Advances of CE-ICP-MS in speciation analysis related to metalloproteomics of anticancer drugs

Toward the boosted loading of cisplatin drug into liposome nanocarriers

Current challenges in oncology are largely associated with the need to improve the effectiveness of cancer treatment and to reduce drug's side effects. An effective strategy to cope with these challenges is behind designing and developing drug delivery systems based on smart nanomaterials and approved anticancer drugs. The present study offers a novel and straightforward approach to efficiently load the cisplatin drug into the newly constructed liposome-based nanosystems as well a reliable technique for monitoring this process based on capillary electrophoresis hyphenated with inductively coupled plasma tandem mass spectrometry. The proposed drug-loading methodology comprises liposome formation via a simple ethanol-injection method and propels increased drug encapsulation using tailor-made freeze-thawing or lyophilization-hydration procedures. To optimize liposome generation and drug encapsulation, the effects of dilution medium and liposome composition (types of phospholipids and their percentage ratio) have been investigated in detail. It was shown that modest alterations of the composition of three-component phospholipid liposomes and parameters of the freeze-thawing procedure have a strong impact on the formation of cisplatin-liposome systems. The obtained cisplatin-liposome formulation features a remarkable degree of drug encapsulation, over 100 mg L-1, and holds promise for further preclinical development as a potent drug-delivery platform.

Comparative study of the vibrating capillary nebulizer (VCN) and commercially available interfaces for on-line coupling of capillary electrophoresis with ICP-MS

Capillary electrophoresis (CE) is a powerful and sensitive tool for speciation analysis when combined with inductively coupled plasma mass spectrometry (ICP-MS); however, the performance of this technique can be limited by the nature of pneumatic nebulizers. This study compares two commercially available pneumatic nebulizers to a newly introduced vibrating capillary nebulizer (VCN) for on-line coupling of CE with ICP-MS. The VCN is a low-cost, non-pneumatic nebulizer that is based on the design of capillary vibrating sharp-edge spray ionization. As a piezoelectrically driven nebulization source, the VCN creates an aerosol independent of gas flows and does not produce a low-pressure region at the nebulizer orifice. To compare the systems, we performed replicate analyses of sulfate in river water with each nebulizer and the same CE and ICP-MS instruments and determined the figures of merit of each setup. With the CE-VCN-ICP-MS setup, we achieved around 2-4 times lower sensitivity compared to the commercial setups. However, the VCN-based setup provided lower noise levels and better linear correlation from the analysis of calibration standards, which resulted in indistinguishable LOD and LOQ values from the in-house-built VCN-based and commercial setups for CE-ICP-MS analysis. The VCN is found to have the highest baseline stability with a standard deviation of 3500 cts s-1, corresponding to an RSD of 2.7%. High reproducibility is found with the VCN with a peak area RSD of 4.1% between 3 replicate measurements.

Fasten the analysis of metal-binding proteins with GE-ICP-MS via increasing the electrolyte concentration of the running buffer

The coupled system of column gel electrophoresis and inductively coupled plasma mass spectrometry (GE-ICP-MS) is a highly effective technique for detecting metal-binding proteins. However, it takes a long time for this method to test a single sample, which greatly limits its application. In this study, GE-ICP-MS system was optimized by adjusting the analytical conditions, including the concentration and pH of running buffer and the proportion of polyacrylamide gel. The results of the experiment showed that the migration speed of proteins in GE was enhanced by increasing the electrolyte concentration in the running buffer solution. Additionally, the ICP-MS response, which was dramatically decreased because of the change in running buffer solution, can be stabilized by adjusting pH of running buffer. Meanwhile, the optimization of polyacrylamide gel ratio allows GE-ICP-MS to maintain high resolution for proteins of similar molecular weight with increased detection speed. After increasing the concentration of running buffer by 10 times, four iodine labeled proteins were successfully separated at baseline by the GE-ICP-MS system at pH 8.0 in 40 min using a resolving gel (8%, 7 cm) and a stacking gel (4%, 1 cm), which was three times faster than the original one. Finally, the optimized method was proved by detecting a silver-binding protein in rat plasma samples. The above method provided an effective and rapid detection for metal-binding proteins in organism.

