An Orally Available Syk Tyrosine Kinase Inhibitor Induces Apoptosis in Peripheral T-Cell Lymphomas Overexpressing Activated Syk
R Wilcox, D Sun, ED Remstein, A Dogan, S Ansell, AL Feldman. Mayo Clinic, Rochester, MN
Background: Syk is a tyrosine kinase that promotes growth of B cells. An orally available Syk inhibitor, R406, is in clinical trial for B-cell lymphomas. Though absent in normal T cells, Syk is overexpressed in most peripheral T-cell lymphomas (PTCLs; Feldman et al, Leukemia 2008;22:1139-43). We wanted to see if (1) Syk was activated in PTCLs; (2) R406 inactivated Syk; and (3) R406 killed the tumor cells.
Design: The anaplastic large-cell lymphoma cell lines SUDHL-1 and SR786 and the Sezary cell line SeAx were plated at 5 x 105 cells/mL and treated with either R406 (8 mM) or vehicle alone. Total and phosphorylated Syk were assessed at 24 h by western blot and flow cytometry. Apoptosis was assessed at 96 h using an annexin V assay, and expressed as percent apoptotic cells standard deviation. P values were determined using a t-test.
Results: SUDHL-1, SR786, and SeAx all expressed total Syk. SUDHL-1 and SR786 showed phosphorylation of Syk at tyrosine residues Y348 and Y525/526. Treatment with R406 completely dephosphorylated Syk in both cell lines, and caused a significant induction of apoptosis (SUDHL-1: 42.8 9.8 vs. 17.9 3.6 untreated, P=.01; SR786: 41.4 16.2 vs. 12.3 6.0 untreated, P=.04). In SeAx cells, Syk was partially phosphorylated at Y525/526 but showed no phosphorylation at Y348. R406 induced significant apoptosis in these cells also, though the mean apoptotic fraction was lower (22.0 5.8 vs. 10.6 3.2 untreated, P=.04).
Conclusions: R406 inactivates Syk and kills PTCL cells that express phospho-Syk. These findings suggest that Syk may play a critical biologic role in some PTCLs, and represents a feasible therapeutic target for clinical tyrosine kinase inhibition. The relative contribution of phosphorylation of Syk at Y348 and Y525/526 to the functional role of Syk in PTCL merits further study.
Monday, March 9, 2009 2:30 PM
Platform Session: Section D, Monday Afternoon