Discovery of non-steroidal mifepristone mimetics: Pyrazoline-based PR antagonists

Cu(II)-Catalyzed Aminocyclization of N-Propargyl Hydrazones to Substituted Pyrazolines

An efficient route for the copper(II)-catalyzed synthesis of substituted pyrazolines from readily accessible N-propargyl hydrazones has been reported under open flask conditions via intramolecular C-N bond formation. N-acyl and N-tosyl-substituted pyrazolines have been prepared in moderate to excellent yields. Mechanistic investigations using NMR, high-resolution mass spectrometry (HRMS), and Hammett analyses suggest that the Cu(II) catalyst generally acts as a Lewis acid to form an iminium-ion intermediate via cyclization, which afforded the desired pyrazolines upon hydrolysis. One progesterone receptor antagonist has also been synthesized utilizing this reaction methodology.

Oxime Esters: Flexible Building Blocks for Heterocycle Formation

Oxime esters as the applicable building blocks, internal oxidizing agents, and directing groups in the synthesis of -, S-, and O-containing heterocycle scaffolds have gained great attention in the last decade. This review provides an overview of recent advances in the cyclization of oxime esters with various functional group reagents under transition metal and transition metal-free catalyzed conditions. Moreover, the mechanistic aspects of these protocols are explained in detail.

StackPR is a new computational approach for large-scale identification of progesterone receptor antagonists using the stacking strategy

Progesterone receptors (PRs) are implicated in various cancers since their presence/absence can determine clinical outcomes. The overstimulation of progesterone can facilitate oncogenesis and thus, its modulation through PR inhibition is urgently needed. To address this issue, a novel stacked ensemble learning approach (termed StackPR) is presented for fast, accurate, and large-scale identification of PR antagonists using only SMILES notation without the need for 3D structural information. We employed six popular machine learning (ML) algorithms (i.e., logistic regression, partial least squares, k-nearest neighbor, support vector machine, extremely randomized trees, and random forest) coupled with twelve conventional molecular descriptors to create 72 baseline models. Then, a genetic algorithm in conjunction with the self-assessment-report approach was utilized to determine m out of the 72 baseline models as means of developing the final meta-predictor using the stacking strategy and tenfold cross-validation test. Experimental results on the independent test dataset show that StackPR achieved impressive predictive performance with an accuracy of 0.966 and Matthew’s coefficient correlation of 0.925. In addition, analysis based on the SHapley Additive exPlanation algorithm and molecular docking indicates that aliphatic hydrocarbons and nitrogen-containing substructures were the most important features for having PR antagonist activity. Finally, we implemented an online webserver using StackPR, which is freely accessible at http://pmlabstack.pythonanywhere.com/StackPR. StackPR is anticipated to be a powerful computational tool for the large-scale identification of unknown PR antagonist candidates for follow-up experimental validation.

Mn- and Co-Catalyzed Aminocyclizations of Unsaturated Hydrazones Providing a Broad Range of Functionalized Pyrazolines

Manganese- and cobalt-catalyzed aminocyclization reactions of unsaturated hydrazones are reported. Whereas manganese catalysis provides access to pyrazoline and tetrahydropyridazine alcohols, cobalt catalysis for the first time paves the way for the selective formation of pyrazoline aldehydes. Furthermore, various functional groups including hydroperoxide, thiol derivatives, iodide, and bicyclopentane may be introduced via manganese-catalyzed ring-forming aminofunctionalization. A progesterone receptor antagonist was prepared using the aminocyclization protocol.

Structural basis for computational screening of non-steroidal androgen receptor ligands

IMPORTANCE OF THE FIELD

Deep structural and chemical understanding of the protein target and computational methods for detection of receptor-selective ligands are important for the early drug discovery in the steroid receptor field.

AREAS COVERED IN THIS REVIEW

This review focuses on the use of currently available structural information of the androgen receptor (AR) and known AR ligands to make computational strategies for the discovery of AR ligands in order to offer new chemical platforms for drug development.

WHAT THE READER WILL GAIN

AR is a challenging target for drug discovery and modeling even if there is a wealth of experimental data available. First, only the active structure of AR is currently known, which hampers the design of AR antagonists. Second, the structural similarity between the ligand-binding sites of AR and its mutated forms and closely related steroid receptors (SRs) such as progesterone receptors presents challenges for the development of drugs with receptor-selective function.

TAKE HOME MESSAGE

Research indicates that a very small chemical change in the structure of a non-steroidal ligand can cause a complete change in its activity. One source of this effect arises from binding to similar binding sites in related SRs and other proteins in the signaling pathway. Currently, computational methods are not able to predict the subtle differences between AR ligand activities but modeling does offer the possibility of generating new lead structures that might have the desired properties.

Recent advances in the therapeutic applications of pyrazolines

Introduction: Pyrazolines are well-known and important nitrogen-containing five-membered ring heterocyclic compounds. Various methods have been worked out for their synthesis. Several pyrazoline derivatives have been found to possess diverse biological properties, which has stimulated research activity in this field.

