1. ¹Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA, USA
2. ²Department of Clinical Immunology, Warsaw Medical University, Warsaw, Poland
3. ³Department of Medicine, Division of Hematology and Oncology, University of Pennsylvania, Philadelphia, PA, USA
4. ⁴Institute of Medical Microbiology and Immunology, University of Copenhagen, Copenhagen, Denmark

Correspondence: Dr MA Wasik, MD, Department of Pathology and Laboratory Medicine, University of Pennsylvania Medical Center, 3400 Spruce Street, 7.106 Founders Pavillion, Philadelphia, PA 19104, USA. E-mail: wasik@mail.med.upenn.edu

Received 12 May 2005; Revised 27 July 2005; Accepted 3 August 2005; Published online 19 September 2005.

Abstract

Aberrant expression of the ALK tyrosine kinase as a chimeric protein with nucleophosmin (NPM) and other partners plays a key role in malignant cell transformation of T-lymphocytes and other cells. Here we report that two small-molecule, structurally related, quinazoline-type compounds, WHI-131 and WHI-154, directly inhibit enzymatic activity of NPM/ALK as demonstrated by in vitro kinase assays using a synthetic tyrosine-rich oligopeptide and the kinase itself as the substrates. The inhibition of NPM/ALK activity resulted in malignant T cells in suppression of their growth, induction of apoptosis and inhibition of tyrosine phosphorylation of STAT3, the key effector of the NPM/ALK-induced oncogenesis. We also show that the STAT3 tyrosine phosphorylation is mediated in the malignant T cells by NPM/ALK independently of Jak3 kinase as evidenced by the presence of STAT3 phosphorylation in the NPM/ALK-transfected BaF3 cells that do not express detectable Jak3 and in the NPM/ALK-positive malignant T cells with either Jak3 activity impaired by a pan-Jak or Jak3-selective inhibitor or Jak3 expression abrogated by Jak3 siRNA. The above results represent the 'proof-of-principle' experiments with regard to the ALK enzymatic activity as an attractive therapeutic target in T-cell lymphomas and other malignancies that express the kinase in an active form.