The use of inductively coupled plasma mass spectrometry as a detector in drug metabolism studies

Quantification of oxaliplatin- and ioversol-related compounds in pharmaceutical formulations using novel HPLC-ICP-MS methods

PURPOSE

Accurate quantifying of drug-related compounds in medicines is vital for safety. Commonly used structure-dependent methods rely on analytical standards. High-performance liquid chromatography coupled with inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) offers a promising solution, being structure-independent and not requiring standards. In this study, we aim to develop HPLC-ICP-MS methods for the determination of related compounds in oxaliplatin and ioversol injections.

RESULTS

The target analytes were eluted on an XSelect HSS T3 column (2.1 ×50 mm, 5 µm). Specifically, oxaliplatin injection was eluted isocracially for 3.5 min, and ioversol injection was eluted gradient with a total chromatographic run time of 12 min. The measurements to determine dihydroxy oxaliplatin-Pt(IV) and two related compounds of ioversol were performed by monitoring at m/z for 195Pt and 127I, respectively. The calibration curves were established over the range of 0.05-1 μM for Pt and 0.3-15 μM for I with the correlation coefficients greater than 0.999. The limits of quantification were 0.004 μM for dihydroxy oxaliplatin-Pt(IV), 0.022 μM for ioversol related compound A and 0.026 μM for ioversol related compound B. The accuracy (recovery between 93-105%) and precision (repeatability ≤ 6.1% RSD) were fit-for-purpose for dihydroxy oxaliplatin-Pt(IV), and the accuracy (recovery between 95-107%) and precision (repeatability ≤ 3.9% RSD) were also fit-for-purpose for both ioversol related compound A and ioversol related compound B.

CONCLUSION

The quantitation accuracy of HPLC-ICP-MS closely matched that of the standard HPLC-UV approach. HPLC-ICP-MS can be used as a complementary analytical technique for quantitative determination of drug-related compounds.

Half-life determination of inorganic-organic hybrid nanomaterials in mice using laser-induced breakdown spectroscopy

Inorganic or inorganic-organic hybrid nanomaterials have great potential for applications in the biomedical fields. Biological half-life is an essential pharmacokinetic parameter for these materials to function in vivo. Compared to inductively coupled plasma mass spectrometry (ICP-MS), which is the gold standard, laser-induced breakdown spectroscopy (LIBS) is a faster and more efficient elemental detection method. We investigated an efficient way to quantify the metabolic rate using LIBS. Nanoparticle platforms, such as manganese dioxide-bovine serum albumin (MnO2-BSA) or boehmite-bovine serum albumin (AlO(OH)-BSA) were injected into mice through intravenous administration for LIBS spectrum acquisition. First, the spectral background was corrected using the polynomial fitting method; The spectral interference was eliminated by Lorentz fitting for each LIBS spectrum simultaneously. The support vector regression (SVR) was then used for LIBS quantitative analyses. Finally, the LIBS results were compared with the ICP-MS ones. The half-lives of MnO2-BSA calculated by LIBS and ICP-MS were 2.49 and 2.42 h, respectively. For AlO(OH)-BSA, the half-lives detected by LIBS and ICP-MS were 3.46 and 3.57 h, respectively. The relative error of LIBS is within 5% compared to ICP-MS. The results demonstrate that LIBS is a valuable tool for quantifying the metabolic rates with a high degree of accuracy.

The impact of whole human blood on the kinetic inertness of platinum(iv) prodrugs - an HPLC-ICP-MS study

The potential advantage of platinum(iv) complexes as alternatives to classical platinum(ii)-based drugs relies on their kinetic stability in the body before reaching the tumor site and on their activation by reduction inside cancer cells. In this study, an analytical workflow has been developed to investigate the reductive biotransformation and kinetic inertness of platinum(iv) prodrugs comprising different ligand coordination spheres (respectively, lipophilicity and redox behavior) in whole human blood. The distribution of platinum(iv) complexes in blood pellets and plasma was determined by inductively coupled plasma-mass spectrometry (ICP-MS) after microwave digestion. An analytical approach based on reversed-phase (RP)-ICP-MS was used to monitor the parent compound and the formation of metabolites using two different extraction procedures. The ligand coordination sphere of the platinum(iv) complexes had a significant impact on their accumulation in red blood cells and on their degree of kinetic inertness in whole human blood. The most lipophilic platinum(iv) compound featuring equatorial chlorido ligands showed a pronounced penetration into blood cells and a rapid reductive biotransformation. In contrast, the more hydrophilic platinum(iv) complexes with a carboplatin- and oxaliplatin-core exerted kinetic inertness on a pharmacologically relevant time scale with notable amounts of the compound accumulated in the plasma fraction.

