Mechanisms of Skin Toxicity Associated with Metabotropic Glutamate Receptor 5 Negative Allosteric Modulators

Characterization of a small molecule inhibitor of the NLRP3 inflammasome and its potential use for acute lung injury

Accumulating data support the key roles of the NLRP3 inflammasome, an essential component of the innate immune system, in human pathophysiology. As an emerging drug target and a potential biomarker for human diseases, small molecule inhibitors of the NLRP3 inflammasome have been actively pursued. Our recent studies identified a small molecule, MS-II-124, as a potent NLRP3 inhibitor and potential imaging probe. In this report, MS-II-124 was further characterized by an unbiased and comprehensive analysis through Eurofins BioMAP Diversity PLUS panel that contains 12 human primary cell-based systems. The analysis revealed promising activities of MS-II-124 on inflammation and immune functions, further supporting the roles of the NLRP3 inflammasome in these model systems. Further studies of MS-II-124 in mouse model of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) and NLRP3 knockout mice demonstrated its target engagement, efficacy to suppress inflammatory cytokines and infiltration of immune cells in the lung tissues. In summary, the results support the therapeutic potential of MS-II-124 as a NLRP3 inhibitor and warrant future studies of this compound and its analogs to develop therapeutics for ALI/ARDS.

Small-Molecule-Directed Endogenous Regeneration of Visual Function in a Mammalian Retinal Degeneration Model

Degenerative retinal diseases associated with photoreceptor loss are a leading cause of visual impairment worldwide, with limited treatment options. Phenotypic profiling coupled with medicinal chemistry were used to develop a small molecule with proliferative effects on retinal stem/progenitor cells, as assessed in vitro in a neurosphere assay and in vivo by measuring Msx1-positive ciliary body cell proliferation. The compound was identified as having kinase inhibitory activity and was subjected to cellular pathway analysis in non-retinal human primary cell systems. When tested in a disease-relevant murine model of adult retinal degeneration (MNU-induced retinal degeneration), we observed that four repeat intravitreal injections of the compound improved the thickness of the outer nuclear layer along with the regeneration of the visual function, as measured with ERG, visual acuity, and contrast sensitivity tests. This serves as a proof of concept for the use of a small molecule to promote endogenous regeneration in the eye.

Fluoxetine exerts anti-inflammatory effects on human epidermal keratinocytes and suppresses their endothelin release

Fluoxetine is a safe antidepressant with remarkable anti-inflammatory actions; therefore, we aimed to investigate its effects on immortalized (HaCaT) as well as primary human epidermal keratinocytes in a polyinosinic-polycytidylic acid (p(I:C))-induced inflammatory model. We found that a non-cytotoxic concentration (MTT-assay, CyQUANT-assay) of fluoxetine significantly suppressed p(I:C)-induced expression and release of several pro-inflammatory cytokines (Q-PCR, cytokine array, ELISA), and it decreased the release of the itch mediator endothelins (ELISA). These effects were not mediated by the inhibition of the NF-κB or p38 MAPK pathways (western blot), or by the suppression of the p(I:C)-induced elevation of mitochondrial ROS production (MitoSOX Red labeling). Instead, unbiased activity profiling revealed that they were most likely mediated via the inhibition of the phosphoinositide 3-kinase (PI3K) pathway. Importantly, the PI3K-inhibitor GDC0941 fully mimicked the effects of fluoxetine (Q-PCR, ELISA). Although fluoxetine was able to occupy the binding site of GDC0941 (in silico molecular docking), and exerted direct inhibitory effect on PI3K (cell-free PI3K activity assay), it exhibited much lower potency and efficacy as compared to GDC0941. Finally, RNA-Seq analysis revealed that fluoxetine deeply influenced the transcriptional alterations induced by p(I:C)-treatment, and exerted an overall anti-inflammatory activity. Collectively, our findings demonstrate that fluoxetine exerts potent anti-inflammatory effects, and suppresses the release of the endogenous itch mediator endothelins in human keratinocytes, most likely via interfering with the PI3K pathway. Thus, clinical studies are encouraged to explore whether the currently reported beneficial effects translate in vivo following its topical administration in inflammatory and pruritic dermatoses.

