Surface ligand-regulated renal clearance of MRI/SPECT dual-modality nanoprobes for tumor imaging

Background The general sluggish clearance kinetics of functional inorganic nanoparticles tend to raise potential biosafety concerns for in vivo applications. Renal clearance is a possible elimination pathway for functional inorganic nanoparticles delivered through intravenous injection, but largely depending on the surface physical chemical properties of a given particle apart from its size and shape. Results In this study, three small-molecule ligands that bear a diphosphonate (DP) group, but different terminal groups on the other side, i.e. , anionic, cationic, and zwitterionic groups, were synthesized and used to modify ultrasmall Fe 3 O 4 nanoparticles for evaluating the surface structure-dependent renal clearance behaviors. Systematic studies suggested that the variation of the surface ligands did not significantly increase the hydrodynamic diameter of ultrasmall Fe 3 O 4 nanoparticles, nor influence their magnetic resonance imaging (MRI) contrast enhancement effects. Among the three particle samples, Fe 3 O 4 nanoparticle coated with zwitterionic ligands, i.e. , Fe 3 O 4 @DMSA, exhibited optimal renal clearance efficiency and reduced reticuloendothelial uptake. Therefore, this sample was further labeled with 99m Tc through the DP moieties to achieve a renal-clearable MRI/single-photon emission computed tomography (SPECT) dual-modality imaging nanoprobe. The resulting nanoprobe showed satisfactory imaging capacities in a 4T1 xenograft tumor mouse model. Furthermore, the biocompatibility of Fe 3 O 4 @DMSA was evaluated both in vitro and in vivo through safety assessment experiments. Conclusions We believe that the current investigations offer a simple and effective strategy for constructing renal-clearable nanoparticles for precise disease diagnosis. Graphical Abstract