Leukemic Growth Research Articles

Loss of AID exacerbates the malignant progression of CLL

Activation-induced cytidine deaminase (AID) has been implicated as both a positive and a negative factor in the progression of B cell chronic lymphocytic leukemia (CLL), but the role that it plays in the development and progression of this disease is still unclear. We generated an AID knockout CLL mouse model, AID−/−/Eμ-TCL1, and found that these mice die significantly earlier than their AID-proficient counterparts. AID-deficient CLL cells exhibit a higher ER stress response compared to Eμ-TCL1 controls, particularly through activation of the IRE1/XBP1s pathway. The increased production of secretory IgM in AID-deficient CLL cells contributes to their elevated expression levels of XBP1s, while secretory IgM-deficient CLL cells express less XBP1s. This increase in XBP1s in turn leads AID-deficient CLL cells to exhibit higher levels of B cell receptor signaling, supporting leukemic growth and survival. Further, AID−/−/Eμ-TCL1 CLL cells downregulate the tumor suppressive SMAD1/S1PR2 pathway and have altered homing to non-lymphoid organs. Notably, CLL cells from patients with IgHV-unmutated disease express higher levels of XBP1s mRNA compared to those from patients with IgHV-mutated CLL. Our studies thus reveal novel mechanisms by which the loss of AID leads to worsened CLL and may explain why unmutated CLL is more aggressive than mutated CLL.

Genetically diverse mouse platform to xenograft cancer cells.

ABSTRACTThe lack of genetically diverse preclinical animal models in basic biology and efficacy testing has been cited as a potential cause of failure in clinical trials. We developed and characterized five diverse RAG1 null mouse strains as models that allow xenografts to grow. In these strains, we characterized the growth of breast cancer, leukemia and glioma cell lines. We found a wide range of growth characteristics that were far more dependent on strain than tumor type. For the breast cancer cell line, we characterized the spectrum of xenograft/tumor growth at structural, histological, cellular and molecular levels across each strain, and found that each strain captures unique structural components of the stroma. Furthermore, we showed that the increase in tumor-infiltrating myeloid CD45+ cells and the amount of circulating cytokine IL-6 and chemokine KC (also known as CXCL1) is associated with a higher tumor size in different strains. This resource is available to study established human xenografts, as well as difficult-to-xenograft tumors and growth of hematopoietic stems cells, and to decipher the role of myeloid cells in the development of spontaneous cancers.

Signal peptide-CUB-EGF-like repeat-containing protein 1-promoted FLT3 signaling is critical for the initiation and maintenance of MLL-rearranged acute leukemia.

A hallmark of mixed lineage leukemia gene-rearranged (MLL-r) acute myeloid leukemia that offers an opportunity for targeted therapy is addiction to protein tyrosine kinase signaling. One such signal is the receptor tyrosine kinase Fms-like receptor tyrosine kinase 3 (FLT3) upregulated by cooperation of the transcription factors homeobox A9 (HOXA9) and Meis homeobox 1 (MEIS1). Signal peptide-CUB-EGF-like repeat-containing protein (SCUBE) family proteins have previously been shown to act as a co-receptor for augmenting signaling activity of a receptor tyrosine kinase (e.g., vascular endothelial growth factor receptor). However, whether SCUBE1 is involved in the pathological activation of FLT3 during MLL-r leukemogenesis remains unknown. Here we first show that SCUBE1 is a direct target of HOXA9/MEIS1 that is highly expressed on the MLL-r cell surface and predicts poor prognosis in de novo acute myeloid leukemia. We further demonstrate, by using a conditional knockout mouse model, that Scube1 is required for both the initiation and maintenance of MLL-AF9-induced leukemogenesis in vivo. Further proteomic, molecular and biochemical analyses revealed that the membrane-tethered SCUBE1 binds to the FLT3 ligand and the extracellular ligand-binding domains of FLT3, thus facilitating activation of the signal axis FLT3-LYN (a non-receptor tyrosine kinase) to initiate leukemic growth and survival signals. Importantly, targeting surface SCUBE1 by an anti-SCUBE1 monomethyl auristatin E antibody-drug conjugate led to significantly decreased cell viability specifically in MLL-r leukemia. Our study indicates a novel function of SCUBE1 in leukemia and unravels the molecular mechanism of SCUBE1 in MLL-r acute myeloid leukemia. Thus, SCUBE1 is a potential therapeutic target for treating leukemia caused by MLL rearrangements.

