Evaluation of a multiplexed, multispecies nuclear receptor assay for chemical hazard assessment.

Sensitivity to potential endocrine disrupting chemicals in the environment varies across species and is influenced by sequence conservation of their nuclear receptor targets. Here, we evaluated a multiplexed, in vitro assay testing receptors relevant to endocrine and metabolic disruption from five species. The TRANS-FACTORIAL™ system of human nuclear receptors was modified to include additional species: mouse (Mus musculus), frog (Xenopus laevis), zebrafish (Danio rerio), chicken (Gallus gallus), and turtle (Chrysemys picta). Receptors regulating endocrine function and xenobiotic recognition were included, specifically: ERα, ERß, AR, TRα, TRß, PPARγ and PXR. The assay, ECOTOX-FACTORIAL™, was evaluated with 191 chemicals enriched with known receptor ligands. Hierarchical clustering of potency values demonstrated strong coherence of receptor families. Interspecies comparisons of responses within a receptor family showed moderate to high concordance for potencies under 50 µM. PPARγ showed high concordance between mammalian species, 89%, but only 63% between mammalian and zebrafish. For chemicals with potencies below 1 µM, concordances were 89-100% for all receptors except PXR. Concordance showed a strong positive relationship to ligand-binding domain sequence similarity and critical amino acid residues obtained by the Sequence Alignment to Predict Across Species Susceptibility (SeqAPASS) tool. In combination with SeqAPASS, ECOTOX-FACTORIAL may provide efficient screening of important receptors to identify species of high priority for effects monitoring.

Quantitative Transcriptional Biomarkers of Xenobiotic Receptor Activation in Rat Liver for the Early Assessment of Drug Safety Liabilities.

The robust transcriptional plasticity of liver mediated through xenobiotic receptors underlies its ability to respond rapidly and effectively to diverse chemical stressors. Thus, drug-induced gene expression changes in liver serve not only as biomarkers of liver injury, but also as mechanistic sentinels of adaptation in metabolism, detoxification, and tissue protection from chemicals. Modern RNA sequencing methods offer an unmatched opportunity to quantitatively monitor these processes in parallel and to contextualize the spectrum of dose-dependent stress, adaptation, protection, and injury responses induced in liver by drug treatments. Using this approach, we profiled the transcriptional changes in rat liver following daily oral administration of 120 different compounds, many of which are known to be associated with clinical risk for drug-induced liver injury by diverse mechanisms. Clustering, correlation, and linear modeling analyses were used to identify and optimize coexpressed gene signatures modulated by drug treatment. Here, we specifically focused on prioritizing 9 key signatures for their pragmatic utility for routine monitoring in initial rat tolerability studies just prior to entering drug development. These signatures are associated with 5 canonical xenobiotic nuclear receptors (AHR, CAR, PXR, PPARα, ER), 3 mediators of reactive metabolite-mediated stress responses (NRF2, NRF1, P53), and 1 liver response following activation of the innate immune response. Comparing paradigm chemical inducers of each receptor to the other compounds surveyed enabled us to identify sets of optimized gene expression panels and associated scoring algorithms proposed as quantitative mechanistic biomarkers with high sensitivity, specificity, and quantitative accuracy. These findings were further qualified using public datasets, Open TG-GATEs and DrugMatrix, and internal development compounds. With broader collaboration and additional qualification, the quantitative toxicogenomic framework described here could inform candidate selection prior to committing to drug development, as well as complement and provide a deeper understanding of the conventional toxicology study endpoints used later in drug development.

A method for the quantification of biased signalling at constitutively active receptors.

BACKGROUND AND PURPOSE: Biased agonism, the ability of an agonist to differentially activate one of several signal transduction pathways when acting at a given receptor, is an increasingly recognized phenomenon at many receptors. The Black and Leff operational model lacks a way to describe constitutive receptor activity and hence inverse agonism. Thus, it is impossible to analyse the biased signalling of inverse agonists using this model. In this theoretical work, we develop and illustrate methods for the analysis of biased inverse agonism. EXPERIMENTAL APPROACH: Methods were derived for quantifying biased signalling in systems that demonstrate constitutive activity using the modified operational model proposed by Slack and Hall. The methods were illustrated using Monte Carlo simulations. KEY RESULTS: The Monte Carlo simulations demonstrated that, with an appropriate experimental design, the model parameters are 'identifiable'. The method is consistent with methods based on the measurement of intrinsic relative activity (RAi ) (ΔΔlogR or ΔΔlog(τ/Ka )) proposed by Ehlert and Kenakin and their co-workers but has some advantages. In particular, it allows the quantification of ligand bias independently of 'system bias' removing the requirement to normalize to a standard ligand. CONCLUSIONS AND IMPLICATIONS: In systems with constitutive activity, the Slack and Hall model provides methods for quantifying the absolute bias of agonists and inverse agonists. This provides an alternative to methods based on RAi and is complementary to the ΔΔlog(τ/Ka ) method of Kenakin et al. in systems where use of that method is inappropriate due to the presence of constitutive activity.