Novel substituted 4-(Arylethynyl)-Pyrrolo[2,3-d]pyrimidines negative allosteric modulators (NAMs) of the metabotropic glutamate receptor subtype 5 (mGlu5) Treat depressive disorder in mice

In view of the fact that the G-protein-coupled receptors (GPCRs) sit at the top of the signaling pathways triggering a diverse range of signaling cascades towards a cellular event, GPCRs are regarded as central drug targets. mGlu5, a type of classical GPCRs, is highly expressed in the central nervous system (CNS) and responds to the neurotransmitter glutamate. Researches show that mGlu5 is a potential drug target for the treatment of depression. Up to now, multiple mGlu5 negative allosteric modulators (NAMs) have entered clinical trials, but no small molecule mGlu5 NAM has yet to reach market. Herein, we report the structural optimization and structure-activity relationship studies of a series of novel mGlu5 NAMs. Among them, the novel compound 10b is a high-affinity mGluR5 antagonist, with an IC50 value of 11.5 nM. Besides, we evaluated the anti-depressant effect of compound 10b using the chronic unpredictable mild stress (CUMS)-induced depression model. The data showed that the mice in CUMS group were featured by decreased level of serum 5-HT and increased level of serum CORT, and the expression of synaptic proteins were reduced, including GluA1, GluA2, p-PKA, BDNF and TrkB. However, those factors for identifying sensitivity to depression-like behaviors could be improved by compound 10b treatment. The preliminary toxicology evaluations indicated that compound 10b had a good safety profile in vivo. Collectively, the compound 10b represents a promising lead compound for the treatment of depressive disorder.

Characterization and translational development of IOA-289, a novel autotaxin inhibitor for the treatment of solid tumors

Background

Autotaxin-lysophosphatidic acid (ATX-LPA) signaling has a predominant role in immunological and fibrotic processes, including cancer. Several ATX inhibitors and LPA receptor antagonists have been clinically evaluated, but none in patients with solid tumors. Many cancers are burdened with a high degree of fibrosis and an immune desert phenotype (so-called 'cold' tumors). In these cold tumors, the fibrotic stroma provides an intrinsic cancer-supporting mechanism. Furthermore, the stroma prevents penetration and limits the effectiveness of existing therapies. IOA-289 is a novel ATX inhibitor with a unique chemical structure, excellent potency and an attractive safety profile.

Materials and methods

In vitro and in vivo pharmacology studies have been carried out to elucidate the pharmaceutical properties and mechanism of action of IOA-289. A phase I clinical study in healthy volunteers was carried out to determine the pharmacokinetics and pharmacodynamics of IOA-289 following a single oral dose.

Results

In vitro and in vivo studies showed that IOA-289 is a potent inhibitor of ATX and, as a monotherapy, is able to slow progression of lung fibrosis and tumor growth in mouse models. In a clinical study, IOA-289 showed a dose-dependent increase in plasma exposure levels and a corresponding decrease in circulating LPA.

Conclusions

Our data show that IOA-289 is a novel ATX inhibitor with a unique chemical structure, excellent potency and an attractive safety profile. Our data support the further development of IOA-289 as a novel therapeutic approach for the treatment of cancer, particularly those with a high fibrotic and immunologically cold phenotype.

MyMD-1 Improves Health Span and Prolongs Life Span in Old Mice: A Noninferiority Study to Rapamycin

Aging and age-related diseases represent a compelling therapeutic goal for senolytics and drugs targeting inflammatory or metabolic pathways. We compared MyMD-1, a synthetic derivative of the alkaloid myosmine capable of suppressing TNF-α production, to rapamycin, the best characterized drug endowed with antiaging properties. In vivo, a longitudinal cohort of 54 C57BL/6 mice, 19-month-old at the start, was randomized to receive MyMD-1, high-dose (126 ppm) rapamycin, or low-dose (14 ppm) rapamycin plus metformin. Each treatment arm included 18 mice (10 females and 8 males) and was followed for 16 months or until death. Life span was significantly longer in MyMD-1 than rapamycin (p = .019 vs high-dose and .01 vs low-dose) in a Cox survival model that accounted for sex and serum levels of IL-6, TNF-α, and IL-17A. MyMD-1 also improved several health span characteristics, resulting in milder body weight loss, greater muscle strength, and slower progression to frailty. In vitro, MyMD-1 and rapamycin were compared using a panel of 12 human primary cell systems (BioMAP Diversity PLUS), where a total of 148 biomarkers were measured. MyMD-1 possessed antiproliferative, anti-inflammatory, and antifibrotic properties. Many were shared with rapamycin, but MyMD-1 was more active in the inhibition of proinflammatory and profibrotic biomarkers. Overall, MyMD-1 emerges as a new compound that, even when begun at an advanced age, induces beneficial effects on health and life span by modulating inflammation and tissue remodeling.

