Perspective on high-throughput bioanalysis to support in vitro assays in early drug discovery.

As the desire for a shortened design/make/test/learn cycle increases in early drug discovery, the pressure to rapidly deliver drug metabolism pharmacokinetic data continues to rise. From a bioanalytical standpoint, in vitro assays are challenging because they are amenable to automation and thus capable of generating a high number of samples for analysis. To keep up with analysis demands, automated method development workflows, rapid sample analysis approaches and efficient data analysis software must be utilized. This work provides an outline of how we implemented those three aspects to provide bioanalytical support for in vitro drug metabolism pharmacokinetic assays, which include developing hundreds of mass spectrometry methods and analyzing thousands of samples per week, while delivering a median bioanalytical turnaround time of 1-2 business days.

Identification of a Human Whole Blood-Based Endothelial Cell Impedance Assay for Assessing Clinical Transient Receptor Potential Vanilloid 4 Target Engagement Ex Vivo.

Transient receptor potential vanilloid 4 (TRPV4) channels expressed on pulmonary endothelial cells are activated by elevated pulmonary vascular pressure, resulting in endothelial shape change, pulmonary barrier disruption, and edema. As such, TRPV4 blocker GSK2798745 was recently investigated in phase I/IIa trials to reduce pulmonary edema caused by heart failure (HF). In the absence of a suitable TRPV4 target engagement biomarker, we hypothesized that an ex vivo assay could be used to predict pharmacological activity at the intended site of action (endothelial cells) of subjects. In this assay, the ability of GSK2798745 to block TRPV4 agonist GSK1016790-induced impendence reduction in human umbilical vein endothelial cells (HUVECs) in the presence of human whole blood was assessed. Blood from healthy volunteers drawn 1-12 hours after single or repeated dose of GSK2798745 (5 mg) inhibited GSK1016790-induced impedance reduction by ≥85%. Similarly, blood samples from 16 subjects with HF dosed with GSK2798745 (2.4 mg) inhibited GSK1016790-induced HUVEC impedance reduction by ≥58% 1-24 hours after single dosing and ≥78% 1-24 hours after 7 days of repeated dosing. No inhibition was detected using blood from placebo subjects. Using matched GSK2798745 plasma levels, a pharmacokinetic/pharmacodynamic (PK/PD) relationship was calculated as 2.9 nM IC50, consistent with the 6.5 nM IC50 of GSK2798745 obtained from a rat in vivo PK/PD model of pulmonary edema after correcting for rat-to-human differences. These results indicate that circulating levels of GSK2798745 in the recently completed phase I/IIa trials were sufficient to block TRPV4 in lung vascular endothelial cells to a large extent, supporting this dosing regimen for assessing efficacy in HF. SIGNIFICANCE STATEMENT: In the absence of a suitable target engagement biomarker, we developed an ex vivo assay to predict the pharmacological activity of the transient receptor potential vanilloid 4 (TRPV4) blocker GSK2798745 in healthy volunteers and subjects with heart failure (HF) from phase I/IIa trials. The potency values from the ex vivo assay were consistent with those predicted from a rat in vivo pharmacokinetic/pharmacodynamic model of pulmonary edema, strongly suggesting that circulating levels of GSK2798745 were sufficient to robustly block TRPV4, supporting use of GSK2798745 for assessing efficacy in HF.

Design and Optimization of an Acyclic Amine Series of TRPV4 Antagonists by Electronic Modulation of Hydrogen Bond Interactions.

Investigation of TRPV4 as a potential target for the treatment of pulmonary edema associated with heart failure generated a novel series of acyclic amine inhibitors displaying exceptional potency and PK properties. The series arose through a scaffold hopping approach, which relied on use of an internal H-bond to replace a saturated heterocyclic ring. Optimization of the lead through investigation of both aryl regions revealed approaches to increase potency through substituents believed to enhance separate intramolecular and intermolecular H-bond interactions. A proposed internal H-bond between the amine and neighboring benzenesulfonamide was stabilized by electronically modulating the benzenesulfonamide. In the aryl ether moiety, substituents para to the nitrile demonstrated an electronic effect on TRPV4 recognition. Finally, the acyclic amines inactivated CYP3A4 and this liability was addressed by modifications that sterically preclude formation of a putative metabolic intermediate complex to deliver advanced TRPV4 antagonists as leads for discovery of novel medicines.

