Defining the mechanism of galectin-3-mediated TGF-β1 activation and its role in lung fibrosis

Integrin-mediated activation of the pro-fibrotic mediator transforming growth factor-β1 (TGF-β1), plays a critical role in idiopathic pulmonary fibrosis (IPF) pathogenesis. Galectin-3 is believed to contribute to the pathological wound healing seen in IPF, although its mechanism of action is not precisely defined. We hypothesised that galectin-3 potentiates TGF-β1 activation and/or signaling in the lung to promote fibrogenesis. We show that galectin-3 induces TGF-β1 activation in human lung fibroblasts (HLFs) and specifically that extracellular galectin-3 promotes oleoyl-L-α-lysophosphatidic acid sodium salt (LPA)-induced integrin-mediated TGF-β1 activation. Surface plasmon resonance (SPR) analysis confirmed that galectin-3 binds to αv integrins, αvβ1, αvβ5 and αvβ6 and to the TGFβRII subunit in a glycosylation-dependent manner. This binding is heterogeneous and not a 1:1 binding stoichiometry. Binding interactions were blocked by small molecule inhibitors of galectin-3 which target the carbohydrate recognition domain. Galectin-3 binding to β1 integrin was validated in vitro by co-immunoprecipitation in HLFs. Proximity ligation assays indicated galectin-3 and β1 integrin colocalize closely (≤40 nm) on the cell surface, that colocalization is increased by TGF-β1 treatment and blocked by galectin-3 inhibitors. In the absence of TGF-β1 stimulation, colocalization was detectable only in HLFs from IPF patients suggesting the proteins are inherently more closely associated in the disease state. Galectin-3 inhibitor treatment of precision cut lung slices from IPF patients reduced Col1a1, TIMP1 and HA secretion to a similar degree as TGF-β type I receptor inhibitor. These data suggest galectin-3 promotes TGF-β1 signaling and may induce fibrogenesis by interacting directly with components of the TGF-β1 signaling cascade.

Discovery of Selective and Orally Available Galectin-1 Inhibitors

A new series of orally available α-d-galactopyranosides with high affinity and specificity toward galectin-1 have been discovered. High affinity and specificity were achieved by changing six-membered aryl-triazolyl substituents in a series of recently published galectin-3-selective α-d-thiogalactosides (e.g., GB1107 Kd galectin-1/3 3.7/0.037 μM) for five-membered heterocycles such as thiazoles. The in vitro pharmacokinetic properties were optimized, resulting in several galectin-1 inhibitors with favorable properties. One compound, GB1490 (Kd galectin-1/3 0.4/2.7 μM), was selected for further characterization toward a panel of galectins showing a selectivity of 6- to 320-fold dependent on galectin. The X-ray structure of GB1490 bound to galectin-1 reveals the compound bound in a single conformation in the carbohydrate binding site. GB1490 was shown to reverse galectin-1-induced apoptosis of Jurkat cells at low μM concentrations. No cell cytotoxicity was observed for GB1490 up to 90 μM in the A549 cells. In pharmacokinetic studies in mice, GB1490 showed high oral bioavailability (F% > 99%).

Resistance to anti-PD-1/anti-PD-L1: galectin-3 inhibition with GB1211 reverses galectin-3-induced blockade of pembrolizumab and atezolizumab binding to PD-1/PD-L1

Background

Galectin-3 (Gal-3) is a β-galactoside-binding lectin that is highly expressed within the tumor microenvironment of aggressive cancers and has been suggested to predict a poor response to immune checkpoint therapy with the anti-PD-1 monoclonal antibody pembrolizumab. We aimed to assess if the effect of Gal-3 was a result of direct interaction with the immune checkpoint receptor.

Methods

The ability of Gal-3 to interact with the PD-1/PD-L1 complex in the absence and presence of blocking antibodies was assessed in in vitro biochemical and cellular assays as well as in an in vivo syngeneic mouse cancer model.

Results

Gal-3 reduced the binding of the checkpoint inhibitors pembrolizumab (anti-PD-1) and atezolizumab (anti-PD-L1), by potentiating the interaction between the PD-1/PD-L1 complex. In the presence of a highly selective Gal-3 small molecule inhibitor (GB1211) the binding of the anti-PD-1/anti-PD-L1 therapeutics was restored to control levels. This was observed in both a surface plasmon resonance assay measuring protein-protein interactions and via flow cytometry. Combination therapy with GB1211 and an anti-PD-L1 blocking antibody reduced tumor growth in an in vivo syngeneic model and increased the percentage of tumor infiltrating T lymphocytes.

Conclusion

Our study suggests that Gal-3 can potentiate the PD-1/PD-L1 immune axis and potentially contribute to the immunosuppressive signalling mechanisms within the tumor microenvironment. In addition, Gal-3 prevents atezolizumab and pembrolizumab target engagement with their respective immune checkpoint receptors. Reversal of this effect with the clinical candidate GB1211 offers a potential enhancing combination therapeutic with anti-PD-1 and -PD-L1 blocking antibodies.

Evaluating the affinity and kinetics of small molecule glycomimetics for human and mouse galectin-3 using surface plasmon resonance

Galectin-3 is a beta-galactoside-binding mammalian lectin that is one of a 15-member galectin family that can bind several cell surface glycoproteins via its carbohydrate recognition domain (CRD). As a result, it can influence a range of cellular processes including cell activation, adhesion and apoptosis. Galectin-3 has been implicated in various diseases, including fibrotic disorders and cancer, and is now being therapeutically targeted by both small and large molecules. Historically, the screening and triaging of small molecule glycomimetics that bind to the galectin-3 CRD has been completed in fluorescence polarisation (FP) assays to determine KD values. Surface plasmon resonance (SPR) has not been widely used for compound screening and in this study it was used to compare human and mouse galectin-3 affinity measures between FP and SPR, as well as investigate compound kinetics. The KD estimates for a set of compounds selected from mono- and di-saccharides with affinities across a 550-fold range, correlated well between FP and SPR assay formats for both human and mouse galectin-3. Increases in affinity for compounds binding to human galectin-3 were driven by changes in both kon and koff whilst for mouse galectin-3 this was primarily due to kon. The reduction in affinity observed between human to mouse galectin-3 was also comparable between assay formats. SPR has been shown to be a viable alternative to FP for early drug discovery screening and determining KD values. In addition, it can also provide early kinetic characterisation of small molecule galectin-3 glycomimetics with robust kon and koff values generated in a high throughput manner.

