Structure-Guided Design of Substituted Biphenyl Butanoic Acid Derivatives as Neprilysin Inhibitors.

Inhibition of neprilysin (NEP) is widely studied as a therapeutic target for the treatment of hypertension, heart failure, and kidney disease. Sacubitril/valsartan (LCZ696) is a drug approved to reduce the risk of cardiovascular death in heart failure patients with reduced ejection fraction. LBQ657 is the active metabolite of sacubitril and an inhibitor of NEP. Previously, we have reported the crystal structure of NEP bound with LBQ657, whereby we noted the presence of a subsite in S1' that has not been explored before. We were also intrigued by the zinc coordination made by one of the carboxylic acids of LBQ657, leading us to explore alternative linkers to efficiently engage zinc for NEP inhibition. Structure-guided design culminated in the synthesis of selective, orally bioavailable, and subnanomolar inhibitors of NEP. A 17-fold boost in biochemical potency was observed upon addition of a chlorine atom that occupied the newly found subsite in S1'. We report herein the discovery and preclinical profiling of compound 13, which paved the path to our clinical candidate.

Pharmacological Characterization of a Novel 5-Hydroxybenzothiazolone-Derived ß 2-Adrenoceptor Agonist with Functional Selectivity for Anabolic Effects on Skeletal Muscle Resulting in a Wider Cardiovascular Safety Window in Preclinical Studies.

The anabolic effects of ß 2-adrenoceptor (ß 2-AR) agonists on skeletal muscle have been demonstrated in various species. However, the clinical use of ß 2-AR agonists for skeletal muscle wasting conditions has been limited by their undesired cardiovascular effects. Here, we describe the preclinical pharmacological profile of a novel 5-hydroxybenzothiazolone (5-HOB) derived ß 2-AR agonist in comparison with formoterol as a representative ß 2-AR agonist that have been well characterized. In vitro, 5-HOB has nanomolar affinity for the human ß 2-AR and selectivity over the ß 1-AR and ß 3-AR. 5-HOB also shows potent agonistic activity at the ß 2-AR in primary skeletal muscle myotubes and induces hypertrophy of skeletal muscle myotubes. Compared with formoterol, 5-HOB demonstrates comparable full-agonist activity on cAMP production in skeletal muscle cells and skeletal muscle tissue-derived membranes. In contrast, a greatly reduced intrinsic activity was determined in cardiomyocytes and cell membranes prepared from the rat heart. In addition, 5-HOB shows weak effects on chronotropy, inotropy, and vascular relaxation compared with formoterol. In vivo, 5-HOB significantly increases hind limb muscle weight in rats with attenuated effects on heart weight and ejection fraction, unlike formoterol. Furthermore, changes in cardiovascular parameters after bolus subcutaneous treatment in rats and rhesus monkeys are significantly lower with 5-HOB compared with formoterol. In conclusion, the pharmacological profile of 5-HOB indicates superior tissue selectivity compared with the conventional ß 2-AR agonist formoterol in preclinical studies and supports the notion that such tissue-selective agonists should be investigated for the safe treatment of muscle-wasting conditions without cardiovascular limiting effects.

Sacubitril/valsartan (LCZ696) significantly reduces aldosterone and increases cGMP circulating levels in a canine model of RAAS activation.

Simultaneous blockade of angiotensin receptors and enhancement of natriuretic peptides (NP) by the first-in-class angiotensin receptor neprilysin (NEP) inhibitor sacubitril/valsartan constitutes an effective approach to treating heart failure. This study examined the effects of sacubitril/valsartan (225 and 675 mg/day) vs. placebo, sacubitril (360 mg/day), valsartan (900 mg/day), and benazepril (5 mg/day) on the dynamics of the renin-angiotensin-aldosterone system (RAAS) and the NP system in dogs. Beagle dogs (n = 18) were fed a low-salt diet (0.05% Na) for 15 days to model RAAS activation observed in clinical heart failure. Drugs were administered once daily during the last 10 days, while the effects on the RAAS and NPs were assessed on Day 1, 5, and 10. Steady-state pharmacokinetics of the test agents were evaluated on Day 5. Compared with placebo, sacubitril/valsartan (675 mg) substantially increased cGMP circulating levels, while benazepril and valsartan showed no effect. Additionally, sacubitril/valsartan (675 mg) and valsartan significantly increased plasma renin activity, angiotensin I and angiotensin II concentrations. Finally, sacubitril/valsartan (both doses), and valsartan significantly decreased plasma aldosterone vs. placebo. Systemic exposure to valsartan following sacubitril/valsartan 675 mg administration was similar to that observed with valsartan 900 mg administration alone. Sacubitril/valsartan favorably modulates the dynamics of the renin and NP cascades through complementary NEP and RAAS inhibition.

