pi103 and Precursor-T-Cell-Lymphoblastic-Leukemia-Lymphoma

PI3K, mTOR and NOTCH pathways are frequently dysregulated in T-cell acute lymphoblastic leukaemia (T-ALL). Blockade of PI3K and mTOR with the dual inhibitor PI-103 decreased proliferation in all 15 T-ALL cell lines tested, inducing cell death in three. Combined PI3K/mTOR/NOTCH inhibition (with a γ-secretase inhibitor (GSI)) led to enhanced cell-cycle arrest and to subsequent cell death in 7/11 remaining NOTCH mutant cell lines. Commitment to cell death occurred within 48-72 h and was maximal when PI3K, mTOR and NOTCH activities were inhibited. PI-103 addition led to upregulation of c-MYC, which was blocked by coincubation with a GSI, indicating that PI3K/mTOR inhibition resulted in activation of the NOTCH-MYC pathway. Microarray studies showed a global increase in NOTCH target gene expression upon PI3K/mTOR inhibition. NOTCH-MYC-induced resistance to PI3K/mTOR inhibition was supported by synergistic cell death induction by PI-103 and a small molecule c-MYC inhibitor, and by reduction of the cytotoxic effect of PI-103+GSI by c-MYC overexpression. These results show that drugs targeting PI3K/mTOR can upregulate NOTCH-MYC activity, have implications for the use of PI3K inhibitors for the treatment of other malignancies with activated NOTCH, and provide a rational basis for the use of drug combinations that target both the pathways.

Topics: Apoptosis; Biomarkers, Tumor; Blotting, Western; Cell Cycle; Cell Proliferation; Furans; Gene Expression Profiling; Humans; Oligonucleotide Array Sequence Analysis; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Proto-Oncogene Proteins c-akt; Proto-Oncogene Proteins c-myc; Pyridines; Pyrimidines; Real-Time Polymerase Chain Reaction; Receptors, Notch; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Signal Transduction; TOR Serine-Threonine Kinases; Tumor Cells, Cultured; Up-Regulation

Recent investigations have documented that constitutively activated phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling is a common feature of T-cell acute lymphoblastic leukemia (T-ALL), where it strongly influences growth and survival. These findings lend compelling weight for the application of PI3K/Akt/mTOR inhibitors in T-ALL. However, our knowledge of PI3K/Akt/mTOR signaling in T-ALL is limited and it is not clear whether it could be an effective target for innovative therapeutic strategies. Here, we have analyzed the therapeutic potential of the dual PI3K/mTOR inhibitor PI-103, a small synthetic molecule of the pyridofuropyrimidine class, on both T-ALL cell lines and patient samples, which displayed constitutive activation of PI3K/Akt/mTOR signaling. PI-103 inhibited the growth of T-ALL cells, including 170-kDa P-glycoprotein overexpressing cells. PI-103 cytotoxicity was independent of p53 gene status. PI-103 was more potent than inhibitors that are selective only for PI3K (Wortmannin, LY294002) or for mTOR (rapamycin). PI-103 induced G(0)-G(1) phase cell cycle arrest and apoptosis, which was characterized by activation of caspase-3 and caspase-9. PI-103 caused Akt dephosphorylation, accompanied by dephosphorylation of the Akt downstream target, glycogen synthase kinase-3beta. Also, mTOR downstream targets were dephosphorylated in response to PI-103, including p70S6 kinase, ribosomal S6 protein, and 4E-BP1. PI-103 strongly synergized with vincristine. These findings indicate that multitargeted therapy toward PI3K and mTOR alone or with existing drugs may serve as an efficient treatment toward T-ALL cells, which require up-regulation of PI3K/Akt/mTOR signaling for their survival and growth.

Topics: Antineoplastic Combined Chemotherapy Protocols; Caspase 3; Caspase 9; Cell Line, Tumor; Drug Synergism; Enzyme Activation; Furans; Humans; Jurkat Cells; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Protein Kinase Inhibitors; Protein Kinases; Proto-Oncogene Proteins c-akt; Pyridines; Pyrimidines; Signal Transduction; TOR Serine-Threonine Kinases; Vincristine