Galectin-3: therapeutic targeting in liver disease

INTRODUCTION

The rising incidence of liver diseases is a worldwide healthcare concern. However, the therapeutic options to manage chronic inflammation and fibrosis, the processes at the basis of morbidity and mortality of liver diseases, are very limited. Galectin 3 (Gal-3) is a protein implicated in fibrosis in multiple organs. Several Gal-3 inhibitors are currently in clinical development.

AREAS COVERED

This review describes our current understanding of the role of Gal-3 in chronic liver diseases, with special emphasis on fibrosis. Also, we review therapeutic advances based on Gal-3 inhibition, describing drug properties and their current status in clinical research.

EXPERT OPINION

Currently, the known effects of Gal-3 point to a direct activation of the NLRP3 inflammasome leading to its activation in liver macrophages and activated macrophages play a key role in tissue fibrogenesis. However, more research is needed to elucidate the role of Gal-3 in the different activation pathways, dissecting the intracellular and extracellular mechanisms of Gal-3, and its role in pathogenesis. Gal-3 could be a target for early therapy of numerous hepatic diseases and, given the lack of therapeutic options for liver fibrosis, there is a strong pharmacologic potential for Gal-3-based therapies.

Safety and pharmacokinetics of GB1211, an oral galectin-3 inhibitor: a single- and multiple-dose first-in-human study in healthy participants

PURPOSE

Galectin-3, a β-galactoside-binding lectin, plays a key role in several cellular pathways involved in chronic inflammation, heart disease and cancer. GB1211 is an orally bioavailable galectin-3 inhibitor, developed to be systemically active. We report safety and pharmacokinetics (PK) of GB1211 in healthy participants.

METHODS

This phase 1, double-blind, placebo-controlled, first-in-human study (NCT03809052) included a single ascending-dose phase (with a food-effect cohort) where participants across seven sequential cohorts were randomized 3:1 to receive oral GB1211 (5, 20, 50, 100, 200 or 400 mg) or placebo. In the multiple ascending-dose phase, participants received 50 or 100 mg GB1211 or placebo twice daily for 10 days. All doses were administered in the fasted state except in the food-effect cohort where doses were given 30 min after a high-fat meal.

RESULTS

All 78 participants received at least one GB1211 dose (n = 58) or placebo (n = 20) and completed the study. No safety concerns were identified. Following single and multiple oral doses under fasted conditions, maximum GB1211 plasma concentrations were reached at 1.75-4 h (median) post-dose; mean half-life was 11-16 h. There was a ~ twofold GB1211 accumulation in plasma with multiple dosing, with steady-state reached within 3 days; 30% of the administered dose was excreted in urine as unchanged drug. Absorption in the fed state was delayed by 2 h but systemic exposure was unaffected.

CONCLUSION

GB1211 was well tolerated, rapidly absorbed, and displayed favorable PK, indicating a potential to treat multiple disease types. These findings support further clinical development of GB1211.

CLINICAL TRIAL REGISTRATION

The study was registered with ClinicalTrials.gov (identifier: NCT03809052).

An Inhaled Galectin-3 Inhibitor in COVID-19 Pneumonitis: A Phase Ib/IIa Randomized Controlled Clinical Trial (DEFINE)

Rationale: High circulating galectin-3 is associated with poor outcomes in patients with coronavirus disease (COVID-19). We hypothesized that GB0139, a potent inhaled thiodigalactoside galectin-3 inhibitor with antiinflammatory and antifibrotic actions, would be safely and effectively delivered in COVID-19 pneumonitis. Objectives: Primary outcomes were safety and tolerability of inhaled GB0139 as an add-on therapy for patients hospitalized with COVID-19 pneumonitis. Methods: We present the findings of two arms of a phase Ib/IIa randomized controlled platform trial in hospitalized patients with confirmed COVID-19 pneumonitis. Patients received standard of care (SoC) or SoC plus 10 mg inhaled GB0139 twice daily for 48 hours, then once daily for up to 14 days or discharge. Measurements and Main Results: Data are reported from 41 patients, 20 of which were assigned randomly to receive GB0139. Primary outcomes: the GB0139 group experienced no treatment-related serious adverse events. Incidences of adverse events were similar between treatment arms (40 with GB0139 + SoC vs. 35 with SoC). Secondary outcomes: plasma GB0139 was measurable in all patients after inhaled exposure and demonstrated target engagement with decreased circulating galectin (overall treatment effect post-hoc analysis of covariance [ANCOVA] over days 2-7; P = 0.0099 vs. SoC). Plasma biomarkers associated with inflammation, fibrosis, coagulopathy, and major organ function were evaluated. Conclusions: In COVID-19 pneumonitis, inhaled GB0139 was well-tolerated and achieved clinically relevant plasma concentrations with target engagement. The data support larger clinical trials to determine clinical efficacy. Clinical trial registered with ClinicalTrials.gov (NCT04473053) and EudraCT (2020-002230-32).

Discovery and Optimization of the First Highly Effective and Orally Available Galectin-3 Inhibitors for Treatment of Fibrotic Disease

Galectin-3 is a carbohydrate-binding protein central to regulating mechanisms of diseases such as fibrosis, cancer, metabolic, inflammatory, and heart disease. We recently found a high affinity (nM) thiodigalactoside GB0139 which currently is in clinical development (PhIIb) as an inhaled treatment of idiopathic pulmonary fibrosis. To enable treatment of systemically galectin-3 driven disease, we here present the first series of selective galectin-3 inhibitors combining high affinity (nM) with oral bioavailability. This was achieved by optimizing galectin-3 specificity and physical chemical parameters for a series of disubstituted monogalactosides. Further characterization showed that this class of compounds reduced profibrotic gene expression in liver myofibroblasts and displayed antifibrotic activity in CCl₄-induced liver fibrosis and bleomycin-induced lung fibrosis mouse models. On the basis of the overall pharmacokinetic, pharmacodynamic, and safety profile, GB1211 was selected as the clinical candidate and is currently in phase IIa clinical trials as a potential therapy for liver cirrhosis and cancer.

Galectin-3 inhibitor GB0139 protects against acute lung injury by inhibiting neutrophil recruitment and activation

Rationale: Galectin-3 (Gal-3) drives fibrosis during chronic lung injury, however, its role in acute lung injury (ALI) remains unknown. Effective pharmacological therapies available for ALI are limited; identifying novel concepts in treatment is essential. GB0139 is a Gal-3 inhibitor currently under clinical investigation for the treatment of idiopathic pulmonary fibrosis. We investigate the role of Gal-3 in ALI and evaluate whether its inhibition with GB0139 offers a protective role. The effect of GB0139 on ALI was explored in vivo and in vitro.