Integration of a microfluidic multicellular coculture array with machine learning analysis to predict adverse cutaneous drug reactions

Adverse cutaneous reactions are potentially life-threatening skin side effects caused by drugs administered into the human body. The availability of a human-specific in vitro platform that can prospectively screen drugs and predict this risk is therefore of great importance to drug safety. However, since adverse cutaneous drug reactions are mediated by at least 2 distinct mechanisms, both involving systemic interactions between liver, immune and dermal tissues, existing in vitro skin models have not been able to comprehensively recapitulate these complex, multi-cellular interactions to predict the skin-sensitization potential of drugs. Here, we report a novel in vitro drug screening platform, which comprises a microfluidic multicellular coculture array (MCA) to model different mechanisms-of-action using a collection of simplistic cellular assays. The resultant readouts are then integrated with a machine-learning algorithm to predict the skin sensitizing potential of systemic drugs. The MCA consists of 4 cell culture compartments connected by diffusion microchannels to enable crosstalk between hepatocytes that generate drug metabolites, antigen-presenting cells (APCs) that detect the immunogenicity of the drug metabolites, and keratinocytes and dermal fibroblasts, which collectively determine drug metabolite-induced FasL-mediated apoptosis. A single drug screen using the MCA can simultaneously generate 5 readouts, which are integrated using support vector machine (SVM) and principal component analysis (PCA) to classify and visualize the drugs as skin sensitizers or non-skin sensitizers. The predictive performance of the MCA and SVM classification algorithm is then validated through a pilot screen of 11 drugs labelled by the US Food and Drug Administration (FDA), including 7 skin-sensitizing and 4 non-skin sensitizing drugs, using stratified 4-fold cross-validation (CV) on SVM. The predictive performance of our in vitro model achieves an average of 87.5% accuracy (correct prediction rate), 75% specificity (prediction rate of true negative drugs), and 100% sensitivity (prediction rate of true positive drugs). We then employ the MCA and the SVM training algorithm to prospectively identify the skin-sensitizing likelihood and mechanism-of-action for obeticholic acid (OCA), a farnesoid X receptor (FXR) agonist which has undergone clinical trials for non-alcoholic steatohepatitis (NASH) with well-documented cutaneous side effects.

The Interleukin-1 Receptor-Associated Kinase 4 Inhibitor PF-06650833 Blocks Inflammation in Preclinical Models of Rheumatic Disease and in Humans Enrolled in a Randomized Clinical Trial

OBJECTIVE

To investigate the role of PF-06650833, a highly potent and selective small-molecule inhibitor of interleukin-1-associated kinase 4 (IRAK4), in autoimmune pathophysiology in vitro, in vivo, and in the clinical setting.

METHODS

Rheumatoid arthritis (RA) inflammatory pathophysiology was modeled in vitro through 1) stimulation of primary human macrophages with anti-citrullinated protein antibody immune complexes (ICs), 2) RA fibroblast-like synoviocyte (FLS) cultures stimulated with Toll-like receptor (TLR) ligands, as well as 3) additional human primary cell cocultures exposed to inflammatory stimuli. Systemic lupus erythematosus (SLE) pathophysiology was simulated in human neutrophils, dendritic cells, B cells, and peripheral blood mononuclear cells stimulated with TLR ligands and SLE patient ICs. PF-06650833 was evaluated in vivo in the rat collagen-induced arthritis (CIA) model and the mouse pristane-induced and MRL/lpr models of lupus. Finally, RNA sequencing data generated with whole blood samples from a phase I multiple-ascending-dose clinical trial of PF-06650833 were used to test in vivo human pharmacology.

