Insight into the antitumor actions of sterically hindered platinum(ii) complexes by a combination of STD NMR and LCMS techniques

Sterically hindered platinum(ii) complexes have shown great advantages in overcoming platinum drug resistance. In this study, the antitumor actions of sterically hindered platinum(ii) complex 1 (cis-dichloro[(1R,2R)-N1-(2-fluorobenzyl)-1,2-diaminocyclohexane-N,N']platinum(ii), C13H19FPtCl2) were investigated by using saturation transfer difference nuclear magnetic resonance (STD NMR) and liquid chromatography-mass spectrometry (LCMS) techniques. STD NMR was applied to study the HSA (human serum albumin) binding properties, while the interactions between guanosine 5'-monophosphate (5'-GMP) and complex 1 were studied by LCMS. For HSA binding experiments, strong STD signals were observed for protons of sterically hindered parts of carrier ligands, indicating that the sterically hindered moieties of the carrier ligand could be situated inside the binding pocket of HSA. A 19F NMR experiment indicated that complex 1 could interact with HSA. Furthermore, the binding modes of complex 1 with guanosine 5'-monophosphate (5'-GMP) were studied in the absence and presence of glutathione by LCMS. According to the HPLC profiles, a mono-functional binding mode was observed for complex 1 both in the presence and in the absence of glutathione, while a bi-adduct was observed for Pt(DACH)Cl2, which may be one of the reasons for their different biological activities. Hence, this study demonstrated that the NMR method combined with the LCMS technique could provide valuable information to understand the transport and the underlying anticancer mechanisms of the platinum(ii) complex at the molecular level. Moreover, the results reported here can help to reveal the binding mechanisms of the sterically hindered platinum(ii) compounds with biomolecules, which may shed light on the design of novel platinum(ii) anticancer agents with suitable sterically hindered groups.

Inhibition of Type IV Secretion Activity and Growth of Helicobacter pylori by Cisplatin and Other Platinum Complexes

Type IV secretion systems are protein secretion machineries that are frequently used by pathogenic bacteria to inject their virulence factors into target cells of their respective hosts. In the case of the human gastric pathogen Helicobacter pylori, the cytotoxin-associated gene (Cag) type IV secretion system is considered a major cause for severe disease, such as gastric cancer, and thus constitutes an attractive target for specific treatment options against H. pylori infections. Here, we have used a Cag type IV secretion reporter assay for screening a repurposing compound library for inhibitors targeting this system. We found that the antitumor agent cisplatin, a platinum coordination complex that kills target cells by formation of DNA crosslinks, is a potent inhibitor of the Cag type IV secretion system. Strikingly, we found that this inhibitory activity of cisplatin depends on a ligand exchange reaction which incorporates a solvent molecule (dimethylsulfoxide) into the complex, a modification which is known to be deleterious for DNA crosslinking, and for its anticancer activity. We extended our analysis to several analogous platinum complexes containing N-heterocyclic carbene, as well as DMSO or other ligands, and found varying inhibitory activities toward the Cag system which were not congruent with their DNA-binding properties, suggesting that protein interactions may cause the inhibitory effect. Inhibition experiments under varying conditions revealed effects on adherence and bacterial viability as well, and showed that the type IV secretion-inhibitory capacity of platinum complexes can be inactivated by sulfur-containing reagents and in complex bacterial growth media. Taken together, our results demonstrate DNA binding-independent inhibitory effects of cisplatin and other platinum complexes against different H. pylori processes including type IV secretion.

Bacterial Cytological Profiling Reveals the Mechanism of Action of Anticancer Metal Complexes

Target identification and mechanistic studies of cytotoxic agents are challenging processes that are both time-consuming and costly. Here we describe an approach to mechanism of action studies for potential anticancer compounds by utilizing the simple prokaryotic system, E. coli, and we demonstrate its utility with the characterization of a ruthenium polypyridyl complex [Ru(bpy)₂dmbpy²⁺]. Expression of the photoconvertible fluorescent protein Dendra2 facilitated both high throughput studies and single-cell imaging. This allowed for simultaneous ratiometric analysis of inhibition of protein production and phenotypic investigations. The profile of protein production, filament size and population, and nucleoid morphology revealed important differences between inorganic agents that damage DNA vs more selective inhibitors of transcription and translation. Trace metal analysis demonstrated that DNA is the preferred nucleic acid target of the ruthenium complex, but further studies in human cancer cells revealed altered cell signaling pathways compared to the commonly administrated anticancer agent cisplatin. This study demonstrates E. coli can be used to rapidly distinguish between compounds with disparate mechanisms of action and also for more subtle distinctions within in studies in mammalian cells.

Studies on the structures, cytotoxicity and apoptosis mechanism of 8-hydroxylquinoline rhodium(iii) complexes in T-24 cells

Two rhodium(iii) complexes showed good cytotoxicity. The underlying investigation of the apoptosis mechanism suggested that the mitochondrial apoptotic pathway was involved.