Managing the challenge of chemically reactive metabolites in drug development

Detection and Quantification of Drug-Protein Adducts in Human Liver

Covalent protein adducts formed by drugs or their reactive metabolites are risk factors for adverse reactions, and inactivation of cytochrome P450 (CYP) enzymes. Characterization of drug-protein adducts is limited due to lack of methods identifying and quantifying covalent adducts in complex matrices. This study presents a workflow that combines data-dependent and data-independent acquisition (DDA and DIA) based liquid chromatography with tandem mass spectrometry (LC-MS/MS) to detect very low abundance adducts resulting from CYP mediated drug metabolism in human liver microsomes (HLMs). HLMs were incubated with raloxifene as a model compound and adducts were detected in 78 proteins, including CYP3A and CYP2C family enzymes. Experiments with recombinant CYP3A and CYP2C enzymes confirmed adduct formation in all CYPs tested, including CYPs not subject to time-dependent inhibition by raloxifene. These data suggest adducts can be benign. DIA analysis showed variable adduct abundance in many peptides between livers, but no concomitant decrease of unadducted peptides. This study sets a new standard for adduct detection in complex samples, offering insights into the human adductome resulting from reactive metabolite exposure. The methodology presented will aid mechanistic studies to identify, quantify and differentiate between adducts that result in adverse drug reactions and those that are benign.

Innate immune regulation in inflammation resolution and liver regeneration in drug-induced liver injury

Drug-induced liver injury (DILI) is an acute liver injury that poses a significant threat to human health. In severe cases, it can progress into chronic DILI or even lead to liver failure. DILI is typically caused by either intrinsic hepatotoxicity or idiosyncratic metabolic or immune responses. In addition to the direct damage drugs inflict on hepatocytes, the immune responses and liver inflammation triggered by hepatocyte death can further exacerbate DILI. Initially, we briefly discussed the differences in immune cell activation based on the type of liver cell death (hepatocytes, cholangiocytes, and LSECs). We then focused on the role of various immune cells (including macrophages, monocytes, neutrophils, dendritic cells, liver sinusoidal endothelial cells, eosinophils, natural killer cells, and natural killer T cells) in both the liver injury and liver regeneration stages of DILI. This article primarily reviews the role of innate immune regulation mediated by these immune cells in resolving inflammation and promoting liver regeneration during DILI, as well as therapeutic approaches targeting these immune cells for the treatment of DILI. Finally, we discussed the activation and function of liver progenitor cells (LPCs) during APAP-induced massive hepatic necrosis and the involvement of chronic inflammation in DILI.

Design of a Lead-Like Cysteine-Targeting Covalent Library and the Identification of Hits to Cys55 of Bfl-1

Covalent hit identification is a viable approach to identify chemical starting points against difficult-to-drug targets. While most researchers screen libraries of <2k electrophilic fragments, focusing on lead-like compounds can be advantageous in terms of finding hits with improved affinity and with a better chance of identifying cryptic pockets. However, due to the increased molecular complexity, larger numbers of compounds (>10k) are desirable to ensure adequate coverage of chemical space. Herein, the approach taken to build a library of 12k covalent lead-like compounds is reported, utilizing legacy compounds, robust library chemistry, and acquisitions. The lead-like covalent library was screened against the antiapoptotic protein Bfl-1, and six promising hits that displaced the BIM peptide from the PPI interface were identified. Intriguingly, X-ray crystallography of lead-like compound 8 showed that it binds to a previously unobserved conformation of the Bfl-1 protein and is an ideal starting point for the optimization of Bfl-1 inhibitors.

Drug hypersensitivity reactions: review of the state of the science for prediction and diagnosis

Drug hypersensitivity reactions (DHRs) are a type of adverse drug reaction that can occur with different classes of drugs and affect multiple organ systems and patient populations. DHRs can be classified as allergic or non-allergic based on the cellular mechanisms involved. Whereas nonallergic reactions rely mainly on the innate immune system, allergic reactions involve the generation of an adaptive immune response. Consequently, drug allergies are DHRs for which an immunological mechanism, with antibody and/or T cell, is demonstrated. Despite decades of research, methods to predict the potential for a new chemical entity to cause DHRs or to correctly attribute DHRs to a specific mechanism and a specific molecule are not well-established. This review will focus on allergic reactions induced by systemically administered low-molecular weight drugs with an emphasis on drug- and patient-specific factors that could influence the development of DHRs. Strategies for predicting and diagnosing DHRs, including potential tools based on the current state of the science, will also be discussed.

Development of a fluorous trapping reagent for rapid detection of electrophilic reactive metabolites

A cysteine-based fluorous trapping reagent, Rf8CYS, was developed. Rf8CYS formed adducts with soft and hard electrophilic reactive metabolites. These fluorous-tagged adducts were purified via both fluorous solid-phase extraction and the direct injection method. The highly sensitive mass spectrometric detection of an unprecedented adduct of the ticlopidine metabolite was realized.

Synthesis of 2,4-dihydroxyacetophenone derivatives as potent PDE-1 and -3 inhibitors: in vitro and in silico insights

Aim: Synthesis of novel bis-Schiff bases having potent inhibitory activity against phosphodiesterase (PDE-1 and -3) enzymes, potentially offering therapeutic implications for various conditions. Methods: Bis-Schiff bases were synthesized by refluxing 2,4-dihydroxyacetophenone with hydrazine hydrate, followed by treatment of substituted aldehydes with the resulting hydrazone to obtain the product compounds. After structural confirmation, the compounds were screened for their in vitro PDE-1 and -3 inhibitory activities. Results: The prepared compounds exhibited noteworthy inhibitory efficacy against PDE-1 and -3 enzymes by comparing with suramin standard. To clarify the binding interactions between the drugs, PDE-1 and -3 active sites, molecular docking studies were carried out. Conclusion: The potent compounds discovered in this study may be good candidates for drug development.

Insight into chemically reactive metabolites of aliphatic amine pollutants: A de novo prediction strategy and case study of sertraline

The uncommon metabolic pathways of organic pollutants are easily overlooked, potentially leading to idiosyncratic toxicity. Prediction of their biotransformation associated with the toxic effects is the very purpose that this work focuses, to develop a de novo method to mechanistically predict the reactive toxicity pathways of uncommon metabolites from start aliphatic amine molecules, which employed sertraline triggered by CYP450 enzymes as a model system, as there are growing concerns about the effects on human health posed by antidepressants in the aquatic environment. This de novo prediction strategy combines computational and experimental methods, involving DFT calculations upon sequential growth, in vitro and in vivo assays, dissecting chemically reactive mechanism relevant to toxicity, and rationalizing the fundamental factors. Significantly, desaturation and debenzylation-aromatization as the emerging metabolic pathways of sertraline have been elucidated, with the detection of DNA adducts of oxaziridine metabolite in mice, highlighting the potential reactive toxicity. Molecular orbital analysis supports the reactivity preference for toxicological-relevant C-N desaturation over N-hydroxylation of sertraline, possibly extended to several other aliphatic amines based on the Bell-Evans-Polanyi principle. It was further validated toward some other wide-concerned aliphatic amine pollutants involving atrazine, ε-caprolactam, 6PPD via in silico and in vitro assays, thereby constituting a complete path for de novo prediction from case study to general applications.

