Radioiodination and astatination of octreotide by conjugation labeling

Octreotide was coupled to 3-iodobenzoyl and 3-iodonicotinoyl moieties to ob tain [N-(3-iodobenzoyl)-D-Phe(1)]octreotide (IBO) and [N-(3-iodonicotinoyl) -D-Phe(1)]octreotide (INO), respectively. The IC50 values for the binding o f IBO and INO to CA20948 rat pancreatic tumor membranes were 0.90 and 0.13 nM, respectively, compared with 0.35 nM for octreotide itself. Starting fro m N-succinimidyl 3-[I-131]iodobenzoate and N-succinimidyl 5-[I-131]iodopyri dine-3-carboxylate, [I-131]IBO and [I-131]INO were prepared in overall radi ochemical yields of 35%-50%. Likewise, {N-(3-[At-211]astatobenzoyl)-D-Phe(1 )}octreotide ([At-211]ABO) was prepared in similar yield from N-succinimidy l 3-[At-211]astatobenzoate. In vitro assays with AR42J rat pancreatic tumor cells demonstrated a higher retention of cell-internalized radioiodine act ivity for [I-131]INO compared with [I-125]IBO. Tissue distribution studies with both conjugates revealed low levels of activity in the thyroid suggest ing that dehalogenation of these peptides was minimal. NUCL MED BIOL 27;4:3 29-337, 2000. (C) 2000 Elsevier Science Inc. All rights reserved.