Target-or-Clear Zirconium-89 Labeled Silica Nanoparticles for Enhanced Cancer-Directed Uptake in Melanoma: A Comparison of Radiolabeling Strategies

Designing a nanomaterials platform with high target to-background ratios has long been one of the major challenges in the field of nanomedicine. Here, we introduce a "target-or-clear" multifunctional nanoparticle platform that demonstrates high tumor-targeting efficiency and retention while minimizing off-target effects. Encouraged by the. favorable preclinical and clinical pharmacokinetic profiles derived after fine-tuning surface chemical properties of radioiodinated (I-124, t(1/2) = 100.2 h) ultrasmall cRGDY-conjugated fluorescent silica nanoparticles (C dots), we sought to investigate how the biological properties of these radioconjugates could be influenced by the conjugation of radiometals such as zirconium-89 (Zr-89, t(1/2) = 78.4 h) using two different strategies: chelator-free and chelator-based radiolabeling. The attachment of Zr-89 to newer, surface-aminated, integrin-targeting C' dots using a two-pot synthesis approach led to favorable pharmacokinetics and clearance profiles as well as high tumor uptake and target-to background ratios in human melanoma models relative to biological controls while maintaining particle sizes below the effective renal glomerular filtration size cutoff <10 nm. Nanoconjugates were also characterized in terms of their radiostability and plasma residence half-lives. Our Zr-89-labeled ultrasmall hybrid organic-inorganic particle is a clinically promising positron emission tomography tracer offering radiobiological properties suitable for enhanced molecularly targeted cancer imaging applications.