Mario Kubanik

Impact of Stepwise NH2-Methylation of Triapine on the Physicochemical Properties, Anticancer Activity, and Resistance Circumvention

One of the most promising classes of iron chelators are α-N-heterocyclic thiosemicarbazones with Triapine as the most prominent representative. In several clinical trials Triapine showed anticancer activity against hematological diseases, however, studies on solid tumors failed due to widely unknown reasons. Some years ago, it was recognized that “terminal dimethylation” of thiosemicarbazones can lead to a more than 100-fold increased activity, probably due to interactions with cellular copper depots. To better understand the structural requirements for the switch to nanomolar cytotoxicity, we systematically synthesized all eight possible N-methylated derivatives of Triapine and investigated their potential against Triapine-sensitive as well as -resistant cell lines. While only the “completely” methylated compound exerted nanomolar activity, the data revealed that all compounds with at least one N-dimethylation were not affected by acquired Triapine resistance. In addition, these compounds were highly synergistic with copper treatment accompanied by induction of reactive oxygen species and massive necrotic cell death.

Anticancer activity of Ru- and Os(arene) compounds of a maleimide-functionalized bioactive pyridinecarbothioamide ligand

With the aim of increasing the accumulation of Ru anticancer agents in the tumor, a targeted delivery strategy based on a maleimide anchor for the biological vector human serum albumin (HSA) was developed. A group of piano stool Ru- and Os(η6-arene) complexes carrying a maleimide-functionalized N-phenyl-2-pyridinecarbothioamide (PCA) ligand was designed allowing for covalent conjugation to biological thiols. The complexes were characterized by NMR spectroscopy, ESI-MS, elemental analysis and single-crystal X-ray diffraction analysis. The compounds were shown to undergo halido/aqua ligand exchange reactions in aqueous solution, depending mainly on the metal center and the nature of the halide. In vitro cytotoxicity studies revealed low potency which is explained by the observed high reactivity of the maleimide to the thiol of l-cysteine (Cys), while the metal center itself shows little affinity to amino acids of the model protein lysozyme.

Anti-Inflammatory Oxicams as Multi-donor Ligand Systems: pH- and Solvent-Dependent Coordination Modes of Meloxicam and Piroxicam to Ru and Os

The nitrogen- and sulfur-containing 1,2-benzothiazines meloxicam and piroxicam are widely used as nonsteroidal anti-inflammatory drugs. Intrigued by the presence of multiple donor atoms and therefore potentially rich coordination chemistry, we prepared a series of organometallic Ru and Os compounds with meloxicam and piroxicam featuring either as mono- or bidentate ligand systems. The choice of the solvent and the pH value was identified as the critical parameter to achieve selectively mono- or bidentate coordination. The coordination modes were confirmed experimentally by NMR spectroscopy and single crystal X-ray diffraction analysis. Using DFT calculations, it was established that complexes in which meloxicam acts as a bidentate N,O donor are energetically more favorable than coordination as O,O and S,O donor systems. Since meloxicam and piroxicam derivatives have shown anticancer activity in the past, we aimed to compare the complexes with mono- and bidentate ligands on their in vitro anticancer activity. However, stability studies revealed that only the latter complexes were stable in [D6 ]DMSO/D2 O (5:95) and therefore no direct comparisons could be made. The meloxicam complexes 1 and 2 showed moderate cytotoxicity, whereas the piroxicam derivatives 5 and 6 were hardly active against the utilized cell lines.

Anticancer Ru( η 6 - p -cymene) complexes of 2-pyridinecarbothioamides: A structure–activity relationship study

Ru(II) and Os(II) complexes of 2-pyridinecarbothioamide ligands were introduced as orally administrable anticancer agents (S.M. Meier, M. Hanif, Z. Adhireksan, V. Pichler, M. Novak, E. Jirkovsky, M.A. Jakupec, V.B. Arion, C.A. Davey, B.K. Keppler, C.G. Hartinger, Chem. Sci., 2013, 4, 1837-1846). In order to identify structure-activity relationships, a series of N-phenyl substituted pyridine-2-carbothiamides (PCAs) were obtained by systematically varying the substituents at the phenyl ring. The PCAs were then converted to their corresponding RuII(η6-p-cymene) complexes and characterized spectroscopically and by X-ray diffraction as well as in terms of stability in water and HCl. The cytotoxic activity of the PCA ligands and their respective organoruthenium compounds was evaluated in a panel of cell lines (HCT116, H460, SiHa and SW480). The lipophilic PCAs 1-4 showed cytotoxicity in the low micromolar range and 6 was the most potent compound of the series with an IC50 value of 1.1μM against HCT116 colon cancer cells. These observations were correlated with calculated octanol/water partition coefficient (clogP) data and quantitative estimated druglikeness. A similar trend as for the PCAs was found in their Ru complexes, where the complexes with more lipophilic ligands proved to be more cytotoxic in all tested cell lines. In general, the PCAs and their organoruthenium derivatives demonstrated excellent drug-likeness and cytotoxicity with IC50 values in the low micromolar range, making them interesting candidates for further development as orally active anticancer agents.

