Coumarin-based Fluorescent Probes for Selectively Targeting and Imaging the Endoplasmic Reticulum in Mammalian Cells.

Abstract

Developing improved fluorescent probes for imaging the endoplasmic reticulum (ER) is necessary for structure-activity studies of this dynamic organelle. Two coumarin-based compounds with sulfonamide side groups were synthesized and characterized as ER-targeting probes. Their selectivity to target the ER in HeLa and GM07373 mammalian cells was shown with co-localization experiments using commercially available probes that localize in the ER, mitochondria, or lysozymes. The hydrophobicity of the coumarin-based probes was comparable to known probes that partition into the ER membrane. Their cytotoxicity in mammalian cells was low with IC50 values that range from 205 to 252μm. The fluorescent quantum yields of the coumarin-based probes when excited with 400nm light were 0.60, and they have a much narrower emission spectrum (from 435 to 525nm in methanol) than that of the only commercially available ER probe that is exited with 400nm light (ER-Tracker™ Blue-White DPX). Thus, the coumarin-based probes are more useful for multicolor imaging with yellow and red emitting fluorophores. In addition to the above benefits, ER labeling was achieved with the coumarin-based probes in both live cells and fixed cells, revealing their versatility for a wide range of cellular imaging applications.