Design of Ga–DOTA-based bifunctional radiopharmaceuticals: Two functional moieties can be conjugated to radiogallium–DOTA without reducing the complex stability
作者:Takahiro Mukai、Jun Suwada、Kohei Sano、Mayumi Okada、Fumihiko Yamamoto、Minoru Maeda
DOI:10.1016/j.bmc.2009.05.041
日期:2009.7
From the X-ray crystal structures of Ga-DOTA chelates, we were able to deduce that two free carboxylate groups of the radiogallium-DOTA complex may be utilized for coupling to functional moieties that recognize molecular targets for in vivo imaging without reducing the radiogallium-complex stability. Thus, we designed 2,2'-[4,10-bis(2-[2-(2-methyl-5-nitro-1H-imidazol-1-yl) ethyl]amino}-2-oxoethyl)1,4,7,10-tetraazacyclododecane-1,7-diyl]diacetic acid (DOTA-MN2) (7), employing a metronidazole moiety as the recognition site of hypoxic lesions, based on the drug design concept of bifunctional radiopharmaceuticals. Coupling of DOTA-bis(tert-butyl) ester 5 with 1-(2-aminoethyl)-2-methyl-5-nitroimidazole dihydrochloride, followed by deprotection, afforded the required 7 (DOTA-MN2). Ga-67-labeling was carried out by reaction of DOTA-MN2 with Ga-67-citrate. When Ga-67-DOTA-MN2 was incubated in phosphate-buffered saline or mouse plasma, no measurable decomposition occurred over a 24-h period. In biodistribution experiments in NFSa tumor-bearing mice, Ga-67-DOTA-MN2 displayed not only a significant tumor uptake, but also rapid blood clearance and low accumulations in nontarget tissues, resulting in high target-to-nontarget ratios of radioactivity. These results indicate the potential benefits of the drug design of Ga-67-DOTA-MN2. The present findings provide helpful information for the development of radiogallium-labeled radiopharmaceuticals for SPECT and PET studies. (C) 2009 Elsevier Ltd. All rights reserved.