Inhibition of MALT1 and BCL2 Induces Synergistic Antitumor Activity in Models of B-Cell Lymphoma.

The activated B cell (ABC) subset of diffuse large B-cell lymphoma (DLBCL) is characterized by chronic B-cell receptor signaling and associated with poor outcomes when treated with standard therapy. In ABC-DLBCL, MALT1 is a core enzyme that is constitutively activated by stimulation of the B-cell receptor or gain-of-function mutations in upstream components of the signaling pathway, making it an attractive therapeutic target. We discovered a novel small-molecule inhibitor, ABBV-MALT1, that potently shuts down B-cell signaling selectively in ABC-DLBCL preclinical models leading to potent cell growth and xenograft inhibition.

Targeting MCL-1 and BCL-2 with polatuzumab vedotin and venetoclax overcomes treatment resistance in R/R non-Hodgkin lymphoma: Results from preclinical models and a Phase Ib study.

The treatment of patients with relapsed or refractory lymphoid neoplasms represents a significant clinical challenge. Here, we identify the pro-survival BCL-2 protein family member MCL-1 as a resistance factor for the BCL-2 inhibitor venetoclax in non-Hodgkin lymphoma (NHL) cell lines and primary NHL samples. Mechanistically, we show that the antibody-drug conjugate polatuzumab vedotin promotes MCL-1 degradation via the ubiquitin/proteasome system.

Combined heterozygosity of FLT3 ITD, TET2, and DNMT3A results in aggressive leukemia.

Heterozygous mutations in FLT3ITD, TET2, and DNMT3A are associated with hematologic malignancies in humans. In patients, cooccurrence of mutations in FLT3ITD combined with TET2 (TF) or FLT3ITD combined with DNMT3A (DF) are frequent. However, in some rare complex acute myeloid leukemia (AML), all 3 mutations cooccur - i.

Driver Mutations in Leukemia Promote Disease Pathogenesis through a Combination of Cell-Autonomous and Niche Modulation.

Studies of patients with acute myeloid leukemia (AML) have led to the identification of mutations that affect different cellular pathways. Some of these have been classified as preleukemic, and a stepwise evolution program whereby cells acquire additional mutations has been proposed in the development of AML. How the timing of acquisition of these mutations and their impact on transformation and the bone marrow (BM) microenvironment occurs has only recently begun to be investigated.

Inhibition of Inflammatory Signaling in Tet2 Mutant Preleukemic Cells Mitigates Stress-Induced Abnormalities and Clonal Hematopoiesis.

Inflammation is a risk factor for cancer development. Individuals with preleukemic TET2 mutations manifest clonal hematopoiesis and are at a higher risk of developing leukemia. How inflammatory signals influence the survival of preleukemic hematopoietic stem and progenitor cells (HSPCs) is unclear.

Loss of epigenetic regulator TET2 and oncogenic KIT regulate myeloid cell transformation via PI3K pathway.

Mutations in KIT and TET2 are associated with myeloid malignancies. We show that loss of TET2-induced PI3K activation and -increased proliferation is rescued by targeting the p110α/δ subunits of PI3K. RNA-Seq revealed a hyperactive c-Myc signature in Tet2-/- cells, which is normalized by inhibiting PI3K signaling.

S6K1 regulates hematopoietic stem cell self-renewal and leukemia maintenance.

Hyperactivation of the mTOR pathway impairs hematopoietic stem cell (HSC) functions and promotes leukemogenesis. mTORC1 and mTORC2 differentially control normal and leukemic stem cell functions. mTORC1 regulates p70 ribosomal protein S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E-binding (eIF4E-binding) protein 1 (4E-BP1), and mTORC2 modulates AKT activation.

ROCK1 via LIM kinase regulates growth, maturation and actin based functions in mast cells.

Understanding mast cell development is essential due to their critical role in regulating immunity and autoimmune diseases. Here, we show how Rho kinases (ROCK) regulate mast cell development and can function as therapeutic targets for treating allergic diseases. Rock1 deficiency results in delayed maturation of bone marrow derived mast cells (BMMCs) in response to IL-3 stimulation and reduced growth in response to stem cell factor (SCF) stimulation.