UDCA for Drug-Induced Liver Disease: Clinical and Pathophysiological Basis

Drug-induced liver injury (DILI) is an adverse reaction to medications and other xenobiotics that leads to liver dysfunction. Based on differential clinical patterns of injury, DILI is classified into hepatocellular, cholestatic, and mixed types; although hepatocellular DILI is associated with inflammation, necrosis, and apoptosis, cholestatic DILI is associated with bile plugs and bile duct paucity. Ursodeoxycholic acid (UDCA) has been empirically used as a supportive drug mainly in cholestatic DILI, but both curative and prophylactic beneficial effects have been observed for hepatocellular DILI as well, according to preliminary clinical studies. This could reflect the fact that UDCA has a plethora of beneficial effects potentially useful to treat the wide range of injuries with different etiologies and pathomechanisms occurring in both types of DILI, including anticholestatic, antioxidant, anti-inflammatory, antiapoptotic, antinecrotic, mitoprotective, endoplasmic reticulum stress alleviating, and immunomodulatory properties. In this review, a revision of the literature has been performed to evaluate the efficacy of UDCA across the whole DILI spectrum, and these findings were associated with the multiple mechanisms of UDCA hepatoprotection. This should help better rationalize and systematize the use of this versatile and safe hepatoprotector in each type of DILI scenarios.

INTEDE 2.0: the metabolic roadmap of drugs

The metabolic roadmap of drugs (MRD) is a comprehensive atlas for understanding the stepwise and sequential metabolism of certain drug in living organisms. It plays a vital role in lead optimization, personalized medication, and ADMET research. The MRD consists of three main components: (i) the sequential catalyses of drug and its metabolites by different drug-metabolizing enzymes (DMEs), (ii) a comprehensive collection of metabolic reactions along the entire MRD and (iii) a systematic description on efficacy & toxicity for all metabolites of a studied drug. However, there is no database available for describing the comprehensive metabolic roadmaps of drugs. Therefore, in this study, a major update of INTEDE was conducted, which provided the stepwise & sequential metabolic roadmaps for a total of 4701 drugs, and a total of 22 165 metabolic reactions containing 1088 DMEs and 18 882 drug metabolites. Additionally, the INTEDE 2.0 labeled the pharmacological properties (pharmacological activity or toxicity) of metabolites and provided their structural information. Furthermore, 3717 drug metabolism relationships were supplemented (from 7338 to 11 055). All in all, INTEDE 2.0 is highly expected to attract broad interests from related research community and serve as an essential supplement to existing pharmaceutical/biological/chemical databases. INTEDE 2.0 can now be accessible freely without any login requirement at: http://idrblab.org/intede/.

Pharmacokinetics, metabolism, excretion and safety of iruplinalkib (WX-0593), a novel ALK inhibitor, in healthy subjects: a phase I human radiolabeled mass balance study

BACKGROUND

Iruplinalkib is a novel anaplastic lymphoma kinase (ALK) inhibitor for the treatment of ALK-positive crizotinib-resistant NSCLC.

RESEARCH DESIGN AND METHODS

A single oral dose of 120 mg/3.7 MBq [14C]iruplinalkib was administered to healthy subjects. Blood, urine and fecal samples were collected and analyzed for iruplinalkib and its metabolites. The safety of iruplinalkib was also assessed.

RESULTS

Iruplinalkib was absorbed quickly and eliminated slowly from plasma, with a Tmax of 1.5 h and t1/2 of 28.6 h. About 88.85% of iruplinalkib was excreted at 312 h, including 20.23% in urine and 68.63% in feces. Seventeen metabolites of iruplinalkib were identified, and M3b (demethylation), M7 (cysteine conjugation), M11 (oxidative dehydrogenation and cysteine conjugation of M3b) and M12 (oxidative dehydrogenation and cysteine conjugation) were considered the prominent metabolites in humans. Iruplinalkib-related compounds were found to be covalently bound to proteins, accounting for 7.70% in plasma and 17.96% in feces, which suggested chemically reactive metabolites were formed. There were no serious adverse events observed in the study.

CONCLUSIONS

Iruplinalkib was widely metabolized and excreted mainly through feces in humans. Unchanged iruplinalkib, cysteine conjugates and covalent protein binding products were the main drug-related compounds in circulation. Iruplinalkib was well tolerated at the study dose.

TRIAL REGISTRATION

The trial is registered at ClinicalTrials.gov (Identifier: Anonymized).

Synthesis of Metabolites and Metabolite-like Compounds Using Biocatalytic Systems

Methodologies for the synthesis and purification of metabolites, which have been developed following their discovery, analysis, and structural identification, have been involved in numerous life science milestones. The renewed focus on the small molecule domain of biological cells has also created an increasing awareness of the rising gap between the metabolites identified and the metabolites which have been prepared as pure compounds. The design and engineering of resource-efficient and straightforward synthetic methodologies for the production of the diverse and numerous metabolites and metabolite-like compounds have attracted much interest. The variety of metabolic pathways in biological cells provides a wonderful blueprint for designing simplified and resource-efficient synthetic routes to desired metabolites. Therefore, biocatalytic systems have become key enabling tools for the synthesis of an increasing number of metabolites, which can then be utilized as standards, enzyme substrates, inhibitors, or other products, or for the discovery of novel biological functions.

Preclinical evaluation of chemically reactive metabolites and mitigation of bioactivation in drug discovery

The formation of reactive metabolites (RMs) is thought to be one of the pathogeneses for some idiosyncratic adverse drug reactions (IADRs) which are considered one of the leading causes of some drug attritions and/or recalls. Minimizing or eliminating the formation of RMs via chemical modification is a useful tactic to reduce the risk of IADRs and time-dependent inhibition (TDI) of cytochrome P450 enzymes (CYPs). The RMs should be carefully handled before making a go-no-go decision. Herein, we highlight the role of RMs in the occurrence of IADRs and CYP TDI, the risk of structural alerts, the approaches of RM assessment at the discovery stage and strategies to minimize or eliminate RM liability. Finally, some considerations for developing a RM-positive drug candidate are suggested.

The Promises of Proteomics and Metabolomics for Unravelling the Mechanism and Side Effect Landscape of Beta-Adrenoceptor Antagonists in Cardiovascular Therapeutics

Cardiovascular medicine witnessed notable advances for the past decade. Multiomics research offers a new lens for precision/personalized medicine for existing and emerging drugs used in the cardiovascular clinic. Beta-blockers are vital in treating hypertension and chronic heart failure. However, clinical use of beta-blockers is also associated with side effects and person-to-person variations in their pharmacokinetics and pharmacodynamics. A comprehensive understanding of the mechanisms that underpin the side effect landscape of beta-blockers is imperative to optimize their therapeutic value. In addition, current research emphasizes the circadian clock's vital roles in regulating pharmacological parameters. Administration of the beta-blockers at specific dosing times could potentially improve their effectiveness and reduce their toxic effects. The rapid development of mass spectrometry technologies with chemical proteomics and thermal proteome profiling methods has also substantially advanced our understanding of underlying side effects mechanisms by unbiased deconvolution of drug targets and off-targets. Metabolomics is steadily demonstrating its utility for conducting mechanistic and toxicological analyses of pharmacological compounds. This article discusses the promises of cutting-edge proteomics and metabolomics approaches to investigate the molecular targets, mechanism of action, adverse effects, and dosing time dependency of beta-blockers.

