In vivo evaluation of stability and metabolic pathway of radiolabeled polymeric nanoparticles

Objectives The goal of this study was to determine the in vivo stability, distribution, and metabolic pathway of C-atrial natriuretic factor (CANF) conjugated to comb-like nanoparticles. The 64Cu-CANF-Comb has been shown to bind to the natriuretic peptide receptor-C (NPR-C) upregulated in atherosclerosis.

Methods The radiolabeling stability of 64Cu-CANF-Comb nanoparticles was determined by incubating the particles with mouse serum and analyzing with fast protein liquid chromatography (FPLC). After intravenous injection of 64Cu-CANF-Comb in C57 mice, blood samples were collected and separated into red blood cells, platelet-rich plasma, platelet-poor plasma, and the platelet pellet via centrifugation and counted with a gamma counter. The platelet-poor plasma was analyzed with FPLC to assess the stability of 64Cu-CANF-Comb. The longitudinal distribution of CANF-Comb in vivo was performed via 67Cu radiolabeling up to 2 weeks. The excretion of 67Cu-CANF-Comb was collected to evaluate its metabolic pathway.

Results FPLC analysis showed 71.4±0.8% (n=3) intact 64Cu-CANF-Comb after 48h incubation with mouse serum. The longitudinal in vivo evaluation of 67Cu-CANF-Comb showed < 4% association with red blood cells with the rest remaining in plasma. The stability study demonstrated the in vivo integrity of CANF-Comb with no degradation up to 2 weeks. At 3 weeks post injection, 30% of the injected dose remained in mice, mainly in liver. The metabolism study showed 60% clearance of 67Cu-CANF-Comb through feces.

Conclusions The in vivo evaluation of radiolabeled CANF-Comb showed radiolabeling stability for PET imaging with minimal non-specific binding to blood cells. The longitudinal stability and significant clearance of CANF-Comb suggests its potential for translational research.

Research Support This work is supported by the National Institutes of Health as a Program of Excellence in Nanotechnology (HHSN268201000046C).