Cobalt complexes as internal standards for capillary zone electrophoresis–mass spectrometry studies in biological inorganic chemistry

Run-by-run variations are very common in capillary electrophoretic (CE) separations and cause imprecision in both the migration times and the peak areas. This makes peak and kinetic trend identification difficult and error prone. With the aim to identify suitable standards for CE separations which are compatible with the common detectors UV, ESI-MS, and ICP-MS, the CoIII complexes [Co(en)3]Cl3, [Co(acac)3] and K[Co(EDTA)] were evaluated as internal standards in the reaction of the anticancer drug cisplatin and guanosine 5′-monophosphate as an example of a classical biological inorganic chemistry experiment. These CoIII chelate complexes were considered for their stability, accessibility, and the low detection limit for Co in ICP-MS. Furthermore, the CoIII complexes are positively and negatively charged as well as neutral, allowing the detection in different areas of the electropherograms. The background electrolytes were chosen to cover a wide pH range. The compatibility to the separation conditions was dependent on the ligands attached to the CoIII centers, with only the acetylacetonato (acac) complex being applicable in the pH range 2.8–9.0. Furthermore, because of being charge neutral, this compound could be used as an electroosmotic flow (EOF) marker. In general, employing Co complexes resulted in improved data sets, particularly with regard to the migration times and peak areas, which resulted, for example, in higher linear ranges for the quantification of cisplatin.Graphical abstract

Analysis of ruthenium anticancer agents by MEEKC-UV and MEEKC–ICP-MS: Impact of structural motifs on lipophilicity and biological activity

We present here the first comprehensive study on the lipophilicity of ruthenium anticancer agents encompassing compounds with broad structural diversity, ranging from octahedral RuIII(azole) through to RuII(arene) complexes. MEEKC was used to determine the capacity factors of the Ru complexes, and after a complex peak was unambiguously assigned using MEEKC–ICP‐MS, the results were validated through comparison with the log P determined by octanol/water partitioning experiments. Correlation of the two data sets demonstrated a close relationship despite the limited structural overlap of the compounds studied. The capacity factors found by MEEKC allowed for the clustering of complexes based on their structure and this could be used to rationalize the observed cytotoxicity in the human colon carcinoma HCT116 cell line. It was demonstrated that rather than modification of the mono‐ or bidentate coordinated ligands much tighter control over a complexes lipophilic properties could be achieved through modification of the Ru(arene) ligand, with minimal detriment to cytotoxicity. This demonstrates the flexibility and potential of the Ru piano‐stool scaffold. MEEKC proved to be a highly efficient means of screening the anticancer potential of preclinical ruthenium complex candidates for their lipophilic properties and correlate them with their biological activity and structural properties.

Hyphenation of capillary electrophoresis to inductively coupled plasma mass spectrometry with a modified coaxial sheath-flow interface

Capillary electrophoretic analyses benefit significantly from hyphenation to mass spectrometric techniques. While the coupling to ESI-MS is routinely performed, for example by using a coaxial sheath-flow interface, hyphenating it to inductively coupled plasma mass spectrometry is more technically challenging. We use a commercially available coaxial sheath-flow interface (CSFI) and a simple PTFE-based end-cap for easy, inexpensive CE-ICP-MS hyphenation with improved sensitivity and analytical performance compared to commercially available interfaces. We have optimized key nebulizer parameters such as capillary position, sheath liquid flow rate, and carrier gas flow rate, and compared the CSFI with a commercially available interface. In a set of proof-of-principle experiments employing the anticancer agent cisplatin it was demonstrated that the signal to noise response and sensitivity were considerably improved leading to detection limits for 195Pt of 0.08 μM.