title: A Cell-Permeable Fluorescent Prochelator Responds to Hydrogen Peroxide and Metal Ions by Decreasing Fluorescence.
abstract: Described here is the development of two boronic ester-based fluorescent prochelators, FloB (2-(6-hydroxy-3-oxo-3H-xanthen-9-yl)-4(5)-[2-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-benzylidene-hydrazinocarbonyl]-benzoic acid) and FloB-SI (2-(6-hydroxy-3-oxo-3Hxanthen-9-yl)-4(5)-[2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyloxy)-benzylidene-hydrazinocarbonyl]-benzoic acid) that show a fluorescence response to a variety of transition metal ions only after reaction with H(2)O(2). Both prochelators' boronic ester masks are oxidized by H(2)O(2) to reveal a fluorescein-tagged metal chelator, FloS (4(5)-(2-hydroxy-benzylidenehydrazinocarbonyl)-2-(6-hydroxy-3-oxo-3H-xanthen-9-yl)-benzoic acid). Chelation of Fe(3+) or Cu(2+) elicits a 70% decrease in the emission signal of FloS, while Zn(2+), Ni(2+), and Co(2+) produce a more modest fluorescence decrease. The conversion of FloB to FloS proceeds in organic solvents, but hydrolytic decomposition of its hydrazone backbone is observed in aqueous solution. However, FloB-SI oxidizes cleanly with H(2)O(2) within 1 h in aqueous solutions to produce FloS. Fluorescence microscopy studies in HeLa cells with FloB-SI show that the sensor's fluorescence intensity remains unchanged until incubation with exogenous H(2)O(2), which results in a decreased fluorescent signal. Incubation with a competitive chelator restores the emission response, thus suggesting that FloB-SI can effectively report on a H(2)O(2)-induced increase in intracellular labilized metal.
authors.affiliation: Department of Chemistry, Duke University, Durham, NC 27708.
authors.forename: Lynne M
authors.initials: LM
authors.lastname: Hyman
authors.forename: Katherine J
authors.initials: KJ
authors.lastname: Franz