Mode of action of DNA-competitive small molecule inhibitors of tyrosyl DNA phosphodiesterase 2.

Tyrosyl-DNA phosphodiesterase 2 (TDP2) is a 5'-tyrosyl DNA phosphodiesterase important for the repair of DNA adducts generated by non-productive (abortive) activity of topoisomerase II (TOP2). TDP2 facilitates therapeutic resistance to topoisomerase poisons, which are widely used in the treatment of a range of cancer types. Consequently, TDP2 is an interesting target for the development of small molecule inhibitors that could restore sensitivity to topoisomerase-directed therapies. Previous studies identified a class of deazaflavin-based molecules that showed inhibitory activity against TDP2 at therapeutically useful concentrations, but their mode of action was uncertain. We have confirmed that the deazaflavin series inhibits TDP2 enzyme activity in a fluorescence-based assay, suitable for high-throughput screen (HTS)-screening. We have gone on to determine crystal structures of these compounds bound to a 'humanized' form of murine TDP2. The structures reveal their novel mode of action as competitive ligands for the binding site of an incoming DNA substrate, and point the way to generating novel and potent inhibitors of TDP2.

An atom-efficient and convergent approach to the preparation of NS5A inhibitors by C-H activation.

A novel approach of the convergent functionalisation of aryl dibromides to form NS5A type inhibitors using C-H activation is reported. The focus of investigation was to reduce the formation of homodimeric side product, as well as to investigate the scope of different aryl dibromides that were tolerated under the reaction conditions. The C-H activation methodology was found to give a viable synthetic route to NS5A inhibitors, with late stage functionalisation of the core portion of the molecule, albeit with some chemical functionalities not tolerated.

Neurosteroid Modulation of Synaptic and Extrasynaptic GABAA Receptors of the Mouse Nucleus Accumbens.

The recent approval of formulations of the endogenous neurosteroid allopregnanolone (brexanolone) and the synthetic neuroactive steroid SAGE-217 (zuranolone) to treat postpartum depression (PPD) has encouraged further research to elucidate why these potent enhancers of GABAAR function are clinically effective in this condition. Dopaminergic projections from the ventral tegmental area (VTA) to the nucleus accumbens are associated with reward/motivation and brain imaging studies report that individuals with PPD show reduced activity of this pathway in response to reward and infant engagement. However, the influence of neurosteroids on GABA-ergic transmission in the nucleus accumbens has received limited attention. Here, we investigate, in the medium spiny neurons (MSNs) of the mouse nucleus accumbens core, the effect of allopregnanolone, SAGE-217 and other endogenous and synthetic steroids of interest on fast phasic and tonic inhibition mediated by synaptic (α1/2ßγ2) and extrasynaptic (α4ßδ) GABAARs, respectively. We present evidence suggesting the resident tonic current results from the spontaneous opening of δ-GABAARs, where the steroid-enhanced tonic current is GABA-dependent. Furthermore, we demonstrate local neurosteroid synthesis in the accumbal slice preparation and reveal that GABA-ergic neurotransmission of MSNs is influenced by an endogenous neurosteroid tone. Given the dramatic fluctuations in allopregnanolone levels during pregnancy and postpartum, this neurosteroid-mediated local fine-tuning of GABAergic transmission in the MSNs will probably be perturbed.

Synthesis of novel histamine H4 receptor antagonists.

This letter describes the discovery and synthesis of a series of octahydropyrrolo[3,4-c]pyrrole based selective histamine hH4 receptor antagonists. The amidine compound 20 was found to be a potent and selective histamine H4 receptor antagonist with moderate clearance and a high volume of distribution.

Challenges of drug discovery in novel target space. The discovery and evaluation of PF-3893787: a novel histamine H4 receptor antagonist.

We describe the development of novel benzimidazoles as small molecule histamine H4 receptor (H4R) antagonists and their profiling in rat early toxicity studies. The discovery and optimisation of a second series of pyrimidine based antagonists is then described culminating in the identification of the clinical development candidate 13 (PF-3893787). The pre-clinical profile of 13 (PF-3893787) is presented including the development of a translatable biomarker. Our pragmatic approach to target selection, safety assessment, and testing for efficacy faced numerous challenges and we share a number of lessons which the team learned and which will assist us and others in future drug discovery projects.

Discovery of Sisunatovir (RV521), an Inhibitor of Respiratory Syncytial Virus Fusion.

RV521 is an orally bioavailable inhibitor of respiratory syncytial virus (RSV) fusion that was identified after a lead optimization process based upon hits that originated from a physical property directed hit profiling exercise at Reviral. This exercise encompassed collaborations with a number of contract organizations with collaborative medicinal chemistry and virology during the optimization phase in addition to those utilized as the compound proceeded through preclinical and clinical evaluation. RV521 exhibited a mean IC50 of 1.2 nM against a panel of RSV A and B laboratory strains and clinical isolates with antiviral efficacy in the Balb/C mouse model of RSV infection. Oral bioavailability in preclinical species ranged from 42 to >100% with evidence of highly efficient penetration into lung tissue. In healthy adult human volunteers experimentally infected with RSV, a potent antiviral effect was observed with a significant reduction in viral load and symptoms compared to placebo.

