Rohan Mendonca

Discovery of Selective Irreversible Inhibitors for Bruton’s Tyrosine Kinase

The importance of B cells in rheumatoid arthritis (RA) pathogenesis has been recently demonstrated in several clinical studies using the anti-CD20 antibody rituximab, which selectively depletes B cells. A recent phase III clinical trial led to the FDA approval of rituximab for a subset of RA patients. Bruton’s tyrosine kinase (Btk), a member of Tec family kinases, is a key component in the B-cell receptor signal pathway (BCR). Upon activation by upstream kinases (for example, Lyn and Syk), Btk phosphorylates and thereby activates phospholipase-Cg (PLCg), leading to several important downstream events including calcium ion transportation, NF-kB activation, and (auto)antibody generation. Previous biological studies (genetic loss of function and siRNA knockdown) strongly suggest that Btk is also a mediator of proinflammatory signals. Taken together, these studies indicate Btk may be a potential target for the treatment of RA. However, despite the previous discovery of LFM-A13 as a selective Btk inhibitor, there is no published study that has demonstrated that inhibition of Btk activity leads to in vivo efficacy in an animal model of rheumatoid arthritis. As ATP binding sites in kinases are highly conserved, it is a formidable task to develop selective ATP competitive kinase inhibitors. Among several approaches, the use of electrophilic inhibitors has been shown as a viable method to achieve selectivity. Considering the relative scarcity of knowledge on “chemical knockdown” of Btk activity, it is crucial to discover a potent and selective tool compound for this kinase. Herein, we describe the discovery of a selective, irreversible Btk inhibitor and its efficacy in a mouse RA model. An initial campaign to scan for scaffolds capable of inhibiting Btk’s kinase activity identified compound 1 as having

Identification of Imidazo-Pyrrolopyridines as Novel and Potent JAK1 Inhibitors.

A therapeutic rationale is proposed for the treatment of inflammatory diseases, such as rheumatoid arthritis (RA), by specific targeting of the JAK1 pathway. Examination of the preferred binding conformation of clinically effective, pan-JAK inhibitor 1 led to identification of a novel, tricyclic hinge binding scaffold 3. Exploration of SAR through a series of cycloamino and cycloalkylamino analogues demonstrated this template to be highly tolerant of substitution, with a predisposition to moderate selectivity for the JAK1 isoform over JAK2. This study culminated in the identification of subnanomolar JAK1 inhibitors such as 22 and 49, having excellent cell potency, good rat pharmacokinetic characteristics, and excellent kinase selectivity. Determination of the binding modes of the series in JAK1 and JAK2 by X-ray crystallography supported the design of analogues to enhance affinity and selectivity.

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.

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.