⁶⁴Cu labeled a new integrin targeted probe and its in vivo multimodal imaging

Objectives: Integrin α_vβ₃ is a very important receptor overexpressed in angiogenic and many tumor cells. Porphyrin based photosensitizers are useful agents for fluorescence imaging of cancer. Porphyrins are also excellent metal chelators forming highly stable metal-complexes making them efficient delivery vehicles for radioisotopes such as ⁶⁴Cu. Here our aim is to synthesis and evaluate a new tracer that combined porphyrins with peptide 3PRGD₂ radiolabeled with ⁶⁴Cu for PET and fluorescence imaging of α_vβ₃.

Methods: Porphyrin-3PRGD₂ was synthesized by solid phase peptide synthesis and radiolabelled with ⁶⁴Cu on a 20 μg scale in 0.1 M NH4OAc buffer (pH = 5.5)at 100^oC in 30 min and purified by Sep-Pak C18 cartridge .After cooling to room temperature, the resulting solution was analyzed by radio-HPLC. Porphyrin-3PRGD₂(≍20nm/ml) was incubation with α_vβ₃-positive U87MG cells in 2 h at 37 ℃ and using confocal fluorescence microscopy to see the targeting efficacy. ⁶⁴Cu - porphyrin-3PRGD₂ for in vivo MicroPET and fluorescence imaging in U87MG tumor-bearing mice with RGD blocking studies conducted to confirm the integrin αVβ3specificity.

Results: ⁶⁴Cu-porphyrin-3PRGD₂ can be prepared in a very high radiochemical purity after purified by Sep-Pak C18 cartridge(>95%). The tumors were clearly visualized by both the MicroPET and fluorescence imaging .The cell confocal fluorescence imaging consistent with the multimodal imaging results. Blocking study showed a significant inhibition of U87MG tumor uptake, indicating it is integrin α_vβ₃ mediated. Conclusion: Possessing dual PET and fluorescence imaging, ⁶⁴Cu-porphyrin-3PRGD₂ is very promising for tumor diagnosis. This study confirmed that ⁶⁴Cu-porphyrin-3PRGD₂ can serve as a safe cancer diagnosis agent with cancer-targeting ability and using the tracer in the mice for the Photodynamic therapy is in progress.