ITK inhibition induced in vitro and in vivo anti-tumor activity through downregulating TCR signaling pathway in malignant T cell lymphoma

Background: Angioimmunoblastic T cell lymphoma (AITL) is a distinct subtype of peripheral T cell lymphoma and associated with poor outcomes. The activation status of T cell receptor (TCR) signaling has recently become a focus of attention in terms of the therapeutic targets. However, the molecular pathogenesis mechanisms and novel therapeutic targets are largely unknown.

Methods: Antibodies specific to phosphorylated ZAP70, Itk and PLCγ1 were used to identify the activation status of intracellular proteins involved in TCR signaling in AITL patients. Malignant T cell lymphoma cells were transduced with a lentiviral construct containing Itk shRNA for cellular and functional assays. The antitumor effects of the selective Itk inhibitor BMS-509744 were determined in vitro and in vivo.

Results: Immunohistochemistry staining showed that more than half of the AITL patients (n = 38) exhibited continuously activated intracellular TCR signaling pathway. Patients positive for phosphorylated Itk showed a lower rate of complete response (20% vs. 75%, P = 0.004) and a shorter progression-free survival (5.17 months vs. 25.1 months, P = 0.022) than patients negative for phosphorylated Itk. Genetic and pharmacological cellular Itk inhibition significantly compromised the proliferation, invasion and migration of malignant T cells. The selective Itk inhibitor BMS-509744 also induced the pro-apoptotic effects and G2/M phase cell cycle arrest in vitro and in vivo. Finally, inhibition of Itk synergistically enhanced the antitumor effect of vincristine and doxorubicin on malignant T cell lymphoma cell lines.

Conclusions: Our findings suggest that Itk may be a novel candidate therapeutic target for the treatment of patients with ITK-expressing malignant T-cell lymphomas.