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Identification of the Soluble in Vivo Metabolites of Indium-111-Diethylenetriaminepentaacetic Acid-D-Phe1-Octreotide

Summary: Identification of the Soluble in Vivo Metabolites of
Indium-111-Diethylenetriaminepentaacetic Acid-D-Phe1-Octreotide
Laura A. Bass, Margaret V. Lanahan, James R. Duncan, Jack L. Erion, Ananth Srinivasan,
Michelle A. Schmidt, and Carolyn J. Anderson*,
Division of Radiological Sciences, Washington University School of Medicine, St. Louis, Missouri 63110, and
Mallinckrodt Inc., St. Louis, Missouri 63134. Received August 13, 1997;
Revised Manuscript Received December 23, 1997
Indium-111-diethylenetriaminepentaacetic Acid-D-phenylalanine1-octreotide (111In-DTPA-octreotide)
is a cyclic eight amino acid somatostatin analogue which is approved for gamma scintigraphy of
neuroendocrine tumors. To address the factors that contribute to liver and kidney retention of this
radiopharmaceutical, its metabolism was evaluated in normal and tumor-bearing rats. The soluble
fractions from nontarget (liver and kidney) and target (tumor, pancreas, adrenals) organ homogenates
were analyzed out to 21 h postinjection, and urine was analyzed out to 12 h postinjection. The blood
was analyzed at shorter time intervals due to the rapid clearance of 111In-DTPA-octreotide. Radio-
TLC and HPLC were used to analyze organ homogenates, blood, and urine. By TLC, intact 111
DTPA-octreotide was resolved from the soluble metabolites, and a similar apparent rate of metabolism
was observed in the liver, kidney, tumor, and pancreas with 30% intact 111In-DTPA-octreotide at 4
h postinjection. In the adrenals, metabolism occurred more slowly with 60% intact 111In-DTPA-
octreotide at 4 h postinjection. At 4 h postinjection, the activity excreted in the urine consisted of


Source: Anderson, Carolyn J. - Department of Molecular Biology and Pharmacology, Washington University in St. Louis


Collections: Biology and Medicine