Regulation of Stat5 by FAK and PAK1 in Oncogenic FLT3- and KIT-Driven Leukemogenesis.

Oncogenic mutations of FLT3 and KIT receptors are associated with poor survival in patients with acute myeloid leukemia (AML) and myeloproliferative neoplasms (MPNs), and currently available drugs are largely ineffective. Although Stat5 has been implicated in regulating several myeloid and lymphoid malignancies, how precisely Stat5 regulates leukemogenesis, including its nuclear translocation to induce gene transcription, is poorly understood. In leukemic cells, we show constitutive activation of focal adhesion kinase (FAK) whose inhibition represses leukemogenesis.

Therapeutic potential of targeting the oncogenic SHP2 phosphatase.

The Src homology 2 domain containing protein tyrosine phosphatase-2 (SHP2) is an oncogenic phosphatase associated with various kinds of leukemia and solid tumors. Thus, there is substantial interest in developing SHP2 inhibitors as potential anticancer and antileukemia agents. Using a structure-guided and fragment-based library approach, we identified a novel hydroxyindole carboxylic acid-based SHP2 inhibitor 11a-1, with an IC50 value of 200 nM and greater than 5-fold selectivity against 20 mammalian PTPs.

Role of Rho kinases in abnormal and normal hematopoiesis.

Purpose Of Review: Rho kinases (ROCKs) are involved in regulating a variety of physiologic functions including cytoskeletal reorganization, migration, adhesion, survival and proliferation. They do so via activating several different downstream substrates such as myosin light chain phosphatase, LIM kinase and ezrin/radixin/moesin proteins. To date, most of the conclusions with regard to the function of ROCKs have involved the use of cell line models, pharmacologic inhibitors and dominant negative approaches.

PI3K p110δ uniquely promotes gain-of-function Shp2-induced GM-CSF hypersensitivity in a model of JMML.

Although hyperactivation of the Ras-Erk signaling pathway is known to underlie the pathogenesis of juvenile myelomonocytic leukemia (JMML), a fatal childhood disease, the PI3K-Akt signaling pathway is also dysregulated in this disease. Using genetic models, we demonstrate that inactivation of phosphatidylinositol-3-kinase (PI3K) catalytic subunit p110δ, but not PI3K p110α, corrects gain-of-function (GOF) Shp2-induced granulocyte macrophage-colony-stimulating factor (GM-CSF) hypersensitivity, Akt and Erk hyperactivation, and skewed hematopoietic progenitor distribution. Likewise, potent p110δ-specific inhibitors curtail the proliferation of GOF Shp2-expressing hematopoietic cells and cooperate with mitogen-activated or extracellular signal-regulated protein kinase kinase (MEK) inhibition to reduce proliferation further and maximally block Erk and Akt activation.

Pak and Rac GTPases promote oncogenic KIT-induced neoplasms.

An acquired somatic mutation at codon 816 in the KIT receptor tyrosine kinase is associated with poor prognosis in patients with systemic mastocytosis and acute myeloid leukemia (AML). Treatment of leukemic cells bearing this mutation with an allosteric inhibitor of p21-activated kinase (Pak) or its genetic inactivation results in growth repression due to enhanced apoptosis. Inhibition of the upstream effector Rac abrogates the oncogene-induced growth and activity of Pak.

Targeting Rho associated kinases in leukemia and myeloproliferative neoplasms.

If ROCKs are going to be targeted as anti-leukemic agents either as a monotherapy or in combination with existing drugs, a better characterization of the relative contribution of ROCK1 and ROCK2 in disease progression is essential.

Single nucleotide polymorphism array lesions, TET2, DNMT3A, ASXL1 and CBL mutations are present in systemic mastocytosis.

We hypothesized that analysis of single nucleotide polymorphism arrays (SNP-A) and new molecular defects may provide new insight in the pathogenesis of systemic mastocytosis (SM). SNP-A karyotyping was applied to identify recurrent areas of loss of heterozygosity and bidirectional sequencing was performed to evaluate the mutational status of TET2, DNMT3A, ASXL1, EZH2, IDH1/IDH2 and the CBL gene family. Overall survival (OS) was analyzed using the Kaplan-Meier method.