RESULTS

In vitro, PF-06650833 inhibited human primary cell inflammatory responses to physiologically relevant stimuli generated with RA and SLE patient plasma. In vivo, PF-06650833 reduced circulating autoantibody levels in the pristane-induced and MRL/lpr murine models of lupus and protected against CIA in rats. In a phase I clinical trial (NCT02485769), PF-06650833 demonstrated in vivo pharmacologic action pertinent to SLE by reducing whole blood interferon gene signature expression in healthy volunteers.

CONCLUSION

These data demonstrate that inhibition of IRAK4 kinase activity can reduce levels of inflammation markers in humans and provide confidence in the rationale for clinical development of IRAK4 inhibitors for rheumatologic indications.

Use of a rapid human primary cell-based disease screening model, to compare next generation products to combustible cigarettes

A growing number of public health bodies, regulators and governments around the world consider electronic vapor products a lower risk alternative to conventional cigarettes. Of critical importance are rapid new approach methodologies to enable the screening of next generation products (NGPs) also known as next generation tobacco and nicotine products. In this study, the activity of conventional cigarette (3R4F) smoke and a range of NGP aerosols (heated tobacco product, hybrid product and electronic vapor product) captured in phosphate buffered saline, were screened by exposing a panel of human cell-based model systems using Biologically Multiplexed Activity Profiling (BioMAP® Diversity PLUS® Panel, Eurofins Discovery). Following exposure, the biological activity for a wide range of biomarkers in the BioMAP panel were compared to determine the presence of toxicity signatures that are associated with specific clinical findings. NGP aerosols were found to be weakly active in the BioMAP Diversity PLUS Panel (≤3/148 biomarkers) whereas significant activity was observed for 3R4F (22/148 biomarkers). Toxicity associated biomarker signatures for 3R4F included immunosuppression, skin irritation and thrombosis, with no toxicity signatures seen for the NGPs. BioMAP profiling could effectively be used to differentiate between complex mixtures of cigarette smoke or NGP aerosol extracts in a panel of human primary cell-based assays. Clinical validation of these results will be critical for confirming the utility of BioMAP for screening NGPs for potential adverse human effects.

The DHODH inhibitor PTC299 arrests SARS-CoV-2 replication and suppresses induction of inflammatory cytokines

The coronavirus disease 2019 (COVID-19) pandemic has created an urgent need for therapeutics that inhibit the SARS-COV-2 virus and suppress the fulminant inflammation characteristic of advanced illness. Here, we describe the anti-COVID-19 potential of PTC299, an orally bioavailable compound that is a potent inhibitor of dihydroorotate dehydrogenase (DHODH), the rate-limiting enzyme of the de novo pyrimidine nucleotide biosynthesis pathway. In tissue culture, PTC299 manifests robust, dose-dependent, and DHODH-dependent inhibition of SARS-COV-2 replication (EC50 range, 2.0-31.6 nM) with a selectivity index >3,800. PTC299 also blocked replication of other RNA viruses, including Ebola virus. Consistent with known DHODH requirements for immunomodulatory cytokine production, PTC299 inhibited the production of interleukin (IL)-6, IL-17A (also called IL-17), IL-17 F, and vascular endothelial growth factor (VEGF) in tissue culture models. The combination of anti-SARS-CoV-2 activity, cytokine inhibitory activity, and previously established favorable pharmacokinetic and human safety profiles render PTC299 a promising therapeutic for COVID-19.

