Sirtuin deacetylases, which are present in mammalians in 7 different isoforms (SIRT1-7), are important for cell survival and have been related to the pathophysiology of many age-related diseases including cancer. Sirtinol is a cell-permeable inhibitor of sirtuin proteins and was identified over a decade ago by high-throughput screening. The molecular structure of sirtinol exhibits a metal-binding unit similar to that of previously established iron chelators such as 2-hydroxy-1-naphthaldehyde isonicotinoyl hydrazone. Our in-vitro spectroscopic studies indicate that sirtinol binds Fe(II), Fe(III), Cu(II) and Zn(II) in both organic solvents and neutral aqueous solutions. Prompt oxidation takes place on exposure of the Fe(II) complex of sirtinol, which is converted to a Fe(III) species. Both FeIII(sirtinol−H)(NO3)2 and CuII(sirtinol−H)2 were fully characterized and found to be stable in aqueous solutions (pH 7.40). Electron paramagnetic resonance (EPR) experiments on intact Jurkat cells reveal that sirtinol binds iron intracellularly and affects the activity of iron-dependent enzyme ribonucleotide reductase. Viability assays on breast adenocarcinoma cell lines (MDA-MB-231 and MCF-7) showed that both FeIII(sirtinol−H)(NO3)2 and CuII(sirtinol−H)2 exhibit increased toxicity compared to sirtinol. Consistently, flow cytometry experiments employing a fluorescent probe (DCFH2-DA) of oxidative stress indicate that FeIII(sirtinol−H)(NO3)2 is involved in the intracellular generation of reactive oxygen species. This study demonstrates that sirtinol coordinates transition metals both in vitro and intracellularly, and that the Cu(II) and Fe(III) complexes show enhanced cytotoxicity. Considerations of metal coordination and related redox chemistry can therefore complicate the biological activity profile of this compound beyond its established role as an inhibitor of sirtuin proteins.

In-vitro and intracellular metal chelation properties of sirtuin inhibitor sirtinol

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.