Development of a simplified assay for determination of the antimineralocorticoid activity of compounds dosed in rats

Role of electrolyte concentrations and renin-angiotensin-aldosterone activation in the staging of canine heart disease

Background

Refractory congestive heart failure (CHF) and associated diuretic resistance are not well defined.

Objectives

To characterize renal function, electrolyte concentrations, indices of diuretic efficacy, and renin‐angiotensin‐aldosterone system (RAAS) activation in dogs with naturally occurring heart disease (HD) in American College of Veterinary Internal Medicine stages B1, B2, C, and D and to determine their usefulness in defining HD stages.

Animals

Group 1:149 dogs with HD stages B1, B2, C, and D. Group 2:22 dogs with HD stages C and D.

Methods

Group 1: Renal parameters, serum and urine electrolyte and diuretic concentrations, and urine aldosterone concentrations were measured. Medication dosages and measured variables were compared among stages. Correlation of furosemide dosages to serum concentrations was explored. Group 2: Angiotensin‐converting enzyme activity and RAAS components were measured and compared among CHF stages.

Results

Serum chloride concentration was the best differentiator of HD stage. Furosemide PO dosages (≤6 mg/kg/day) were weakly correlated with serum furosemide concentrations, whereas higher dosages were not significantly correlated. Angiotensin‐converting enzyme inhibitor dosage and RAAS inhibition were greater in stage D, compared to stage C dogs.

Conclusions and Clinical Importance

Hypochloremia is a useful marker for stage D HD in dogs. Poor furosemide dosage correlation to serum concentration may indicate variable and poor absorption, especially at higher dosages, advanced disease, or both. A small number of stage D dogs met proposed criteria for diuretic resistance. Greater RAAS inhibition in stage D versus stage C indicates effectiveness of RAAS‐suppressive treatments in this group of dogs with refractory CHF.

The selective mineralocorticoid receptor modulator AZD9977 reveals differences in mineralocorticoid effects of aldosterone and fludrocortisone

Introduction:

AZD9977 is a novel mineralocorticoid receptor (MR) modulator, which in preclinical studies demonstrated organ protection without affecting aldosterone-regulated urinary electrolyte excretion. However, when tested in humans, using fludrocortisone as an MR agonist, AZD9977 exhibited similar effects on urinary Na⁺/K⁺ ratio as eplerenone. The aim of this study is to understand whether the contradictory results seen in rats and humans are due to the mineralocorticoid used.

Materials and methods:

Rats were treated with single doses of AZD9977 or eplerenone in combination with either aldosterone or fludrocortisone. Urine was collected for five to six hours and total amounts excreted Na⁺ and K⁺ were assessed.

Results:

AZD9977 dose-dependently increased urinary Na⁺/K⁺ ratio in rats when tested against fludrocortisone, but not when tested against aldosterone. Eplerenone dose-dependently increased urinary Na⁺/K⁺ ratio when tested against fludrocortisone as well as aldosterone.

Conclusions:

The data suggest that the contrasting effects of AZD9977 on urinary electrolyte excretion observed in rats and humans are due to the use of the synthetic mineralocorticoid fludrocortisone. Future clinical studies are required to confirm the reduced electrolyte effects of AZD9977 and the subsequent lower predicted hyperkalemia risk.

Pharmacodynamic assessment of diuretic efficacy and braking in a furosemide continuous infusion model

INTRODUCTION

Diuretic failure is a potential life-ending event but is unpredictable and poorly understood. The objectives of this study were to evaluate pharmacodynamic markers of furosemide-induced diuresis and to investigate mechanisms of diuretic braking in dogs receiving constant rate infusion (CRI) of furosemide.

ANIMALS

Six healthy male dogs.

METHODS

Raw data and stored samples from one arm of a previously published study were further analyzed to mechanistically investigate causes of diuretic braking in these dogs. Urine volume was recorded hourly during a 5-h furosemide CRI. Urine and blood samples were collected hourly to measure serum and urine electrolytes, urine aldosterone, and plasma and urine furosemide. Serum electrolyte fractional excretion was calculated. Urine sodium concentration was indexed to urine potassium (uNa:uK) and urine furosemide (uNa:uFur) concentrations, plasma furosemide concentration was indexed to urine furosemide concentration (pFur:uFur), and urine aldosterone was indexed to urine creatinine (UAldo:C). Temporal change and the relationship to urine volume were evaluated for these measured and calculated variables.

RESULTS

Urine volume was significantly correlated with urine electrolyte amounts and with uNa:uK. The ratio of pFur:uFur decreased during the infusion, whereas furosemide excretion was unchanged.

CONCLUSIONS

There was a strong relationship between urine volume and absolute urine electrolyte excretion. Urine volume was strongly correlated to uNa:uK, giving it potential as a spot indicator of urine production during diuresis. The decrease in uNa:uK over time during the infusion is consistent with mineralocorticoid modification of urinary electrolyte excretion, supporting renin-angiotensin-aldosterone activation as a cause of diuretic braking in this model.

