Fluoromethylcyclopropylamine derivatives as potential in vivo toxicophores - A cautionary disclosure.

Fluorination of metabolic hotspots in a molecule is a common medicinal chemistry strategy to improve in vivo half-life and exposure and, generally, this strategy offers significant benefits. Here, we report the application of this strategy to a series of poly-ADP ribose glycohydrolase (PARG) inhibitors, resulting in unexpected in vivo toxicity which was attributed to this single-atom modification.

Cell-Active Small Molecule Inhibitors of the DNA-Damage Repair Enzyme Poly(ADP-ribose) Glycohydrolase (PARG): Discovery and Optimization of Orally Bioavailable Quinazolinedione Sulfonamides.

DNA damage repair enzymes are promising targets in the development of new therapeutic agents for a wide range of cancers and potentially other diseases. The enzyme poly(ADP-ribose) glycohydrolase (PARG) plays a pivotal role in the regulation of DNA repair mechanisms; however, the lack of potent drug-like inhibitors for use in cellular and in vivo models has limited the investigation of its potential as a novel therapeutic target. Using the crystal structure of human PARG in complex with the weakly active and cytotoxic anthraquinone 8a, novel quinazolinedione sulfonamides PARG inhibitors have been identified by means of structure-based virtual screening and library design. 1-Oxetan-3-ylmethyl derivatives 33d and 35d were selected for preliminary investigations in vivo. X-ray crystal structures help rationalize the observed structure-activity relationships of these novel inhibitors.

Discovery of potent inhibitors of the lysophospholipase autotaxin.

The autotaxin-lysophosphatidic acid (ATX-LPA) axis has been implicated in several disease conditions including inflammation, fibrosis and cancer. This makes ATX an attractive drug target and its inhibition may lead to useful therapeutic agents. Through a high throughput screen (HTS) we identified a series of small molecule inhibitors of ATX which have subsequently been optimized for potency, selectivity and developability properties. This has delivered drug-like compounds such as 9v (CRT0273750) which modulate LPA levels in plasma and are suitable for in vivo studies. X-ray crystallography has revealed that these compounds have an unexpected binding mode in that they do not interact with the active site zinc ions but instead occupy the hydrophobic LPC pocket extending from the active site of ATX together with occupying the LPA 'exit' channel.

Anilinoquinazoline inhibitors of the RET kinase domain-Elaboration of the 7-position.

We have previously reported a series of anilinoquinazoline derivatives as potent and selective biochemical inhibitors of the RET kinase domain. However, these derivatives displayed diminished cellular potency. Herein we describe further optimisation of the series through modification of their physicochemical properties, delivering improvements in cell potency. However, whilst cellular selectivity against key targets could be maintained, combining cell potency and acceptable pharmacokinetics proved challenging.

The discovery of 2-substituted phenol quinazolines as potent RET kinase inhibitors with improved KDR selectivity.

Deregulation of the receptor tyrosine kinase RET has been implicated in medullary thyroid cancer, a small percentage of lung adenocarcinomas, endocrine-resistant breast cancer and pancreatic cancer. There are several clinically approved multi-kinase inhibitors that target RET as a secondary pharmacology but additional activities, most notably inhibition of KDR, lead to dose-limiting toxicities. There is, therefore, a clinical need for more specific RET kinase inhibitors. Herein we report our efforts towards identifying a potent and selective RET inhibitor using vandetanib 1 as the starting point for structure-based drug design. Phenolic anilinoquinazolines exemplified by 6 showed improved affinities towards RET but, unsurprisingly, suffered from high metabolic clearance. Efforts to mitigate the metabolic liability of the phenol led to the discovery that a flanking substituent not only improved the hepatocyte stability, but could also impart a significant gain in selectivity. This culminated in the identification of 36; a potent RET inhibitor with much improved selectivity against KDR.

Toxoflavins and deazaflavins as the first reported selective small molecule inhibitors of tyrosyl-DNA phosphodiesterase II.

The recently discovered enzyme tyrosyl-DNA phosphodiesterase 2 (TDP2) has been implicated in the topoisomerase-mediated repair of DNA damage. In the clinical setting, it has been hypothesized that TDP2 may mediate drug resistance to topoisomerase II (topo II) inhibition by etoposide. Therefore, selective pharmacological inhibition of TDP2 is proposed as a novel approach to overcome intrinsic or acquired resistance to topo II-targeted drug therapy. Following a high-throughput screening (HTS) campaign, toxoflavins and deazaflavins were identified as the first reported sub-micromolar and selective inhibitors of this enzyme. Toxoflavin derivatives appeared to exhibit a clear structure-activity relationship (SAR) for TDP2 enzymatic inhibition. However, we observed a key redox liability of this series, and this, alongside early in vitro drug metabolism and pharmacokinetics (DMPK) issues, precluded further exploration. The deazaflavins were developed from a singleton HTS hit. This series showed distinct SAR and did not display redox activity; however low cell permeability proved to be a challenge.

