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.

Multiorgan Crystal Deposition of an Amphoteric Drug in Rats Due to Lysosomal Accumulation and Conversion to a Poorly Soluble Hydrochloride Salt

Poor solubility of drug candidates mainly affects bioavailability, but poor solubility of drugs and metabolites can also lead to precipitation within tissues, particularly when high doses are tested. RO0728617 is an amphoteric compound bearing basic and acidic moieties that has previously demonstrated good solubility at physiological pH but underwent widespread crystal deposition in multiple tissues in rat toxicity studies. The aim of our investigation was to better characterize these findings and their underlying mechanism(s), and to identify possible screening methods in the drug development process. Main microscopic features observed in rat RO0728617 toxicity studies were extensive infiltrates of crystal-containing macrophages in multiple organs. Matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry revealed that these crystals contained the orally administered parent compound, and locality was confirmed to be intracytoplasmic and partly intralysosomal by electron microscopic examination. Crystal formation was explained by lysosomal accumulation of the compound followed by precipitation of the hydrochloride salt under physiological conditions in the lysosomes, which have a lower pH and higher chloride concentration in comparison to the cytosol. This study demonstrates that risk of drug precipitation can be assessed by comparing the estimated lysosomal drug concentration at a given dose with the solubility of the compound at lysosomal conditions.

Safety, Tissue Distribution, and Metabolism of LNA-Containing Antisense Oligonucleotides in Rats

Antisense oligonucleotides (ASOs) are chemically modified nucleic acids with therapeutic potential, some of which have been approved for marketing. We performed a study in rats to investigate mechanisms of toxicity after administration of 3 tool locked nucleic acid (LNA)-containing ASOs with differing established safety profiles. Four male rats per group were dosed once, 3, or 6 times subcutaneously, with 7 days between dosing, and sacrificed 3 days after the last dose. These ASOs were either unconjugated (naked) or conjugated with N-acetylgalactosamine for hepatocyte-targeted delivery. The main readouts were in-life monitoring, clinical and anatomic pathology, exposure assessment and metabolite identification in liver and kidney by liquid chromatography coupled to tandem mass spectrometry, ASO detection in liver and kidney by immunohistochemistry, in situ hybridization, immune electron microscopy, and matrix-assisted laser desorption/ionization mass spectrometry imaging. The highly toxic compounds showed the greatest amount of metabolites and a low degree of tissue accumulation. This study reveals different patterns of cell death associated with toxicity in liver (apoptosis and necrosis) and kidney (necrosis only) and provides new ultrastructural insights on the tissue accumulation of ASOs. We observed that the immunostimulatory properties of ASOs can be either primary from sequence-dependent properties or secondary to cell necrosis.

THE SPACE DIMENSION AT THE MICRO LEVEL: MASS SPECTROMETRY IMAGING OF DRUGS IN TISSUES

Mass spectrometry imaging (MSI) has seen remarkable development in recent years. The possibility of getting quantitative or semiquantitative data, while maintaining the spatial component in the tissues has opened up unique study possibilities. Now with a spatial window of few tens of microns, we can characterize the events occurring in tissue subcompartments in physiological and pathological conditions. For example, in oncology-especially in preclinical models-we can quantitatively measure drug distribution within tumors, correlating it with pharmacological treatments intended to modify it. We can also study the local effects of the drug in the tissue, and their effects in relation to histology. This review focuses on the main results in the field of drug MSI in clinical pharmacology, looking at the literature on the distribution of drugs in human tissues, and also the first preclinical evidence of drug intratissue effects. The main instrumental techniques are discussed, looking at the different instrumentation, sample preparation protocols, and raw data management employed to obtain the sensitivity required for these studies. Finally, we review the applications that describe in situ metabolic events and pathways induced by the drug, in animal models, showing that MSI makes it possible to study effects that go beyond the simple concentration of the drug, maintaining the space dimension. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Identification of biomarkers to diagnose diseases and find adverse drug reactions by metabolomics