Discovery of GSK3527497: A Candidate for the Inhibition of Transient Receptor Potential Vanilloid-4 (TRPV4).

GSK3527497, a preclinical candidate for the inhibition of TRPV4, was identified starting from the previously reported pyrrolidine sulfonamide TRPV4 inhibitors 1 and 2. Optimization of projected human dose was accomplished by specifically focusing on in vivo pharmacokinetic parameters CLu, Vdssu, and MRT. We highlight the use of conformational changes as a novel approach to modulate Vdssu and present results that suggest that molecular-shape-dependent binding to tissue components governs Vdssu in addition to bulk physicochemical properties. Optimization of CLu within the series was guided by in vitro metabolite identification, and the poor FaSSIF solubility imparted by the crystalline properties of the pyrrolidine diol scaffold was improved by the introduction of a charged moiety to enable excellent exposure from high crystalline doses. GSK3527497 is a preclinical candidate suitable for oral and iv administration that is projected to inhibit TRPV4 effectively in patients from a low daily clinical dose.

Discovery of GSK2798745: A Clinical Candidate for Inhibition of Transient Receptor Potential Vanilloid 4 (TRPV4).

GSK2798745, a clinical candidate, was identified as an inhibitor of the transient receptor potential vanilloid 4 (TRPV4) ion channel for the treatment of pulmonary edema associated with congestive heart failure. We discuss the lead optimization of this novel spirocarbamate series and specifically focus on our strategies and solutions for achieving desirable potency, rat pharmacokinetics, and physicochemical properties. We highlight the use of conformational bias to deliver potency and optimization of volume of distribution and unbound clearance to enable desirable in vivo mean residence times.

Design and Optimization of Sulfone Pyrrolidine Sulfonamide Antagonists of Transient Receptor Potential Vanilloid-4 with in Vivo Activity in a Pulmonary Edema Model.

Pulmonary edema is a common ailment of heart failure patients and has remained an unmet medical need due to dose-limiting side effects associated with current treatments. Preclinical studies in rodents have suggested that inhibition of transient receptor potential vanilloid-4 (TRPV4) cation channels may offer an alternative-and potentially superior-therapy. Efforts directed toward small-molecule antagonists of the TRPV4 receptor have led to the discovery of a novel sulfone pyrrolidine sulfonamide chemotype exemplified by lead compound 6. Design elements toward the optimization of TRPV4 activity, selectivity, and pharmacokinetic properties are described. Activity of leading exemplars 19 and 27 in an in vivo model suggestive of therapeutic potential is highlighted herein.

Discovery of Pyrrolidine Sulfonamides as Selective and Orally Bioavailable Antagonists of Transient Receptor Potential Vanilloid-4 (TRPV4).

A novel series of pyrrolidine sulfonamide transient receptor potential vanilloid-4 (TRPV4) antagonists was developed by modification of a previously reported TRPV4 inhibitor (1). Several core-structure modifications were identified that improved TRPV4 activity by increasing structural rigidity and reducing the entropic energy penalty upon binding to the target protein. The new template was initially discovered as a minor regio-isomeric side product formed during routine structure-activity relationship (SAR) studies, and further optimization resulted in highly potent compounds with a novel pyrrolidine diol core. Further improvements in potency and pharmacokinetic properties were achieved through SAR studies on the sulfonamide substituent to give an optimized lead compound GSK3395879 (52) that demonstrated the ability to inhibit TRPV4-mediated pulmonary edema in an in vivo rat model. GSK3395879 is a tool for studying the biology of TRPV4 and an advanced lead for identifying new heart failure medicines.

Reverse Hydroxamate Inhibitors of Bone Morphogenetic Protein 1.

