Primary Chronic Myeloid Leukemia Research Articles

Abstract 187: Macrophage instead of leukemia cell expressed PD-L1 drives T cell exhaustion and immune evasion of BCRABL1 chronic myeloid leukemia

Abstract BCR-ABL1 fusion gene is the hall marker of chronic myeloid leukemia (CML). Currently, the immune microenvironment of BCRABL1 CML remains largely unexplored. Our recent investigation in a transgenic mouse model of BCRABL1 CML revealed a continuous increase in CD11b+Ly6Cint PMN-MDSC with the progression of the disease. Concurrently, there was an increase in CD11b+Ly6Chigh M-MDSC and F4/80+ macrophages. However, The levels of CD4+ T cells, CD8+ T cells, CD19+ B cells, and CD49b+ NK cells, which are essential for tumor-killing significantly decreased. This immune phenotype was consistently observed in both primary leukemia induction and following serial transplantation of cells from primary leukemic mice. Intriguingly, only recipient mice subjected to sublethal irradiation developed the disease, while mice with intact immune system remained disease-free, which underscores the vital role of the immune system in the development of CML. The predominant presence of CD11b+Ly6Cint PMN-MDSC in the peripheral blood, bone marrow and spleen implies these cells may be at least partially consisted of CML leukemia cells. To examine the hypothesis, qRT-PCR and immunofluorescence (IF) staining were conducted. In both assays, Ly6G+ cells from BCRABL1 mice coexpressed the BCRABL1 oncogene. Furthermore, when co-cultured with CD4 T cells, the division of T cells was significantly inhibited, implying immune suppression by the Ly6G+ PMN-MDSCs and/or CML leukemia cells. In addition, the immuosuppressive pathway genes including Arg1, Hif1a, Enptd1, TGFβ were significantly upregulated. To investigate the possible role of the PD1/PDL1 axis in the BCRABL1 model, flow cytometry analysis was conducted. Unexpectedly, PDL1 was barely expressed in CML leukemia cells, whereas the expression of PDL1 in M-MDSCs and macrophages significantly increased, accompanied by remarkable upregulation of PD1 expression on CD4 T cells and CD8 T cells during leukemia progression. In other words, PDL1 expression on macrophages, rather than leukemia cells, was found to induce T cell exhaustion. For translational purpose, mice transplanted with the primary CML leukemia cells were treated with chemotherapy drugs ponatinib alone or in combination with the anti-PD1 antibody. Compared with the chemotherapy alone group, the mice in the combinational therapy group exhibited rapid remission and better disease control. Most importantly, the disease relapse occurred at a slower rate after treatment discontinuation, suggesting the value of combinational therapy in achieving treatment free remission. In summary, our study not only revealed the dynamic changes of immune microenvironment in the BCRABL1 CML mouse model, but also revealed the different mechanisms underlying immune evasion of BCR-ABL1 CML leukemia cells, which sheds light on a combinational treatment for achieving the treatment free remission of CML. Citation Format: Xiaocui Lu, Hui Fang, Xuexiu Fang, Atsuko Matsunaga, Kebin Liu, Jorge Cortes, John K. Cowell, Tianxiang Hu. Macrophage instead of leukemia cell expressed PD-L1 drives T cell exhaustion and immune evasion of BCRABL1 chronic myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 187.

Immortalised chronic myeloid leukemia (CML) derived mesenchymal stromal cells (MSCs) line retains the immunomodulatory and chemoprotective properties of CML patient-derived MSCs

Despite the success of Tyrosine kinase inhibitors (TKIs) in treating chronic myeloid leukemia (CML), leukemic stem cells (LSCs) persist, contributing to relapse and resistance. CML Mesenchymal Stromal Cells (MSCs) help in LSC maintenance and protection from TKIs. However, the limited passage and self-differentiation abilities of primary CML MSCs hinder extensive research. To overcome this, we generated and characterized an immortalised CML patient-derived MSC (iCML MSC) line and assessed its role in LSC maintenance. We also compared the immunophenotype and differentiation potential between primary CML MSCs at diagnosis, post-treatment, and with normal bone marrow MSCs. Notably, CML MSCs exhibited enhanced chondrogenic differentiation potential compared to normal MSCs. The iCML MSC line retained the trilineage differentiation potential and was genetically stable, enabling long-term investigations. Functional studies demonstrated that iCML MSCs protected CML CD34+ cells from imatinib-induced apoptosis, recapitulating the bone marrow microenvironment-mediated resistance observed in patients. iCML MSC-conditioned media enabled CML CD34+ and AML blast cells to proliferate rapidly, with no impact on healthy donor CD34+ cells. Gene expression profiling revealed dysregulated genes associated with calcium metabolism in CML CD34+ cells cocultured with iCML MSCs, providing insights into potential therapeutic targets. Further, cytokine profiling revealed that the primary CML MSC lines abundantly secreted 25 cytokines involved in immune regulation, supporting the hypothesis that CML MSCs create an immune modulatory microenvironment that promotes growth and protects against TKIs. Our study establishes the utility of iCML MSCs as a valuable model to investigate leukemic-stromal interactions and study candidate genes involved in mediating TKI resistance in CML LSCs.