Methods: The pharmacokinetic profile of intra-tracheal (i.t.) GB0139 was investigated in C57BL/6 mice to support the daily dosing regimen. GB0139 (1–30 µg) was then assessed following acute i.t. lipopolysaccharide (LPS) and bleomycin administration. Histology, broncho-alveolar lavage fluid (BALf) analysis, and flow cytometric analysis of lung digests and BALf were performed. The impact of GB0139 on cell activation and apoptosis was determined in vitro using neutrophils and THP-1, A549 and Jurkat E6 cell lines.

Results: GB0139 decreased inflammation severity via a reduction in neutrophil and macrophage recruitment and neutrophil activation. GB0139 reduced LPS-mediated increases in interleukin (IL)-6, tumor necrosis factor alpha (TNFα) and macrophage inflammatory protein-1-alpha. In vitro, GB0139 inhibited Gal-3-induced neutrophil activation, monocyte IL-8 secretion, T cell apoptosis and the upregulation of pro-inflammatory genes encoding for IL-8, TNFα, IL-6 in alveolar epithelial cells in response to mechanical stretch.

Conclusion: These data indicate that Gal-3 adopts a pro-inflammatory role following the early stages of lung injury and supports the development of GB0139, as a potential treatment approach in ALI.

Pharmacological characterisation of GSK3335103, an oral αvβ6 integrin small molecule RGD-mimetic inhibitor for the treatment of fibrotic disease

Fibrosis is the formation of scar tissue due to injury or long-term inflammation and is a leading cause of morbidity and mortality. Activation of the pro-fibrotic cytokine transforming growth factor-β (TGFβ) via the alpha-V beta-6 (αvβ6) integrin has been identified as playing a key role in the development of fibrosis. Therefore, a drug discovery programme to identify an orally bioavailable small molecule αvβ6 arginyl-glycinyl-aspartic acid (RGD)-mimetic was initiated. As part of a medicinal chemistry programme GSK3335103 was identified and profiled in a range of pre-clinical in vitro and in vivo systems. GSK3335103 was shown to bind to the αvβ6 with high affinity and demonstrated fast binding kinetics. In primary human lung epithelial cells, GSK3335103-induced concentration- and time-dependent internalisation of αvβ6 with a rapid return of integrin to the cell surface observed after washout. Following sustained engagement of the αvβ6 integrin in vitro, lysosomal degradation was induced by GSK3335103. GSK3335103 was shown to engage with the αvβ6 integrin and inhibit the activation of TGFβ in both ex vivo IPF tissue and in a murine model of bleomycin-induced lung fibrosis, as measured by αvβ6 engagement, TGFβ signalling and collagen deposition, with a prolonged duration of action observed in vivo. In summary, GSK3335103 is a potent αvβ6 inhibitor that attenuates TGFβ signalling in vitro and in vivo with a well-defined pharmacokinetic/pharmacodynamic relationship. This translates to a significant reduction of collagen deposition in vivo and therefore GSK3335103 represents a potential novel oral therapy for fibrotic disorders.

Emerging therapeutic opportunities for integrin inhibitors

Integrins are cell adhesion and signalling proteins crucial to a wide range of biological functions. Effective marketed treatments have successfully targeted integrins αIIbβ3, α4β7/α4β1 and αLβ2 for cardiovascular diseases, inflammatory bowel disease/multiple sclerosis and dry eye disease, respectively. Yet, clinical development of others, notably within the RGD-binding subfamily of αv integrins, including αvβ3, have faced significant challenges in the fields of cancer, ophthalmology and osteoporosis. New inhibitors of the related integrins αvβ6 and αvβ1 have recently come to the fore and are being investigated clinically for the treatment of fibrotic diseases, including idiopathic pulmonary fibrosis and nonalcoholic steatohepatitis. The design of integrin drugs may now be at a turning point, with opportunities to learn from previous clinical trials, to explore new modalities and to incorporate new findings in pharmacological and structural biology. This Review intertwines research from biological, clinical and medicinal chemistry disciplines to discuss historical and current RGD-binding integrin drug discovery, with an emphasis on small-molecule inhibitors of the αv integrins.

Integrins are key signalling molecules that are present on the surface of subsets of cells and are therefore good potential therapeutic targets. In this Review, Hatley and colleagues discuss the development of integrin inhibitors, particularly the challenges in developing inhibitors for integrins that contain an αv-subunit, and suggest how these challenges could be addressed.

Target inhibition of galectin-3 by inhaled TD139 in patients with idiopathic pulmonary fibrosis

Galectin (Gal)-3 is a profibrotic β-galactoside-binding lectin that plays a key role in the pathogenesis of idiopathic pulmonary fibrosis (IPF) and IPF exacerbations. TD139 is a novel and potent small-molecule inhibitor of Gal-3.

A randomised, double-blind, multicentre, placebo-controlled, phase 1/2a study was conducted to assess the safety, tolerability, pharmacokinetics and pharmacodynamics of inhaled TD139 in 36 healthy subjects and 24 patients with IPF. Six dose cohorts of six healthy subjects were evaluated (4:2 TD139:placebo ratio) with single doses of TD139 (0.15–50 mg) and three dose cohorts of eight patients with IPF (5:3 TD139:placebo ratio) with once-daily doses of TD139 (0.3–10 mg) for 14 days.

Inhaled TD139 was well tolerated with no significant treatment-related side-effects. TD139 was rapidly absorbed, with mean time taken to reach maximum plasma concentration (C_max) values ranging from 0.6 to 3 h and a plasma half-life (T_1/2) of 8 h. The concentration of TD139 in the lung was >567-fold higher than in the blood, with systemic exposure predicting exposure in the target compartment. Gal-3 expression on alveolar macrophages was reduced in the 3 and 10 mg dose groups compared with placebo, with a concentration-dependent inhibition demonstrated. Inhibition of Gal-3 expression in the lung was associated with reductions in plasma biomarkers centrally relevant to IPF pathobiology (platelet-derived growth factor-BB, plasminogen activator inhibitor-1, Gal-3, CCL18 and YKL-40).