Discovery and Computational Studies of Potent Covalent Kinase Inhibitors with α-Substituent Electrophiles Targeting Cysteine

Both reversible noncovalent inhibitors and irreversible covalent inhibitors targeting tyrosine kinases have their disadvantages. The reversible covalent inhibitors with electrophilic group cyanoacrylamide as warheads reacting with cysteine residues could solve the dilemmas. However, there are still several unresolved issues regarding the electrophilic groups. In this manuscript, a series of EGFR inhibitors with double electron-withdrawing substituents introduced into the Cα position on the olefin bond were designed and synthesized. The binding structures and characteristics of inhibitors with the kinase in both the first noncovalent binding phase and the second covalent binding step were explored and combined with molecular docking and molecular dynamics simulations. Then, the reverse β-elimination reactions of the thiol-Michael adducts were investigated by applying density functional theory calculations. In addition, the effects of different electrophilic substituents of Cα on the binding between the inhibitors and kinase were elucidated. The results suggested that the electrophilicity and size of the electron-withdrawing groups play an important role in the specific interactions during the reaction. The compounds with the electron-withdrawing groups that had medium electrostatic and steric complementarity to the kinase active site could cooperatively stabilize the complexes and showed relatively good potent activities in the kinase assay experiment. The mechanical and structural information in this study could enhance our understanding of the functioning of the electron-withdrawing groups in the covalent inhibitors. The results might help to design efficient cysteine targeting inhibitors in the future.

Covalent Binding Mechanism of Furmonertinib and Osimertinib With Human Serum Albumin

As third-generation tyrosine kinase inhibitors, furmonertinib and osimertinib exhibit better efficacy than first- and second-generation tyrosine kinase inhibitors in patients with advanced non-small cell lung cancer. However, radioactive pharmacokinetics studies showed that parent-related components remain in human plasma for at least 21 days after oral administration. Similar pharmacokinetic profiles were found in pyrotinib and neratinib, which have been identified to covalently bind with human serum albumin at Lys-190, leading to low extraction recovery in protein precipitation. However, the binding mechanism of furmonertinib and osimertinib in human plasma has not been confirmed. Comprehensive techniques were used to investigate the mechanism of this binding, including ultra high-performance liquid chromatography coupled with high-resolution mass spectrometry and online/offline radioactivity profiling. SDS-PAGE and further autoradiography were also used to detect drug-protein adducts. We found that most furmonertinib exists in the human plasma following ex vivo incubation in the form of protein-drug adducts. Only lysine-furmonertinb adducts were found in pronase digests. A standard reference of lysine-furmonertinib was synthesized and confirmed by NMR. Through peptide mapping analysis, we confirmed that furmonertinib almost exclusively binds with human serum albumin (HSA) in plasma following ex vivo incubation, via Michael addition at Lys-195 and Lys-199, instead of Lys-190. Two peptides found to bond with furmonertinib were ASSAKQR and LKCASLQK. Osimertinib was also found to bond with Lys-195 and Lys-199 of HSA via peptide mapping analysis. SIGNIFICANCE STATEMENT: Here we report that furmonertinib and osimertinib can covalently bind with human serum albumin at the site of Lys-195 and Lys-199 instead of Lys-190, potentially leading to the long duration of drug-protein adducts in the human body.

Distal kinetic deuterium isotope effect: Phenyl ring deuteration attenuates N-demethylation of Lu AF35700

The N-demethylation of zicronapine (7) and three of its deuterated analogs 8 - 10 has been studied in human in vitro metabolism systems. While the N-deuterio-methyl analog 8 did not behave differently from the parent in human liver microsomes, a significantly reduced rate of N-demethylation was observed as a consequence of benzene ring deuteration (compound 7vs.9). Additional deuteration of the N-methyl group, which as mentioned had shown no effect in isolation, further decreased the rate of the N-demethylation reaction (compound 10vs.9). This paper presents and discusses this unprecedented 'distal kinetic isotope effect' that was observed when incubating the test compounds with human liver microsomes or recombinant human CYP450 liver enzymes.

Mechanism-driven modeling of chemical hepatotoxicity using structural alerts and an in vitro screening assay

Traditional experimental approaches to evaluate hepatotoxicity are expensive and time-consuming. As an advanced framework of risk assessment, adverse outcome pathways (AOPs) describe the sequence of molecular and cellular events underlying chemical toxicities. We aimed to develop an AOP that can be used to predict hepatotoxicity by leveraging computational modeling and in vitro assays. We curated 869 compounds with known hepatotoxicity classifications as a modeling set and extracted assay data from PubChem. The antioxidant response element (ARE) assay, which quantifies transcriptional responses to oxidative stress, showed a high correlation to hepatotoxicity (PPV=0.82). Next, we developed quantitative structure-activity relationship (QSAR) models to predict ARE activation for compounds lacking testing results. Potential toxicity alerts were identified and used to construct a mechanistic hepatotoxicity model. For experimental validation, 16 compounds in the modeling set and 12 new compounds were selected and tested using an in-house ARE-luciferase assay in HepG2-C8 cells. The mechanistic model showed good hepatotoxicity predictivity (accuracy = 0.82) for these compounds. Potential false positive hepatotoxicity predictions by only using ARE results can be corrected by incorporating structural alerts and vice versa. This mechanistic model illustrates a potential toxicity pathway for hepatotoxicity, and this strategy can be expanded to develop predictive models for other complex toxicities.

Covalent Protein Modification: An Unignorable Factor for Bisphenol A-Induced Hepatotoxicity

Covalent modification of proteins by reactive pollutants/metabolites might trigger various toxicities resulting from the disruption of protein structures and/or functions, which is critical for understanding the mechanism of pollutants-induced toxicity. However, this mechanism has rarely been touched on due to the lack of a methodology. In this research, the protein modification of bisphenol A (BPA) in rats was characterized using a series of liquid chromatography-tandem mass spectrometry (LC-MS) approaches. BPA-modified cysteine (Cys1) was first released from proteins via enzymatic hydrolysis and identified using LC-MS. Moreover, the positive correlation between Cys1 and hepatotoxicity indicated the involvement of protein modification in BPA toxicity. Then, in vitro incubation of BPA with amino acids and protein confirmed that BPA could specifically modify cysteine residues of proteins after bioactivation and provided four additional modification patterns. Finally, 24 BPA-modified proteins were identified from the liver of BPA-exposed rats using proteomic analysis, and they were mainly enriched in oxidative stress-related pathways. The modification on superoxide dismutases, catalase, and glutathione S-transferases disrupted their enzymatic functions, leading to oxidative damage. These results revealed that the covalent protein modification is an unignorable factor for BPA hepatotoxicity. Moreover, the workflow can be applied to identify protein adducts of other emerging contaminants and possible risk.

