Leukemic stem cells and therapy resistance in acute myeloid leukemia

Engineered cell membrane vesicles loaded with lysosomophilic drug for acute myeloid leukemia therapy via organ-cell-organelle cascade-targeting

Acute myeloid leukemia (AML) presents significant treatment challenges due to the severe toxicities and limited efficacy of conventional therapies, highlighting the urgency for innovative approaches. Organelle-targeting therapies offer a promising avenue to enhance therapeutic outcomes while minimizing adverse effects. Herein, inspired that primary AML cells are enriched with lysosomes and sensitive to lysosomophilic drugs (e.g., LLOMe), we developed a smart nanodrug (Cas-CMV@LM) including the engineered cell membrane vesicles (CMVs) nanocarrier and the encapsulated drug cargo LLOMe (LM). Briefly, the nanodrug with organ-cell-organelle cascade-targeting function could firstly home to the bone marrow guided by CMVs derived from CXCR4-overexpressing bone marrow mesenchymal stem cells (BMSC), subsequently target leukemia cells via CD33 and CD123 aptamers anchored on the vesicles, eventually precisely attack the lysosomes of leukemia cells. Consequently, Cas-CMV@LM specifically inhibited leukemia cell proliferation and triggered necroptosis in vitro. Importantly, the cascade-targeting nanodrug displayed high biosafety and significantly impeded leukemia progression in AML patient-derived xenograft (PDX) model. Collectively, this study provides a paradigm for precision leukemia treatment from the perspective of targeting organelle-lysosome.

mRNA m5C Alteration in Azacitidine Demethylation Treatment of Acute Myeloid Leukemia

The DNA demethylating therapy with azacitidine (AZA) is a promising therapeutic strategy for elderly patients with acute myeloid leukemia (AML). AZA primarily inhibits DNA methylation, promotes cell differentiation and apoptosis in AML. However, as a cytosine nucleoside analog, AZA also has the potential to be incorporated into RNA molecules. To assess the impact of AZA on RNA m5C methylation during demethylating therapy, we conducted Nanopore direct-RNA sequencing on samples from three AML patients pre and after demethylating therapy, as well as on HL-60 cells pretreated with AZA. We performed an integrated analysis of the transcriptome and the m5C methylome, contrasting the states of complete remission with those of active disease (AML). Our results revealed an extensive demethylation effect at the RNA level attributable to AZA and found that mRNA m5C modification may play a pivotal role in the progression of AML. Additionally, S100P was identified as a biomarker with significant prognostic implications. We also conducted a conjoint analysis of the transcriptome and the m5C methylome of the full-length transcripts, uncovering several dysregulated mRNA isoforms. Collectively, our findings indicate that mRNA m5C methylation is implicated during AML progression, and AZA exhibits an overall suppressive effect on this process.

A phase 2 study of chidamide in combination with CAG and venetoclax-azacitidine in acute myeloid leukemia: Clinical safety, efficacy, and correlative analysis

Acute myeloid leukemia (AML) is a highly heterogeneous hematopoietic malignancy characterized by elevated mortality. Epigenetic therapy plays an essential role in the treatment of AML. However, the clinical outcomes of the combination of multiple epigenetic agents and conventional chemotherapy remain unclear. We conducted a phase 2 study to evaluate the clinical safety and efficacy of chidamide combined with CAG and venetoclax-azacitidine (referred to as CACAG-VEN) in AML patients (NCT05659992). Patients received induction treatment with aclarubicin (10 mg/m2/d on days 1, 3, and 5), azacitidine (75 mg/m2 on days 1-7), cytarabine (75 mg/m2 bid on days 1-5), chidamide (30 mg, twice/week for 2 weeks), and venetoclax (100 mg on day 1, 200 mg on day 2, 400 mg on days 3-14). Granulocyte colony-stimulating factor 5 μg/kg/day was administered. After one cycle of CACAG-VEN, the overall response rate was 96.7 %, with a composite complete response (CRc) rate of 93.3 %. The CRc rates (86.7 %) were remarkable among patients with adverse NCCN risk. Patients receiving two cycles of CACAG-VEN achieved a CRc rate of 100 %. The 12-month overall survival rate was 69.7 %. The median time to recovery was 19 days for platelets ≥50,000/μL and 17 days for an absolute neutrophil count ≥500 cells/μL after induction therapy. The single-cell RNA sequence showed most immune cells exhibited no significant change in proportion after removing tumor cells. In conclusion, this regimen resulted in a high CRc rate in newly diagnosed AML patients, particularly in adverse-risk patients. And this regimen had minimal impact on immune cells.

IHCH9033, a novel class I HDAC inhibitor, synergizes with FLT3 inhibitor and rescues quizartinib resistance in FLT3-ITD AML via enhancing DNA damage response

BACKGROUND

Despite initial success with FLT3 inhibitors (FLT3is), outcomes for FLT3-ITD acute myeloid leukemia (AML) patients remain unsatisfactory, underscoring the need for more effective treatment options. Epigenetic modifications, such as histone acetylation, contribute to AML's onset and persistence, advocating the potential for epigenetic therapies. However, the poor specificity of pan-histone deacetylase inhibitors (HDACis) leads to undesirable adverse effects, prompting the need for isoform-specific HDACis. This study aims to explore the antileukemic activities and mechanisms of IHCH9033, a novel class I HDACi, alone or combined with FLT3i in FLT3-ITD AML.

METHODS

The viability of AML cell lines and primary AML cells treated with HDACis alone or in combination with FLT3i was detected by MTT or CCK8 assay. Flow cytometry was utilized to examine cell apoptosis, cell cycle progression and ROS production. RNA sequencing analysis, RT-qPCR, western blotting, and co-immunoprecipitation assays were employed to elucidate the molecule mechanisms. The in vivo anti-leukemia efficacy was tested in xenografted mice models derived from FLT3-ITD cell lines and primary AML patients.

RESULTS

Here, we identified IHCH9033, a novel selective class I HDACi, which exhibited an increased antitumor effect in FLT3-ITD AML through effectively eliminating leukemia burden and overcoming resistance to FLT3i. Mechanically, IHCH9033 selectively inhibited DNA repair in FLT3-ITD AML cells, leading to the accumulation of DNA damage that eventually resulted in cell cycle arrest and apoptosis. Additionally, IHCH9033 induced HSP90 acetylation, FLT3 ubiquitination, and proteasomal degradation of FLT3, thereby inhibiting FLT3 downstream signaling. Notably, IHCH9033 maintained its potency in both FLT3i-resistant AML cell lines and primary-resistant patient samples, and exerted strong synergy with the FLT3i quizartinib, leading to tumor regression in FLT3-ITD/TKD AML xenografts. In patient-derived xenografts, the treatment with IHCH9033, both alone and in combination, led to nearly complete eradication of the AML burden, without significant adverse effects.

CONCLUSIONS

Our study shows that IHCH9033, a novel class I HDACi with a desirable pharmacological profile, is a promising drug candidate for FLT3-ITD AML, and suggests a strategy of combining class I HDACis and FLT3is in AML clinical trials to increase efficacy and overcome resistance, thus potentially providing a curative treatment option.

Unveiling the potential of CLL-1: a promising target for AML therapy

Acute myeloid leukemia (AML) remains a formidable blood cancer, despite recent advances in treatment. A significant challenge persists in improving patient outcomes, particularly in addressing relapse and treatment resistance. Identifying new therapeutic targets is critical for advancing AML therapy. C-type lectin-like molecule-1 (CLL-1) has emerged as a promising therapeutic target in AML. This cell surface receptor is highly expressed on AML blasts and demonstrates stable expression throughout disease progression. CLL-1's consistent presence makes it an ideal candidate for monitoring minimal residual disease (MRD), which is a critical indicator for predicting relapse. Beyond its utility as a diagnostic marker, CLL-1 offers exciting potential in the development of immunotherapies. Emerging strategies, such as CAR-T-cell therapy and antibody-drug conjugates (ADCs), are being investigated to leverage the immune system against CLL-1-expressing AML cells. This review examines the structure, function, and expression patterns of CLL-1 in AML and other hematologic malignancies, providing insights into its role in disease pathogenesis and treatment potential. Exploring CLL-1 as a target for diagnosis, MRD monitoring, and immunotherapy opens new avenues for AML treatment. A deeper understanding of its relationship with AML pathogenesis will aid in the development of targeted therapies, offering hope for improved patient outcomes in the future.