TD139 is safe and well tolerated in healthy subjects and IPF patients. It was shown to suppress Gal-3 expression on bronchoalveolar lavage macrophages and, in a concerted fashion, decrease plasma biomarkers associated with IPF progression.

TD139 is a potent inhibitor of galectin-3, a key driver of fibrosis in the lung. In this phase 1/2a clinical study, inhaled TD139 was safe, well tolerated, and demonstrated target engagement and decreased plasma biomarkers associated with IPF progression.https://bit.ly/2JREKx6

Downregulation of the αvβ6 Integrin via RGD Engagement Is Affinity and Time Dependent

The arginyl-glycinyl-aspartic acid (RGD) integrin alpha-v beta-6 (αvβ6) has been identified as playing a key role in the activation of transforming growth factor-β (TGFβ) that is hypothesized to be pivotal in the development of fibrosis and other diseases. In this study, αvβ6 small molecule inhibitors were characterized in a range of in vitro systems to determine affinity, kinetics, and duration of TGFβ inhibition. High αvβ6 binding affinity was shown to be correlated with slow dissociation kinetics. Compound 1 (high αvβ6 affinity, slow dissociation) and SC-68448 (low αvβ6 affinity, fast dissociation) induced concentration- and time-dependent internalization of αvβ6 in normal human bronchial epithelial (NHBE) cells. After washout, the αvβ6 cell surface repopulation was faster for SC-68448 compared with compound 1 In addition, αvβ6-dependent release of active TGFβ from NHBE cells was inhibited by compound 1 and SC-68448. After washout of SC-68448, release of active TGFβ was restored, whereas after washout of compound 1 the inhibition of TGFβ activation was maintained and only reversible in the presence of a lysosomal inhibitor (chloroquine). However, SC-68448 was able to reduce total levels of αvβ6 in NHBE cells if present continuously. These observations suggest αvβ6 can be degraded after high affinity RGD binding that sorts the integrin for lysosomal degradation after internalization, likely due to sustained engagement as a result of slow dissociation kinetics. In addition, the αvβ6 integrin can also be downregulated after sustained engagement of the RGD binding site with low affinity ligands that do not sort the integrin for immediate lysosomal degradation. SIGNIFICANCE STATEMENT: The fate of RGD integrin after ligand binding has not been widely investigated. Using the αvβ6 integrin as a case study, we have demonstrated that RGD-induced downregulation of αvβ6 is both affinity and time dependent. High affinity ligands induced downregulation via lysosomal degradation, likely due to slow dissociation, whereas sustained low affinity ligand engagement was only able to decrease αvβ6 expression over longer periods of time. Our study provides a potential unique mechanism for obtaining duration of action for drugs targeting integrins.

Translational pharmacology of an inhaled small molecule αvβ6 integrin inhibitor for idiopathic pulmonary fibrosis

The αvβ6 integrin plays a key role in the activation of transforming growth factor-β (TGFβ), a pro-fibrotic mediator that is pivotal to the development of idiopathic pulmonary fibrosis (IPF). We identified a selective small molecule αvβ6 RGD-mimetic, GSK3008348, and profiled it in a range of disease relevant pre-clinical systems. To understand the relationship between target engagement and inhibition of fibrosis, we measured pharmacodynamic and disease-related end points. Here, we report, GSK3008348 binds to αvβ6 with high affinity in human IPF lung and reduces downstream pro-fibrotic TGFβ signaling to normal levels. In human lung epithelial cells, GSK3008348 induces rapid internalization and lysosomal degradation of the αvβ6 integrin. In the murine bleomycin-induced lung fibrosis model, GSK3008348 engages αvβ6, induces prolonged inhibition of TGFβ signaling and reduces lung collagen deposition and serum C3M, a marker of IPF disease progression. These studies highlight the potential of inhaled GSK3008348 as an anti-fibrotic therapy.

The αvβ6 integrin is key in activating the pro-fibrotic cytokine TGFβ in idiopathic pulmonary fibrosis. Here, the authors show an inhaled small molecule αvβ6 inhibitor GSK3008348 induces prolonged inhibition of TGFβ signaling pathways in human and murine models of lung fibrosis via αvβ6 degradation.

A positron emission tomography imaging study to confirm target engagement in the lungs of patients with idiopathic pulmonary fibrosis following a single dose of a novel inhaled αvβ6 integrin inhibitor

Background

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive lung disease with poor prognosis and a significant unmet medical need. This study evaluated the safety, pharmacokinetics (PK) and target engagement in the lungs, of GSK3008348, a novel inhaled alpha-v beta-6 (αvβ6) integrin inhibitor, in participants with IPF.

Methods

This was a phase 1b, randomised, double-blind (sponsor unblind) study, conducted in the UK (two clinical sites, one imaging unit) between June 2017 and July 2018 (NCT03069989). Participants with a definite or probable diagnosis of IPF received a single nebulised dose of 1000 mcg GSK3008348 or placebo (ratio 5:2) in two dosing periods. In period 1, safety and PK assessments were performed up to 24 h post-dose; in period 2, after a 7-day to 28-day washout, participants underwent a total of three positron emission tomography (PET) scans: baseline, Day 1 (~ 30 min post-dosing) and Day 2 (~ 24 h post-dosing), using a radiolabelled αvβ6-specific ligand, [¹⁸F]FB-A20FMDV2. The primary endpoint was whole lung volume of distribution (V_T), not corrected for air volume, at ~ 30 min post-dose compared with pre-dose. The study success criterion, determined using Bayesian analysis, was a posterior probability (true % reduction in V_T > 0%) of ≥80%.

Results

Eight participants with IPF were enrolled and seven completed the study. Adjusted posterior median reduction in uncorrected V_T at ~ 30 min after GSK3008348 inhalation was 20% (95% CrI: − 9 to 42%). The posterior probability that the true % reduction in V_T > 0% was 93%. GSK3008348 was well tolerated with no reports of serious adverse events or clinically significant abnormalities that were attributable to study treatment. PK was successfully characterised showing rapid absorption followed by a multiphasic elimination.

Conclusions

This study demonstrated engagement of the αvβ6 integrin target in the lung following nebulised dosing with GSK3008348 to participants with IPF. To the best of our knowledge this is the first time a target-specific PET radioligand has been used to assess target engagement in the lung, not least for an inhaled drug.

Trial registration

clinicaltrials.gov: NCT03069989; date of registration: 3 March 2017.

