PROTACs have recently emerged as a novel paradigm in drug discovery. They can hijack existing biological machinery to selectively degrade proteins of interest, in a catalytic fashion. Here we describe the design, optimisation and biological activity of a set of novel PROTACs targeting the Janus kinase family (JAK1, JAK2, JAK3 and TYK2) of proximal membrane-bound proteins. The JAK family proteins display membrane localisation by virtue of their association with cytoplasmic tails of cytokine receptors and there are no reports of a successful PROTAC strategy being deployed against this class of proteins. JAK PROTACs from two distinct JAK chemotypes were designed optimising the physicochemical properties for each template to enhance cell permeation. These PROTACs are capable of inducing JAK1 and JAK2 degradation, demonstrating an extension of the PROTAC methodology to an unprecedented class of protein targets. A number of the known ligase binders were explored, and it was found that PROTACs bearing an inhibitor of apoptosis protein (IAP) ligand induced significantly more JAK degradation over Von Hippel-Lindau (VHL) and Cereblon (CRBN) PROTACs. In addition, the mechanism of action of the JAK PROTACs was elucidated, and it was confirmed that JAK degradation was both IAP-and proteasome-dependant.

The bromodomain and extraterminal (BET) family of bromodomain-containing proteins are important regulators of the epigenome through their ability to recognize N-acetyl lysine (KAc) post-translational modifications on histone tails. These interactions have been implicated in various disease states and, consequently, disruption of BET− KAc binding has emerged as an attractive therapeutic strategy with a number of small molecule inhibitors now under investigation in the clinic. However, until the utility of these advanced candidates is fully assessed by these trials, there remains scope for the discovery of inhibitors from new chemotypes with alternative physicochemical, pharmacokinetic, and pharmacodynamic profiles. Herein, we describe the discovery of a candidate-quality dimethylpyridone benzimidazole compound which originated from the hybridization of a dimethylphenol benzimidazole series, identified using encoded library technology, with an N-methyl pyridone series identified through fragment screening. Optimization via structure-and propertybased design led to I-BET469, which possesses favorable oral pharmacokinetic properties, displays activity in vivo, and is projected to have a low human efficacious dose.

The bromodomain and extra terminal (BET) family of proteins are an integral part of human epigenome regulation, the dysregulation of which is implicated in multiple oncology and inflammatory diseases. Disrupting the BET family bromodomain acetyl-lysine (KAc) histone protein–protein interaction with small-molecule KAc mimetics has proven to be a disease-relevant mechanism of action, and multiple molecules are currently undergoing oncology clinical trials. This work describes an efficiency analysis of published GSK pan-BET bromodomain inhibitors, which drove a strategic choice to focus on the identification of a ligand-efficient KAc mimetic with the hypothesis that lipophilic efficiency could be drastically improved during optimization. This focus drove the discovery of the highly ligand-efficient and structurally distinct benzoazepinone KAc mimetic. Following crystallography to identify suitable growth vectors, the benzoazepinone core was optimized through an explore-exploit structure–activity relationship (SAR) approach while carefully monitoring lipophilic efficiency to deliver I-BET432 (41) as an oral candidate quality molecule.

The Janus family of tyrosine kinases (JAK1, JAK2, JAK3, and TYK2) play an essential role in the receptor signaling of cytokines that have been implicated in the pathogenesis of severe asthma, and there is emerging interest in the development of smallmolecule-inhaled JAK inhibitors as treatments. Here, we describe the optimization of a quinazoline series of JAK inhibitors and the results of mouse lung pharmacokinetic (PK) studies where only low concentrations of parent compound were observed. Subsequent investigations revealed that the low exposure was due to metabolism by aldehyde oxidase (AO), so we sought to identify quinazolines that were not metabolized by AO. We found that specific substituents at the quinazoline 2-position prevented AO metabolism and this was rationalized through computational docking studies in the AO binding site, but they compromised kinome selectivity. Results presented here highlight that AO metabolism is a potential issue in the lung.