Cell Marker Accordion: interpretable single-cell and spatial omics annotation in health and disease

Single-cell technologies offer a unique opportunity to explore cellular heterogeneity in health and disease. However, reliable identification of cell types and states represents a bottleneck. Available databases and analysis tools employ dissimilar markers, leading to inconsistent annotations and poor interpretability. Furthermore, current tools focus mostly on physiological cell types, limiting their applicability to disease. We developed the Cell Marker Accordion, a user-friendly platform providing automatic annotation and unmatched biological interpretation of single-cell populations, based on consistency weighted markers. We validated our approach on multiple single-cell and spatial datasets from different human and murine tissues, improving annotation accuracy in all cases. Moreover, we show that the Cell Marker Accordion can identify disease-critical cells and pathological processes, extracting potential biomarkers in a wide variety of disease contexts. The breadth of these applications elevates the Cell Marker Accordion as a fast, flexible, faithful and standardized tool to annotate and interpret single-cell and spatial populations in studying physiology and disease.

Bispecific Aptamer-Drug Conjugates Selectively Eliminate Malignant Hematologic Cells for Treating Acute Myeloid Leukemia

Surface antigen-directed immunotherapy is a curative treatment modality for acute myeloid leukemia (AML) that is characterized by the abundance and stability expression of surface antigens. However, current surface antigen-directed immunotherapies have shown poor outcomes and undesirable mortality rates in treating AML patients, primarily due to acquired resistance that arises from using single-target therapies to address the heterogeneous expression of surface antigens. Hence, in order to improve the efficacy of antigen-specific therapies for treating AML, we designed a bispecific aptamer-drug conjugate. In particular, cell-SELEX incorporating cell lysate-SELEX for aptamers with HEL cells yielded AptCD117, which specifically binds to CD117 (a highly expressed marker on both hematopoietic stem cells and primary AML cells) and has excellent performance in targeting human AML cells. Combined with CD71-binding aptamer LXD-11b (another broadly expressed surface antigen on leukemia cells), bispecific aptamers were designed to couple with monomethyl auristatin F (MMAF) for fabricating aptamer-drug conjugates. Results demonstrated that bispecific aptamer-MMAF conjugates efficiently kill different CD117 and CD71 expression levels of target AML cell lines in vitro. Importantly, the exposure of AML marrow specimens to bispecific aptamer-MMAF conjugates resulted in the selective elimination of primary AML cells in vitro and had no effect on healthy lymphocytes within the same specimens. Thus, these results provide a proof of concept for the generation of bispecific aptamer-drug conjugates directed against human AML cells, which hold the promise of advancing treatment strategies and improving AML patient outcomes.

Concurrent inhibition of p300/CBP and FLT3 enhances cytotoxicity and overcomes resistance in acute myeloid leukemia

FMS-like tyrosine kinase-3 (FLT3), a class 3 receptor tyrosine kinase, can be activated by mutations of internal tandem duplication (FLT3-ITD) or point mutations in the tyrosine kinase domain (FLT3-TKD), leading to constitutive activation of downstream signaling cascades, including the JAK/STAT5, PI3K/AKT/mTOR and RAS/MAPK pathways, which promote the progression of leukemic cells. Despite the initial promise of FLT3 inhibitors, the discouraging outcomes in the treatment of FLT3-ITD-positive acute myeloid leukemia (AML) promote the pursuit of more potent and enduring therapeutic approaches. The histone acetyltransferase complex comprising the E1A binding protein P300 and its paralog CREB-binding protein (p300/CBP) is a promising therapeutic target, but the development of effective p300/CBP inhibitors faces challenges due to inherent resistance and low efficacy, often exacerbated by the absence of reliable clinical biomarkers for patient stratification. In this study we investigated the role of p300/CBP in FLT3-ITD AML and evaluated the therapeutic potential of targeting p300/CBP alone or in combination with FLT3 inhibitors. We showed that high expression of p300 was significantly associated with poor prognosis in AML patients and positively correlated with FLT3 expression. We unveiled that the p300/CBP inhibitors A485 or CCS1477 dose-dependently downregulated FLT3 transcription via abrogation of histone acetylation in FLT3-ITD AML cells; in contrast, the FLT3 inhibitor quizartinib reduced the level of H3K27Ac. Concurrent inhibition of p300/CBP and FLT3 enhanced the suppression of FLT3 signaling and H3K27 acetylation, concomitantly reducing the phosphorylation of STAT5, AKT, ERK and the expression of c-Myc, thereby leading to synergistic antileukemic effects both in vitro and in vivo. Moreover, we found that p300/CBP-associated transcripts were highly expressed in quizartinib-resistant AML cells with FLT3-TKD mutation. Targeting p300/CBP with A485 or CCS1477 retained the efficacy of quizartinib, suggesting marked synergy when combined with p300/CBP inhibitors in quizartinib-resistant AML models, as well as primary FLT3-ITD+ AML samples. These results demonstrate a potential therapeutic strategy of combining p300/CBP and FLT3 inhibitors to treat FLT3-ITD and FLT3-TKD AML.

Effective eradication of acute myeloid leukemia stem cells with FLT3-directed antibody-drug conjugates

Refractory disease and relapse are major challenges in acute myeloid leukemia (AML) therapy attributed to survival of leukemic stem cells (LSC). To target LSCs, antibody-drug conjugates (ADCs) provide an elegant solution, combining the specificity of antibodies with highly potent payloads. We aimed to investigate if FLT3-20D9h3-ADCs delivering either the DNA-alkylator duocarmycin (DUBA) or the microtubule-toxin monomethyl auristatin F (MMAF) can eradicate quiescent LSCs. We show here that DUBA more potently kills cell-cycle arrested AML cells compared to microtubule-targeting auristatins. Due to limited stability of 20D9h3-DUBA ADC in vivo, we analyzed both ADCs in advanced in vitro stem cell assays. 20D9h3-DUBA successfully eliminated leukemic progenitors in vitro in colony-forming unit and long-term culture initiating cell assays, both in patient cells and in patient-derived xenograft (PDX) cells. Further, it completely prevented engraftment of AML PDX leukemia-initiating cells in NSG mice. 20D9h3-MMAF had a similar effect in engraftment assays, but a less prominent effect in colony assays. Both ADCs did not affect healthy stem and progenitor cells at comparable doses providing the rationale for FLT3 as therapeutic LSC target. Collectively, we show that FLT3-directed ADCs with DUBA or MMAF have potent activity against AML LSCs and represent promising candidates for further clinical development.

Inhibition of TOX exerts anti-tumor effects in acute myeloid leukemia by upregulating IRF7 expression

Thymocyte selection-associated high mobility group box protein (TOX) is regarded as a crucial transcription factor involved in T cell exhaustion in acute myeloid leukemia (AML). Previous studies have identified aberrant TOX expression as a major oncogenic driver in hematologic malignancies, indicating that TOX may potentially be both an immune biomarker and an immunotherapy target. However, due to heterogeneity in the distribution patterns of TOX and its correlation with clinical prognosis, the mechanism underlying TOX-mediated tumor immune responses remains unclear. In this study, we demonstrate that high TOX expression in AML patients is associated with poor prognosis, and TOX overexpression promotes AML cell proliferation and restricts apoptosis. In vitro TOX inhibition promoted the apoptosis of AML cells, suppressed cell viability, and induced cell cycle arrest in the G0/G1 phase. Moreover, TOX knockdown could reduce tumor burden in vivo in immunodeficient mice and prolong their survival. Furthermore, the anti-AML effects of inhibiting TOX may act through activation of the IFN-α signal pathway and upregulating IRF7 expression. In summary, we report for the first time that TOX knockdown exerts powerful anti-tumor effects in AML. These findings will provide a theoretical basis for targeted therapy in AML patients.

Cancer immune evasion, immunoediting and intratumour heterogeneity

Cancers can avoid immune-mediated elimination by acquiring traits that disrupt antitumour immunity. These mechanisms of immune evasion are selected and reinforced during tumour evolution under immune pressure. Some immunogenic subclones are effectively eliminated by antitumour T cell responses (a process known as immunoediting), which results in a clonally selected tumour. Other cancer cells arise to resist immunoediting, which leads to a tumour that includes several distinct cancer cell populations (referred to as intratumour heterogeneity (ITH)). Tumours with high ITH are associated with poor patient outcomes and a lack of responsiveness to immune checkpoint blockade therapy. In this Review, we discuss the different ways that cancer cells evade the immune system and how these mechanisms impact immunoediting and tumour evolution. We also describe how subclonal antigen presentation in tumours with high ITH can result in immune evasion.

Acute myeloid leukemia stem cell signature gene EMP1 is not an eligible therapeutic target

BACKGROUND

Relapse in pediatric acute myeloid leukemia (pedAML) patients is known to be associated with residual leukemic stem cells (LSC). We have previously shown that epithelial membrane protein 1 (EMP1) is significantly overexpressed in LSC compared to hematological stem cell fractions. EMP1 was also documented as part of the 17-gene stemness score and a 6-membrane protein gene score, both correlating high EMP1 expression with worse overall survival. However, its potential as a therapeutic target in pedAML is still unexplored.

METHODS

Association analyses of EMP1 expression with clinical and molecular AML characteristics were performed. Expression of EMP1 was evaluated in pedAML and cord blood samples. Expression in normal blood cells and tissues was evaluated by flow cytometry and immunohistochemistry, respectively.