Preclinical evaluation of [18F]FB-A20FMDV2 as a selective marker for measuring αVβ6 integrin occupancy using positron emission tomography in rodent lung

Purpose

Integrin α_vβ₆ belongs to the RGD subset of the integrin family, and its expression levels are a prognostic and theranostic factor in some types of cancer and pulmonary fibrosis. This paper describes the GMP radiolabelling of the synthetic 20 amino acid peptide A20FMDV2 (NAVPNLRGDLQVLAQKVART), derived from the foot-and-mouth disease virus, and characterises the use of [¹⁸F]FB-A20FMDV2 as a high affinity, specific and selective PET radioligand for the quantitation and visualisation of α_vβ₆ in rodent lung to support human translational studies.

Methods

The synthesis of [¹⁸F]FB-A20FMDV2 was performed using a fully automated and GMP-compliant process. Sprague-Dawley rats were used to perform homologous (unlabelled FB-A20FMDV2) and heterologous (anti-α_vβ₆ antibody 8G6) blocking studies. In order to generate a dosimetry estimate, tissue residence times were generated, and associated tissue exposure and effective dose were calculated using the Organ Level Internal Dose Assessment/Exponential Modelling (OLINDA/EXM) software.

Results

[¹⁸F]FB-A20FMDV2 synthesis was accomplished in 180 min providing ~800 MBq of [¹⁸F]FB-A20FMDV2 with a molar activity of up to 150 GBq/μmol and high radiochemical purity (> 97%). Following i.v. administration to rats, [¹⁸F]FB-A20FMDV2 was rapidly metabolised with intact radiotracer representing 5% of the total radioactivity present in rat plasma at 30 min. For the homologous and heterologous block in rats, lung-to-heart SUV ratios at 30–60 min post-administration of [¹⁸F]FB-A20FMDV2 were reduced by 38.9 ± 6.9% and 56 ± 19.2% for homologous and heterologous block, respectively. Rodent biodistribution and dosimetry calculations using OLINDA/EXM provided a whole body effective dose in humans 33.5 μSv/MBq.

Conclusion

[¹⁸F]FB-A20FMDV2 represents a specific and selective PET ligand to measure drug-associated αvβ6 integrin occupancy in lung. The effective dose, extrapolated from rodent data, is in line with typical values for compounds labelled with fluorine-18 and combined with the novel fully automated and GMP-compliant synthesis and allows for clinical use in translational studies.

Electronic supplementary material

The online version of this article (10.1007/s00259-019-04653-5) contains supplementary material, which is available to authorized users.

The Design of Potent, Selective and Drug-Like RGD αvβ1 Small-Molecule Inhibitors Derived from non-RGD α4β1 Antagonists

Up to 45 % of deaths in developed nations can be attributed to chronic fibroproliferative diseases, highlighting the need for effective therapies. The RGD (Arg-Gly-Asp) integrin αvβ1 was recently investigated for its role in fibrotic disease, and thus warrants therapeutic targeting. Herein we describe the identification of non-RGD hit small-molecule αvβ1 inhibitors. We show that αvβ1 activity is embedded in a range of published α4β1 (VLA-4) ligands; we also demonstrate how a non-RGD integrin inhibitor (of α4β1 in this case) was converted into a potent non-zwitterionic RGD integrin inhibitor (of αvβ1 in this case). We designed urea ligands with excellent selectivity over α4β1 and the other αv integrins (αvβ3, αvβ5, αvβ6, αvβ8). In silico docking models and density functional theory (DFT) calculations aided the discovery of the lead urea series.

The effect of divalent metal cations on the αv integrin binding site is ligand and integrin specific

The binding of orthosteric ligands to integrins requires the presence of divalent metal cations bound to metal ion-binding sites located in the I domains of the integrin α and β subunits. In this study the influence of the type and concentration of divalent metal cation present was investigated on a single arginyl-glycinyl-aspartic acid (RGD) ligand across the αv integrin sub-family and single αv integrin (αvβ6) with different ligands. These relationships were determined using radioligand binding studies completed with [³H] ligands and purified αv integrin protein preparations. The binding of [³H]compound 1 to the RGD site on individual αv integrins demonstrated a unique profile in relation to the type and concentration of divalent metal cation present. The use of physiological concentrations of Mg²⁺ and Ca²⁺ in simulated lung fluid altered the αv integrin selectivity profile of [³H]compound 1 in terms of affinity and the level of receptor occupancy. In addition, different RGD ligands for the αvβ6 integrin behaved differently under the same divalent metal cation conditions. In conclusion, this study demonstrates the need to determine the individual relationship between RGD ligands and the integrins they may engage in vivo, especially when determining selectivity profiles for potential RGD-mimetic small molecule therapeutics, with organ and disease state also considered.

Discovery of ( S)-3-(3-(3,5-Dimethyl-1 H-pyrazol-1-yl)phenyl)-4-(( R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic Acid, a Nonpeptidic αvβ6 Integrin Inhibitor for the Inhaled Treatment of Idiopathic Pulmonary Fibrosis

A series of 3-aryl(pyrrolidin-1-yl)butanoic acids were synthesized using a diastereoselective route, via a rhodium catalyzed asymmetric 1,4-addition of arylboronic acids in the presence of ( R)-BINAP to a crotonate ester to provide the ( S) absolute configuration for the major product. A variety of aryl substituents including morpholine, pyrazole, triazole, imidazole, and cyclic ether were screened in cell adhesion assays for affinity against α_vβ₁, α_vβ₃, α_vβ₅, α_vβ₆, and α_vβ₈ integrins. Numerous analogs with high affinity and selectivity for the α_vβ₆ integrin were identified. The analog ( S)-3-(3-(3,5-dimethyl-1 H-pyrazol-1-yl)phenyl)-4-(( R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid hydrochloride salt was found to have very high affinity for α_vβ₆ integrin in a radioligand binding assay (p K_i = 11), a long dissociation half-life (7 h), very high solubility in saline at pH 7 (>71 mg/mL), and pharmacokinetic properties commensurate with inhaled dosing by nebulization. It was selected for further clinical investigation as a potential therapeutic agent for the treatment of idiopathic pulmonary fibrosis.

Design of Phthalazinone Amide Histamine H1 Receptor Antagonists for Use in Rhinitis

The synthesis of potent amide-containing phthalazinone H₁ histamine receptor antagonists is described. Three analogues 3e, 3g, and 9g were equipotent with azelastine and were longer-acting in vitro. Amide 3g had low oral bioavailability, low brain-penetration, high metabolic clearance, and long duration of action in vivo, and it was suitable for once-daily dosing intranasally, with a predicted dose for humans of approximately 0.5 mg per day.