Nutrient-Sensitising Drug Repurposing Screen Identifies Lomerizine As a Mitochondrial Metabolism Inhibitor in Chronic Myeloid Leukaemia

In chronic myeloid leukaemia (CML), the persistence of leukaemic stem cells (LSCs) following first line treatment with tyrosine kinase inhibitors (TKIs) such as imatinib, can lead to disease relapse. We have previously demonstrated that therapy-resistant CML LSCs rely on oxidative phosphorylation (OXPHOS) for survival and that targeting mitochondrial metabolism sensitises CML LSCs to imatinib treatment. However, current OXPHOS inhibitors have demonstrated limited efficacy, or are associated with adverse effects in clinical trials, highlighting that identification of clinically safe oxidative pathway inhibitors is warranted. To identify clinically applicable compounds that target cells dependent on mitochondrial metabolism, we used a nutrient-sensitised repurposing screening strategy. Upon replacement of glucose with galactose as the only sugar source in cell culture media, there is a shift in cellular metabolism towards OXPHOS (as cells are unable to effectively use galactose for glycolysis). Therefore, CML cells grown in galactose-containing media are more sensitive to inhibition of mitochondrial respiration than glucose-grown cells. Using this approach, we screened total of >1,100 unique and structurally diverse FDA-approved drugs in CML cells, cultured in the presence of 11mM glucose or 11mM galactose. This uncovered lomerizine dihydrochloride, a L-type Ca2+ channel blocker used as an anti-migraine drug, as a candidate compound effective against OXPHOS-dependent CML cells. Subsequently, patient derived CML CD34+ cells were shown to have increased ER mass (the main intracellular Ca2+ store) and an increase in mitochondrial Ca2+ levels compared with normal cells. Moreover, transcriptional analysis revealed that Ca2+ channel genes such as voltage-gated CACNA1D and receptor-activated TRPC6 are significantly upregulated in CML LSCs (CD34+CD38-) when compared with normal haematopoietic stem cells (HSCs), which was not reverted following imatinib treatment. Therefore, we hypothesised that the observed increase in mitochondrial metabolism in CML LSCs was dependent on CACNA1D and TRPC6 activity, and the increase in mitochondrial Ca2+ levels, which could be inhibited by lomerizine treatment. Notably, CRISPR-Cas9-mediated CACNA1D or TRPC6 knockout significantly reduced cytoplasmic and mitochondrial Ca2+ levels, and decreased cellular oxygen consumption rate, indicative of reduction in OXPHOS. Similarly, while imatinib treatment did not affect intracellular Ca2+ levels in primary CML CD34+ cells, lomerizine treatment significantly reduced cytoplasmic and mitochondrial Ca2+ levels, and mitochondrial respiration/OXPHOS. Applying liquid chromatography-mass spectrometry and isotope assisted metabolomics, we traced labelled nutrients (glucose and palmitate) in CD34+ cells. This revealed a significant reduction in activity of mitochondria-located Ca2+ dependent dehydrogenases and overall reduction in tricarboxylic acid (TCA) cycle activity in primary CML cells following lomerizine treatment. Of clinical relevance, using combination of cell surface markers, cell division trackers and functional assays, including long-term culture initiating cell (LTC-IC) assay, we demonstrate that lomerizine treatment, alone or in combination with imatinib, targeted CML LSCs when cultured in physiological medium in vitro, without affecting normal HSCs. Notably, combination treatment with imatinib and lomerizine reduced CML tumour burden, targeted CML LSCs and extended survival in xenotransplantation model of human CML. In summary, we reveal for the first time that Ca2+ regulation is disrupted in CML stem cells and influx via CACNA1D and TRPC6 is crucial for maintaining high mitochondrial Ca2+ levels and enhanced mitochondrial OXPHOS. This renders CML stem cells sensitive to lomerizine, an FDA-approved Ca2+ inhibitor identified following metabolism-specific drug-repurposing screening.

Loss of the vitamin D receptor triggers senescence in chronic myeloid leukemia via DDIT4-mediated DNA damage.

Chronic myeloid leukemia (CML) is a hematopoietic malignancy driven by the fusion gene BCR: ABL1. Drug resistance to tyrosine kinase inhibitors (TKIs) due to BCR: ABL1 mutation and residual leukemia stem cells (LSCs) remain major challenges for CML treatment. Here, we revealed the requirement of VDR in the progression of CML, in which VDR was upregulated by BCR: ABL1, accounting for its high expression. Interestingly, VDR knockdown inhibited the CML cell proliferation driven by BCR: ABL1 regardless of its mutations with resistance to TKIs. Mechanistically, VDR transcriptionally regulated DDIT4 expression, and the inhibition of DDIT4 triggered DNA damage-induced senescence via p53 signaling activation in CML cells. Furthermore, VDR deficiency was sufficient to not only ameliorate the diseaseburden and progression in primary CML mice but also reduce the self-renewal of CML-LSCs. Together, our study demonstrated that targeting VDR is a promising strategy to overcome TKI resistance and eradicate leukemia stem cells in CML.

