Bioreductive markers for hypoxic cells: 2-nitroimidazoles with biotinylated 1-substituents

The interference by oxygen with the bioreductive metabolism and binding within cells of 2-nitroimidazoles has been used to identify hypoxic cells. Three novel compounds were synthesized with a 1-substituent containing a biotin moiety. Bound adducts of these compounds could be identified in hypoxic cells in vitro by the biotin binding proteins, avidin or streptavidin, labeled with fluorescein. The metabolism and discrimination of these compounds between well-oxygenated and hypoxic cells was evaluated by flow cytometry. Ester or amide links between the 2-nitroimidazole and the biotin were degraded in the presence of mouse serum, but a compound with a C5 hydrocarbon link was stable, and this compound was suitable for evaluation in an in vivo tumor model.