Potential targeting of FLT3 acute myeloid leukemia

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.

Combination Therapies in Drug Repurposing: Personalized Approaches to Combatting Leukaemia and Multiple Myeloma

Despite advances in cancer research, treating malignancies remains challenging due to issues like drug resistance, disease heterogeneity, and the limited efficacy of current therapies, particularly in relapsed or refractory cases. In recent years, several drugs originally approved for non-cancer indications have shown potential in cancer treatment, demonstrating anti-proliferative, anti-metastatic, and immunomodulatory effects. Drug repurposing has shown immense promise due to well-established safety profiles and mechanisms of action of the compounds. However, the implementation is fraught with clinical, logistical, regulatory, and ethical challenges, especially in diseases such as leukaemia and multiple myeloma. This chapter examines the treatment challenges in leukaemia and multiple myeloma, focusing on the role of drug repurposing in addressing therapeutic resistance and disease variability. It highlights the potential of personalized, tailored combination therapies, using repurposed drug components, to offer more effective, targeted, and cost-efficient treatment strategies, overcoming resistance and improving patient outcomes.

Investigation into biased signaling, glycosylation, and drug vulnerability of acute myeloid leukemia

Understanding and harnessing biased signaling offers significant potential for developing novel therapeutic strategies or enhancing existing treatments. By managing biased signaling, it is possible to minimize adverse effects, including toxicity, and to optimize therapeutic outcomes by selectively targeting beneficial pathways. In the context of acute myeloid leukemia (AML), a highly aggressive blood cancer characterized by the rapid proliferation of abnormal myeloid cells in the bone marrow and blood, the dysregulation of these signaling pathways, particularly those involving G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs), significantly contributes to disease progression and therapeutic resistance. Traditional therapies for AML often struggle with resistance and toxicity, leading to poor patient outcomes. However, by exploiting the concept of biased signaling, researchers may be able to design drugs that selectively activate pathways that inhibit cancer cell growth while avoiding those that contribute to resistance or toxicity. Glycosylation, a key post-translational modification (PTM), plays a crucial role in biased signaling by altering receptor conformation and ligand-binding affinity, thereby affecting the outcome of biased signaling. Chemokine receptors like CXCR4, which are often overexpressed and heavily glycosylated in AML, serve as targets for therapeutic intervention. By externally inducing or inhibiting specific PTMs, it may be possible to further refine therapeutic strategies, unlocking new possibilities for developing more effective and less toxic treatments. This review highlights the importance of understanding the dynamic relationship between glycosylation and biased signaling in AML, which is essential for the development of more effective treatments and overcoming drug resistance, ultimately leading to better patient outcomes.

Upfront intensive treatment analysis of the Italian Cohort Study on FLT3-mutated AML patients (FLAM): The impact of a FLT3 inhibitor addition to standard chemotherapy in the real-life setting

BACKGROUND

The addition of a FLT3 inhibitor (FLT3i) to standard chemotherapy to treat fit newly diagnosed (ND) patients with FLT3-mutated acute myeloid leukemia (AML) represents the standard of care resulting from clinical trial results. However, evidence regarding FLT3i adoption in routine clinical practice is still scarce.

METHODS

Clinical data are reported from 394 ND patients with FLT3-mutated AML enrolled in the retrospective observational Italian Cohort Study on FLT3-mutated patients with AML and treated with an upfront intensive regimen with (FLT3i group, n = 92) or without (CT group, n = 302) the addition of a FLT3i.

RESULTS

With a median follow-up time of 34.5 months, an effectiveness benefit obtained by FLT3i incorporation both in terms of overall survival (median, 34.9 in the FLT3i vs 12.7 months in the CT group, p < .01) and relapse-free survival (median, 18.9 in the FLT3i vs 7.6 months in the CT group, p = .01) was documented, with a higher composite complete remission rate (75.4% in the FLT3i vs 62.4% in the CT group, p = .052). FLT3i benefit seemed to be independent from the transplant rate.

CONCLUSIONS

In conclusion, the benefit of FLT3i addition to upfront intensive treatment in newly diagnosed FLT3-mutated AML patients was confirmed in a large, real-life cohort study.