A truncated derivative of FGFR1 kinase cooperates with FLT3 and KIT to transform hematopoietic stem cells in syndromic and de novo AML

BackgroundMyeloid and lymphoid malignancies associated with chimeric FGFR1 kinases are the hallmark of stem cell leukemia and lymphoma syndrome (SCLL). In all cases, FGFR1 kinase is constitutively phosphoactivated as a result of chromosome translocations, which lead to acquisition of dimerization motifs in the chimeric proteins. Recently, we demonstrated that these chimeric kinases could be cleaved by granzyme B to generate a truncated derivative, tnFGFR1, which localized exclusively into the nucleus and was not phosphorylated.MethodsStem cell transduction and transplantation in syngeneic mice was used to assess the transforming ability of tnFGFR1 in bone marrow stem cells, and RPPA and RNA-Seq was used to examine the related signaling pathways and regulated target genes.ResultsFor the first time, we show that this non-classical truncated form of FGFR1 can independently lead to oncogenic transformation of hematopoietic stem cells in an animal model in vivo. These leukemia cells show a mixed immunophenotype with a B-cell B220 + Igm- profile in the majority of cells and Kit+ in virtually all cells, suggesting a stem cell disease. tnFGFR1, however, does not activate classic FGFR1 downstream signaling pathways but induces a distinct profile of altered gene expression with significant upregulation of transmembrane signaling receptors including FLT3 and KIT. We further show that de novo human AML also express tnFGFR1 which correlates with upregulation of FLT3 and KIT as in mouse leukemia cells. ChIP analysis demonstrates tnFGFR1 occupancy at the Flt3 and Kit promoters, suggesting a direct transcriptional regulation. Cells transformed with tnFGFR1 are insensitive to FGFR1 inhibitors but treatment of these cells with the Quizartinib (AC220) FLT3 inhibitor, suppresses in vitro growth and development of leukemia in vivo. Combined treatment with FGFR1 and FLT3 inhibitors provides increased survival compared to FGFR1 inhibition alone.ConclusionsThis study demonstrates a novel model for transformation of hematopoietic stem cells by chimeric FGFR1 kinases with the combined effects of direct protein activation by the full-length kinases and transcriptional regulation by the truncated nuclear tnFGFR1 derivative, which is associated with GZMB expression levels. Genes significantly upregulated by tnFGFR1 include Flt3 and Kit which promote a leukemia stem cell phenotype. In human AML, tnFGFR1 activation leads to increased FLT3 and KIT expression, and higher FLT3 and GZMB expression levels are associated with an inferior prognosis. These observations provide insights into the relative therapeutic value of targeting FGFR1 and FLT3 in treating AML with this characteristic gene expression profile.

In vivo genome-wide CRISPR screening in murine acute myeloid leukemia uncovers microenvironmental dependencies

AbstractGenome-wide CRISPR screens have been extremely useful in identifying therapeutic targets in diverse cancers by defining genes that are essential for malignant growth. However, most CRISPR screens were performed in vitro and thus cannot identify genes that are essential for interactions with the microenvironment in vivo. Here, we report genome-wide CRISPR screens in 2 in vivo murine models of acute myeloid leukemia (AML) driven by the KMT2A/MLLT3 fusion or by the constitutive coexpression of Hoxa9 and Meis1. Secondary validation using a focused library identified 72 genes specifically essential for leukemic growth in vivo, including components of the major histocompatibility complex class I complex, Cd47, complement receptor Cr1l, and the β-4-galactosylation pathway. Importantly, several of these in vivo–specific hits have a prognostic effect or are inferred to be master regulators of protein activity in human AML cases. For instance, we identified Fermt3, a master regulator of integrin signaling, as having in vivo–specific dependency with high prognostic relevance. Overall, we show an experimental and computational pipeline for genome-wide functional screens in vivo in AML and provide a genome-wide resource of essential drivers of leukemic growth in vivo.

Combination regimen of granulocyte colony-stimulating factor and recombinant human thrombopoietin improves the curative effect on elderly patients with leukemia through inducing pyroptosis and ferroptosis of leukemia cells

Leukemia ranks as the one of most common causes of death from tumor. 51.4% of patients with leukemia are over 65 years old. However, the median overall survival (OS) of elderly leukemia patients is less than one year. It is urgent to explore more effective treatments for elderly patients with leukemia. Our recent prospective phase II single-arm study has revealed that combination regimen of granulocyte colony-stimulating factor (G-CSF) and recombinant human thrombopoietin (rhTPO) could improve the curative effect on elderly patients with leukemia, yet the precise mechanism remains unknown. This study demonstrated that combination of G-CSF and rhTPO showed greater effect on suppressing leukemia growth than G-CSF or rhTPO alone in vitro and in vivo. Mechanistically, G-CSF induced pyroptosis through ELANE in leukemia cells. Besides, rhTPO triggered ferroptosis by EP300 in leukemia cells. Moreover, rhTPO suppressed glutathione peroxidase 4 (GPX4) expression to induce ferroptosis through blocking the interaction between EP300 and GPX4 gene promoter via associating with EP300. In summary, this study illuminated that combination regimen of G-CSF and rhTPO improved the curative effect on elderly patients with leukemia through inducing pyroptosis and ferroptosis of leukemia cells. Therefore, our results provided a theoretical basis for combination regimen of G-CSF and rhTPO treating leukemia and potential therapeutic targets for leukemia.

