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, 99mTcethylenedicysteine- bis-misonidazole (99mTc-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 99mTc in the second step. 99mTc-pertechnetate (99mTcO4 -) was reduced by tin chloride (SnCl2) for radiolabeling. 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 99mTc-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 99mTc-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.