RESULTS

In silico analyses showed variable mRNA expression of EMP1 in multiple pedAML datasets, and a significant correlation between high EMP1 transcript levels and the presence of inv(16). Flow cytometry showed overexpression of EMP1 in pedAML samples, as well as expression in normal blood subsets. Importantly, immunohistochemistry revealed EMP1 expression in multiple normal tissues.

CONCLUSION

Although EMP1 presents as an interesting membrane-associated target in pedAML, its abundant expression in normal blood cells and tissues will impede it from further exploration as a therapeutic target.

IMPACT

EMP1 is highly expressed in multiple cancer types, but expression in acute myeloid leukemia (AML) and normal tissues is unexplored. As EMP1 is investigated in other cancer types, expression in normal tissues and blood cells is relevant in predicting the success of EMP1-targeted therapies. In this study, we showed expression of EMP1 in multiple tissues, predicting high on-target off-tumor toxicity, which will warn other researchers of possible toxicities when generating EMP1-targeted therapy. Finally, we showed that high EMP1 expression is associated with better overall survival of pediatric AML patients, reducing the need for EMP1-targeted therapy.

The AXL inhibitor bemcentinib overcomes microenvironment-mediated resistance to pioglitazone in acute myeloid leukemia

Prognosis of acute myeloid leukemia (AML) remains poor especially in older patients who are ineligible for standard chemotherapy or have refractory disease. Here, we study the potential of Peroxisome Proliferator-Activated Receptor (PPAR)-γ agonist pioglitazone to improve the treatment of AML. We show that pioglitazone exerts an anti-proliferative and anti-clonogenic effect on AML cell lines KG-1a, MOLM-14 and OCI-AML3 and on primary cultures from AML patients. However, co-culture of AML cells with stromal cells mimicking the bone marrow microenvironment counteracts this effect, suggesting the existence of a stroma-mediated resistance mechanism to pioglitazone. We show that pioglitazone treatment upregulates the receptor AXL in AML cells at the mRNA and protein level, allowing AXL to be phosphorylated by its ligand Gas6, which is secreted by the stroma. Addition of exogenous Gas6 or stromal cell conditioned medium also abolishes the anti-proliferative effect of pioglitazone, with an increase in AXL phosphorylation observed in both conditions. Co-incubation with the AXL inhibitor bemcentinib restored the anti-leukemic activity of pioglitazone in the presence of stromal cells by reducing AXL phosphorylation to its baseline level. We also confirm that this resistance mechanism is PPAR-γ-dependent as stromal cells invalidated for PPAR-γ are unable to inhibit the antileukemic effect of pioglitazone. Altogether, we suggest that pioglitazone treatment exerts an anti-leukemic effect but concomitantly triggers a stroma-mediated resistance mechanism involving the Gas6/AXL axis. We demonstrate that a combination of pioglitazone with an AXL inhibitor overcomes this mechanism in primary cultures and AML cell lines and exerts potent anti-leukemic activity requiring further evaluation in vivo through murine xenograft pre-clinical models.

Analysis of synthetic polymer hydrogel-based generation of leukemia stem cells

Leukemia stem cells (LSCs), capable of simultaneous self-renewal and differentiation, are resistant to chemotherapy and the cause of relapse in refractory cases of leukemia. As a method to rapidly generate LSCs has not been established, research on LSCs as therapeutic targets has been hampered. Here, we demonstrate that K562 leukemia cells acquired LSC properties with increase in stemness markers such as CD34, Oct3/4, and Nanog and metabolic alterations towards OXPHOS by culturing cells on synthetic polymer hydrogels. In this hydrogel-generated LSCs, single-cell RNA sequencing identified the increase in expression levels of AKR1B1 and TSPYL5, which play an essential role for stemness generation. Decrease in expression of CD34, Oct3/4, and Nanog were observed in K562 cells with knockdown of AKR1B1 and TSPYL5. These results indicate that cell culturing on synthetic polymer hydrogels can be a useful system to generate LSCs and AKR1B1 and TSPYL5 may become therapeutic targets for LSCs.

Radioimmunotherapy of acute myeloid leukemia: a critical assessment of its prospects and limitations

INTRODUCTION

Leukemic stem cells (LSC) are the source of relapse in acute myeloid leukemia (AML). Thus, eliminating LSC is one of the overarching goals of AML research. Radioimmunotherapy is an immunotherapeutic approach which utilizes radioactive isotopes as effector molecules based on the proven ability of ionizing radiation (IR) to kill LSC.It has the potential to eliminate target-antigen negative LSC.

AREAS COVERED

LSC biology, radiobiological principles of RIT, an overview of published and unpublished clinical results of RIT in AML. Issues of practical implementation of RIT in clinical trials.

EXPERT OPINION

RIT for AML isat a critical juncture. Its ability to target antigen negative LSC gives it an advantage compared with other forms of immunotherapy. In order to compete with other forms of targeted therapy the procedure has to be simplified.

Flow cytometry in acute myeloid leukemia and detection of minimal residual disease

Acute myeloid leukemia (AML) is a common type of acute leukemia (AL), belonging to malignant tumors of the hematopoietic system with the characteristics of rapid disease development, control with extreme difficulties, easy recurrence, poor prognosis, and incidence rate increasing with age. The traditionally diagnostic standard of French American British (FAB), being based on the morphological examination with high human subjectivity, can no longer meet the demand of clinical diagnosis and treatment of AML. Requirements of objective accuracy and low-dose sample, have become the indispensable method for AML diagnosis and monitoring prognosis. Flow cytometry is a modern technology that can quickly and accurately detect the series, antigen distribution, differentiation stage of AML cells, minimal residual lesions after AML therapy, so as to provide the great significance in guiding clinical diagnosis, hierarchical treatment, and prognosis judgement. This article will systematically elaborate on the application of flow cytometry in the diagnosis and classification of AML, and the detection of minimal residual lesions, thereby providing reference significance for dynamic monitoring and prognostic observation of AML with different immune subtypes of FAB.

Engineering and characterization of Hu3A4: A novel humanized antibody with potential as a therapeutic agent against myeloid lineage leukemias

Leukemia stem cells (LSCs) play a critical role in the initiation, recurrence, and resistance to treatment of leukemia. Eradicating LSCs is crucial for the complete elimination of the disease. CD45RA is identified as an important marker for LSC subsets in acute myeloid leukemia (AML), providing a strategic target for therapy. In this report, we introduce Hu3A4, an innovative humanized CD45RA antibody devised to target LSCs expressing this antigen. Hu3A4 retains the antigen-recognition ability of its parental antibody while removing sequences from the variable region that could elicit human anti-mouse immune reactions. The modified variable regions of the heavy and light chains were intricately fused with the constant regions of human IgG1 heavy and light chains, respectively, producing a humanized antibody that emulates the structure of natural IgG. Hu3A4 was produced through recombinant expression in Chinese Hamster Ovary (CHO) cells, which ensured stable gene integration. In vitro tests revealed that Hu3A4 could effectively target and lyse the cells. Further, in vivo studies highlighted Hu3A4's substantial anti-leukemic activity, significantly prolonging survival times in treated animal models compared to controls (P < 0.01). To summarize, Hu3A4 exhibits remarkable bioactivity and offers a promising therapeutic potential for the treatment of leukemia patients. Progressing Hu3A4 through additional preclinical and clinical studies is crucial to validate its efficacy as a therapeutic agent for leukemia.

CEBPA repression by MECOM blocks differentiation to drive aggressive leukemias

Acute myeloid leukemias (AMLs) have an overall poor prognosis with many high-risk cases co-opting stem cell gene regulatory programs, yet the mechanisms through which this occurs remain poorly understood. Increased expression of the stem cell transcription factor, MECOM, underlies one key driver mechanism in largely incurable AMLs. How MECOM results in such aggressive AML phenotypes remains unknown. To address existing experimental limitations, we engineered and applied targeted protein degradation with functional genomic readouts to demonstrate that MECOM promotes malignant stem cell-like states by directly repressing pro-differentiation gene regulatory programs. Remarkably and unexpectedly, a single node in this network, a MECOM-bound cis-regulatory element located 42 kb downstream of the myeloid differentiation regulator CEBPA, is both necessary and sufficient for maintaining MECOM-driven leukemias. Importantly, targeted activation of this regulatory element promotes differentiation of these aggressive AMLs and reduces leukemia burden in vivo, suggesting a broadly applicable differentiation-based approach for improving therapy.