Determining the True Selectivity Profile of αv Integrin Ligands Using Radioligand Binding: Applying an Old Solution to a New Problem

The arginyl-glycinyl-aspartic acid (RGD) integrin subfamily contains five members that partner with the αv subunit: αvβ1, αvβ3, αvβ5, αvβ6, and αvβ8. Within the αv integrins, the epithelially restricted αvβ6 has been identified as playing a key role in the activation of transforming growth factor β that is hypothesized to be pivotal in the development of idiopathic pulmonary fibrosis (IPF). As part of a drug discovery program to identify a selective αvβ6 RGD mimetic for IPF, cell adhesion and radioligand binding assays were investigated to screen compounds to determine affinity and αv integrin selectivity. In this study, a pan-αv radioligand was characterized against all the αv integrins and used to determine accurate selectivity profiles for literature and novel RGD ligands, as well as enable an early readout on αvβ6 dissociation kinetics. It has been shown that while cell adhesion offers a high throughput and reliable format for ranking compounds, there are downsides to this format when comparing selectivity across αv integrins. By accurately defining the relationship between these assay formats, a medicinal chemistry effort has identified novel, high-affinity, and selective αvβ6 RGD mimetics with slow dissociation kinetics, with the potential to be developed into clinical candidates for IPF.

Characterisation of a novel, high affinity and selective αvβ6 integrin RGD-mimetic radioligand

The alpha-v beta-6 (αvβ6) integrin has been identified as playing a key role in the activation of transforming growth factor-β (TGFβ) that is hypothesised to be pivotal in the development of cancer and fibrotic diseases. Therefore, the αvβ6 integrin is an attractive therapeutic target for these debilitating diseases and a drug discovery programme to identify small molecule αvβ6 selective arginyl-glycinyl-aspartic acid (RGD)-mimetics was initiated within GlaxoSmithKline. The primary aim of this study was to pharmacologically characterise the binding to αvβ6 of a novel clinical candidate, compound 1, using a radiolabelled form. Radioligand binding studies were completed with [(3)H]compound 1 against the human and mouse soluble protein forms of αvβ6 to determine accurate affinity estimates and binding kinetics. The selectivity of compound 1 for the RGD integrin family was also determined using saturation binding studies (αvβ1, αvβ3, αvβ5, αvβ8, α5β1 and α8β1 integrins) and fibrinogen-induced platelet aggregation (αIIbβ3 integrin). In addition, the relationship between divalent metal cation type and concentration and αvβ6 RGD site binding was also investigated. Compound 1 has been demonstrated to bind with extremely high affinity and selectivity for the αvβ6 integrin and has the potential as a clinical tool and therapeutic for investigating the role of αvβ6 in a range of disease states both pre-clinically and clinically. In addition, this is the first study that has successfully applied radioligand binding to the RGD integrin field to accurately determine the affinity and selectivity profile of a small molecule RGD-mimetic.

Pharmacological Characterization of the αvβ6 Integrin Binding and Internalization Kinetics of the Foot-and-Mouth Disease Virus Derived Peptide A20FMDV2

A20FMDV2 is a peptide derived from the foot-and-mouth disease virus with a high affinity and selectivity for the alpha-v beta-6 (αvβ6) arginyl-glycinyl-aspartic acid (RGD)-binding integrin. It has been shown to be an informative tool ligand in pre-clinical imaging studies for selective labelling of the αvβ6 integrin in a number of disease models. In a radioligand binding assay using a radiolabelled form of the peptide ([3H]A20FMDV2), its high affinity (K(D): 0.22 nmol/l) and selectivity (at least 85-fold) for αvβ6 over the other members of the RGD integrin family was confirmed. [3H]A20FMDV2 αvβ6 binding could be fully reversed only in the presence of EDTA, whereas a partial reversal was observed in the presence of excess concentrations of an RGD-mimetic small molecule (SC-68448) or unlabelled A20FMDV2. Using flow cytometry on bronchial epithelial cells, the ligand-induced internalization of αvβ6 by A20FMDV2 and latency-associated peptide-1 was shown to be fast (t(1/2): 1.5 and 3.1 min, respectively), concentration-dependent (EC50: values 1.1 and 3.6 nmol/l, respectively) and was followed by a moderately slow return of integrin to the surface. The results of the radioligand binding studies suggest that the binding of A20FMDV2 to the RGD-binding site on αvβ6 is required to maintain its engagement with the hypothesised A20FMDV2 synergy site on the integrin. In addition, there is evidence from flow cytometric studies that the RGD-ligand engagement of αvβ6 post-internalization plays a role in delaying recycling of the integrin to the cell surface. This mechanism may act as a homeostatic control of membrane αvβ6 following RGD ligand engagement.

Antagonism of human CC-chemokine receptor 4 can be achieved through three distinct binding sites on the receptor

Chemokine receptor antagonists appear to access two distinct binding sites on different members of this receptor family. One class of CCR4 antagonists has been suggested to bind to a site accessible from the cytoplasm while a second class did not bind to this site. In this report, we demonstrate that antagonists representing a variety of structural classes bind to two distinct allosteric sites on CCR4. The effects of pairs of low-molecular weight and/or chemokine CCR4 antagonists were evaluated on CCL17- and CCL22-induced responses of human CCR4⁺ T cells. This provided an initial grouping of the antagonists into sets which appeared to bind to distinct binding sites. Binding studies were then performed with radioligands from each set to confirm these groupings. Some novel receptor theory was developed to allow the interpretation of the effects of the antagonist combinations. The theory indicates that, generally, the concentration-ratio of a pair of competing allosteric modulators is maximally the sum of their individual effects while that of two modulators acting at different sites is likely to be greater than their sum. The low-molecular weight antagonists could be grouped into two sets on the basis of the functional and binding experiments. The antagonistic chemokines formed a third set whose behaviour was consistent with that of simple competitive antagonists. These studies indicate that there are two allosteric regulatory sites on CCR4.