Precision Medicine in Myeloid Neoplasia: Challenges and Opportunities

High-risk myeloid neoplasms encompass a group of hematologic malignancies known to cause significant cytopenias, which are accompanied by the risk of end-organ damage. They tend to have an aggressive clinical course and limit life expectancy in the absence of effective treatments. The adoption of precision medicine approaches has been limited by substantive diversity in somatic mutations, limited fraction of patients with targetable genetic lesions, and the prolonged turnaround times of pertinent genetic tests. Efforts to incorporate targeted agents into first-line treatment, rapidly determine pre-treatment molecular or cytogenetic aberrations, and evaluate functional vulnerabilities ex vivo hold promise for advancing the use of precision medicine in these malignancies. Given the relative accessibility of malignant cells from blood and bone marrow, precision medicine strategies hold great potential to shape future standard-of-care approaches to patients with high-risk myeloid malignancies. This review aims to summarize the development of the targeted therapies currently available to treat these blood cancers, most notably acute myeloid leukemia, and also evaluate future opportunities and challenges related to the integration of personalized approaches.

Discovery of SILA-123 as a Highly Potent FLT3 Inhibitor for the Treatment of Acute Myeloid Leukemia with Various FLT3 Mutations

The FLT3-ITD (internal tandem duplication) mutant has been a promising target for acute myeloid leukemia (AML) drug discovery but is now facing the challenge of resistance due to point mutations. Herein, we have discovered a type II FLT3 inhibitor, SILA-123. This inhibitor has shown highly potent inhibitory effects against FLT3-WT (IC50 = 2.1 nM) and FLT3-ITD (IC50 = 1.0 nM), tumor cells with the FLT3-ITD mutant such as MOLM-13 (IC50 = 0.98 nM) and MV4-11 (IC50 = 0.19 nM), as well as BaF3 cells associated with the FLT3-ITD mutant and point mutations like BaF3-FLT3-ITD-G697R (IC50 = 3.0 nM). Moreover, SILA-123 exhibited promising kinome selectivity against 310 kinases (S score (10) = 0.06). In in vivo studies, SILA-123 significantly suppressed the tumor growth in MV4-11 (50 mg/kg/d, TGI = 87.3%) and BaF3-FLT3-ITD-G697R (50 mg/kg/d, TGI = 60.0%) cell-inoculated allograft models. Our data suggested that SILA-123 might be a promising drug candidate for FLT3-ITD-positive AML.

Simultaneous inhibition of FLT3 and HDAC by novel 6-ethylpyrazine-2-Carboxamide derivatives provides therapeutic advantages in acute myelocytic leukemia

Synergetic inhibition of FMS-like tyrosine kinase 3 (FLT3) and histone deacetylase (HDAC) by small molecule chimera presents a promising therapeutic approach for acute myeloid leukemia (AML) with FLT3 mutations. In this study, we first observed that the combined use of FLT3 inhibitor gilteritinib and HDAC inhibitor vorinostat increased the survival rate of leukemia xenograft mouse model. Then, we employed a pharmacophore fusion strategy to develop a novel series of FLT3/HDAC dual inhibitors. Among them, compound 25h demonstrated superior inhibitory activity against both FLT3 and HDAC. In particular, compound 25h exhibited enhanced anti-proliferation activity against MOLM-13 cells in comparison to gilteritinib, vorinostat, and their combination, while maintaining reduced cytotoxicity towards normal cells. Mechanistically, the heightened anti-tumor effect of compound 25h was attributed to its more potent regulation of intracellular pathways, notably phosphorylation of ERK, compared to single drug and combination treatments. Furthermore, compound 25h demonstrated superior anti-tumor efficacy in the MOLM-13 xenograft model compared to combination therapy, along with reduced in vivo toxicity. To conclude, we have identified a novel FLT3/HDAC dual inhibitor that could serve as a potential candidate for the treatment of AML.

The unexpected and unresolved roles of PDGFRA and PDGFRB in T-cell acute lymphoblastic leukemia

Not available.