A Scale of Agonism and Allosteric Modulation for Assessment of Selectivity, Bias, and Receptor Mutation.

An index of agonism is described that can be used to quantify agonist receptor selectivity, bias, cell-based agonism, and the effects of receptor mutation on signaling. The parameter is derived from agonist concentration-response curves and comprises the maximal response to the agonist (max) and the EC50 in the form of Δlog(max/EC50). This parameter is derived from equations describing agonists as positive allosteric facilitators of receptor-signaling protein interaction. A similar index is also derived to quantify the potentiating effects of positive allosteric modulators, which can be used to quantify in situ positive allosteric modulator activity in vivo. These indices lend themselves to statistical analysis and are system-independent in that the effects of the system processing of agonist response and differences in assay sensitivity and receptor expression are cancelled. The various applications of the Δlog(max/EC50) scale are described for each pharmacologic application.

Primary Biliary Cholangitis: Medical and Specialty Pharmacy Management Update.

BACKGROUND: Chronic liver disease and cirrhosis are a leading cause of morbidity and mortality in the United States. Primary biliary cholangitis (PBC), previously known as primary biliary cirrhosis and which has been designated an orphan condition, is a chronic autoimmune disease resulting in the destruction of the small bile ducts in the liver. Without effective treatment, disease progression frequently leads to liver failure and death. Until May 2016, the only FDA-approved treatment for PBC was ursodiol (UDCA), an oral hydrophilic bile acid, which can slow progression of liver damage due to PBC. However, 1 out of 3 patients taking UDCA has an inadequate biochemical response, leading to increased risk of disease progression, liver transplantation, and mortality. Given this unmet clinical need, new therapies are in development for the treatment of PBC. To provide pharmacists with an overview of the latest research on the pathophysiology of PBC and potential new treatment options and to highlight medical and specialty pharmacy approaches to managing access to drugs to treat orphan diseases such as PBC, a 2-hour satellite symposium was presented in conjunction with the 2015 Academy of Managed Care Pharmacy (AMCP) Nexus meeting. Although obeticholic acid was approved by the FDA for the treatment of PBC in May 2016, this development occurred after the symposium presentation. The symposium was supported by an independent educational grant from Intercept Pharmaceuticals and was managed by Analysis Group. Robert Navarro, PharmD, moderated the CPE-accredited symposium titled "Medical and Specialty Pharmacy Management Update on Primary Biliary Cirrhosis." Expert panelists included Christopher L. Bowlus, MD; James T. Kenney, RPh, MBA; and Gary Rice, RPh, MS, MBA, CSP. OBJECTIVE: To summarize the educational satellite symposium presentations and discussions. SUMMARY: Autoimmune liver diseases, including PBC, are responsible for 15% of all liver transplants performed and an equal percentage of deaths related to liver disease. UDCA is the only FDA-approved therapy for treatment of PBC and is considered the standard of care. Nevertheless, many patients do not respond to UDCA, creating the need for new therapeutic options to improve clinical outcomes for PBC patients with inadequate response to treatment. While several agents are being studied in combination with UDCA, monotherapy with the novel agent obeticholic acid, a farnesoid X receptor agonist, has also shown promising results. Health plans are anticipated to assign any newly introduced therapy for the treatment of PBC to specialty pharmacy given its orphan disease status. This assignment enables the health plan to receive disease education, which is particularly important when new drugs are indicated for orphan diseases, and assistance with designing appropriate prior authorization criteria. The clinical value of any new therapeutic options that will inform formulary decisions and prior authorization criteria will be assessed based on evidence of efficacy, safety, and tolerability, among other factors, such as the potential to reduce or delay medical resource utilization (e.g., liver transplant). Key considerations for prior authorization of a new therapy will be determining which PBC patients are appropriate candidates for the new therapy and developing criteria for that determination. These are likely to include clinical diagnostic criteria and degree of response to prior treatment with UDCA. Initially, any new therapy would likely be positioned as noncovered until appropriate prior authorization criteria are established. CONCLUSIONS: PBC is a chronic liver disease with significant morbidity and mortality, as well as a significant burden on the health care system if the disease progresses to the point at which a liver transplant is needed. Although UDCA, the current standard of care, has improved outcomes for many patients, others have an inadequate response to this treatment. This symposium discussed these issues and also addressed the overall treatment paradigm for orphan drug therapies, key implications for patient management, and the role of specialty pharmacy management and any associated needs both in general and specifically for new therapeutic options for PBC.