Identification of Morpholino-2H-pyrido[3,2-b][1,4]oxazin-3(4H)-ones as Nonsteroidal Mineralocorticoid Antagonists

A novel series of morpholine-based nonsteroidal mineralocorticoid receptor antagonists is reported. Starting from a pyrrolidine HTS hit 9 that possessed modest potency but excellect selectivity versus related nuclear hormone receptors, a series of libraries led to identification of morpholine lead 10. After further optimization, cis disubstituted morpholine 22 was discovered, which showed a 45-fold boost in binding affinity and corresponding functional potency compared to 13. While 22 had high clearance in rat, it provided sufficient exposure at high doses to favorably assess in vivo efficacy (increased urinary Na⁺/K⁺ ratio) and safety. In contrast to rat, the dog and human MetID and PK profiles of 22 were adequate, suggesting that it could be suitable as a potential clinical asset.

Finerenone, a novel selective nonsteroidal mineralocorticoid receptor antagonist protects from rat cardiorenal injury

Pharmacological blockade of the mineralocorticoid receptor (MR) ameliorates end-organ damage in chronic heart failure. However, the clinical use of available steroidal MR antagonists is restricted because of concomitant hyperkalemia especially in patients with diminished kidney function. We have recently identified a novel nonsteroidal MR antagonist, finerenone, which uniquely combines potency and selectivity toward MR. Here, we investigated the tissue distribution and chronic cardiorenal end-organ protection of finerenone in comparison to the steroidal MR antagonist, eplerenone, in 2 different preclinical rat disease models. Quantitative whole-body autoradiography revealed that [C]-labeled finerenone equally distributes into rat cardiac and renal tissues. Finerenone treatment prevented deoxycorticosterone acetate-/salt-challenged rats from functional as well as structural heart and kidney damage at dosages not reducing systemic blood pressure. Finerenone reduced cardiac hypertrophy, plasma prohormone of brain natriuretic peptide, and proteinuria more efficiently than eplerenone when comparing equinatriuretic doses. In rats that developed chronic heart failure after coronary artery ligation, finerenone (1 mg·kg·d), but not eplerenone (100 mg·kg·d) improved systolic and diastolic left ventricular function and reduced plasma prohormone of brain natriuretic peptide levels. We conclude that finerenone may offer end-organ protection with a reduced risk of electrolyte disturbances.

DSR-71167, a novel mineralocorticoid receptor antagonist with carbonic anhydrase inhibitory activity, separates urinary sodium excretion and serum potassium elevation in rats

Mineralocorticoid receptor (MR) antagonists, such as spironolactone (SPI) and eplerenone (EPL), are useful for treating hypertension and heart failure. However, these two agents have the serious side effect of hyperkalemia. We hypothesized that adding the ability to inhibit carbonic anhydrase (CA) would reduce the risk of hyperkalemia associated with MR antagonists. We investigated the profiles of DSR-71167 [2-([(2,2-difluoroethyl)amino]methyl)-2'-fluoro-N-(3-methoxy-4-sulfamoylphenyl)biphenyl-4-carboxamide hydrochloride; an MR antagonist with weak CA inhibitory activity] with regard to antimineralocorticoid actions by examining relationships between the urinary excretion of sodium (index of antimineralocorticoid action) in deoxycorticosterone acetate-treated rats and elevation of serum levels of potassium in potassium-loaded rats compared with a DSR-71167 derivative without CA inhibition (2-(hydroxymethyl)-N-[4-(methylsulfonyl)phenyl]-2'-(trifluoromethyl)biphenyl-4-carboxamide), SPI, and EPL. DSR-71167 dose-dependently increased urinary excretion of sodium in deoxycorticosterone acetate-treated rats without elevating serum levels of potassium in potassium-loaded rats. 2-(Hydroxymethyl)-N-[4-(methylsulfonyl)phenyl]-2'-(trifluoromethyl)biphenyl-4-carboxamide, SPI, and EPL elevated serum levels of potassium significantly in potassium-loaded rats at doses that increased MR inhibitory activity. We confirmed that DSR-71167 significantly increases urinary bicarbonate and decreases blood bicarbonate, as pharmacodynamic markers of CA inhibition, in intact rats. Chronic DSR-71167 administration showed antihypertensive effects in high salt-loaded Dahl hypertensive rats. These results demonstrate that DSR-71167 is a novel type of MR antagonist, with CA inhibitory activity, which is expected to become a safer MR antagonist with a low potential risk for hyperkalemia.