Discovery of a Novel Piperidine-Based Inhibitor of Cholesteryl Ester Transfer Protein (CETP) That Retains Activity in Hypertriglyceridemic Plasma.

Herein we describe the discovery and characterization of a novel, piperidine-based inhibitor of cholesteryl ester transfer protein (CETP) with a core structure distinct from other reported CETP inhibitors. A versatile synthesis starting from 4-methoxypyridine enabled an efficient exploration of the SAR, giving a lead molecule with potent CETP inhibition in human plasma. The subsequent optimization focused on improvement of pharmacokinetics and mitigation of off-target liabilities, such as CYP inhibition, whose improvement correlated with increased lipophilic efficiency. The effort led to the identification of an achiral, carboxylic acid-bearing compound 16 (TAP311) with excellent pharmacokinetics in rats and robust efficacy in hamsters. Compared to anacetrapib, the compound showed substantially reduced lipophilicity, had only modest distribution into adipose tissue, and retained potency in hypertriglyceridemic plasma in vitro and in vivo. Furthermore, in contrast to torcetrapib, the compound did not increase aldosterone secretion in human adrenocortical carcinoma cells nor in chronically cannulated rats. On the basis of its preclinical efficacy and safety profile, the compound was advanced into clinical trials.

Optimization of Allosteric With-No-Lysine (WNK) Kinase Inhibitors and Efficacy in Rodent Hypertension Models.

The observed structure-activity relationship of three distinct ATP noncompetitive With-No-Lysine (WNK) kinase inhibitor series, together with a crystal structure of a previously disclosed allosteric inhibitor bound to WNK1, led to an overlay hypothesis defining core and side-chain relationships across the different series. This in turn enabled an efficient optimization through scaffold morphing, resulting in compounds with a good balance of selectivity, cellular potency, and pharmacokinetic profile, which were suitable for in vivo proof-of-concept studies. When dosed orally, the optimized compound reduced blood pressure in mice overexpressing human WNK1, and induced diuresis, natriuresis and kaliuresis in spontaneously hypertensive rats (SHR), confirming that this mechanism of inhibition of WNK kinase activity is effective at regulating cardiovascular homeostasis.

Characterization and Prediction of Cardiovascular Effects of Fingolimod and Siponimod Using a Systems Pharmacology Modeling Approach.

Sphingosine 1-phosphate (S1P) receptor agonists are associated with cardiovascular effects in humans. This study aims to develop a systems pharmacology model to identify the site of action (i.e., primary hemodynamic response variable) of S1P receptor agonists, and to predict, in a quantitative manner, the cardiovascular effects of novel S1P receptor agonists in vivo. The cardiovascular effects of once-daily fingolimod (0, 0.1, 0.3, 1, 3, and 10 mg/kg) and siponimod (3 and 15 mg/kg) were continuously recorded in spontaneously hypertensive rats and Wistar-Kyoto rats. The results were analyzed using a recently developed systems cardiovascular pharmacology model, i.e. the CVS model; total peripheral resistance and heart rate were identified as the site of action for fingolimod. Next, the CVS model was interfaced with an S1P agonist pharmacokinetic-pharmacodynamic (PKPD) model. This combined model adequately predicted, in a quantitative manner, the cardiovascular effects of siponimod using in vitro binding assays. In conclusion, the combined CVS and S1P agonist PKPD model adequately describes the hemodynamic effects of S1P receptor agonists in rats and constitutes a basis for the prediction, in a strictly quantitative manner, of the cardiovascular effects of novel S1P receptor agonists.

