X-ray fluorescence imaging of single human cancer cells reveals that the N-heterocyclic ligands of iodinated analogues of ruthenium anticancer drugs remain coordinated after cellular uptake

Single-Cell Chemistry of Photoactivatable Platinum Anticancer Complexes

The Pt(IV) prodrug trans, trans, trans-[Pt(pyridine)2(N3)2(OH)2] (Pt1) and its coumarin derivative trans, trans, trans-[Pt(pyridine)2(N3)2(OH)(coumarin-3-carboxylate)] (Pt2) are promising agents for photoactivated chemotherapy. These complexes are inert in the dark but release Pt(II) species and radicals upon visible light irradiation, resulting in photocytotoxicity toward cancer cells. Here, we have used synchrotron techniques to investigate the in-cell behavior of these prodrugs and visualize, for the first time, changes in cellular morphology and Pt localization upon treatment with and without light irradiation. We show that photoactivation of Pt2 induces remarkable cellular damage with extreme alterations to multiple cellular components, including formation of vacuoles, while also significantly increasing the cellular accumulation of Pt species compared to dark conditions. X-ray absorption near-edge structure (XANES) measurements in cells treated with Pt2 indicate only partial reduction of the prodrug upon irradiation, highlighting that phototoxicity in cancer cells may involve not only Pt(II) photoproducts but also photoexcited Pt(IV) species.

Copper(II) Pyridyl Aminophenolates: Hypoxia-Selective, Nucleus-Targeting Cytotoxins, and Magnetic Resonance Probes

Targeting the low-oxygen (hypoxic) environments found in many tumours by using redox-active metal complexes is a strategy that can enhance efficacy and reduce the side effects of chemotherapies. We have developed a series of Cu^II complexes with tridentate pyridine aminophenolate-based ligands for preferential activation in the reduction window provided by hypoxic tissues. Furthermore, ligand functionalization with a pendant CF₃ group provides a ¹⁹ F spectroscopic handle for magnetic-resonance studies of redox processes at the metal centre and behaviour in cellular environments. The phenol group in the ligand backbone was substituted at the para position with H, Cl, and NO₂ to modulate the reduction potential of the Cu^II centre, giving a range of values below the window expected for hypoxic tissues. The NO₂ -substituted complex, which has the highest reduction potential, showed enhanced cytotoxic selectivity towards HeLa cells grown under hypoxic conditions. Cell death occurs by apoptosis, as determined by analysis of the cell morphology. A combination of ¹⁹ F NMR and ICP-OES indicates localization of the NO₂ complex in HeLa cell nuclei and increased cellular accumulation under hypoxia. This correlates with DNA nuclease activity being the likely origin of cytotoxic activity, as demonstrated by cleavage of DNA plasmids in the presence of the Cu^II nitro complex and a reducing agent. Selective detection of the paramagnetic Cu^II complexes and their diamagnetic ligands by ¹⁹ F MRI suggests hypoxia-targeting theranostic applications by redox activation.

[Ru(phen)2podppz]2+ significantly inhibits glioblastoma growth in vitro and vivo with fewer side-effects than cisplatin

To overcome the acquired resistance and the significant side-effects of the reported drugs, four new ruthenium(ii) complexes with alkynyl (Ru1, Ru2, Ru3, Ru4) were designed and synthesized. Ru1, Ru2, Ru3 and Ru4 were characterized by ESI-MS, 1H NMR, 1H-1H COSY NMR and elemental analysis. Compared with Ru2, Ru3, Ru4 and cisplatin, the anti-tumor experiments in vitro and vivo confirmed that Ru1 could most effectively inhibit tumor growth. In the experiments of safety evaluation in vivo, Ru1 could avoid any detectable side-effects compared with cisplatin. DNA binding experiments and cell cycle experiments showed that Ru1 exhibited the strongest DNA binding ability and interfered with the cell cycle by inserting DNA to inhibit tumor growth. The study demonstrated that Ru1 had the potential to be an exciting new drug candidate for glioblastoma treatment.

Rhenium carbonyl complexes bearing methylated triphenylphosphonium cations as antibody-free mitochondria trackers for X-ray fluorescence imaging

A convenient rhenium-based multimodal mitochondrial-targeted probe compatible with Synchrotron Radiation X-ray Fluorescence nano-imaging.

