Identification of a novel inhibitor of JAK2 tyrosine kinase by structure-based virtual screening

Abstract

Janus kinase 2 (JAK2) plays a crucial role in the pathomechanism of myeloproliferative disorders and hematologic malignancies. A somatic mutation of JAK2 (Val617Phe) was previously shown to occur in 98% of patients with polycythemia vera and 50% of patients with essential thrombocythemia and primary myelofibrosis. Thus, effective JAK2 kinase inhibitors may be of significant therapeutic importance. Here, we applied a structure-based virtual screen to identify novel JAK2 inhibitors. One JAK2 inhibitor in particular, G6, demonstrated remarkable potency as well as specificity, which makes it as a potential lead candidate against diseases related to elevated JAK2 tyrosine kinase activity. KeywordsJanus kinase 2; Virtual screening; Inhibitor; Pharmacological evaluation Janus kinases (JAKs) are cytoplasmic protein kinases that play a crucial role in cytokinemediated signal transduction. In the absence of ligand, JAK kinases are constitutively bound to the cytoplasmic tails of cytokine receptors. The binding of ligand to the extracellular portion of the receptor results in a conformational change of the receptor itself and subsequent activation of the JAKs. Activated JAKs tyrosine autophosphorylate and phosphorylate specific tyrosine residues on the C-terminal end of the receptors. This results in the recruitment and activation of the Signal Transducers and Activators of Transcription (STAT) proteins. Activated STATs subsequently translocate into the nucleus where they alter specific gene transcription patterns. 1 JAKs contain seven conserved Janus homology (JH) 2 domains: a tyrosine kinase domain at the C-terminus (JH1), a pseudokinase domain (JH2) and five further * Corresponding author. Tel.: +36 1 4314605; fax: +36 1 4326002. gy.keseru@richter.hu (G.M. Keserű).

The Stilbenoid Tyrosine Kinase Inhibitor, G6, Suppresses Jak2-V617F-mediated Human Pathological Cell Growth in Vitro and in Vivo

“…Furthermore, the reduction in phospho-STAT5 correlates very well with G6-mediated reduction in HEL cell growth (Fig. 1) and inhibition of Jak2 kinase activity (19). As such, our data suggest that G6 inhibits HEL cell growth via a Jak2/STAT5-dependent mechanism.…”

“…G6 Inhibits Jak2-V617F-dependent Constitutive Activation of STAT5-We previously showed that G6-mediated reduction in HEL cell numbers directly correlates with suppression of Jak2 kinase activity (19). We now wanted to determine whether treatment with G6 and subsequent HEL cell growth inhibition also correlated with reduced STAT signaling.…”

“…This stilbenoid compound demonstrated good potency and specificity for Jak2 tyrosine kinase as it inhibited Jak2-V617F enzymatic activity (IC 50 ϭ 60 nM) while having no effect on c-Src tyrosine kinase activity at concentrations as high as 25 M (19). Furthermore, it significantly inhibited the growth of cells whose proliferation was driven by the Jak2-V617F mutation while having little to no effect on cells whose proliferation was driven by other mechanisms including a JAK3-A572V-activating mutation, a c-Myc gene translocation, or immortalization via the SV-40 large T antigen (19). As such, we hypothesized that G6 would suppress Jak2-V617F-mediated pathological cell growth.…”

“…Inhibits Jak2-V617F-dependent Cell Proliferation-Using structure-based virtual screening, we recently identified a Jak2 tyrosine kinase inhibitor called G6 (19). This stilbenoid compound demonstrated good potency and specificity for Jak2 tyrosine kinase as it inhibited Jak2-V617F enzymatic activity (IC 50 ϭ 60 nM) while having no effect on c-Src tyrosine kinase activity at concentrations as high as 25 M (19).…”

Myeloproliferative disorders and its associated mutations

“…Finally, tyk2 with JAK1 and JAK2 is associated with type I interferon, P40, IL-12 and IL-23 (10). Hyperactive Janus kinase leads to an abnormal proliferation in a series of hematological malignancies such as myeloid and lymphoid leukemia, Hodgkin lymphoma and B-cell non-Hodgkin lymphomas (11). In 1985, the first study related to interaction of mutations in JAK kinases and hematological malignancies were performed.…”