The dual specificity PI3K/mTOR inhibitor PKI-587 displays efficacy against T-cell acute lymphoblastic leukemia (T-ALL)

Although significant improvements have been made in the treatment of acute lymphoblastic leukemia (ALL), there is a substantial subset of high-risk T-cell ALL (T-ALL) patients with relatively poor prognosis. Like in other leukemia types, alterations of the PI3K/mTOR pathway are predominant in ALL which is also responsible for treatment failure and relapse. In this study, we show that relapsed T-ALL patients display an enrichment of the PI3K/mTOR pathway. Using a panel of inhibitors targeting multiple components of the PI3K/mTOR pathway, we observed that the dual-specific PI3K/mTOR inhibitor PKI-587 was the most selective inhibitor for T-ALL cells dependent on the PI3K/mTOR pathway. Furthermore, we observed that PKI-587 blocked proliferation and colony formation of T-ALL cell lines. Additionally, PKI-587 selectively abrogated PI3K/mTOR signaling without affecting MAPK signaling both in in vitro and in vivo. Inhibition of the PI3K/mTOR pathway using PKI-587 delayed tumor progression, reduced tumor load and enhanced the survival rate in immune-deficient mouse xenograft models without inducing weight loss in the inhibitor treated mice. This preclinical study shows beneficial effects of PKI-587 on T-ALL that warrants further investigation in the clinical setting

The role of HOXB2 and HOXB3 in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a heterogeneous aggressive disease and the most common form of adult leukemia. Mutations in the type III receptor tyrosine kinase FLT3 are found in more than 30% of patients. Drugs against FLT3 have been developed for the treatment of AML, but they lack specificity, show poor response and lead to the development of a resistant phenotype upon treatment. Therefore, a deeper understanding of FLT3 signaling will facilitate identification of additional pharmacological targets in FLT3-driven AML. In this report, we identify HOXB2 and HOXB3 as novel regulators of oncogenic FLT3-ITD-driven AML. We show that HOXB2 and HOXB3 expression is upregulated in a group of AML patients carrying FLT3-ITD. Overexpression of HOXB2 or HOXB3 in mouse pro-B cells resulted in decreased FLT3-ITD-dependent cell proliferation as well as decreased colony formation and increased apoptosis. Expression of HOXB2 or HOXB3 resulted in a significant decrease in FLT3-ITD-induced AKT, ERK, p38 and STAT5 phosphorylation. Our data suggest that HOXB2 and HOXB3 act as a tumor suppressors in FLT3-ITD driven AML

T-cell acute lymphoblastic leukemia cells display activation of different survival pathways

T-cell acute lymphoblastic leukemia (T-ALL) is a disease of the blood affecting T-lymphocytes. Although notable improvements have been achieved in T-ALL treatment, half of the adult T-ALL patients still experience treatment failure. In order to develop a targeted therapy, we need a better understanding of T-ALL pathogenesis. In this study, we used patient-derived cell lines which display resistance to glucocorticoids. We observed that different cell lines are dependent on different survival signaling pathways. Aberrant activation of AKT, p38, S6K or ERK signaling was not found to the same degree in all cell lines studied. To understand the molecular differences in T-ALL cells, we compared gene expression and somatic mutations. Gene set enrichment analysis showed enrichment of the mTORC1, MAPK or TGF-beta signaling pathways. Loss-of-function mutations in the TP53 and FBXW7 genes were identified in all cell lines investigated. Thus, we suggest that T-ALL cells from different patients are addicted to different mutations and thereby to different signaling pathways. Therefore, understanding the enrichment of molecular pathways for each individual patient will provide us with a more precise and specific treatment plan

Acute leukemia cells resistant to PI3K/mTOR inhibition display upregulation of P2RY14 expression

