Novel strategy for preparing Cu-64 nanoparticles with ultrahigh specific activity using metal-free click chemistry
576 Objectives The objective is to develop a novel strategy to prepare Cu-64 labeled Shell-Cross-linked Knedel nanoparticles(SCKs) with ultrahigh Specific Activity(SA) via Metal-Free Click Chemistry(MFCC). Methods The SCKs contain a large amount of azide in the core, which facilitate the radiolabeling of SCKs with ultrahigh SA via MFCC. DOTA conjugated MFCC agent DBCO-DOTA was chelated with Cu-64, and was then purified by HPLC. The hydrophobic complex, DBCO-DOTA(Cu-64) migrated into the core of SCKs and clicked with the azide groups there, while the acetylenes in its shell allow the attachment of targeting group. The Cu-64 incorporated SCKs were purified with desalting column and analyzed by radio-FPLC. The advantages of MFCC include: 1) elimination of copper exchange between non-radioactive Cu in the catalyst and DOTA-chelated Cu-64; 2) elimination of the internal “click” reactions between the azide and acetylene groups in the same SCKs; 3) an increase in the “click” efficiency because water soluble Cu(I) does not need to reach the hydrophobic core of the SCKs. Results Over 80% radiolabeling yield was obtained after ~100 fold of DBCO-DOTA was incubated with Cu-64 for 30 min. The crude product was purified by HPLC, and both the unchelated metal and large excess ligand were separated, which significantly increased the effective SA of DBCO-DOTA(Cu-64). The complex, DBCO-DOTA(Cu-64) was then incorporated into the SCKs (containing 10% azide) via MFCC. Starting with 3.0 mCi Cu-64 (effective SA: 0.79 mCi/µmMol), the SA of Cu-64 labeled SCKs was 6.0 mCi/nmol. The radiochemical purity was ≥95% after purification. Conclusions A metal-free click chemistry approach for preparing Cu-64 labeled SCKs has been developed. By increasing the amount of Cu-64 and introducing more azide in the SCKs, the specific activity of Cu-64 labeled NPs can be as high as 300 mCi/nmol. Research Support It was supported by DOE Grant #ER64671