Elemental bioimaging of Cisplatin in Caenorhabditis elegans by LA-ICP-MS

cis-Diamminedichloroplatinum(II) (Cisplatin) is one of the most important and frequently used cytostatic drugs for the treatment of various solid tumors. Herein, a laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) method incorporating a fast and simple sample preparation protocol was developed for the elemental mapping of Cisplatin in the model organism Caenorhabditis elegans (C. elegans). The method allows imaging of the spatially-resolved elemental distribution of platinum in the whole organism with respect to the anatomic structure in L4 stage worms at a lateral resolution of 5 μm. In addition, a dose- and time-dependent Cisplatin uptake was corroborated quantitatively by a total reflection X-ray fluorescence spectroscopy (TXRF) method, and the elemental mapping indicated that Cisplatin is located in the intestine and in the head of the worms. Better understanding of the distribution of Cisplatin in this well-established model organism will be instrumental in deciphering Cisplatin toxicity and pharmacokinetics. Since the cytostatic effect of Cisplatin is based on binding the DNA by forming intra- and interstrand crosslinks, the response of poly(ADP-ribose)metabolism enzyme 1 (pme-1) deletion mutants to Cisplatin was also examined. Loss of pme-1, which is the C. elegans ortholog of human poly(ADP-ribose) polymerase 1 (PARP-1) led to disturbed DNA damage response. With respect to survival and brood size, pme-1 deletion mutants were more sensitive to Cisplatin as compared to wildtype worms, while Cisplatin uptake was indistinguishable.

The metabolism of 4-bromoaniline in the bile-cannulated rat: application of ICPMS ((79/81)Br), HPLC-ICPMS & HPLC-oaTOFMS

1. An excretion balance study was performed following i.p. administration of 4-bromoaniline (50 mg kg⁻¹) to bile-cannulated rats, using bromine-detected (^79/81Br) ICPMS for quantification. Approximately 90% of the dose was recovered in urine (68.9 ± 3.6%) and bile (21.4 ± 1.4%) by 48 h post-administration.

2. HPLC-ICPMS (^79/81Br) was used to selectively detect and profile the major urinary and biliary-excreted metabolites and determined that the 0–12 h urine contained at least 21 brominated metabolites with 19 bromine-containing peaks observed in the 6–12 h bile samples.

3. The urinary and biliary metabolites were subsequently profiled using HPLC-oaTOFMS. By exploiting the distinctive bromine isotope pattern ca. 60 brominated metabolites were detected in the urine in negative electrospray ionisation (ESI) mode while bile contained ca. 21.

4. While a large number of bromine-containing metabolites were detected, the profiles were dominated by a few major components with the bulk of the 4-bromoaniline-related material in urine accounted for by 4-bromoanaline O-sulfate (∼75% of the total by ICPMS, 84% by TOFMS). In bile a hydroxylated N-acetyl compound was the major metabolite detected, forming some ∼65% of the 4-bromoaniline-related material by ICPMS (37% by TOFMS).

A nonradioactive approach to investigate the metabolism of therapeutic peptides by tagging with 127i and using inductively-coupled plasma mass spectrometry analysis

