Development of 99mTc-N4-NIM for Molecular Imaging of Tumor Hypoxia

The nitro group of 2-nitroimidazole (NIM) enters the tumor cells and is bioreductively activated and fixed in the hypoxia cells. 1,4,8,11-tetraazacyclotetradecane (N4) has shown to be a stable chelator for 99mTc. The present study was aimed to develop 99mTc-cyclam-2-nitroimidazole (99mTc-N4-NIM) for tumor hypoxia imaging. N4-NIM precursor was synthesized by reacting N4-oxalate and 1,3-dibromopropane-NIM, yielded 14% (total synthesis). Cell uptake of 99mTc-N4-NIM and 99mTc-N4 was obtained in 13762 rat mammary tumor cells and mesothelioma cells in 6-well plates. Tissue distribution of 99mTc-N4-NIM was evaluated in breast-tumor-bearing rats at 0.5–4 hrs. Tumor oxygen tension was measured using an oxygen probe. Planar imaging was performed in the tumor-bearing rat and rabbit models. Radiochemical purity of 99mTc-N4-NIM was >96% by HPLC. Cell uptake of 99mTc-N4-NIM was higher than 99mTc-N4 in both cell lines. Biodistribution of 99mTc-N4-NIM showed increased tumor-to-blood and tumor-to-muscle count density ratios as a function of time. Oxygen tension in tumor tissue was 6–10 mmHg compared to 40–50 mmHg in normal muscle tissue. Planar imaging studies confirmed that the tumors could be visualized clearly with 99mTc-N4-NIM in animal models. Efficient synthesis of N4-NIM was achieved. 99mTc-N4-NIM is a novel hypoxic probe and may be useful in evaluating cancer therapy

Synthesis of \u3csup\u3e99m\u3c/sup\u3eTc-EC-AMT as an imaging probe for amino acid transporter systems in breast cancer

Objective: This study was to develop a 99mTc-labeled α-methyl tyrosine (AMT) using L,L-ethylenedicysteine (EC) as a chelator and to evaluate its potential in breast tumor imaging in rodents. METHODS: EC-AMT was synthesized by reacting EC and 3-bromopropyl AMT (N-BOC, ethyl ester) in ethanol/potassium carbonate solution. EC-AMT was labeled with Tc in the presence of tin (II) chloride. Rhenium-EC-AMT (Re-EC-AMT) was synthesized as a reference standard for 99mTc-EC-AMT. To assess the cellular uptake kinetics of 99mTc-EC-AMT, 13762 rat breast cancer cells were incubated with 99mTc-EC-AMT for 0-2h. To investigate the transport mechanism, the same cell line was used to conduct the competitive inhibition study using L-tyrosine. Tissue distribution of 99mTc-EC-AMT was determined in normal rats at 0.5-4h. Planar imaging of breast tumor-bearing rats was performed at 30 and 90min. The data were compared with those of 18F-2-fluoro-2-deoxy-glucose. Blocking uptake study using unlabeled AMT was conducted to investigate the transport mechanism of 99mTc-EC- AMT in vivo. Results: Structures of EC-AMT and Re-EC-AMT were confirmed by nuclear magnetic resonance, high performance liquid chromatography and mass spectra. In-vitro cellular uptake of 99mTc-EC-AMT in 13762 cells was increased as compared with that of 99mTc-EC and could be inhibited by L-tyrosine. Biodistribution in normal rats showed high in-vivo stability of 99mTc-EC-AMT. Planar scintigraphy at 30 and 90min showed that 99mTc-EC-AMT could clearly visualize tumors. 99mTc-EC-AMT uptake could be significantly blocked by unlabeled AMT in vivo. Conclusion: The results indicate that 99mTc-EC-AMT, a new amino acid transporter-based radiotracer, is suitable for breast tumor imaging. © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins