Unique Small Molecule Inhibitor Strategy to Selectively Block Oncogenic JAK2 Kinase in Myeloproliferative Disorders

Project Overview

• Mutated JAK2 protein kinase drives the majority of myeloproliferative neoplasms (MPNs) and its activation mechanism provides a rationale for developing selective therapeutics for improved patient outcomes.
• Dana-Farber scientists have created a strategy that led to chemical compounds with the ability to shut down JAK2 kinase activity by inducing an inhibitory allosteric conformational change.
• The strategy provides the basis for next-generation, mutant-specific small molecule inhibitors.
• These assets are available for licensing or co-development within a research collaboration.

Technology

Myeloproliferative disorders or neoplasms (MPNs) are a group of rare chronic blood cancers in which genetic mutations in bone marrow stem cells result in the uncontrollable and excessive production of often dysfunctional, mature blood cells. While often progressing slowly, MPNs occasionally develop into acute leukemias and increase the risk of bleeding and blood clots. Activating (gain-of-function) mutations in the cytokine receptor-associated kinase JAK2 (Janus Kinase 2), most commonly V617F, account for about 95% of Polycythemia Vera (PV) cases and 50% of Essential Thrombocythemia (ET) and Myelofibrosis (PMF) cases, which are three of the major MPN subtypes. Developing potent JAK2 inhibitors therefore has been a major thrust for drug developers.

In bone marrow, JAK2 functions as a critical signal transducer in resident stem cells by binding to various cytokine receptors that receive stimulating ligands from the bone marrow environment. These ligand-receptor interactions induce JAK2 to phosphorylate its bound receptors and thus activate the JAK/STAT pathway to promote stem cell growth, division, and maturation. In MPNs driven by mutated JAK2, this pathway is constitutively “on,” or active, and cannot be turned off anymore.

Currently approved JAK2 inhibitors target the kinase domain of JAK2, but often also inhibit other members of the JAK family, as well as unrelated kinases in various cell types. Importantly, they cannot discriminate between wild-type JAK2 required for normal cell functions and mutant JAK2. This limits their efficacies and can lead to serious side effects, including low platelet counts, anemia, and immune suppression, which can also increase the risk for infections. Thus, there is an urgent need for drugs that can selectively inhibit mutated JAK2.

Dr. Michael Eck and his laboratory, through a specifically designed drug discovery campaign, has identified a new strategy for developing small molecule inhibitors to selectively target constitutively active JAK2 V617F, while sparing wild-type JAK signaling. Interestingly, the V617F mutation of JAK2 is located in an enzymatically inactive “pseudokinase domain,” which regulates the activity of the enzyme’s separate functional kinase domain. As confirmed by x-ray crystallography and mass-spectometry methods, an identified lead compound specifically engages the L677 residue of JAK2, which like V617 helps form the ATP binding site (ATP is the universal phosphate donor for protein kinase reactions) within the pseudokinase domain, but is not conserved in the active kinase domain. By forming a covalent chemical bond with L677, the compound induces an allosteric conformational change in the pseudokinase domain that prevents it from activating JAK2’s functional kinase domain, thus blocking JAK2 activity.

While the current compounds are not mutant selective, they establish proof-of-concept for allosteric inhibition of JAK2 via its pseudokinase domain by covalently targeting Lys677of JAK2. This newly discovered mechanism-of-action has potential for also identifying compounds that can specifically target V617F in mutated JAK2.

Team Members: Michael J. Eck, M.D., Ph.D.

Applications

• Improving treatment of patients with different MPS subtypes driven by the same mutation.
• Leveraging a unique mechanism-of-action as an opportunity to develop selective inhibitors for V617F mutant JAK2.
• Using the allosteric approach as a foundation to develop next-generation JAK2 inhibitors with improved selectivity, pharmacology, and tolerability in MPS patients.

Team Members

Michael Eck, MD, PhD

Professor, Cancer Biology, Dana-Farber

Professor of Biological Chemistry and Molecular Pharmacology, Harvard Medical School

Michael's Bio