Selection of new chemical entities with decreased potential for adverse drug reactions

New Perspectives about Drug Candidates Targeting HTLV-1 and Related Diseases

Among the human T-lymphotropic virus (HTLV) types, HTLV-1 is the most prevalent, and it has been linked to a spectrum of diseases, including HAM/TSP, ATLL, and hyperinfection syndrome or disseminated strongyloidiasis. There is currently no globally standard first-line treatment for HTLV-1 infection and its related diseases. To address this, a comprehensive review was conducted, analyzing 30 recent papers from databases PubMed, CAPES journals, and the Virtual Health Library (VHL). The studies encompassed a wide range of therapeutic approaches, including antiretrovirals, immunomodulators, antineoplastics, amino acids, antiparasitics, and even natural products and plant extracts. Notably, the category with the highest number of articles was related to drugs for the treatment of ATLL. Studies employing mogamulizumab as a new perspective for ATLL received greater attention in the last 5 years, demonstrating efficacy, safe use in the elderly, significant antitumor activity, and increased survival time for refractory patients. Concerning HAM/TSP, despite corticosteroid being recommended, a more randomized clinical trial is needed to support treatment other than corticoids. The study also included a comprehensive review of the drugs used to treat disseminated strongyloidiasis in co-infection with HTLV-1, including their administration form, in order to emphasize gaps and facilitate the development of other studies aiming at better-directed methodologies. Additionally, docking molecules and computer simulations show promise in identifying novel therapeutic targets and repurposing existing drugs. These advances are crucial in developing more effective and targeted treatments against HTLV-1 and its related diseases.

Transformation products of pharmaceuticals in the environment: Their fate, (eco)toxicity and bioaccumulation potential

Nowadays, a huge scientific attention is being paid to the chemicals of emerging concern, which may pose a significant risk to the human and whole ecosystems. Among them, residues of pharmaceuticals are a widely investigated group of chemicals. In recent years it has been repeatedly demonstrated that pharmaceuticals are present in the environment and that some of them can be toxic to organisms as well as accumulate in their tissues. However, even though the knowledge of the presence, fate and possible threats posed by the parent forms of pharmaceuticals is quite extensive, their transformation products (TPs) have been disregarded for long time. Since last few years, this aspect has gained more scientific attention and recently published papers proved their common presence in the environment. Also the interest in terms of their toxicity, bioconcentration and stability in the environment has increased. Therefore, the aim of our paper was to revise and assess the current state of knowledge on the fate and effects resulting from the presence of the pharmaceuticals' transformation drugs in the environment. This review discusses the metabolites of compounds belonging to six major pharmaceutical groups: SSRIs, anticancer drugs, antibiotics, antihistamines, NSAIDs and opioids, additionally discussing other individual compounds for which literature data exist. The data presented in this paper prove that some TPs may be as harmful as their native forms, however for many groups of drugs this data is still insufficient to assess the risk posed by their presence in the environment.

Protective effect and mechanism of chitooligosaccharides on acetaminophen-induced liver injury

Currently, drug-induced liver injury caused by acetaminophen (APAP) is the second leading cause of human liver transplantation. The only clinical antidote treatment for APAP-induced liver injury is N-acetyl-L-cysteine (NAC), which has many side effects. Chitooligosaccharides (COS) are processed from naturally occurring chitin through chemical desalting and deproteinization, biological enzymatic hydrolysis and other processes. In this study, we constructed in vitro and in vivo models of APAP-induced liver injury to study COS of two molecular weights (MWs), which are COST (MW ≤ 1000 Da) and COSM (MW ≤ 3000 Da). The results showed that COST and COSM can significantly reduce the levels of serum ALT and AST and liver MDA, TNF-α, IL-1β and IL-6, and increase the levels and activity of GSH, SOD, GSH-Px and CAT. A mechanistic study found that COST and COSM can significantly reduce the expression of liver CYP2E1, Keap1, p-ASK1/ASK1, p-MKK4/MKK4, p-JNK/JNK, Caspase-3 and Bax and increase the expression of Nrf2, HO-1, eNOS, SOD and Bcl-XL. COST and COSM can inhibit toxic APAP metabolism, inhibit oxidative damage and the apoptosis pathway, increase activation of the liver antioxidant pathway, and ultimately ameliorate APAP-induced liver oxidative damage.