Design and Synthesis of Novel Bis-Imidazolyl Phenyl Butadiyne Derivatives as HCV NS5A Inhibitors

In today’s global plan to completely eradicate hepatitis C virus (HCV), the essential list of medications used for HCV treatment are direct-acting antivirals (DAAs), as interferon-sparing regimens have become the standard-of-care (SOC) treatment. HCV nonstructural protein 5A (NS5A) inhibitors are a very common component of these regimens. Food and Drug Administration (FDA)-approved NS5A inhibitors, although very potent, do not have the same potency against all eight genotypes of HCV. Therefore, this study aims to synthesize NS5A inhibitor analogues with high potency pan-genotypic activity and high metabolic stability. Starting from an NS5A inhibitor scaffold previously identified by our research group, we made several modifications. Two series of compounds were created to test the effect of changing the length and spatial conformation (para-para vs. meta-meta-positioned bis-imidazole-proline-carbamate), replacing amide groups in the linker with imidazole groups, as well as different end-cap compositions and sizes. The frontrunner inhibits genotype 1b (Con1) replicon, with an EC50 value in the picomolar range, and showed high genotypic coverage with nanomolar range EC50 values against four more genotypes. This together with its high metabolic stability (t½ > 120 min) makes it a potential preclinical candidate.

The Ascension of Targeted Covalent Inhibitors

Covalent drugs have made a major impact on human health but until recently were shunned by the pharmaceutical industry over concerns about the potential for toxicity. A resurgence has occurred driven by the clinical success of targeted covalent inhibitors (TCIs), with eight drugs approved over the past decade. The opportunity to create unique drugs by exploiting the covalent mechanism of action has enabled clinically decisive target product profiles to be achieved. TCIs have revolutionized the treatment paradigm for non-small-cell lung cancer and chronic lymphocytic leukemia. This Perspective will highlight the clinical and financial success of this class of drugs and provide early insight into toxicity, a key factor that had hindered progress in the field. Further innovation in the TCI approach, including expanding beyond cysteine-directed electrophiles, kinases, and cancer, highlights the broad opportunity to deliver a new generation of breakthrough therapies.

Diminishing GSH-Adduct Formation of Tricyclic Diazepine-based Mutant IDH1 Inhibitors

Mutant isocitrate dehydrogenase 1 (IDH1) has been identified as an attractive oncology target for which >70% of grade II and III gliomas and ∼10% of acute myeloid leukemia (AML) harbor somatic IDH1 mutations. These mutations confer a neomorphic gain of function, leading to the production of the oncometabolite (R)-2-hydroxyglutarate (2-HG). We identified and developed a potent, selective, and orally bioavailable brain-penetrant tricyclic diazepine scaffold that inhibits mutant IDH1. During the course of in vitro metabolism studies, GSH-adduct metabolites were observed. The hypothesis for GSH-adduct formation was driven by the electron-rich nature of the tricyclic core. Herein, we describe our efforts to reduce the electron-rich nature of the core. Ultimately, a strategy focused on core modifications to block metabolic hot spots coupled with substitution pattern changes (C8 N → C linked) led to the identification of new tricyclic analogues with minimal GSH-adduct formation across species while maintaining an overall balanced profile.

Interactions of selected cardiovascular active natural compounds with CXCR4 and CXCR7 receptors: a molecular docking, molecular dynamics, and pharmacokinetic/toxicity prediction study

BACKGROUND

The chemokine CXCL12 and its two receptors (CXCR4 and CXCR7) are involved in inflammation and hematopoietic cell trafficking. This study was designed to investigate molecular docking interactions of four popular cardiovascular-active natural compounds; curcumin, resveratrol, quercetin, and eucalyptol; with these receptors and to predict their drug-like properties. We hypothesize that these compounds can modify CXCL12/CXCR4/CXCR7 pathway offering benefits for coronary artery disease patients.

METHODS

Docking analyses were carried and characterized by Molecular Environment (MOE) software. Protein Data Bank ( http://www.rcsb.org/ ) has been retrieved from protein structure generation and crystal structures of CXCR4 and CXCR7 receptors (PDB code = 3ODU and 6K3F). The active sites of these receptors were evaluated and extracted from full protein and molecular docking protocol was done for compounds against them. The presented parameters included docking scores, ligand binding efficiency, and hydrogen bonding. The pharmacokinetic/toxic properties (ADME/T) were calculated using SwissADME, ProTox-II, and Pred-hERG softwares to predict drug-like properties of the compounds. The thermochemical and molecular orbital analysis, and molecular dynamics simulations were also done.

RESULTS

All compounds showed efficient interactions with the CXCR4 and CXCR7 receptors. The docking scores toward proteins 3ODU of CXCR4 and 6K3F of CXCR7 were - 7.71 and - 7.17 for curcumin, - 5.97 and - 6.03 for quercetin, - 5.68 and - 5.49 for trans-resveratrol, and - 4.88 and - 4.70 for (1 s,4 s)-eucalyptol respectively indicating that all compounds, except quercetin, have more interactions with CXCR4 than with CXCR7. The structurally and functionally important residues in the interactive sites of docked CXCR4-complex and CXCR7-complex were identified. The ADME analysis showed that the compounds have drug-like properties. Only (1 s,4 s)-Eucalyptol has potential weak cardiotoxicity. The results of thermochemical and molecular orbital analysis and molecular dynamics simulation validated outcomes of molecular docking study.

CONCLUSIONS

Curcumin showed the top binding interaction against active sites of CXCR4 and CXCR7 receptors, with the best safety profile, followed by quercetin, resveratrol, and eucalyptol. All compounds demonstrated drug-like properties. Eucalyptol has promising potential because it can be used by inhalation or skin massage. To our knowledge, this is the first attempt to find binding interactions of these natural agents with CXCR4 and CXCR7 receptors and to predict their druggability.

Conventional and Recent Trends of Scaffolds Fabrication: A Superior Mode for Tissue Engineering

Tissue regeneration is an auto-healing mechanism, initiating immediately following tissue damage to restore normal tissue structure and function. This falls in line with survival instinct being the most dominant instinct for any living organism. Nevertheless, the process is slow and not feasible in all tissues, which led to the emergence of tissue engineering (TE). TE aims at replacing damaged tissues with new ones. To do so, either new tissue is being cultured in vitro and then implanted, or stimulants are implanted into the target site to enhance endogenous tissue formation. Whichever approach is used, a matrix is used to support tissue growth, known as ‘scaffold’. In this review, an overall look at scaffolds fabrication is discussed, starting with design considerations and different biomaterials used. Following, highlights of conventional and advanced fabrication techniques are attentively presented. The future of scaffolds in TE is ever promising, with the likes of nanotechnology being investigated for scaffold integration. The constant evolvement of organoids and biofluidics with the eventual inclusion of organ-on-a-chip in TE has shown a promising prospect of what the technology might lead to. Perhaps the closest technology to market is 4D scaffolds following the successful implementation of 4D printing in other fields.