Hydroxycitric Acid Inhibits Chronic Myelogenous Leukemia Growth through Activation of AMPK and mTOR Pathway.

Metabolic regulation of cancer cell growth via AMP-activated protein kinase (AMPK) activation is a widely studied strategy for cancer treatment, including leukemias. Recent notions that naturally occurring compounds might have AMPK activity led to the search for nutraceuticals with potential AMPK-stimulating activity. We found that hydroxycitric acid (HCA), a natural, safe bioactive from the plant Garcinia gummi-gutta (cambogia), has potent AMPK activity in chronic myelogenous leukemia (CML) cell line K562. HCA is a known competitive inhibitor of ATP citrate lyase (ACLY) and is widely used as a weight loss inducer. We found that HCA was able to inhibit the growth of K562 cells in in vitro and in vivo xenograft models. At the mechanistic level, we identified a direct interaction between AMPK and ACLY that seems to be sensitive to HCA treatment. Additionally, HCA treatment resulted in the co-activation of AMPK and the mammalian target of rapamycin (mTOR) pathways. Moreover, we found an enhanced unfolded protein response as observed by activation of the eIF2α/ATF4 pathway that could explain the induction of cell cycle arrest at the G2/M phase and DNA fragmentation upon HCA treatment in K562 cells. Overall, these findings suggest HCA as a nutraceutical approach for the treatment of CMLs.

S252: M2-POLARIZED MACROPHAGES CONTROL LEUKEMIC STEM CELL FATE BY PROMOTING METABOLIC REPROGRAMMING

Background: Being a crucial part of the tumor microenvironment (TME) in solid tumors, tumor-associated macrophages are often associated with poor prognosis (Bruni et al. Nat Rev Cancer 2020). Yet, in acute myeloid leukemia (AML) the role of macrophages remains unclear. Aims: Here, we evaluated the impact of M2 macrophages in AML using a patient derived xenograft (PDX) model. Methods: To do so, we first injected 1x105 peripheral blood (PB) derived M2 macrophages into NSGS mice and next transplanted notoriously difficult to engraft primary Acute Promyelocytic Leukemia (APL) cells (1 x 106 cells - n=7 different patient samples) via the retro-orbital vein. Results: As a result, mice with co-injected human M2-macrophages developed full-blown leukemia with increased spleen weight in comparison with the control. Perhaps even more strikingly, ex vivo culture of APL and other favorable AML subtypes such as inv (16) or NPM1 mutant leukemic cells on M2-macrophages for 48h was sufficient to “train” these cells to engraft and induce fatal leukemia. Maintenance of self-renewal was shown in a secondary transplant assay and an enhanced frequency of leukemic stem cells was assessed by in vivo LTC-IC assays (LSC frequency: Control: 1/6x106 cells vs M2 pre-culture: 1/7.2x104 cells). To better understand the biological changes induced on leukemic blast when exposed to M2 macrophages, we performed an RNA sequencing analysis comparing AML/APL samples at diagnosis to cells that were “trained” (48h) on M2-macrophages or on MS5 mesenchymal bone marrow stromal cells, as a control. Gene ontology and gene set enrichment analysis on the genes up regulated upon M2 co-culture were significantly enriched for oxidative phosphorylation (OxPhos) signatures. Evaluation of functional respiration using seahorse measurements, confirmed the increase of oxygen consumption rate (OCR, basal and maximum) in primary AML/APL cells (n=7) after exposure to M2 macrophages compared to MS5. The increase of basal and maximum OCR suggested enhanced mitochondrial metabolism, which prompted us to determine whether macrophages, similar to MSC cells, can transfer mitochondria to primary AML cells (van der Vlist et al. Neuron 2022). Flow cytometry analysis revealed an efficient mitochondrial transfer from M2 macrophages to leukemic blasts, which was more efficient compared to mitochondrial exchange from MS5 cells. Treatment with the CPT1A inhibitor Etomoxir (50 µM), prevented the gain in functional respiration and enhanced proliferation of AML cells when those were co-cultured on M2-macrophages, while no changes were observed for MS5 co-cultures. These results suggest increased fatty acid oxidation to drive the OXPHO-like state in AML. Summary/Conclusion: Overall, we revealed that M2 macrophages can support leukemic growth of favorable AML subtypes that are commonly difficult to engraft in PDX models. Even an in vitro exposure to M2 macrophages suffices to alter the biology of AML cells transforming a non-engraftable cell into a cell with high leukemic potential. In vitro we show that AML blast cells cultured on M2 macrophage adapt a more OxPhos-like state linked to intrinsic changes associated with increased uptake of mitochondria. In summary, our study uncovers how the TME can contribute to leukemic transformation which provides alternative avenues for therapeutic interventions.

