To more comprehensively assess the pathogenic contribution of the PTEN-PI3K-AKT pathway to T-cell acute lymphoblastic leukemia (T-ALL), we examined diagnostic DNA samples from children with T-ALL using array comparative genomic hybridization and sequence analysis. Alterations of PTEN, PI3K, or AKT were identified in 47.7% of 44 cases.There was a striking clustering of PTEN mutations in exon 7 in 12 cases, all of which were predicted to truncate the C2 domain without disrupting the phosphatase domain of PTEN. Induction chemotherapy failed to induce remission in 3 of the 4 patients whose lymphoblasts harbored PTEN deletions at the time of diagnosis, compared with none of the 12 patients with mutations of PTEN exon 7 (P ‫؍‬ .007), suggesting that PTEN deletion has more adverse therapeutic consequences than mutational disruptions that preserve the phosphatase domain. These findings add significant support to the rationale for the development of therapies targeting the PTEN-PI3K-AKT pathway in T-ALL. IntroductionDespite recent improvements in therapy, approximately 25% of children and 50% to 70% of adults with T-cell acute lymphoblastic leukemia (T-ALL) develop treatment-resistant disease, 1,2 which carries a dire prognosis. 3 Molecularly targeted agents hold considerable promise for the treatment of T-ALL, although limits in our current understanding of the key pathways that drive T-ALL pathogenesis restrict our ability to use these agents effectively.PTEN is a negative regulator of oncogenic PI3K-AKT signaling, 4 and recent studies have demonstrated the inactivation of PTEN in human T-ALL cell lines and primary samples. [5][6][7][8] Furthermore, the inactivation of PTEN has been shown to play a prominent role in resistance to NOTCH inhibition in T-ALL cell lines, an effect that appears to be mediated by AKT. 7 The activation of PI3K-AKT signaling can also occur by mutation of PI3K or AKT genes, which have not previously been assessed in T-ALL. Finally, the spectrum of PTEN mutations has not been extensively analyzed in clinical samples of primary T-ALL. Here we investigated the frequency and prognostic implications of PTEN, PI3K, and AKT abnormalities in childhood T-ALL, using array comparative genomic hybridization (CGH), fluorescence in situ hybridization (FISH), and sequence analysis.

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive cancer that is frequently associated with activating mutations in NOTCH1 and dysregulation of MYC. Here, we performed 2 complementary screens to identify FDA-approved drugs and drug-like small molecules with activity against T-ALL. We developed a zebrafish system to screen small molecules for toxic activity toward MYC-overexpressing thymocytes and used a human T-ALL cell line to screen for small molecules that synergize with Notch inhibitors. We identified the antipsychotic drug perphenazine in both screens due to its ability to induce apoptosis in fish, mouse, and human T-ALL cells. Using ligand-affinity chromatography coupled with mass spectrometry, we identified protein phosphatase 2A (PP2A) as a perphenazine target. T-ALL cell lines treated with perphenazine exhibited rapid dephosphorylation of multiple PP2A substrates and subsequent apoptosis. Moreover, shRNA knockdown of specific PP2A subunits attenuated perphenazine activity, indicating that PP2A mediates the drug's antileukemic activity. Finally, human T-ALLs treated with perphenazine exhibited suppressed cell growth and dephosphorylation of PP2A targets in vitro and in vivo. Our findings provide a mechanistic explanation for the recurring identification of phenothiazines as a class of drugs with anticancer effects. Furthermore, these data suggest that pharmacologic PP2A activation in T-ALL and other cancers driven by hyperphosphorylated PP2A substrates has therapeutic potential.

No abstract

Lymphoblasts from children with T-ALL should be evaluated at diagnosis for deletion within the TCRgamma locus. Patients lacking biallelic deletion, which confers a high probability of induction failure with contemporary therapy, should be assigned to alternative therapy in the context of a prospective clinical trial.