The metabolic fate of adrenocorticotropic hormone (ACTH) fragment 4-10 (4-10) was evaluated following incorporation of a nonradioactive (127)I-tag and with selective detection of I(+) at m/z 127 by inductively coupled plasma mass spectrometry (ICP-MS). (127)I has all the advantages of radioactive (125)I as a metabolite tracer and, together with its detection in the femtogram range, has led to a successful metabolite profiling of (127)I-ACTH (4-10) in vitro. The observed metabolic stability of this peptide in tissue preparations from human was plasma > kidney S9 > liver microsomes > liver cytosol, liver S9. Metabolic turnover of (127)I-ACTH (4-10) was not NADPH-dependent and, together with inhibition by protease inhibitor cocktail and EDTA, is consistent with metabolism exclusively by proteases. Our preliminary studies using chemical inhibitors suggested the involvement of metalloprotease, serine peptidase, and aminopeptidase in (127)I-ACTH (4-10) metabolism. The liver is the primary site of metabolic clearance of (127)I-ACTH (4-10), with kidney S9 taking four times longer to produce a metabolite profile comparable to that produced by liver S9. A total of six metabolites retaining the (127)I-tag was detected by ICP-MS, and their structures were elucidated using a LTQ/Orbitrap. (127)I-ACTH (4-10) underwent both N- and C-terminal proteolysis to produce (127)I-Phe as the major metabolite. The (127)I-tag had minimal effect on the metabolic turnover and site of proteolysis of ACTH (4-10), which, together with ICP-MS providing essentially equimolar responses, suggests that the use of a (127)I-tag may have general utility as an alternative to radioiodination to investigate the metabolism of peptide therapeutics.

Inductively coupled plasma mass spectrometry for metallodrug development: albumin binding and serum distribution of cytotoxic cis- and trans-isomeric platinum(II) complexes

Binding to plasma proteins is one of the major metabolic pathways of metallodrugs. In the case of platinum-based anticancer drugs, it is the interaction with serum albumin that affects most strongly their in vivo behavior. Since both the configuration, i.e. cis-trans-isomerism, and the nature of leaving groups have an effect on the reactivity of Pt(II) coordination compounds toward biomolecules, a set of cis- and trans-configured complexes with halide leaving groups (Cl(-), Br(-), and I(-)) and 2-propanone oxime as carrier ligands was chosen for this study. Binding experiments were performed both with albumin and human serum and the Pt content in ultrafiltrates was quantified using inductively coupled plasma mass spectrometry. In order to shed light on the binding mechanism, the albumin binding constant (KHSA) and the octanol-water partition coefficient (P) were experimentally determined and relationships between log KHSA and log P were explored. The correlation was found significant only for cis-configured platinum complexes (R(2)=0.997 and standard deviation=0.02), indicating a certain contribution of the nonspecific binding which is largely dominated by the lipophilicity of compounds. In contrast, for trans-complexes a specific molecular recognition element plays a significant role. The participation of albumin in drug distribution in blood serum was assessed using an equilibrium distribution model and by comparing the percentage binding in the albumin and serum-protein fractions. Irrespective of the compound polarity, albumin contributes from 85 to 100% to the overall binding in serum.

Complementarity of MALDI and LA ICP mass spectrometry for platinum anticancer imaging in human tumor

The follow-up of the Heated Intraoperative Chemotherapy (HIPEC) of peritoneal carcinomatosis would benefit from the monitoring of the penetration, distribution and metabolism of the drug within the tumor.

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%.

Inductively coupled plasma-MS in drug development: bioanalytical aspects and applications

The vast majority of today's modern bioanalytical methods for pharmacokinetic, pharmacodynamic and immunogenicity purposes are based on LC-MS/MS and immunoanalytical approaches. Indeed, these methodologies are suitable for a wide range of molecules from small to large. For a smaller but not insignificant group of compounds, LC-MS/MS is not suitable - or in some cases much less suitable - as a reliable bioanalytical methodology, and inductively coupled plasma (ICP)-MS is a more appropriate methodology. ICP-MS is one of these less widely used techniques in drug development. This methodology is predominantly used for elemental bioanalysis for pharmacokinetics, for imaging purposes, for mass-balance, food-effect and biomarker studies. In addition, in the last couple of years an increasing number of applications has been published, where ICP-MS and its various hyphenations (LC-ICP-MS, CE-ICP-MS) have been used for speciation/metabolism and proteomics studies. Here, the analytical potential, the quantitative bioanalytical aspects, the various modes of operation and the challenges of the application of ICP-MS in life sciences applications are given. This includes an overview of recent applications in this area in scientific literature, the various hyphenation possibilities and their application areas and the analysis of the various sample matrices applicable to these fields. It also provides a brief outlook of where the potential of this technique lies in the future of regulated bioanalysis and drug development.

