Evaluation of 99mTc-sulfonamide and sulfocoumarin derivatives for imaging carbonic anhydrase IX expression

With the aim to prepare hypoxia tumor imaging agents, technetium(I) and rhenium(I) tricarbonyl complexes with dipyridylamine (L1 = N-{[1-(2,2-dioxido-1,2-benzoxathiin-6-yl)-1H-1,2,3-triazol-4-yl]methyl}-N-(2-pyridinylmethyl)-2-pyridinemethanamine; L3 = N-{[1-[N-(4-aminosulfonylphenyl)]-1H-1,2,3-triazol-4-yl]methyl}- N-(2-pyridinyl-methyl)-2-pyridinemethanamine), and iminodiacetate (H(2)L2 = N-{[1-(2,2-dioxido-1,2-benzoxathiin-6-yl)-1H-1,2,3-triazole- 4-yl]methyl}-N-(carboxy-methyl)-glycine; H(2)L4 = N-{[1-[N-(4-aminosulfonyl- phenyl]-1H-1,2,3-triazole 4-yl]methyl}-N-(carboxymethyl)-glycine) ligands appended to sulfonamide or sulfocoumarin carbonic anhydrase inhibitors were synthesized. The Re(I) complexes were characterized using H-1/C-13 NMR, MS, EA, and in one case the X-ray structure of [Et3NH][Re(CO)(3)(L2)] was obtained. As expected, the Re coordination geometry is distorted octahedral, with a tridentate iminodiacetate ligand in a fac arrangement dictated by the three strong-field CO ligands. Inhibition studies of human carbonic anhydrases (hCAs) showed that the Re sulfocoumarin derivatives were inactive against hCA-I, -II and -IV, but had moderate affinity for hCA-IX. The Re sulfonamides showed improved affinity against all tested hCAs, with [Re(CO)(3)(L4)](-) being the most active and selective for the hCA-IX isoform. The corresponding Tc-99m complexes were synthesized from fac-[Tc-99m(CO)(3)(H2O)3](+), purified by HPLC, and obtained with average 41-76% decay-corrected radiochemical yields and with > 99% radiochemical purity. Uptake in HT-29 tumors at 1 h post-injection was highest for [Tc-99m(CO)(3)(L4)](-) (0.14 +/- 0.10%ID/g) in comparison to [Tc-99m(CO)(3)(L1)](+) (0.06 +/- 0.01%ID/g), [Tc-99m (CO)(3)(L2)](-) (0.03 +/- 0.00%ID/g), and [Tc-99m(CO)(3)(L3)](+) (0.07 +/- 0.03%ID/g). The uptake in tumors was further reduced at 4 h post-injection. For potential imaging application with single photon emission computed tomography, further optimization is needed to improve the affinity to hCA-IX and uptake in hCA-IX expressing tumors.