A challenge finding P2X1 and P2X4 ligands.

Identifying novel small-molecule P2X1 and P2X4 ligands with sub-type specificity and high-affinity remains a pharmacological challenge. Here we use computational methods, electrophysiology and fluorescent microplate assays to screen for ligand candidates acting at these receptors. Modelling and docking identified 80 compounds for testing at P2X4 receptors, and 20 of these showed >50% inhibition in fluorescence-based assays, making them appealing for further SAR studies. Confirmation of activity by two-electrode voltage clamp, followed by their elaboration resulted in only minor improvements in potency, with the highest IC50 being 295 µM. Testing on P2X1 receptors, resulted in a series of biguanide compounds that yielded a maximum IC50 of 100 µM, but no consistent SAR could be found. Potencies of established antagonists gave expected results, although the measured potencies varied between techniques and no antagonism could be found for compounds such as paroxetine, carbamazepine, 9(10H)-acridanone, acridinol and phenoxazine-type heterocycles. This study highlights the challenge of identifying P2X4 and P2X1 ligands and suggests that a combination of complimentary approaches is needed if we are to be confident of ligand activities at these receptors.

African trypanosomiasis: Synthesis & SAR enabling novel drug discovery of ubiquinol mimics for trypanosome alternative oxidase.

African trypanosomiasis is a parasitic disease affecting 5000 humans and millions of livestock animals in sub-Saharan Africa every year. Current treatments are limited, difficult to administer and often toxic causing long term injury or death in many patients. Trypanosome alternative oxidase is a parasite specific enzyme whose inhibition by the natural product ascofuranone (AF) has been shown to be curative in murine models. Until now synthetic methods to AF analogues have been limited, this has restricted both understanding of the key structural features required for binding and also how this chemotype could be developed to an effective therapeutic agent. The development of 3 amenable novel synthetic routes to ascofuranone-like compounds is described. The SAR generated around the AF chemotype is reported with correlation to the inhibition of T. b. brucei growth and corresponding selectivity in cytotoxic assessment in mammalian HepG2 cell lines. These methods allow access to greater synthetic diversification and have enabled the synthesis of compounds that have and will continue to facilitate further optimisation of the AF chemotype into a drug-like lead.

The discovery of potent nonstructural protein 5A (NS5A) inhibitors with a unique resistance profile-Part†1.

Nonstructural protein 5A (NS5A) represents a novel target for the treatment of hepatitis C virus (HCV). Daclatasvir, recently reported by Bristol-Myers-Squibb, is a potent NS5A inhibitor currently under investigation in phase 3 clinical trials. While the performance of daclatasvir has been impressive, the emergence of resistance could prove problematic and as such, improved analogues are being sought. By varying the biphenyl-imidazole unit of daclatasvir, novel inhibitors of HCV NS5A were identified with an improved resistance profile against mutant strains of the virus while retaining the picomolar potency of daclatasvir. One compound in particular, methyl ((S)-1-((S)-2-(4-(4-(6-(2-((S)-1-((methoxycarbonyl)-L-valyl)pyrrolidin-2-yl)-1H-imidazol-5-yl)quinoxalin-2-yl)phenyl)-1H-imidazol-2-yl)pyrrolidin-1-yl)-3-methyl-1-oxobutan-2-yl)carbamate (17), exhibited very promising activity and showed good absorption and a long predicted human pharmacokinetic half-life. This compound represents a promising lead that warrants further evaluation.

The discovery of potent nonstructural protein 5A (NS5A) inhibitors with a unique resistance profile-Part†2.

In ongoing studies towards novel hepatitis C virus (HCV) therapeutics, inhibitors of nonstructural protein 5A (NS5A) were evaluated. Specifically, starting from previously reported lead compounds, peripheral substitution patterns of a series of biaryl-linked pyrrolidine NS5A replication complex inhibitors were probed and structure-activity relationships were elucidated. Using molecular modelling and a supercritical fluid chromatographic (SFC) technique, intramolecular H-bonding and peripheral functional group topology were evaluated as key determinants of activity and membrane permeability. The novel compounds exhibited retained potency as compared with the lead compounds, and also showed promising results against a panel of resistance viruses. Together, the results of the study take us a step closer towards understanding the potency of daclatasvir, a clinical candidate upon which the compounds were based, and to designing improved analogues as second-generation antiviral agents targeting NS5A.

Incorporation by coordination and release of the iron chelator drug deferiprone from zinc-based metal-organic frameworks.

A series of new zinc-based metal-organic framework materials has been prepared in which deferiprone is incorporated as a chelating ligand on infinite or tri-zinc secondary building units following deprotonation. Deferiprone is immediately released from the MOFs on treatments with 1 N hydrochloric acid or buffer, but slow release is observed in ethanoic acid.

Regiocontrolled rearrangement of isobenzofurans.

The regioselective alkylation and oxidative rearrangement of isobenzofurans has been achieved to generate substituted 4,8-dihydroxyisochromanones in good yields and with complete regiocontrol.