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.

Mechanism-Based Inactivation of Cytochrome P450 3A4 by Benzbromarone

Benzbromarone (BBR), a potent uricosuric agent for the management of gout, is known to cause fatal fulminant hepatitis. Although the mechanism of BBR-induced idiosyncratic hepatotoxicity remains unelucidated, cytochrome P450 enzyme-mediated bioactivation of BBR to electrophilic reactive metabolites is commonly regarded as a key molecular initiating event. However, apart from causing aberrant toxicities, reactive metabolites may result in mechanism-based inactivation (MBI) of cytochrome P450. Here, we investigated and confirmed that BBR inactivated CYP3A4 in a time-, concentration-, and NADPH-dependent manner with K _I, k _inact, and partition ratio of 11.61 µM, 0.10 minutes^-1, and 110, respectively. Coincubation with ketoconazole, a competitive inhibitor of CYP3A4, attenuated the MBI of CYP3A4 by BBR, whereas the presence of glutathione and catalase did not confer such protection. The lack of substantial recovery of enzyme activity postdialysis and after oxidation with potassium ferricyanide, combined with the absence of a Soret peak in spectral difference scans, implied that MBI of CYP3A4 by BBR did not occur through the formation of quasi-irreversible metabolite-intermediate complexes. Analysis of the reduced CO-difference spectrum revealed an ∼44% reduction in ferrous-CO binding and hinted that inactivation is mediated via irreversible covalent adduction to both the prosthetic heme moiety and the apoprotein. Finally, our in silico covalent docking analysis further suggested the modulation of substrate binding to CYP3A4 via the covalent adduction of epoxide-derived reactive intermediates of BBR to two key cysteine residues (Cys239 and Cys58) vicinal to the entrance of the orthosteric binding site. SIGNIFICANCE STATEMENT: Although the bioactivation of benzbromarone (BBR) to reactive metabolites has been well characterized, its potential to cause mechanism-based inactivation (MBI) of cytochrome P450 has not been fully investigated. This study reports the MBI of CYP3A4 by BBR via irreversible covalent adduction and develops a unique covalent docking methodology to predict the structural molecular determinants underpinning the inactivation for the first time. These findings lay the groundwork for future investigation of clinically relevant drug-drug interactions implicating BBR and mechanisms of BBR-induced idiosyncratic hepatotoxicity.

Acyl glucuronide metabolites: Implications for drug safety assessment

Acyl glucuronides are important metabolites of compounds with carboxylic acid moieties and have unique properties that distinguish them from other phase 2 metabolites. In particular, in addition to being often unstable, acyl glucuronide metabolites can be chemically reactive leading to covalent binding with macromolecules and toxicity. While there is circumstantial evidence that drugs forming acyl glucuronide metabolites can be associated with rare, but severe idiosyncratic toxic reactions, many widely prescribed drugs with good safety records are also metabolized through acyl glucuronidation. Therefore, there is a need to understand the various factors that can affect the safety of acyl glucuronide-producing drugs including the rate of acyl glucuronide formation, the relative reactivity of the acyl glucuronide metabolite formed, the rate of elimination, potential proteins being targeted, and the rate of aglucuronidation. In this review, these factors are discussed and various approaches to de-risk the safety liabilities of acyl glucuronide metabolites are evaluated.

Discovery and development of pyrotinib: A novel irreversible EGFR/HER2 dual tyrosine kinase inhibitor with favorable safety profiles for the treatment of breast cancer

The discovery and development of a novel irreversible EGFR/HER2 dual tyrosine kinase inhibitor SHR1258 (pyrotinib) for the treatment of HER2-postive breast cancer is presented. The structure-activity relationship of lead series and their pharmacokinetic properties were evaluated to identify the potential candidates for further in vivo efficacy studies and preclinical safety assessments. Metabolic pathway and drug-drug interaction were also investigated in preclinical settings. In particular, major metabolites in human and animal species were assessed with regard to potential toxicity or off-target side effects. Overall, the potent and selective EGFR/HER2 dual inhibitor, pyrotinib, displayed robust anti-tumor effects on HER2-overexpressing xenograft models and sufficiently safety windows in animals as well as favorable pharmacokinetic properties in human, which substantially ensures current clinical development. Finally, recent advances of pyrotinib in clinical studies are highlighted with very encouraging outcomes in patients with HER2-postive advanced breast cancer.

