Realgar (As4S4) nanoparticles and arsenic trioxide (As2O3) induced autophagy and apoptosis in human melanoma cells in vitro

Abstract

The aim of the present study was to compare the effect of realgar nanoparticles and arsenic trioxide (ATO) on viability, DNA damage, proliferation, autophagy and apoptosis in the human melanoma cell lines BOWES and A375. The application of various flow cytometric methods for measurements cell viability, DNA cell cycle, mitochondrial potential, lysosomal activity, and intracellular content of glutathione was used. In addition, quantitative PCR, western blotting and multiplex bead array analyses were applied for evaluation of redox stress, autophagic flux, and cell signaling alterations.The results showed that realgar treatment of studied cells caused modulation of cell proliferation, induced a block in G2/M phase of the cell cycle and altered phosphorylation of IκB, Akt, ERK1/2, p38, and JNK kinases, as well as decreased mitochondrial membrane potential. Additionally, it appeared that induction of cell death by both realgar and ATO was dose-dependent, when lower (0.3 µM) dosage increased lysosomal activity and induced autophagy and higher (1.25 µM) concentration resulted in the appearance of apoptosis, while pan-caspase inhibitor attenuated more efficiently realgar-than ATO-induced cell death. Furthermore, low concentrations of ATO and realgar nanoparticles increased the content of intracellular glutathione and elevated γ-H2AX expression confirmed DNA damage preferentially at higher concentrations of both drugs used. Further analysis revealed slight differences in time-dependent phosphorylation pattern due to both realgar and ATO treatments, while significant differences were noticed between cell lines.In conclusion, realgar nanoparticles and ATO treatment induced dose-dependent activation of autophagy and apoptosis in both melanoma cell lines, when autophagy flux was determined at lower drug concentrations and the switch to apoptosis occurred at higher concentrations of both arsenic forms.Key words : realgar, autophagy, cell cycle, DNA damage, Nrf2, chloroquine, glutathione Arsenic has been accepted to be a poison for years and it is generally considered as an extremely effective environmental co-carcinogen for some human malignancies, especially for skin and lung cancer [1]. The toxicity of arsenicals depends on their chemical states, exposure dose, the biological species, age and gender, as well as on individual susceptibilities, genetic and nutritional factors [2]. Largely, to living organisms methylated trivalent arsenicals are more toxic and pentavalent metabolites are less toxic than arsenite (iAs III ) [3,4]. In 2002, a pilot clinical study of pure realgar in treatment of patients with APL was conducted in China, and impressive responses were achieved and reported [5]. Realgar is a mineral composed mainly of tetra-arsenic tetra-sulfide (As 4 S 4 ), which is also called red arsenic due to its a deep red color (Xionghuang in Chinese). Low solubility of arsenic in realgar, using water as a solvent (0.4%), can be increased to approximately 1.5% by leaching in artificial body fluid [6]. Higher proportion of...

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