Emission under hypoxia: one-electron reduction and fluorescence characteristics of an indolequinone-coumarin conjugate

Chembiochem. 2008 Feb 15;9(3):426-32. doi: 10.1002/cbic.200700458.


A characteristic feature of the reactivity of indolequinone derivatives, substituents of which can be removed by one-electron reduction under hypoxic conditions, was applied to the development of a new class of fluorescent probes for disease-relevant hypoxia. A reducing indolequinone parent molecule conjugated with fluorescent coumarin chromophores could suppress efficiently the fluorescence emission of the coumarin moieties by an intramolecular electron-transfer quenching mechanism and a conventional internal-filter effect. Under hypoxic conditions, however, the conjugate, denoted IQ-Cou, underwent a one-electron reduction triggered by X irradiation or the action of a reduction enzyme to release a fluorescent coumarin chromophore, whereupon an intense fluorescence emission with a maximum intensity at 420 nm was observed. The one-electron reduction of IQ-Cou was suppressed by molecular oxygen under aerobic conditions. IQ-Cou also showed intense fluorescence in a hypoxia-selective manner upon incubation with a cell lysate of the human fibrosarcoma cell line HT-1080. The IQ-Cou conjugate has several unique properties that are favorable for a fluorescent probe of hypoxia-specific imaging.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Coumarins / chemistry*
  • Electrons
  • Hypoxia / metabolism*
  • Indolequinones / chemistry*
  • Oxidation-Reduction
  • Spectrometry, Fluorescence / methods*


  • Coumarins
  • Indolequinones