Synthesis and structure-activity relationships of indazole arylsulfonamides as allosteric CC-chemokine receptor 4 (CCR4) antagonists

A series of indazole arylsulfonamides were synthesized and examined as human CCR4 antagonists. Methoxy- or hydroxyl-containing groups were the more potent indazole C4 substituents. Only small groups were tolerated at C5, C6, or C7, with the C6 analogues being preferred. The most potent N3-substituent was 5-chlorothiophene-2-sulfonamide. N1 meta-substituted benzyl groups possessing an α-amino-3-[(methylamino)acyl]-group were the most potent N1-substituents. Strongly basic amino groups had low oral absorption in vivo. Less basic analogues, such as morpholines, had good oral absorption; however, they also had high clearance. The most potent compound with high absorption in two species was analogue 6 (GSK2239633A), which was selected for further development. Aryl sulfonamide antagonists bind to CCR4 at an intracellular allosteric site denoted site II. X-ray diffraction studies on two indazole sulfonamide fragments suggested the presence of an important intramolecular interaction in the active conformation.

In vitro pharmacological characterization of vilanterol, a novel long-acting β2-adrenoceptor agonist with 24-hour duration of action

Vilanterol trifenatate (vilanterol) is a novel, long-acting β(2)-adrenoceptor (β(2)-AR) agonist with 24 h activity. In this study, we describe the preclinical pharmacological profile of vilanterol using radioligand binding and cAMP studies in recombinant assays as well as human and guinea pig tissue systems to characterize β(2)-AR binding and functional properties. Vilanterol displayed a subnanomolar affinity for the β(2)-AR that was comparable with that of salmeterol but higher than olodaterol, formoterol, and indacaterol. In cAMP functional activity studies, vilanterol demonstrated similar selectivity as salmeterol for β(2)- over β(1)-AR and β(3)-AR, but a significantly improved selectivity profile than formoterol and indacaterol. Vilanterol also showed a level of intrinsic efficacy that was comparable to indacaterol but significantly greater than that of salmeterol. In cellular cAMP production and tissue-based studies measuring persistence and reassertion, vilanterol had a persistence of action comparable with indacaterol and longer than formoterol. In addition, vilanterol demonstrated reassertion activity in both cell and tissue systems that was comparable with salmeterol and indacaterol but longer than formoterol. In human airways, vilanterol was shown to have a faster onset and longer duration of action than salmeterol, exhibiting a significant level of bronchodilation 22 h after treatment. From these investigations, the data for vilanterol are consistent, showing that it is a novel, potent, and selective β(2)-AR receptor agonist with a long duration of action. This pharmacological profile combined with clinical data is consistent with once a day dosing of vilanterol in the treatment of both asthma and chronic obstructive pulmonary disease (COPD).

Development of operational models of receptor activation including constitutive receptor activity and their use to determine the efficacy of the chemokine CCL17 at the CC chemokine receptor CCR4

BACKGROUND AND PURPOSE The operational model provides a key conceptual framework for the analysis of pharmacological data. However, this model does not include constitutive receptor activity, a frequent phenomenon in modern pharmacology, particularly in recombinant systems. Here, we developed extensions of the operational model which include constitutive activity and applied them to effects of agonists at the chemokine receptor CCR4. EXPERIMENTAL APPROACH The effects of agonists of CCR4 on [(35) S]GTPγS binding to recombinant cell membranes and on the filamentous (F-) actin content of human CD4(+) CCR4(+) T cells were determined. The basal [(35) S]GTPγS binding was changed by varying the GDP concentration whilst the basal F-actin contents of the higher expressing T cell populations were elevated, suggesting constitutive activity of CCR4. Both sets of data were analysed using the mathematical models. RESULTS The affinity of CCL17 (also known as TARC) derived from analysis of the T cell data (pK(a) = 9.61 ± 0.17) was consistent with radioligand binding experiments (9.50 ± 0.11) while that from the [(35) S]GTPγS binding experiments was lower (8.27 ± 0.09). Its intrinsic efficacy differed between the two systems (110 in T cells vs. 11). CONCLUSIONS AND IMPLICATIONS The presence of constitutive receptor activity allows the absolute intrinsic efficacy of agonists to be determined without a contribution from the signal transduction system. Intrinsic efficacy estimated in this way is consistent with Furchgott's definition of this property. CCL17 may have a higher intrinsic efficacy at CCR4 in human T cells than that expressed recombinantly in CHO cells.

Synthesis and pharmacological investigation of azaphthalazinone human histamine H(1) receptor antagonists

5-Aza, 6-aza, 7-aza and 8-aza-phthalazinone, and 5,8-diazaphthalazinone templates were synthesised by stereoselective routes starting from the appropriate pyridine/pyrazine dicarboxylic acids by activation with CDI, reaction with 4-chlorophenyl acetate ester enolate to give a β-ketoester, which was hydrolysed, and decarboxylated. The resulting ketone was condensed with hydrazine to form the azaphthalazinone core. The azaphthalazinone cores were alkylated with N-Boc-D-prolinol at N-2 by Mitsunobu reaction, de-protected, and then alkylated at the pyrrolidine nitrogen to provide the target H(1) receptor antagonists. All four mono-azaphthalazinone series had higher affinity (pK(i)) for the human H(1) receptor than azelastine, but were not as potent as the parent non-aza phthalazinone. The 5,8-diazaphthalazinone was equipotent with azelastine. The least potent series were the 7-azaphthalazinones, whereas the 5-azaphthalazinones were the most lipophilic. The more hydrophilic series were the 8-aza series. Replacement of the N-methyl substituent on the pyrrolidine with the n-butyl group caused an increase in potency (pA(2)) and a corresponding increase in lipophilicity. Introduction of a β-ether oxygen in the n-butyl analogues (2-methoxyethyl group) decreased the H(1) pA(2) slightly, and increased the selectivity against hERG. The duration of action in vitro was longer in the 6-azaphthalazinone series. The more potent and selective 6-azaphthalazinone core was used to append an H(3) receptor antagonist fragment, and to convert the series into the long acting single-ligand, dual H(1) H(3) receptor antagonist 44. The pharmacological profile of 44 was very similar to our intranasal clinical candidate 1.

Pharmacological characterization of GSK1004723, a novel, long-acting antagonist at histamine H(1) and H(3) receptors

BACKGROUND AND PURPOSE

Preclinical pharmacological characterization of GSK1004723, a novel, dual histamine H(1) and H(3) receptor antagonist.

EXPERIMENTAL APPROACH

GSK1004723 was characterized in vitro and in vivo using methods that included radioligand binding, intracellular calcium mobilization, cAMP production, GTPγS binding, superfused human bronchus and guinea pig whole body plethysmography.