TIM-3 marks measurable residual leukemic stem cells responsible for relapse after allogeneic stem cell transplantation

In this study, we investigated the measurable residual leukemic stem cell (MR-LSC) population after allogeneic stem cell transplantation (allo-SCT) for high-risk acute myeloid leukemia (AML), utilizing T-cell immunoglobulin mucin-3 (TIM-3) expression as a functional marker of AML leukemic stem cells (LSCs). Analysis of the CD34+CD38- fraction of bone marrow cells immediately after achievement of engraftment revealed the presence of both TIM-3+LSCs and TIM-3- donor hematopoietic stem cells (HSCs) at varying ratios. Genetic analysis confirmed that TIM-3+ cells harbored patient-specific mutations identical to those found in AML clones, whereas TIM-3- cells did not, indicating that TIM-3+CD34+CD38- cells represent residual AML LSCs. In 92 allo-SCT occasions involving 83 AML patients, we enumerated the frequencies of TIM-3+LSCs immediately after achieving hematologic complete remission with complete donor cell chimerism. Notably, only 22.2% of patients who achieved a TIM-3+MR-LSClow status (<60%) experienced relapse, with a median event-free survival (EFS) of 1581 days (median follow-up duration was 2177 days among event-free survivors). Conversely, 87.5% of patients with TIM-3+MR-LSCint/high (≥60%) relapsed, with a median EFS of 140.5 days. Furthermore, MR-LSC status emerged as a significant independent risk factor for relapse (hazard ratio, 8.56; p < 0.0001), surpassing the impact of patient disease status prior to allo-SCT, including failure to achieve complete remission (hazard ratio, 1.98; p = 0.048). These findings suggest that evaluating TIM-3+ MR-LSCs immediately after engraftment, which reflects the competitive reconstitution of residual TIM-3+ LSCs and donor HSCs, may be valuable for predicting outcomes in AML patients undergoing allo-SCT.

The epigenetic role of EZH2 in acute myeloid leukemia

Acute myeloid leukemia (AML), a malignant disease of the bone marrow, is characterized by the clonal expansion of myeloid progenitor cells and a block in differentiation. The high heterogeneity of AML significantly impedes the development of effective treatment strategies. Enhancer of zeste homolog 2 (EZH2), the catalytic subunit of the polycomb repressive complex 2 (PRC2), regulates the expression of downstream target genes through the trimethylation of lysine 27 on histone 3 (H3K27me3). Increasing evidence suggests that the dysregulation of EZH2 expression in various cancers is closely associated with tumorigenesis. In the review, we examine the role of EZH2 in AML, highlighting its crucial involvement in regulating stemness, proliferation, differentiation, immune response, drug resistance and recurrence. Furthermore, we summarize the application of EZH2 inhibitors in AML treatment and discuss their potential in combination with other therapeutic modalities. Therefore, targeting EZH2 may represent a novel and promising strategy for the treatment of AML.

Selective translation of nuclear mitochondrial respiratory proteins reprograms succinate metabolism in AML development and chemoresistance

Mitochondrial adaptations dynamically reprogram cellular bioenergetics and metabolism and confer key properties for human cancers. However, the selective regulation of these mitochondrial responses remains largely elusive. Here, inspired by a genetic screening in acute myeloid leukemia (AML), we identify RAS effector RREB1 as a translational regulator and uncover a unique translation control system for nuclear-encoded mitochondrial proteins in human cancers. RREB1 deletion reduces mitochondrial activities and succinate metabolism, thereby damaging leukemia stem cell (LSC) function and AML development. Replenishing complex II subunit SDHD rectifies these deficiencies. Notably, inhibition of complex II re-sensitizes AML cells to venetoclax treatment. Mechanistically, a short RREB1 variant binds to a conserved motif in the 3' UTRs and cooperates with elongation factor eEF1A1 to enhance protein translation of nuclear-encoded mitochondrial mRNAs. Overall, our findings reveal a unique translation control mechanism for mitochondrial adaptations in AML pathogenesis and provide a potential strategy for targeting this vulnerability of LSCs.

Integrin-α9 overexpression underlies the niche-independent maintenance of leukemia stem cells in acute myeloid leukemia

Leukemia stem cells (LSCs) are widely believed to reside in well-characterized bone marrow (BM) niches; however, the capacity of the BM niches to accommodate LSCs is insufficient, and a significant proportion of LSCs are instead maintained in regions outside the BM. The molecular basis for this niche-independent behavior of LSCs remains elusive. Here, we show that integrin-α9 overexpression (ITGA9 OE) plays a pivotal role in the extramedullary maintenance of LSCs by molecularly mimicking the niche-interacting status, through the binding with its soluble ligand, osteopontin (OPN). Retroviral insertional mutagenesis conducted on leukemia-prone Runx-deficient mice identified Itga9 OE as a novel leukemogenic event. Itga9 OE activates Akt and p38MAPK signaling pathways. The elevated Myc expression subsequently enhances ribosomal biogenesis to overcome the cell integrity defect caused by the preexisting Runx alteration. The Itga9-Myc axis, originally discovered in mice, was further confirmed in multiple human acute myeloid leukemia (AML) subtypes, other than RUNX leukemias. In addition, ITGA9 was shown to be a functional LSC marker of the best prognostic value among 14 known LSC markers tested. Notably, the binding of ITGA9 with soluble OPN, a known negative regulator against HSC activation, induced LSC dormancy, while the disruption of ITGA9-soluble OPN interaction caused rapid cell propagation. These findings suggest that the ITGA9 OE increases both actively proliferating leukemia cells and dormant LSCs in a well-balanced manner, thereby maintaining LSCs. The ITGA9 OE would serve as a novel therapeutic target in AML.

Identification of PANoptosis-based signature for predicting the prognosis and immunotherapy response in AML

Background

In recent years, the incidence of acute myeloid leukemia (AML) has increased rapidly with a suboptimal prognosis. In AML, cell death is independent of tumorigenesis, tumor invasion, and drug resistance. PANoptosis is a newly discovered form of cell death that combines pyroptosis, apoptosis, and necroptosis. However, no studies have explored the role of PANoptosis-based signatures in AML.

Methods

We screened for PANoptosis-related genes and established a PANoptosis-risk signature using the least absolute shrinkage and selection operator (LASSO) and Cox regression analysis. We combined TCGA, bulk RNA sequencing, and single-cell sequencing to investigate the correlation between candidate genes and the AML tumor microenvironment.

Results

The PANoptosis risk signature effectively predicted prognosis with good sensitivity and specificity. The risk score emerged as an independent prognostic factor. Functional enrichment analysis of PANoptosis-related differentially expressed genes suggested that the risk score may be related to cell immunity. Patients with high-risk scores exhibited increased immune cell infiltration, implying a hot tumor immune microenvironment. The risk score was positively correlated with the immune scores and expression levels of immune checkpoints. Therefore, we identified three model factors, BIRC3, PELI1, and PRKACG, as predictors for immunotherapy efficacy. Single-cell sequencing analysis demonstrated that PELI1 and BIRC3 may participate in the regulation of the AML immune microenvironment. Finally, we performed a drug sensitivity analysis to target BIRC3 and PELI1 using molecular docking and molecular dynamics simulations.

Conclusion

Our study established and verified a PANoptosis risk signature to predict the survival and immunological treatment response in AML.

Deciphering cell states and the cellular ecosystem to improve risk stratification in acute myeloid leukemia

Acute myeloid leukemia (AML) demonstrates significant cellular heterogeneity in both leukemic and immune cells, providing valuable insights into clinical outcomes. Here, we constructed an AML single-cell transcriptome atlas and proposed sciNMF workflow to systematically dissect underlying cellular heterogeneity. Notably, sciNMF identified 26 leukemic and immune cell states that linked to clinical variables, mutations, and prognosis. By examining the co-existence patterns among these cell states, we highlighted a unique AML cellular ecosystem (ACE) that signifies aberrant tumor milieu and poor survival, which is confirmed by public RNA-seq cohorts. We further developed the ACE signature (ACEsig), comprising 12 genes, which accurately predicts AML prognosis, and outperforms existing signatures. When applied to cytogenetically normal AML or intensively treated patients, the ACEsig continues to demonstrate strong performance. Our results demonstrate that large-scale systematic characterization of cellular heterogeneity has the potential to enhance our understanding of AML heterogeneity and contribute to more precise risk stratification strategy.

Senescent T Cells: The Silent Culprit in Acute Myeloid Leukemia Progression?

Malignant tumors can evade immune surveillance and elimination through multiple mechanisms, with the induction of immune cell dysfunction serving as a crucial strategy. Mounting evidence indicates that T cell senescence constitutes the primary mechanism underlying T cell dysfunction in acute myeloid leukemia (AML) and represents one of the potential causes of immunotherapy failure. AML usually progresses rapidly and is highly susceptible to drug resistance, thereby resulting in recurrence and patient mortality. Hence, disrupting the immune interface within the bone marrow microenvironment of AML has emerged as a critical objective for synergistically enhancing tumor immunotherapy. In this review, we summarize the general characteristics, distinctive phenotypes, and regulatory signaling networks of senescent T cells and highlight their potential clinical significance in the bone marrow microenvironment of AML. Additionally, we discuss potential therapeutic strategies for alleviating and reversing T cell senescence.

