Comparison of Two Kinds of ⁶⁴Cu Labelled Octreotide Analogues

Octreotide analogues DOTA-TOC and DOTA-TATE were labeled with ⁶⁴Cu. The influences of the ratio of peptide mass to ⁶⁴Cu activity, pH value, temperature and reaction time on labeling yield were investigated. The optimum labeling was determined. In vitro stability tests in saline and 10% bovine serum had been carried out. Biodistribution of the two radiolabelled compounds in normal mice and Micro PET imaging in nude mice bearing U87MG tumor had been evaluated. The results showed that the labeling yields of ⁶⁴Cu-DOTA-TOC and ⁶⁴Cu-DOTA-TATE were higher than 95%. Two kinds of octreotide analogues labeled with ⁶⁴Cu were quite stable in saline and decomposed slowly in 10% bovine serum at 37 ℃. Biodistribution results in normal mice showed that two ⁶⁴Cu labelled tracers had similar profiles. Both of the compounds washed out from the blood quickly. High uptake of radioactivity in liver and kidneys indicated the tracers were excreted via both hepatobiliary system and renal system. At the same time, compared to ⁶⁴Cu-DOTA-TOC, higher radioactivity accumulation of ⁶⁴Cu-DOTA-TATE in liver and kidneys was observed. Micro PET images of U87MG tumor-bearing nude mice with ⁶⁴Cu-DOTA-TOC and ⁶⁴Cu-DOTA-TATE showed the tumors very clearly. The radioactivity uptake of ⁶⁴Cu-DOTA-TATE in tumor was higher than that of ⁶⁴Cu-DOTA-TOC. This work has paved the way for further preclinical and clinical application of ⁶⁴Cu-DOTA-TOC and ⁶⁴Cu-DOTA-TATE as PET tumor imaging agents.