Protective effects of silymarin against acetaminophen-induced hepatotoxicity and nephrotoxicity in mice

This study was designed to estimate protective effects of silymarin on acetaminophen ( N-acetyl- p-aminophenol, paracetamol; APAP)-induced hepatotoxicity and nephrotoxicity in mice. Treatment of mice with overdose of APAP resulted in the elevation of aspartate aminotransferase (AST), alanine transaminase (ALT), blood urea nitrogen (BUN), and serum creatinine (SCr) levels in serum, liver, and kidney nitric oxide (NO) levels and significant histological changes including decreased body weight, swelling of hepatocytes, cell infiltration, dilatation and congestion, necrosis and apoptosis in liver, and dilatation of Bowman’s capsular space and glomerular capillaries, pale-stained tubules epithelium, cell infiltration, and apoptosis in kidney. Posttreatment with silymarin 1 h after APAP injectionfor 7 days, however, significantly normalized the body weight, histological damage, serum ALT, AST, BUN, SCr, and tissue NO levels. Our observation suggested that silymarin ameliorated the toxic effects of APAP-induced hepatotoxicity and nephrotoxicity in mice. The protective role of silymarin against APAP-induced damages might result from its antioxidative and anti-inflammatory effects.

Applications of stable isotopes in clinical pharmacology

This review aims to present an overview of the application of stable isotope technology in clinical pharmacology. Three main categories of stable isotope technology can be distinguished in clinical pharmacology. Firstly, it is applied in the assessment of drug pharmacology to determine the pharmacokinetic profile or mode of action of a drug substance. Secondly, stable isotopes may be used for the assessment of drug products or drug delivery systems by determination of parameters such as the bioavailability or the release profile. Thirdly, patients may be assessed in relation to patient-specific drug treatment; this concept is often called personalized medicine. In this article, the application of stable isotope technology in the aforementioned three areas is reviewed, with emphasis on developments over the past 25 years. The applications are illustrated with examples from clinical studies in humans.

Alternative (non-animal) methods for cosmetics testing: current status and future prospects-2010

The 7th amendment to the EU Cosmetics Directive prohibits to put animal-tested cosmetics on the market in Europe after 2013. In that context, the European Commission invited stakeholder bodies (industry, non-governmental organisations, EU Member States, and the Commission's Scientific Committee on Consumer Safety) to identify scientific experts in five toxicological areas, i.e. toxicokinetics, repeated dose toxicity, carcinogenicity, skin sensitisation, and reproductive toxicity for which the Directive foresees that the 2013 deadline could be further extended in case alternative and validated methods would not be available in time. The selected experts were asked to analyse the status and prospects of alternative methods and to provide a scientifically sound estimate of the time necessary to achieve full replacement of animal testing. In summary, the experts confirmed that it will take at least another 7-9 years for the replacement of the current in vivo animal tests used for the safety assessment of cosmetic ingredients for skin sensitisation. However, the experts were also of the opinion that alternative methods may be able to give hazard information, i.e. to differentiate between sensitisers and non-sensitisers, ahead of 2017. This would, however, not provide the complete picture of what is a safe exposure because the relative potency of a sensitiser would not be known. For toxicokinetics, the timeframe was 5-7 years to develop the models still lacking to predict lung absorption and renal/biliary excretion, and even longer to integrate the methods to fully replace the animal toxicokinetic models. For the systemic toxicological endpoints of repeated dose toxicity, carcinogenicity and reproductive toxicity, the time horizon for full replacement could not be estimated.

Approaches for minimizing metabolic activation of new drug candidates in drug discovery

A large body of circumstantial evidence suggests that metabolic activation of drug candidates to chemically reactive electrophilic metabolites that are capable of covalently modifying cellular macromolecules may result in acute and/or immune system-mediated idiosyncratic toxicities in humans. Thus, minimizing the potential for metabolic activation of new drug candidates during the drug discovery and lead optimization stage represents a prudent strategy to help discover and develop the next generation of safe and effective therapeutic agents. In the present chapter, we discuss the scientific methodologies that currently are available to industrial pharmaceutical scientists for assessing and minimizing metabolic activation during drug discovery, their attributes and limitations, and future scientific directions that have the potential to help advance progress in this field. We also propose a roadmap that should help utilize the armamentarium of available scientific tools in a logical way and contribute to addressing metabolic activation issues in the drug discovery-setting in a rapid, scientifically appropriate, and resource-conscious manner.

