Nitroimidazole radiopharmaceuticals in bioimaging: part I: synthesis and imaging applications

The paper is review on synthesis of nitroimidazole radiosensitizers useful in imaging of tumor cells. Nitroimidazole compounds are radiolabeled probes for specific use in imaging such as 18F for positron emission tomography; 99mTc for single photon emission computed tomography; 123I, or 131I for computer assisted tomography and 19F for magnetic resonance imaging. In synthesis of radiopharmaceutical compounds, parent nitroimidazole is modified to thiopyranosyl nucleosides, neuraminic acid derivatives followed by nitro group deprotection-substitution and radiolabeling by specific isotopes. Commercial attempts have been made to radiolabel the nitroimidazole by [18F]fluorine, [131I or 123I]iodine, [99mTc]technicium and [64Cu]copper on modified side chain of nitroimidazole compounds to design multimodal and multifunctional imaging techniques to detect and monitor the tumor hypoxia by measuring distribution of radiatiolabel or radiation. Nitroimidazole initially showed poor diffusion and poor stability in tissues with neurotoxicity concern limited its use as radiosensitizer. In last decade, several nitroimidazole derivatives were developed as potent less toxic and highly stable radiopharmaceuticals with optimized radiolabel concentration with high detectability of tumor oxygen or hypoxia. Currently, nitroimidazole based radiopharmaceuticals have emerged as multimodal and multifunctional hypoxia reporters with antitumor, anti-ischemic, anti-inflammatory and tumor targeting properties. In conclusion, nitroimidazole based radiopharmaceuticals are a new generation hypoxia biosensors for localized theradiagnostic utility in clinical medicine.