Efficacy and Safety of Flumatinib in Treatment of Patients with Chronic Myeloid Leukemia

To analyze the efficacy and safety of flumatinib in the treatment of patients with chronic myeloid leukemia (CML). The clinical data of 56 CML patients treated with flumatinib from January 2020 to December 2021 in the First Affiliated Hospital of Nanchang University were retrospectively analyzed. Patients were divided into three groups: 35 new diagnosed CML patients treated with flumatinib (group A), 10 patients with imatinib/dasatinib intolerance (group B) and 11 patients with imatinib/dasatinib resistance (group C) switched to flumatinib treatment, respectively. The molecular response and adverse effects of flumatinib treatment were evaluated. In group A, the early molecular response (EMR) at 3 months was 40.0%, and the major molecular response (MMR) at 6 and 12 months was 43.7% and 46.2%, respectively. In group B, the EMR was 50.0% at 3 months, and the MMR was 70.0% and 66.2% at 6 and 12 months, respectively. Among evaluable patients, 6 cases in group B achieved molecular response of 4.5 (MR4.5) at 12 months after switching to flumatinib treatment. In group C, 3 cases who switched from imatinib resistance to flumatinib achieved MR4.5 at 12 months, but 2 cases who switched from dasatinib resistance to flumatinib failed. Subgroup analysis showed significant differences in EUTOS long-term survival (ELTS) scores for patients in the medium-risk/high-risk group compared with those in the low-risk group for 3-month EMR (18.8% vs 57.9%), 6-month MMR (15.4% vs 63.2%) and 12-month MR4.5 (15.4% vs 69.2%) (P =0.036, P =0.012,P =0.015). The most common adverse effect in group A was thrombocytopenia, accounting for 54.5%, and 22.8% (8/35) patients discontinued the drug due to haematological adverse effects. Compared with patients who did not discontinue the drug or whose recovery time from discontinuation due to haematological toxicity was <1 month, patients whose recovery time from discontinuation was ≥1 month had a significantly worse 3-month EMR, 6-month MMR and 12-month MR4.5 (P =0.028, P =0.021, P =0.002). Flumatinib has better molecular response and tolerance in patients with primary, imatinib/dasatinib-intolerant or resistant CML. Medium-risk/high-risk in ELTS score and time to recovery from discontinuation due to haematological toxicity ≥1 month are important factors influencing achievement of better molecular response in flumatinib treatment.

Arginine dependency is a therapeutically exploitable vulnerability in chronic myeloid leukaemic stem cells.

To fuel accelerated proliferation, leukaemic cells undergo metabolic deregulation, which can result in specific nutrient dependencies. Here, we perform an amino acid drop-out screen and apply pre-clinical models of chronic phase chronic myeloid leukaemia (CML) to identify arginine as a nutrient essential for primary human CML cells. Analysis of the Microarray Innovations in Leukaemia (MILE) dataset uncovers reduced ASS1 levels in CML compared to most other leukaemia types. Stable isotope tracing reveals repressed activity of all urea cycle enzymes in patient-derived CML CD34+ cells, rendering them arginine auxotrophic. Thus, arginine deprivation completely blocks proliferation of CML CD34+ cells and induces significantly higher levels of apoptosis when compared to arginine-deprived cell lines. Similarly, primary CML cells, but not normal CD34+ samples, are particularly sensitive to treatment with the arginine-depleting enzyme, BCT-100, which induces apoptosis and reduces clonogenicity. Moreover, BCT-100 is highly efficacious in a patient-derived xenograft model, causing > 90% reduction in the number of human leukaemic stem cells (LSCs). These findings indicate arginine depletion to be a promising and novel strategy to eradicate therapy resistant LSCs.

Modulating retinoid-X-receptor alpha (RXRA) expression sensitizes chronic myeloid leukemia cells to imatinib in vitro and reduces disease burden in vivo.

Introduction: The ligand-activated transcription factors, nuclear hormone receptors (NHRs), remain unexplored in hematological malignancies except for retinoic acid receptor alpha (RARA). Methods: Here we profiled the expression of various NHRs and their coregulators in Chronic myeloid leukemia (CML) cell lines and identified a significant differential expression pattern between inherently imatinib mesylate (IM)-sensitive and resistant cell lines. Results: Retinoid-X-receptor alpha (RXRA) was downregulated in CML cell lines inherently resistant to IM and in primary CML CD34+ cells. Pre-treatment with clinically relevant RXRA ligands improved sensitivity to IM in-vitro in both CML cell lines and primary CML cells. This combination effectively reduced the viability and colony-forming capacity of CML CD34+ cells in-vitro. In-vivo, this combination reduced leukemic burden and prolonged survival. Overexpression (OE) of RXRA inhibited proliferation and improved sensitivity to IM in-vitro. In-vivo, RXRA OE cells showed reduced engraftment of cells in the bone marrow, improved sensitivity to IM, and prolonged survival. Both RXRA OE and ligand treatment markedly reduced BCR::ABL1 downstream kinase activation, activating apoptotic cascades and improving sensitivity to IM. Importantly, RXRA OE also led to the disruption of the oxidative capacity of these cells. Conclusion: Combining IM with clinically available RXRA ligands could form an alternative treatment strategy in CML patients with suboptimal response to IM.

Repurposing the Bis-Biguanide Alexidine in Combination with Tyrosine Kinase Inhibitors to Eliminate Leukemic Stem/Progenitor Cells in Chronic Myeloid Leukemia.

