A reactivity-based probe of the intracellular labile ferrous iron pool

Editorial Summary A reactivity-based probe containing an iron-sensitive 1,2,4-trixolane ring conjugated to a small molecule payload combined with a high-throughput immunofluorescence assay enables the selective detection of labile intracellular ferrous iron. Improved methods for studying intracellular reactive Fe( II ) are of significant interest for studies of iron metabolism and disease-relevant changes in iron homeostasis. Here we describe a highly selective reactivity-based probe in which a Fenton-type reaction with intracellular labile Fe( II ) leads to unmasking of the aminonucleoside puromycin. Puromycin leaves a permanent and dose-dependent mark on treated cells that can be detected with high sensitivity and precision using a high-content, plate-based immunofluorescence assay. Using this new probe and screening approach, we detected alteration of cellular labile Fe( II ) in response extracellular iron conditioning, overexpression of iron storage and/or export proteins, and post-translational regulation of iron export. We also used this new tool to demonstrate that labile Fe( II ) pools are larger in cancer cells than in nontumorigenic cells.