Small-molecule WNK inhibition regulates cardiovascular and renal function.

The With-No-Lysine (K) (WNK) kinases play a critical role in blood pressure regulation and body fluid and electrolyte homeostasis. Herein, we introduce the first orally bioavailable pan-WNK-kinase inhibitor, WNK463, that exploits unique structural features of the WNK kinases for both affinity and kinase selectivity. In rodent models of hypertension, WNK463 affects blood pressure and body fluid and electro-lyte homeostasis, consistent with WNK-kinase-associated physiology and pathophysiology.

Discovery of N-[5-(6-Chloro-3-cyano-1-methyl-1H-indol-2-yl)-pyridin-3-ylmethyl]-ethanesulfonamide, a Cortisol-Sparing CYP11B2 Inhibitor that Lowers Aldosterone in Human Subjects.

Human clinical studies conducted with LCI699 established aldosterone synthase (CYP11B2) inhibition as a promising novel mechanism to lower arterial blood pressure. However, LCI699's low CYP11B1/CYP11B2 selectivity resulted in blunting of adrenocorticotropic hormone-stimulated cortisol secretion. This property of LCI699 prompted its development in Cushing's disease, but limited more extensive clinical studies in hypertensive populations, and provided an impetus for the search for cortisol-sparing CYP11B2 inhibitors. This paper summarizes the discovery, pharmacokinetics, and pharmacodynamic data in preclinical species and human subjects of the selective CYP11B2 inhibitor 8.

Structure-Activity Relationships, Pharmacokinetics, and in Vivo Activity of CYP11B2 and CYP11B1 Inhibitors.

CYP11B2, the aldosterone synthase, and CYP11B1, the cortisol synthase, are two highly homologous enzymes implicated in a range of cardiovascular and metabolic diseases. We have previously reported the discovery of LCI699, a dual CYP11B2 and CYP11B1 inhibitor that has provided clinical validation for the lowering of plasma aldosterone as a viable approach to modulate blood pressure in humans, as well normalization of urinary cortisol in Cushing's disease patients. We now report novel series of aldosterone synthase inhibitors with single-digit nanomolar cellular potency and excellent physicochemical properties. Structure-activity relationships and optimization of their oral bioavailability are presented. An illustration of the impact of the age of preclinical models on pharmacokinetic properties is also highlighted. Similar biochemical potency was generally observed against CYP11B2 and CYP11B1, although emerging structure-selectivity relationships were noted leading to more CYP11B1-selective analogs.

trans-3,4-Disubstituted pyrrolidines as inhibitors of the human aspartyl protease renin. Part II: prime site exploration using an oxygen linker.

Inhibition of the aspartyl protease renin is considered as an efficient approach for treating hypertension. Lately, we described the discovery of a novel class of direct renin inhibitors which comprised a pyrrolidine scaffold (e.g., 2). Based on the X-ray structure of the lead compound 2 bound to renin we predicted that optimization of binding interactions to the prime site could offer an opportunity to further expand the scope of this chemotype. Pyrrolidine-based inhibitors were synthesized in which the prime site moieties are linked to the pyrrolidine core through an oxygen atom, resulting in an ether or a carbamate linker subseries. Especially the carbamate derivatives showed a pronounced increase in in vitro potency compared to 2. Here we report the structure-activity relationship of both subclasses and demonstrate blood pressure lowering effects for an advanced prototype in a hypertensive double-transgenic rat model after oral dosing.

Aldosterone synthase inhibition: cardiorenal protection in animal disease models and translation of hormonal effects to human subjects.