ILB® resolves inflammatory scarring and promotes functional tissue repair

Fibrotic disease is a major cause of mortality worldwide, with fibrosis arising from prolonged inflammation and aberrant extracellular matrix dynamics. Compromised cellular and tissue repair processes following injury, infection, metabolic dysfunction, autoimmune conditions and vascular diseases leave tissues susceptible to unresolved inflammation, fibrogenesis, loss of function and scarring. There has been limited clinical success with therapies for inflammatory and fibrotic diseases such that there remains a large unmet therapeutic need to restore normal tissue homoeostasis without detrimental side effects. We investigated the effects of a newly formulated low molecular weight dextran sulfate (LMW-DS), termed ILB^®, to resolve inflammation and activate matrix remodelling in rodent and human disease models. We demonstrated modulation of the expression of multiple pro-inflammatory cytokines and chemokines in vitro together with scar resolution and improved matrix remodelling in vivo. Of particular relevance, we demonstrated that ILB^® acts, in part, by downregulating transforming growth factor (TGF)β signalling genes and by altering gene expression relating to extracellular matrix dynamics, leading to tissue remodelling, reduced fibrosis and functional tissue regeneration. These observations indicate the potential of ILB^® to alleviate fibrotic diseases.

cPLA2α Enzyme Inhibition Attenuates Inflammation and Keratinocyte Proliferation

As a regulator of cellular inflammation and proliferation, cytosolic phospholipase A₂ α (cPLA₂α) is a promising therapeutic target for psoriasis; indeed, the cPLA₂α inhibitor AVX001 has shown efficacy against plaque psoriasis in a phase I/IIa clinical trial. To improve our understanding of the anti-psoriatic properties of AVX001, we sought to determine how the compound modulates inflammation and keratinocyte hyperproliferation, key characteristics of the psoriatic epidermis. We measured eicosanoid release from human peripheral blood mononuclear cells (PBMC) and immortalized keratinocytes (HaCaT) and studied proliferation in HaCaT grown as monolayers and stratified cultures. We demonstrated that inhibition of cPLA₂α using AVX001 produced a balanced reduction of prostaglandins and leukotrienes; significantly limited prostaglandin E₂ (PGE₂) release from both PBMC and HaCaT in response to pro-inflammatory stimuli; attenuated growth factor-induced arachidonic acid and PGE₂ release from HaCaT; and inhibited keratinocyte proliferation in the absence and presence of exogenous growth factors, as well as in stratified cultures. These data suggest that the anti-psoriatic properties of AVX001 could result from a combination of anti-inflammatory and anti-proliferative effects, probably due to reduced local eicosanoid availability.

The activities of drug inactive ingredients on biological targets

Excipients, considered "inactive ingredients," are a major component of formulated drugs and play key roles in their pharmacokinetics. Despite their pervasiveness, whether they are active on any targets has not been systematically explored. We computed the likelihood that approved excipients would bind to molecular targets. Testing in vitro revealed 25 excipient activities, ranging from low-nanomolar to high-micromolar concentration. Another 109 activities were identified by testing against clinical safety targets. In cellular models, five excipients had fingerprints predictive of system-level toxicity. Exposures of seven excipients were investigated, and in certain populations, two of these may reach levels of in vitro target potency, including brain and gut exposure of thimerosal and its major metabolite, which had dopamine D3 receptor dissociation constant K _d values of 320 and 210 nM, respectively. Although most excipients deserve their status as inert, many approved excipients may directly modulate physiologically relevant targets.

The DHODH Inhibitor PTC299 Arrests SARS-CoV-2 Replication and Suppresses Induction of Inflammatory Cytokines

The coronavirus disease 2019 (COVID-19) pandemic has created an urgent need for therapeutics that inhibit the SARS-CoV-2 virus and suppress the fulminant inflammation characteristic of advanced illness. Here, we describe the anti-COVID-19 potential of PTC299, an orally available compound that is a potent inhibitor of dihydroorotate dehydrogenase (DHODH), the rate-limiting enzyme of the de novo pyrimidine biosynthesis pathway. In tissue culture, PTC299 manifests robust, dose-dependent, and DHODH-dependent inhibition of SARS CoV-2 replication (EC ₅₀ range, 2.0 to 31.6 nM) with a selectivity index >3,800. PTC299 also blocked replication of other RNA viruses, including Ebola virus. Consistent with known DHODH requirements for immunomodulatory cytokine production, PTC299 inhibited the production of interleukin (IL)-6, IL-17A (also called IL-17), IL-17F, and vascular endothelial growth factor (VEGF) in tissue culture models. The combination of anti-SARS-CoV-2 activity, cytokine inhibitory activity, and previously established favorable pharmacokinetic and human safety profiles render PTC299 a promising therapeutic for COVID-19.

