JAK1, JAK2, JAK3, and TYK2 belong to the JAK (Janus kinase) family. They play critical roles in cytokine signaling. Constitutive activation of JAK/STAT pathways is associated with a wide variety of diseases. Particularly, pSTAT3 is observed in response to the treatment with inhibitors of oncogenic signaling pathways such as EGFR, MAPK, and AKT and is associated with resistance or poorer response to agents targeting these pathways. Among the JAK family kinases, JAK1 has been shown to be the primary driver of STAT3 phosphorylation and signaling; therefore, selective JAK1 inhibition can be a viable means to overcome such treatment resistances. Herein, an account of the medicinal chemistry optimization from the promiscuous kinase screening hit 3 to the candidate drug 21 (AZD4205), a highly selective JAK1 kinase inhibitor, is reported. Compound 21 has good preclinical pharmacokinetics. Compound 21 displayed an enhanced antitumor activity in combination with an approved EGFR inhibitor, osimertinib, in a preclinical non-small-cell lung cancer (NSCLC) xenograft NCI-H1975 model.

We report the first disclosure of IRAK3 degraders in the scientific literature. Taking advantage of an opportune byproduct obtained during our efforts to identify IRAK4 inhibitors, we identified ready-to-use, selective IRAK3 ligands in our compound collection with the required properties for conversion into proteolysis-targeting chimera (PROTAC) degraders. This work culminated with the discovery of PROTAC 23, which we demonstrated to be a potent and selective degrader of IRAK3 after 16 h in THP1 cells. 23 induced proteasome-dependent degradation of IRAK3 and required both CRBN and IRAK3 binding for activity. We conclude that PROTAC 23 constitutes an excellent in vitro tool with which to interrogate the biology of IRAK3.

Gastrointestinal stromal tumor (GIST) is the most common human sarcoma driven by mutations in KIT or platelet-derived growth factor α (PDGFRα). Although first-line treatment, imatinib, has revolutionized GIST treatment, drug resistance due to acquisition of secondary KIT/PDGFRα mutations develops in a majority of patients. Second- and third-line treatments, sunitinib and regorafenib, lack activity against a plethora of mutations in KIT/PDGFRα in GIST, with median time to disease progression of 4 to 6 months and inhibition of vascular endothelial growth factor receptor 2 (VEGFR2) causing high-grade hypertension. Patients with GIST have an unmet need for a well-tolerated drug that robustly inhibits a range of KIT/PDGFRα mutations. Here, we report the discovery and pharmacological characterization of AZD3229, a potent and selective small-molecule inhibitor of KIT and PDGFRα designed to inhibit a broad range of primary and imatinib-resistant secondary mutations seen in GIST. In engineered and GIST-derived cell lines, AZD3229 is 15 to 60 times more potent than imatinib in inhibiting KIT primary mutations and has low nanomolar activity against a wide spectrum of secondary mutations. AZD3229 causes durable inhibition of KIT signaling in patient-derived xenograft (PDX) models of GIST, leading to tumor regressions at doses that showed no changes in arterial blood pressure (BP) in rat telemetry studies. AZD3229 has a superior potency and selectivity profile to standard of care (SoC) agents—imatinib, sunitinib, and regorafenib, as well as investigational agents, avapritinib (BLU-285) and ripretinib (DCC-2618). AZD3229 has the potential to be a best-in-class inhibitor for clinically relevant KIT/PDGFRα mutations in GIST.

Pre-clinical animal models in translational research are fundamental to the understanding of disease and drug pharmacology but are often limited in their utility to robustly define an efficacious dose in the clinic. A reverse translational strategy using known clinical information from the bedside to bench can play a crucial role in improving this situation. In this work we evaluate the translational pharmacokinetic-pharmacodynamic (PKPD) assumptions for the KIT/PDGFRα inhibitor AZD3229 by using drug exposure and known clinical activity of standard of care (SoC) agents across the population of KIT driven gastro intestinal stromal tumor (GIST) patients to correlate against in vitro potency data for a spectrum of primary and secondary KIT mutations. AZD3229 has potential as a best in class treatment for GIST patients with mutations in KIT and PDGFRα and this compound may overcome the limitations experienced with existing treatment options in the clinic which are limited by off-target effects leading to drug holidays and dose reductions leading to lack of optimum efficacy.