S109: ONCOGENIC DEUBIQUITINATION CONTROLS TYROSINE KINASE SIGNALING AND THERAPY RESPONSE IN ACUTE LYMPHOBLASTIC LEUKEMIA

Background: Dysregulation of kinase signaling pathways via mutations favors tumor cell survival and resistance to therapy and it is common in cancer. Our data unveil how dysregulated deubiquitination controls signaling pathways, leading to cancer cell survival and drug non-response, and suggest novel therapeutic combinations towards targeting T-cell acute lymphoblastic leukemia (T-ALL). Here, we reveal a novel mechanism of post-translational regulation of kinase signaling and nuclear receptor activity via deubiquitination in acute leukemia. Aims: This study aims at 1) characterizing the function of an oncogenic complex composed by two deubiquitinating enzymes in in vitro and in vivo leukemia systems and 2) testing the association of deubiquitinase activity with resistance to therapy in acute lymphoblastic leukemia. Methods: We use genetic mouse and human:mouse xenograft models of T-cell leukemia, biochemical studies (quantitative global proteomics, phosphoproteomics and ubiquitination analysis) and high-throughput molecular biology (chromatin conformation capture (HiC), chromatin accessibility (ATAC-Seq) and gene expression (RNA-Seq)) analyses. Results: We observed that the ubiquitin specific protease 11 (USP11) is highly expressed in lymphoblastic leukemia and associates with poor prognosis in this disease. USP11 ablation inhibits leukemia growth in vitro and in vivo, sparing normal hematopoiesis and thymus development, suggesting that USP11 could be a therapeutic target in leukemia. USP11 forms a complex with USP7 to deubiquitinate the oncogenic lymphocyte cell-specific protein-tyrosine kinase (LCK). Deubiquitination of LCK controls its activity, thereby altering T cell receptor signaling. Impairment of LCK activity leads to increased expression of the glucocorticoid receptor transcript, culminating into transcriptional activation of pro-apoptotic target genes, and sensitizes cells to glucocorticoids in T cell leukemia patient samples. The transcriptional activation of pro-apoptotic target genes, such as BCL2L11, is orchestrated by the deubiquitinase activity and mediated via an increase in enhancer-promoter interaction intensity. Pharmacological inhibition of USP7 or genetic knockout of USP7 in combination treatment of glucocorticoid displayed improved anti-T-ALL efficacy in vivo. Image:Summary/Conclusion: Our data unveil how dysregulated deubiquitination controls signaling pathways, leading to cancer cell survival and drug non-response, and suggest novel therapeutic combinations towards targeting T-cell leukemia.

Abstract 1555: circPVT1 and linear PVT1 isoforms regulate cell growth, metabolic and DNA damage response related gene signatures in acute myeloid leukemia

Abstract Non-coding (nc)RNAs, including circular (circ)RNAs, contribute to tumor development and progression. Several ncRNAs were shown to affect the onset, prognosis, and treatment of acute myeloid leukemia (AML) in the past years. The human Plasmacytoma Variant Translocation 1 (PVT1) gene maps on the long arm of chromosome 8 (8q24), in the same genomic region hosting MYC and encoding for 83 linear (PVT1, lncipedia.org) and 26 high-confidence circular isoforms (circPVT1, www.circbase.org). The most common isoform of circPVT1 is a product of back-splicing of 410 nt and contains the whole exon 2 of PVT1 in a closed loop-like structure (hsa_circ_0001821). The study aims to investigate the role of PVT1 isoforms and circPVT1 in AML. Firstly, we focused on the various PVT1 isoforms and their differential expression in leukemia. Fourteen out of the 83 linear isoforms are expressed in the hematopoietic tissues (lymph node and white blood cells, www.noncode.org), and 6 of them were detectable in AML cell lines, including the t(8;21) KASUMI-1 and the NPM1-mutated OCI-AML3 models, together with circPVT1. We designed two antisense-oligonucleotides (ASOs), mapping on common exonic region and targeting the linear isoforms expressed in OCI-AML3 and KASUMI-1 cells, and one ASO spanning the junction region of circPVT1. ASOs-mediated knockdown (KD) showed a relevant decrease of PVT1 signals, especially by ASO combination, and circPVT1 level using the specific ASO in both cell lines, under normoxia and hypoxia (1% O2). The downregulation led to a significant decrease in cell growth, but, interestingly, only circPVT1-KD induced apoptosis under both conditions in OCI-AML3. To further investigate the biological consequences of circPVT1-KD, we performed RNAseq assays. Data analysis was performed by pseudo alignment of paired-end reads to the human transcriptome, then counted with the Kallisto tool. Differential expression analysis of single isoforms was performed with the Sleuth tool on normalized transcript per million. We identified a core of 644 and 838 commonly regulated genes by circPVT1 in both cell lines under normoxia and hypoxia, respectively. Pathway analysis (performed by EnrichR) revealed that these genes are involved not only in the RNA regulatory pathways, as expected according to circRNA functions, but also in metabolic (e.g., KDM3A, GPI, NFKBA, RBM3, XBP1) and DNA damage response (e.g., PIDD1, MUC1, BCLAF1, BABAM2) pathways, opening a new scenario for synthetic lethality approaches. In conclusion, our findings show that silencing of circPVT1 or the predominantly expressed PVT1 isoforms dampens leukemia cell growth, indicating a role in AML pathogenesis, and suggest that targeting them may have therapeutic potentials in AML. Citation Format: Martina Ghetti, Antonella Padella, Eugenio Fonzi, Lorenzo Ledda, Andrea Ghelli Lusernadi Rorà, Matteo Paganelli, Doron Tolomeo, Clelia Tiziana Storlazzi, Giovanni Martinelli, Giorgia Simonetti. circPVT1 and linear PVT1 isoforms regulate cell growth, metabolic and DNA damage response related gene signatures in acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1555.