Conventional and Recent Trends of Scaffolds Fabrication: A Superior Mode for Tissue Engineering

Tissue regeneration is an auto-healing mechanism, initiating immediately following tissue damage to restore normal tissue structure and function. This falls in line with survival instinct being the most dominant instinct for any living organism. Nevertheless, the process is slow and not feasible in all tissues, which led to the emergence of tissue engineering (TE). TE aims at replacing damaged tissues with new ones. To do so, either new tissue is being cultured in vitro and then implanted, or stimulants are implanted into the target site to enhance endogenous tissue formation. Whichever approach is used, a matrix is used to support tissue growth, known as 'scaffold'. In this review, an overall look at scaffolds fabrication is discussed, starting with design considerations and different biomaterials used. Following, highlights of conventional and advanced fabrication techniques are attentively presented. The future of scaffolds in TE is ever promising, with the likes of nanotechnology being investigated for scaffold integration. The constant evolvement of organoids and biofluidics with the eventual inclusion of organ-on-a-chip in TE has shown a promising prospect of what the technology might lead to. Perhaps the closest technology to market is 4D scaffolds following the successful implementation of 4D printing in other fields.

B-nor-methylene Colchicinoid PT-100 Selectively Induces Apoptosis in Multidrug-Resistant Human Cancer Cells via an Intrinsic Pathway in a Caspase-Independent Manner

Colchicine, the main active alkaloid from Colchicum autumnale L., is a potent tubulin binder and represents an interesting lead structure for the development of potential anticancer chemotherapeutics. We report on the synthesis and investigation of potentially reactive colchicinoids and their surprising biological activities. In particular, the previously undescribed colchicinoid PT-100, a B-ring contracted 6-exo-methylene colchicinoid, exhibits extraordinarily high antiproliferative and apoptosis-inducing effects on various types of cancer cell lines like acute lymphoblastic leukemia (Nalm6), acute myeloid leukemia (HL-60), Burkitt-like lymphoma (BJAB), human melanoma (MelHO), and human breast adenocarcinoma (MCF7) cells at low nanomolar concentrations. Apoptosis induction proved to be especially high in multidrug-resistant Nalm6-derived cancer cell lines, while healthy human leukocytes and hepatocytes were not affected by the concentration range studied. Furthermore, caspase-independent initiation of apoptosis via an intrinsic pathway was observed. PT-100 also shows strong synergistic effects in combination with vincristine on BJAB and Nalm6 cells. Cocrystallization of PT-100 with tubulin dimers revealed its (noncovalent) binding to the colchicine-binding site of β-tubulin at the interface to the α-subunit. A pronounced effect of PT-100 on the cytoskeleton morphology was shown by fluorescence microscopy. While the reactivity of PT-100 as a weak Michael acceptor toward thiols was chemically proven, it remains unclear whether this contributes to the remarkable biological properties of this unusual colchicinoid.

Proteomic analysis suggests that monoterpenes in lemongrass disrupt Ca2+ homeostasis in Haemaphysalis longicornis leading to mitochondrial depolarization and cytotoxicity

Complex mixtures of bioactive ingredients in plant essential oils present complex chemistries which involve different modes of action. An increasing body of scientific reports has recently focused on the acaricidal activities of plant essential oils attributed to their monoterpene components, but information about their underlying molecular mechanism of action is scarce. Here, after the chemical analysis of lemongrass oil, a proteomic analysis of the ovary, salivary gland, and midgut of Haemaphysalis longicornis exposed to Cymbopogon citratus (lemongrass) essential oil was performed via data-independent acquisition mass spectrometry (DIA-MS) technology to further elucidate the molecular mechanisms involved. Pathway analysis reveals the activation of metabolic pathways mediated by oxidoreductases and transferases. Furthermore, the upregulation of various calcium-associated proteins and the upregulation of cytochrome c1, cytochrome c oxidase polypeptide IV, and programmed cell death protein 6-like isoform X1 suggest a cytotoxic mode of action via the formation of reactive oxygen species (ROS), mitochondrial Ca²⁺ overload, mitochondrial uncoupling, and depolarization, and ATP depletion leading to either apoptotic or necrotic death. Morphological alterations observed after the RNAi of a major detoxification enzyme (glutathione S-transferase) merit further investigation. Hence, the cytotoxic mode of action exhibited by C. citratus oil could be vital for the development of eco-friendly acaricide.

Reactive metabolites of the anticonvulsant drugs and approaches to minimize the adverse drug reaction

Several generations of antiepileptic drugs (AEDs) are available in the market for the treatment of seizures, but these are amalgamated with acute to chronic side effects. The most common side effects of AEDs are dose-related, but some are idiosyncratic adverse drug reactions (ADRs) that transpire due to the formation of reactive metabolite (RM) after the bioactivation process. Because of the adverse reactions patients usually discontinue the medication in between the treatment. The AEDs such as valproic acid, lamotrigine, phenytoin etc., can be categorized under such types because they form the RM which may prevail with life-threatening adverse effects or immune-mediated reactions. Hepatotoxicity, teratogenicity, cutaneous hypersensitivity, dizziness, addiction, serum sickness reaction, renal calculi, metabolic acidosis are associated with the metabolites of drugs such as arene oxide, N-desmethyldiazepam, 2-(1-hydroxyethyl)-2-methylsuccinimide, 2-(sulphamoy1acetyl)-phenol, E-2-en-VPA and 4-en-VPA and carbamazepine-10,11-epoxide, etc. The major toxicities are associated with the moieties that are either capable of forming RM or the functional groups may itself be too reactive prior to the metabolism. These functional groups or fragment structures are typically known as structural alerts or toxicophores. Therefore, minimizing the bioactivation potential of lead structures in the early phases of drug discovery by a modification to low-risk drug molecules is a priority for the pharmaceutical companies. Additionally, excellent potency and pharmacokinetic (PK) behaviour help in ensuring that appropriate (low dose) candidate drugs progress into the development phase. The current review discusses about RMs in the anticonvulsant drugs along with their mechanism vis-a-vis research efforts that have been taken to minimize the toxic effects of AEDs therapy.

Site-specific protein modification by 3-n-butylphthalide in primary hepatocytes: Covalent protein adducts diminished by glutathione and N-acetylcysteine

AIMS

3-n-Butylphthalide (NBP) is widely used for the treatment of cerebral ischaemic stroke but can causeliver injury in clinical practice. This study aims to elucidate the underlying mechanisms and propose potential preventive strategies.

MAIN METHODS

NBP and its four major metabolites, 3-hydroxy-NBP (3-OH-NBP), 10-hydroxy-NBP, 10-keto-NBP and NBP-11-oic acid, were synthesized and evaluated in primary human or rat hepatocytes (PHHs, PRHs). NBP-related substances or amino acid adducts were identified and semi-quantitated by ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS). The target proteins and binding sites were identified by shotgun proteomics based on peptide mass fingerprinting coupled with tandem mass spectrometry and verified by molecular docking.