Bone Morphogenetic Protein 1 (BMP1) inhibition is a potential method for treating fibrosis because BMP1, a member of the zinc metalloprotease family, is required to convert pro-collagen to collagen. A novel class of reverse hydroxamate BMP1 inhibitors was discovered, and cocrystal structures with BMP1 were obtained. The observed binding mode is unique in that the small molecule occupies the nonprime side of the metalloprotease pocket providing an opportunity to build in metalloprotease selectivity. Structure-guided modification of the initial hit led to the identification of an oral in vivo tool compound with selectivity over other metalloproteases. Due to irreversible inhibition of cytochrome P450 3A4 for this chemical class, the risk of potential drug-drug interactions was managed by optimizing the series for subcutaneous injection.

Activation of the Amino Acid Response Pathway Blunts the Effects of Cardiac Stress.

BACKGROUND: The amino acid response (AAR) is an evolutionarily conserved protective mechanism activated by amino acid deficiency through a key kinase, general control nonderepressible 2. In addition to mobilizing amino acids, the AAR broadly affects gene and protein expression in a variety of pathways and elicits antifibrotic, autophagic, and anti-inflammatory activities. However, little is known regarding its role in cardiac stress. Our aim was to investigate the effects of halofuginone, a prolyl-tRNA synthetase inhibitor, on the AAR pathway in cardiac fibroblasts, cardiomyocytes, and in mouse models of cardiac stress and failure. METHODS AND RESULTS: Consistent with its ability to inhibit prolyl-tRNA synthetase, halofuginone elicited a general control nonderepressible 2-dependent activation of the AAR pathway in cardiac fibroblasts as evidenced by activation of known AAR target genes, broad regulation of the transcriptome and proteome, and reversal by l-proline supplementation. Halofuginone was examined in 3 mouse models of cardiac stress: angiotensin II/phenylephrine, transverse aortic constriction, and acute ischemia reperfusion injury. It activated the AAR pathway in the heart, improved survival, pulmonary congestion, left ventricle remodeling/fibrosis, and left ventricular function, and rescued ischemic myocardium. In human cardiac fibroblasts, halofuginone profoundly reduced collagen deposition in a general control nonderepressible 2-dependent manner and suppressed the extracellular matrix proteome. In human induced pluripotent stem cell-derived cardiomyocytes, halofuginone blocked gene expression associated with endothelin-1-mediated activation of pathologic hypertrophy and restored autophagy in a general control nonderepressible 2/eIF2α-dependent manner. CONCLUSIONS: Halofuginone activated the AAR pathway in the heart and attenuated the structural and functional effects of cardiac stress.

Discovery of GSK2193874: An Orally Active, Potent, and Selective Blocker of Transient Receptor Potential Vanilloid 4.

Transient Receptor Potential Vanilloid 4 (TRPV4) is a member of the Transient Receptor Potential (TRP) superfamily of cation channels. TRPV4 is expressed in the vascular endothelium in the lung and regulates the integrity of the alveolar septal barrier. Increased pulmonary vascular pressure evokes TRPV4-dependent pulmonary edema, and therefore, inhibition of TRPV4 represents a novel approach for the treatment of pulmonary edema associated with conditions such as congestive heart failure. Herein we report the discovery of an orally active, potent, and selective TRPV4 blocker, 3-(1,4'-bipiperidin-1'-ylmethyl)-7-bromo-N-(1-phenylcyclopropyl)-2-[3-(trifluoromethyl)phenyl]-4-quinolinecarboxamide (GSK2193874, 28) after addressing an unexpected off-target cardiovascular liability observed from in vivo studies. GSK2193874 is a selective tool for elucidating TRPV4 biology both in vitro and in vivo.

Discovery of 1-(1,3,5-triazin-2-yl)piperidine-4-carboxamides as inhibitors of soluble epoxide hydrolase.