KEY RESULTS

In cell membranes over-expressing human recombinant H(1) and H(3) receptors, GSK1004723 displayed high affinity, competitive binding (H(1) pKi = 10.2; H(3) pKi = 10.6). In addition, GSK1004723 demonstrated slow dissociation from both receptors with a t(1/2) of 1.2 and 1.5 h for H(1) and H(3) respectively. GSK1004723 specifically antagonized H(1) receptor mediated increases in intracellular calcium and H(3) receptor mediated increases in GTPγS binding. The antagonism exerted was retained after cell washing, consistent with slow dissociation from H(1) and H(3) receptors. Duration of action was further evaluated using superfused human bronchus preparations. GSK1004723 (100 nmol·L(-1) ) reversed an established contractile response to histamine. When GSK1004723 was removed from the perfusate, only 20% recovery of the histamine response was observed over 10 h. Moreover, 21 h post-exposure to GSK1004723 there remained almost complete antagonism of responses to histamine. In vivo pharmacology was studied in conscious guinea pigs in which nasal congestion induced by intranasal histamine was measured indirectly (plethysmography). GSK1004723 (0.1 and 1 mg·mL(-1) intranasal) antagonized the histamine-induced response with a duration of up to 72 h.

CONCLUSIONS AND IMPLICATIONS

GSK1004723 is a potent and selective histamine H(1) and H(3) receptor antagonist with a long duration of action and represents a potential novel therapy for allergic rhinitis.

Priority water research questions as determined by UK practitioners and policy makers

Several recent studies have emphasised the need for a more integrated process in which researchers, policy makers and practitioners interact to identify research priorities. This paper discusses such a process with respect to the UK water sector, detailing how questions were developed through inter-disciplinary collaboration using online questionnaires and a stakeholder workshop. The paper details the 94 key questions arising, and provides commentary on their scale and scope. Prioritization voting divided the nine research themes into three categories: (1) extreme events (primarily flooding), valuing freshwater services, and water supply, treatment and distribution [each >150/1109 votes]; (2) freshwater pollution and integrated catchment management [100-150 votes] and; (3) freshwater biodiversity, water industry governance, understanding and managing demand and communicating water research [50-100 votes]. The biggest demand was for research to improve understanding of intervention impacts in the water environment, while a need for improved understanding of basic processes was also clearly expressed, particularly with respect to impacts of pollution and aquatic ecosystems. Questions that addressed aspects of appraisal, particularly incorporation of ecological service values into decision making, were also strongly represented. The findings revealed that sustainability has entered the lexicon of the UK water sector, but much remains to be done to embed the concept operationally, with key sustainability issues such as resilience and interaction with related key sectors, such as energy and agriculture, relatively poorly addressed. However, the exercise also revealed that a necessary condition for sustainable development, effective communication between scientists, practitioners and policy makers, already appears to be relatively well established in the UK water sector.

The management of household hazardous waste in the United Kingdom

Waste legislation in the United Kingdom (UK) implements European Union (EU) Directives and Regulations. However, the term used to refer to hazardous waste generated in household or municipal situations, household hazardous waste (HHW), does not occur in UK, or EU, legislation. The EU's Hazardous Waste Directive and European Waste Catalogue are the principal legislation influencing HHW, although the waste categories described are difficult to interpret. Other legislation also have impacts on HHW definition and disposal, some of which will alter current HHW disposal practices, leading to a variety of potential consequences. This paper discusses the issues affecting the management of HHW in the UK, including the apparent absence of a HHW-specific regulatory structure. Policy and regulatory measures that influence HHW management before disposal and after disposal are considered, with particular emphasis placed on disposal to landfill.

Evaluation of Patient Navigation in a Community Radiation Oncology Center Involved in Disparities Studies: A Time-to-Completion-of-Treatment Study

PURPOSE: To evaluate whether data on length of time from patient referral to treatment completion, collected routinely as part of a quality improvement program, can be used to measure the effectiveness of a patient navigator program. PATIENTS AND METHODS: During a calendar year, 72 disparities patients, 38 of whom received navigator services, and a group of 157 nondisparate, un-navigated patients received external beam radiation therapy at a community center. Data from referral time through completion of treatment, which had been collected routinely under an existing continuous quality improvement program, were compared retrospectively, as well as missed treatments and the percentage of planned treatments completed, for three patient groups. RESULTS: The average number of days from referral to consult and from consult to start of treatment were lower for the navigated disparate group (6.66 and 14.56 days, respectively) than un-navigated groups (disparate: 7.37 and 15.97 days; non-disparate: 8.97 and 16.24 days, respectively). The percentage of patients completing treatment was lower for the navigated group (85%) than the un-navigated groups (95% and 97%), despite equivalent treatment percentage completion rates for all groups (97.0% to 98.8%). The navigated group missed more treatment days (1.86 days/patient) than the un-navigated disparate group (0.47 days/patient) or the non-disparate group (0.83 days/patient.) CONCLUSION: Some statistically insignificant differences were noted in favor of patient navigation (PN) but the significance is unclear because of the large data spread and the small numbers of patients. Given that the study was retrospective, it is also unclear whether these differences were influenced by the patient navigator. Repeat studies using the same data elements will provide a better platform for assessing whether such data can provide a measure of the effectiveness of PN in the radiation oncology setting. Given that the patients were not observed routinely by the navigator after the start of treatment unless a particular barrier was identified, there is an opportunity to assess whether interventions by the navigator could improve treatment completion rates and reduce the number of missed treatments.

Household hazardous waste in municipal landfills: contaminants in leachate

Household hazardous waste (HHW) includes waste from a number of household products such as paint, garden pesticides, pharmaceuticals, photographic chemicals, certain detergents, personal care products, fluorescent tubes, waste oil, heavy metal-containing batteries, wood treated with dangerous substances, waste electronic and electrical equipment and discarded CFC-containing equipment. Data on the amounts of HHW discarded are very limited and are hampered by insufficient definitions of what constitutes HHW. Consequently, the risks associated with the disposal of HHW to landfill have not been fully elucidated. This work has focused on the assessment of data concerning the presence of hazardous chemicals in leachates as evidence of the disposal of HHW in municipal landfills. Evidence is sought from a number of sources on the occurrence in landfill leachates of hazardous components (heavy metals and xenobiotic organic compounds [XOC]) from household products and the possible disposal-to-emissions pathways occurring within landfills. This review demonstrates that a broad range of xenobiotic compounds occurring in leachate can be linked to HHW but further work is required to assess whether such compounds pose a risk to the environment and human health as a result of leakage/seepage or through treatment and discharge.