[99mTc]Technetium labelled PnAo-azomycin glucuronides: a novel class of imaging markers of tissue hypoxia

Azomycin glucuronate was coupled to a PnAO ligand to create azomycin-based ligands that would form water-soluble 99mTc-azomycin complexes for imaging hypoxic tissue. 1-β-D-(2-Nitroimidazolyl)glucuronic acid, 1, was synthesized by coupling 2-nitroimidazole with 1-α-bromo-2,3,4-tri-O-acetyl-6-methyl glucuronate, followed by deprotection. Reaction of 1 with 6-methyl-6-methylamino-HMPnAO (Pn-44) in the presence of BOP reagent in anhydrous dimethyl sulfoxide afforded the PnAO-glucuronides 5 and 6. Compound 5 was isolated in three rotomeric forms. Biological evaluation of 7 (99mTc-5) indicated selective binding to hypoxic EMT-6 cells, and cytotoxicity to fibroblasts and HeLa, sk24, sk23, and g361 cancer cell lines, at an IC20 <2.5 μg/ml. In vivo biodistribution of two formulations of 7 in Balb/c mice with EMT-6 tumor produced diverse results, with one formulation showing no tumor preference, and the other providing a tumor/blood ratio of 2.3 at 4 h post-injection. The latter formulation delineated tumor, large intestine and liver in scintigraphic images.