Rapid and Sensitive Drug Quantification in Tissue Sections Using Matrix Assisted Laser Desorption Ionization-Ion Mobility-Mass Spectrometry Profiling

Desorption Kinetics Evaluation for the Development of Validated Desorption Electrospray Ionization-Mass Spectrometric Assays for Drug Quantification in Tissue Sections

The development of desorption/ionization (DI) mass spectrometric (MS) assays for drug quantification in tissue sections and their validation according to regulatory guidelines would enable their universalization for applications in (clinical) pharmacology. Recently, new enhancements in desorption electrospray ionization (DESI) have highlighted the reliability of this ion source for the development of targeted quantification methods that meet requirements for method validation. However, it is necessary to consider subtle parameters leading to the success of such method developments, such as the morphology of desorption spots, the analytical time, and sample surface, to cite but a few. Here, we provide additional experimental data highlighting an additional important parameter, based on the unique advantage of DESI-MS on continuous extraction during analysis. We demonstrate that considering desorption kinetics during DESI analyses would largely help (i) reducing analytical time during profiling analyses, (ii) verifying solvent-based drug extraction using the selected sample preparation method for profiling and imaging modes, and (iii) predicting the feasibility of imaging assays using samples in a given expected concentration range of the targeted drug. These observations will likely serve as precious guidance for the development of validated DESI-profiling and imaging methods in the future.

Important Requirements for Desorption/Ionization Mass Spectrometric Measurements of Temozolomide-Induced 2'-Deoxyguanosine Methylations in DNA

In clinical pharmacology, drug quantification is mainly performed from the circulation for pharmacokinetic purposes. Finely monitoring the chemical effect of drugs at their chemical sites of action for pharmacodynamics would have a major impact in several contexts of personalized medicine. Monitoring appropriate drug exposure is particularly challenging for alkylating drugs such as temozolomide (TMZ) because there is no flow equilibrium that would allow reliable conclusions to be drawn about the alkylation of the target site from plasma concentrations. During the treatment of glioblastoma, it appears, therefore, promising to directly monitor the alkylating effect of TMZ rather than plasma exposure, ideally at the site of action. Mass spectrometry (MS) is a method of choice for the quantification of methylated guanines and, more specifically, of O6-methylguanines as a marker of TMZ exposure at the site of action. Depending on the chosen strategy to analyze modified purines and 2'-deoxynucleosides, the analysis of methylated guanines and 2'-deoxyguanosines is prone to important artefacts due to the overlap between masses of (i) guanines from DNA and RNA, and (ii) different methylated species of guanines. Therefore, the specific analysis of O6-methyl-2'deoxyguanosine, which is the product of the TMZ effect, is highly challenging. In this work, we report observations from matrix-assisted laser desorption/ionization (MALDI), and desorption electrospray ionization (DESI) MS analyses. These allow for the construction of a decision tree to initiate studies using desorption/ionization MS for the analysis of 2'-deoxyguanosine methylations induced by TMZ.

Analytical Performance Evaluation of New DESI Enhancements for Targeted Drug Quantification in Tissue Sections

Desorption/ionization (DI)-mass spectrometric (MS) methods offer considerable advantages of rapidity and low-sample input for the analysis of solid biological matrices such as tissue sections. The concept of desorption electrospray ionization (DESI) offers the possibility to ionize compounds from solid surfaces at atmospheric pressure, without the addition of organic compounds to initiate desorption. However, severe drawbacks from former DESI hardware stability made the development of assays for drug quantification difficult. In the present study, the potential of new prototype source setups (High Performance DESI Sprayer and Heated Transfer Line) for the development of drug quantification assays in tissue sections was evaluated. It was demonstrated that following dedicated optimization, new DESI XS enhancements present promising options regarding targeted quantitative analyses. As a model compound for these developments, ulixertinib, an inhibitor of extracellular signal-regulated kinase (ERK) 1 and 2 was used.

Important Requirements for the Selection of Internal Standards during the Development of Desorption/Ionization Assays for Drug Quantification in Biological Matrices-A Practical Example

Desorption/ionization mass spectrometry (DI-MS) approaches allow for the rapid quantification of drugs in biological matrices using assays that can be validated according to regulatory guidelines. However, specific adaptations must be applied to create reliable quantification methods, depending on the approach and instrumentation used. In the present article, we demonstrate the importance of the molecular weight, the fragmentation pattern, and the purity of the internal standard for the development of matrix-assisted laser desorption/ionization (MALDI)-ion mobility (IM)-tandem MS and MS/MS methods. We present preliminary results of method development for the quantification of selinexor in microdialysis fluids with a stable isotopically labeled internal standard. In addition, we discuss the selection of internal standards for MALDI-MS assays using different instrumentations.

Approaching Sites of Action of Temozolomide for Pharmacological and Clinical Studies in Glioblastoma

Temozolomide (TMZ), together with bulk resection and focal radiotherapy, is currently a standard of care for glioblastoma. Absorption, distribution, metabolism, and excretion (ADME) parameters, together with the mode of action of TMZ, make its biochemical and biological action difficult to understand. Accurate understanding of the mode of action of TMZ and the monitoring of TMZ at its anatomical, cellular, and molecular sites of action (SOAs) would greatly benefit precision medicine and the development of novel therapeutic approaches in combination with TMZ. In the present perspective article, we summarize the known ADME parameters and modes of action of TMZ, and we review the possible methodological options to monitor TMZ at its SOAs. We focus our descriptions of methodologies on mass spectrometry-based approaches, and all related considerations are taken into account regarding the avoidance of artifacts in mass spectrometric analysis during sampling, sample preparation, and the evaluation of results. Finally, we provide an overview of potential applications for precision medicine and drug development.

