Metal and Ligand Control of Sulfenate Reactivity: Arene Ruthenium Thiolato-Mono-S-Oxides

Selective Targeting of the Zinc Finger Domain of HIV Nucleocapsid Protein NCp7 with Ruthenium Complexes

Nucleocapsid protein 7 (NCp7) is an attractive target for anti-HIV drug development. Here we found that ruthenium complexes are reactive to NCp7 and various Ru-agents exhibit significantly different reactivity. Interestingly, the zinc-finger domains of NCp7 also demonstrate different affinity to Ru-complexes; the C-terminal domain is much more reactive than the N-terminal domain. Each zinc-finger domain of NCp7 binds up to three Ru-motifs, and the ruthenium binding causes zinc-ejection from NCp7 and disrupts the protein folding. Therefore, ruthenium complexes interfere with the DNA binding of NCp7 and interrupt the protein function. The different reactivity of Ru-agents suggests a feasible strategy for improving the targeting of NCp7 by ligand design. This work provides an insight into the mechanism of ruthenium complex with NCp7, and suggests more potential application of ruthenium drugs.

In-Cell Activation of Organo-Osmium(II) Anticancer Complexes

The family of iodido OsII arene phenylazopyridine complexes [Os(η6 -p-cym)(5-R1 -pyridylazo-4-R2 -phenyl))I]+ (where p-cym=para-cymene) exhibit potent sub-micromolar antiproliferative activity towards human cancer cells and are active in vivo. Their chemical behavior is distinct from that of cisplatin: they do not readily hydrolyze, nor bind to DNA bases. We report here a mechanism by which they are activated in cancer cells, involving release of the I- ligand in the presence of glutathione (GSH). The X-ray crystal structures of two active complexes are reported, 1-I (R1 =OEt, R2 =H) and 2-I (R1 =H, R2 =NMe2 ). They were labelled with the radionuclide 131 I (β- /γ emitter, t1/2 8.02 d), and their activity in MCF-7 human breast cancer cells was studied. 1-[131 I] and 2-[131 I] exhibit good stability in both phosphate-buffered saline and blood serum. In contrast, once taken up by MCF-7 cells, the iodide ligand is rapidly pumped out. Intriguingly, GSH catalyzes their hydrolysis. The resulting hydroxido complexes can form thiolato and sulfenato adducts with GSH, and react with H2 O2 generating hydroxyl radicals. These findings shed new light on the mechanism of action of these organo-osmium complexes.

A computational approach to tuning the photochemistry of platinum(IV) anticancer agents

Diazido Pt(IV) complexes are inert stable prodrugs that can be photoactivated to produce Pt(II) species with promising anticancer activity. Our studies of the photochemistry of Pt(IV) complexes, [Pt(X)(2) (Y)(2) (Z)(2) ](0/-1) (X=N-ligands (NH(3) , pyridine, etc.)/S(CH(3) )(2) /H(-) , Y=(pseudo)halogen (N(3) (-) , I(-) ), Z=OR(-) , R=H, Ac) by time-dependent density functional theory (TDDFT) show close agreement with spectroscopic data. Broad exploration of cis/trans geometries, trans influences, the nature of the OR(-) and (pseudo)halogen ligands, electron-withdrawing/donating/delocalising substituents on the N-ligands, and intramolecular H bonds shows that: 1) the design of platinum(IV) complexes with intense bands shifted towards longer wavelengths (from 289 to ∼330 nm) can be achieved by introducing intramolecular H bonds involving the OH ligands and 2-hydroxyquinoline or by iodido ligands; 2) mesomeric electron-withdrawing substituents on pyridine result in low-energy absorption with significant intensity in the visible region; and 3) the distinct makeup of the molecular orbitals involved in the electronic transitions for cis/trans-{Pt(N(3) )(2) } isomers results in different photoproducts. In general, the comparison of the optimised geometries shows that Pt(IV) complexes with longer PtL bonds are more likely to undergo photoreduction with longer-wavelength light. The novel complex trans,trans,trans-[Pt(N(3) )(2) (OH)(2) (NH(3) )(4-nitropyridine)] with predicted absorption in the visible region has been synthesised. The experimental UV/Vis spectrum in aqueous solution correlates well with the intense band in the computed spectrum, whereas the overlay in the low-energy region can be improved by a solvent model. This combined computational and experimental study shows that TDDFT can be used to tune the coordination environment for optimising photoactive Pt(IV) compounds as anticancer agents.