Encapsulating ¹¹¹In in Nanocontainers for Scintigraphic Imaging: Synthesis, Characterization, and In Vivo Biodistribution

A new strategy for the radiolabeling of porous nanocontainers has been developed, and the first experiments in vivo are reported. Our approach consists of the use of nanometer-sized zeolites whose channels have been filled with the positively charged gamma-emitter (111)In(3+) via simple ion exchange. To avoid leaching of the isotope under physiological conditions, the entrances of the channels have been closed using a specifically designed molecular stopcock. This stopcock has a positively charged group that enters the channels and entraps the loaded radionuclides via electrostatic and steric repulsion. The other side of the stopcock is a bulky triethoxysilane group that can covalently bind to the walls of the zeolite entrances, thereby irreversibly closing the channels. The surface of the zeolites has been functionalized with different chemical groups in order to investigate the different biodistributions depending of the nature of the functionalizations. Preliminary in vivo experiments with Wistar rats have been performed and showed the potential of the approach. This strategy leads to a nanoimaging probe with a very high density of radioisotopes in a confined space, which is highly stable in physiological solution and could allow a large variety of functionalities on its external surface.