Johanna Niesel

Cellular Uptake, Cytotoxicity, and Metabolic Profiling of Human Cancer Cells Treated with Ruthenium(II) Polypyridyl Complexes [Ru(bpy)2(N-N)]Cl2 with N-N = bpy, phen, dpq, dppz, and dppn

A series of five ruthenium(II) polypyridyl complexes [Ru(bpy)2(NN)]Cl2 was tested against human HT‐29 and MCF‐7 cancer cell lines. Cellular uptake efficiency and cytotoxicity were found to increase with the size of the aromatic surface area of the NN ligand. The most active compound carrying the dppn ligand exhibits a low micromolar IC50 value against both cell lines comparable to that of cisplatin under similar conditions. Continuous measurement of oxygen consumption, extracellular acidification rate, and impedance of the cell layer with a chip‐based sensor system upon exposure to the complexes showed only small changes for the first two parameters throughout the series. A significant and irreversible decrease in impedance was, however, found for the dppn compound. This suggests that its biological activity is related to modifications in cell morphology or cell–cell and cell–matrix contacts.

Label‐Free Imaging of Metal–Carbonyl Complexes in Live Cells by Raman Microspectroscopy

The search for novel metal complexes with therapeutic activity, in particular against cancer and infectious diseases, is an active and important area of research in medicinal inorganic chemistry. In addition to the well-studied platinumand ruthenium-based coordination complexes, organometallic compounds have gained considerable importance in recent years. Of those, metal–carbonyl compounds are steadily increasing in interest, with some exhibiting remarkable antitumor activity. The most prominent example is probably the use of such compounds as “solid storage forms” for carbon monoxide. These CO-releasing molecules (CORMs) allow the biological action of this important small molecule messenger to be investigated. To elucidate the biological mode of action of any drug candidate it is mandatory to obtain a detailed picture of the intracellular distribution of such substances and how it evolves over time. Until now, the localization of metal complexes inside cells has been studied using X-ray fluorescence (XRF) 14] and atomic absorption spectroscopy (AAS). While AAS offers high sensitivity but almost no spatial resolution, XRF requires intense X-ray sources such as synchrotrons which will cause damage to biological tissue and is also not routinely available as an analytical technique. Most cellular studies therefore use fluorescence microscopy. Furthermore, this technique requires the additional attachment of a fluorescent label, which might be difficult. Optical excitation can also cause additional problems such as the onset of photochemical reactions or photobleaching. Moreover, the label can alter the biodistribution and properties of the molecule of interest, as recently shown for ruthenium–bipyridyl complexes. Efforts have been made to overcome these limitations by identifying biologically active metal complexes which show inherent fluorescence in vivo, but this has only been possible for a small number of metal–ligand combinations. Thus, it is highly desirable to develop innovative and generally applicable imaging techniques for the study of the uptake and distribution of bioactive metal complexes which do not require any labeling or special photophysical properties but instead use the intrinsic spectroscopic signature of the compound of interest. Raman microspectroscopy is emerging as a powerful noninvasive method to assess and image cellular compartments and processes without further sample preparation or labeling. Since Puppels et al. first showed the feasibility of confocal Raman microspectroscopy for imaging cells, its ability to study whole cells and subcellular organelles such as the nucleus and chromatin, mitochondria, and lipid bodies has been demonstrated by various research groups. Apart from imaging subcellular features, Raman imaging has been used to follow the uptake of molecules by cells. So far, however, these investigations have been restricted to the incorporation of deuterated building blocks as sensitive and specific markers into bio(macro)molecules. Herein, we investigate the uptake and cellular distribution of the new manganese-based CORM [Mn(tpm)(CO)3]Cl (tpm = tris(1-pyrazolyl)methane), which has photoinduceable cytotoxic activity against cancer cells. Metal–carbonyl complexes such as [Mn(tpm)(CO)3]Cl show strong C O stretching vibrations between 1800 and 2200 cm , a region where vibrational signals from the constituents of the cell are negligible. We show that the C O vibrations of this compound can be used as an ideal marker for imaging these complexes in living cancer cells. Although the spectroscopic signature of metal–carbonyl compounds has already been used in bioanalytical techniques such as the carbonyl–metal immunoassay (CMIA), their use in cellular imaging is so far unprecedented, except for an investigation of osmium–carbonyl clusters in dried cells by using infrared microscopy. The IR and Raman spectra of solid [Mn(tpm)(CO)3]Cl show strong C O stretching vibrations at about 1944 and 2050 cm , as expected for local C3v symmetry (Figures S1 and S2 A in the Supporting Information). The different relative intensities of the two peaks can be explained by the distinct selection rules for Raman and IR spectroscopy. The O H stretching vibration localized at about 3400 cm 1 dominates the spectrum of a 2 mm aqueous solution of [Mn(tpm)[*] K. Meister, Dr. D. A. Schmidt, Prof. Dr. M. Havenith Lehrstuhl f r Physikalische Chemie II, Ruhr-Universit t Bochum Universit tsstrasse 150, 44801 Bochum (Germany) E-mail: martina.havenith@rub.de Homepage: www.rub.de/pc2

