Synthesis and photodynamic properties of pyrazole-indole hybrids in the human skin melanoma cell line G361

Three conjugated pyrazole-indole hybrids, 5, 7 and 10, were synthesized from easily accessible 3-(hexyloxy)-1-phenyl-1H-pyrazole-4-carbaldehyde 1 and 5-iodo-3,3-dimethyl-2-phenyl-3H-indole 4 employing olefination reactions (Wittig, Ramirez), Vilsmeier-Haack formylation and palladium-catalysed cross coupling reactions (ligand-free Heck, Sonogashira). The compounds displayed no cytotoxicity in the melanoma cell line G361 unless irradiated with visible blue light (414 nm), and the potency of the compounds increased with light intensity. Lead compound 7 displayed EC50 values of 3.08, 0.26 and 0.05 mu M in cells irradiated with 1, 10 and 50 J/cm(2), respectively. The following experiments revealed increased levels of reactive oxygen species in treated cells and a decrease in JC-1 polymer aggregation within the mitochondria, suggesting mitochondrial membrane depolarization. In addition, extensive DNA fragmentation was detected using the comet assay and by detection of phosphorylated histone H2A.X, the level of which increased with both increased compound concentration and irradiation energy. In control experiments, cells kept either in the dark or without compound 7 did not show any DNA damage. Overall, the results demonstrated that fluorescent pyrazole-indole hybrids may serve as an interesting source of photosensitizing compounds with anticancer activity.