Tracing the anticancer compound [RuII(η6-p-cymene)(8-oxyquinolinato)Cl] in a biological environment by mass spectrometric methods

Masking the Bioactivity of Hydroxamic Acids by Coordination to Cobalt: Towards Bioreductive Anticancer Agents

The clinical use of many potent anticancer agents is limited by their non-selective toxicity to healthy tissue. One of these examples is vorinostat (SAHA), a pan histone deacetylase inhibitor, which shows high cytotoxicity with limited discrimination for cancerous over healthy cells. In an attempt to improve tumor selectivity, we exploited the properties of cobalt(III) as a redox-active metal center through stabilization with cyclen and cyclam tetraazamacrocycles, masking the anticancer activity of SAHA and other hydroxamic acid derivatives to allow for the complex to reach the hypoxic microenvironment of the tumor. Biological assays demonstrated the desired low in vitro anticancer activity of the complexes, suggesting effective masking of the activity of SAHA. Once in the tumor, the bioactive moiety may be released through the reduction of the CoIII center. Investigations revealed long-term stability of the complexes, with cyclic voltammetry and chemical reduction experiments supporting the design hypothesis of SAHA release through the reduction of the CoIII prodrug. The results highlight the potential for further developing this complex class as novel anticancer agents by masking the high cytotoxicity of a given drug, however, the cellular uptake needs to be improved.

In vitro and in vivo accumulation of the anticancer Ru complexes [RuII(cym)(HQ)Cl] and [RuII(cym)(PCA)Cl]Cl

The cellular accumulation and the underlying mechanisms for the two ruthenium-based anticancer complexes [RuII(cym)(HQ)Cl] 1 (cym = η6-p-cymene, HQ = 8-hydroxyquinoline) and [RuII(cym)(PCA)Cl]Cl 2 (PCA = N-fluorophenyl-2-pyridinecarbothioamide) were investigated in HCT116 human colorectal carcinoma cells. The results showed that the cellular accumulation of both complexes increased over time and with higher concentrations, and that 2 accumulates in greater quantities in cells than 1. Inhibition studies of selected cellular accumulation mechanisms indicated that both 1 and 2 may be transported into the cells by both passive diffusion and active transporters, similar to cisplatin. Efflux experiments indicated that 1 and 2 are subjected to efflux through a mechanism that does not involve p-glycoprotein, as addition of verapamil did not make any difference. Exploring the influence of the Cu transporter by addition of CuCl2 resulted in a higher accumulation of 1 and 2 whilst the amount of Pt detected was slightly reduced when cells were treated with cisplatin. Complexes 1 and 2 were further explored in zebrafish where accumulation and distribution were determined with ICP-MS and LA-ICP-MS. The results correlated with the in vitro observations and zebrafish treated with 2 showed higher Ru contents than those treated with 1. The distribution studies suggested that both complexes mainly accumulated in the intestines of the zebrafish.

Critical evaluation of cell lysis methods for metallodrug studies in cancer cells

Intracellular accumulation studies are a key step in metallodrug development but often variable results are obtained. Therefore, we aimed here to investigate different protocols for efficient and reproducible lysis of cancer cells in terms of protein content in lysates and in cell uptake studies of the Ru anticancer complex [chlorido(8-oxyquinolinato)(η6-p-cymene)ruthenium(II)] ([Ru(cym)(HQ)Cl]). The physical lysis methods osmosis and sonication were chosen for comparison with chemical lysis with the radioimmunoprecipitation assay (RIPA) buffer. Based on the protein content and the total Ru accumulated in the lysates, the latter determined using inductively coupled plasma-mass spectrometry, RIPA buffer was the most efficient lysis method. Measurements of plastic adsorption blanks revealed that the higher Ru content determined in the RIPA buffer lysis samples may be due a higher amount of Ru extracted from the plastic incubation plates compared with osmosis and sonication. Overall, we found that the choice of lysis method needs to be matched to the information sought and we suggest the least disruptive osmosis method might be the best choice for labile drug-biomolecule adducts. Minimal differences were found for experiments aimed at measuring the overall cell uptake of the Ru complex.