Abstract 3737: DNA-methylation is tightly linked with super-enhancer marks to upregulate ERG in ETO2-GLIS2 positive leukemia

Abstract Infants and young children (> 3 yrs.) harboring ETO2-GLIS2 have the worst outcomes amongst all pediatric acute myeloid leukemia (AML) subtypes, with poor responses to induction therapy, high incidence of relapse, and dismal 5-year survival rates. Previous studies demonstrated that the ETO2-GLIS2 fusion leads to imbalance in the expression of ETS-related transcription factor ERG and GATA1 with neo-super enhancer (SE) activities in a single oncogenic hit (Thirant et al. 2017). ERG was found to co-localize with ETO2-GLIS2 fusion at 90% (372/419) of H3K27ac marked SE-regions and was strongly upregulated (9.44-fold). Herein, we aimed to investigate cooperativity of DNA methylation and chromatin marks on ERG overexpression in this AML subtype. We analyzed transcriptomic data from pediatric ETO2-GLIS2 AML patients (n=40) from dbGAP (phs000465.v19. p8) in comparison to normal bone marrow (NBM) (n=71) samples, confirming upregulation (median log FC: 2.4-fold) in ERG expression in the ETO2-GLIS2 subgroup compared to NBM. Next, we performed an unbiased genome-wide methylation array using Infinium MethylationEPIC 850K-arrays (Illumina). Differences in mean methylation (β-value) at individual CpG sites between NBM and AML samples were considered significant at differences greater than ±10%. We observed reduced methylation at 72% (5/7) CpGs at the ERG-promoter (1500bp upstream of transcription start site) in ETO2-GLIS2 subgroup compared to NBM. Overall median methylation across the promoter was reduced by 12% in the AML subgroup. In comparison, 22 differentially methylated CpGs were observed in the body, of which methylation increased at 68% (15/22) of the CpGs, with median methylation similarly increased by 15% in the AML patients. This represents a classic example of methylation-expression relation, having a promoter demethylation and body-hypermethylation, linked to upregulation of the gene-expression. Next, we investigated the overlaps between CpGs and the distribution of DNAse clusters and H3K27ac marks based on ENCODE data on myeloid leukemia cell line K562. We observed frequent overlaps between demethylated CpGs and DNAse clusters, while H3K27ac broad peaks were coincident with both demethylated CpGs at promoter or hypermethylated CpGs at body. Based on our findings, we thus conclude that DNA-methylation both at the ERG promoter and body is tightly linked to the overlapping chromatin marks of the gene. DNA-methylation might aid in opening of adjacent chromatin on ERG to possibly facilitate SE enrichment and over-expression the gene. Future studies will investigate targeted alterations of DNA-methylation on the gene to test the impact on ERG expression and leukemic growth. Citation Format: Samrat Roy Choudhury, Jordan T. Bird, Stephanie Byrum, Jason E. Farrar. DNA-methylation is tightly linked with super-enhancer marks to upregulate ERG in ETO2-GLIS2 positive leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3737.

Abstract 5837: A truncated nucleus-located derivative of FGFR1 contributes to the transformation of leukemia stem cell in leukemogenesis driven by FGFR1 fusion kinases

