Peter Barton

Identification of pyrazolo-pyrimidinones as GHS-R1a antagonists and inverse agonists for the treatment of obesity

A pyrazolo-pyrimidinone based series of growth hormone secretagogue receptor type 1a (GHS-R1a) antagonists and inverse agonists were identified using a scaffold hop from known quinazolinone GHS-R1a modulators. Lipophilicity was reduced to decrease hERG activity while maintaining GHS-R1a affinity. SAR exploration of a piperidine substituent was used to identify small cyclic groups as a functional switch from partial agonists to neutral antagonists and inverse agonists. A tool compound was identified which had good overall properties and sufficient oral plasma and CNS exposure to demonstrate reduced food intake in mice through a mechanism involving GHS-R1a.

Discovery of pyrazolo[1,5-a]pyrimidine B-cell lymphoma 6 (BCL6) binders and optimization to high affinity macrocyclic inhibitors

Inhibition of the protein-protein interaction between B-cell lymphoma 6 (BCL6) and corepressors has been implicated as a therapeutic target in diffuse large B-cell lymphoma (DLBCL) cancers and profiling of potent and selective BCL6 inhibitors are critical to test this hypothesis. We identified a pyrazolo[1,5-a]pyrimidine series of BCL6 binders from a fragment screen in parallel with a virtual screen. Using structure-based drug design, binding affinity was increased 100000-fold. This involved displacing crystallographic water, forming new ligand-protein interactions and a macrocyclization to favor the bioactive conformation of the ligands. Optimization for slow off-rate constant kinetics was conducted as well as improving selectivity against an off-target kinase, CK2. Potency in a cellular BCL6 assay was further optimized to afford highly selective probe molecules. Only weak antiproliferative effects were observed across a number of DLBCL lines and a multiple myeloma cell line without a clear relationship to BCL6 potency. As a result, we conclude that the BCL6 hypothesis in DLBCL cancer remains unproven.

Identification, optimization, and pharmacology of acylurea GHS-R1a inverse agonists.

Ghrelin plays a major physiological role in the control of food intake, and inverse agonists of the ghrelin receptor (GHS-R1a) are widely considered to offer utility as antiobesity agents by lowering the set-point for hunger between meals. We identified an acylurea series of ghrelin modulators from high throughput screening and optimized binding affinity through structure-activity relationship studies. Furthermore, we identified specific substructural changes, which switched partial agonist activity to inverse agonist activity, and optimized physicochemical and DMPK properties to afford the non-CNS penetrant inverse agonist 22 (AZ-GHS-22) and the CNS penetrant inverse agonist 38 (AZ-GHS-38). Free feeding efficacy experiments showed that CNS exposure was necessary to obtain reduced food intake in mice, and it was demonstrated using GHS-R1a null and wild-type mice that this effect operates through a mechanism involving GHS-R1a.

Indazole-6-phenylcyclopropylcarboxylic Acids as Selective GPR120 Agonists with in Vivo Efficacy

GPR120 agonists have therapeutic potential for the treatment of diabetes, but few selective agonists have been reported. We identified an indazole-6-phenylcyclopropylcarboxylic acid series of GPR120 agonists and conducted SAR studies to optimize GPR120 potency. Furthermore, we identified a (S,S)-cyclopropylcarboxylic acid structural motif which gave selectivity against GPR40. Good oral exposure was obtained with some compounds displaying unexpected high CNS penetration. Increased MDCK efflux was utilized to identify compounds such as 33 with lower CNS penetration, and activity in oral glucose tolerance studies was demonstrated. Differential activity was observed in GPR120 null and wild-type mice indicating that this effect operates through a mechanism involving GPR120 agonism.

Design and synthesis of a novel series of cyclohexyloxy-pyridyl derivatives as inhibitors of diacylglycerol acyl transferase 1

A novel series of potent diacylglycerol acyl transferase 1 inhibitors was developed from the clinical candidate AZD3988. Replacement of the phenyl cyclohexyl-ethanoate side chain with substituted oxy-linked side chains to introduce changes in shape and polarity, reduce lipophilicity and mask the hydrogen bond donors with internal hydrogen bond acceptors led to improvements in solubility, unbound clearance and excellent selectivity over the related enzyme acyl-coenzyme A:cholesterol acyltransferase 1. A comparison of the small molecule crystal structures of compound 4 and compound 28 is described. Compounds in this series have good ADMET properties and provide an exposure-dependent decrease in circulating plasma triglyceride levels in a rat oral lipid tolerance test.

Reduction of acyl glucuronidation in a series of acidic 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) inhibitors: the discovery of AZD6925

Inhibition of 11β-HSD1 is viewed as a potential target for the treatment of obesity and other elements of the metabolic syndrome. We report here the optimisation of a carboxylic acid class of inhibitors from AZD4017 (1) to the development candidate AZD6925 (11). A central aim of this optimisation campaign was the modulation of clearance mechanism to reduce the extent of acyl glucuronidation. This was achieved by modulation of the acid substructure together with a redistribution of lipophilicity in order to achieve the desired profile.

Experimental testing of quantum mechanical predictions of mutagenicity: aminopyrazoles.

A computational method for predicting the likelihood of aromatic amines being active in the Ames test for mutagenicity was trialed on a set of aminopyrazoles. A virtual array of compounds was generated from the available sets of hydrazines and α-cyanoaldehydes (or ketones) and quantum mechanical calculations used to compute a probability of being active in the Ames test. The compounds selected for synthesis and testing were not based on the predictions and so spanned the range of predicted probabilities. The subsequently generated results of the Ames test were in good correspondence with the predictions and confirm this approach as a useful means of predicting likely mutagenic risk.

Development of a Novel B-Cell Lymphoma 6 (BCL6) PROTAC To Provide Insight into Small Molecule Targeting of BCL6

B-cell lymphoma 6 (BCL6) inhibition is a promising mechanism for treating hematological cancers but high quality chemical probes are necessary to evaluate its therapeutic potential. Here we report potent BCL6 inhibitors that demonstrate cellular target engagement and exhibit exquisite selectivity for BCL6 based on mass spectrometry analyses following chemical proteomic pull down. Importantly, a proteolysis-targeting chimera (PROTAC) was also developed and shown to significantly degrade BCL6 in a number of diffuse large B-cell lymphoma (DLBCL) cell lines, but neither BCL6 inhibition nor degradation selectively induced marked phenotypic response. To investigate, we monitored PROTAC directed BCL6 degradation in DLBCL OCI-Ly1 cells by immunofluorescence and discovered a residual BCL6 population. Analysis of subcellular fractions also showed incomplete BCL6 degradation in all fractions despite having measurable PROTAC concentrations, together providing a rationale for the weak antiproliferative response seen with both BCL6 inhibitor and degrader. In summary, we have developed potent and selective BCL6 inhibitors and a BCL6 PROTAC that effectively degraded BCL6, but both modalities failed to induce a significant phenotypic response in DLBCL despite achieving cellular concentrations.