Tracking Response and Resistance in Acute Myeloid Leukemia through Single-Cell DNA Sequencing Helps Uncover New Therapeutic Targets

Acute myeloid leukemia (AML) is an aggressive hematologic neoplasia with a complex polyclonal architecture. Among driver lesions, those involving the FLT3 gene represent the most frequent mutations identified at diagnosis. The development of tyrosine kinase inhibitors (TKIs) has improved the clinical outcomes of FLT3-mutated patients (Pt). However, overcoming resistance to these drugs remains a challenge. To unravel the molecular mechanisms underlying therapy resistance and clonal selection, we conducted a longitudinal analysis using a single-cell DNA sequencing approach (MissionBioTapestri® platform, San Francisco, CA, USA) in two patients with FLT3-mutated AML. To this end, samples were collected at the time of diagnosis, during TKI therapy, and at relapse or complete remission. For Pt #1, disease resistance was associated with clonal expansion of minor clones, and 2nd line TKI therapy with gilteritinib provided a proliferative advantage to the clones carrying NRAS and KIT mutations, thereby responsible for relapse. In Pt #2, clonal architecture was less complex, and 1st line TKI therapy with midostaurin was able to eradicate the leukemic clones. Our results corroborate previous findings about clonal selection driven by TKIs, highlighting the importance of a deeper characterization of individual clonal architectures for choosing the best treatment plan for personalized approaches aimed at optimizing outcomes.

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.

Phase I Study of GS-3583, an FMS-like Tyrosine Kinase 3 Agonist Fc Fusion Protein, in Patients with Advanced Solid Tumors

PURPOSE

GS-3583, an FMS-like tyrosine kinase 3 (FLT3) agonist Fc fusion protein, expanded conventional dendritic cells (cDC) in the periphery of healthy volunteers, suggesting potential for GS-3583 to increase cDCs in the tumor microenvironment and promote T cell-mediated antitumor activity in cancer patients. This phase Ib open-label study assessed GS-3583 in adults with advanced solid tumors.

PATIENTS AND METHODS

Multiple escalating doses of GS-3583 (standard 3+3 design) were administered intravenously on days 1 and 15 of cycle 1 and day 1 of each subsequent 28-day cycle for up to 52 weeks. Dose-limiting toxicity (DLT) was evaluated during the first 28 days of GS-3583 at each dose level.

RESULTS

Thirteen participants enrolled in four dose-escalation cohorts, after which the study was terminated following safety review. Median (range) age was 71 (44-79), and 7 (54%) participants were male. There were no DLTs. Seven participants had grade ≥3 AEs; 2 participants had grade 5 AEs, including a second primary malignancy (acute myeloid leukemia) considered treatment-related. Dose-dependent increase in GS-3583 serum exposure was observed in the dose range of 2-20 mg with GS-3583 accumulation at higher dose levels. Expansions of cDCs occurred at all four doses with a dose-dependent trend in the durability of the cDC expansion.

CONCLUSIONS

GS-3583 was relatively well tolerated and induced dose-dependent expansion of cDCs in the periphery of patients with advanced solid tumors. However, development of a second primary malignancy provides a cautionary tale for the FLT3 agonist mechanism. See related commentary by Raeder and Drazer, p. 2857.

A phase 1 study of the irreversible FLT3 inhibitor FF-10101 in relapsed or refractory acute myeloid leukemia

ABSTRACT

FLT3 tyrosine kinase inhibitors (TKIs) have clinical efficacy for patients with FLT3-mutated AML (acute myeloid leukemia), but their impact is limited by resistance in the setting of monotherapy and by tolerability problems when used in combination therapies. FF-10101 is a novel compound that covalently binds to a cysteine residue near the active site of FLT3, irreversibly inhibiting receptor signaling. It is effective against most FLT3 activating mutations, and, unlike other inhibitors, is minimally vulnerable to resistance induced by FLT3 ligand. We conducted a phase 1 dose escalation study of oral FF-10101 in patients with relapsed and/or refractory AML, the majority of whom harbored FLT3-activating mutations and/or had prior exposure to FLT3 inhibitors. Fifty-four participants enrolled in cohorts receiving doses ranging from 10 to 225 mg per day and 50 to 100 mg twice daily (BID). The dose limiting toxicities were diarrhea and QT prolongation. Among 40 response-evaluable participants, the composite complete response rate was 10%, and the overall response rate (including partial responses) was 12.5%, including patients who had progressed on gilteritinib. Overall, 56% of participants had prior exposure to FLT3 inhibitors. The recommended phase 2 dose was 75 mg BID. FF-10101 potentially represents a next-generation advance in the management of FLT3-mutated AML. This trial was registered at www.ClinicalTrials.gov as #NCT03194685.

