Construction of 3D models of the CYP11B family as a tool to predict ligand binding characteristics

Aldosterone is synthesised by aldosterone synthase (CYP11B2). CYP11B2 has a highly homologous isoform, steroid 11β-hydroxylase (CYP11B1), which is responsible for the biosynthesis of aldosterone precursors and glucocorticoids. To investigate aldosterone biosynthesis and facilitate the search for selective CYP11B2 inhibitors, we constructed three-dimensional models for CYP11B1 and CYP11B2 for both human and rat. The models were constructed based on the crystal structure of Pseudomonas Putida CYP101 and Oryctolagus Cuniculus CYP2C5. Small steric active site differences between the isoforms were found to be the most important determinants for the regioselective steroid synthesis. A possible explanation for these steric differences for the selective synthesis of aldosterone by CYP11B2 is presented. The activities of the known CYP11B inhibitors metyrapone, R-etomidate, R-fadrazole and S-fadrazole were determined using assays of V79MZ cells that express human CYP11B1 and CYP11B2, respectively. By investigating the inhibitors in the human CYP11B models using molecular docking and molecular dynamics simulations we were able to predict a similar trend in potency for the inhibitors as found in the in vitro assays. Importantly, based on the docking and dynamics simulations it is possible to understand the enantioselectivity of the human enzymes for the inhibitor fadrazole, the R-enantiomer being selective for CYP11B2 and the S-enantiomer being selective for CYP11B1

Effects of Thyrotropin and Thyrotropin-Receptor-Stimulating Graves' Disease Immunoglobulin G on Cyclic Adenosine Monophosphate and Hyaluronan Production in Nondifferentiated Orbital Fibroblasts of Graves' Ophthalmopathy Patients

Background: Orbital fibroblasts are involved in the pathogenesis of Graves' ophthalmopathy (GO) by producing hyaluronan (HA), synthesized by three types of hyaluronan synthases (HAS1, HAS2, and HAS3). Thyrotropin receptors (TSHR) expressed in orbital fibroblasts activate the cyclic adenosine monophosphate (cAMP) pathway. Only sparse data are available at present supporting a role for TSHR activation in the regulation of HA in GO orbital fibroblasts. We hypothesize that TSHR activation, via cAMP signaling, results in induction of HAS1-3 mRNA expression and HA production by nondifferentiated GO orbital fibroblasts. Methods: Cultured nondifferentiated orbital fibroblasts obtained during orbital decompression surgery from 15 GO patients were stimulated with recombinant human TSH (rhTSH), TSHR-stimulating Graves' disease immunoglobulin G (GD-IgG) or forskolin (FSK), or interleukin-1 beta (IL-1 beta). Results: FSK significantly stimulated cAMP production, HAS1 and HAS3 mRNA expression, and HA secretion in orbital fibroblasts. IL-1 beta slightly induced cAMP production, but induced HAS mRNA expression of all three isoforms and HA secretion. In contrast, the effects of rhTSH and GD-IgG on cAMP were modest and absent, respectively, and on HAS mRNA and HA synthesis were completely absent. Conclusions: The strong increase in cAMP synthesis by FSK in nondifferentiated GO orbital fibroblasts results in increased HA synthesis, but TSHR activation by rhTSH or GD-IgG does not result in altered HA synthesis. Our results do not support a predominant role for GD-IgGs in the accumulation of orbital glycosaminoglycans; cytokines like IL-1 beta seem largely responsible for excessive glycosaminoglycan production by nondifferentiated orbital fibroblasts in early immunopathogenesis of G

Complete Inhibition of rhTSH-, Graves' Disease IgG-, and M22-Induced cAMP Production in Differentiated Orbital Fibroblasts by a Low-Molecular-Weight TSHR Antagonist

The TSH receptor (TSHR) on orbital fibroblasts (OF) is a proposed target of the autoimmune attack in Graves' ophthalmopathy. In the present study, we tested whether the novel low-molecular-weight (LMW) TSHR antagonist Org-274179-0 inhibits cAMP production induced by rhTSH, Graves' disease IgG (GD-IgG), or M22 (a potent human monoclonal TSHR stimulating antibody) in cultured and differentiated OF from Graves' ophthalmopathy patients. cAMP production significantly increased after incubation either with 10 mU/ml rhTSH (3-fold; P <= 0.05), 1 mg/ml GD-IgG (2-fold; P <= 0.05), or 500 ng/ml M22 (5-fold; P <= 0.05). Incubation with the LMW TSHR antagonist dose dependently inhibited rhTSH, GD-IgG as well as the M22-induced cAMP production at nanomolar concentrations; complete blockade was affected at 10(-6) M. Our results suggest that GD-IgG- and M22-induced cAMP production in differentiated OF is exclusively mediated via the TSHR because it can be completely blocked by the LMWTSHR antagonist, Org 274179-0. (J Clin Endocrinol Metab 97: E781-E785, 2012

