The somalostatin analogue octreotide (Sandostatin has been labeled with 123I (T1/2 = 13 h) and 111ln (T1/2 = 67 h)(2) for SPECT imaging, as well as 68Ga (Tl/2 =1.1 h)(3) and 18F (Tl/2 =1.8 h)(4) for PET imaging of somatostatin receptor positive tumors. Due to high background activity in the body, optimal SPECT images of tumors in patients of 111In-DTPA-D-Phe1-octreotide were obtained at 24 hours post-injection. For PET imaging, the short half-lives of 68Ga and 18F may not allow for optimal Imaging times when labeled to octreotide, therefore we have focused on labeling octreotide with 64Cu, a posltron-emitting radionuclide with a half-life of 12.8 h. Octreotide has been labeled with 64Cu using the macrocyclic chelates; 1,4,8,11-tetraazacyclotetradecane.N,N',N"""""""",N'''tetraacetic acid (TETA) and 4-[1,8,11-tetraazacyclotetradec-1-yl)-methyl]benzoic acid (CPTA) In conclusion, our studies have shown that metabolism of the three octreotide conjugates studied occur rather rapidly, especially in the clearance organs. Further studies are in progress to more accurately correlate the metabolism and biodistribution of 64Cu- and 111In~ octreotide conjugates.
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