Desorption/Ionization-MS Methods for Drug Quantification in Biological Matrices and Their Validation Following Regulatory Guidance

Desorption/ionization (DI) methods play an important role among the panel of mass spectrometric (MS) approaches for the rapid and sensitive quantification of drugs from the surface of solid samples. The possibility to implement these approaches for pharmacokinetic/pharmacodynamic investigations in early phase clinical trials depends on the ability to validate quantification assays according to regulatory guidelines (e.g., US Food and Drug Administration and European Medicines Agency) for bioanalytical method validation. However, these guidelines were designed for the validation of liquid chromatography-MS (LC-MS) methods and ligand binding assays. To apply the validation parameters to DI-MS methods (also referred here as on-surface MS) for drug quantification, it is important to consider the particularities of DI approaches compared to LC-MS methods. In this Perspective, we summarize the various applications of on-surface MS methods for drug quantification with their advantages over other MS methods, and provide our point of view regarding future proper method development and validation.

Ion Mobility–Mass Spectrometry for Bioanalysis

This paper aims to cover the main strategies based on ion mobility spectrometry (IMS) for the analysis of biological samples. The determination of endogenous and exogenous compounds in such samples is important for the understanding of the health status of individuals. For this reason, the development of new approaches that can be complementary to the ones already established (mainly based on liquid chromatography coupled to mass spectrometry) is welcomed. In this regard, ion mobility spectrometry has appeared in the analytical scenario as a powerful technique for the separation and characterization of compounds based on their mobility. IMS has been used in several areas taking advantage of its orthogonality with other analytical separation techniques, such as liquid chromatography, gas chromatography, capillary electrophoresis, or supercritical fluid chromatography. Bioanalysis is not one of the areas where IMS has been more extensively applied. However, over the last years, the interest in using this approach for the analysis of biological samples has clearly increased. This paper introduces the reader to the principles controlling the separation in IMS and reviews recent applications using this technique in the field of bioanalysis.

Rapid MALDI-MS Assays for Drug Quantification in Biological Matrices: Lessons Learned, New Developments, and Future Perspectives

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has rarely been used in the field of therapeutic drug monitoring, partly because of the complexity of the ionization processes between the compounds to be quantified and the many MALDI matrices available. The development of a viable MALDI-MS method that meets regulatory guidelines for bioanalytical method validation requires prior knowledge of the suitability of (i) the MALDI matrix with the analyte class and properties for ionization, (ii) the crystallization properties of the MALDI matrix with automation features, and (iii) the MS instrumentation used to achieve sensitive and specific measurements in order to determine low pharmacological drug concentrations in biological matrices. In the present hybrid article/white paper, we review the developments required for the establishment of MALDI-MS assays for the quantification of drugs in tissues and plasma, illustrated with concrete results for the different steps. We summarize the necessary parameters that need to be controlled for the successful development of fully validated MALDI-MS methods according to regulatory authorities, as well as currently unsolved problems and promising ways to address them. Finally, we propose an expert opinion on future perspectives and needs in order to establish MALDI-MS as a universal method for therapeutic drug monitoring.

Approaching sites of action of drugs in clinical pharmacology: New analytical options and their challenges

Clinical pharmacology is an important discipline for drug development aiming to define pharmacokinetics (PK), pharmacodynamics (PD) and optimum exposure to drugs, i.e. the concentration-response relationship and its modulators. For this purpose, information on drug concentrations at the anatomical, cellular and molecular sites of action is particularly valuable. In pharmacological assays, the limited accessibility of target cells in readily available samples (i.e. blood) often hampers mass spectrometry-based monitoring of the absolute quantity of a compound and the determination of its molecular action at the cellular level. Recently, new sample collection methods have been developed for the specific capture of rare circulating cells, especially for the diagnosis of circulating tumour cells. In parallel, new advances and developments in mass spectrometric instrumentation now allow analyses to be scaled down to the cellular level. Together, these developments may permit the monitoring of minute drug quantities and show their effect at the cellular level. In turn, such PK/PD associations on a cellular level would not only enrich our pharmacological knowledge of a given compound but also expand the basis for PK/PD simulations. In this review, we describe novel concepts supporting clinical pharmacology at the anatomical, cellular and molecular sites of action, and highlight the new challenges in mass spectrometry-based monitoring. Moreover, we present methods to tackle these challenges and define future needs.

Rapid and Sensitive Quantification of Osimertinib in Human Plasma Using a Fully Validated MALDI-IM-MS/MS Assay

The third-generation tyrosine kinase inhibitor (TKI), osimertinib, has revolutionized the treatment of patients with non-small cell lung carcinoma with epidermal growth factor receptor (EGFR)-activating mutation, and resistant to first- and second-generation TKIs. Osimertinib is now also proposed as a first-line therapy, thus extending the scope of applications in lung oncology. Personalized medicine approaches are still necessary to monitor if patients are exposed to adequate concentrations of osimertinib during their treatment. It would also help to understand the appearance of new resistances in patients after several months of dosing with osimertinib. Liquid chromatography–tandem mass spectrometry (LC–MS/MS) is currently the gold standard for the quantification of drugs in plasma enabling pharmacokinetic analyses and patient monitoring. In the present study, we propose an alternative to LC–MS/MS methods for the rapid and sensitive quantification of osimertinib in plasma using matrix-assisted laser desorption/ionization (MALDI) –MS. The presented assay requires only 3 min per sample for their preparation, analysis, and data extraction, and less than 3 h for quantification. A lower limit of quantification (LLOQ) of 5 ng/mL in plasma was retrieved. The method was fully validated, following the guidelines of the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for bioanalytical method validation. The present developments prove the importance to consider alternative MS assays for time-efficient quantification of small molecule inhibitors in plasma in the context of personalized medicine for targeted therapies.