Abstract Myeloid and lymphoid malignancies associated with chimeric FGFR1 kinases are the hallmark of stem cell leukemia and lymphoma syndrome (SCLL). In all cases, FGFR1 kinase is constitutively phosphoactivated as a result of chromosome translocations, which lead to acquisition of dimerization motifs in the chimeric proteins. Recently, we demonstrated that these chimeric kinases could be cleaved by granzyme B to generate a truncated derivative, tnFGFR1, which localized exclusively into the nucleus and was not phosphorylated. Stem cell transduction and transplantation in syngeneic mice were used to assess the transforming ability of tnFGFR1 in bone marrow stem cells, and the results showed that tnFGFR1 can independently lead to oncogenic transformation of hematopoietic stem cells. These leukemia cells show a mixed immunophenotype with a B-cell B220+Igm- profile in the majority of cells and Kit+ in virtually all cells, suggesting a stem cell disease. RPPA and RNA-Seq examination of the related signaling pathways and target genes revealed that tnFGFR1, however, does not activate classic FGFR1 downstream signaling pathways but induces a distinct profile of altered gene expression with significant upregulation of transmembrane signaling receptors including FLT3 and KIT. De novo human AML also expressed tnFGFR1 which correlates with upregulation of FLT3 and KIT as in mouse leukemia cells. ChIP analysis demonstrates tnFGFR1 occupancy at the Flt3 and Kit promoters, suggesting a direct transcriptional regulation. Cells transformed with tnFGFR1 are insensitive to FGFR1 inhibitors but treatment of these cells with the Quizartinib (AC220) FLT3 inhibitor, suppresses in vitro growth and development of leukemia in vivo suggesting an alternative approach for treatment of SCLL. This study demonstrates a novel model for transformation of hematopoietic stem cells by chimeric FGFR1 kinases results with the combined effects of direct protein activation by the full-length kinases and gene regulation by the truncated nucleus derivative tnFGFR1, which is associated with GZMB expression levels. Genes significantly upregulated by tnFGFR1 include Flt3 and Kit which promote a leukemia stem cell phenotype. In human AML, tnFGFR1 activation leads to increased FLT3 and KIT expression, and higher FLT3 and GZMB expression levels are associated with inferior prognosis. These observations provide insights into the relative therapeutic value of targeting FGFR1 and FLT3 in treating AML with this characteristic gene expression profile. Citation Format: Baohuan Cai, Yun Liu, Yating Chong, Hualei Zhang, Stephanie Mori, Atsuko Matsunaga, Xuexiu Fang, John Cowell, Tianxiang Hu. A truncated nucleus-located derivative of FGFR1 contributes to the transformation of leukemia stem cell in leukemogenesis driven by FGFR1 fusion kinases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5837.

Synthesis of 2-Oxoquinoline Derivatives as Dual Pim and mTORC Protein Kinase Inhibitors.

Compound VBT-5445 was identified as an inhibitor to block the association of Pim and the protein Enhancer of Decapping 3 (EDC3), a Pim substrate, which normally functions to enhance the decapping of messenger RNA (mRNA). It was also shown to inhibit both the Pim and mTORC protein kinases. The activity of this compound class can be fine-tuned by structural modification. A series of VBT analogs were designed, synthesized, and evaluated. These compounds decrease the growth of multiple cancer types, including pancreas, prostate, breast, lung, and leukemia. Notably, 6-methyl (GRG-1-31, 6d), 4-Bromo (GRG-1-34, 6e), 4-Chloro (GRG-1-35, 6f), and phenylthio substituted (GRG-1-104, 6n) derivatives are highly potent at inhibiting tumor growth. The ability of these compounds to block cancer growth in vitro is highly correlated with their activity as mTORC inhibitors. The toxicity of GRG 1-34 is low in mice treated with twice-daily gavage for 30 days and did not induce weight loss. Pharmacokinetics of a single oral dose demonstrated a peak concentration at 0.5 hours after gavage. In summary, further development of this compound class has the potential to inhibit important signaling pathways and impact cancer treatment.

Therapeutic targeting of LCK tyrosine kinase and mTOR signaling in T-cell acute lymphoblastic leukemia

AbstractRelapse and refractory T-cell acute lymphoblastic leukemia (T-ALL) has a poor prognosis, and new combination therapies are sorely needed. Here, we used an ex vivo high-throughput screening platform to identify drug combinations that kill zebrafish T-ALL and then validated top drug combinations for preclinical efficacy in human disease. This work uncovered potent drug synergies between AKT/mTORC1 (mammalian target of rapamycin complex 1) inhibitors and the general tyrosine kinase inhibitor dasatinib. Importantly, these same drug combinations effectively killed a subset of relapse and dexamethasone-resistant zebrafish T-ALL. Clinical trials are currently underway using the combination of mTORC1 inhibitor temsirolimus and dasatinib in other pediatric cancer indications, leading us to prioritize this therapy for preclinical testing. This combination effectively curbed T-ALL growth in human cell lines and primary human T-ALL and was well tolerated and effective in suppressing leukemia growth in patient-derived xenografts (PDX) grown in mice. Mechanistically, dasatinib inhibited phosphorylation and activation of the lymphocyte-specific protein tyrosine kinase (LCK) to blunt the T-cell receptor (TCR) signaling pathway, and when complexed with mTORC1 inhibition, induced potent T-ALL cell killing through reducing MCL-1 protein expression. In total, our work uncovered unexpected roles for the LCK kinase and its regulation of downstream TCR signaling in suppressing apoptosis and driving continued leukemia growth. Analysis of a wide array of primary human T-ALLs and PDXs grown in mice suggest that combination of temsirolimus and dasatinib treatment will be efficacious for a large fraction of human T-ALLs.