In CML, Leukemic Stem Cells (LSCs) that are insensitive to Tyrosine Kinase Inhibitors are responsible for leukemia maintenance and relapses upon TKI treatment arrest. We previously showed that downregulation of the BMI1 polycomb protein that is crucial for stem/progenitor cells self-renewal induced a CCNG2/dependent proliferation arrest leading to elimination of Chronic Myeloid Leukemia (CML) cells. Unfortunately, as of today, pharmacological inhibition of BMI1 has not made its way to the clinic. We used the Connectivity Map bioinformatic database to identify pharmacological molecules that could mimick BMI1 silencing, to induce CML cell death. We selected the bis-biguanide Alexidin (ALX) that produced a transcriptomic profile positively correlating with the one obtained after BMI silencing in K562 CML cells. We then evaluated the efficiency of ALX in combination with TKI on CML cells. Here we report that cell growth and clonogenic activity of K562 and LAMA-84 CML cell lines were strongly inhibited by ALX. ALX didn't modify BCR::ABL1 phosphorylation and didn't affect BMI1 expression but was able to increase CCNG2 expression leading to autophagic processes that preceed cell death. Besides, ALX could enhance the apoptotic response induced by any Tyrosine Kinase Inhibitors (TKI) of the three generations. We also noted a strong synergism between ALX and TKIs to increase expression of caspase-9 and caspase-3 and induce PARP cleavage, Bad expression and significantly decreased Bcl-xL family member expression. We also observed that the blockage of the mitochondrial respiratory chain by ALX can be associated with inhibition of glycolysis by 2-DG to achieve an enhanced inhibition of K562 proliferation and clonogenicity. ALX specifically affected the differentiation of BCR::ABL1-transduced healthy CD34+ cells but not of mock-infected healthy CD34+ control cells. Importantly, ALX strongly synergized with TKIs to inhibit clonogenicity of primary CML CD34+ cells from diagnosed patients. Long Term Culture of Initiating Cell (LTC-IC) and dilution of the fluorescent marker CFSE allowed us to observe that ALX and Imatinib (IM) partially reduced the number of LSCs by themselves but that the ALX/IM combination drastically reduced this cell compartment. Using an in vivo model of NSG mice intravenously injected with K562-Luciferase transduced CML cells, we showed that ALX combined with IM improved mice survival. Collectively, our results validate the use of ALX bis-biguanide to potentiate the action of conventional TKI treatment as a potential new therapeutic solution to eradicate CML LSCs.

The role of CSE1L silencing in the regulation of proliferation and apoptosis via the AMPK/mTOR signaling pathway in chronic myeloid leukemia

ABSTRACTObjectivesChromosome segregation 1-like (CSE1L) is abundant and strongly expressed in solid tumors. However, the expression and role of CSE1L in chronic myeloid leukemia(CML) remain largely unknown.Materials and methodsThe relative expression levels of CSE1L in bone marrow granulocytes from patients with primary CML and non-hematologic controls were measured by flow cytometry. Cell counting kit-8 analysis, DNA Content Quantitation Assay, and Annexin V-PE/7-AAD staining were applied to assess the effects of CSE1L knockdown on cell proliferation, cell cycle progression, and apoptosis.ResultsElevated expression of CSE1L was detected in bone marrow granulocytes of patients with primary CML. In the CML cell line K562 cells, CSE1L knockdown impaired cell proliferation blocked the cell cycle shift from G0/G1 phase to the S phase, and promoted apoptosis. Knockdown of CSE1L reduced Bcl-2 protein expression and increased Bax protein expression. Meanwhile, knockdown of CSE1L enhanced the expression of phospho-AMPK protein and decreased the expression of phospho-mTOR protein. The expression of total AMPK and mTOR proteins was not affected. In addition, CSE1L expression levels were decreased in imatinib-treated K562 cells.ConclusionsCSE1L plays a pivotal role in K562 cell survival and growth. These functions may be partially dependent on the AMPK/mTOR signaling pathway to achieve. In addition, CSE1L may have had a future impact on the treatment of CML patients.

Integrated High-Throughput Drug Profiling and CRISPR Screening Identify Novel Pathway Vulnerabilities of Leukemic Stem Cells in Chronic Myeloid Leukemia

