The presence of FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD) is one of the most frequent mutations in acute myeloid leukemia (AML) and is associated with an unfavorable prognosis. FLT3 inhibitors, such as midostaurin, are used clinically but fail to entirely eradicate FLT3-ITD + AML. This study introduces a new perspective and highlights the impact of RAC1-dependent actin cytoskeleton remodeling on resistance to midostaurin in AML. RAC1 hyperactivation leads resistance via hyperphosphorylation of the positive regulator of actin polymerization N-WASP and antiapoptotic BCL-2. RAC1/N-WASP, through ARP2/3 complex activation, increases the number of actin filaments, cell stiffness and adhesion forces to mesenchymal stromal cells (MSCs) being identified as a biomarker of resistance. Midostaurin resistance can be overcome by a combination of midostaruin, the BCL-2 inhibitor venetoclax and the RAC1 inhibitor Eht1864 in midostaurin-resistant AML cell lines and primary samples, providing the first evidence of a potential new treatment approach to eradicate FLT3-ITD + AML.

The pathogenesis of acute myeloid leukemia (AML) involves serial acquisition of mutations controlling several cellular processes, requiring combination therapies affecting key downstream survival nodes in order to treat the disease effectively. The BCL2 selective inhibitor venetoclax has potent anti-leukemia efficacy; however, resistance can occur due to its inability to inhibit MCL1, which is stabilized by the MAPK pathway. In this study, we aimed to determine the anti-leukemia efficacy of concomitant targeting of the BCL2 and MAPK pathways by venetoclax and the MEK1/2 inhibitor cobimetinib, respectively. The combination demonstrated synergy in seven of 11 AML cell lines, including those resistant to single agents, and showed growth-inhibitory activity in over 60% of primary samples from patients with diverse genetic alterations. The combination markedly impaired leukemia progenitor functions, while maintaining normal progenitors. Mass cytometry data revealed that BCL2 protein is enriched in leukemia stem/progenitor cells, primarily in venetoclax-sensitive samples, and that cobimetinib suppressed cytokine-induced pERK and pS6 signaling pathways. Through proteomic profiling studies, we identified several pathways inhibited downstream of MAPK that contribute to the synergy of the combination. In OCI-AML3 cells, the combination downregulated MCL1 protein levels and disrupted both BCL2:BIM and MCL1:BIM complexes, releasing BIM to induce cell death. RNA sequencing identified several enriched pathways, including MYC, mTORC1, and p53 in cells sensitive to the drug combination. In vivo, the venetoclax-cobimetinib combination reduced leukemia burden in xenograft models using genetically engineered OCI-AML3 and MOLM13 cells. Our data thus provide a rationale for combinatorial blockade of MEK and BCL2 pathways in AML.
Copyright© 2020 Ferrata Storti Foundation.

Long non-coding RNAs (lncRNAs) are critical for regulating HOX genes, aberration of which is a dominant mechanism for leukemic transformation. How HOX gene-associated lncRNAs regulate hematopoietic stem cell (HSC) function and contribute to leukemogenesis remains elusive. We found that HOTTIP is aberrantly activated in acute myeloid leukemia (AML) to alter HOXA-driven topologically associated domain (TAD) and gene expression. HOTTIP loss attenuates leukemogenesis of transplanted mice, while reactivation of HOTTIP restores leukemic TADs, transcription, and leukemogenesis in the CTCF-boundary-attenuated AML cells. Hottip aberration in mice abnormally promotes HSC self-renewal leading to AML-like disease by altering the homeotic/hematopoietic gene-associated chromatin signature and transcription program. Hottip aberration acts as an oncogenic event to perturb HSC function by reprogramming leukemic-associated chromatin and gene transcription.
Copyright © 2019 Elsevier Inc. All rights reserved.

Constitutively activated FLT3 signaling is common in acute myeloid leukemia, and is currently under evaluation for targeted therapy, whereas little data is available in T-cell acute lymphoblastic leukemia (T-ALL). We analyzed 357 T-ALL cases for FLT3 mutations and transcript expression. FLT3 mutations (3% overall) and overexpression (FLT3 high expresser (FLT3(High))) were restricted to immature/TCRγδ T-ALLs. In vitro FLT3 inhibition induced apoptosis in only 30% of FLT3(High) T-ALLs and did not correlate with mutational status. In order to investigate the mechanisms of primary resistance to FLT3 inhibition, a broad quantitative screen for receptor kinome transcript deregulation was performed by Taqman Low Density Array. FLT3 deregulation was associated with overexpression of a network of receptor kinases (RKs), potentially responsible for redundancies and sporadic response to specific FLT3 inhibition. In keeping with this resistance to FLT3 inhibition could be reversed by dual inhibition of FLT3 and KIT with a synergistic effect. We conclude that immature T-ALL may benefit from multitargeted RK inhibition and that exploration of the receptor kinome defines a rational strategy for testing multitarget kinase inhibition in malignant diseases.

Aging and apolipoprotein E4 (apoE4) expression are strong risk factors for the development of Alzheimer's disease (AD); however, their pathological roles remain to be clarified. In the process of AD development, the conversion of the nontoxic amyloid beta-protein (Abeta) monomer to its toxic aggregates is a fundamental process. We previously hypothesized that Abeta aggregation is accelerated through the generation of GM1 ganglioside (GM1)-bound Abeta which acts as a seed for Abeta fibril formation. Here we report that GM1 level in detergent-resistant membrane microdomains (DRMs) of synaptosomes increased with age and that this increase was significantly pronounced in the apoE4- than the apoE3-knock-in mouse brain. Furthermore, we show that Abeta aggregation is markedly accelerated in the presence of the synaptosomes of the aged apoE4-knock-in mouse brain. These observations suggest that aging and apoE4 expression cooperatively accelerate Abeta aggregation in the brain through an increase in the level of GM1 in neuronal membranes.