Figure 1: Selection of polymethine dyes with organ-selective elimination.

(a) A variety of polymethine dyes with varying numbers of sulfonic residues were screened in rats regarding net organ-specific clearance by liver and kidneys and their applicability for biophotonic detection, for example, by IVM; (n=3; mean±s.e.m.). (b) Structures of DY-635, a dye with preferential hepatobiliary clearance and DY-704 with preferential renal elimination and their cell-specific uptake as visualised by intravital laser scanning confocal microscopy in liver and kidney (scale bars 150 μm). (c) DY-635 was further characterised regarding its affinity to transporters responsible for uptake of substrates into the liver in a heterologous expression system (HEK cells). While DY-635 exhibited moderate affinity to several transporters, its affinity to OATP1B1 and OATP1B3 exceeded that of rifampicin or cyclosporine A, that is, the FDA-proposed competitors for drug development purposes. Bars show mean±s.e.m.; significance was tested by one-way ANOVA followed by Tukey’s test; ** indicates P<0.01 for uptake of the substrate in the presence of DY-635 (hatched bars) or the FDA-proposed competitor (black bars) compared with substrate alone. † and †† indicate P<0.05 and P<0.01, respectively, for the comparison between DY-635 and the FDA-proposed competitor. (d) Uptake of DY-635 by primary murine hepatocytes is temperature sensitive and inhibited by cyclosporine A in a dose dependent manner with an IC₅₀ of 379 nM.