Hepcidin-20 (human) trifluoroacetate salt – Key iron-regulatory peptide for human iron metabolism and ferroportin research.

Highlights

• Inhibiting CYP11B2 with small molecules offers a promising treatment for aldosterone-related diseases.
• Different classes of compounds targeting CYP11B2 are summarized.
• Application prospects and future development directions of CYP11B2 inhibitors were proposed.

Abstract

Aldosterone synthase (CYP11B2) is the rate-limiting enzyme in aldosterone production. In recent years, CYP11B2 has become an appealing target for treating conditions associated with excess aldosterone, such as hypertension, heart failure, and cardiometabolic diseases. Several small-molecule inhibitors of CYP11B2 have demonstrated efficacy in both preclinical studies and clinical trials. Among them, the tetrahydroisoquinoline derivative Baxdrostat has entered clinical trial phases and demonstrated efficacy in treating patients with hypertension. However, the high homology (>93%) between CYP11B2 and steroid-11β-hydroxylase (CYP11B1), which catalyzes cortisol production, implies that insufficient drug specificity can lead to severe side effects. Developing selective inhibitors for CYP11B2 remains a considerable challenge that requires ongoing attention. This review summarizes recent research progress on small-molecule inhibitors targeting CYP11B2, focusing on structure-activity relationships (SAR) and structural optimization. It discusses strategies for enhancing the specificity and inhibitory activity of inhibitors, while also exploring potential applications and future prospects for CYP11B2 inhibitors, providing a theoretical foundation for developing the new generation of CYP11B2-targeted medications.

Introduction

Aldosterone synthase (CYP11B2) is an enzyme belonging to the cytochrome P450 superfamily (CYPs), primarily expressed in the adrenal cortex. CYPs are a class of monooxygenases that require heme as a cofactor and can catalyze various biochemical reactions, including hydroxylation, epoxidation, dealkylation, carbon-carbon bond formation, and oxidative cleavage [1,2]. To date, at least 57 cytochrome P450 genes have been identified, divided into 18 families and 43 subfamilies, playing major roles in drug metabolism and the synthesis of cholesterol, steroids, and other lipids in the human body [3]. In the synthesis of steroid hormones, up to six CYPs are involved: cholesterol-20,22-desmolase (CYP11A1), 17α-hydroxylase (CYP17A1), steroid 21-hydroxylase (CYP21A2), steroid-11β-hydroxylase (CYP11B1), and CYP11B2 [4,5]. Among these, CYP11B2 is located in the mitochondrial inner membrane, comprising 503 amino acids and featuring a mitochondrial membrane localization sequence of 24 residues, possessing both hydroxylase and oxidase activities [6,7]. CYP11B2 catalyzes three consecutive reactions with the substrate 11-deoxycorticosterone (DOC) to produce aldosterone: the 11-β-hydroxylation of DOC to corticosterone, the 18-hydroxylation of corticosterone to 18-hydroxycorticosterone, and the 18-oxidation of 18-hydroxycorticosterone to aldosterone (Fig. 1A). It is the sole enzyme responsible for the final step in aldosterone synthesis.

Aldosterone is the crucial mineralocorticoid hormone for regulating sodium-potassium balance, which is mainly regulated by blood potassium levels and the renin-angiotensin-aldosterone system (RAAS). Aldosterone activates mineralocorticoid receptors (MRs) in distal nephron principal cells, leading to the transport of the aldosterone-MR complex into the nucleus, where it binds to hormone response elements necessary for the transcription of the epithelial sodium channel (ENaC) and Na+-K+ ATPase. This process increases Na+ reabsorption and increases K+ excretion (Fig. 1B) [[8], [9], [10]]. Additionally, aldosterone promotes the expression of the renal outer medullary potassium (ROMK) channel, further facilitating K+ secretion. Pathologically elevated aldosterone levels can result from the overproduction of aldosterone due to adrenal hyperplasia or adrenal adenoma or from reduced cardiac output, leading to secondary hyperaldosteronism (Fig. 1C) [11]. Left ventricular systolic dysfunction leads to a decrease in renal blood flow, which stimulates renin secretion by the juxtaglomerular apparatus. Renin cleaves angiotensinogen to angiotensin I (AT I), which is converted to angiotensin II (AT II) in the pulmonary arteries by angiotensin-converting enzyme (ACE) [12,13]. AT II stimulates the zona glomerulosa cells of the adrenal cortex to secrete aldosterone, raising plasma aldosterone levels, which can negatively impact the cardiovascular system [[14], [15], [16], [17]].

