Cell‐based studies of the first‐in‐class half‐sandwich Ir(III) complex containing histone deacetylase inhibitor 4‐phenylbutyrate

Abstract

We report on a cytotoxic half-sandwich iridium(III) complex [Ir(η 5 -Cp ph )(phen) (PB)]PF 6 (1-PB), containing a monodentate coordinated O-donor 4phenylbutyrato ligand (PB) belonging to the family of histone deacetylase inhibitors (HDACi); HCp ph = (2,3,4,5-tetramethylcyclopenta-2,4-dien-1-yl)benzene, phen = 1,10-phenanthroline. The solution behaviour studies indicated that complex 1-PB partially hydrolysed in the mixture of methanol and water (1:4, v/v), resulting in the release of the PB ligand. The extent of the PB ligand release increased in the presence of 2 molar equiv. of the reduced glutathione (GSH). Complex 1-PB exhibited comparable in vitro cytotoxicity against the cisplatin-sensitive (IC 50 = 15.8 μM) and -resistant (IC 50 = 13.0 μM) variants of the A2780 human ovarian carcinoma cells, while its potency against the MRC-5 human normal fibroblast cells was markedly lower (IC 50 = 124.1 μM). The cytotoxicity studies revealed an ability of complex 1-PB to overcome the acquired resistance against cisplatin, with the resistance factor (RF = 0.8) being markedly lower than for complex 1-Cl (RF = 1.8) and cisplatin (RF = 2.9). The A2780 cell-based flow cytometry experiments showed different cell cycle modification induced by complex 1-PB and cisplatin, induction of production of reactive oxygen species, and higher mitochondria membrane potential depleted cell populations after the treatment by complex 1-PB as compared with cisplatin. In the cell-free assay, complex 1-PB inhibited the HDAC activity to ca 66% as compared to ca 74% valid for NaPB. The [Ir(η 5 -Cp ph )(phen)(H 2 O)] 2+ species (1-OH 2 ), representing the hydrolysis product of both complexes 1-PB and 1-Cl, induced hydroxyl radical from the hydrogen peroxide, as proved by the EPR spin trapping studies with the 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO) spin trap.

Half-Sandwich Ir(III) Complex of N1-Pyridyl-7-azaindole Exceeds Cytotoxicity of Cisplatin at Various Human Cancer Cells and 3D Multicellular Tumor Spheroids

“…The MTT assay, commonly used for cytotoxicity testing (and also used in the previous experiment with ovarian cancer cells), requires mitochondrial metabolic activity (measures mitochondria dehydrogenase activity as a marker of cell viability) to convert the colorless tetrazolium to the purple-colored formazan dye. However, a large number of Ir complexes have been shown to interfere with mitochondrial activity so that the metabolization of MTT can reflect an effect of the Ir complexes on the mitochondrial metabolism rather than the viability of cells. Conversely, the neutral red uptake assay is based on the abilities of viable cells to incorporate and bind the dye in lysosomes, so that it is not affected by changes in the mitochondrial metabolism.…”