1-(1,3,5-Triazin-yl)piperidine-4-carboxamide inhibitors of soluble epoxide hydrolase were identified from high through-put screening using encoded library technology. The triazine heterocycle proved to be a critical functional group, essential for high potency and P450 selectivity. Phenyl group substitution was important for reducing clearance, and establishing good oral exposure. Based on this lead optimization work, 1-[4-methyl-6-(methylamino)-1,3,5-triazin-2-yl]-N-{[[4-bromo-2-(trifluoromethoxy)]-phenyl]methyl}-4-piperidinecarboxamide (27) was identified as a useful tool compound for in vivo investigation. Robust effects on a serum biomarker, 9, 10-epoxyoctadec-12(Z)-enoic acid (the epoxide derived from linoleic acid) were observed, which provided evidence of robust in vivo target engagement and the suitability of 27 as a tool compound for study in various disease models.

Optimization of a Novel Series of TRPV4 Antagonists with In Vivo Activity in a Model of Pulmonary Edema.

High-throughput screening and subsequent hit optimization identified 1-piperidinylbenzimidazoles, exemplified by compound 1, as TRPV4 inhibitors. Lead optimization identified potent TRPV4 blocker 19, which has good target activity and pharmacokinetic properties. Inhibitor 19 was then profiled in an in vivo rat model, demonstrating its ability to inhibit TRPV4-mediated pulmonary edema.

An orally active TRPV4 channel blocker prevents and resolves pulmonary edema induced by heart failure.

Pulmonary edema resulting from high pulmonary venous pressure (PVP) is a major cause of morbidity and mortality in heart failure (HF) patients, but current treatment options demonstrate substantial limitations. Recent evidence from rodent lungs suggests that PVP-induced edema is driven by activation of pulmonary capillary endothelial transient receptor potential vanilloid 4 (TRPV4) channels. To examine the therapeutic potential of this mechanism, we evaluated TRPV4 expression in human congestive HF lungs and developed small-molecule TRPV4 channel blockers for testing in animal models of HF. TRPV4 immunolabeling of human lung sections demonstrated expression of TRPV4 in the pulmonary vasculature that was enhanced in sections from HF patients compared to controls. GSK2193874 was identified as a selective, orally active TRPV4 blocker that inhibits Ca(2+) influx through recombinant TRPV4 channels and native endothelial TRPV4 currents. In isolated rodent and canine lungs, TRPV4 blockade prevented the increased vascular permeability and resultant pulmonary edema associated with elevated PVP. Furthermore, in both acute and chronic HF models, GSK2193874 pretreatment inhibited the formation of pulmonary edema and enhanced arterial oxygenation. Finally, GSK2193874 treatment resolved pulmonary edema already established by myocardial infarction in mice. These findings identify a crucial role for TRPV4 in the formation of HF-induced pulmonary edema and suggest that TRPV4 blockade is a potential therapeutic strategy for HF patients.

The discovery of potent and long-acting oral factor Xa inhibitors with tetrahydroisoquinoline and benzazepine P4 motifs.

The discovery and evaluation of potent and long-acting oral sulfonamidopyrrolidin-2-one factor Xa inhibitors with tetrahydroisoquinoline and benzazepine P4 motifs are described. Unexpected selectivity issues versus tissue plasminogen activator in the former series were addressed in the later, delivering a robust candidate for progression towards clinical studies.

Antagonists of the calcium receptor. 2. Amino alcohol-based parathyroid hormone secretagogues.

When administered as a single agent to rats, the previously reported calcium receptor antagonist 3 elicited a sustained elevation of plasma PTH resulting in no increase in overall bone mineral density. The lack of a bone building effect for analogue 3 was attributed to the large volume of distribution (V(dss)(rat) = 11 L/kg), producing a protracted plasma PTH profile. Incorporation of a carboxylic acid functionality into the amino alcohol template led to the identification of 12 with a lower volume of distribution (V(dss)(12) = 1.18 L/kg) and a shorter half-life. The zwitterionic nature of antagonist 12 necessitated the utility of an ester prodrug approach to increase overall permeability. Antagonist 12 elicited a rapid and transient increase in circulating levels of PTH following oral dosing of the ester prodrug 11 in the dog. The magnitude and duration of the increases in plasma levels of PTH would be expected to stimulate new bone formation.

Antagonists of the calcium receptor I. Amino alcohol-based parathyroid hormone secretagogues.