Synchrotron X-Ray Fluorescence Nanoprobe Reveals Target Sites for Organo-Osmium Complex in Human Ovarian Cancer Cells

A variety of transition metal complexes exhibit anticancer activity, but their target sites in cells need to be identified and mechanisms of action elucidated. Here, it was found that the sub-cellular distribution of [Os(η6 -p-cym)(Azpy-NMe2 )I]+ (p-cym=p-cymene, Azpy-NMe2 =2-(p-[dimethylamino]phenylazo)pyridine) (1), a promising drug candidate, can be mapped in human ovarian cancer cells at pharmacological concentrations using a synchrotron X-ray fluorescence nanoprobe (SXRFN). SXRFN data for Os, Zn, Ca, and P, as well as TEM and ICP analysis of mitochondrial fractions suggest localization of Os in mitochondria and not in the nucleus, accompanied by mobilization of Ca from the endoplasmic reticulum, a signaling event for cell death. These data are consistent with the ability of 1 to induce rapid bursts of reactive oxygen species and especially superoxide formed in the first step of O2 reduction in mitochondria. Such metabolic targeting differs from the action of Pt drugs, offering promise for combatting Pt resistance, which is a current clinical problem.

Albumin binding and ligand-exchange processes of the Ru(III) anticancer agent NAMI-A and its bis-DMSO analogue determined by ENDOR spectroscopy

The ruthenium anticancer compound NAMI-A, imidazolium [trans-RuCl4(1H-imidazole)(DMSO-S)], is currently undergoing advanced clinical evaluation. As with other Ru(iii) chemotherapeutic candidates, interactions with human serum albumin (HSA) have been identified as a key component of the speciation of NAMI-A following intravenous administration. To characterize coordination to HSA, we have performed electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) spectroscopic analysis of deuterium-labelled isotopologues of both NAMI-A and its bis-DMSO analogue, [(DMSO)2H][trans-RuCl4(DMSO-S)2] (Ru-bis-DMSO). Samples were prepared using phosphate buffered saline, in the presence of HSA, and with the individual amino acids histidine, cysteine, and alanine. Analysis of (1)H ENDOR spectra shows characteristic hyperfine interactions from DMSO, water, and imidazole ligands. Furthermore, coordination of imidazole ligands was confirmed from diagnostic (14)N ENDOR signals. Combined with the EPR data from the complexes following incubation in the presence of histidine, the ENDOR data demonstrate that both complexes bind to HSA via histidine imidazoles. Furthermore, the protein-bound species are shown to have water ligands and, in the case of Ru-bis-DMSO, one species has a remaining coordinated DMSO.

Metallomic and metalloproteomic strategies in elucidating the molecular mechanisms of metallodrugs

Advances in the mechanistic studies of metallodrugs by metallomic and metalloproteomic approaches will improve our understanding of the mechanism of action and allow more metallodrugs to be developed.

The H.G. Smith Award Article: Fluorescent Analogues of NAMI-A: Synthesis, Characterisation, Fluorescent Properties, and Preliminary Biological Studies in Human Lung Cancer Cells

Two new fluorescent ruthenium(iii) complexes, namely 7-azaindolium trans-tetrachlorido(7-azaindole)(dimethylsulfoxide)ruthen(iii)ate (F1) and N-[histaminedihydrolium]-1,8-naphthalenecarboximidic trans-tetracholoro(dimethylsulfoxide)(N-[histaminedihydro]-1,8-naphthalenecarboximide)ruthen(iii)ate (F2) and their respective tetramethylammonium analogues (F3 and F4) are reported herein. The compounds were characterised by elemental analysis, mass spectrometry, UV-vis spectrophotometry, and fluorescence spectroscopy. Molar extinction coefficients (ϵmax) and fluorescence emission spectra were compared to evaluate the electronic properties of the synthesised fluorescent analogues, and hence their value as intracellular fluorescence probes. F3 and F4 were synthesised and characterised in order to eliminate fluorescence arising from the counter-cations in F1 and F2 and thus to obtain a fluorescence quantum yield that reflects only a contribution from the metal complex anion. Half-inhibitory concentrations (IC50) were determined for A549 cells exposed to the Ru complexes for 24 h: F3 (203 ± 26 μM) and F4 (185 ± 20 μM).