Metal Complexes of a 5-Nitro-8-Hydroxyquinoline-Proline Hybrid with Enhanced Water Solubility Targeting Multidrug Resistant Cancer Cells

Multidrug resistance (MDR) in cancer is one of the major obstacles of chemotherapy. We have recently identified a series of 8-hydroxyquinoline Mannich base derivatives with MDR-selective toxicity, however with limited solubility. In this work, a novel 5-nitro-8-hydroxyquinoline-proline hybrid and its Rh(η5-C5Me5) and Ru(η6-p-cymene) complexes with excellent aqueous solubility were developed, characterized, and tested against sensitive and MDR cells. Complex formation of the ligand with essential metal ions was also investigated using UV-visible, circular dichroism, 1H NMR (Zn(II)), and electron paramagnetic resonance (Cu(II)) spectroscopic methods. Formation of mono and bis complexes was found in all cases with versatile coordination modes, while tris complexes were also formed with Fe(II) and Fe(III) ions, revealing the metal binding affinity of the ligand at pH 7.4: Cu(II) > Zn(II) > Fe(II) > Fe(III). The ligand and its Rh(III) complex displayed enhanced cytotoxicity against the resistant MES-SA/Dx5 and Colo320 human cancer cell lines compared to their chemosensitive counterparts. Both organometallic complexes possess high stability in solution, however the Ru(II) complex has lower chloride ion affinity and slower ligand exchange processes, along with the readiness to lose the arene ring that is likely connected to its inactivity.

The aqueous stability and interactions of organoruthenium compounds with serum proteins, cell culture medium and human serum

Metal complexes bind to a wide variety of biomolecules and the control of the reactivity is essential when designing anticancer metallodrugs with a specific mode of action in mind. In this study, we used the highly cytotoxic compound [RuII(cym)(8-HQ)Cl] (cym = η6-p-cymene, 8-HQ = 8-hydroxyquinoline), the more inert derivative [RuII(cym)(8-HQ)(PTA)](SO3CF3) (PTA = 1,3,5-triaza-7-phosphaadamantane), and [RuII(cym)(PCA)Cl]Cl (PCA = pyridinecarbothioamide) as a derivative with a different coordination environment about the Ru center and investigated their stability, interactions with proteins and behavior in medium (αMEM) and human serum by capillary zone electrophoresis (CZE). The developed method was found to be robust and provides a quick and low-cost technique to monitor the interactions of such complexes with biomolecules. Each complex was found to behave very differently, emphasizing the importance of the choice of ligands and demonstrating the applicability of the developed method. Additionally, the human serum albumin binding site preference of [RuII(cym)(8-HQ)Cl] was investigated through displacement studies, revealing that the compound was able to bind to both sites I and site II, and the type of adducts formed with transferrin was determined by mass spectrometry.

Identification of synthetic cannabinoid methyl 2-{[1-(cyclohexylmethyl)-1H-indol-3-yl] formamido}-3-methylbutanoate using modern mass spectrometry and nuclear magnetic resonance techniques

The samples of plant material suspected to contain new psychoactive substances are very often the subject of chemical-toxicological analyses. Gas chromatography-mass spectrometry (MS), liquid chromatography-quadrupole time-of-flight-MS, and liquid chromatography-tandem MS were applied with the aim to identify synthetic cannabinoid, methyl 2-{[1-(cyclohexylmethyl)-1H-indol-3-yl] formamido}-3-methylbutanoate (MMB-CHMICA) without the analytical standard, which is very often the case when a new drug arrives. The structure of compound was also confirmed by one-dimensional and two-dimensional nuclear magnetic resonance spectroscopy and conformational analysis. After identification, methanolic extract of plant material containing MMB-CHMICA was successfully used for developing a multiple reaction monitoring method on liquid chromatography-tandem MS instrument. The optimization procedure is shown in detail. The complete fragmentation pattern and also the optimization of the extraction procedure of MMB-CHMICA from plant material were shown. The obtained data are useful for forensic, toxicological, and clinical purposes.

Current and emerging mass spectrometry methods for the preclinical development of metal-based drugs: a critical appraisal

This Trends article highlights the multiple ways in which the state-of-the-art molecular mass spectrometry can support the preclinical development of novel metal-based anticancer drugs. Examples from the recent literature-beyond routine characterization applications-are presented to illustrate what analytical and experimental design challenges are to be addressed to facilitate the translation of promising drug candidates to clinical practice.