Despite BCR-ABL-targeting tyrosine kinase inhibitors (TKIs) have dramatically improved the management of chronic myeloid leukemia (CML) patients, TKIs fail to eradicate leukemic stem cells (LSCs). CML-LSCs are recognized as BCR-ABL-kinase activity independent and responsible for TKI-resistance and relapse upon treatment discontinuation. Systematic mapping of druggable signaling pathways enables the identification of novel CML-LSCs effectively targeting drugs, which is critical to enhance the achievement of sustained treatment free remission in CML patients. We implemented ex-vivo drug testing of 80 targeted drugs and 18 drug combinations across 10 000-fold concentration, to evaluate drug sensitivity profiles of primary CML-LSCs and progenitors (CD34+ cells) from twenty patients in addition to CD34+ cells from three healthy donors. We identified novel drug vulnerabilities of CML-LSCs including VEGFR-, CDK2/WEE-, MDM2-, and PI3K/mTOR- inhibitors. Combination of imatinib with idasanutlin, venetoclax, AZD1775 and dexamethasone led to synergistic inhibition of CML-LSCs. To delineate the phenotype-specific sensitivity profile of CML CD34+ cells, we applied ex-vivo flowcytometry-based drug screening approach to bone marrow samples from ten CML patients using a custom library of 20 drugs. We identified specific sensitivity of CML CD34+CD38- cells to mepacrine, RG7112, idasanutlin, and navitoclax. In particular, mepacrine showed striking ability to induce differentiation of CML-LSCs, which was further validated in a separate cohort of primary CML samples and cell lines. To characterize the mechanisms of action of the discovered drugs, we applied genome-scale CRISPR screening in CML cells to identify potential sensitizing and resistance targets for five selected drugs. Imatinib, dasatinib, and tivozanib showed a similar profile of resistance and sensitizing genes, while AZD1775 and mepacrine had unique profiles. We identified knockout targets that confer BCR-ABL1-independent resistance common to different TKIs including mediator complex (MED23, MED26, CCNC), and apoptosis related (APAF1) genes in addition to other genes with uncharacterized role in CML, such as KCTD5 and EIF2AK1. On the other hand, knockout of certain genes was associated with increased sensitivity to specific drugs such as IGF1R-dasatinib and SPNS1-mepacrine associations. KCTD5 was consistently identified as the top resistance gene to all tested TKIs, and therefore we next investigated the potential role of KCTD5 in CML pathogenesis and TKI resistance. In RNA sequencing data, KCTD5 was significantly downregulated in CML-CD34+ cells compared to healthy counterparts. Using co-immunoprecipitation, we revealed that KCTD5 directly interacts with BCR-ABL and mediate TKI-induced ubiquitination by E3 ligase, as shown by WB assay, that can destine BCR-ABL for subsequent degradation. Knockout of KCTD5 was associated with decreased ubiquitination of BCR-ABL and resistance to imatinib in CML cell lines and primary CML-CD34+ cells. Furthermore, combination of TKI with deubiquitinase inhibitors induced enhanced TKI sensitivity in KCTD5-KO cells. In conclusion, we discovered novel mechanisms of primary TKI-resistance and drug vulnerabilities of CML-LSCs, which potentially enable eradication of LSCs in CML patients and hence pave the way for the achievement of functional cure in CML patients. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Expansions of tumor-reactive Vdelta1 gamma-delta T cells in newly diagnosed patients with chronic myeloid leukemia

Recent studies have underscored the importance of gamma-delta (γδ) T cells in mediating potent MHC-unrestricted cytotoxicity in numerous malignancies. Here, we analyzed Vδ1 and Vδ2 γδ T cell subsets in newly diagnosed chronic myeloid leukemia (CML) patients (n = 40) who had initiated tyrosine kinase inhibitor (TKI) therapy including imatinib (n = 22), nilotinib (n = 14) and dasatinib (n = 4). Patient peripheral blood samples were analyzed at diagnosis and monitored prospectively at 3, 6, 12 and 18 months post-TKI. γδ T cells isolated from healthy donors and CML patients were used against K562, LAMA-84 and KYO-1 cell lines and against primary CML cells in cytotoxicity assays. We found large expansions of Vδ1 and Vδ2 T cells in patients at diagnosis compared to age-matched healthy donors (n = 40) (p < 0.0001). The γδ T cell reconstitution in patients on imatinib and also on nilotinib showed significant reductions of Vδ1 T cell and Vδ2 T cell absolute counts at 3 months compared to diagnosis. Importantly, Vδ1 and Vδ2 T absolute cell counts remained at normal levels from 3 months throughout the follow-up. Next, we observed susceptibility to specific lysis of primary CML tumor cells by Vδ1 T cells from healthy donors. Furthermore, we determined inherent cytotoxic reactivity by autologous patients’ Vδ1 T lymphocytes against primary CML tumor cells. Finally, the TCR clonality profiles showed in CML patients mostly polyclonal repertoires regardless of the TKI. Our results provide further evidence into γδ T cell antileukemia immunity in CML that might be beneficial for long-term disease control and treatment outcome.

CML-164 Dihydroorotate Dehydrogenase Inhibition Reveals Metabolic Vulnerability in Chronic Myeloid Leukemia

There are chronic myeloid leukemia (CML) patients who show resistance to TKI therapy and are prone to progress to more advanced phases of the disease, and new therapeutic approaches are needed. Our study shows that CML cells are vulnerable to dihydroorotate dehydrogenase (DHODH) inhibition mediated by Meds433, a potent DHODH inhibitor developed by our group. Pyrimidine supply in resting and differentiated cells primarily relies on the salvage pyrimidine pathway, which is energetically affordable. This level of nucleotide production for fast-proliferating leukemic cells is insufficient, and they have to fulfill their needs via the de novo pathway. In this study, we shed light on the role of DHODH inhibition in CML and how it can be a promising approach for targeting leukemic cells. Sixty bone marrow samples and peripheral blood of newly diagnosed CML patients and 4 TKI-resistant patients were collected. In-vivo, in-vitro, and ex-vivo experiments were performed on primary CML CD34+ and various CML cell lines. Our data showed that DHODH is highly active in CML stem/progenitor cells, which supports a high proliferation capacity. Meds433, by targeting DHODH enzyme activity, induced apoptosis, cell growth, and cell cycle arrest in leukemic cells. Meanwhile, the administration of Meds433 reduced tumor growth and tumor burden in treated mice. Interestingly, the addition of exogenous uridine rescued all of the biological effects caused by DHODH inhibition, demonstrating the selectivity of Meds433. Based on RNA-seq data, most upregulated gene sets were related to apoptosis and immune response and most downregulated gene sets were related to MYC targets and metabolism pathways, which was confirmed by metabolic profile analysis. Also, we found that glutamic pyruvic acid transaminase 1 (GPT1) is among the top downregulated genes after treating CML cells with Meds433, and overexpressing GPT1 in CML cells interfered with the effect of Meds433. These data show that GPT1 downregulation could be one of the possible mechanisms in which Meds433 acts in CML. Our study shows that DHODH inhibition is a promising approach for targeting CML stem/progenitor cells and may help more patients discontinue the therapy. This work was supported by Associazione Italiana per la Ricerca sul Cancro: IG-23344.