KEY FINDINGS

The toxicity of NBP and its four major metabolites were compared in both PHHs and PRHs, and 3-OH-NBP was found to be the most toxic metabolite. 3-OH-NBP induced remarkable cell death and oxidative stresses in hepatocytes, which correlated well with the levels of glutathione and N-acetylcysteine adducts (3-GSH-NBP and 3-NAC-NBP) in cell supernatants. Additionally, 3-OH-NBP covalently conjugated with intracellular Cys, Lys and Ser, with preferable binding to Cys sites at Myh9 Cys1380, Prdx4 Cys53, Vdac2 Cys48 and Vdac3 Cys36. Furthermore, we found that CYP3A4 induction by rifampicin augmented NBP-induced cell toxicity and supplementing with GSH or NAC alleviated the oxidative stresses and reactive metabolites caused by 3-OH-NBP.

SIGNIFICANCE

Our work suggests that glutathione depletion, mitochondrial injury and covalent protein modification are the main causes of NBP-induced hepatotoxicity, which may be prevented by exogenous GSH or NAC supplementation and avoiding concomitant use of CYP3A4 inducers.

Scientific Opinion of the Scientific Panel on Plant Protection Products and their Residues (PPR Panel) on testing and interpretation of comparative in vitro metabolism studies

EFSA asked the Panel on Plant Protection Products and their residues to deliver a Scientific Opinion on testing and interpretation of comparative in vitro metabolism studies for both new active substances and existing ones. The main aim of comparative in vitro metabolism studies of pesticide active substances is to evaluate whether all significant metabolites formed in the human in vitro test system, as a surrogate of the in vivo situation, are also present at comparable level in animal species tested in toxicological studies and, therefore, if their potential toxicity has been appropriately covered by animal studies. The studies may also help to decide which animal model, with regard to a particular compound, is the most relevant for humans. In the experimental strategy, primary hepatocytes in suspension or culture are recommended since hepatocytes are considered the most representative in vitro system for prediction of in vivo metabolites. The experimental design of 3 × 3 × 3 (concentrations, time points, technical replicates, on pooled hepatocytes) will maximise the chance to identify unique (UHM) and disproportionate (DHM) human metabolites. When DHM and UHM are being assessed, test item-related radioactivity recovery and metabolite profile are the most important parameters. Subsequently, structural characterisation of the assigned metabolites is performed with appropriate analytical techniques. In toxicological assessment of metabolites, the uncertainty factor approach is the first alternative to testing option, followed by new approach methodologies (QSAR, read-across, in vitro methods), and only if these fail, in vivo animal toxicity studies may be performed. Knowledge of in vitro metabolites in human and animal hepatocytes would enable toxicological evaluation of all metabolites of concern, and, furthermore, add useful pieces of information for detection and evaluation of metabolites in different matrices (crops, livestock, environment), improve biomonitoring efforts via better toxicokinetic understanding, and ultimately, develop regulatory schemes employing physiologically based or physiology-mimicking in silico and/or in vitro test systems to anticipate the exposure of humans to potentially hazardous substances in plant protection products.

The emergence of the C-H functionalization strategy in medicinal chemistry and drug discovery

Owing to the market competitiveness and urgent societal need, an optimum speed of drug discovery is an important criterion for successful implementation. Despite the rapid ascent of artificial intelligence and computational and bioanalytical techniques to accelerate drug discovery in big pharma, organic synthesis of privileged scaffolds predicted in silico for in vitro and in vivo studies is still considered as the rate-limiting step. C-H activation is the latest technology added into an organic chemist's toolbox for the rapid construction and late-stage modification of functional molecules to achieve the desired chemical and physical properties. Particularly, elimination of prefunctionalization steps, exceptional functional group tolerance, complexity-to-diversity oriented synthesis, and late-stage functionalization of privileged medicinal scaffolds expand the chemical space. It has immense potential for the rapid synthesis of a library of molecules, structural modification to achieve the required pharmacological properties such as absorption, distribution, metabolism, excretion, toxicology (ADMET) and attachment of chemical reporters for proteome profiling, metabolite synthesis, etc. for preclinical studies. Although heterocycle synthesis, late-stage drug modification, ¹⁸F labelling, methylation, etc. via C-H functionalization have been reviewed from the synthetic standpoint, a general overview of these protocols from medicinal and drug discovery aspects has not been reviewed. In this feature article, we will discuss the recent trends of C-H activation methodologies such as synthesis of medicinal scaffolds through C-H activation/annulation cascade; C-H arylation for sp²-sp² and sp²-sp³ cross-coupling; C-H borylation/silylation to introduce a functional linchpin for further manipulation; C-H amination for N-heterocycles and hydrogen bond acceptors; C-H fluorination/fluoroalkylation to tune polarity and lipophilicity; C-H methylation: methyl magic in drug discovery; peptide modification and macrocyclization for therapeutics and biologics; fluorescent labelling and radiolabelling for bioimaging; bioconjugation for chemical biology studies; drug-metabolite synthesis for biodistribution and excretion studies; late-stage diversification of drug-molecules to increase efficacy and safety; cutting-edge DNA encoded library synthesis and improved synthesis of drug molecules via C-H activation in medicinal chemistry and drug discovery.

Next-Generation Intestinal Toxicity Model of Human Embryonic Stem Cell-Derived Enterocyte-Like Cells

The gastrointestinal tract is the most common exposure route of xenobiotics, and intestinal toxicity can result in systemic toxicity in most cases. It is important to develop intestinal toxicity assays mimicking the human system; thus, stem cells are rapidly being developed as new paradigms of toxicity assessment. In this study, we established human embryonic stem cell (hESC)-derived enterocyte-like cells (ELCs) and compared them to existing in vivo and in vitro models. We found that hESC-ELCs and the in vivo model showed transcriptomically similar expression patterns of a total of 10,020 genes than the commercialized cell lines. Besides, we treated the hESC-ELCs, in vivo rats, Caco-2 cells, and Hutu-80 cells with quarter log units of lethal dose 50 or lethal concentration 50 of eight drugs—chloramphenicol, cycloheximide, cytarabine, diclofenac, fluorouracil, indomethacin, methotrexate, and oxytetracycline—and then subsequently analyzed the biomolecular markers and morphological changes. While the four models showed similar tendencies in general toxicological reaction, hESC-ELCs showed a stronger correlation with the in vivo model than the immortalized cell lines. These results indicate that hESC-ELCs can serve as a next-generation intestinal toxicity model.

