Multifunctional polyethyleneimine-coated gold nanoparticles for CD13-targeted cancer imaging

Objectives: The unique properties of gold nanoparticles (AuNPs) offer a great opportunity for developing multimodality imaging probes. In this study, we developed multifunctional polyethyleneimine (PEI)-coated AuNPs and radiolabel the AuNPs with ⁶⁴Cu for PET, CT, and fluorescence imaging of CD13 receptor expression in human tumor xenografts.

Methods: Cy5.5 fluorophore, PEGylated NGR peptide, and sarcophagine (Sar) chelator were conjugated on the surface of PEI, and followed by acetylation of the remaining amines. The resulting multifunctional AuNPs were characterized, and the cytotoxicity of AuNPs was evaluated by MTT cell viability assay. The specific binding of AuNPs with HT-1080 cells overexpressing CD13 receptors was confirmed by flow cytometry and confocal microscopy. The multifunctional AuNPs were then radiolabeled with ⁶⁴Cu and subjected to small animal PET, CT, and fluorescence imaging, and biodistribution studies. The CD13 binding specificity of AuNPs was further evaluated by in vivo blocking studies.

Results: Multifunctional CD13-targeted AuNPs were successfully synthesized, and radiolabeled with ⁶⁴Cu in >85% decay-corrected yield with radiochemical purity of >99%. The MTT assay showed that multifunctional AuNPs are non-cytotoxic at the concentration of 100 µg/mL. The NGR peptide renders the AuNPs with targeting specificity to HT-1080 cancer cells overexpressing CD13 receptors, which is confirmed by flow cytometry and confocal microscopy studies. MicroPET imaging results showed that ⁶⁴Cu-labeled AuNPs exhibit excellent tumor uptake in CD13-positive HT-1080 tumor xenografts (T/M ratio: 7.36 ± 0.75 at 5 h pi), and significantly lower tumor uptake in CD13-blocking group (T/M ratio: 2.11 ± 0.59 at 5 h pi). Tumor binding specificity was confirmed by ex vivo PET/fluorescence imaging and biodistribution studies. Enhanced CT imaging was also accomplished with CD13-targeted AuNPs.

Conclusion: The ⁶⁴Cu-labeled multifunctional AuNPs have been successfully developed for multimodality imaging of CD13 receptor expression. Multimodality imaging with ⁶⁴Cu-labeled AuNPs may provide a unique approach to quantitatively localize and characterize CD13-expressing tumors. Research Support: This work was supported by the Ming Hsieh Research Grant for Cancer Research and the USC Department of Radiology.