BACKGROUND: Aldosterone synthase inhibition provides the potential to attenuate both the mineralocorticoid receptor-dependent and independent actions of aldosterone. In vitro studies with recombinant human enzymes showed LCI699 to be a potent, reversible, competitive inhibitor of aldosterone synthase (K i = 1.4 ± 0.2 nmol/L in humans) with relative selectivity over 11ß-hydroxylase. METHODS: Hormonal effects of orally administered LCI699 were examined in rat and monkey in vivo models of adrenocorticotropic hormone (ACTH) and angiotensin-II-stimulated aldosterone release, and were compared with the mineralocorticoid receptor antagonist eplerenone in a randomized, placebo-controlled study conducted in 99 healthy human subjects. The effects of LCI699 and eplerenone on cardiac and renal sequelae of aldosterone excess were investigated in a double-transgenic rat (dTG rat) model overexpressing human renin and angiotensinogen. RESULTS: Rat and monkey in vivo models of stimulated aldosterone release predicted human dose- and exposure-response relationships, but overestimated the selectivity of LCI699 in humans. In the dTG rat model, LCI699 dose-dependently blocked increases in aldosterone, prevented development of cardiac and renal functional abnormalities independent of blood pressure changes, and prolonged survival. Eplerenone prolonged survival to a similar extent, but was less effective in preventing cardiac and renal damage. In healthy human subjects, LCI699 0.5 mg selectively reduced plasma and 24 h urinary aldosterone by 49 ± 3% and 39 ± 6% respectively (Day 1, mean ± SEM; P < 0.001 vs placebo), which was associated with natriuresis and an increase in plasma renin activity. Doses of LCI699 greater than 1 mg inhibited basal and ACTH-stimulated cortisol. Eplerenone 100 mg increased plasma and 24 h urinary aldosterone while stimulating natriuresis and increasing renin activity. In contrast to eplerenone, LCI699 increased the aldosterone precursor 11-deoxycorticosterone and urinary potassium excretion. CONCLUSIONS: These results provide new insights into the cardiac and renal effects of inhibiting aldosterone synthase in experimental models and translation of the hormonal effects to humans. Selective inhibition of aldosterone synthase appears to be a promising approach to treat diseases associated with aldosterone excess.

Structure-based design of substituted piperidines as a new class of highly efficacious oral direct Renin inhibitors.

A cis-configured 3,5-disubstituted piperidine direct renin inhibitor, (syn,rac)-1, was discovered as a high-throughput screening hit from a target-family tailored library. Optimization of both the prime and the nonprime site residues flanking the central piperidine transition-state surrogate resulted in analogues with improved potency and pharmacokinetic (PK) properties, culminating in the identification of the 4-hydroxy-3,5-substituted piperidine 31. This compound showed high in vitro potency toward human renin with excellent off-target selectivity, 60% oral bioavailability in rat, and dose-dependent blood pressure lowering effects in the double-transgenic rat model.

Chronic measurement of left ventricular pressure in freely moving rats.

Measurements of left ventricular pressure (LVP) in conscious freely moving animals are uncommon, yet could offer considerable opportunity for understanding cardiovascular disease progression and treatment. The aim of this study was to develop surgical methods and validate the measurements of a new high-fidelity, solid-state pressure-sensor telemetry device for chronically measuring LVP and dP/dt in rats. The pressure-sensor catheter tip (2-Fr) was inserted into the left ventricular chamber through the apex of the heart, and the telemeter body was implanted in the abdomen. Data were measured up to 85 days after implant. The average daytime dP/dt max was 9,444 ± 363 mmHg/s, ranging from 7,870 to 10,558 mmHg/s (n = 7). A circadian variation in dP/dt max and heart rate (HR) was observed with an average increase during the night phase in dP/dt max of 918 ± 84 mmHg/s, and in HR of 38 ± 3 bpm. The ß-adrenergic-agonist isoproterenol, ß1-adrenergic agonist dobutamine, Ca(2+) channel blocker verapamil, and the calcium sensitizer levosimendan were administered throughout the implant period, inducing dose-dependent time course changes and absolute changes in dP/dt max of -6,000 to +13,000 mmHg/s. The surgical methods and new technologies demonstrated long-term stability, sensitivity to circadian variation, and the ability to measure large drug-induced changes, validating this new solution for chronic measurement of LVP in conscious rats.

The discovery of novel potent trans-3,4-disubstituted pyrrolidine inhibitors of the human aspartic protease renin from in silico three-dimensional (3D) pharmacophore searches.