Metabolomics has been widely used for investigating the biological functions of disease expression and has the potential to discover biomarkers in circulating biofluids or tissue extracts that reflect in phenotypic changes. Metabolic profiling has advantages because of the use of unbiased techniques, including multivariate analysis, and has been applied in pharmacological studies to predict therapeutic and adverse reactions of drugs, which is called pharmacometabolomics (PMx). Nuclear magnetic resonance (NMR)- and mass spectrometry (MS)-based metabolomics has contributed to the discovery of recent disease biomarkers; however, the optimal strategy for the study purpose must be selected from many established protocols, methodologies and analytical platforms. Additionally, information on molecular localization in tissue is essential for further functional analyses related to therapeutic and adverse effects of drugs in the process of drug development. MS imaging (MSI) is a promising technology that can visualize molecules on tissue surfaces without labeling and thus provide localized information. This review summarizes recent uses of MS-based global and wide-targeted metabolomics technologies and the advantages of the MSI approach for PMx and highlights the PMx technique for the biomarker discovery of adverse drug effects.

Raman2imzML converts Raman imaging data into the standard mass spectrometry imaging format

BACKGROUND

Multimodal imaging that combines mass spectrometry imaging (MSI) with Raman imaging is a rapidly developing multidisciplinary analytical method used by a growing number of research groups. Computational tools that can visualize and aid the analysis of datasets by both techniques are in demand.

RESULTS

Raman2imzML was developed as an open-source converter that transforms Raman imaging data into imzML, a standardized common data format created and adopted by the mass spectrometry community. We successfully converted Raman datasets to imzML and visualized Raman images using open-source software designed for MSI applications.

CONCLUSION

Raman2imzML enables both MSI and Raman images to be visualized using the same file format and the same software for a straightforward exploratory imaging analysis.

Only Hyperuricemia with Crystalluria, but not Asymptomatic Hyperuricemia, Drives Progression of Chronic Kidney Disease

BACKGROUND

The roles of asymptomatic hyperuricemia or uric acid (UA) crystals in CKD progression are unknown. Hypotheses to explain links between UA deposition and progression of CKD include that (1) asymptomatic hyperuricemia does not promote CKD progression unless UA crystallizes in the kidney; (2) UA crystal granulomas may form due to pre-existing CKD; and (3) proinflammatory granuloma-related M1-like macrophages may drive UA crystal-induced CKD progression.

METHODS

MALDI-FTICR mass spectrometry, immunohistochemistry, 3D confocal microscopy, and flow cytometry were used to characterize a novel mouse model of hyperuricemia and chronic UA crystal nephropathy with granulomatous nephritis. Interventional studies probed the role of crystal-induced inflammation and macrophages in the pathology of progressive CKD.

RESULTS

Asymptomatic hyperuricemia alone did not cause CKD or drive the progression of aristolochic acid I-induced CKD. Only hyperuricemia with UA crystalluria due to urinary acidification caused tubular obstruction, inflammation, and interstitial fibrosis. UA crystal granulomas surrounded by proinflammatory M1-like macrophages developed late in this process of chronic UA crystal nephropathy and contributed to the progression of pre-existing CKD. Suppressing M1-like macrophages with adenosine attenuated granulomatous nephritis and the progressive decline in GFR. In contrast, inhibiting the JAK/STAT inflammatory pathway with tofacitinib was not renoprotective.

CONCLUSIONS

Asymptomatic hyperuricemia does not affect CKD progression unless UA crystallizes in the kidney. UA crystal granulomas develop late in chronic UA crystal nephropathy and contribute to CKD progression because UA crystals trigger M1-like macrophage-related interstitial inflammation and fibrosis. Targeting proinflammatory macrophages, but not JAK/STAT signaling, can attenuate granulomatous interstitial nephritis.

