Preparation and Biodistribution of Technetium-99m-Labeled Bis-Misonidazole (MISO) as an Imaging Agent for Tumour Hypoxia

Diagnosis of tumour hypoxia is an important aspect in determining the course of tumour therapy. In this study, we developed a novel imaging agent, Tc-99m-ethylenedicysteine-bis-misonidazole (Tc-99m-EC-MISO), for diagnosing tumour hypoxia. We used 2-nitroimidazole as a reactant to synthesize the amino derivative of misonidazole (MISO) in the first step and then conjugated the di-amino derivative of MISO to the chelating agent ethylenedicysteine (EC) for labelling Tc-99m in the second step. Tc-99m-pertechnetate ((TcO4-)-Tc-99m) was reduced by tin chloride (SnCl2) for radio-labeling. The radiochemical purity was up to 94%. Tissue biodistribution and SPECT/CT imaging studies were conducted on subcutaneous gliomal tumour-bearing mice. The tumour-to-muscle ratio in the Tc-99m-EC-MISO group increased with time, up to 4.6 at 4 h after injection. SPECT/CT imaging confirmed that the tumours could be visualized clearly with Tc-99m-EC-MISO at 2 h. By introducing a second 2-nitroimidazole redox centre, an apparent hypoxic accumulation of this novel 99mTc-labeled imaging agent in the Tumour was observed.