The PI3K/mTOR pathway is the second most frequently deregulated pathway in a majority of cancers such as breast cancer, lung cancer, and melanomas as well as leukemia. Mutations in the genes coding for receptor tyrosine kinases (RTKs) and G-protein-coupled receptors (GPCRs) are quite common in all forms of acute leukemia. This can be a major cause of deregulation of the PI3K-mTOR pathway. To understand how cells display resistance to the dual PI3K/mTOR inhibitor, we used a panel of 25 acute leukemia cell lines. We observed that while a number of cell lines displayed sensitivity to the dual PI3K/mTOR pathway inhibitor PKI-587, many cells displayed substantial resistance. Cells sensitive to PKI-587 also showed aberrant activation of PI3K/mTOR pathway components such as AKT and S6K and also displayed sensitivity to a panel of various other PI3K/mTOR inhibitors. Using RNA sequencing data, we observed that expression of a G protein-coupled receptor, P2RY14, was upregulated nine-fold in cells showing resistance to the PI3K/mTOR inhibitor. P2RY14 has not been much studied in hematologic malignancies. However, this receptor seems to have a role in the localization of hematopoietic stem cells (HSCs) and in promoting regenerative capabilities following injury. We observed that acute lymphoblastic leukemia (ALL) and FLT3-ITD-positive acute myeloid leukemia (AML) patients with higher expression of P2RY14 mRNA displayed relatively poor survival compared to patients carrying lower expression of P2RY14 suggesting a role of P2RY14 in patient survival. To understand the role of this receptor in cell signaling, we used phospho-protein arrays and observed activation of distinct signaling cascades. Furthermore, array data were verified using murine pro-B cell line Ba/F3 stably transfected with P2RY14. We observed that activation of P2RY14 by its ligand, UDP-glucose, resulted in selective induction of ERK1/2 phosphorylation. Taken together, our data suggest that acute leukemia cells resistant to PI3K/mTOR inhibition display upregulation of a GPCR, P2RY14, which has a role in patient survival and also couples to the activation of ERK signaling

SRC-like adaptor protein 2 (SLAP2) is a negative regulator of KIT-D816V-mediated oncogenic transformation

Abstract KIT is a receptor tyrosine kinase (RTK) involved in several cellular processes such as regulation of proliferation, survival and differentiation of early hematopoietic cells, germ cells and melanocytes. Activation of KIT results in phosphorylation of tyrosine residues in the receptor, and recruitment of proteins that mediate downstream signaling and also modulate receptor signaling. Here we show that the SRC-like adaptor protein 2 (SLAP2) binds to wild-type KIT in a ligand-dependent manner and is furthermore found constitutively associated with the oncogenic mutant KIT-D816V. Peptide fishing analysis mapped pY568 and pY570 as potential SLAP2 association sites in KIT, which overlaps with the SRC binding sites in KIT. Expression of SLAP2 in cells expressing the transforming mutant KIT-D816V led to reduced cell viability and reduced colony formation. SLAP2 also partially blocked phosphorylation of several signal transduction molecules downstream of KIT such as AKT, ERK, p38 and STAT3. Finally, SLAP2 expression enhanced ubiquitination of KIT and its subsequent degradation. Taken together, our data demonstrate that SLAP2 negatively modulates KIT-D816V-mediated transformation by enhancing degradation of the receptor

Glucocorticoid-resistant B cell acute lymphoblastic leukemia displays receptor tyrosine kinase activation

The response of childhood acute lymphoblastic leukemia (ALL) to dexamethasone predicts the long-term remission outcome. To explore the mechanisms of dexamethasone resistance in B cell ALL (B-ALL), we generated dexamethasone-resistant clones by prolonged treatment with dexamethasone. Using RNA-sequencing and high-throughput screening, we found that dexamethasone-resistant cells are dependent on receptor tyrosine kinases. Further analysis with phosphokinase arrays showed that the type III receptor tyrosine kinase FLT3 is constitutively active in resistant cells. Targeted next-generation and Sanger sequencing identified an internal tandem duplication mutation and a point mutation (R845G) in FLT3 in dexamethasone-resistant cells, which were not present in the corresponding sensitive clones. Finally, we showed that resistant cells displayed sensitivity to second-generation FLT3 inhibitors both in vitro and in vivo. Collectively, our data suggest that long-term dexamethasone treatment selects cells with a distinct genetic background, in this case oncogenic FLT3, and therefore therapies targeting FLT3 might be useful for the treatment of relapsed B-ALL patients

Efficacy of the CDK inhibitor dinaciclib in vitro and in vivo in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is a heterogeneous disease of the blood affecting children, adolescents and adults. Although current treatment protocols for T-ALL have improved overall survival, a portion of T-ALL patients still experiences treatment failure. Thus, the development of novel therapies is needed. In this study, we used several patient-derived T-ALL cell lines to screen for an effective drug for T-ALL. Using a panel of 378 inhibitors against different kinases, we identified the CDK inhibitor dinaciclib as a potential drug for T-ALL. Dinaciclib treatment significantly reduced cell viability and completely blocked colony formation. Furthermore, cells treated with dinaciclib showed decreased expression of several pro-survival proteins including survivin, cyclin T1 and c-MYC. Dinaciclib treatment also increased accumulation of cells in G2/M phase and significantly induced apoptosis. Finally, dinaciclib extended survival of mice in a T-ALL cell xenograft model. Collectively, these data suggest that the CDK inhibitor dinaciclib is an active drug for T-ALL in the preclinical settings