Radiolabeled bombesin analogs for prostate cancer diagnosis: preclinical studies Bluma Linkowski Faintuch a, ⁎ , Rodrigo Teodoro a , Adriano Duatti b , Emiko Muramoto a , Salomao Faintuch c , Charles J. Smith d a Radiopharmacy Center, Institute of Energetic and Nuclear Research, Sao Paulo, SP 05508-000, Brazil b Laboratory of Nuclear Medicine, Department of Clinical and Experimental Medicine, University of Ferrara, Ferrara, 44100, Italy c Department of Radiology, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA d Department of Radiology, Missouri University Research Reactor, and Radiopharmaceutical Sciences Institute, University of Missouri-Columbia, The Harry S. Truman Memorial Veterans' Hospital, Columbia, MO 65201, USA Received 22 July 2007; received in revised form 17 February 2008; accepted 28 February 2008 Abstract Introduction: Radionuclide imaging can be a useful tool for the diagnosis of prostate cancer. Bombesin (BBN) is a molecule with high affinity for gastrin releasing peptide (GRP) receptors which are over-expressed in that tumor. This report compares 99m Tc-HYNIC-βAla-BBN (7-14)NH2 [ 99m Tc-HYNIC-BBN] and 99m Tc≡N(PNP6)-Cys-βAla-BBN(7-14)NH2 [ 99m TcN(PNP6)-Cys-BBN] with regard to labeling procedures as well as in vitro and in vivo evaluation (biodistribution and scintigraphic imaging). Methods: Peptide synthesis was performed in an automated peptide synthesizer. HYNIC-BBN was radiolabeled with pertechnetate using tricine and ethylenediamine diacetic acid (EDDA) as coligands. Cys- BBN was radiolabeled in a two-step procedure with the preparation of the precursor 99m Tc-Nitrido first and then introducing diphosphine (PNP6). Radiochemical evaluation of conjugates, as well as studies of stability, transchelation toward cysteine, and partition coefficient were done. Biological studies included internalization, biodistribution in healthy animals and in animals bearing PC3 cancer cells with acquisition of images from the tumor-bearing animals. Results: Both complexes showed a high radiochemical yield along with good stability. Biodistribution studies pointed out strong renal excretion for the former complex due to its hydrophilic profile and marked hepatobiliary excretion for the latter, corresponding to observed lipophilicity. Tumor uptake was higher for 99m Tc-HYNIC-BBN and the same occurred with internalization findings, which exceeded those of 99m TcN(PNP6)-BBN. Blocking studies in mice bearing PC-3 tumor cells revealed significantly reduced pancreas and tumor uptake, demonstrating receptor specificity of the conjugates. Conclusion: The best radiotracer was 99m Tc-HYNIC-BBN on the basis of high radiochemical yield, fast radiolabeling procedure without need for a purification step, and more consistent tumor uptake. © 2008 Elsevier Inc. All rights reserved. Keywords: Bombesin analogs; technetium 99m ( 99m Tc)-HYNIC-BBN; Prostate cancer; 99m TcN(PNP6)-Cys-BBN 1. Introduction Small receptor-binding peptides are currently the agents of choice for receptor imaging and tumor targeting. Several malignant tumors overexpress cell surface receptors, which can be targeted with radiolabeled receptor-specific peptides for imaging and therapy [1]. Bombesin (BBN), first isolated from frog skin, is a 14- amino-acid neuropeptide with high affinity for gastrin- releasing peptide (GRP) receptors [2,3]. BBN and its mammalian counterpart GRP, which is a 27-amino-acid peptide, have similar biological properties and share a nearly identical C-terminal amino acid sequence. GRP may function as a paracrine/autocrine growth stimulator in many neoplasms [4–6]. Four subtypes of BBN/GRP receptors have been identified. The first two to be cloned were designated BB1 Available online at www.sciencedirect.com Nuclear Medicine and Biology 35 (2008) 401 – 411 www.elsevier.com/locate/nucmedbio ⁎ Corresponding author. Tel.: +55 11 38169252; fax: +55 11 38120253. E-mail address: blfaintuch@hotmail.com (B.L. Faintuch). 0969-8051/$ – see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.nucmedbio.2008.02.005