Spleen Tyrosine Kinase (SYK) is a non-receptor cytoplasmic tyrosine kinase that is primarily expressed in hematopoietic cells. SYK is a key mediator for a variety of inflammatory cells, including B cells, mast cells, macrophages and neutrophils[3]. TAK-659 hydrochloride is a potent, selective and orally available spleen tyrosine kinase (Syk) inhibitor with an IC50 of 3.2 nM[3]. In a cell proliferation assay, TAK-659 shows inhibition toward a SYK-dependent cell line (OCILY10)[3]. TAK-659 inhibited the microenvironment-induced activation of Syk and downstream signaling molecules, without inhibiting the protein homologue ZAP-70 in T cells. Importantly, the pro-survival, proliferative, chemoresistant and activation effects promoted by the microenvironment were abrogated by TAK-659, which furthermore blocked CLL cell migration toward BMSC, CXCL12, and CXCL13[4]. TAK-659 blocks anti-IgD (immune-globulin D antibody) stimulated CD86 expression in mouse peripheral B cells in vivo. In the OCI-LY10 xenograft and DLBCL PHTX-95L (primary human tumor graft from DLBCL patient) mouse models, TAK-659 demonstrates potent tumor growth inhibition (TGI) after 20 days of treatment. In the FLT3-dependent MV4-11 xenograft model, TAK-659 shows tumor regression at 60 mg/kg daily after 20 days of dosing[3].
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