Rebecca Pulk

A class of 2,4-bisanilinopyrimidine Aurora A inhibitors with unusually high selectivity against Aurora B.

The two major Aurora kinases carry out critical functions at distinct mitotic stages. Selective inhibitors of these kinases, as well as pan-Aurora inhibitors, show antitumor efficacy and are now under clinical investigation. However, the ATP-binding sites of Aurora A and Aurora B are virtually identical, and the structural basis for selective inhibition has therefore not been clear. We report here a class of bisanilinopyrimidine Aurora A inhibitors with excellent selectivity for Aurora A over Aurora B, both in enzymatic assays and in cellular phenotypic assays. Crystal structures of two of the inhibitors in complex with Aurora A implicate a single amino acid difference in Aurora B as responsible for poor inhibitory activity against this enzyme. Mutation of this residue in Aurora B (E161T) or Aurora A (T217E) is sufficient to swap the inhibition profile, suggesting that this difference might be exploited more generally to achieve high selectivity for Aurora A.

Discovery and Optimization of C-2 Methyl Imidazopyrrolopyridines as Potent and Orally Bioavailable JAK1 Inhibitors with Selectivity over JAK2.

Herein we report the discovery of the C-2 methyl substituted imidazopyrrolopyridine series and its optimization to provide potent and orally bioavailable JAK1 inhibitors with selectivity over JAK2. The C-2 methyl substituted inhibitor 4 exhibited not only improved JAK1 potency relative to unsubstituted compound 3 but also notable JAK1 vs JAK2 selectivity (20-fold and >33-fold in biochemical and cell-based assays, respectively). Features of the X-ray structures of 4 in complex with both JAK1 and JAK2 are delineated. Efforts to improve the in vitro and in vivo ADME properties of 4 while maintaining JAK1 selectivity are described, culminating in the discovery of a highly optimized and balanced inhibitor (20). Details of the biological characterization of 20 are disclosed including JAK1 vs JAK2 selectivity levels, preclinical in vivo PK profiles, performance in an in vivo JAK1-mediated PK/PD model, and attributes of an X-ray structure in complex with JAK1.

Identification of C-2 Hydroxyethyl Imidazopyrrolopyridines as Potent JAK1 Inhibitors with Favorable Physicochemical Properties and High Selectivity over JAK2.

Herein we report on the structure-based discovery of a C-2 hydroxyethyl moiety which provided consistently high levels of selectivity for JAK1 over JAK2 to the imidazopyrrolopyridine series of JAK1 inhibitors. X-ray structures of a C-2 hydroxyethyl analogue in complex with both JAK1 and JAK2 revealed differential ligand/protein interactions between the two isoforms and offered an explanation for the observed selectivity. Analysis of historical data from related molecules was used to develop a set of physicochemical compound design parameters to impart desirable properties such as acceptable membrane permeability, potent whole blood activity, and a high degree of metabolic stability. This work culminated in the identification of a highly JAK1 selective compound (31) exhibiting favorable oral bioavailability across a range of preclinical species and robust efficacy in a rat CIA model.

2-Amino-[1,2,4]triazolo[1,5-a]pyridines as JAK2 inhibitors.

The advancement of a series of ligand efficient 2-amino-[1,2,4]triazolo[1,5-a]pyridines, initially identified from high-throughput screening, to a JAK2 inhibitor with pharmacodynamic activity in a mouse xenograft model is disclosed.

A new regulatory switch in a JAK protein kinase

Members of the JAK family of protein kinases mediate signal transduction from cytokine receptors to transcription factor activation. Over‐stimulation of these pathways is causative in immune disorders like rheumatoid arthritis, psoriasis, lupus, and Crohns disease. A search for selective inhibitors of a JAK kinase has led to our characterization of a previously unknown kinase conformation arising from presentation of Tyr962 of TYK2 to an inhibitory small molecule via an H‐bonding interaction. A small minority of protein kinase domains has a Tyrosine residue in this position within the αC‐β4 loop, and it is the only amino acid commonly seen here with H‐bonding potential. These discoveries will aid design of inhibitors that discriminate among the JAK family and more widely among protein kinases. Proteins 2011.

Structure-based discovery of C-2 substituted imidazo-pyrrolopyridine JAK1 inhibitors with improved selectivity over JAK2.

Herein we describe our successful efforts in obtaining C-2 substituted imidazo-pyrrolopyridines with improved JAK1 selectivity relative to JAK2 by targeting an amino acid residue that differs between the two isoforms (JAK1: E966; JAK2: D939). Efforts to improve cellular potency by reducing the polarity of the inhibitors are also detailed. The X-ray crystal structure of a representative inhibitor in complex with the JAK1 enzyme is also disclosed.

Novel triazolo-pyrrolopyridines as inhibitors of Janus kinase 1.

The identification of a novel fused triazolo-pyrrolopyridine scaffold, optimized derivatives of which display nanomolar inhibition of Janus kinase 1, is described. Prototypical example 3 demonstrated lower cell potency shift, better permeability in cells and higher oral exposure in rat than the corresponding, previously reported, imidazo-pyrrolopyridine analogue 2. Examples 6, 7 and 18 were subsequently identified from an optimization campaign and demonstrated modest selectivity over JAK2, moderate to good oral bioavailability in rat with overall pharmacokinetic profiles comparable to that reported for an approved pan-JAK inhibitor (tofacitinib).