Areas covered: The present review sheds light on the recent therapeutic patent literature (2000 – 2011) describing the applications of pyrazolines and their derivatives on selected activities. Many of the therapeutic applications of pyrazoline derivatives have been discussed, either in the patent or in the general literature areas in this review. In addition to selected biological data, a wide range of pharmaceutical applications and pharmaceutical compositions are also summarized.

Expert opinion: Pyrazoline derivatives have numerous prominent pharmacological effects, such as antimicrobial (antibacterial, antifungal, antiamoebic, antimycobacterial), anti-inflammatory, analgesic, antidepressant and anticancer. Further pharmacological effects include cannabinoid CB1 receptor antagonists, antiepileptic, antitrypanosomal, antiviral activity, MAO-inhibitory, antinociceptive activity, insecticidal, hypotensive, nitric oxide synthase inhibitor, antioxidant, steroidal and antidiabetic. Lastly, they also effect ACAT inhibition, urotensin II and somatostatin-5 receptors, TGF-β signal transduction inhibitors and neurocytotoxicity inhibitors activities. Many new pyrazoline derivatives have been synthesized and patented, but there are still new aspects to explore and work on.

Pharmacology and clinical use of sex steroid hormone receptor modulators

Sex steroid receptors are ligand-triggered transcription factors. Oestrogen, progesterone and androgen receptors form, together with the glucocorticoid and mineralocorticoid receptors, a subgroup of the superfamily of nuclear receptors. They share a common mode of action, namely translating a hormone-i.e. a small-molecule signal-from outside to changes in gene expression and cell fate, and thereby represent "natural" pharmacological targets.For pharmacological therapy, these receptors have originally been addressed by hormones and synthetic hormone analogues in order to overcome pathologies related to deficiencies in the natural ligands. Another major use for female sex hormone receptor modulators is oral contraception, i.e. birth control.On the other side, blocking the activity of sex steroid receptors has become an established way to treat hormone-dependent malignancies, such as breast and prostate cancer.In this review, we will discuss how the experience gained from the classical pharmacology of these receptors and their molecular similarities led to new options for the treatment of gender-specific diseases and highlight recent progress in medicinal chemistry of sex hormone-modulating drugs.

The translational efficacy of a nonsteroidal progesterone receptor antagonist, 4-[3-cyclopropyl-1-(mesylmethyl)-5-methyl-1H-pyrazol-4-yl]oxy,-2,6-dimethylbenzonitrile (PF-02413873), on endometrial growth in macaque and human

There is considerable ongoing investment in the research and development of selective progesterone receptor (PR) modulators for the treatment of gynecological conditions such as endometriosis. Here, we provide the first report on the clinical evaluation of a nonsteroidal progesterone receptor antagonist 4-[3-cyclopropyl-1-(mesylmethyl)-5-methyl-1H-pyrazol-4-yl]oxy,-2,6-dimethylbenzonitrile (PF-02413873) in healthy female subjects. In in vitro assays, PF-02413873 behaved as a selective and fully competitive PR antagonist, blocking progesterone binding and PR nuclear translocation. The pharmacological mode of action of PF-02413873 seems to differ from the founding member of the class of steroidal PR antagonists, 11β-4-dimethylaminophenyl-17β-hydroxy-17α-propinyl-4,9-estradiene-3-one (RU-486; mifepristone). Exposure-effect data from studies in the cynomolgus macaque, however, demonstrated that PF-02413873 reduced endometrial functionalis thickness to a comparable degree to RU-486 and this effect was accompanied by a decrease in proliferation rate (as measured by bromodeoxyuridine incorporation) for both RU-486 and high-dose PF-02413873. These data were used to underwrite a clinical assessment of PF-02413873 in a randomized, double-blinded, third-party open, placebo-controlled, dose-escalation study in healthy female volunteers with dosing for 14 days. PF-02413873 blocked the follicular phase increase in endometrial thickness, the midcycle lutenizing hormone surge, and elevation in estradiol in a dose-dependent fashion compared with placebo. This is the first report of translational efficacy data with a nonsteroidal PR antagonist in cynomolgus macaque and human subjects.

Structural basis for agonism and antagonism for a set of chemically related progesterone receptor modulators

The progesterone receptor is able to bind to a large number and variety of ligands that elicit a broad range of transcriptional responses ranging from full agonism to full antagonism and numerous mixed profiles inbetween. We describe here two new progesterone receptor ligand binding domain x-ray structures bound to compounds from a structurally related but functionally divergent series, which show different binding modes corresponding to their agonistic or antagonistic nature. In addition, we present a third progesterone receptor ligand binding domain dimer bound to an agonist in monomer A and an antagonist in monomer B, which display binding modes in agreement with the earlier observation that agonists and antagonists from this series adopt different binding modes.