Targeting autophagy: polydatin's role in inducing cell death in AML

Acute myeloid leukemia (AML), a malignant disorder of the hematopoietic system, arises from leukemic stem cells (LSCs) and is the most prevalent form of blood cancer in adults. This study aimed to evaluate the therapeutic potential of polydatin (PD) in AML through ex vivo and in vivo studies, respectively. This study was prompted by PD's novel role in enhancing tumor apoptosis and modulating autophagy. In vitro studies were conducted using the PD-responsive AML cell line KASUMI-1 and found that PD was able to suppress cell proliferation and induce apoptosis by regulating the autophagy pathway. Subsequently, molecular docking was employed to predict the interaction between PD and Autophagy-related protein 5 (ATG5), a key regulator in the autophagy pathway. It was observed that PD inhibited the ubiquitination of ATG5 and enhanced its protein stability, leading to an increase in ATG5 protein levels and subsequent activation of the autophagy pathway (see in Abstract Graphed). The effectiveness and safety of PD in treating AML were confirmed through in vivo experiments using a mouse transplant tumor model, yielding definitive results. Collectively, these results suggest that PD is a promising candidate for the early therapeutic intervention of AML, with a strong potential for clinical application.

Outcomes and genetic dynamics of acute myeloid leukemia at first relapse

Patients with relapsed acute myeloid leukemia (AML) experience dismal outcomes. We performed a comprehensive analysis of patients with relapsed AML to determine the genetic dynamics and factors predicting survival. We analyzed 875 patients with newly diagnosed AML who received intensive treatment or low-intensity treatment. Of these patients, 197 subsequently relapsed. Data were available for 164 of these patients, with a median time from complete remission/complete remission with incomplete blood count recovery to relapse of 6.5 months. Thirty-five of the 164 patients (21%) experienced relapse after allogeneic hematopoietic stem cell transplantation. At relapse, mutations in genes involved in pathway signaling tended to disappear, whereas clonal hematopoiesis-related mutations or TP53 tended to persist. Patients with normal karyotypes tended to acquire cytogenetic abnormalities at relapse. Patients treated intensively had a higher rate of emergence of TP53 mutations (16%), compared to patients given low-intensity treatment (1%, P=0.009). The overall response rates were 38% and 35% for patients treated with salvage intensive treatment or low-intensity treatment, respectively. Seventeen patients (10%) underwent allogeneic stem cell transplantation after salvage therapy. The median overall survival duration after relapse was 5.3 months, with a 1-year overall survival rate of 17.6%. Complex karyotype (hazard ratio [HR]=2.14, P<0.001), a KMT2A rearrangement (HR=3.52, P=0.011), time in remission <12 months (HR=1.71, P=0.011), and an elevated white blood cell count at relapse (HR=2.38, P=0.005) were independent risk factors for overall survival duration. More effective frontline and maintenance therapies are warranted to prevent relapsed AML.

Single-cell transcriptional mapping reveals genetic and non-genetic determinants of aberrant differentiation in AML

In acute myeloid leukemia (AML), genetic mutations distort hematopoietic differentiation, resulting in the accumulation of leukemic blasts. Yet, it remains unclear how these mutations intersect with cellular origins and whether they converge upon similar differentiation patterns. Single-cell RNA sequencing (scRNA-seq) has enabled high-resolution mapping of the relationship between leukemia and normal cell states, yet this application is hampered by imprecise reference maps of normal hematopoiesis and small sample sizes among patient cohorts. As a first step we constructed a reference atlas of human bone marrow hematopoiesis from 263,519 single-cell transcriptomes spanning 55 cellular states, that was benchmarked against independent datasets of immunophenotypically pure hematopoietic stem and progenitor cells. Using this reference atlas, we mapped over 1.2 million single-cell transcriptomes spanning 318 AML, mixed phenotype acute leukemia (MPAL), and acute erythroid leukemia (AEL) samples. This large-scale analysis, together with systematic mapping of genotype-to-phenotype associations between driver mutations and differentiation landscapes, revealed convergence of diverse genetic alterations on twelve recurrent patterns of aberrant differentiation in AML. This included unconventional lymphoid and erythroid priming linked to RUNX1 and TP53 mutations, respectively. We also identified non-genetic determinants of AML differentiation such as two subgroups of KMT2A-rearranged AML that differ in the identity of their leukemic stem cells (LSCs), likely reflecting distinct cellular origins. Furthermore, distinct LSC-driven hierarchies can co-exist within individual patients, providing insights into AML evolution. Together, precise mapping of normal and malignant cell states provides a framework for advancing the study and disease classification of hematologic malignancies thereby informing therapy development.

Advances in the pathogenesis of FLT3 -mutated acute myeloid leukemia and targeted treatments

PURPOSE OF REVIEW

FLT3 mutations are among the most common myeloid drivers identified in adult acute myeloid leukemia (AML). Their identification is crucial for the precise risk assessment because of the strong prognostic significance of the most recurrent type of FLT3 alterations, namely internal tandem duplications (ITDs). Recent advances in the pathogenesis and biology of FLT3 -mutated AML have opened an opportunity for development and application of selective inhibition of FLT3 pathway.

RECENT FINDINGS

In the last decade, at least three targeted treatments have been approved by regulatory agencies and several others are currently under investigations. Here, we review the latest advance in the role of FLT3 mutations in AML, providing an outline of the available therapeutic strategies, their mechanisms of actions and of resistance, as well as routes for potential improvement.

SUMMARY

The availability of FLT3 inhibitors has improved outcomes in AML harboring such mutations, currently also reflected in disease stratification and recommendations. Newer inhibitors are under investigations, and combinations with chemotherapy or other targeted treatments are being explored to further improve disease outcomes.

Single-cell landscape of innate and acquired drug resistance in acute myeloid leukemia

Deep single-cell multi-omic profiling offers a promising approach to understand and overcome drug resistance in relapsed or refractory (rr) acute myeloid leukemia (AML). Here, we combine single-cell ex vivo drug profiling (pharmacoscopy) with single-cell and bulk DNA, RNA, and protein analyses, alongside clinical data from 21 rrAML patients. Unsupervised data integration reveals reduced ex vivo response to the Bcl-2 inhibitor venetoclax (VEN) in patients treated with both a hypomethylating agent (HMA) and VEN, compared to those pre-exposed to chemotherapy or HMA alone. Integrative analysis identifies both known and unreported mechanisms of innate and treatment-related VEN resistance and suggests alternative treatments, like targeting increased proliferation with the PLK inhibitor volasertib. Additionally, high CD36 expression in VEN-resistant blasts associates with sensitivity to CD36-targeted antibody treatment ex vivo. This study demonstrates how single-cell multi-omic profiling can uncover drug resistance mechanisms and treatment vulnerabilities, providing a valuable resource for future AML research.

Single-cell dissection reveals promotive role of ENO1 in leukemia stem cell self-renewal and chemoresistance in acute myeloid leukemia

BACKGROUND

Quiescent self-renewal of leukemia stem cells (LSCs) and resistance to conventional chemotherapy are the main factors leading to relapse of acute myeloid leukemia (AML). Alpha-enolase (ENO1), a key glycolytic enzyme, has been shown to regulate embryonic stem cell differentiation and promote self-renewal and malignant phenotypes in various cancer stem cells. Here, we sought to test whether and how ENO1 influences LSCs renewal and chemoresistance within the context of AML.

METHODS

We analyzed single-cell RNA sequencing data from bone marrow samples of 8 relapsed/refractory AML patients and 4 healthy controls using bioinformatics and machine learning algorithms. In addition, we compared ENO1 expression levels in the AML cohort with those in 37 control subjects and conducted survival analyses to correlate ENO1 expression with clinical outcomes. Furthermore, we performed functional studies involving ENO1 knockdown and inhibition in AML cell line.

RESULTS

We used machine learning to model and infer malignant cells in AML, finding more primitive malignant cells in the non-response (NR) group. The differentiation capacity of LSCs and progenitor malignant cells exhibited an inverse correlation with glycolysis levels. Trajectory analysis indicated delayed myeloid cell differentiation in NR group, with high ENO1-expressing LSCs at the initial stages of differentiation being preserved post-treatment. Simultaneously, ENO1 and stemness-related genes were upregulated and co-expressed in malignant cells during early differentiation. ENO1 level in our AML cohort was significantly higher than the controls, with higher levels in NR compared to those in complete remission. Knockdown of ENO1 in AML cell line resulted in the activation of LSCs, promoting cell differentiation and apoptosis, and inhibited proliferation. ENO1 inhibitor can impede the proliferation of AML cells. Furthermore, survival analyses associated higher ENO1 expression with poorer outcome in AML patients.

