Recent evidence suggests that inhibition of
protein phosphatase 2A (PP2A)
tumor suppressor activity via the SET
oncoprotein contributes to the pathogenesis of various
cancers. Here we demonstrate that both SET and c-MYC expression are frequently elevated in
T-ALL cell lines and primary samples compared to healthy T cells. Treatment of
T-ALL cells with the SET antagonist OP449 restored the activity of PP2A and reduced SET interaction with the PP2A catalytic subunit, resulting in a decrease in cell viability and c-MYC expression in a dose-dependent manner. Since a tight balance between
phosphatases and
kinases is required for the growth of both normal and malignant cells, we sought to identify a
kinase inhibitor that would synergize with SET antagonism. We tested various
T-ALL cell lines against a small-molecule inhibitor screen of 66 compounds targeting two-thirds of the
tyrosine kinome and found that combined treatment of
T-ALL cells with
dovitinib, an orally active multi-targeted small-molecule
receptor tyrosine kinase inhibitor, and OP449 synergistically reduced the viability of all tested
T-ALL cell lines. Mechanistically, combined treatment with OP449 and
dovitinib decreased total and phospho c-MYC levels and reduced ERK1/2, AKT, and p70S6
kinase activity in both NOTCH-dependent and independent
T-ALL cell lines. Overall, these results suggest that combined targeting of
tyrosine kinases and activation of
serine/
threonine phosphatases may offer novel therapeutic strategies for the treatment of
T-ALL.