The small-molecule trans-3,4-disubstituted pyrrolidine 6 was identified from in silico three-dimensional (3D) pharmacophore searches based on known X-ray structures of renin-inhibitor complexes and demonstrated to be a weakly active inhibitor of the human enzyme. The unexpected binding mode of the more potent enantiomer (3S,4S)-6a in an extended conformation spanning the nonprime and S1' pockets of the recombinant human (rh)-renin active site was elucidated by X-ray crystallography. Initial structure-activity relationship work focused on modifications of the hydrophobic diphenylamine portion positioned in S1 and extending toward the S2 pocket. Replacement with an optimized P3-P1 pharmacophore interacting to the nonsubstrate S3(sp) cavity eventually resulted in significantly improved in vitro potency and selectivity. The prototype analogue (3S,4S)-12a of this new class of direct renin inhibitors exerted blood pressure lowering effects in a hypertensive double-transgenic rat model after oral administration.

A novel class of oral direct renin inhibitors: highly potent 3,5-disubstituted piperidines bearing a tricyclic p3-p1 pharmacophore.

A small library of fragments comprising putative recognition motifs for the catalytic dyad of aspartic proteases was generated by in silico similarity searches within the corporate compound deck based on rh-renin active site docking and scoring filters. Subsequent screening by NMR identified the low-affinity hits 3 and 4 as competitive active site binders, which could be shown by X-ray crystallography to bind to the hydrophobic S3-S1 pocket of rh-renin. As part of a parallel multiple hit-finding approach, the 3,5-disubstituted piperidine (rac)-5 was discovered by HTS using a enzymatic assay. X-ray crystallography demonstrated the eutomer (3S,5R)-5 to be a peptidomimetic inhibitor binding to a nonsubstrate topography of the rh-renin prime site. The design of the potent and selective (3S,5R)-12 bearing a P3(sp)-tethered tricyclic P3-P1 pharmacophore derived from 3 is described. (3S,5R)-12 showed oral bioavailability in rats and demonstrated blood pressure lowering activity in the double-transgenic rat model.

Discovery and in Vivo Evaluation of Potent Dual CYP11B2 (Aldosterone Synthase) and CYP11B1 Inhibitors.

Aldosterone is a key signaling component of the renin-angiotensin-aldosterone system and as such has been shown to contribute to cardiovascular pathology such as hypertension and heart failure. Aldosterone synthase (CYP11B2) is responsible for the final three steps of aldosterone synthesis and thus is a viable therapeutic target. A series of imidazole derived inhibitors, including clinical candidate 7n, have been identified through design and structure-activity relationship studies both in vitro and in vivo. Compound 7n was also found to be a potent inhibitor of 11ß-hydroxylase (CYP11B1), which is responsible for cortisol production. Inhibition of CYP11B1 is being evaluated in the clinic for potential treatment of hypercortisol diseases such as Cushing's syndrome.

The discovery of potent inhibitors of aldosterone synthase that exhibit selectivity over 11-beta-hydroxylase.

Aldosterone, the final component of the renin-angiotensin-aldosterone system, plays an important role in the pathophysiology of hypertension and congestive heart failure. Aldosterone synthase (CYP11B2) catalyzes the last three steps of aldosterone biosynthesis, and as such appears to be a target for the treatment of these disorders. A sulfonamide-imidazole scaffold has proven to be a potent inhibitor of CYP11B2. Furthermore, this scaffold can achieve high levels of selectivity for CYP11B2 over CYP11B1, a key enzyme in the biosynthesis of cortisol.

Pharmacodynamic and pharmacokinetic characterization of the aldosterone synthase inhibitor FAD286 in two rodent models of hyperaldosteronism: comparison with the 11beta-hydroxylase inhibitor metyrapone.

