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Comparison of 99m Tc octreotide‐tetramine conjugates with in vitro and in vivo affinity for the somatostatin receptor
Author(s) -
Nikolopoulou A.,
Maina T.,
Nock B.,
Tsipra C.,
Poppe M.,
Mäcke H.,
Chiotellis E.
Publication year - 2001
Publication title -
journal of labelled compounds and radiopharmaceuticals
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.432
H-Index - 47
eISSN - 1099-1344
pISSN - 0362-4803
DOI - 10.1002/jlcr.25804401204
Subject(s) - in vivo , chemistry , somatostatin receptor , octreotide , receptor , somatostatin , in vitro , conjugate , pharmacology , biochemistry , medicine , biology , mathematical analysis , microbiology and biotechnology , mathematics
Given that many cancer cells overexpress somatostatin (SMS) receptors on their membrane, several SMS analogs labeled with radionuclides have been developed aiming at the scintigraphic diagnosis and/or radiotherapy of SMS‐positive neoplasms. Thus, a synthetic analog of the peptide hormone somatostatin (SMS) labeled with 111 In (OctreoScan® 111) is routinely used for the in vivo localization of SMS‐positive tumors in the clinic. Given that 99m Tc remains the gold standard in Diagnostic Nuclear Medicine, we have synthesized two metabolically stabilized SMS analogs, N 4 ‐Bzl‐Glyc‐Tyr 3 ‐octreotide, 1, and N 4 ‐Bzl‐Suc‐octreotide, 2, by covalent coupling of a N 4 bifunctional ligand to the N‐terminal of the peptide backbone. The two analogs can be easily labeled with 99m Tc under mild conditions leading to a single radiolabeled product in high yields and high specific activities. Both analogs significantly retain their ability to bind to the SMS receptor, as shown by proper competition binding experiments. After their administration in healthy mice both radiolabeled analogs were rapidly excreted from the body into the urine through the kidneys. The accumulation of the radioactivity in the SMS receptor rich organs, like pancreas and adrenals, was found specific by in vivo blocking tests.