ROCK1 functions as a critical regulator of stress erythropoiesis and survival by regulating p53.

Erythropoiesis is a dynamic, multistep process whereby hematopoietic stem cells differentiate toward a progressively committed erythroid lineage through intermediate progenitors. Although several downstream signaling molecules have been identified that regulate steady-state erythropoiesis, the major regulators under conditions of stress remain poorly defined. Rho kinases (ROCKs) belong to a family of serine/threonine kinases.

Role of SHP2 phosphatase in KIT-induced transformation: identification of SHP2 as a druggable target in diseases involving oncogenic KIT.

Intracellular mechanism(s) that contribute to promiscuous signaling via oncogenic KIT in systemic mastocytosis and acute myelogenous leukemia are poorly understood. We show that SHP2 phosphatase is essential for oncogenic KIT-induced growth and survival in vitro and myeloproliferative disease (MPD) in vivo. Genetic disruption of SHP2 or treatment of oncogene-bearing cells with a novel SHP2 inhibitor alone or in combination with the PI3K inhibitor corrects MPD by disrupting a protein complex involving p85α, SHP2, and Gab2.

SH2 domain-containing phosphatase 2 is a critical regulator of connective tissue mast cell survival and homeostasis in mice.

Mast cells require KIT receptor tyrosine kinase signaling for development and survival. Here, we report that SH2 domain-containing phosphatase 2 (SHP2) signaling downstream of KIT is essential for mast cell survival and homeostasis in mice. Using a novel mouse model with shp2 deletion within mature mast cells (MC-shp2 knockout [KO]), we find that SHP2 is required for the homeostasis of connective tissue mast cells.

The role of SHIP in the development and activation of mouse mucosal and connective tissue mast cells.

Although SHIP is a well-established suppressor of IgE plus Ag-induced degranulation and cytokine production in bone marrow-derived mast cells (BMMCs), little is known about its role in connective tissue (CTMCs) or mucosal (MMCs) mast cells. In this study, we compared SHIP's role in the development as well as the IgE plus Ag and TLR-induced activation of CTMCs, MMCs, and BMMCs and found that SHIP delays the maturation of all three mast cell subsets and, surprisingly, that it is a positive regulator of IgE-induced BMMC survival. We also found that SHIP represses IgE plus Ag-induced degranulation of all three mast cell subsets and that TLR agonists do not trigger their degranulation, whether SHIP is present or not, nor do they enhance IgE plus Ag-induced degranulation.

p85β regulatory subunit of class IA PI3 kinase negatively regulates mast cell growth, maturation, and leukemogenesis.

We show that loss of p85α inhibits the growth and maturation of mast cells, whereas loss of p85β enhances this process. Whereas restoring the expression of p85α in P85α(-/-) cells restores these functions, overexpression of p85β has the opposite effect. Consistently, overexpression of p85β in WT mast cells represses KIT-induced proliferation and IL-3-mediated maturation by inhibiting the expression of Microphthalmia transcription factor.

Role of intracellular tyrosines in activating KIT-induced myeloproliferative disease.

Gain-of-function mutations in KIT receptor in humans are associated with gastrointestinal stromal tumors, systemic mastocytosis and acute myelogenous leukemia. The intracellular signals that contribute to oncogenic KIT-induced myeloproliferative disease (MPD) are poorly understood. Here, we show that oncogenic KITD814V-induced MPD occurs in the absence of ligand stimulation.

Class I(A) PI3Kinase regulatory subunit, p85α, mediates mast cell development through regulation of growth and survival related genes.

Stem cell factor (SCF) mediated KIT receptor activation plays a pivotal role in mast cell growth, maturation and survival. However, the signaling events downstream from KIT are poorly understood. Mast cells express multiple regulatory subunits of class 1(A) PI3Kinase (PI3K) including p85α, p85β, p50α, and p55α.