Use of relative 12C/14C isotope ratios to estimate metabolite concentrations in the absence of authentic standards

Background: There is considerable interest in the determination of relative abundances of human metabolites in plasma (and potentially excreta) with reasonable accuracy early on in the drug development process in order to make scientifically sound decisions with regard to the presence of potentially active or toxic disproportionate metabolites. At this point, authentic metabolite standards are generally not available. Results: A new methodology is proposed for the estimation of metabolite concentrations in the absence of authentic standards. A reference sample containing radiolabeled metabolites of interest is produced by incubating the 14C-labeled drug in vitro, and mixed with a sample to be quantitated containing the unlabeled metabolites. The 12C/14C isotope ratio is measured with high-resolution ESI–MS for each metabolite, and used as a basis for quantitation of the cold metabolite based on the concentration of radioactive metabolite, determined from independent analysis of the radioactive sample with LC-radiochemical detection. The 14C-labeled metabolite serves as an isotopically labeled internal standard, which corrects for any variations in injection volume, sample preparation, MS intensity drift, matrix effects and/or saturation of electrospray ionization. The approach was validated by the analysis of solutions containing variable amounts of the analyte with a fixed amount of radioactive standard on a QToF Synapt® G2 MS system. The same methodology was also successfully applied to first-in-human plasma samples analyzed on a LTQ-Orbitrap®. Conclusion: The metabolite abundances obtained by 12C/14C isotope ratio measurements showed suitable accuracy and precision and were very close to those obtained with matrix mixing. The parent drug concentrations also corresponded well with the bioanalytical results obtained with a validated LC–MS/MS method.

Approaches for the rapid identification of drug metabolites in early clinical studies

Understanding the metabolism of a novel drug candidate in drug discovery and drug development is as important today as it was 30 years ago. What has changed in this period is the technology available for proficient metabolite characterization from complex biological sources. High-efficiency chromatography, sensitive MS and information-rich NMR spectroscopy are approaches that are now commonplace in the modern laboratory. These advancements in analytical technology have led to unequivocal metabolite identification often being performed at the earliest opportunity, following the first dose to man. For this reason an alternative approach is to shift from predicting and extrapolating possible human metabolism from in silico and nonclinical sources, to actual characterization at steady state within early clinical trials. This review provides an overview of modern approaches for characterizing drug metabolites in these early clinical studies. Since much of this progress has come from technology development over the years, the review is concluded with a forward-looking perspective on how this progression may continue into the next decade.

Looking back through the MIST: a perspective of evolving strategies and key focus areas for metabolite safety analysis

The publication of the US FDA MIST guidance document in 2008 reignited the debate around the most appropriate strategies to underwrite metabolite safety for novel compounds. Whilst some organizations have suggested that the guidelines necessitate a paradigm shift to more thorough metabolite analysis during early development, an evaluation of historical practices shows that the principles of the guidelines have always largely underpinned metabolism studies within the pharmaceutical industry. Therefore, it is argued that existing practices, when coupled to appropriate emerging analytical tools and a case-by-case consideration of the relevance of the generated metabolism data in terms of structure, physicochemisty, abundance and activity, represent a fit-for-purpose approach to metabolite-safety assessments.

Platinum speciation used for elucidating activation or inhibition of Pt-containing anti-cancer drugs

This article reviews approaches on platinum speciation with respect to Pt drugs in anti-cancer therapies. The paper starts with the introduction of available platinum-based drugs and describes their assumed principle of action. It is now generally accepted that these Pt complexes exhibit their therapeutic action by coordination to DNA which leads to bending of the DNA structure and to an inhibition of the DNA polymerase progression. But dose-limiting side effects, including nephrotoxicity as well as resistance to some of these Pt compounds, are still a major problem. Platinum speciation moved increasingly into the focus of interest when it became clear that (1) the active drugs were the hydrolyzation products rather than the originally administered ones and (2) that the parallel formation of inactive Pt-protein complexes, which additionally reduce the efficacy of Pt anti-tumor agents, compete with the formation of the cytotoxic Pt-DNA lesions. Speciation analysis methods were employed based on chromatography or capillary electrophoresis respectively, each coupled to inductively coupled plasma (ICP)-mass spectrometry (MS) or electrospray ionization (ESI)-MS. The paper describes these Pt-speciation investigations, which started with exploring hydrolyzation kinetics in aqueous solutions. These experiments were followed by the speciation investigations in model solutions containing proteins or other sulphur-containing ligands, which could also be responsible for deactivation of the Pt agent in vivo. The experiments improved the understanding of the metabolite form, by which the metal complex enters the tumor cells, and whether and how this metabolized complex is already inactivated at this time. As an example, reaction kinetics of cisplatin (cis-[diamminedichloroplatinum(II)]) with albumin, transferrin, myoglobin, ubiquitin, and metallothionein were investigated and reaction products were speciated. Finally, Pt-speciation in serum of medicated cancer patients was conducted by several research groups, which are outlined in the Section "Investigations in serum". The section "Investigations in urine of cancer treated patients" deals with speciation experiments on the Pt-metabolites excreted by the organism. By these means an assessment of the in vivo metabolism of Pt-drugs may be possible. Finally, the development of new anti-cancer metallodrugs needs the respective analytical techniques reported in the last section of the paper.