Tissue Imaging by Mass Spectrometry: A Practical Guide for the Medicinal Chemist

Understanding the tissue distribution of therapeutic molecules is often critical for assessing their efficacy and toxicity. Unfortunately, standard methods for monitoring localized drug distribution are resource-intensive and are typically performed late in the discovery process. As a result, early development efforts often progress without detailed information on the effect that changes in structure and/or formulation have on drug localization. Recent innovations in mass spectrometry (MS) provide new options for mapping the spatial distribution of drug in tissue and allow parallel detection of endogenous species. These advances are improving access to drug distribution data early in discovery and provide insight into local biochemical changes that are directly related to drug activity. The literature on these topics is voluminous, and the technology is advancing rapidly, offering a bewildering array of options for researchers who are new to the field. To guide medicinal chemists who wish to apply these methods in their research, this technology perspective provides our views on practical applications that are currently enabled by various MS imaging (MSI) approaches, along with recommendations for how best to implement these methods in pharmaceutical R&D.

Assessing the risk of drug crystallization in vivo

INTRODUCTION

Low intrinsic solubility leading to poor oral bioavailability is a common challenge in drug discovery that can often be overcome by formulation strategies, however, it remains a potential limitation that can pose challenges for early risk assessment and represent a significant obstacle to drug development. We identified a selective inhibitor (BMS-986126) of the IL-1 receptor-associated kinase 4 (IRAK4) with favorable properties as a lead candidate, but with unusually low intrinsic solubility of <1 μg/mL.

METHODS

Conventional histopathology identified the issue of crystal formation in vivo. Subsequent investigative work included confocal Raman micro-spectroscopy, MALDI-MS, polarized light microscopy of fresh wet-mount tissue scrapings and transmission electron microscopy.

RESULTS

BMS-986126 was advanced into a 2-week toxicology study in rats. The main finding in this study was minimal granulomatous inflammation in the duodenum, associated with the presence of birefringent crystals at the highest dosage of 100 mg/kg/day. Considering the safety margin, and the single location of the lesion, BMS-986126 was further progressed into IND-enabling toxicology studies where tolerability deteriorated with increasing dosing duration. Birefringent crystals and granulomatous inflammation were detected in multiple organs at dosages ≥20 mg/kg/day. Raman spectroscopy confirmed the identity of the crystals as BMS-986126. Therefore, follow up investigations were conducted to further characterize drug crystallization and to evaluate detection methods for their potential to reliably detect in vivo crystallization early.

DISCUSSION

The purpose of our efforts was to identify critical factors influencing in vivo drug crystallization and to provide a preliminary assessment (based on one compound) which method would be best suited for identifying crystals. Results indicated a combination of methods was required to provide a complete assessment of drug crystallization and that a simple technique, scraping of freshly collected tissue followed by evaluation under polarizing light was suitable for detecting crystals. However, dosing for 2 weeks was required for crystals to grow to a clearly detectable size.

Imaging Mass Microscopy of Kidneys from Azithromycin-Treated Rats with Phospholipidosis

Drug-induced phospholipidosis is a lysosomal storage disorder characterized by the excess accumulation of tissue phospholipids. Although azithromycin can be used to induce phospholipidosis, no experimental studies evaluating the relationship between drug accumulation and phospholipid localization have been performed. In this study, azithromycin was orally administered to rats for 7 days, and the relationship between drug and phospholipid accumulation was performed using imaging mass microscopy. The administration of azithromycin induced tubular epithelial vacuolation in the inner stripe of the outer medulla of the kidney, consistent with the lamellar bodies that are typical manifestations of drug-induced phospholipidosis. Azithromycin and phospholipid tissue levels were extensively elevated in the kidneys of azithromycin-treated rats. Imaging mass microscopy revealed that both azithromycin and its metabolites were found in the kidneys of azithromycin-treated rats but not in control animals. The vacuolated areas of the kidneys were primarily found in the inner stripe of the outer medulla, consistent with the areas of high azithromycin concentration. Azithromycin was colocalized with several phospholipids-phosphatidylinositol (18:0/20:4), phosphatidylethanolamine (18:0/20:4 and 16:0/20:4), and possibly didocosahexaenoyl (C22:6)-bis(monoacylglycerol) phosphate, a putative biomarker of drug-induced phospholipidosis. In summary, we found correlations between regions of kidney damage and the accumulation of azithromycin, its metabolites, and phospholipids using imaging mass microscopy. Such analyses may help reveal the mechanism and identify putative biomarkers of drug-induced phospholipidosis.