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Potent Half-Sandwich Iridium(III) Anticancer Complexes Containing C?N-Chelated and Pyridine Ligands.

ABSTRACT: We report the synthesis and characterization of eight half-sandwich cyclopentadienyl IrIII pyridine complexes of the type [(?5-Cpxph)Ir(phpy)Z]PF6, in which Cpxph = C5Me4C6H5 (tetramethyl(phenyl)cyclopentadienyl), phpy = 2-phenylpyridine as C?N-chelating ligand, and Z = pyridine (py) or a pyridine derivative. Three X-ray crystal structures have been determined. The monodentate py ligands blocked hydrolysis; however, antiproliferative studies showed that all the Ir compounds are highly active toward A2780, A549, and MCF-7 human cancer cells. In general the introduction of an electron-donating group (e.g., Me, NMe2) at specific positions on the pyridine ring resulted in increased antiproliferative activity, whereas electron-withdrawing groups (e.g., COMe, COOMe, CONEt2) decreased anticancer activity. Complex 5 displayed the highest anticancer activity, exhibiting submicromolar potency toward a range of cancer cell lines in the National Cancer Institute NCI-60 screen, ca. 5 times more potent than the clinical platinum(II) drug cisplatin. DNA binding appears not to be the major mechanism of action. Although complexes [(?5-Cpxph)Ir(phpy)(py)]+ (1) and [(?5-Cpxph)Ir(phpy)(4-NMe2-py)]+ (5) did not cause cell apoptosis or cell cycle arrest after 24 h drug exposure in A2780 human ovarian cancer cells at IC50 concentrations, they increased the level of reactive oxygen species (ROS) dramatically and led to a loss of mitochondrial membrane potential (??m), which appears to contribute to the anticancer activity. This class of organometallic Ir complexes has unusual features worthy of further exploration in the design of novel anticancer drugs.

SUBMITTER: Liu Z

PROVIDER: S-EPMC4195516 | biostudies-literature | 2014 Oct

REPOSITORIES: biostudies-literature

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Potent Half-Sandwich Iridium(III) Anticancer Complexes Containing C∧N-Chelated and Pyridine Ligands.

Liu Zhe Z Romero-Canelón Isolda I Habtemariam Abraha A Clarkson Guy J GJ Sadler Peter J PJ

Organometallics 20140909 19

We report the synthesis and characterization of eight half-sandwich cyclopentadienyl IrIII pyridine complexes of the type [(η5-Cpxph)Ir(phpy)Z]PF6, in which Cpxph = C5Me4C6H5 (tetramethyl(phenyl)cyclopentadienyl), phpy = 2-phenylpyridine as C∧N-chelating ligand, and Z = pyridine (py) or a pyridine derivative. Three X-ray crystal structures have been determined. The monodentate py ligands ...[more]

PMID: 25328266

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Project description:We report the synthesis, characterization, and antiproliferative activity of 15 iridium(III) half-sandwich complexes of the type [(?5-Cp*)Ir(2-(R'-phenyl)-R-pyridine)Cl] bearing either an electron-donating (-OH, -CH2OH, -CH3) or electron-withdrawing (-F, -CHO, -NO2) group at various positions on the 2-phenylpyridine (2-PhPy) chelating ligand giving rise to six sets of structural isomers. The X-ray crystal structures of [(?5-Cp*)Ir(2-(2'-fluorophenyl)pyridine)Cl] (1) and [(?5-Cp*)Ir(2-(4'-fluorophenyl)pyridine)Cl] (2) exhibit the expected "piano-stool" configuration. DFT calculations showed that substituents caused only localized effects on the electrostatic potential surface of the chelating 2-PhPy ligand of the complexes. Hydrolysis of all complexes is rapid, but readily reversed by addition of NaCl. The complexes show preferential binding to 9-ethylguanine over 9-methyladenine and are active catalysts for the oxidation of NADH to NAD+. Antiproliferative activity experiments in A2780 ovarian, MCF-7 breast, A549 lung, and HCT116 colon cancer cell lines showed IC50 values ranging from 1 to 89 ?M, with the most potent complex, [(?5-Cp*)Ir(2-(2'-methylphenyl)pyridine)Cl] (13) (A2780 IC50 = 1.18 ?M), being 10× more active than the parent, [(?5-Cp*)Ir(2-phenylpyridine)Cl], and 2× more active than [(?5-CpxPh)Ir(2-phenylpyridine)Cl]. Intriguingly, contrasting biological activities are observed between structural isomers despite exhibiting similar chemical reactivity. For pairs of structural isomers both the nature and position of the functional group can affect the hydrophobicity of the complex. An increase in hydrophobicity resulted in enhanced cellular-iridium accumulation in A2780 ovarian cells, which generally gave rise to an increase in potency. The structural isomers [(?5-Cp*)Ir(2-(4'-fluorophenyl)pyridine)Cl] (2) and [(?5-Cp*)Ir(2-phenyl-5-fluoropyridine)Cl] (4) preferentially localized in the cytosol > membrane and particulate > nucleus > cytoskeleton. This work highlights the strong dependence of biological behavior on the nature and position of the substituent on the chelating ligand and shows how this class of organometallic anticancer complexes can be fine-tuned to increase their potency without using extended cyclopentadienyl systems.

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Potent Half-Sandwich Iridium(III) Anticancer Complexes Containing C?N-Chelated and Pyridine Ligands.

Publications

Potent Half-Sandwich Iridium(III) Anticancer Complexes Containing C<sup>∧</sup>N-Chelated and Pyridine Ligands.

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