Inductively-coupled plasma mass spectrometry in proteomics, metabolomics and metallomics studies

The potential of inductively-coupled plasma mass spectrometry (ICP-MS) and its complementarity to soft- ionization MS techniques are discussed in the context of the analysis for biomolecules. ICP-MS offers detection limits in the attomolar range, regardless of the molecular environment of the target element. The sensitivity is hardly affected by the sample matrix, chromatographic mobile phase, or co-eluted compounds. The abundance sensitivity over six decades and the linear dynamic range over nine decades make simultaneous multi-isotopic analysis routinely possible. The manuscript discusses the state-of-the-art of ICP-MS for the detection of proteins in gel electrophoresis and of peptides in 2D high-performance liquid chromatography. The possibilities of quantification to the degree of some post-translational modifications are highlighted. Attention is also paid to the role of ICP-MS in protein quantification via metal-coded labeling and to the use of differentially-labeled antibodies for the multiplexed biomarker analysis. The key role of ICP-MS in the emerging area of metallomics is briefly discussed.

Metabolite quantitation: detector technology and MIST implications

HPLC detector technology has advanced dramatically over the past 20 years, with a range of highly sensitive and specific detectors becoming available. What is still missing from the bioanalyst’s armoury, however, is a highly sensitive detector that gives an equimolar response independent of the compound. This would allow for quantification of compounds without the requirement for a synthetic standard or a radiolabeled analogue. In particular, such a detector applied to metabolism studies would establish the relative significance of the various metabolic routes. The recently issued US FDA guidelines on metabolites in safety testing (MIST) focus on the relative quantitation of human metabolites being obtained as soon as feasible in the drug-development process. In this article, current detector technology is reviewed with respect to its potential for quantitation without authentic standards or a radiolabel and put in the context of the MIST guidelines. The potential for future developments are explored.

Which human metabolites have we MIST? Retrospective analysis, practical aspects, and perspectives for metabolite identification and quantification in pharmaceutical development

With the recent publication of the FDA guidance on metabolites in safety testing (MIST), a reflection is provided that describes the impact of this guidance on the processes of drug metabolite identification and quantification at various stages of drug development. First, a retrospective analysis is described that was conducted on 12 human absorption, metabolism, and excretion (AME) trials with the application of these MIST criteria. This analysis showed that the number of metabolites requiring identification, (semi)-quantification, and coverage in the toxicology species would substantially increase. However, a significant proportion of these metabolites were direct or indirect conjugates, a class of metabolites that was specifically addressed in the guidance as being largely innocuous. The nonconjugated metabolites were all covered in at least one toxicology animal species, with no need for additional safety evaluation. Second, analytical considerations pertaining to the efficient identification of metabolites are discussed. Topics include software-assisted detection and structural identification of metabolites, the emerging hyphenation of ultraperformance liquid chromatography (UPLC) with radioactivity detection, and the various ways to estimate metabolite abundance in the absence of an authentic standard. Technical aspects around the analysis of metabolite profiles are also presented, focusing on precautions to be taken in order not to introduce artifacts. Finally, a tiered approach for metabolite quantification is proposed, starting with quantification of metabolites prior to the multiple ascending dose study (MAD) in humans in only specific cases (Tier A). The following step is the identification and quantification of metabolites expected to be of pharmacological or toxicological relevance (based on MIST and other complementary criteria) in selected samples from the MAD study and preclinical studies in order to assess metabolite exposure coverage (Tier B). Finally, a metabolite quantification strategy for the studies after the MAD phase (Tier C) is proposed.