ionic strength. Therefore, fabrication of dried NDs with minimal change in particle size is highly desirable. In this study, we have developed a dried powder form of NDs with controlled particle size to be eligible for pulmonary delivery, after screening different drying protectants for their effect on NDs particle size and surface charge. Results showed that the nanospray-drying process in the presence of mannitol prevented the aggregation of NDs. Nanospray-dried NDs microparticles exhibited an optimal aerodynamic size for pulmonary delivery, and the in vitro aerosol deposition testing showed that NDs-embedded mannitol microspheres could deliver more than half of the emitted fraction to the lower stage of the Twin impinger device; indicating high pulmonary delivery potential. Upon loading NDs with doxorubicin (NDX) prior to spray dryng, they were able to deliver 2.6 times more drug to A549 lung cancer cell line compared to the free drug. Pharmacokinetics study in rats showed that inhaled NDX microparticles could efficiently limit the biodistribution of the drug to the lungs, and minimize the drug fraction reaching the systemic circulation. To conclude, nanospray-dried NDs microparticles present a promising vehicle for the pulmonary delivery of chemotherapeutic agents for treatment of lung cancer.