CONCLUSIONS

Our findings underscore the critical role of ENO1 as a plausible driver of LSC self-renewal, a potential target for AML target therapy and a biomarker for AML prognosis.

Design, synthesis, and biological activity evaluation of novel HDAC3 selective inhibitors for combination with Venetoclax against acute myeloid leukemia

Histone deacetylases (HDACs) are highly attractive targets in the drug development process, and the development of subtype-selective HDAC inhibitors is the research direction for HDAC inhibitors. As an important member of the HDAC family, HDAC3 has been found to be closely related to the pathological progression of many diseases due to its abnormal expression. In previous studies, we discovered compound 13a, which has potent inhibitory activity against HDAC1, 2, and 3. In this work, we improved the HDAC3 isotype selectivity of 13a, and obtained compound 9c through rational drug design. 9c shows a selectivity of 71 fold for HDAC3 over HDAC1 and can significantly inhibit the proliferation activity of MV4-11 cells in vitro. Furthermore, when combined with Venetoclax, 9c can effectively induce apoptosis in MV4-11 cells in vitro and reduce the expression of anti-apoptotic proteins, the development of HDAC3 selective inhibitors may serve as a potential lead compound to reverse Venetoclax resistance.

A millifluidic bioreactor allows the long term culture of primary lymphocytes or CD34+ hematopoietic cells while allowing the detection of tumorigenic expansion

Long-term culture of primary lymphocytes and hematopoietic stem and progenitor cells (HSPCs) is pivotal to their expansion and study. Furthermore, genetic engineering of the above-mentioned primary human cells has several safety needs, including the requirement of efficient in vitro assays for unwanted tumorigenic events. In this work, we tested and optimized the Miniaturized Optically Accessible Bioreactor (MOAB) platform. The MOAB consists of a millifluidic cell culture device with three optically-accessible culture chambers. Inside the MOAB, we inserted a silk-based framework that resembles some properties of the bone marrow environment and cultivated in this device either CD4+ T lymphocytes isolated from healthy donor buffy coat or cord blood-derived hematopoietic CD34+ cells. A fraction of these cells is viable for up to 3 months. Next, we tested the capability of the MOAB to detect tumorigenic events. Serial dilutions of engineered fluorescent tumor cells were mixed with either CD4+ or CD34+ primary cells, and their growth was followed. By this approach, we successfully detected as little as 100 tumorigenic cells mixed with 100,000 primary cells. We found that non-tumorigenic primary cells colonized the silk environment, whereas tumor cells, after an adaptation phase, expanded and entered the circulation. We conclude that the millifluidic platform allows the detection of rare tumorigenic events in the long-term culture of human cells.

Finding potential targets in cell-based immunotherapy for handling the challenges of acute myeloid leukemia

Acute myeloid leukemia (AML) is a hostile hematological malignancy under great danger of relapse and poor long-term survival rates, despite recent therapeutic advancements. To deal with this unfulfilled clinical necessity, innovative cell-based immunotherapies have surfaced as promising approaches to improve anti-tumor immunity and enhance patient outcomes. In this comprehensive review, we provide a detailed examination of the latest developments in cell-based immunotherapies for AML, including chimeric antigen receptor (CAR) T-cell therapy, T-cell receptor (TCR)-engineered T-cell therapy, and natural killer (NK) cell-based therapies. We critically evaluate the unique mechanisms of action, current challenges, and evolving strategies to improve the efficacy and safety of these modalities. The review emphasizes how promising these cutting-edge immune-based strategies are in overcoming the inherent complexities and heterogeneity of AML. We discuss the identification of optimal target antigens, the importance of mitigating on-target/off-tumor toxicity, and the need to enhance the persistence and functionality of engineered immune effector cells. All things considered, this review offers a thorough overview of the rapidly evolving field of cell-based immunotherapy for AML, underscoring the significant progress made and the ongoing efforts to translate these innovative approaches into more effective and durable treatments for this devastating disease.

Acute myeloid leukemia cells adhere to bone marrow and acquire chemoresistance by downregulating UNC5B expression

Acute myeloid leukemia (AML) is a malignant tumor of the hematological system. Because of its characteristics of recurrence, refractory and chemoresistance, new therapeutic targets need to be identified. Adhesion and proliferation are characteristics of AML cells, and critical steps in inducing chemotherapy resistance. In this study, we reported that UNC5B inhibits AML cell bone marrow adhesion, inhibits AML cell proliferation and increases sensitivity to chemotherapy. Mechanistically, RNA sequencing (RNA-seq) and experimental results revealed that overexpression of UNC5B inhibits adhesion and proliferation signaling pathways and inhibits the expression of MPZL1, CLDN23, IGF2 and WNT7B. In conclusion, our findings suggest that UNC5B serves as a prognostic indicator and a potential therapeutic target for AML.

BRD4 degraders may effectively counteract therapeutic resistance of leukemic stem cells in AML and ALL

Acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) are life-threatening hematopoietic malignancies characterized by clonal expansion of leukemic blasts in the bone marrow and peripheral blood. The epigenetic reader BRD4 and its downstream effector MYC have recently been identified as potential drug targets in human AML and ALL. We compared anti-leukemic efficacies of the small-molecule BET inhibitor JQ1 and the recently developed BRD4 degraders dBET1 and dBET6 in AML and ALL cells. JQ1, dBET1, and dBET6 were found to suppress growth and viability in all AML and ALL cell lines examined as well as in primary patient-derived AML and ALL cells, including CD34+/CD38- and CD34+/CD38+ leukemic stem and progenitor cells, independent of the type (variant) of leukemia or molecular driver expressed in leukemic cells. Moreover, we found that dBET6 overcomes osteoblast-induced drug resistance in AML and ALL cells, regardless of the type of leukemia or the drug applied. Most promising cooperative or even synergistic drug combination effects were seen with dBET6 and the FLT3 ITD blocker gilteritinib in FLT3 ITD-mutated AML cells, and with dBET6 and the multi-kinase blocker ponatinib in BCR::ABL1+ ALL cells. Finally, all BRD4-targeting drugs suppressed interferon-gamma- and tumor necrosis factor-alpha-induced expression of the resistance-related checkpoint antigen PD-L1 in AML and ALL cells, including LSC. In all assays examined, the BRD4 degrader dBET6 was a superior anti-leukemic drug compared with dBET1 and JQ1. Together, BRD4 degraders may provide enhanced inhibition of multiple mechanisms of therapy resistance in AML and ALL.

Ferroptosis in health and disease

Ferroptosis is a pervasive non-apoptotic form of cell death highly relevant in various degenerative diseases and malignancies. The hallmark of ferroptosis is uncontrolled and overwhelming peroxidation of polyunsaturated fatty acids contained in membrane phospholipids, which eventually leads to rupture of the plasma membrane. Ferroptosis is unique in that it is essentially a spontaneous, uncatalyzed chemical process based on perturbed iron and redox homeostasis contributing to the cell death process, but that it is nonetheless modulated by many metabolic nodes that impinge on the cells' susceptibility to ferroptosis. Among the various nodes affecting ferroptosis sensitivity, several have emerged as promising candidates for pharmacological intervention, rendering ferroptosis-related proteins attractive targets for the treatment of numerous currently incurable diseases. Herein, the current members of a Germany-wide research consortium focusing on ferroptosis research, as well as key external experts in ferroptosis who have made seminal contributions to this rapidly growing and exciting field of research, have gathered to provide a comprehensive, state-of-the-art review on ferroptosis. Specific topics include: basic mechanisms, in vivo relevance, specialized methodologies, chemical and pharmacological tools, and the potential contribution of ferroptosis to disease etiopathology and progression. We hope that this article will not only provide established scientists and newcomers to the field with an overview of the multiple facets of ferroptosis, but also encourage additional efforts to characterize further molecular pathways modulating ferroptosis, with the ultimate goal to develop novel pharmacotherapies to tackle the various diseases associated with - or caused by - ferroptosis.

Enhancing Therapeutic Efficacy of FLT3 Inhibitors with Combination Therapy for Treatment of Acute Myeloid Leukemia

FMS-like tyrosine kinase 3 (FLT3) mutations are genetic changes found in approximately thirty percent of patients with acute myeloid leukemia (AML). FLT3 mutations in AML represent a challenging clinical scenario characterized by a high rate of relapse, even after allogeneic hematopoietic stem cell transplantation (allo-HSCT). The advent of FLT3 tyrosine kinase inhibitors (TKIs), such as midostaurin and gilteritinib, has shown promise in achieving complete remission. However, a substantial proportion of patients still experience relapse following TKI treatment, necessitating innovative therapeutic strategies. This review critically addresses the current landscape of TKI treatments for FLT3+ AML, with a particular focus on gilteritinib. Gilteritinib, a highly selective FLT3 inhibitor, has demonstrated efficacy in targeting the mutant FLT3 receptor, thereby inhibiting aberrant signaling pathways that drive leukemic proliferation. However, monotherapy with TKIs may not be sufficient to eradicate AML blasts. Specifically, we provide evidence for integrating gilteritinib with mammalian targets of rapamycin (mTOR) inhibitors and interleukin-15 (IL-15) complexes. The combination of gilteritinib, mTOR inhibitors, and IL-15 complexes presents a compelling strategy to enhance the eradication of AML blasts and enhance NK cell killing, offering a potential for improved patient outcomes.

