Aim: Investigation of cytotoxic effects of newly synthesized and untested polyoxometalates Pd1 and Pd2 on human neuroblastoma cells SH-SY5Y.
Introduction: Polyoxometalates (POMs) are transitional metal complexes, which are important in medicinal chemistry, as potent anticancer, antiviral and antibacterial agents. Inefficiently selective drugs and problems with dosing of usual chemotherapeutics directed the research towards investigation of new agents, such as POM.
Methods: Effects on viability rate of treated cells was tested using acid phosphatase assay. The mechanism of a cell death was examined using flow cytometry. JC-1, dihydroethidium, ApoStat, propidium iodide and acridin orange stainings were conducted in order to elucidate mitochondrial depolarisation, production of superoxide anion, caspase activation, DNA fragmentation and intracellular acidity.
Results: Pd1 and Pd2 have shown dose and time dependent decrease in cell viability rate. Complexes induced mitochondrial depolarisation after 2h of treatment, which was shown as increase in FL1/FL2 ratio from 1 to 1.3 (Pd1, 6μM) and from 1 to 1.7 (Pd2, 40μM). Superoxide anion production was increased after 5h of treatment using Pd1 and 2h of treatment using Pd2. Pd1 complex exhibits increase in percentage of cells with fragmented DNA (subG0) and activated caspases after 24h treatment. Pd2 complex induced increase in SubG0 and S phase without caspase activaction after 24h treatment. POMs have shown intracellular acidification after 48h (FL3/FL1 ratio: control 1, Pd1 2.3, Pd2 1.8).
Conclusion: POM complexes indicated cytotoxic effects on examined cell line. The mechanism by which these complexes exert those effects differ from one another. It was shown that both induce oxidative stress and mitochondrial depolarisation, accompanied by activation of caspases and DNA fragmentation in Pd1-treated cells, all indicative of apoptosis. In Pd2-treated group there was no increase in activation of caspases. Complexes have shown increase in intracellular acidification, which may suggest autophagy.
Acknowledgements: This research was a part of bilateral project between University of Belgrade, Belgrade, Serbia and Jacobs University, Bremen, Germany; 451-03-01038/2015-09/16.