title: Design, synthesis, and initial evaluation of high-affinity technetium bombesin analogues.
abstract: Potent antagonists of bombesin-like peptides have shown great potential for applications in cancer therapy. A 99mTc-labeled agent capable of identifying patients who could benefit from these emerging therapies would have a great impact on patient management. This study involves the synthesis and initial evaluation of technetium diaminedithiolate analogues derived from the potent bombesin analogue Pyr-Gln-Lys-Leu-Gly-Asn-Gln-Trp-Ala-Val-Gly-His-Leu-Met-NH2 (Lys3-bombesin). We coupled two diaminedithiol (DADT) bifunctional chelating agents (BCAs 1 and 2) to the Lys3 residue at the N-terminal region that is not required for binding to the receptor. 99mTc labeling was performed by ligand exchange on addition of [99mTc]glucoheptonate to a solution of the adduct at room temperature. Two products were obtained from each adduct on analysis by HPLC. The major to minor product ratios of the 99mTc-labeled analogues were 3:1 for products from BCA 1 and 9:1 for the products from BCA 2. Macroscopic amounts of the 99Tc analogues were similarly prepared using [99Tc]glucoheptonate. In this case, the major to minor ratios were 2:1 for the products from both BCAs. For initial evaluation of the binding of the Tc-labeled peptides to bombesin receptors, the 99Tc analogues were used in vitro in competitive binding assays in rat brain cortex membranes against [125I-Tyr4]bombesin. Results of the in vitro assays showed that the inhibition constants (Ki) of the major and minor products were 3.5+/-0.7 and 3.9+/-1.5 nM, respectively, for the products from BCA 1; and 7.4+/-2.0 and 5.2+/-1.5 nM for the products derived from BCA 2, respectively. The high affinity exhibited by these technetium analogues is an indication of their potential for use in non-invasive in vivo biochemical characterization of cancers that possess receptors for bombesin.
authors.affiliation: Department of Environmental Health Sciences, The Johns Hopkins University, Baltimore, Maryland 21205, USA. kbaidoo@jhsph.edu
authors.forename: K E
authors.initials: KE
authors.lastname: Baidoo
authors.forename: K S
authors.initials: KS
authors.lastname: Lin
authors.forename: Y
authors.initials: Y
authors.lastname: Zhan
authors.forename: P
authors.initials: P
authors.lastname: Finley
authors.forename: U
authors.initials: U
authors.lastname: Scheffel
authors.forename: H N
authors.initials: HN
authors.lastname: Wagner
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001839:Bombesin / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics; D002614:Chelating Agents; D002851:Chromatography, High Pressure Liquid; D015195:Drug Design; D007553:Isotope Labeling; D008297:Male; D051379:Mice; D015394:Molecular Structure; D009025:Morpholines / Q000737:chemistry*; D009369:Neoplasms / Q000000981:diagnostic imaging; D011877:Radionuclide Imaging; D051381:Rats; D017207:Rats, Sprague-Dawley; D018004:Receptors, Bombesin / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013667:Technetium; D014018:Tissue Distribution
chemical_list: C112076:6,6-dimethyl-4-(2-((2-methyl-2-thiopropyl)methylamino)ethyl)thiamorpholin-2-one; C112053:6,6-dimethyl-4-(2-(2,2-dimethyl-2-(2-methyl-2-thiopropyl)amino)ethyl)thiamorpholin-2-one; D002614:Chelating Agents; D009025:Morpholines; D018004:Receptors, Bombesin; D013438:Sulfhydryl Compounds; C112054:bombesin, Lys(3)-; D013667:Technetium; D001839:Bombesin