99mTc-labeling studies of a modified metronidazole and its biodistribution in tumor bearing animal models.

A cysteine-based bifunctional chelating agent viz. N-(2'-hydroxybenzyl)-cysteine with a free carboxylic acid group (CAA) was synthesized. Bearing in mind the affinity of localization of nitroimidazoles in hypoxic tissues, this bifunctional chelating agent was coupled to metronidazole (MNZ). The (99m)Tc labeling studies of the novel agent (MNZCAA) thus obtained, was carried out and the radiolabeled product was subsequently purified. The complexation yield under optimized condition was approximately 85%. Biodistribution studies carried out in Swiss mice bearing 'barcl-95' tumors showed selective accumulation of the injected activity in the tumor (1.70%/g at 30 min p.i.) with renal as well as hepatobiliary clearance. High tumor/muscle ratio (14.7 at 3 h post-injection) of the novel agent indicates considerable promise towards further evaluation.