Aldosterone synthase (CYP11B2) inhibitors (ASIs) represent an attractive therapeutic approach for mitigating the untoward effects of aldosterone. We characterized the pharmacokinetic/pharmacodynamic relationships of a prototypical ASI, (+)-(5R)-4-(5,6,7,8-tetrahydroimidazo[1,5-a]pyridin-5-yl]benzonitrile hydrochloride (CGS020286A, FAD286, FAD) and compared these profiles to those of the 11beta-hydroxylase inhibitor metyrapone (MET) in two rodent models of secondary hyperaldosteronism and corticosteronism. In chronically cannulated Sprague-Dawley rats, angiotensin II (ANG II) (300 ng/kg bolus + 100 ng/kg/min infusion) or adrenocorticotropin (100 ng/kg + 30 ng/kg/min) acutely elevated plasma aldosterone concentration (PAC) from approximately 0.26 nM to a sustained level of approximately 2.5 nM for 9 h. Adrenocorticotropin but not ANG II elicited a sustained increase in plasma corticosterone concentration (PCC) from approximately 300 to approximately 1340 nM. After 1 h of Ang II or adrenocorticotropin infusion, FAD (0.01-100 mg/kg p.o.) or MET (0.1-300 mg/kg p.o.) dose- and drug plasma concentration-dependently reduced the elevated PACs over the ensuing 8 h. FAD was approximately 12 times more dose-potent than MET in reducing PAC but of similar or slightly greater potency on a plasma drug concentration basis. Both agents also decreased PCC in the adrenocorticotropin model at relatively higher doses and with similar dose potencies, whereas FAD was 6-fold weaker based on drug exposures. FAD was approximately 50-fold selective for reducing PAC versus PCC, whereas MET was only approximately 3-fold selective. We conclude that FAD is a potent, orally active, and relatively selective ASI in two rat models of hyperaldosteronism. MET is an order of magnitude less selective than FAD but is, nevertheless, more potent as an ASI than as an 11beta-hydroxylase inhibitor.

Pharmacokinetics and pharmacodynamics of LCZ696, a novel dual-acting angiotensin receptor-neprilysin inhibitor (ARNi).

Angiotensin receptor blockade and neprilysin (NEP) inhibition together offer potential benefits for the treatment of hypertension and heart failure. LCZ696 is a novel single molecule comprising molecular moieties of valsartan and NEP inhibitor prodrug AHU377 (1:1 ratio). Oral administration of LCZ696 caused dose-dependent increases in atrial natriuretic peptide immunoreactivity (due to NEP inhibition) in Sprague-Dawley rats and provided sustained, dose-dependent blood pressure reductions in hypertensive double-transgenic rats. In healthy participants, a randomized, double-blind, placebo-controlled study (n = 80) of single-dose (200-1200 mg) and multiple-dose (50-900 mg once daily for 14 days) oral administration of LCZ696 showed that peak plasma concentrations were reached rapidly for valsartan (1.6-4.9 hours), AHU377 (0.5-1.1 hours), and its active moiety, LBQ657 (1.8-3.5 hours). LCZ696 treatment was associated with increases in plasma cGMP, renin concentration and activity, and angiotensin II, providing evidence for NEP inhibition and angiotensin receptor blockade. In a randomized, open-label crossover study in healthy participants (n = 56), oral LCZ696 400 mg and valsartan 320 mg were shown to provide similar exposure to valsartan (geometric mean ratio [90% confidence interval]: AUC(0-infinity) 0.90 [0.82-0.99]). LCZ696 was safe and well tolerated. These data support further clinical development of LCZ696, a novel, orally bioavailable, dual-acting angiotensin receptor-NEP inhibitor (ARNi) for hypertension and heart failure.

Echocardiographic examination in rats and mice.

Rats and mice are the predominant experimental species in cardiovascular research due to the widespread availability of genetic and transgenic rodent models of heart disease. Phenotyping of these models requires reliable and reproducible methods to noninvasively and serially assess cardiovascular structure and function. However, the small size of rodents has presented a challenge. Many of these challenges have been overcome in recent years due to significant technological advances in echocardiographic capabilities. For example, improved spatial resolution and increased frame rates have allowed more precise and accurate quantification of diminutive structures, myocardial function, and blood flow in mice. Consequently, transthoracic echocardiography (TTE) has emerged as a popular and powerful tool for cardiac phenotypic characterization in rodents. This chapter will focus on the use of TTE in rodents for evaluating (1) left ventricular (LV) chamber dimensions and wall thickness, (2) LV mass, (3) global LV systolic and diastolic function, (4) regional LV systolic function by newly developed tissue Doppler imaging (TDI), and (5) hemodynamic parameters. Reliability of these measurements depends on various factors such as the skill and experience of the sonographer and the image analyzer, the type, depth, and duration of anesthesia, and animal characteristics. These topics will also be discussed.