Elevated aldosterone levels in pathological conditions can cause endothelial dysfunction, reduce vascular reactivity, activate vascular inflammation, and promote tissue fibrosis. Other cardiovascular complications of hyperaldosteronism include activation of the sympathetic nervous system, decreased baroreceptor sensitivity, and cardiomyocyte apoptosis (Fig. 1C). Aberrant expression or activation of CYP11B2 is closely associated with hypertension and other adrenal disorders, making it a critical target for treating primary aldosteronism (PA), congestive heart failure (CHF), and hypertension [[18], [19], [20], [21]]. The final steps in the biosynthesis of aldosterone and cortisol (the primary glucocorticoid in humans) are carried out by CYP11B2 and CYP11B1, respectively [5,22]. While CYP11B2 produces aldosterone in the zona glomerulosa of the adrenal cortex, CYP11B1 converts 11-deoxycortisol and DOC to cortisol and corticosterone in the zona fasciculata. The genes for CYP11B2 and CYP11B1 are located on chromosome 8q22, approximately 40 kb apart, with identical arrangements of 8 introns and 9 exons. The exon sequences share 95% homology, the intron sequences share 90% homology, and the encoded proteins share 93% homology, differing in only 29 amino acids, most of which are outside the active sites of enzymes [7,23,24]. This high level of similarity presents a challenge when developing selective CYP11B2 inhibitors that do not affect the activity of CYP11B1, allowing the synthesis of cortisol to remain unimpeded [25].

This review analyzes the critical role of CYP11B2 in regulating aldosterone synthesis from the standpoint of protein structure and biological function, while summarizing the development and optimization of small-molecule inhibitors in recent years. It provides a detailed analysis of the structure-activity relationships (SARs) pertaining to CYP11B2's inhibitory potency and its selectivity over CYP11B1 or other CYP enzymes. This analysis is useful for understanding which chemical structural features enhance target specificity and biological activity, serving as an important theoretical foundation for developing the new generation of more selective and effective inhibitors targeting CYP11B2.

Crystal structure of CYP11B2

The crystal structure of CYP11B2 in complex with its substrate DOC (PDB code: 4DVQ) was first reported in 2013 by Natalia Strushkevich and colleagues (Fig. 2A) [26]. As a member of the CYPs family, CYP11B2 has a typical cytochrome P450 fold structure which encapsulates the heme group [27]. At the active site, the heme-iron group is held in place through coordination between iron and the sulfur atom of a cysteine residue at position 450, leaving the 6th coordination position vacant. This is

Small molecule inhibitors of CYP11B2

Selective inhibitors targeting CYP11B2 represent an effective approach for treating hypertension, congestive heart failure, and myocardial fibrosis. Early aldosterone synthase inhibitors (ASIs) included steroid-based compounds and non-selective non-steroidal compounds [25,39]. Tests conducted on rat or bovine tissues showed that various progesterone and deoxycorticosterone derivatives exhibited a certain level of CYP11B2 inhibition. Mespirenone (1) (Fig. 3A) reduced aldosterone and

The development value of selective CYP11B2 inhibitors

The therapeutic potential of ASIs in PA and cardiovascular-related diseases has been firmly established. To minimize potential side effects, future research and development efforts will focus on creating highly selective CYP11B2 inhibitors, targeting aldosterone synthase activity while reducing the impact on other related enzymes. For instance, at the 2023 American College of Cardiology Annual Meeting, a novel ASI from China, JX09 (formerly known as PB 6440), was noted for its selectivity

Conclusions and perspectives

Aldosterone is a crucial mineralocorticoid [138], and its overexpression or deficiency can lead to various pathological conditions, including heart failure, high blood pressure, kidney disease, tissue fibrosis, or salt-wasting syndrome [139]. Clinically, mineralocorticoid receptor antagonists (MRAs) or RAAS inhibitors are used to suppress the harmful effects of aldosterone. However, the use of steroidal MRAs has been associated with adverse reactions, particularly the accumulation of

CRediT authorship contribution statement

Cuiyu Guo: Writing – review & editing, Writing – original draft, Data curation, Conceptualization. Guangbing Zhang: Writing – review & editing, Writing – original draft, Data curation. Chengyong Wu: Visualization, Data curation. Yi Lei: Supervision, Validation. Yuxi Wang: Validation, Supervision, Conceptualization. Jinliang Yang: Validation, Supervision, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This review was supported by Research Unit of Gene and Immunotherapy, Chinese Academy of Medical Sciences (No. 2019RU067).

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