Functional screening of the former SmithKline Beecham compound collection against the human calcium receptor (CaR) resulted in the identification of the amino alcohol-based hit 2 (IC(50) = 11 microM). Structure-activity studies of 2 focused on the optimization of the right- and left-hand side aromatic moieties as well as the amino alcohol linker region. Critical to the optimization of this antagonist template was the discovery that the chirality of the C-2 secondary alcohol played a key role in enhancing both CaR potency as well as selectivity over the beta-adrenergic receptor subtypes. These SAR studies ultimately led to the identification of 38 (NPS 2143; SB-262470A), a potent and orally active CaR antagonist. Pharmacokinetic characterization of 38 in the rat revealed that this molecule had a large volume of distribution (11 L/kg), which resulted in a prolonged systemic exposure, protracted increases in the plasma levels of PTH, and an overall lack of net bone formation effect in a rodent model of osteoporosis.

Potent and selective small-molecule human urotensin-II antagonists with improved pharmacokinetic profiles.

Lead compound 1 was successfully redesigned to provide compounds with improved pharmacokinetic profiles for this series of human urotensin-II antagonists. Replacement of the 2-pyrrolidinylmethyl-3-phenyl-piperidine core of 1 with a substituted N-methyl-2-(1-pyrrolidinyl)ethanamine core as in compound 7 resulted in compounds with improved oral bioavailability in rats. The relationship between stereochemistry and selectivity for hUT over the kappa-opioid receptor was also explored.

Development of potent and selective small-molecule human Urotensin-II antagonists.

This work describes the development of potent and selective human Urotensin-II receptor antagonists starting from lead compound 1, (3,4-dichlorophenyl)methyl{2-oxo-2-[3-phenyl-2-(1-pyrrolidinylmethyl)-1-piperidinyl]ethyl}amine. Several problems relating to oral bioavailability, cytochrome P450 inhibition, and off-target activity at the kappa opioid receptor and cardiac sodium channel were addressed during lead development. hUT binding affinity relative to compound 1 was improved by more than 40-fold in some analogs, and a structural modification was identified which significantly attenuated both off-target activities.

Comparison of N,N'-diarylsquaramides and N,N'-diarylureas as antagonists of the CXCR2 chemokine receptor.

N,N'-diarylsquaramides were prepared and evaluated as antagonists of CXCR2. The compounds were found to be potent and selective antagonists of CXCR2. Significant differences in SAR was observed relative to the previously described N,N'-diarylurea series. As was the case in the N,N'-diarylurea series, placing sulfonamide substituent adjacent to the acidic phenol significantly reduced the clearance in rat pharmacokinetic studies.

Structure activity relationships of 5-, 6-, and 7-methyl-substituted azepan-3-one cathepsin K inhibitors.

The syntheses, in vitro characterizations, and rat and monkey in vivo pharmacokinetic profiles of a series of 5-, 6-, and 7-methyl-substituted azepanone-based cathepsin K inhibitors are described. Depending on the particular regiochemical substitution and stereochemical configuration, methyl-substituted azepanones were identified that had widely varied cathepsin K inhibitory potency as well as pharmacokinetic properties compared to the 4S-parent azepanone analogue, 1 (human cathepsin K, K(i,app) = 0.16 nM, rat oral bioavailability = 42%, rat in vivo clearance = 49.2 mL/min/kg). Of particular note, the 4S-7-cis-methylazepanone analogue, 10, had a K(i,app) = 0.041 nM vs human cathepsin K and 89% oral bioavailability and an in vivo clearance rate of 19.5 mL/min/kg in the rat. Hypotheses that rationalize some of the observed characteristics of these closely related analogues have been made using X-ray crystallography and conformational analysis. These examples demonstrate the potential for modulation of pharmacological properties of cathepsin inhibitors by substituting the azepanone core. The high potency for inhibition of cathepsin K coupled with the favorable rat and monkey pharmacokinetic characteristics of compound 10, also known as SB-462795 or relacatib, has made it the subject of considerable in vivo evaluation for safety and efficacy as an inhibitor of excessive bone resorption in rat, monkey, and human studies, which will be reported elsewhere.