Human Cell-Based in vitro Phenotypic Profiling for Drug Safety-Related Attrition

Ensuring the safety of new drugs is critically important to regulators, pharmaceutical researchers and patients alike. Even so, unexpected toxicities still account for 20–30% of clinical trial failures, in part due to the persistence of animal testing as the primary approach for de-risking new drugs. Clearly, improved methods for safety attrition that incorporate human-relevant biology are needed. This recognition has spurred interest in non-animal alternatives or new approach methodologies (NAMs) including in vitro models that utilize advances in the culture of human cell types to provide greater clinical relevance for assessing risk. These phenotypic assay systems use human primary and induced pluripotent stem cell-derived cells in various formats, including co-cultures and advanced cellular systems such as organoids, bioprinted tissues, and organs-on-a-chip. Despite the promise of these human-based phenotypic approaches, adoption of these platforms into drug discovery programs for reducing safety-related attrition has been slow. Here we discuss the value of large-scale human cell-based phenotypic profiling for incorporating human-specific biology into the de-risking process. We describe learnings from our experiences with human primary cell-based assays and analysis of clinically relevant reference datasets in developing in vitro-based toxicity signatures. We also describe how Adverse Outcome Pathway (AOP) frameworks can be used to integrate results from diverse platforms congruent with weight-of-evidence approaches from risk assessment to improve safety-related decisions in early discovery.

Comparative phenotypic profiling of the JAK2 inhibitors ruxolitinib, fedratinib, momelotinib, and pacritinib reveals distinct mechanistic signatures

Janus kinase-signal transducers and activators of transcription (JAK-STAT) signaling is critical to multiple cellular processes, including survival, differentiation, and proliferation. JAK-STAT signaling dysregulation has been noted in inflammatory disorders, and aberrant JAK2 pathway activation has been implicated in myelofibrosis and polycythemia vera. Moreover, 4 therapeutic JAK2 inhibitors (ruxolitinib, fedratinib, momelotinib, and pacritinib) have either been approved or are in advanced clinical development for myelofibrosis. Although all inhibit JAK2, reports indicate that they also inhibit other kinases. Profiling based solely on in vitro potencies is insufficient to predict the observed clinical effects. To provide further translational insights into clinical outcomes, we compared phenotypic biomarker profiles of ruxolitinib, fedratinib, momelotinib, and pacritinib in the BioMAP^® Diversity PLUS panel of 12 human primary cell systems designed to recapitulate key aspects of tissue and disease states. Biomarker activity profiles that represent mechanistic signatures for each agent were compared with each other and a database of reference benchmark profiles. At clinically relevant concentrations, these agents had distinct biomarker impacts indicating diverse mechanistic signatures, suggesting divergent clinical effects for each agent. They disparately modulated inflammatory cytokine production and immune function. At clinically relevant concentrations, ruxolitinib had the broadest scope of activities across all 12 cellular systems, whereas pacritinib was more specific for the BT system (modelling T cell-dependent B cell activation) and exhibited the strongest inhibition of sIL-17A, sIL-2, and sIL-6. All 4 agents were antiproliferative to B cells, but ruxolitinib and momelotinib were also antiproliferative to T cells. These differential activities likely reflect distinct secondary pharmacology for these agents known primarily as JAK2 inhibitors. The phenotypic analysis reported herein represents key data on distinct modes-of-action that may provide insights on clinical outcomes reported for these agents. Such translational findings may also inform the development of next-generation molecules with improved efficacy and safety.

Evaluation of Amides, Carbamates, Sulfonamides, and Ureas of 4-Prop-2-ynylidenecycloalkylamine as Potent, Selective, and Bioavailable Negative Allosteric Modulators of Metabotropic Glutamate Receptor 5

Negative allosteric modulators (NAMs) of the metabotropic glutamate receptor 5 (mGlu₅) hold great promise for the treatment of a variety of central nervous system disorders. We have recently reported that prop-2-ynylidenecycloalkylamine derivatives are potent and selective NAMs of the mGlu₅ receptor. In this work, we explored the amide, carbamate, sulfonamide, and urea derivatives of prop-2-ynylidenecycloalkylamine compounds with the aim of improving solubility and metabolic stability. In silico and experimental analyses were performed on the synthesized series of compounds to investigate structure-activity relationships. Compounds 12, 32, and 49 of the carbamate, urea, and amide classes, respectively, showed the most suitable cytochrome inhibition and metabolic stability profiles. Among them, compound 12 showed excellent selectivity, solubility, and stability profiles as well as suitable in vitro and in vivo pharmacokinetic properties. It was highly absorbed in rats and dogs and was active in anxiety, neuropathic pain, and lower urinary tract models.