Development of an in vitro high content imaging assay for quantitative assessment of CAR-dependent mouse, rat, and human primary hepatocyte proliferation.

Rodent liver tumors promoted by constitutive androstane receptor (CAR) activation are known to be mediated by key events that include CAR-dependent gene expression and hepatocellular proliferation. Here, an in vitro high content imaging based assay was developed for quantitative assessment of nascent DNA synthesis in primary hepatocyte cultures from mouse, rat, and human species. Detection of DNA synthesis was performed using direct DNA labeling with the nucleoside analog 5-ethynyl-2'-deoxyuridine (EdU). The assay was multiplexed to enable direct quantitation of DNA synthesis, cytotoxicity, and cell count endpoints. An optimized defined medium cocktail was developed to sensitize hepatocytes to cell cycle progression. The baseline EdU response to defined medium was greatest for mouse, followed by rat, and then human. Hepatocytes from all three species demonstrated CAR activation in response to the CAR agonists TCPOBOP, CITCO, and phenobarbital based on increased gene expression for Cyp2b isoforms. When evaluated for a proliferation phenotype, TCPOBOP and CITCO exhibited significant dose-dependent increases in frequency of EdU labeling in mouse and rat hepatocytes that was not observed in hepatocytes from three human donors. The observed species differences are consistent with CAR activators inducing a proliferative response in rodents, a key event in the liver tumor mode of action that is not observed in humans.

Lowering bile acid pool size with a synthetic farnesoid X receptor (FXR) agonist induces obesity and diabetes through reduced energy expenditure.

We evaluated the metabolic impact of farnesoid X receptor (FXR) activation by administering a synthetic FXR agonist (GW4064) to mice in which obesity was induced by a high fat diet. Administration of GW4064 accentuated body weight gain and glucose intolerance induced by the high fat diet and led to a pronounced worsening of the changes in liver and adipose tissue. Mechanistically, treatment with GW4064 decreased bile acid (BA) biosynthesis, BA pool size, and energy expenditure, whereas reconstitution of the BA pool in these GW4064-treated animals by BA administration dose-dependently reverted the metabolic abnormalities. Our data therefore suggest that activation of FXR with synthetic agonists is not useful for long term management of the metabolic syndrome, as it reduces the BA pool size and subsequently decreases energy expenditure, translating as weight gain and insulin resistance. In contrast, expansion of the BA pool size, which can be achieved by BA administration, could be an interesting strategy to manage the metabolic syndrome.

A formulation-enabled preclinical efficacy assessment of a farnesoid X receptor agonist, GW4064, in hamsters and cynomolgus monkeys.

The farnesoid X receptor (FXR) belongs to one of the human nuclear receptor superfamilies that regulate gene transcription. FXR is widely expressed in liver, gall bladder, intestine, kidney, and adrenal glands. It serves as a key controller of bile acid homeostasis through its regulation of bile acid synthesis, conjugation, secretion, and absorption. FXR is also known to play a role in lipid regulation, triglyceride synthesis, and lipoprotein metabolism and clearance. We used a commercially available FXR agonist, GW4064, as a model compound to assess preclinical efficacy in two species (hamster and cynomolgus monkey). The crystalline GW4064, however, was found to have limited solubility, which resulted in poor oral bioavailability. This made it difficult to assess in vivo efficacy at the exposure levels desired. The physiochemical properties of GW4064 were assessed and both salt and self-emulsifying drug delivery system (SEDDS) formulation were developed and tested. The SEDDS formulation was found to greatly improve the oral bioavailability of GW4064, and permitted the evaluation of FXR agonist target efficacy.

A retrospective assessment of the effectiveness of fenofibrate 267 mg on high-density lipoprotein cholesterol levels in patients attending a lipid clinic.