Apoptosis inhibition in T-cell acute lymphoblastic leukemia by UNC13B

T-cell acute lymphoblastic leukemia is a type of leukemia that is difficult to treat and has a complex pathogenesis, with no effective treatment currently available. This research group found that the mRNA expression of a new gene, UNC13B, was increased in T-cell acute lymphoblastic leukemia patients. Subsequently, we used T-cell acute lymphoblastic leukemia Jurkat cells to study the mechanism of UNC13B. We constructed a lentiviral vector expressing siRNA to target UNC13B and transfected it into the T-cell acute lymphoblastic leukemia Jurkat cell line. Using CCK-8, flow cytometry, and western blotting analyses, we found that knockdown of UNC13B inhibited the growth of T-cell acute lymphoblastic leukemia Jurkat cells via the downregulation of signaling proteins of the cell proliferation pathway and upregulation of apoptosis signaling proteins. Based on the bioinformatics analysis results, we found that the mechanism of UNC13B responsible for promoting the growth of T-cell acute lymphoblastic leukemia can be experimentally achieved by triggering AK2, MAP3K7, and PINK1. This study demonstrates that UNC13B is a new potential target for T-cell acute lymphoblastic leukemia.

Epigenetic downregulation of Socs2 contributes to mutant N-Ras-mediated hematopoietic dysregulation.

ABSTRACTRAS mutations occur in a broad spectrum of human hematopoietic malignancies. Activating Ras mutations in blood cells leads to hematopoietic malignancies in mice. In murine hematopoietic stem cells (HSCs), mutant N-RasG12D activates Stat5 to dysregulate stem cell function. However, the underlying mechanism remains elusive. In this study, we demonstrate that Stat5 activation induced by a hyperactive Nras mutant, G12D, is dependent on Jak2 activity. Jak2 is activated in Nras mutant HSCs and progenitors (HSPCs), and inhibiting Jak2 with ruxolitinib significantly decreases Stat5 activation and HSPC hyper-proliferation in vivo in NrasG12D mice. Activation of Jak2-Stat5 is associated with downregulation of Socs2, an inhibitory effector of Jak2/Stat5. Restoration of Socs2 blocks NrasG12D HSC reconstitution in bone marrow transplant recipients. SOCS2 downregulation is also observed in human acute myeloid leukemia (AML) cells that carry RAS mutations. RAS mutant AML cells exhibited suppression of the enhancer active marker H3K27ac at the SOCS2 locus. Finally, restoration of SOCS2 in RAS mutant AML cells mitigated leukemic growth. Thus, we discovered a novel signaling feedback loop whereby hyperactive Ras signaling activates Jak2/Stat5 via suppression of Socs2.

MicroRNA networks in FLT3-ITD acute myeloid leukemia

MiR-126 and miR-155 are key microRNAs (miRNAs) that regulate, respectively, hematopoietic cell quiescence and proliferation. Herein we showed that in acute myeloid leukemia (AML), the biogenesis of these two miRNAs is interconnected through a network of regulatory loops driven by the FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD). In fact, FLT3-ITD induces the expression of miR-155 through a noncanonical mechanism of miRNA biogenesis that implicates cytoplasmic Drosha ribonuclease III (DROSHA). In turn, miR-155 down-regulates SH2-containing inositol phosphatase 1 (SHIP1), thereby increasing phosphor-protein kinase B (AKT) that in turn serine-phosphorylates, stabilizes, and activates Sprouty related EVH1 domain containing 1 (SPRED1). Activated SPRED1 inhibits the RAN/XPO5 complex and blocks the nucleus-to-cytoplasm transport of pre-miR-126, which cannot then complete the last steps of biogenesis. The net result is aberrantly low levels of mature miR-126 that allow quiescent leukemia blasts to be recruited into the cell cycle and proliferate. Thus, miR-126 down-regulation in proliferating AML blasts is downstream of FLT3-ITD–dependent miR-155 expression that initiates a complex circuit of concatenated regulatory feedback (i.e., miR-126/SPRED1, miR-155/human dead-box protein 3 [DDX3X]) and feed-forward (i.e., miR-155/SHIP1/AKT/miR-126) regulatory loops that eventually converge into an output signal for leukemic growth.

Gab2 promotes acute myeloid leukemia growth and migration through the SHP2-Erk-CREB signaling pathway.