Protein Targets of Acetaminophen Covalent Binding in Rat and Mouse Liver Studied by LC-MS/MS

Acetaminophen (APAP) is a mild analgesic and antipyretic used commonly worldwide. Although considered a safe and effective over-the-counter medication, it is also the leading cause of drug-induced acute liver failure. Its hepatotoxicity has been linked to the covalent binding of its reactive metabolite, N-acetyl p-benzoquinone imine (NAPQI), to proteins. The aim of this study was to identify APAP-protein targets in both rat and mouse liver, and to compare the results from both species, using bottom-up proteomics with data-dependent high resolution mass spectrometry and targeted multiple reaction monitoring (MRM) experiments. Livers from rats and mice, treated with APAP, were homogenized and digested by trypsin. Digests were then fractionated by mixed-mode solid-phase extraction prior to liquid chromatography-tandem mass spectrometry (LC-MS/MS). Targeted LC-MRM assays were optimized based on high-resolution MS/MS data from information-dependent acquisition (IDA) using control liver homogenates treated with a custom alkylating reagent yielding an isomeric modification to APAP on cysteine residues, to build a modified peptide database. A list of putative in vivo targets of APAP were screened from data-dependent high-resolution MS/MS analyses of liver digests, previous in vitro studies, as well as selected proteins from the target protein database (TPDB), an online resource compiling previous reports of APAP targets. Multiple protein targets in each species were found, while confirming modification sites. Several proteins were modified in both species, including ATP-citrate synthase, betaine-homocysteine S-methyltransferase 1, cytochrome P450 2C6/29, mitochondrial glutamine amidotransferase-like protein/ES1 protein homolog, glutamine synthetase, microsomal glutathione S-transferase 1, mitochondrial-processing peptidase, methanethiol oxidase, protein/nucleic acid deglycase DJ-1, triosephosphate isomerase and thioredoxin. The targeted method afforded better reproducibility for analysing these low-abundant modified peptides in highly complex samples compared to traditional data-dependent experiments.

Antiparkinsonian activity of Cucurbita pepo seeds along with possible underlying mechanism

Cucurbita pepo is used as a vegetable in Pakistan and its seeds are also rich in tocopherol. Data showed the pivotal role of tocopherol in the treatment of Parkinson's disease (PD). The current study was designed to probe into the antiparkinson activity of methanolic extract of C. pepo (MECP) seeds in the haloperidol-induced Parkinson rat model. Behavioral studies showed improvement in motor functions. The increase in catalase, superoxide dismutase, glutathione levels whereas the decreases in the malondialdehyde and nitrite levels were noted in a dose-dependent manner. Acetylcholine-esterase (AchE) activity was increased. Molecular docking results revealed significant binding interaction of selected phytoconstituents within an active site of target protein AchE (PDB ID: 4EY7). Furthermore, α-synuclein was up regulated with down regulation of TNF-α and IL-1β in the qRT-PCR study. Subsequently, ADMET results on the basis of structure to activity predictions in terms of pharmacokinetics and toxicity estimations show that selected phytochemicals exhibited moderately acceptable properties. These properties add knowledge towards the structural features which could improve the bioavailability of selected phytochemicals before moving towards the initial phase of the drug development. Our integrated drug discovery scheme concluded that C. pepo seeds could ameliorate symptoms of PD and may prove a lead remedy for the treatment of PD.

Efficacy and safety of levetiracetam versus (fos)phenytoin for second-line treatment of epilepticus: a meta-analysis of latest randomized controlled trials

OBJECTIVES

To assess the efficiency and safety profiles of levetiracetam and (fos)phenytoin (phenytoin or fosphenytoin) for second-line treatment of seizures by performing a meta-analysis of RCTs.

METHODS

We systematically searched PubMed, Embase, Cochrane, FDA.gov, and ClinicalTrials.gov for RCTs (published before July 31, 2020; no language restrictions). Two independent reviewers screened abstracts and titles against inclusion and exclusion criteria published previously in the PROSPERO: CRD42020202736. Eleven studies fulfilled the established criteria. We assessed pooled data by using a random-effects model. Quality analysis was performed by using version 2 of the Cochrane risk-of-bias tool (RoB 2). RevMan v.5.3 was used to perform statistical analyses, and publication bias (egger's test) was assessed with Stata MP v.14.0.

RESULTS

Levetiracetam was similar to (fos)phenytoin in seizure termination rate (risk ratio [RR] 0.94; 95% CI 0.87 to 1.01), time of seizure termination (mean difference [MD] 0.44; -0.60 to 1.49), and drug resistance ([RR] 1.12, 0.86 to 1.45). The safety outcome showed a significant statistical difference between fosphenytoin group and levetiracetam group ([RR] 1.44, 1.14 to 1.81), while there was no significant difference observed between phenytoin treatment and levetiracetam treatment ([RR] 1.26, 0.99 to 1.60).

CONCLUSION

Levetiracetam was similar to (fos)phenytoin in cessation rate convulsive status epilepticus, and drug resistance, while it was superior (fos)phenytoin in pooled safety outcome. Further exploration is still needed as to whether it is the first choice for second-line drugs.

Identification of average molecular weight (AMW) as a useful chemical descriptor to discriminate liver injury-inducing drugs

Drug-induced liver injury (DILI) is one of major causes of discontinuing drug development and withdrawing drugs from the market. In this study, we investigated chemical properties associated with DILI using in silico methods, to identify a physicochemical property useful for DILI screening at the early stages of drug development. Total of 652 drugs, including 432 DILI-positive drugs (DILI drugs) and 220 DILI-negative drugs (no-DILI drugs) were selected from Liver Toxicity Knowledge Base of US Food and Drug Administration. Decision tree models were constructed using 2,473 descriptors as explanatory variables. In the final model, the descriptor AMW, representing average molecular weight, was found to be at the first node and showed the highest importance value. With AMW alone, 276 DILI drugs (64%) and 156 no-DILI drugs (71%) were correctly classified. Discrimination with AMW was then performed using therapeutic category information. The performance of discrimination depended on the category and significantly high performance (>0.8 balanced accuracy) was obtained in some categories. Taken together, the present results suggest AMW as a novel descriptor useful for detecting drugs with DILI risk. The information presented may be valuable for the safety assessment of drug candidates at the early stage of drug development.

Bioactivation of Isoxazole-Containing Bromodomain and Extra-Terminal Domain (BET) Inhibitors

The 3,5-dimethylisoxazole motif has become a useful and popular acetyl-lysine mimic employed in isoxazole-containing bromodomain and extra-terminal (BET) inhibitors but may introduce the potential for bioactivations into toxic reactive metabolites. As a test, we coupled deep neural models for quinone formation, metabolite structures, and biomolecule reactivity to predict bioactivation pathways for 32 BET inhibitors and validate the bioactivation of select inhibitors experimentally. Based on model predictions, inhibitors were more likely to undergo bioactivation than reported non-bioactivated molecules containing isoxazoles. The model outputs varied with substituents indicating the ability to scale their impact on bioactivation. We selected OXFBD02, OXFBD04, and I-BET151 for more in-depth analysis. OXFBD’s bioactivations were evenly split between traditional quinones and novel extended quinone-methides involving the isoxazole yet strongly favored the latter quinones. Subsequent experimental studies confirmed the formation of both types of quinones for OXFBD molecules, yet traditional quinones were the dominant reactive metabolites. Modeled I-BET151 bioactivations led to extended quinone-methides, which were not verified experimentally. The differences in observed and predicted bioactivations reflected the need to improve overall bioactivation scaling. Nevertheless, our coupled modeling approach predicted BET inhibitor bioactivations including novel extended quinone methides, and we experimentally verified those pathways highlighting potential concerns for toxicity in the development of these new drug leads.