From innate to adaptive immune responses in contact hypersensitivity

PURPOSE OF REVIEW

To summarize recent findings that highlight the importance of the innate inflammatory immune responses in contact dermatitis and their role for the adaptive T-cell response to contact allergens. Implications for anti-inflammatory therapy based on recent reports are discussed.

RECENT FINDINGS

Allergic contact dermatitis is studied widely in the mouse model. Recent work has identified an important role of innate pattern recognition receptors and innate immune cells in contact hypersensitivity. The role of skin dendritic cells has been studied with novel approaches for in-vivo depletion. New findings were made in the field of anti-inflammatory therapy either by uncovering new aspects of pathomechanisms or by the use of drugs that target different elements of the inflammatory cascade.

SUMMARY

Inflammation is a pivotal element of allergic contact dermatitis. Studies in the mouse contact hypersensitivity model are beginning to shed light on the still largely unknown molecular mechanisms that enable contact allergens such as chemicals, metal ions and plant compounds to initiate the inflammatory innate immune response. This is a prerequisite for the adaptive immune response to occur. The recent progress in research points out the great potential of anti-inflammatory therapy covering a wide range of molecular targets.

Filling and mining the reactive metabolite target protein database

The post-translational modification of proteins is a well-known endogenous mechanism for regulating protein function and activity. Cellular proteins are also susceptible to post-translational modification by xenobiotic agents that possess, or whose metabolites possess, significant electrophilic character. Such non-physiological modifications to endogenous proteins are sometimes benign, but in other cases they are strongly associated with, and are presumed to cause, lethal cytotoxic consequences via necrosis and/or apoptosis. The Reactive Metabolite Target Protein Database (TPDB) is a searchable, freely web-accessible (http://tpdb.medchem.ku.edu:8080/protein_database/) resource that attempts to provide a comprehensive, up-to-date listing of known reactive metabolite target proteins. In this report we characterize the TPDB by reviewing briefly how the information it contains came to be known. We also compare its information to that provided by other types of "-omics" studies relevant to toxicology, and we illustrate how bioinformatic analysis of target proteins may help to elucidate mechanisms of cytotoxic responses to reactive metabolites.

Protein targets of reactive metabolites of thiobenzamide in rat liver in vivo

Thiobenzamide (TB) is a potent hepatotoxin in rats, causing dose-dependent hyperbilirubinemia, steatosis, and centrolobular necrosis. These effects arise subsequent to and appear to result from the covalent binding of the iminosulfinic acid metabolite of TB to cellular proteins and phosphatidylethanolamine lipids [ Ji et al. ( 2007) Chem. Res. Toxicol. 20, 701- 708 ]. To better understand the relationship between the protein covalent binding and the toxicity of TB, we investigated the chemistry of the adduction process and the identity of the target proteins. Cytosolic and microsomal proteins isolated from the livers of rats treated with a hepatotoxic dose of [ carboxyl- (14)C]TB contained high levels of covalently bound radioactivity (25.6 and 36.8 nmol equiv/mg protein, respectively). These proteins were fractionated by two-dimensional gel electrophoresis, and radioactive spots (154 cytosolic and 118 microsomal) were located by phosphorimaging. Corresponding spots from animals treated with a 1:1 mixture of TB and TB- d 5 were similarly separated, the spots were excised, and the proteins were digested in gel with trypsin. Peptide mass mapping identified 42 cytosolic and 24 microsomal proteins, many of which appeared in more than one spot on the gel; however, only a few spots contained more than one identifiable protein. Eighty-six peptides carrying either a benzoyl or a benzimidoyl adduct on a lysine side chain were clearly recognized by their d 0/ d 5 isotopic signature (sometimes both in the same digest). Because model studies showed that benzoyl adducts do not arise by hydrolysis of benzimidoyl adducts, it was proposed that TB undergoes S-oxidation twice to form iminosulfinic acid 4 [PhC(NH)SO 2H], which either benzimidoylates a lysine side chain or undergoes hydrolysis to 9 [PhC(O)SO 2H] and then benzoylates a lysine side chain. The proteins modified by TB metabolites serve a range of biological functions and form a set that overlaps partly with the sets of proteins known to be modified by several other metabolically activated hepatotoxins. The relationship of the adduction of these target proteins to the cytotoxicity of reactive metabolites is discussed in terms of three currently popular mechanisms of toxicity: inhibition of enzymes important to the maintenance of cellular energy and homeostasis, the unfolded protein response, and interference with kinase-based signaling pathways that affect cell survival.

