BCR::ABL1-independent pathways contribute to primary resistance to tyrosine kinase inhibitor (TKI) treatment in chronic myeloid leukemia (CML) and play a role in leukemic stem cell persistence. Here, we perform ex vivo drug screening of CML CD34+ leukemic stem/progenitor cells using 100 single drugs and TKI-drug combinations and identify sensitivities to Wee1, MDM2, and BCL2 inhibitors. These agents effectively inhibit primitive CD34+CD38- CML cells and demonstrate potent synergies when combined with TKIs. Flow-cytometry-based drug screening identifies mepacrine to induce differentiation of CD34+CD38- cells. We employ genome-wide CRISPR-Cas9 screening for six drugs, and mediator complex, apoptosis, and erythroid-lineage-related genes are identified as key resistance hits for TKIs, whereas the Wee1 inhibitor AZD1775 and mepacrine exhibit distinct resistance profiles. KCTD5, a consistent TKI-resistance-conferring gene, is found to mediate TKI-induced BCR::ABL1 ubiquitination. In summary, we delineate potential mechanisms for primary TKI resistance and non-BCR::ABL1-targeting drugs, offering insights for optimizing CML treatment.
Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.

Clonal hematopoiesis (CH) refers to the age-related expansion of specific clones in the blood system, and manifests from somatic mutations acquired in hematopoietic stem cells (HSCs). Most CH variants occur in the gene DNMT3A, but while DNMT3A-mutant CH becomes almost ubiquitous in aging humans, a unifying molecular mechanism to illuminate how DNMT3A-mutant HSCs outcompete their counterparts is lacking. Here, we used interferon gamma (IFNγ) as a model to study the mechanisms by which Dnmt3a mutations increase HSC fitness under hematopoietic stress. We found Dnmt3a-mutant HSCs resist IFNγ-mediated depletion, and IFNγ-signaling is required for clonal expansion of Dnmt3a-mutant HSCs in vivo. Mechanistically, DNA hypomethylation-associated overexpression of Txnip in Dnmt3a-mutant HSCs leads to p53 stabilization and upregulation of p21. This preserves the functional potential of Dnmt3a-mutant HSCs through increased quiescence and resistance to IFNγ-induced apoptosis. These data identify a previously undescribed mechanism to explain increased fitness of DNMT3A-mutant clones under hematopoietic stress.DNMT3A mutations are common variants in clonal hematopoiesis, and recurrent events in blood cancers. Yet the mechanisms by which these mutations provide hematopoietic stem cells a competitive advantage as a precursor to malignant transformation remain unclear. Here, we use inflammatory stress to uncover molecular mechanisms leading to this fitness advantage.See related commentary by De Dominici and DeGregori, p. 178. This article is highlighted in the In This Issue feature, p. 171.©2022 American Association for Cancer Research.

Myeloproliferative neoplasms (MPN) are chronic blood diseases with significant morbidity and mortality. Although sequencing studies have elucidated the genetic mutations that drive these diseases, MPNs remain largely incurable with a significant proportion of patients progressing to rapidly fatal secondary acute myeloid leukemia (sAML). Therapeutic discovery has been hampered by the inability of genetically engineered mouse models to generate key human pathologies such as bone marrow fibrosis. To circumvent these limitations, here we present a humanized animal model of myelofibrosis (MF) patient-derived xenografts (PDX). These PDXs robustly engrafted patient cells that recapitulated the patient's genetic hierarchy and pathologies such as reticulin fibrosis and propagation of MPN-initiating stem cells. The model can select for engraftment of rare leukemic subclones to identify patients with MF at risk for sAML transformation and can be used as a platform for genetic target validation and therapeutic discovery. We present a novel but generalizable model to study human MPN biology.
Although the genetic events driving MPNs are well defined, therapeutic discovery has been hampered by the inability of murine models to replicate key patient pathologies. Here, we present a PDX system to model human myelofibrosis that reproduces human pathologies and is amenable to genetic and pharmacologic manipulation. This article is highlighted in the In This Issue feature, p. 2945.
©2021 American Association for Cancer Research.

The aberrant expression of dopamine receptors (DRDs) in acute myeloid leukemia (AML) cells has encouraged the repurposing of DRD antagonists such as thioridazine (TDZ) as anti-leukemic agents. Here, we access patient cells from a Phase I dose escalation trial to resolve the cellular and molecular bases of response to TDZ, and we extend these findings to an additional independent cohort of AML patient samples tested preclinically. We reveal that in DRD2+ AML patients, DRD signaling in leukemic progenitors provides leukemia-exclusive networks of sensitivity that spare healthy hematopoiesis. AML progenitor cell suppression can be increased by the isolation of the positive enantiomer from the racemic TDZ mixture (TDZ+), and this is accompanied by reduced cardiac liability. Our study indicates that the development of DRD-directed therapies provides a targeting strategy for a subset of AML patients and potentially other cancers that acquire DRD expression upon transformation from healthy tissue.
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