Screening of transcytosable iron oxide nanoparticles (TIONs) for deep tissue-penetrating imaging

Nanoparticle probes are advantageous over small molecular agents in medical imaging due to their prolonged circulation time, high payload capacity, and enhanced signal intensity. However, nanoparticle imaging probes are hindered by limited tissue penetration, often failing to provide sufficient contrast enhancement for imaging deep tissues. Herein, we developed a series of transcytosable iron oxide nanoparticles (TIONs) that penetrate deep tissue via cell transcytosis, enabling the T₂-weighted magnetic resonance imaging (MRI) of the internal tissues. To fabricate TIONs, we prepared iron oxide nanoparticles (IONs) modified with in situ growth of polylysine dendrimers of third generation, terminated with different β-carboxylic amides. The capacity of these IONs to induce cell internalization, exocytosis, and transcytosis was evaluated using a fluorescence-based high-throughput screening assay. Among them, G3-FiA and G3-DiA TIONs exhibited efficient transcytosis capability towards cancer cells. We further demonstrated the feasibility and efficacy of these TIONs for deep MRI of 4T1 subcutaneous tumors, GL261 subcutaneous and orthotopic glioma tumors. Additionally, we identified TIONs as effective agents for kidney-targeted deep tissue imaging, highlighting the applicability of the strategy for non-tumor tissue imaging. This study offers critical insights for designing nanoparticle-based delivery systems with enhanced tissue penetration, thereby advancing their potential for deep-tissue imaging applications.