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.

How versatile is the use of ultrafiltration to study biointeractions of therapeutic metallodrugs?

For a representative number of approved or investigational anticancer metallodrugs varying in lipophilicity, unspecific adsorption onto ultracentrifugal filter units was studied. It was found that for fairly hydrophilic compounds, such as cisplatin and oxaliplatin, the binding to filters does not substantially affect their amount measured (by ICP-MS) after ultrafiltration (>95%). In the case of metal complexes with moderate lipophilicity (log P > -0.1), adsorption effects turn out to be substantial. This might impede using ultrafiltration for studying the transformations of such drugs in human serum, unless they are rapidly converted into the protein adducts. The adsorption-suppressing effect of proteins was proved for indazolium trans-[tetrachloridobis(1H-indazole)ruthenate(III)] whose recovery from the filters was 61 and 14% in free and HSA-bound form, respectively.

Determination of oxaliplatin enantiomers at attomolar levels by capillary electrophoresis connected with inductively coupled plasma mass spectrometry

The aim of this study was to develop a method for the separation of oxaliplatin enantiomers at attomolar concentration levels. A combination of capillary electrophoresis and inductively coupled plasma mass spectrometry was chosen due to their unique characteristics, including fast and easy modification of separation selectivity, and significant limits of detection and linearity. In the first step, we optimized conditions for the separation of oxaliplatin enantiomers including background electrolyte composition and concentration, pH, and type and concentration of the chiral selector. Under optimal conditions, sodium borate buffer pH 9.5, ionic strength 40 mmol L^-1, with 60 mg mL^-1 sulfated β-cyclodextrin, separation was obtained with a resolution of 2.0. This electrolyte system was then used in the 'in-house' connection of capillary electrophoresis with inductively coupled plasma mass spectrometer. In this instance, separation lasted for 9.5 min. Calibrations were linear in the range of 0.1-500 μg mL^-1 with R² of 0.9999. LOD and LOQ values were of 64 ng mL^-1 and 116 ng mL^-1 of oxaliplatin, respectively. This represents detection of 49 fg or 125 attomol of oxaliplatin enantiomers in the capillary electrophoresis injected sample zone. Finally, the method was successfully applied for detection of oxaliplatin enantiomers in spiked urine samples.

Combination of ICP-MS, capillary electrophoresis, and their hyphenation for probing Ru(III) metallodrug-DNA interactions

Determination of the DNA-binding reactivity and affinity is an important part of a successful program for the selection of metallodrug candidates. For such assaying, a range of complementary analytical techniques was proposed and tested here using one of few anticancer metal-based drugs that are currently in clinical trials, indazolium trans-[tetrachloridobis(1H-indazole)ruthenate(III), and a DNA oligonucleotide. A high reactivity of the Ru drug was confirmed in affinity capillary electrophoresis (CE) mode, where adduct formation takes place in situ (i.e., in the capillary filled with an oligonucleotide-containing electrolyte). To further characterize the binding kinetics, a drug–oligonucleotide mixture was incubated for a different period of time, followed by ultrafiltration separation into two different in molecular weight fractions (>3 and <3 kDa). The time-dependent distribution profiles of the Ru drug were then assessed by CE-inductively coupled plasma mass spectrometry (ICP-MS), revealing that at least two DNA adducts exist at equilibrium conditions. Using standalone ICP-MS, dominant equilibrium amount of the bound ruthenium was found to occur in a fraction of 5–10 kDa, which includes the oligonucleotide (ca. 6 kDa). Importantly, in all three assays, the drug was used for the first time in in-vitro studies, not in the intact form but as its active species released from the transferrin adduct at simulated cancer cytosolic conditions. This circumstance makes the established analytical platform promising to provide a detailed view on metallodrug targeting, including other possible biomolecules and ex vivo samples.

