Structure-performance relationships of four lysosomal markers used for the imaging of HT-29 cancer cells and a cellular model of lysosomal storage disease (Niemann-Pick C)

Abstract

Four new BODIPY derivatives with a potential tendency to aggregation have been synthesized and characterized by means of NMR techniques, mass spectrometry and UV–Vis/fluorescence spectroscopies. The objective of this study is to determine which structural factors of the new molecules influence most notably the cellular uptake, intracellular location and fluorescence imaging abilities. The behaviour of the compounds in organic solvent and aqueous solution has been studied. In organic solvents (DMSO, ethanol and toluene), the photophysical properties of the new molecules are almost independent of the building blocks used to synthesize the pendant moieties (non-fluorogenic parts). In an aqueous environment (HEPES Buffer Solution, pH 7), at 10 μM, three of the compounds (1, 2 and 4) tend to form weakly emissive nanoparticles (DLS determination) whereas one of them (3) remains soluble and highly fluorescent. In the nanomolar range of concentration, all the compounds are aqueous soluble. The cellular internalisation of the compounds (10 nM) has been studied in human colon adenocarcinoma HT-29 cells by means of flow cytometry and confocal laser scanning microscopy. All the compounds were uptaken by HT-29 cells, but notably molecule 3 (made with lysine as a building block) was the one displaying a higher loading and a more clear lysosomal location (0.88 Pearson's correlation coefficient in colocalization assays using lysosomal fluorescent probe LysoTracker DND-99). Molecule 3 also performed better than the valine derivative 1 as a lysosomal marker in a cellular model (human adrenal carcinoma SW13/cl.2 cells) of lysosomal storage disease (Niemann-Pick type C).