Tyrosol Derivatives, Bearing 3,5-Disubstituted Isoxazole and 1,4-Disubstituted Triazole, as Potential Antileukemia Agents by Promoting Apoptosis.

In the present study, we assess tyrosol derivatives bearing 3,5-disubstituted isoxazoles and 1,4-disubstituted triazoles for their ability to inhibit the proliferation of K562 cells derived from leukemia as well as primary chronic myeloid leukemia (CML) cells obtained from the peripheral blood of 15 CML patients including 10 patients with untreated chronic phase and 5 patients with resistance against imatinib or multiple TKI. Our results showed that most derivatives displayed significant anti-proliferative activity against K562 cells in a dose-dependent manner. Among them, compounds 3d and 4a exhibited greater potent anticancer activity with respective IC50 values of 16 and 18 µg/mL (45 µM and 61 µM). Interestingly, compound 3d inhibited CML cell proliferation not only in newly diagnosed but also in imatinib-resistant patients. We demonstrated that the anti-proliferative effect of this compound is mediated by a pro-apoptotic activity by promoting oxidative stress and modulating the activity of the Akt, p38 MAPK and Erk 1/2 pathways. In conclusion, our data highlight the potential of this class of derivative as a novel promising therapeutic agent for CML therapy.

BRD4 degradation blocks expression of MYC and multiple forms of stem cell resistance in Ph+ chronic myeloid leukemia.

In most patients with chronic myeloid leukemia (CML) clonal cells can be kept under control by BCR::ABL1 tyrosine kinase inhibitors (TKI). However, overt resistance or intolerance against these TKI may occur. We identified the epigenetic reader BRD4 and its downstream‐effector MYC as growth regulators and therapeutic targets in CML cells. BRD4 and MYC were found to be expressed in primary CML cells, CD34+/CD38− leukemic stem cells (LSC), and in the CML cell lines KU812, K562, KCL22, and KCL22T315I. The BRD4‐targeting drug JQ1 was found to suppress proliferation in KU812 cells and primary leukemic cells in the majority of patients with chronic phase CML. In the blast phase of CML, JQ1 was less effective. However, the BRD4 degrader dBET6 was found to block proliferation and/or survival of primary CML cells in all patients tested, including blast phase CML and CML cells exhibiting the T315I variant of BCR::ABL1. Moreover, dBET6 was found to block MYC expression and to synergize with BCR::ABL1 TKI in inhibiting the proliferation in the JQ1‐resistant cell line K562. Furthermore, BRD4 degradation was found to overcome osteoblast‐induced TKI resistance of CML LSC in a co‐culture system and to block interferon‐gamma‐induced upregulation of the checkpoint antigen PD‐L1 in LSC. Finally, dBET6 was found to suppress the in vitro survival of CML LSC and their engraftment in NSG mice. Together, targeting of BRD4 and MYC through BET degradation sensitizes CML cells against BCR::ABL1 TKI and is a potent approach to overcome multiple forms of drug resistance in CML LSC.

RHOA-regulated IGFBP2 promotes invasion and drives progression of BCR-ABL1 chronic myeloid leukemia.

The Philadelphia 9;22 chromosome translocation has two common isoforms that are preferentially associated with distinct subtypes of leukemia. The p210 variant is the hallmark of chronic myeloid leukemia (CML) whereas p190 is frequently associated with B-cell acute lymphoblastic leukemia. The only sequence difference between the two isoforms is the guanidine exchange factor domain. This guanidine exchange factor is reported to activate RHO family GTPases in response to diverse extracellular stimuli. It is not clear whether and, if so, how RHOA contributes to progression of p210 CML. Here we show that knockout of RHOA in the K562 and KU812, p210-expressing cell lines leads to suppression of leukemogenesis in animal models in vivo. RNA-sequencing analysis of the mock control and null cells demonstrated a distinct change in the gene expression profile as a result of RHOA deletion, with significant downregulation of genes involved in cell activation and cell adhesion. Cellular analysis revealed that RHOA knockout leads to impaired cell adhesion and migration and, most importantly, the homing ability of leukemia cells to the bone marrow, which may be responsible for the attenuated leukemia progression. We also identified IGFBP2 as an important downstream target of RHOA. Further mechanistic investigation showed that RHOA activation leads to relocation of the serum response factor (SRF) into the nucleus, where it directly activates IGFBP2. Knockout of IGFBP2 in CML cells suppressed cell adhesion/invasion, as well as leukemogenesis in vivo. This elevated IGFBP2 expression was confirmed in primary CML samples. Thus, we demonstrate one mechanism whereby the RHOA-SRF-IGFBP2 signaling axis contributes to the development of leukemia in cells expressing the p210 BCR-ABL1 fusion kinase.

