EF-5 (EF5; 2-Nitroimidazole) is a hypoxia labeling agent used to identify hypoxia in cells.
Overexpression of CYPOR induces similar 2- to 4-fold increases in EF-5 binding and metabolic reduction of tirapazamine and CEN-209 in SiHa and HCT116 cell lines, and similar enhancement of γH2AX formation. EF-5 binding and metabolic reduction of the prodrugs are highly correlated in a panel of 14 hypoxic tumor cell lines[1].
EF-5 binding is a promising stratification biomarker for benzotriazine-N-oxide bioreductive prodrugs. In HCT116 xenografts, CYPOR overexpression also significantly increases EF-5 binding and CEN-209 reduction, and modification of tumor hypoxia causes similar changes to the bioreductive activation of both agents, resulting in a strong correlation between EF-5 binding and CEN209-induced DNA damage at the individual tumor level[1]. Following intravenous injection of EF-5, binding and detection using a monoclonal antibody in 9L gliomas is specific and oxygen dependent. Detection of binding using fluorescence microscopy can be performed on frozen tissues; tissue sections can be counterstained with haematoxylin and eosin for light microscopic analysis. Alternatively, the distribution of hypoxia in a tumor can be inferred by examining individual tumor cells using flow cytometric techniques[2].
[1]. Wang J, et al. The 2-nitroimidazole EF5 is a biomarker for oxidoreductases that activate the bioreductive prodrug CEN-209 under hypoxia. Clin Cancer Res. 2012 Mar 15;18(6):1684-95. [2]. Evans SM, et al. Identification of hypoxia in cells and tissues of epigastric 9L rat glioma using EF5 [2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl) acetamide]. Br J Cancer. 1995 Oct;72(4):875-82.