Preparation and Preliminary Biodistribution Study of ⁶⁴Cu-NOTA-NOC

The radiolabeling of somatostatin octapeptide analogue NOTA-NOC with ⁶⁴Cu was carried out. The preliminary study of ⁶⁴Cu-NOTA-NOC on the in vitro stability, the lipid-water partition coefficient, and the distribution in normal and tumor-bearing mice was conducted. The labeling and quality control methods of ⁶⁴Cu-NOTA-NOC were developed. The in vitro stability of ⁶⁴Cu-NOTA-NOC was investigated in buffer solution and 10% fetal bovine serum solution at 37 ℃. The lipid-water partition coefficient of ⁶⁴Cu-NOTA-NOC was also determined. Biodistribution studies were performed in normal KM mice and nude mice bearing BON-1 tumor and small-animal PET imaging studies were performed on nude mice bearing BON-1 tumor. The results showed that radiolabeling of NOTA-NOC with ⁶⁴Cu was straightforward and fast (～15 min) at room temperature in high yield and >95% of radiochemical purity. ⁶⁴Cu-NOTA-NOC showed good stability in buffer solution and 10% fetal bovine serum solution at 37 ℃. The value of LogP was -1.12±0.005 6 which indicated 64Cu-NOTA-NOC was hydrophilic. Biodistribution studies in normal mice revealed high uptake of radioactivity in kidneys, suggesting that ⁶⁴Cu-NOTA-NOC was mainly metabolized by the kidneys, and the blood uptake decreases significantly 4 h, indicating rapid blood clearance rate. ⁶⁴Cu-NOTA-NOC was mainly metabolized by the kidney in nude mice bearing BON-1 tumor. At 1 h, 2 h, 4 h, tumor uptake was (3.74±1.23)%ID/g, (4.80±0.92)%ID/g and (1.31±0.27)%ID/g respectively, and tumor/muscle ratio reached to 10.38 at 2 h. The results of PET/CT imaging of nude mice bearing BON-1 tumor showed that the tumor uptake of ⁶⁴Cu-NOTA-NOC peaked at 1 h, which was 7.7%ID/g，and after co-administration of the blocker, the tumor uptake of ⁶⁴Cu-NOTA-NOC was significantly reduced to 0.94%ID/g. ⁶⁴Cu-NOTA-NOC could be prepared under mild reaction conditions; and it had good stability in buffer solution and 10% fetal bovine serum. ⁶⁴Cu-NOTA-NOC was mainly metabolized by kidneys, and cleared fast from the body in normal mice as well as in model mice. The tumor/muscle ratio could reach 10.38 at 2 h. The results of PET/CT imaging showed that the tumor uptake of ⁶⁴Cu-NOTA-NOC was specific. These results demonstrated the potential of ⁶⁴Cu-NOTA-NOC in the diagnosis of SSTR positive tumors, and it is worthy of further evaluation.