Profile and survival outcomes among patients with second malignancies following a primary chronic myeloid leukemia: An analysis of the SEER database (1975-2016).

e19060 Background: A major concern of cancer survivors is the occurrence of a subsequent cancer. A small proportion of patients with CML develop second cancers. Little is known about these patients. In the present study, we determined the profile and determinants of survival among patients with a primary CML who developed subsequent malignancies. Methods: We utilized the SEER 18 Registry 1975-2016 to conduct a retrospective analysis of patients who developed a subsequent malignancy following a primary CML diagnosis. The outcome of interest was the latency interval between the initial primary CML diagnosis and a subsequent malignancy. Utilizing the cox regression model, we determined the factors associated with the overall survival after controlling for disease stage, treatment modalities, and social determinants of health. Results: There were 2, 312 CML Patients who developed a subsequent malignancy in the study period. Among these patients, 76.3% were non-Hispanic Whites, 9.6% were non-Hispanic Blacks, and 8.7% were Hispanics. 63.0% of the study population were males. The mean age at primary diagnosis of CML was 63.2 ± 15.6 yrs. While the mean age at diagnosis of the subsequent malignancy was 66.9 ± 14.5 yrs. The commonest subsequent malignancies were Acute Myeloid Leukemia (12.9%), Prostate cancers (12.7%), Lung and Bronchi cancers (11.5%), and Breast cancers (5.9%). The mean latency interval for developing a subsequent malignancy following a CML was 3.7± 4.4 years. Significant predictors of reduced survival include increasing age (HR = 1.02; 95% CI 1.01-1.03), Latency interval &lt; 5years (HR = 0.32; 95% CI 0.17-0.60) and Hispanic ethnicity (HR = 1.78; 95% CI 1.09-2.92). Conclusions: Common second malignancies following a primary diagnosis of CML include prostate cancers, lung and bronchi cancers, and breast malignancies. Major predictors of adverse outcomes include advanced age, development of second cancers within 5 years of primary CML diagnosis, and Hispanic ethnicity.

Loss of PRMT7 reprograms glycine metabolism to selectively eradicate leukemia stem cells in CML

Our group has reported previously on the role of various members of the protein arginine methyltransferase (PRMT) family, which are involved in epigenetic regulation, in the progression of leukemia. Here, we explored the role of PRMT7, given its unique function within the PRMT family, in the maintenance of leukemia stem cells (LSCs) in chronic myeloid leukemia (CML). Genetic loss of Prmt7, and the development and testing of a small-molecule specific inhibitor of PRMT7, showed that targeting PRMT7 delayed leukemia development and impaired self-renewal of LSCs in a CML mouse model and in primary CML CD34+ cells from humans without affecting normal hematopoiesis. Mechanistically, loss of PRMT7 resulted in reduced expressions of glycine decarboxylase, leading to the reprograming of glycine metabolism to generate methylglyoxal, which is detrimental to LSCs. These findings link histone arginine methylation with glycine metabolism, while suggesting PRMT7 as a potential therapeutic target for the eradication of LSCs in CML.

Inhibition of Folate Metabolism Drives Autophagy-Dependent Differentiation and Reduces Survival of Therapy-Resistant Leukaemic Stem Cells