Application of a Ligand-Based Theoretical Approach to Derive Conversion Paths and Ligand Conformations in CYP11B2-Mediated Aldosterone Formation

The biosynthesis of the mineralocorticoid hormone aldosterone involves a multistep hydroxylation of 11-deoxycorticosterone at the 11- and 18-positions, resulting in the formation of corticosterone and 18-hydroxycorticosterone, the final precursor of aldosterone. Two members of the cytochrome P450 11B family, CYP11B1 and CYP11B2, are known to catalyze these 11- and 18-hydroxylations, however, only CYP11B2 can oxidize 18-hydroxycorticosterone to aldosterone. It is unknown what sequence of hydroxylations leads to the formation of 18-hydroxycorticosterone. In this study we have investigated which of the possible conversion paths towards formation of 18-hydroxycorticosterone and aldosterone are most likely from the ligand perspective. Therefore, we combined quantum mechanical investigations on the steroid conformations of 11-deoxycorticosterone and its ensuing reaction intermediates with Fukui indices calculations to predict the reactivity of their carbon atoms for an attack by the iron-oxygen species. Both F(-) and F(0) were calculated to account for different mechanisms of substrate conversion. We show which particular initial conformations of 11-deoxycorticosterone and which conversion paths are likely to result in the successful synthesis of aldosterone, and thereby may be representative for the mechanism of aldosterone biosynthesis by CYP11B2. Moreover, we found that the most likely path for aldosterone synthesis coincides with the substrate conformation proposed in an earlier publication (Ref. (2)). To summarize, we show that on a theoretical and strictly ligand-directed basis only a limited number of reaction paths in the conversion of 11-deoxycorticosterone to aldosterone is possible. Despite its theoretical nature, this knowledge may help to understand the catalytic function of CYP11B1 and CYP11B2

Mechanism of Action of a Nanomolar Potent, Allosteric Antagonist of the Thyroid-Stimulating Hormone Receptor

Background and purpose  Graves' disease (GD) is an autoimmune disease in which the thyroid is overactive, producing excessive amounts of thyroid hormones, caused by TSHR-stimulating immunoglobulins (TSIs). A large proportion of GD patients also suffer from thyroid eye disease (Graves' ophthalmopathy or GO), with the TSIs considered to activate TSHRs in orbital tissue also. We recently developed LMW TSHR antagonists as a novel therapeutic strategy for the treatment of GD and GO. In the present study, we determined the molecular pharmacology of a prototypic, nanomolar potent LMW TSHR antagonist, Org 274179-0. Experimental approach  First, we determined the potency and efficacy of Org 274179-0 in antagonizing TSH- and TSI-induced TSHR signaling and its cross-reactivity at the related FSHR and LHR. Second, we explored in depth the allosteric mode of interaction of Org 274179-0. Third, we determined whether Org 274179-0 is an inverse agonist at five naturally occurring, constitutively active TSHR mutants. Key results  Org 274179-0 fully inhibited TSH (and TSI)-mediated TSHR activation with nanomolar potency without hardly affecting the potency of TSH, in accordance with an allosteric mechanism of action. On the reverse, increasing levels of TSHR stimulation only marginally reduced the antagonistic potency of Org 274179-0. Finally, Org 274179-0 fully blocked the increased basal activity of all tested constitutively active TSHR mutants with nanomolar potencies. Conclusions and implications  We conclude that nanomolar potent TSHR antagonists like Org 274179-0 have the potential of being developed to treat GD and GO

Synthesis, Biological Evaluation, and Molecular Modeling of 1-Benzyl-1H-imidazoles as Selective Inhibitors of Aldosterone Synthase (CYP11B2)

Reducing aldosterone action is beneficial in various major diseases such as heart failure. Currently, flits is achieved with mineralocorticoid receptor antagonists, however, aldosterone synthase (CYP11B2) inhibitors may offer a promising alternative. In this study, WC used three-dimensional modeling of CYP11B2 to model the binding modes of the natural substrate 18-hydroxycorticosterone and the recently published CYP11B2 inhibitor R-fadrozole as a rational guide to design 44 structurally simple and achiral 1-benzyl-1H-imidazoles. Their syntheses, in vitro inhibitor potencies, and in silico docking are described. Some promising CYP11B2 inhibitors were identified, with our novel lead MOERAS115 (4-((5-phenyl-1H-imidazol-1-y1)methyl)benzonitrile) displaying an IC50 for CYP11B2 of 1.7 nM, and a CYP11B2 (versus CYP11B1) selectivity of 16.5, comparable to R-fadrozole (IC50 for CYP11B2 6.0 nM. Selectivity 19.8). Molecular docking of the Inhibitors in the models enabled us to generate posthoc hypotheses oil their binding modes, providing a Valuable basis for future Studies and further design of CYP11B2 inhibitors