Metabolic NADH/FAD/FMN FLIM and oxygen PLIM: multiphoton luminescence lifetime imaging on the way to clinical diagnosis
Simultaneous metabolic and oxygen imaging is a promising idea to follow up therapy response, disease development and to determine prognostic factors. A common property during tumor development is altered energy metabolism, which could lead to a switch between oxidative phosphorylation (OXPHOS) and glycolysis. The impact of this switch for theranostic applications is significant. FLIM of metabolic coenzymes, as NAD(P)H, FAD and FMN, is now widely accepted to be the most reliable method to determine cell metabolism and different algorithms are actually proved to get reproducible results. The phosphorescence lifetime of newly developed drugs is able to indicate local oxygen changes. Therefore, simultaneous imaging of phosphorescence and fluorescence lifetime parameters enables analysis of bioenergetic alterations and oxygen consumption. Dyes based on ruthenium (II) and Iridium (III) coordination complexes, were used for PLIM. For example, TLD1433, a Ru(II) complex possess a variety of different triplet states, which enables complex photochemistry and redox reactions. TLD1433 can be used as a phosphor to follow up local oxygen concentration and consumption during treatment. Alternatively ISK-1, an Ir(III) complex seems to be a perfect sensor for oxygen imaging. Within this presentation correlated luminescence lifetime imaging will be presented, applications will be demonstrated and pitfalls discussed. With respect to the last point the different redox pairs involved in cell metabolism (as FAD/FMN) will be revalued.