BACKGROUND: A high-density lipoprotein cholesterol level (HDL-C) <1 mmol/L is associated with increased cardiovascular morbidity and mortality. In clinical trials, fibrates have been shown to increase levels of HDL-C, with subsequent reduction in cardiovascular risk. OBJECTIVE: This study evaluated the use of fenofibrate 267 mg/d in a routine lipid clinic setting to determine how much HDL-C could be increased in everyday clinical practice. METHODS: Blood samples from patients who had taken fenofibrate 267 mg/d between 1998 and 2001 at the Lipid Clinic, Charing Cross Hospital, London, United Kingdom, were analyzed for changes in total cholesterol (TC), HDL-C, and triglycerides during follow-up. RESULTS: Sixty-five consecutive patients (49 men, 16 women; mean age, 54 +/- 1.2 years) were included in the study. The follow-up period ranged from 1 to 36 months (mean, 9.6 months +/- 26.7 days). Patients achieved a 6% overall increase in HDL-C, from 0.91 +/- 0.03 mmol/L to 0.97 +/- 0.03 mmol/L (P = 0.016). The TC/HDL-C ratio decreased by 21% from 7.0 +/- 0.3 mmol/L to 5.5 +/- 0.2 mmol/L (P < 0.001). Patients with lower levels of HDL-C at baseline (<0.9 mmol/L) showed the most improvement, with an 8% increase (P < 0.05). Twenty-eight patients (43%) reached a target HDL-C posttherapy value >1.0 mmol/L. Thirty-nine patients (responders) had increases in their HDL-C levels; 26 patients (nonresponders) had decreases or no change in their HDL-C levels. For the 26 (40%) patients in whom HDL-C did not increase, the TC/HDL-C ratio decreased by 12% from 6.5 +/- 0.3 mmol/L to 5.7 +/- 0.3 mmol/L (P = 0.003). CONCLUSIONS: Fenofibrate 267 mg/d is well tolerated and can achieve significant increases in HDL-C levels in clinical practice. However, these results should be confirmed in a larger routine clinical setting because of the discrepancies between the results of some clinical trials.

A peroxisome proliferator-activated receptor gamma agonist influenced daily profile of energy expenditure in genetically obese diabetic rats.

Otsuka Long Evans Tokushima Fatty (OLETF) rats were developed as a model of non-insulin-dependent diabetes mellitus (NIDDM) with mild obesity. We reported that the daily profiles of energy expenditure associated with two peaks (one between 05:00 and 08:00 and the other between 20:00 and 22:00) were observed at 8 weeks of age (without NIDDM), while these two peaks disappeared at 24 weeks of age with NIDDM. As a new anti-diabetic drug, a peroxisome proliferator-activated receptor y agonist pioglitazone hydrochloride has been developed, we examined whether pioglitazone normalized daily profiles of energy expenditure at 24 weeks of age. A control diet and pioglitazone (0.1%)-containing diet were fed from 6 weeks of age. The two peaks of daily profiles of energy expenditure, which disappeared in OLETF rats with the control diet at 24 weeks of age, were reproduced by administration of pioglitazone. The respiratory quotient was lower and fat derived energy used for combustion was increased by pioglitazone at both ages. The body weight, daily food intake, plasma levels of fat, insulin, leptin and the wet weight of visceral fat were not influenced, but the levels of blood hemoglobin Alc and plasma tumor necrosis factor a were decreased by pioglitazone. Administration of pioglitazone improved daily profiles of energy expenditure via affecting glucose and fat metabolisms.

Rational discovery of novel nuclear hormone receptor antagonists.

Nuclear hormone receptors (NRs) are potential targets for therapeutic approaches to many clinical conditions, including cancer, diabetes, and neurological diseases. The crystal structure of the ligand binding domain of agonist-bound NRs enables the design of compounds with agonist activity. However, with the exception of the human estrogen receptor-alpha, the lack of antagonist-bound "inactive" receptor structures hinders the rational design of receptor antagonists. In this study, we present a strategy for designing such antagonists. We constructed a model of the inactive conformation of human retinoic acid receptor-alpha by using information derived from antagonist-bound estrogen receptor-alpha and applied a computer-based virtual screening algorithm to identify retinoic acid receptor antagonists. Thus, the currently available crystal structures of NRs may be used for the rational design of antagonists, which could lead to the development of novel drugs for a variety of diseases.