Reduced Glutathione Rather than Oxygen Concentration Determines the Reduction Rate of Nitroimizadol Probes Used as Hypoxia Markers.

Jesus Pacheco-Torres^1,2, Paloma Ballesteros², Pilar Lopez-Larrubia¹, Sebastian Cerdan¹

Nitroimidazolyl derivatives (Pimonidazole, Misonidazole, EF5) have been traditionally used by different imaging methods as markers for hypoxia due to their preferential reduction and subsequent trapping in vivo under hypoxic conditions. However, these results remained difficult to interpret since the reduction mechanism and its rate determining steps remained largely unexplored. We address here the latter two aspects. We show that it is the intracellular redox state (NADP/NADPH, GSSG/GSH), rather than the oxygen tension, what determines the reduction rate of these compounds, the rection rate being limited mainly by the GSH concentration. This is a general mechanism occurring in all nitromidazolyl derivatives investigated.