The use of elemental mass spectrometry in phosphoproteomic applications

Reversible phosphorylation is one of the most important post-translational modifications in mammalian cells. Because this molecular switch is an important mechanism that diversifies and regulates proteins in cellular processes, knowledge about the extent and quantity of phosphorylation is very important to understand the complex cellular interplay. Although phosphoproteomics strategies are applied worldwide, they mainly include only molecular mass spectrometry (like MALDI or ESI)-based experiments. Although identification and relative quantification of phosphopeptides is straightforward with these techniques, absolute quantification is more complex and usually requires for specific isotopically phosphopeptide standards. However, the use of elemental mass spectrometry, and in particular inductively coupled plasma mass spectrometry (ICP-MS), in phosphoproteomics-based experiments, allow one to absolutely quantify phosphopeptides. Here, these phosphoproteomic applications with ICP-MS as elemental detector are reviewed. Pioneering work and recent developments in the field are both described. Additionally, the advantage of the parallel use of molecular and elemental mass spectrometry is stressed.

A sensitive and versatile method for characterization of protein-mediated transformations of quantum dots

We report the development and application of an analytical system consisting of capillary electrophoresis (CE) interfaced with inductively coupled plasma mass spectrometry (ICP-MS) for sensitive and high-resolution characterization of quantum dots (QDs) interacting with serum proteins. Separation resolution between the intact CdSeS/ZnS QDs and their protein conjugates was optimized by varying the type and concentration of background electrolyte, applied voltage, and sample loading. Special attention was paid to the CE system compatibility with physiological conditions, avoiding aggregation effects, and analyte recovery. Optimization trials allowed for acquiring satisfactory stability of migration times (within 6.0% between different days), peak area precision of 5.2-8.0%, capillary recoveries in the range of 90-96%, and a lower limit of detection of 7.5 × 10(-9) mol L(-1) Cd. With the developed method distinct metal-specific profiles were obtained for the QDs in combination with individual serum proteins, their mixtures, and in human serum. Particularly, it was found that albumin binding to the particle surface is completed after 1 h, without noticeable disruption of the core-shell integrity. The transferrin adsorption is accompanied by the removal of the ZnS shell, resulting in evolving two different metal-protein conjugated forms. On the other hand, proteinization in real-serum environment occurs without binding to major transport proteins, the QDs also lose their the shell (the higher the dose the longer is the time they stay unbroken). The concomitant changes in migration behavior can be attributed to interactions with serum proteins other than albumin and transferrin. Speciation information provided by CE-ICP-MS may shed light on the mechanism of QD delivery to the target regions of the body.

Metallomics for drug development: serum protein binding and analysis of an anticancer tris(8-quinolinolato)gallium(III) drug using inductively coupled plasma mass spectrometry

The application of an inductively coupled plasma mass spectrometry (ICP-MS) assay for quantifying in vitro binding of a gallium-based anticancer drug, tris(8-quinolinolato)gallium(III), to serum albumin and transferrin and in human serum is described. The distribution of the drug between the protein-rich and protein-free fractions was assessed via ICP-MS measurement of total gallium in ultrafiltrates. Comparative kinetic studies revealed that the drug exhibits a different reactivity toward individual proteins. While the maximum possible binding to albumin (~10%) occurs practically immediately, interaction with transferrin has a step-like character and the equilibrium state (with more than 50% binding) is reached for about 48 h. Drug transformation into the bound form in serum, also very fast, results in almost quantitative binding (~95%). The relative affinity of protein-drug binding was characterized in terms of the association constants ranging from 10(3) to 10(4)M(-1). In order to further promote clinical testing of the gallium drug, the ICP-MS method was applied for direct quantification of gallium in human serum spiked with the drug. The detection limit for gallium was found to be as low as 20 ng L(-1). The repeatability was better than 8% (as RSD) and the achieved recoveries were in the range 99-103%.