Synthesis of Apoptosis-Inducing Iminophosphorane Organogold(III) Complexes and Study of Their Interactions with Biomolecular Targets

New stable cationic organogold(III) complexes containing the "pincer' iminophosphorane ligand (2-C6H4-PPh2=NPh) have been prepared by reaction of the previously described [Au{kappa(2)-C,N-C6H4(PPh2=N(C6H5)-2)Cl-2] 1 and a combination of sodium or silver salts and appropriate ligands. The presence of the P atom in the PR3 fragment has been used as a "spectroscopic marker' to study the in vitro stability (and oxidation state) of the new organogold complexes in solvents like dimethyl sulfoxide and water. Compounds with dithiocarbamato ligands and watersoluble phosphines of the general type [Au{kappa(2)-C,N-C6H4(PPh2=N(C6H5)-2}(S2CN-R-2)]PF6 (R = Me 2; Bz 3) and [Au{kappa(2)-C,N-C6H4(PPh2=N(C6H5)-2}(PR3)(n)Cl]PF6 (PR3 = P{Cp(m-C6H4-SO3Na)(2)} n = 1 4, n = 2 TPA {1,3,5-triaza-7-phosphaadamantane} 5) have been synthesized and characterized in solution and in the solid state (the crystal structure of 2 has been determined by X-ray diffraction studies). Complexes 1-5 have been tested as potential anticancer agents, and their cytotoxicity properties were evaluated in vitro against HeLa human cervical carcinoma and Jurkat-T acute lymphoblastic leukemia cells. Compounds 2 and 3 are quite cytotoxic for these two cell lines. There is a preferential induction of apoptosis in HeLa cells after treatment with 1-5. However in the case of the more cytotoxic complex (2), cell death is activated because of both apoptosis and necrosis. The interactions of 1-5 with Calf Thymus DNA have been evaluated by Thermal Denaturation methods. All these complexes show no or little (electrostatic) interaction with DNA The interaction of 2 with two model proteins (cytochrome c and thioredoxin reductase) has been analyzed by spectroscopic methods (vis-UV and fluorescence). Compound 2 manifests a high reactivity toward both proteins. The mechanistic implications of these results are discussed here.