Novel steroid inhibitors of glucose 6-phosphate dehydrogenase.

Novel derivatives of the steroid DHEA 1, a known uncompetitive inhibitor of G6PD, were designed, synthesized, and tested for their ability to inhibit this dehydrogenase enzyme. Several compounds with approximately 10-fold improved potency in an enzyme assay were identified, and this improved activity translated to efficacy in a cellular assay. The SAR for steroid inhibition of G6PD has been substantially developed; the 3ß-alcohol can be replaced with 3ß-H-bond donors such as sulfamide, sulfonamide, urea, and carbamate. Improved potency was achieved by replacing the androstane nucleus with a pregnane nucleus, provided a ketone at C-20 is present. For pregnan-20-ones incorporation of a 21-hydroxyl group is often beneficial. The novel compounds generally have good physicochemical properties and satisfactory in vitro DMPK parameters. These derivatives may be useful for examining the role of G6PD inhibition in cells and will assist the future design of more potent steroid inhibitors with potential therapeutic utility.

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.

Discovery and optimisation of a selective non-steroidal glucocorticoid receptor antagonist.

High-throughput screening of 3.87 million compounds delivered a novel series of non-steroidal GR antagonists. Subsequent rounds of optimisation allowed progression from a non-selective ligand with a poor ADMET profile to an orally bioavailable, selective, stable, glucocorticoid receptor antagonist.

Rapid access towards follow-up NOP receptor agonists using a knowledge based approach.

A knowledge based approach has been adopted to identify novel NOP receptor agonists with simplified hydrophobes. Substitution of the benzimidazol-2-one piperidine motif with a range of hydrophobic groups and pharmacophore guided bio-isosteric replacement of the benzimidazol-2-one moiety was explored. Compound 51 was found to be a high affinity, potent NOP receptor agonist with reduced affinity for the hERG channel.

The in vitro and in vivo enantioselectivity of etomidate implicates the GABAA receptor in general anaesthesia.

General anaesthetics exhibiting enantioselectivity afford valuable tools to assess the fundamental mechanisms underlying anaesthesia. Here, we characterised the actions of the R-(+)- and S-(-)-enantiomers of etomidate. In mice and tadpoles, R-(+)-etomidate was more potent (approximately 10-fold) than S-(-)-etomidate in producing loss of the righting reflex. In electrophysiological and radioligand binding assays, the enantiomers of etomidate positively regulated GABAA receptor function at anaesthetic concentrations and with an enantioselectivity paralleling their in vivo activity. GABA-evoked currents mediated by human recombinant GABAA receptors were potentiated by either R-(+)- or S-(-)-etomidate in a manner dependent upon receptor subunit composition. A direct, GABA-mimetic, effect was similarly subunit dependent. Modulation of GABA receptor activity was selective; R-(+)-etomidate inhibited nicotinic acetylcholine, or 5-hydroxytryptamine3 receptor subtypes only at supra-clinical concentrations and ionotropic glutamate receptor isoforms were essentially unaffected. Acting upon reticulothalamic neurones in rat brain slices, R-(+)-etomidate prolonged the duration of miniature IPSCs and modestly enhanced their peak amplitude. S-(-)-etomidate exerted qualitatively similar, but weaker, actions. In a model of locomotor activity, fictive swimming in Xenopus laevis tadpoles, R-(+)- but not S-(-)-etomidate exerted a depressant influence via enhancement of GABAergic neurotransmission. Collectively, these observations strongly implicate the GABAA receptor as a molecular target relevant to the anaesthetic action of etomidate.

Novel water soluble 2,6-dimethoxyphenyl ester derivatives with intravenous anaesthetic activity.

A number of water soluble bis-amino-2,6-dimethoxyphenyl ester derivatives were found to exhibit improved anaesthetic activity in mice relative to propofol 1. Of the analogues disclosed, 44 was further profiled in rodents and found to be a superior agent to propofol for the induction and maintenance of anaesthesia.

Interaction of steroids with the GABA(A) receptor.

Over the last two decades there has been a resurgence of interest in steroids as potential therapeutics for central nervous system disorders. This interest followed the discovery that neurosteroids and neuroactive steroids are potent modulators of GABA(A) receptor function. This article traces those developments focussing particularly on the structure-activity relationships that have been identified through synthetic modification of established ligands, but also examines the influence of GABA(A) receptor subunit composition for steroid modulation. The review then covers some of the physiological effects such steroids are liable to exert and their therapeutic potential for treating central nervous system disorders including epilepsy, anxiety and insomnia.