Recent Advances on Radionuclide Labeled Hypoxia-Imaging Agents

Hypoxic tissue exists in most of the solid tumors and hypoxia is a common character of these tumors. The existence of hypoxic tissue in the tumor decreases the efficacy of radiotherapy and chemotherapy. Radiolabeled hypoxia markers have been developed to measure the hypoxic tissue together with non-invasive imaging techniques such as PET, SPECT, and PET/CT. This offers a convenient approach to delineate the tumor providing useful information for diagnosing cancer and guiding the treatment plan. Bioreducible or-ganic compounds have been developed as the hypoxia markers to probe tissue hypoxia noninvasively because they can be reduced and metabolized under hypoxic conditions; form adducts with cell components, and thus be trapped in the hypoxic tissue. These compounds include nitroimidazoles and other redox-sensitive compounds such as BnAO and ATSM. Different radionuclides have been used to label these compounds such as technetium-99m, iodine-123, fluorine-18, copper-64, etc. In addition, to detect hypoxia with endogenous hypoxia markers such as carbonic anhydrase IX (CA IX) and hypoxia-inducible factor-1 (HIF-1), some radiolabeled tracers have also been developed. This article is an overview of the progress in this area in the past decade including the development of radiolabeled compounds for hypoxia detection and problems associated with the hypoxia marker development.