Preclinical and Early Clinical Profile of a Highly Selective and Potent Oral Inhibitor of Aldosterone Synthase (CYP11B2)

Abstract

Primary hyperaldosteronism is a common cause of resistant hypertension. Aldosterone is produced in the adrenal by aldosterone synthase (AS, encoded by the gene CYP11B2). AS shares 93% homology to 11β-hydroxylase (encoded by the gene CYP11B1), responsible for cortisol production. This homology has hitherto impeded the development of a drug, which selectively suppresses aldosterone but not cortisol production, as a new treatment for primary hyperaldosteronism. We now report the development of RO6836191 as a potent (Ki 13 nmol/L) competitive inhibitor of AS, with in vitro selectivity >100-fold over 11β-hydroxylase. In cynomolgus monkeys challenged with synthetic adrenocorticotropic hormone, single doses of RO6836191 inhibited aldosterone synthesis without affecting the adrenocorticotropic hormone-induced rise in cortisol. In repeat-dose toxicity studies in monkeys, RO6836191 reproduced the adrenal changes of the AS-/- mouse: expansion of the zona glomerulosa; increased expression of AS (or disrupted green fluorescent protein gene in the AS-/- mouse); hypertrophy, proliferation, and apoptosis of zona glomerulosa cells. These changes in the monkey were partially reversible and partially preventable by electrolyte supplementation and treatment with an angiotensin-converting enzyme inhibitor. In healthy subjects, single doses of RO6836191, across a 360-fold dose range, reduced plasma and urine aldosterone levels with maximum suppression at a dose of 10 mg, but unchanged cortisol, on adrenocorticotropic hormone challenge, up to 360 mg, and increase in the precursors 11-deoxycorticosterone and 11-deoxycortisol only at or >90 mg. In conclusion, RO6836191 demonstrates that it is possible to suppress aldosterone production completely in humans without affecting cortisol production.

Clinical trial registration: URL: http://www.clinicaltrials.gov. Unique identifier: NCT01995383.

Keywords: CYP11B2; adrenal cortex; aldosterone; cytochrome P-450; hydrocortisone; hyperaldosteronism; zona glomerulosa.

© 2016 The Authors.

Figures

Figure 1.

Histopathologic changes in the cynomolgus monkey zona glomerulosa in the high-dose (A) and mechanistic (B) safety studies. A, Histopathology of representative monkeys in the high-dose study. Animals were administered RO6836191 at 0, 1, 7, or 40 mg/kg for 4 weeks and recovery after 40 mg/kg. Staining with hematoxylin-eosin (upper); immunostaining with human anti-CYP11B2 antibody to visualize the zona glomerulosa (lower). Scale bar=100 µm. Dotted lines delineate the demarcation between the zona glomerulosa from the underlying zonal fasciculata. B, Histopathology of representative monkeys in the mechanistic study. Animals were administered RO6836191 at 1 mg/kg for 4 weeks, with or without electrolytes (E) or angiotensin-converting enzyme inhibitor lisinopril 0.5 mg/kg (A), recovery after treatment with 1 mg/kg with electrolytes (E*), control monkeys were administered electrolytes alone. Staining with hematoxylin-eosin (scale bar=100 µm; upper), double-sided arrows delineate width of the zona glomerulosa (ZG), single-sided arrows indicate the transitional zone of the ZG. Immunostaining with human anti-CYP11B2 antibody to visualize the zona glomerulosa (scale bar=50 µm; lower).

Figure 2.

Dose-dependent effect of RO6836191 on plasma aldosterone, cortisol, and precursors in cynomolgus monkeys. Data represent individual % change from vehicle in plasma concentration (measured at 1 hour post-adrenocorticotropic hormone challenge) for aldosterone and precursors (A) and cortisol and precursors (B) by dose group. Means by dose group are connected by a line (n=2/dose group). 11-DOC indicates 11-deoxycorticosterone.

Figure 3.

Dose-dependent effect of RO6836191 on plasma aldosterone, cortisol, and precursors in healthy subjects (study part 1). Aldosterone (A) and cortisol (B) plasma concentration-time profiles after single ascending doses of RO6836191 (0–360 mg) administered orally to healthy subjects 1 hour before the adrenocorticotropic hormone (ACTH) challenge. Downward arrow indicates time of ACTH challenge (1 hour postdose) and upward arrow time of postural change (6 hours postdose). Data represent mean plasma concentrations (+SD) by dose group (n=6/dose group and n=12 for placebo). Below limit of quantification (BLQ) values were set to lower limit of quantification (LLOQ; 5 pg/mL), for doses >10 mg, aldosterone concentrations were BLQ from 2.5 hours postdose onward. Effect of RO6836191 on plasma aldosterone (C), cortisol (D), and precursors after a single oral dose (0–360 mg) in healthy subjects administered 1 hour before the ACTH challenge. Data represent mean (and 90% confidence interval) % change from baseline in plasma exposure (AUC0-24) for aldosterone and precursors (left graph) and cortisol and precursors (right graph) by dose group (n=6/dose group and n=12 for placebo). Filled symbols indicate P<0.01 compared with placebo. 11-DOC indicates 11-deoxycorticosterone.

Figure 4.

Urinary sodium-to-potassium ratio after single-dose administration of 1, 3, 10 mg RO6836191 or placebo to healthy subjects under low-salt diet (study part 2). Box whiskers show interquartile range (box) and min–max (whiskers) for Na/K ratio from 24-hour urine collections, by dose group (n=6/dose group) at baseline (BL), on day 1 and day 2.