Acute myeloid leukemia (AML) is a hematologic malignant disease largely affecting older adults with poor outcomes. Lack of effective targeted treatment is a major challenge in managing the disease in the clinic. Scaffolding adaptor Gab2 is amplified in a subset of AML. However, the causative role of Gab2 in AML remains to be explored. In this study, it was found that Gab2 was expressed at high levels in AML patient samples and AML cell lines. Experiments by knocking down Gab2 expression using shRNA showed that Gab2 promoted AML cell growth and migration in vitro and in vivo. Further studies using Gab2 mutants and pharmacological inhibitors revealed that Gab2 increased CREB phosphorylation via the SHP-2/Erk signaling pathway. CREB phosphorylation contributed to Gab2-induced cell migration by increasing MMP2 and MMP9 expression. This research indicates that high Gab2 expression promotes AML progression through the SHP2-Erk-CREB signaling pathway. CREB suppression may help treat AML with high Gab2 expression.

Acute Myeloid Leukemia Cells Educate Mesenchymal Stromal Cells toward an Adipogenic Differentiation Propensity with Leukemia Promotion Capabilities.

Mesenchymal stromal cells (MSCs) are essential elements of the bone marrow (BM) microenvironment, which have been widely implicated in pathways that contribute to leukemia growth and resistance. Recent reports showed genotypic and phenotypic alterations in leukemia patient‐derived MSCs, indicating that MSCs might be educated/reprogrammed. However, the results have been inconclusive, possibly due to the heterogeneity of leukemia. Here, the authors report that acute myeloid leukemia (AML) induces MSCs towards an adipogenic differentiation propensity. RNAseq analysis reveal significant upregulation of gene expression enriched in the adipocyte differentiation process and reduction in osteoblast differentiation. The alteration is accompanied by a metabolic switch from glycolysis to a more oxidative phosphorylation‐dependent manner. Mechanistic studies identify that AML cell‐derived exosomes play a vital role during the AML cell‐mediated MSCs education/reprogramming process. Pre‐administration of mice BM microenvironment with AML‐derived exosomes greatly enhance leukemia engraftment in vivo. The quantitative proteomic analysis identified a list of exosomal protein components that are differently expressed in AML‐derived exosomes, which represent an opportunity for novel therapeutic strategies based on the targeting of exosome‐based AML cells‐MSCs communication. Collectively, the data show that AML‐educated MSCs tend to differentiate into adipocytes contributing to disease progression, which suggests complex interactions of leukemia with microenvironment components.

Synergy of Venetoclax and 8-Chloro-Adenosine in AML: The Interplay of rRNA Inhibition and Fatty Acid Metabolism.

Simple SummaryTreatment failures of acute myeloid leukemia (AML) have been attributed to the persistence of leukemia stem cells (LSCs), which are refractory to conventional treatments. Venetoclax (VEN), currently FDA-approved in combination with low-dose cytarabine or hypomethylating agents, is highly effective in inducing disease remission in patients with de novo AML; however, most of these patients eventually relapse; thus, novel VEN combinations are urgently needed. In this regard, 8-chloro-adenosine (8-Cl-Ado) is a novel RNA-directed nucleoside analog that targets AML cells, including LSCs. We demonstrate that VEN and 8-Cl-Ado cooperate in targeting ribosomal RNA synthesis and mitochondrial metabolism in LSCs, thereby decreasing LSC survival. Given the emerging concept that LSC behavior is strongly associated with protein synthesis regulation and mitochondrial metabolism, our results suggest that the VEN/8-Cl-Ado combination is a promising regimen for the treatment of patients with relapsed AML.It is known that 8-chloro-adenosine (8-Cl-Ado) is a novel RNA-directed nucleoside analog that targets leukemic stem cells (LSCs). In a phase I clinical trial with 8-Cl-Ado in patients with refractory or relapsed (R/R) AML, we observed encouraging but short-lived clinical responses, likely due to intrinsic mechanisms of LSC resistance. LSC homeostasis depends on amino acid-driven and/or fatty acid oxidation (FAO)-driven oxidative phosphorylation (OXPHOS) for survival. We recently reported that 8-Cl-Ado and the BCL-2-selective inhibitor venetoclax (VEN) synergistically inhibit FAO and OXPHOS in LSCs, thereby suppressing acute myeloid leukemia (AML) growth in vitro and in vivo. Herein, we report that 8-Cl-Ado inhibits ribosomal RNA (rRNA) synthesis through the downregulation of transcription initiation factor TIF-IA that is associated with increasing levels of p53. Paradoxically, 8-Cl-Ado-induced p53 increased FAO and OXPHOS, thereby self-limiting the activity of 8-Cl-Ado on LSCs. Since VEN inhibits amino acid-driven OXPHOS, the addition of VEN significantly enhanced the activity of 8-Cl-Ado by counteracting the self-limiting effect of p53 on FAO and OXPHOS. Overall, our results indicate that VEN and 8-Cl-Ado can cooperate in targeting rRNA synthesis and OXPHOS and in decreasing the survival of the LSC-enriched cell population, suggesting the VEN/8-Cl-Ado regimen as a promising therapeutic approach for patients with R/R AML.