Malignant A-to-I RNA editing by ADAR1 drives T cell acute lymphoblastic leukemia relapse via attenuating dsRNA sensing.

Leukemia-initiating cells (LICs) are regarded as the origin of leukemia relapse and therapeutic resistance. Identifying direct stemness determinants that fuel LIC self-renewal is critical for developing targeted approaches. Here, we show that the RNA-editing enzyme ADAR1 is a crucial stemness factor that promotes LIC self-renewal by attenuating aberrant double-stranded RNA (dsRNA) sensing.

Detection and targeting of splicing deregulation in pediatric acute myeloid leukemia stem cells.

Pediatric acute myeloid leukemia (pAML) is typified by high relapse rates and a relative paucity of somatic DNA mutations. Although seminal studies show that splicing factor mutations and mis-splicing fuel therapy-resistant leukemia stem cell (LSC) generation in adults, splicing deregulation has not been extensively studied in pAML. Herein, we describe single-cell proteogenomics analyses, transcriptome-wide analyses of FACS-purified hematopoietic stem and progenitor cells followed by differential splicing analyses, dual-fluorescence lentiviral splicing reporter assays, and the potential of a selective splicing modulator, Rebecsinib, in pAML.

Reversal of malignant ADAR1 splice isoform switching with Rebecsinib.

Adenosine deaminase acting on RNA1 (ADAR1) preserves genomic integrity by preventing retroviral integration and retrotransposition during stress responses. However, inflammatory-microenvironment-induced ADAR1p110 to p150 splice isoform switching drives cancer stem cell (CSC) generation and therapeutic resistance in 20 malignancies. Previously, predicting and preventing ADAR1p150-mediated malignant RNA editing represented a significant challenge.

A Phase I/II Trial of the Combination of Azacitidine and Gemtuzumab Ozogamicin for Treatment of Relapsed Acute Myeloid Leukemia.

Introduction: Treatment with hypomethylating agent therapy might enhance anti-CD33 monoclonal antibody-mediated cytotoxicity against acute myeloid leukemia (AML) blasts through epigenetic effects on Syk and SHP-1 expression.

Patients And Methods: In the present phase I/II study, we treated patients with relapsed or refractory AML with azacitidine, followed by 2 doses of gemtuzumab ozogamicin (GO) at 6 mg/m, the Food and Drug Administration-approved dose and schedule at study initiation. We sought to determine the maximum tolerated dose and clinical activity of this combination therapy.

RNA Splicing Modulation Selectively Impairs Leukemia Stem Cell Maintenance in Secondary Human AML.

Age-related human hematopoietic stem cell (HSC) exhaustion and myeloid-lineage skewing promote oncogenic transformation of hematopoietic progenitor cells into therapy-resistant leukemia stem cells (LSCs) in secondary acute myeloid leukemia (AML). While acquisition of clonal DNA mutations has been linked to increased rates of secondary AML for individuals older than 60 years, the contribution of RNA processing alterations to human hematopoietic stem and progenitor aging and LSC generation remains unclear. Comprehensive RNA sequencing and splice-isoform-specific PCR uncovered characteristic RNA splice isoform expression patterns that distinguished normal young and aged human stem and progenitor cells (HSPCs) from malignant myelodysplastic syndrome (MDS) and AML progenitors.

ADAR1 Activation Drives Leukemia Stem Cell Self-Renewal by Impairing Let-7 Biogenesis.

Post-transcriptional adenosine-to-inosine RNA editing mediated by adenosine deaminase acting on RNA1 (ADAR1) promotes cancer progression and therapeutic resistance. However, ADAR1 editase-dependent mechanisms governing leukemia stem cell (LSC) generation have not been elucidated. In blast crisis chronic myeloid leukemia (BC CML), we show that increased JAK2 signaling and BCR-ABL1 amplification activate ADAR1.

A Pan-BCL2 inhibitor renders bone-marrow-resident human leukemia stem cells sensitive to tyrosine kinase inhibition.

Leukemia stem cells (LSCs) play a pivotal role in the resistance of chronic myeloid leukemia (CML) to tyrosine kinase inhibitors (TKIs) and its progression to blast crisis (BC), in part, through the alternative splicing of self-renewal and survival genes. To elucidate splice-isoform regulators of human BC LSC maintenance, we performed whole-transcriptome RNA sequencing, splice-isoform-specific quantitative RT-PCR (qRT-PCR), nanoproteomics, stromal coculture, and BC LSC xenotransplantation analyses. Cumulatively, these studies show that the alternative splicing of multiple prosurvival BCL2 family genes promotes malignant transformation of myeloid progenitors into BC LSCS that are quiescent in the marrow niche and that contribute to therapeutic resistance.