Metabolic rewiring is an important hallmark of cancer. The folate metabolism pathway, also known as one-carbon (1C) metabolism, allows for transfer of 1C units through folate intermediates for biosynthetic processes, including precursors for DNA synthesis. Recent studies have shown that enzymes involved in the mitochondrial arm of 1C metabolism are overexpressed in a subset of aggressive cancers and that their expression affects responses to anti-metabolite drug treatments. However, the role of 1C metabolism in therapy resistant leukemic stem cells (LSCs) is currently unknown. Therefore, we aimed to investigate the activity and the impact of genetic and pharmacological inhibition of folate enzymes in primitive chronic myeloid leukaemia (CML) cells.We initially performed transcriptomic analysis of CD34+38- cells, from individuals with chronic phase CML (E-MTAB-2581). This revealed a significant upregulation of folate metabolism genes in CML LSCs, including serine hydroxymethyltransferase (SHMT2; p≤0.05), a key mitochondrial enzyme. To assess the activity of 1C metabolism in primitive cells we performed gas chromatography-mass spectrometry-mediated secretomic analysis using patient-derived, c-KIT enriched CML cells, which revealed a significant increase in the exchange rate of formate (folate intermediate necessary for purine synthesis) in CML cells, when compared to the secretome of normal counterparts (p<0.05). This reinforced the idea that 1C metabolism may be a metabolic dependency in CML.Following CRISPR-Cas9-mediated SHMT2 knockout (KO) in CML cell line, we observed a significant decrease in growth rate, together with a decrease in glycolytic capacity and oxygen consumption rate (p<0.01), suggesting impairment in proliferation and central carbon metabolism. Further metabolic characterisation of CML SHMT2 KO cells using liquid chromatography-mass spectrometry demonstrated a significant increase in AICAR, a purine biosynthesis intermediate and an AMP activated kinase (AMPK) activator. This prompted us to investigate the effect of 1C metabolism inhibition on AMPK. We found that AMPK phosphorylation on the conserved Thr 172 (a site that is phosphorylated under energy stress) was increased in SHMT2 KO cells, with similar effect seen following pharmacological inhibition of both SHMT2 and its cytosolic counterpart SHMT1 using SHIN1,which also promoted AMPK-dependent phosphorylation of the autophagy-inducing kinase ULK1 and downstream ULK1 target ATG13. Moreover, analysis of mitochondrial fraction revealed accumulation of mitochondrial fission related protein DRP1 and the mitophagy receptor NIX on mitochondria, hinting towards cellular interplay between 1C metabolism and mitochondrial homeostasis.Phenotypically, both pharmacological and genetic inhibition of SHMT1/2 induced the expression of erythropoiesis markers CD71 and Glycophorin A, which was reversed following formate supplementation. CRISPR-Cas9-mediated double AMPKα1/α2 KO revealed that the increased expression of these erythropoiesis markers following SHMT1/2 inhibition was independent of AMPK activity. Conversely, while NIX KO had no effect, pharmacological inhibition of ULK1 kinase activity, or genetic inhibition of ULK1 and ATG7 (protein important for autophagosome formation), prevented increased expression of CD71/Glycophorin A following SHMT1/2 inhibition.We next investigated the effect of 1C metabolism inhibition on differentiation and survival of primary CML cells. Of clinical relevance, pharmacological inhibition of SHMT1/2 promoted erythroid maturation of CD34+ CML cells (measured by expression of CD71, CD44, CD36 and Glycophorin A) when challenged with erythropoietin, which sensitises primitive cells to erythroid lineage commitment. Lastly, pharmacological inhibition of 1C metabolism decreased the colony formation capacity of CD34+ CML by 50%, with minimum effect on normal CD34+ cells. Moreover, combination treatment of SHIN1 with imatinib, a frontline treatment for CML patients, further increased the sensitivity of primary CML cells to imatinib by 40%.Overall, our novel findings indicate that disruption of the folate metabolism pathway inhibits central carbon metabolism in CML cells, promotes autophagy dependent, but AMPK independent maturation phenotype and has detrimental effect on the survival of primitive CML cells. DisclosuresNo relevant conflicts of interest to declare.

New insight into the catalytic -dependent and -independent roles of METTL3 in sustaining aberrant translation in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm caused by the presence of tyrosine kinase BCR-ABL1 fusion protein, which deregulate transcription and mRNA translation. Tyrosine kinase inhibitors (TKIs) are the first-choice treatment. However, resistance to TKIs remains a challenge to cure CML patients. Here, we reveal that the m6A methyltransferase complex METTL3/METTL14 is upregulated in CML patients and that is required for proliferation of primary CML cells and CML cell lines sensitive and resistant to the TKI imatinib. We demonstrate that depletion of METTL3 strongly impairs global translation efficiency. In particular, our data show that METTL3 is crucial for the expression of genes involved in ribosome biogenesis and translation. Specifically, we found that METTL3 directly regulates the level of PES1 protein identified as an oncogene in several tumors. We propose a model in which nuclear METTL3/METTL14 methyltransferase complex modified nascent transcripts whose translation is enhanced by cytoplasmic localization of METTL3, independently from its catalytic activity. In conclusion, our results point to METTL3 as a novel relevant oncogene in CML and as a promising therapeutic target for TKI resistant CML.

Pharmacologic targeting of the P-TEFb complex as a therapeutic strategy for chronic myeloid leukemia

BackgroundThe positive transcription elongation factor b (P-TEFb) kinase activity is involved in the process of transcription. Cyclin-dependent kinase 9 (CDK9), a core component of P-TEFb, regulates the process of transcription elongation, which is associated with differentiation and apoptosis in many cancer types. Wogonin, a natural CDK9 inhibitor isolated from Scutellaria baicalensis. This study aimed to investigate the involved molecular mechanisms of wogonin on anti- chronic myeloid leukemia (CML) cells.Materials and methodsmRNA and protein levels were analysed by RT-qPCR and western blot. Flow cytometry was used to assess cell differentiation and apoptosis. Cell transfection, immunofluorescence analysis and co-immunoprecipitation (co-IP) assays were applied to address the potential regulatory mechanism of wogonin. KU-812 cells xenograft NOD/SCID mice model was used to assess and verify the mechanism in vivo.ResultsWe reported that the anti-CML effects in K562, KU-812 and primary CML cells induced by wogonin were regulated by P-TEFb complex. We also confirmed the relationship between CDK9 and erythroid differentiation via knockdown the expression of CDK9. For further study the mechanism of erythroid differentiation induced by wogonin, co-IP experiments were used to demonstrate that wogonin increased the binding between GATA-1 and FOG-1 but decreased the binding between GATA-1 and RUNX1, which were depended on P-TEFb. Also, wogonin induced apoptosis and decreased the mRNA and protein levels of MCL-1 in KU-812 cells, which is the downstream of P-TEFb. In vivo studies showed wogonin had good anti-tumor effects in KU-812 xenografts NOD/ SCID mice model and decreased the proportion of human CD45+ cells in spleens of mice. We also verified that wogonin exhibited anti-CML effects through modulating P-TEFb activity in vivo.ConclusionsOur study indicated a special mechanism involving the regulation of P-TEFb kinase activity in CML cells, providing evidences for further application of wogonin in CML clinical treatment.8cwZMBLp1zasMdEPaNEt3gVideo