IL1RAP-specific T cell engager depletes acute myeloid leukemia stem cells

BACKGROUND

The interleukin-1 receptor accessory protein (IL1RAP) is highly expressed on acute myeloid leukemia (AML) bulk blasts and leukemic stem cells (LSCs), but not on normal hematopoietic stem cells (HSCs), providing an opportunity to target and eliminate the disease, while sparing normal hematopoiesis. Herein, we report the activity of BIF002, a novel anti-IL1RAP/CD3 T cell engager (TCE) in AML.

METHODS

Antibodies to IL1RAP were isolated from CD138+ B cells collected from the immunized mice by optoelectric positioning and single cell sequencing. Individual mouse monoclonal antibodies (mAbs) were produced and characterized, from which we generated BIF002, an anti-human IL1RAP/CD3 TCE using Fab arm exchange. Mutations in human IgG1 Fc were introduced to reduce FcγR binding. The antileukemic activity of BIF002 was characterized in vitro and in vivo using multiple cell lines and patient derived AML samples.

RESULTS

IL1RAP was found to be highly expressed on most human AML cell lines and primary blasts, including CD34+ LSC-enriched subpopulation from patients with both de novo and relapsed/refractory (R/R) leukemia, but not on normal HSCs. In co-culture of T cells from healthy donors and IL1RAPhigh AML cell lines and primary blasts, BIF002 induced dose- and effector-to-target (E:T) ratio-dependent T cell activation and leukemic cell lysis at subnanomolar concentrations. BIF002 administered intravenously along with human T cells led to depletion of leukemic cells, and significantly prolonged survival of IL1RAPhigh MOLM13 or AML patient-derived xenografts with no off-target side effects, compared to controls. Of note, BiF002 effectively redirects T cells to eliminate LSCs, as evidenced by the absence of disease initiation in secondary recipients of bone marrow (BM) from BIF002+T cells-treated donors (median survival not reached; all survived > 200 days) compared with recipients of BM from vehicle- (median survival: 26 days; p = 0.0004) or isotype control antibody+T cells-treated donors (26 days; p = 0.0002).

CONCLUSIONS

The novel anti-IL1RAP/CD3 TCE, BIF002, eradicates LSCs and significantly prolongs survival of AML xenografts, representing a promising, novel treatment for AML.

INA03: A Potent Transferrin-Competitive Antibody-Drug Conjugate against CD71 for Safer Acute Leukemia Treatment

Innovative strategies for enhancing efficacy and overcoming drug resistance in hematologic cancers, such as using antibody-drug conjugates (ADC), have shifted the paradigm of conventional care by delivering promising outcomes in cancer therapies with a significant reduction in the risk of relapse. Transferrin receptor (TfR1), cluster of differentiation 71 (CD71), is known to be overexpressed in malignant cells and considered a potent antitumor target. Therefore, we developed an anti-CD71 ADC, INA03, a humanized antibody conjugated to monomethyl auristatin E through a 3-arylpropiolonitrile-valine-citrulline linker. In this study, we investigated the potency and safety of INA03, in competition with Transferrin (Tf), the CD71's natural ligand, as a novel strategy to specifically target highly proliferative cells. The high expression of CD71 was confirmed on different leukemic cell lines, allowing INA03 to bind efficiently. Subsequently, INA03 rapidly internalizes into lysosomal compartments, in which its cytotoxic drug is released following cathepsin B cleavage. Downregulation of CD71 expression using shRNA highlighted that INA03-induced cell death was dependent on CD71 density at the cell surface. INA03 intravenous treatment in acute leukemia mouse models significantly reduced tumor burden, increased mouse survival, and showed no residual disease compared with conventional chemotherapies. Because INA03 competes with human Tf, a double knock-in (human CD71/human Tf) competent mouse model was generated to mimic human pharmacokinetics and pharmacodynamics. INA03 administration in human CD71/hTf mice did not reveal any improper toxicities, even at high doses. Hence, these data demonstrate the promising preclinical efficacy and safety of INA03 and support its development as a novel acute leukemia treatment. Significance: The Tf receptor is believed to be undruggable because of its ubiquitous expression. By entering into competition with its cognate ligand, the Tf and INA03 ADC can safely achieve potency.

MEG3 in hematologic malignancies: from the role of disease biomarker to therapeutic target

Maternally expressed gene 3 ( MEG3 ) is a noncoding RNA that is known as a tumor suppressor in solid cancers. Recently, a line of studies has emphasized its potential role in hematological malignancies in terms of tumorigenesis, metastasis, and drug resistance. Similar to solid cancers, MEG3 can regulate various cancer hallmarks via sponging miRNA, transcriptional, or posttranslational regulation mechanisms, but may regulate different key elements. In contrast with solid cancers, in some subtypes of leukemia, MEG3 has been found to be upregulated and oncogenic. In this review, we systematically describe the role and underlying mechanisms of MEG3 in multiple types of hematological malignancies. Particularly, we highlight the role of MEG3 in drug resistance and as a novel therapeutic target.

Selective lysis of acute myeloid leukemia cells by CD34/CD3 bispecific antibody through the activation of γδ T-cells

Despite the considerable progress in acute myeloid leukemia (AML) treatment, relapse after allogeneic hematopoietic stem cell transplantation (HSCT) is still frequent and associated with a poor prognosis. Relapse has been shown to be correlated with an incomplete eradication of CD34+ leukemic stem cells prior to HSCT. Previously, we have shown that a novel CD34-directed, bispecific T-cell engager (BTE) can efficiently redirect the T-cell effector function toward cancer cells, thus eliminating leukemic cells in vitro and in vivo. However, its impact on γδ T-cells is still unclear. In this study, we tested the efficacy of the CD34-specific BTE using in vitro expanded γδ T-cells as effectors. We showed that the BTEs bind to γδ T-cells and CD34+ leukemic cell lines and induce target cell killing in a dose-dependent manner. Additionally, γδ T-cell mediated killing was found to be superior to αβ T-cell mediated cytotoxicity. Furthermore, we observed that only in the presence of BTE the γδ T-cells induced primary AML blast killing in vitro. Importantly, our results show that γδ T-cells did not target the healthy CD34intermediate endothelial blood-brain barrier cell line (hCMEC/D3) nor lysed CD34+ HSCs from healthy bone marrow samples.

Anticancer effects of Artemisia campestris extract on acute myeloid leukemia cells: an ex vivo study

Cure rates for acute myeloid leukemia (AML) remain suboptimal; thus, new treatment strategies are needed for this deadly disease. Artemisia campestris leaves hold significant value in traditional medicine. Despite extensive research conducted on this plant globally, the specific anti-AML properties of the leaves have received limited investigation. This study aims to explore the potential anti-leukemic activities of the ethyl acetate extract derived from Artemisia campestris (EAEAC), using mononuclear cells from bone marrow of thirteen AML patients. To this end, cytotoxic effects were evaluated using the MTT assay, and the mechanisms of cell death were investigated through various methods, including propidium iodide staining, annexin V/propidium iodide double staining, mitochondrial depolarization, and caspase-3/7 activation assays. Results demonstrated that EAEAC induced cell apoptosis by increasing DNA fragmentation, causing mitochondrial depolarization, and activating caspases 3/7. On the other hand, we assessed EAEAC's effect on two leukemia stem cell subpopulations, with results suggesting a potential decrease in their frequencies (three/five patients).

Nucleic acid therapeutics as differentiation agents for myeloid leukemias

Differentiation therapy has proven to be a success story for patients with acute promyelocytic leukemia. However, the remaining subtypes of acute myeloid leukemia (AML) are treated with cytotoxic chemotherapies that have limited efficacy and a high likelihood of resistance. As differentiation arrest is a hallmark of AML, there is increased interest in developing differentiation-inducing agents to enhance disease-free survival. Here, we provide a comprehensive review of current reports and future avenues of nucleic acid therapeutics for AML, focusing on the use of targeted nucleic acid drugs to promote differentiation. Specifically, we compare and discuss the precision of small interfering RNA, small activating RNA, antisense oligonucleotides, and aptamers to modulate gene expression patterns that drive leukemic cell differentiation. We delve into preclinical and clinical studies that demonstrate the efficacy of nucleic acid-based differentiation therapies to induce leukemic cell maturation and reduce disease burden. By directly influencing the expression of key genes involved in myeloid maturation, nucleic acid therapeutics hold the potential to induce the differentiation of leukemic cells towards a more mature and less aggressive phenotype. Furthermore, we discuss the most critical challenges associated with developing nucleic acid therapeutics for myeloid malignancies. By introducing the progress in the field and identifying future opportunities, we aim to highlight the power of nucleic acid therapeutics in reshaping the landscape of myeloid leukemia treatment.

