TY - JOUR T1 - Preclinical Comparison of <sup>111</sup>In-Labeled DTPA- or DOTA-Bombesin Analogs for Receptor-Targeted Scintigraphy and Radionuclide Therapy JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1650 LP - 1656 VL - 43 IS - 12 AU - Wouter A.P. Breeman AU - Marion de Jong AU - Jack L. Erion AU - Joseph E. Bugaj AU - Ananth Srinivasan AU - Bert F. Bernard AU - Dik J. Kwekkeboom AU - Theo J. Visser AU - Eric P. Krenning Y1 - 2002/12/01 UR - http://jnm.snmjournals.org/content/43/12/1650.abstract N2 - The 14-amino-acid peptide bombesin (BN) has a high affinity for the gastrin-releasing peptide (GRP) receptor that is expressed by a variety of tumors. Recently, high densities of GRP receptors were identified by in vitro receptor autoradiography in human prostate and breast carcinomas using [125I-Tyr4]BN as radioligand. Radiometal-labeled diethylenetriaminepentaacetic acid (DTPA)-BN derivatives are potentially useful radioligands for receptor-targeted scintigraphy and radiotherapy of GRP receptor-expressing tumors. Methods: [DTPA-Pro1,Tyr4]BN (A), [DOTA-Pro1,Tyr4]BN (B), [DTPA-ε-Lys3,Tyr4]BN (C), and [DOTA-ε-Lys3,Tyr4]BN (D) (where DOTA is dodecanetetraacetic acid) were synthesized and studied for competition with binding of [125I-Tyr4]BN to the GRP receptor. The 111In-labeled BN analogs were studied in vitro for binding and internalization by GRP receptor-expressing CA20948 and AR42J pancreatic tumor cells as well as in vivo for tissue distribution in rats. Specific tissue binding was tested by coinjection of 0.1 mg [Tyr4]BN. Results: All BN analogs competitively inhibited the binding of [125I-Tyr4]BN to the GRP receptor with 50% inhibitory concentration values in the range of 2–9 nmol/L. All 111In-labeled analogs showed high and specific time- and temperature-dependent binding and internalization by CA20948 and AR42J cells. In in vivo studies, high and specific binding was found in GRP receptor-positive tissues such as pancreas (0.90, 1.2, 0.54, and 0.79 percentage injected dose per gram for A–D, respectively). In a rat model, the AR42J tumor could clearly be visualized by scintigraphy using [111In-DTPA-Pro1,Tyr4]BN as the radioligand. Although [111In-DOTA-Pro1,Tyr4]BN showed the highest uptake of radioactivity in GRP receptor-positive tissues as well as higher target-to-blood ratios, [111In-DTPA-Pro1,Tyr4]BN was easier to handle and is more practical to use. Therefore, we decided to start phase I studies with this DTPA-conjugated radioligand. Conclusion: [111In-DTPA-Pro1,Tyr4]BN is a promising radioligand for scintigraphy of GRP receptor-expressing tumors. We are currently performing a phase I study on patients with invasive prostate carcinoma. ER -