Small Molecule Inhibitor of ITK Disrupts TCR Signaling and Demonstrates Anti-Tumor Efficacy

Abstract 3932

ITK (Interluekin-2 Inducible Tyrosine Kinase) is a member of the TEC family of intracellular protein tyrosine kinases. ITK is highly expressed in T cells and NK cells, with expression detected in mast cells. ITK plays a key role in several aspects of T cell biology, including T cell development, differentiation, migration, proliferation and activation. The function of ITK in immunity and allergy is well documented. T cells from ITK knock out mice show several developmental and functional defects, including defective signal transduction, altered CD4+ to CD8+ T cells ratios, reduced Th2 lineage differentiation, diminished IL4 and IL2 production and reduced T cell proliferation. Importantly ITK deficient mice fail to mount an immune response to infection and show reduced allergic asthma reactions.

In contrast to its well described role in immune function, ITK's function in cancer biology is still emerging. Recent studies had reported enhanced ITK expression and activation of the ITK pathway in several types of leukemias and lymphomas. In addition, the dependence of T cell malignancies on an ITK-regulated pathway, namely the IL2/IL2R (CD25) pathway, has also been observed. Taken together, this information indicates that ITK is a therapeutic target, with applicability in leukemias and lymphomas.

MannKind scientists have developed a series of selective small molecule ITK inhibitors, including the orally available tool compound described within, and evaluated their activity in enzyme, cell-based and in vivo studies. In cellular assays, the compounds showed significant inhibition of the T cell-receptor mediated activation of the ITK pathways and related downstream cytokine production. In addition to inhibiting the phosphorylation of ITK and its downstream mediator, PLCg, our tool compounds inhibited the production of IL2 and expression of CD25 in a dose dependent manner. Importantly, our compound regulated the in vitro growth of tumor T cells but not that of unrelated control cells. In vivo studies revealed that the tool compounds inhibited the growth and progression of patient derived ATL tumors in a xenograft pre-clinical model, and prolonged the survival of treated mice in a dose dependent manner, in addition to regulating cytokine production in vivo. In summary, our team has identified ITK selective compounds with demonstrated on-target and anti-tumor activity in vitro and preclinical T cell tumor models, and validated this pathway relative to T cell malignancies. This effort provides a platform for further compound optimization and evaluation for hematologic malignancies.