Iron Metal–Organic Frameworks MIL‐88B and NH2‐MIL‐88B for the Loading and Delivery of the Gasotransmitter Carbon Monoxide

Crystals of MIL-88B-Fe and NH2-MIL-88B-Fe were prepared by a new rapid microwave-assisted solvothermal method. High-purity, spindle-shaped crystals of MIL-88B-Fe with a length of about 2 μm and a diameter of 1 μm and needle-shaped crystals of NH2-MIL-88B-Fe with a length of about 1.5 μm and a diameter of 300 nm were produced with uniform size and excellent crystallinity. The possibility to reduce the as-prepared frameworks and the chemical capture of carbon monoxide in these materials was studied by in situ ultrahigh vacuum Fourier-transform infrared (UHV-FTIR) spectroscopy and Mössbauer spectroscopy. CO binding occurs to unsaturated coordination sites (CUS). The release of CO from the as-prepared materials was studied by a myoglobin assay in physiological buffer. The release of CO from crystals of MIL-88B-Fe with t(1/2) = 38 min and from crystals of NH2-MIL-88B-Fe with t(1/2) = 76 min were found to be controlled by the degradation of the MIL materials under physiological conditions. These MIL-88B-Fe and NH2-MIL-88B-Fe materials show good biocompatibility and have the potential to be used in pharmacological and therapeutic applications as carriers and delivery vehicles for the gasotransmitter carbon monoxide.

New modular manganese(I) tricarbonyl complexes as PhotoCORMs: in vitro detection of photoinduced carbon monoxide release using COP-1 as a fluorogenic switch-on probe

Five manganese(i) tricarbonyl complexes of the general formulae [Mn(bpea(N=CHC6H4R))(CO)3]PF6 and [Mn(bpea(NHCH2C6H4R))(CO)3]PF6 based on the tridentate bis(pyrazolyl)ethylamine (bpea) ligand, each containing a pendant 4-substituted phenyl group with R = H, I, and C≡C-H, were synthesized and fully characterized, including X-ray structure analysis for three compounds. All complexes are stable in the dark in aqueous buffer for an extended period of time. However, CO-release could be triggered by illumination at 365 nm, establishing these compounds as novel photoactivatable CO-releasing molecules (PhotoCORMs). The influence of the imine vs. amine group in the ligands on the electronic structure and the photophysical behavior was investigated with the aid of DFT and TDDFT calculations. Solution IR studies on selected compounds allowed identification of intermediates resulting from the photoreaction. Finally, light-induced CO release from a model compound was demonstrated both in PBS buffer and in vitro in human umbilical vein endothelial cells (HUVECs) using COP-1 as a fluorescent switch-on probe.

Ultrafast Photochemistry of a Manganese-Tricarbonyl CO-Releasing Molecule (CORM) in Aqueous Solution

Ultraviolet irradiation of a manganese-tricarbonyl CO-releasing molecule (CORM) in water eventually leads to the liberation of some of the carbon monoxide ligands. By ultraviolet pump/mid-infrared probe femtosecond transient absorption spectroscopy in combination with quantum chemical calculations, we could disclose for the exemplary compound [Mn(CO)3(tpm)](+) (tpm = tris(2-pyrazolyl)methane) that only one of the three carbonyl ligands is photochemically dissociated on an ultrafast time scale and that some molecules may undergo geminate recombination.