Recent advances in computational metabolite structure predictions and altered metabolic pathways assessment to inform drug development processes

Many drug candidates fail during preclinical and clinical trials due to variable or unexpected metabolism which may lead to variability in drug efficacy or adverse drug reactions. The drug metabolism field aims to address this important issue from many angles which range from the study of drug-drug interactions, pharmacogenomics, computational metabolic modeling, and others. This manuscript aims to provide brief but comprehensive manuscript summaries highlighting the conclusions and scientific importance of seven exceptional manuscripts published in recent years within the field of drug metabolism. Two main topics within the field are reviewed: novel computational metabolic modeling approaches which provide complex outputs beyond site of metabolism predictions, and experimental approaches designed to discern the impacts of interindividual variability and species differences on drug metabolism. The computational approaches discussed provide novel outputs in metabolite structure and formation likelihood and/or extend beyond the saturated field of drug phase I metabolism, while the experimental metabolic pathways assessments aim to highlight the impacts of genetic polymorphisms and clinical animal model metabolic differences on human metabolism and subsequent health outcomes.

The evolution of the concept of stress and the framework of the stress system

Stress is a central concept in biology and has now been widely used in psychological, physiological, social, and even environmental fields. However, the concept of stress was cross-utilized to refer to different elements of the stress system including stressful stimulus, stressor, stress response, and stress effect. Here, we summarized the evolution of the concept of stress and the framework of the stress system. We find although the concept of stress is developed from Selye's "general adaptation syndrome", it has now expanded and evolved significantly. Stress is now defined as a state of homeostasis being challenged, including both system stress and local stress. A specific stressor may potentially bring about specific local stress, while the intensity of stress beyond a threshold may commonly activate the hypothalamic-pituitary-adrenal axis and result in a systematic stress response. The framework of the stress system indicates that stress includes three types: sustress (inadequate stress), eustress (good stress), and distress (bad stress). Both sustress and distress might impair normal physiological functions and even lead to pathological conditions, while eustress might benefit health through hormesis-induced optimization of homeostasis. Therefore, an optimal stress level is essential for building biological shields to guarantee normal life processes.

Development of fluorescent-labeled trapping reagents based on cysteine to detect soft and hard electrophilic reactive metabolites

Trapping assays are conducted at lead optimization stages to detect reactive metabolites (RMs) that can contribute to drug toxicity. The commonly used dansyl glutathione (dGSH) provides a sensitive analysis owing to the fluorescent label, however, it captures only soft electrophilic RMs. TRs for hard electrophilic RMs, few of which are labeled fluorescently, can detect hard electrophilic aldehydes only by forming unstable imine derivatives. In this study, we aimed to develop novel fluorescently labeled TRs that detect both soft and hard electrophilic RMs and form stable ring structures with aldehydes. We designed four dansylated TRs based on cysteine, which has both soft and hard nucleophilic groups. To evaluate the reactivity of the TRs, we incubated them with several substrates and found that one of the TRs (CysGlu-Dan) detected all the soft and hard electrophilic RMs. We also examined the inhibition potential of each TR for seven major CYPs involved in drug metabolism and found that CysGlu-Dan showed an inhibitory profile similar to that of dGSH. In conclusion, CysGlu-Dan can be used to evaluate the risk of RMs in drug discovery.

In-Vitro Approaches to Predict and Study T-Cell Mediated Hypersensitivity to Drugs

Mitigating the risk of drug hypersensitivity reactions is an important facet of a given pharmaceutical, with poor performance in this area of safety often leading to warnings, restrictions and withdrawals. In the last 50 years, efforts to diagnose, manage, and circumvent these obscure, iatrogenic diseases have resulted in the development of assays at all stages of a drugs lifespan. Indeed, this begins with intelligent lead compound selection/design to minimize the existence of deleterious chemical reactivity through exclusion of ominous structural moieties. Preclinical studies then investigate how compounds interact with biological systems, with emphasis placed on modeling immunological/toxicological liabilities. During clinical use, competent and accurate diagnoses are sought to effectively manage patients with such ailments, and pharmacovigilance datasets can be used for stratification of patient populations in order to optimise safety profiles. Herein, an overview of some of the in-vitro approaches to predict intrinsic immunogenicity of drugs and diagnose culprit drugs in allergic patients after exposure is detailed, with current perspectives and opportunities provided.

Bio-activation of simeprevir in liver microsomes and characterization of its glutathione conjugates by liquid chromatography coupled to ultrahigh-resolution quadrupole time-of-flight mass spectrometry

Liquid chromatography coupled to a triple quadrupole and, alternatively, to an ultrahigh-resolution quadrupole time-of-flight (UHR-QqTOF) mass spectrometers was used to collect qualitative and quantitative information from incubations of the anti-hepatitis C drug simeprevir with human and rat liver microsomes, respectively, supplemented with NADPH and glutathione. For this, different chromatographic methods using two different chromatographic columns, Kinetex® 2.6 µm C₁₈ (50 × 3 mm) and Atlantis T3 (100 Å, 3 µm, 4.6 mm × 150 mm), have been employed. For determination and structural characterization of the reactive metabolites, we used information obtained from high-resolution mass spectrometry, namely accurate mass data to calculate the elemental composition, accurate MS/MS fragmentation patterns for confirmation of structural proposals, and the high mass spectral resolution to eliminate false-positive peaks. In this study, the use of high-resolution mass spectrometry (HR-MS) enabled the identification of 19 simeprevir metabolites generated by O- respectively N-demethylation, oxidation, dehydrogenation, hydrolysis, and formation of glutathione conjugates. The in silico study provides insights into the sites of simeprevir most amenable to reactions involving cytochrome P₄₅₀. The developed methods have been successfully applied to analyze simeprevir and its metabolites simultaneously; based on this data, potential metabolic pathways of simeprevir are discussed. In general, the obtained results demonstrate that simeprevir is susceptible to form reactive simeprevir-glutathione adducts and cyclopropansulfonamide, which may explain the implication of simeprevir in idiosyncratic adverse drug reactions (IADRs) or hepatotoxicity.

Engineering Selectivity for Reduced Toxicity of Bacterial Kinase Inhibitors Using Structure-Guided Medicinal Chemistry

Tuberculosis is a major global public health concern, and new drugs are needed to combat both the typical form and the increasingly common drug-resistant form of this disease. The essential tuberculosis kinase PknB is an attractive drug development target because of its central importance in several critical signaling cascades. A major hurdle in kinase inhibitor development is the reduction of toxicity due to nonspecific kinase activity in host cells. Here a novel class of PknB inhibitors was developed from hit aminopyrimidine 1 (GW779439X), which was originally designed for human CDK4 but failed to progress clinically because of high toxicity and low specificity. Replacing the pyrazolopyridazine headgroup of the original hit with substituted pyridine or phenyl headgroups resulted in a reduction of Cdk activity and a 3-fold improvement in specificity over the human kinome while maintaining PknB activity. This also resulted in improved microbiological activity and reduced toxicity in THP-1 cells and zebrafish.