Determination of cellular redox status by stable isotope dilution liquid chromatography/mass spectrometry analysis of glutathione and glutathione disulfide

Oxidation of glutathione (GSH) to glutathione disulfide (GSSG) occurs during cellular oxidative stress. The redox potential of the 2GSH/GSSG couple, which is determined by the Nernst equation, provides a means to assess cellular redox status. It is difficult to accurately quantify GSH and GSSG due to the ease with which GSH is oxidized to GSSG during sample preparation. To overcome this problem, a stable isotope dilution liquid chromatography/multiple reaction monitoring mass spectrometry (LC/MRM-MS) method has been developed using 4-fluoro-7-sulfamoylbenzofurazan (ABD-F) derivatization. ABD-F derivatization of the GSH thiol group was rapid, quantitative, and occurred at room temperature. The LC/MRM-MS method, which requires no sample clean-up, was validated within the calibration ranges of 5 to 400 nmol/mL in cell lysates for GSH and 0.5 to 40 nmol/mL in cell lysates for GSSG. Calibration curves prepared by adding known concentrations of GSH and GSSG to cell lysates were parallel to the standard curve prepared in buffers. GSH and GSSG concentrations were determined in two monocyte/macrophage RAW 267.4 cell lines with or without 15-LOX-1 expression (R15LO and RMock cells, respectively) after treatment with the bifunctional electrophile 4-oxo-2(E)-nonenal (ONE). R15LO cells synthesized much higher concentrations of the lipid hydroperoxide, 15(S)-hydroperoxyeicosatetraenoic acid (15-HPETE), which undergoes homolytic decomposition to ONE. GSH was depleted by ONE treatment in both RMock and R15LO cells, leading to significant increases in their redox potentials. However, R15LO cells had higher GSH concentrations (most likely through increased GSH biosynthesis) and had increased resistance to ONE-mediated GSH depletion than RMock cells. Consequently, R15LO cells had lower reduction potentials at all concentrations of ONE. GSSG concentrations were higher in R15LO cells after ONE treatment when compared with the ONE-treated RMock cells. This suggests that increased expression of 15(S)-HPETE modulates the activity of cellular GSH reductases or the transporters involved in removal of GSSG.

Determining protein adducts of fipexide: mass spectrometry based assay for confirming the involvement of its reactive metabolite in covalent binding

Fipexide is a nootropic drug, withdrawn from the market due to its idiosyncratic drug reactions causing adverse effects in man. Previous work on its metabolites has identified several potential reactive metabolites which could be implicated in protein binding. Here, we investigated the formation of these metabolites in rat and human hepatocytes. Based on these results, the o-quinone of fipexide (FIP), formed via the demethylenation reaction through a catechol intermediate, was chosen for further investigation. Studies were then pursued in order to relate this metabolite to protein binding, and thus better understand potential mechanisms for the toxicity of the parent compound. An assay was developed for determining the fipexide catechol-cysteine adduct in the microsomal protein fractions following in vitro incubations. This method digests the entire protein fraction into amino acids, followed by the detection of the Cys-metabolite adduct by liquid chromatography/mass spectrometry (LC/MS). We have designed a strategy where drug metabolism taking place in microsomal incubations and involved in protein binding can be assessed after the proteins have been digested, with the detection of the specific amino acid adduct. In this study, the structure of the fipexide adduct was hypothesized using knowledge previously gained in glutathione and N-acetylcysteine trapping experiments. Acetaminophen was used as a positive control for detecting a drug metabolite-cysteine adduct by LC/MS. This approach has the potential to be applicable as a protein-binding assay in early drug discovery without the need for radioactive compounds.