The opportunities and challenges of using PD-1/PD-L1 inhibitors for leukemia treatment

Leukemia poses a significant clinical challenge due to its swift onset, rapid progression, and treatment-related complications. Tumor immune evasion, facilitated by immune checkpoints like programmed death receptor 1/programmed death receptor ligand 1 (PD-1/PD-L1), plays a critical role in leukemia pathogenesis and progression. In this review, we summarized the research progress and therapeutic potential of PD-L1 in leukemia, focusing on targeted therapy and immunotherapy. Recent clinical trials have demonstrated promising outcomes with PD-L1 inhibitors, highlighting their role in enhancing treatment efficacy. This review discusses the implications of PD-L1 expression levels on treatment response and long-term survival rates in leukemia patients. Furthermore, we address the challenges and opportunities in immunotherapy, emphasizing the need for personalized approaches and combination therapies to optimize PD-L1 inhibition in leukemia management. Future research prospects include exploring novel treatment strategies and addressing immune-related adverse events to improve clinical outcomes in leukemia. Overall, this review provides valuable insights into the role of PD-L1 in leukemia and its potential as a therapeutic target in the evolving landscape of leukemia treatment.

A 69 long noncoding RNA signature predicts relapse and acts as independent prognostic factor in pediatric AML

ABSTRACT

Risk stratification using genetics and minimal residual disease has allowed for an increase in the cure rates of pediatric acute myeloid leukemia (pedAML) to up to 70% in contemporary protocols. Nevertheless, ∼30% of patients still experience relapse, indicating a need to optimize stratification strategies. Recently, long noncoding RNA (lncRNA) expression has been shown to hold prognostic power in multiple cancer types. Here, we aimed at refining relapse prediction in pedAML using lncRNA expression. We built a relapse-related lncRNA prognostic signature, named AMLlnc69, using 871 transcriptomes of patients with pedAML obtained from the Therapeutically Applicable Research to Generate Effective Treatments repository. We identified a 69 lncRNA signature AMLlnc69 that is highly predictive of relapse risk (c-index = 0.73), with area under the receiver operating characteristic curve (AUC) values for predicting the 1-, 2-, and 3-year relapse-free survival (RFS) of 0.78, 0.77, and 0.77, respectively. The internal validation using a bootstrap method (resampling times = 1000) resulted in a c-index of 0.72 and AUC values for predicting the 1-, 2-, and 3-year RFS of 0.77, 0.76, and 0.76, respectively. Through a Cox regression analysis, AMLlnc69, nucleophosmin mutation, and white blood cell at diagnosis were identified as independent predictors of RFS. Finally, a nomogram was build using these 2 parameters, showing a c-index of 0.80 and 0.71 after bootstrapping (n = 1000). In conclusion, the identified AMLlnc69 will, after prospective validation, add important information to guide the management of patients with pedAML. The nomogram is a promising tool for easy stratification of patients into a novel scheme of relapse-risk groups.

Leukemic Stem Cells and Hematological Malignancies

The association between leukemic stem cells (LSCs) and leukemia development has been widely established in the context of genetic alterations, epigenetic pathways, and signaling pathway regulation. Hematopoietic stem cells are at the top of the bone marrow hierarchy and can self-renew and progressively generate blood and immune cells. The microenvironment, niche cells, and complex signaling pathways that regulate them acquire genetic mutations and epigenetic alterations due to aging, a chronic inflammatory environment, stress, and cancer, resulting in hematopoietic stem cell dysregulation and the production of abnormal blood and immune cells, leading to hematological malignancies and blood cancer. Cells that acquire these mutations grow at a faster rate than other cells and induce clone expansion. Excessive growth leads to the development of blood cancers. Standard therapy targets blast cells, which proliferate rapidly; however, LSCs that can induce disease recurrence remain after treatment, leading to recurrence and poor prognosis. To overcome these limitations, researchers have focused on the characteristics and signaling systems of LSCs and therapies that target them to block LSCs. This review aims to provide a comprehensive understanding of the types of hematopoietic malignancies, the characteristics of leukemic stem cells that cause them, the mechanisms by which these cells acquire chemotherapy resistance, and the therapies targeting these mechanisms.

Traditional Chinese medicine for acute myelocytic leukemia therapy: exploiting epigenetic targets

Acute myeloid leukemia (AML) is a heterogeneous hematological malignancy with historically high mortality rates. The treatment strategies for AML is still internationally based on anthracyclines and cytarabine, which remained unchanged for decades. With the rapid advance on sequencing technology, molecular targets of leukemogenesis and disease progression related to epigenetics are constantly being discovered, which are important for the prognosis and treatment of AML. Traditional Chinese medicine (TCM) is characterized by novel pharmacological mechanisms, low toxicity and limited side effects. Several biologically active ingredients of TCM are effective against AML. This review focuses on bioactive compounds in TCM targeting epigenetic mechanisms to address the complexities and heterogeneity of AML.

Recent Advances in Material Technology for Leukemia Treatments

Leukemia is a widespread hematological malignancy characterized by an elevated white blood cell count in both the blood and the bone marrow. Despite notable advancements in leukemia intervention in the clinic, a large proportion of patients, especially acute leukemia patients, fail to achieve long-term remission or complete remission following treatment. Therefore, leukemia therapy necessitates optimization to meet the treatment requirements. In recent years, a multitude of materials have undergone rigorous study to serve as delivery vectors or direct intervention agents to bolster the effectiveness of leukemia therapy. These materials include liposomes, protein-based materials, polymeric materials, cell-derived materials, and inorganic materials. They possess unique characteristics and are applied in a broad array of therapeutic modalities, including chemotherapy, gene therapy, immunotherapy, radiotherapy, hematopoietic stem cell transplantation, and other evolving treatments. Here, an overview of these materials is presented, describing their physicochemical properties, their role in leukemia treatment, and the challenges they face in the context of clinical translation. This review inspires researchers to further develop various materials that can be used to augment the efficacy of multiple therapeutic modalities for novel applications in leukemia treatment.

Pharmacological p38 MAPK inhibitor SB203580 enhances AML stem cell line KG1a chemosensitivity to daunorubicin by promoting late apoptosis, cell growth arrest in S-phase, and miR-328-3p upregulation

Acute myeloid leukaemia (AML) is characterized by uncontrolled proliferation of myeloid progenitor cells and impaired maturation, leading to immature cell accumulation in the bone marrow and bloodstream, resulting in hematopoietic dysfunction. Chemoresistance, hyperactivity of survival pathways, and miRNA alteration are major factors contributing to treatment failure and poor outcomes in AML patients. This study aimed to investigate the impact of the pharmacological p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 on the chemoresistance potential of AML stem cell line KG1a to the therapeutic drug daunorubicin (DNR). KG1a and chemosensitive leukemic HL60 cells were treated with increasing concentrations of DNR. Cell Titer-Glo®, flow cytometry, phosphokinase and protein arrays, Western blot technology, and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) were employed for assessment of cell viability, half-maximal inhibitory concentration (IC50) determination, apoptotic status detection, cell cycle analysis, apoptosis-related protein and gene expression monitoring. Confocal microscopy was used to visualize caspase and mitochondrial permeability transition pore (mPTP) activities. Exposed at various incubation times, higher DNR IC50 values were determined for KG1a cells than for HL60 cells, confirming KG1a cell chemoresistance potential. Exposed to DNR, late apoptosis induction in KG1a cells was enhanced after SB203580 pretreatment, defined as the combination treatment. This enhancement was confirmed by increased cleavage of poly(ADP-ribose) polymerase, caspase-9, caspase-3, and augmented caspase-3/-7 and mPTP activities in KG1a cells upon combination treatment, compared to DNR. Using phosphokinase and apoptosis protein arrays, the combination treatment decreased survival Akt phosphorylation and anti-apoptotic Bcl-2 expression levels in KG1a cells while increasing the expression levels of the tumor suppressor p53 and cyclin-dependent kinase inhibitor p21, compared to DNR. Cell cycle analysis revealed KG1a cell growth arrest in G2/M-phase caused by DNR, while combined treatment led to cell growth arrest in S-phase, mainly associated with cyclin B1 expression levels. Remarkably, the enhanced KG1a cell sensitivity to DNR after SB203580 pretreatment was associated with an increased upregulation of miR-328-3p and slight downregulation of miR-26b-5p, compared to DNR effect. Altogether, these findings could contribute to the development of a new therapeutic strategy by targeting the p38 MAPK pathway to improve treatment outcomes in patients with refractory or relapsed AML.