Trimethoxyphenyl-BODIPYs as probes for lysosome staining

BODIPYs have been extensively used for biological imaging owing to their high fluorescent quantum yields of stability toward photobleaching. In this work, zwitterionic groups were introduced into trimethoxyphenyl-BODIPY derivatives to improve their water-solubility. The impact of the substitution pattern of the methoxy groups in the phenyl motif and of the alkyl groups at different positions of the BODIPY core was also investigated. Three novel water-soluble trimethoxyphenyl-BODIPYs, herein designated as BDP-12, BDP-13 and BDP-14, were then evaluated as potential markers for lysosome staining. The highest fluorescence quantum yield and molar absorption coefficient were observed for BDP-12. Cellular uptake studies demonstrated that the three BODIPYs are rapidly internalized by cells. It was observed that 5 minutes of incubation time was sufficient to detect BODIPY-associated fluorescence in the treated cells. Cell internalization of the three molecules was inhibited by chloroquine and chlorpromazine, but not by genistein, which indicates that clathrin-mediated endocytosis is the main mechanism of internalization. The three trimethoxyphenyl-BODIPYs displayed excellent biocompatibility, even at high concentrations and in the presence of light. The three BODIPYs accumulate in the lysosomal compartments of live cells and the staining remains stable upon fixation with paraformaldehyde. Due to its optimal optical properties, BDP-12 is suggested as a promising candidate for cell imaging of lysosomes.