PF-03882845, a non-steroidal mineralocorticoid receptor antagonist, prevents renal injury with reduced risk of hyperkalemia in an animal model of nephropathy

The mineralocorticoid receptor (MR) antagonists PF-03882845 and eplerenone were evaluated for renal protection against aldosterone-mediated renal disease in uninephrectomized Sprague-Dawley (SD) rats maintained on a high salt diet and receiving aldosterone by osmotic mini-pump for 27 days. Serum K(+) and the urinary albumin to creatinine ratio (UACR) were assessed following 14 and 27 days of treatment. Aldosterone induced renal fibrosis as evidenced by increases in UACR, collagen IV staining in kidney cortex, and expression of pro-fibrotic genes relative to sham-operated controls not receiving aldosterone. While both PF-03882845 and eplerenone elevated serum K(+) levels with similar potencies, PF-03882845 was more potent than eplerenone in suppressing the rise in UACR. PF-03882845 prevented the increase in collagen IV staining at 5, 15 and 50 mg/kg BID while eplerenone was effective only at the highest dose tested (450 mg/kg BID). All doses of PF-03882845 suppressed aldosterone-induced increases in collagen IV, transforming growth factor-β 1 (Tgf-β 1), interleukin-6 (Il-6), intermolecular adhesion molecule-1 (Icam-1) and osteopontin gene expression in kidney while eplerenone was only effective at the highest dose. The therapeutic index (TI), calculated as the ratio of the EC50 for increasing serum K(+) to the EC50 for UACR lowering, was 83.8 for PF-03882845 and 1.47 for eplerenone. Thus, the TI of PF-03882845 against hyperkalemia was 57-fold superior to that of eplerenone indicating that PF-03882845 may present significantly less risk for hyperkalemia compared to eplerenone.

The use of plasma aldosterone and urinary sodium to potassium ratio as translatable quantitative biomarkers of mineralocorticoid receptor antagonism

BACKGROUND

Accumulating evidence supports the role of the mineralocorticoid receptor (MR) in the pathogenesis of diabetic nephropathy. These findings have generated renewed interest in novel MR antagonists with improved selectivity against other nuclear hormone receptors and a potentially reduced risk of hyperkalemia. Characterization of novel MR antagonists warrants establishing translatable biomarkers of activity at the MR receptor. We assessed the translatability of urinary sodium to potassium ratio (Na+/K+) and plasma aldosterone as biomarkers of MR antagonism using eplerenone (Inspra®), a commercially available MR antagonist. Further we utilized these biomarkers to demonstrate antagonism of MR by PF-03882845, a novel compound.

METHODS

The effect of eplerenone and PF-03882845 on urinary Na+/K+ and plasma aldosterone were characterized in Sprague-Dawley rats and spontaneously hypertensive rats (SHR). Additionally, the effect of eplerenone on these biomarkers was determined in healthy volunteers. Drug exposure-response data were modeled to evaluate the translatability of these biomarkers from rats to humans.

RESULTS

In Sprague-Dawley rats, eplerenone elicited a rapid effect on urinary Na+/K+ yielding an EC50 that was within 5-fold of the functional in vitro IC50. More importantly, the effect of eplerenone on urinary Na+/K+ in healthy volunteers yielded an EC50 that was within 2-fold of the EC50 generated in Sprague-Dawley rats. Similarly, the potency of PF-03882845 in elevating urinary Na+/K+ in Sprague-Dawley rats was within 3-fold of its in vitro functional potency. The effect of MR antagonism on urinary Na+/K+ was not sustained chronically; thus we studied the effect of the compounds on plasma aldosterone following chronic dosing in SHR. Modeling of drug exposure-response data for both eplerenone and PF-03882845 yielded EC50 values that were within 2-fold of that estimated from modeling of drug exposure with changes in urinary sodium and potassium excretion. Importantly, similar unbound concentrations of eplerenone in humans and SHR rats yielded the same magnitude of elevations in aldosterone, indicating a good translatability from rat to human.

CONCLUSIONS

Urinary Na+/K+ and plasma aldosterone appear to be translatable biomarkers of MR antagonism following administration of single or multiple doses of compound, respectively.

TRIAL REGISTRATION

For clinical study reference EE3-96-02-004, this study was completed in 1996 and falls out scope for disclosure requirements. Clinical study reference A6141115: http://clinicaltrials.gov, http://NIHclinicaltrails.gov; NCTID: NCT00990223.

A new mode of mineralocorticoid receptor antagonism by a potent and selective nonsteroidal molecule

Limitations of current steroidal mineralocorticoid receptor (MR) antagonists have stimulated the search for a new generation of molecules. We screened for novel nonsteroidal compounds and identified MR antagonists derived from the chemical class of dihydropyridines. Chemical optimization resulted in BR-4628, which displays high in vitro and in vivo MR potency as well as selectivity with respect to the other steroid hormone receptors and the L-type calcium channel. Biochemical studies demonstrated that BR-4628 forms complexes with MR that do not promote the recruitment of transcriptional co-regulators. Docking experiments, using the crystal structure of the MR ligand-binding domain in an agonist conformation, revealed that BR-4628 accommodates in the MR ligand-binding cavity differently in comparison with the classical steroidal MR antagonists. An alanine scanning mutagenesis approach, based on BR-4628 docking, allowed identifying its anchoring mode within the ligand-binding cavity. Altogether, we propose that BR-4628 is a bulky antagonist that inactivates MR through a passive mechanism. It represents the prototype of a new class of MR antagonists.

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.