ABSTRACT
Nanoparticles offer extraordinary flexibility in the design of injectable formulations of radionuclides. Preclinical studies demonstrate excellent delivery and retention in tumor especially after intratumoral injection, but also intravenously, compared to free radionuclides. However, very little has progressed to clinical trials. While delivery and retention within the tumor of nano-formulations are superior to free radionuclides, more comparison is needed against targeted radionuclides to assess efficacy. In comparison to brachytherapy, retention in the tumor so far has been inferior to conventional seeds and has more complicated dosimetry considerations. Nano-formulations present different biodistributions and prolonged blood circulation compared to free radionuclides. While this improves systemic delivery to tumors, it increases normal tissue exposure and nanoparticles are retained in liver and kidney longer than free isotopes. The flexibility to load multiple or various radionuclides with the same carrier for both diagnostic and therapeutic purposes giving identical biodistributions is a major advantage. The ability to combine radionuclides with additional therapeutics, stimuli-responsive and targeting moieties provides further opportunities for developing formulations with therapeutic advantages.