Molecular modeling on structure-function analysis of human progesterone receptor modulators

Considering the significance of progesterone receptor (PR) modulators, the present study is explored to envisage the biophoric signals for binding to selective PR subtype-A using ligand-based quantitative structure activity relationship (QSAR) and pharmacophore space modeling studies on nonsteroidal substituted quinoline and cyclocymopol monomethyl ether derivatives. Consensus QSAR models (Training set (Tr): n(Tr)=100, R(2) (pred)=0.702; test set (Ts): n(Ts)=30, R(2) (pred)=0.705, R(2) (m)=0.635; validation set (Vs): n(Vs)=40, R(2) (pred)=0.715, R(2) (m)=0.680) suggest that molecular topology, atomic polarizability and electronegativity, atomic mass and van der Waals volume of the ligands have influence on the presence of functional atoms (F, Cl, N and O) and consequently contribute significant relations on ligand binding affinity. Receptor independent space modeling study (Tr: n(Tr)=26, Q(2)=0.927; Ts: n(Ts)=60, R(2) (pred)=0.613, R(2) (m)=0.545; Vs: n(Vs)=84, R(2) (pred)=0.611, R(2) (m)=0.507) indicates the importance of aromatic ring, hydrogen bond donor, molecular hydrophobicity and steric influence for receptor binding. The structure-function characterization is adjudged with the receptor-based docking study, explaining the significance of the mapped molecular attributes for ligand-receptor interaction in the catalytic cleft of PR-A.

The X-ray structure of RU486 bound to the progesterone receptor in a destabilized agonistic conformation

Here we describe the 1.95 A structure of the clinically used antiprogestin RU486 (mifepristone) in complex with the progesterone receptor (PR). The structure was obtained by taking a crystal of the PR ligand binding domain containing the agonist norethindrone and soaking it in a solution containing the antagonist RU486 for extended times. Clear ligand exchange could be observed in one copy of the PR ligand binding domain dimer in the crystal. RU486 binds while PR is in an agonistic conformation without displacing helix 12. Although this is probably because of the constraints of the crystal lattice, it demonstrates that helix 12 displacement is not a prerequisite for RU486 binding. Interestingly, B-factor analysis clearly shows that helix 12 becomes more flexible after RU486 binding, suggesting that RU486, being a model antagonist, does not induce one fixed conformation of helix 12 but changes its positional equilibrium. This conclusion is confirmed by comparing the structures of RU486 bound to PR and RU486 bound to the glucocorticoid receptor.

Investigational developments for the treatment of progesterone-dependent diseases

BACKGROUND

Clinical evidence has shown that conditions such as uterine fibroids, endometriosis and breast cancer are progesterone-dependent diseases. Therefore, progesterone receptor (PR) antagonists and selective PR modulators (SPRMs) are under development for the treatment of these conditions. However, the first PR antagonists that became available exhibit insufficient selectivity or tolerability for the chronic administration required to treat these conditions. Despite initial setbacks, development of second-generation PR antagonists with better selectivity continues forward.

OBJECTIVE

In this review we would like to summarise prospects for using PR antagonists for the treatment of uterine fibroids, endometriosis and breast cancer, and to give an overview of the development of new steroidal and non-steroidal PR antagonists.

METHOD

Available preclinical and clinical data and publications have been reviewed with the focus on scientific background and use in the three mentioned indications.

RESULTS/CONCLUSION

Preclinical and clinical evidence demonstrated that PR antagonists and SPRMs are effective for the treatment of progesterone-dependent diseases. Future development will demonstrate if they can become important drugs.

Structure-directed combinatorial library design

In recent years pharmaceutical companies have utilized structure-based drug design and combinatorial library design techniques to speed up their drug discovery efforts. Both approaches are routinely used in the lead discovery and lead optimization stages of the drug discovery process. Fragment-based drug design, a new power tool in the drug design toolbox, is also gaining acceptance across the pharmaceutical industry. This review will focus on the interplay between these three design techniques and recent developments in computational methodologies that enhance their integration. Examples of successful synergistic applications of these three techniques will be highlighted. Opinion regarding possible future directions of the field will be given.

The evolution of progesterone receptor ligands

Progesterone is one of the first nuclear receptor hormones to be described functionally and subsequently approached as a drug target. Because progesterone (1) affects both menstruation and gestation via the progesterone receptor (PR), research aimed at modulating its activity is usually surrounded by controversy. However, ligands for PR were developed into drugs, and their evolution can be crudely divided into three periods: (1) drug-like steroids that mimic the gestational properties of progesterone; (2) drug-like steroids with different properties from progesterone and expanded therapeutic applications; and (3) non-steroidal PR ligands with improved selectivity and modulator properties and further expanded therapeutic applications. Although the latter have yet to see widespread clinical applications, their development is founded on a half century of research, and they represent the future for this drug target.

Array synthesis of progesterone receptor antagonists: 3-Aryl-1,2-diazepines

New non-steroidal chemotypes are required for the development of drugs targeting the steroid hormone receptors. The parallel array synthesis of 3-aryl-1,2-diazepines employing solid-supported reagents is described. The resulting compounds demonstrated high affinity binding to the progesterone receptor.