Cytotoxic activity of gemtuzumab ozogamicin (Mylotarg) in acute myeloid leukemia correlates with the expression of protein kinase Syk.

Acute myeloid leukemia (AML) cells express the cell surface antigen CD33 that, upon ligation with a monoclonal antibody (mAb), is a downregulator of cell growth in a Syk-dependent manner. An anti-CD33 mAb coupled to a toxin, gemtuzumab ozogamicin (GO), is used for the treatment of AML (Mylotarg). Therefore, we investigated whether the response of AML cells to GO treatment also depends on Syk expression.

Anti-CD33 monoclonal antibodies enhance the cytotoxic effects of cytosine arabinoside and idarubicin on acute myeloid leukemia cells through similarities in their signaling pathways.

Objective: Chemotherapy agents (CA) such as cytosine arabinoside (ara-C), idarubicin (IDA), and etoposide (VP-16) are widely used in the treatment of acute myeloid leukemia (AML) However, their effects on signaling pathways leading to cytotoxicity have only been described recently. Ligation of the leukemia-associated antigen CD33 by anti-CD33 monoclonal antibody (mAb) also results in signaling events that induce a downregulation of cell growth. We examined the possibility that anti-CD33 mAb and CA might cooperate in mediation of growth inhibition in primary AML samples and AML cell lines.

Inhibition of acute myeloid leukemia cell growth by mono-specific and bi-specific anti-CD33 x anti-CD64 antibodies.

Bi-specific anti-CD33 x anti-CD64 antibodies (BsAb) mediated more potent and longer-lasting inhibition of proliferation of human leukemia cell lines and primary acute myeloid leukemia (AML) samples compared to mono-specific anti-CD33 mAb. There were no differences between these two antibodies in cellular internalization over time. The inhibitory effect of BsAb was mimicked by a mouse IgG2a subclass mono-specific anti-CD33 mAb.

The inhibitory effect of anti-CD33 monoclonal antibodies on AML cell growth correlates with Syk and/or ZAP-70 expression.

Objectives: Acute myeloid leukemia (AML) cells express the cell surface antigen CD33 that can function as a downregulator of cell growth, mediating growth arrest and apoptosis. The protein kinase Syk is an essential element in several cascades coupling certain antigen receptors to cell responses. Recently we reported that CD33 recruits Syk for its signaling in AML cell lines.

Direct effect of bispecific anti-CD33 x anti-CD64 antibody on proliferation and signaling in myeloid cells.

Bispecific anti-CD33 x anti-CD64 antibody (BsAb) directly inhibited proliferation and colony formation of human acute myeloid leukemia cell lines, without affecting the function of normal monocytes. Addition of BsAb to normal monocytes induced tyrosine phosphorylation of Cbl and Vav, association of these molecules with CD33, and downstream signaling. In leukemia cells that were insensitive to BsAb treatment, Vav and Cbl were constitutively phosphorylated and, therefore, constitutively associated with CD33.

The human neural cell adhesion molecule L1 functions as a costimulatory molecule in T cell activation.

L1 is a neural cell adhesion molecule (CAM) known to be important for normal neurological development. Despite being described as a neural CAM, we have documented L1 expression by antigen-presenting cells of myelomonocytic origin. Here we demonstrate that L1 can function as a costimulatory molecule in T cell activation.

[Human oncogene expression in the normal state and in various blood system diseases].

A study was made of the expression of the cellular oncogens c--myc, c--sis and c--abl in mononuclears from normal donors and patients with different patterns of leukemia and hemopoietic dysplasia using spot hybridization on nitrocellulose filters with virus homologs of the given oncogens. Altogether 43 persons were examined. No specific expression of the oncogens indicated was established whatever the pattern of leukemia.

[Therapy of patients with myeloid leukemia with small doses of cytosine arabinoside].

A total of 45 patients were given cytosar and daunorubicin therapy at small doses. Of them 23 patients were with acute nonlymphoblastic leukemia, 12--with hemopoietic dysplasia, and 10--with chronic myeloid leukemia. Cytosar was injected subcutaneously every 12 h at a dose of 10 mg/m2 for 10-25 days, daunorubicin was injected intravenously by drop infusion at a dose of 5 mg/m2.