Simultaneous staining of endoplasmic reticulum and lipid droplets by naphthol-aminonaphthalimide conjugates and photoinduced antiproliferative effects

A detailed study of photophysical properties and photochemical reactivity of five novel naphthol-aminonaphthalimide conjugates 1a-1e (differing in the linker length between two chromophores) showed efficient Förster resonance energy transfer (FRET) from naphthol to aminonaphtalimide, preventing the photodehydration reaction to yield quinone methides (QM). Nevertheless, 1a and 1e showed photoinduced bioreactivity. Derivatives 1a and 1e showed moderate affinity toward both, ds-DNA/RNA and serum albumin (BSA), yielding opposite emission response; strong quenching for DNA/RNA and strong increase with remarkable blue shift for BSA. Confocal fluorescent microscopy and collocalisation experiments performed on human cells lines showed efficient cellular uptake with no apparent toxicity and localization of the dyes in intracellular lipidous membranes, mostly endoplasmic reticulum (ER) and lipid droplets (LD). Owing to different fluorescent response in these organelles due to different polarity, compounds 1a-1e have potential for simultaneous staining of ER and lipid droplets. The irradiation at 350 nm of compound-treated cells resulted in very strong cytotoxic effect, evident at micromolar concentration. Thus, presented dyes are promising lead compounds to novel photo-induced theranostic agents.