Application of a phenotypic drug discovery strategy to identify biological and chemical starting points for inhibition of TSLP production in lung epithelial cells

Thymic stromal lymphopoietin (TSLP) is a cytokine released by human lung epithelium in response to external insult. Considered as a master switch in T helper 2 lymphocyte (Th2) mediated responses, TSLP is believed to play a key role in allergic diseases including asthma. The aim of this study was to use a phenotypic approach to identify new biological and chemical starting points for inhibition of TSLP production in human bronchial epithelial cells (NHBE), with the objective of reducing Th2-mediated airway inflammation. To this end, a phenotypic screen was performed using poly I:C / IL-4 stimulated NHBE cells interrogated with a 44,974 compound library. As a result, 85 hits which downregulated TSLP protein and mRNA levels were identified and a representative subset of 7 hits was selected for further characterization. These molecules inhibited the activity of several members of the MAPK, PI3K and tyrosine kinase families and some of them have been reported as modulators of cellular phenotypic endpoints like cell-cell contacts, microtubule polymerization and caspase activation. Characterization of the biological profile of the hits suggested that mTOR could be a key activity involved in the regulation of TSLP production in NHBE cells. Among other targeted kinases, inhibition of p38 MAPK and JAK kinases showed different degrees of correlation with TSLP downregulation, while Syk kinase did not seem to be related. Overall, inhibition of TSLP production by the selected hits, rather than resulting from inhibition of single isolated targets, appeared to be due to a combination of activities with different levels of relevance. Finally, a hit expansion exercise yielded additional active compounds that could be amenable to further optimization, providing an opportunity to dissociate TSLP inhibition from other non-desired activities. This study illustrates the potential of phenotypic drug discovery to complement target based approaches by providing new chemistry and biology leads.

Primary Cell Phenotypic Screening Illuminates ADRs and AOPs

Preclinical, in vitro screening for adverse drug reactions continues to present challenges in the field of drug development. In this issue of Cell Chemical Biology, Shah et al. (2017) employ a phenotypic screening strategy using a panel of human primary cells to define a signature response and an adverse outcome pathway for delayed type IV skin hypersensitivity.

Discovery and Characterization of (R)-6-Neopentyl-2-(pyridin-2-ylmethoxy)-6,7-dihydropyrimido[2,1-c][1,4]oxazin-4(9H)-one (PF-06462894), an Alkyne-Lacking Metabotropic Glutamate Receptor 5 Negative Allosteric Modulator Profiled in both Rat and Nonhuman Primates

We previously observed a cutaneous type IV immune response in nonhuman primates (NHP) with the mGlu₅ negative allosteric modulator (NAM) 7. To determine if this adverse event was chemotype- or mechanism-based, we evaluated a distinct series of mGlu₅ NAMs. Increasing the sp³ character of high-throughput screening hit 40 afforded a novel morpholinopyrimidone mGlu₅ NAM series. Its prototype, (R)-6-neopentyl-2-(pyridin-2-ylmethoxy)-6,7-dihydropyrimido[2,1-c][1,4]oxazin-4(9H)-one (PF-06462894, 8), possessed favorable properties and a predicted low clinical dose (2 mg twice daily). Compound 8 did not show any evidence of immune activation in a mouse drug allergy model. Additionally, plasma samples from toxicology studies confirmed that 8 did not form any reactive metabolites. However, 8 caused the identical microscopic skin lesions in NHPs found with 7, albeit with lower severity. Holistically, this work supports the hypothesis that this unique toxicity may be mechanism-based although additional work is required to confirm this and determine clinical relevance.