A year in pharmacology: new drugs approved by the US Food and Drug Administration in 2023

With 54 new drugs and seven cellular and gene therapy products, the approvals by the US Food and Drug Administration (FDA) recovered 2023 from the 2022 dent back to the levels of 2020-2021. As in previous years of this annual review, we assign these new drugs to one of three levels of innovation: first drug against a condition ("first-in-indication"), first drug using a novel molecular mechanism ("first-in-class"), and "next-in-class," i.e., a drug using an already exploited molecular mechanism. We identify four (7%) "first-in-indication," 22 (36%) "first-in-class," and 35 (57%) "next-in-class" drugs. By treatment area, rare diseases (54%) and cancer drugs (23%) were once again the most prevalent (and partly overlapping) therapeutic areas. Other continuing trends were the use of accelerated regulatory approval pathways and the reliance on biopharmaceuticals (biologics). 2023 marks the approval of a first therapy based on CRISPR/Cas9 gene editing.

Current knowledge about FLT3 gene mutations, exploring the isoforms, and protein importance in AML

Acute myeloid leukaemia (AML) is a complex haematological malignancy characterised by diverse genetic alterations leading to abnormal proliferation of myeloid precursor cells. One of the most significant genetic alterations in AML involves mutations in the FLT3 gene, which plays a critical role in haematopoiesis and haematopoietic homeostasis. This review explores the current understanding of FLT3 gene mutations and isoforms and the importance of the FLT3 protein in AML. FLT3 mutations, including internal tandem duplications (FLT3-ITD) and point mutations in the tyrosine kinase domain (FLT3-TKD), occur in 25-30% in AML and are associated with poor prognosis. FLT3-ITD mutations lead to constitutive activation of the FLT3 signalling pathway, promoting cell survival and proliferation. FLT3-TKD mutations affect the tyrosine kinase domain and affect AML prognosis in various ways. Furthermore, FLT3 isoforms, including shorter variants, contribute to the complexity of FLT3 biology. Additionally, nonpathological polymorphisms in FLT3 are being explored for their potential impact on AML prognosis and treatment response. This review also discusses the development of molecular treatments targeting FLT3, including first-generation and next-generation tyrosine kinase inhibitors, highlighting the challenges of resistance that often arise during therapy. The final chapter describes FLT3 protein domain rearrangements and their relevance to AML pathogenesis.

Study on tissue distribution, metabolite profiling, and excretion of [14C]-labeled flonoltinib maleate in rats

Flonoltinib Maleate (FM) is a dual-target inhibitor that selectively suppresses Janus kinase 2/FMS-like tyrosine kinase 3 (JAK2/FLT3), which is currently in phase I/IIa clinical trial in China for the treatment of myeloproliferative neoplasms (MPNs). In this research, we used [14C]-labeled FM (14C-FM) to investigate the distribution, metabolism, and excretion of FM in rats using High-Performance Liquid Chromatography coupled with High-Resolution Mass Spectrometry/Radioactivity Monitoring (HPLC-HRMS/RAM) and liquid scintillation counter. The results revealed that FM displayed widespread distribution in rats. Furthermore, FM demonstrated rapid clearance without any observed risk of organ toxicity attributed to accumulation. Profiling of FM metabolites in rat plasma, feces, urine, and bile identified a total of 17 distinct metabolites, comprising 7 phase I metabolites and 10 phase II metabolites. The major metabolic reactions involved oxygenation, dealkylation, methylation, sulfation, glucuronidation and glutathione conjugation. Based on these findings, a putative metabolic pathway of FM in rats was proposed. The overall recovery rate in the excretion experiment ranged from 93.04 % to 94.74 %. The results indicated that FM undergoes extensive hepatic metabolism in SD rats, with the majority being excreted through bile as metabolites and ultimately eliminated via feces. A minor fraction of FM (<10 %) was excreted through renal excretion in the form of urine. Integration of the current results with previous pharmacokinetic investigations of FM in rats and dogs enables a comprehensive elucidation of the in vivo ADME processes and characteristics of FM, thereby establishing a solid foundation for subsequent clinical investigations of FM.

Development of machine learning-based malignant pericardial effusion-related model in breast cancer: Implications for clinical significance, tumor immune and drug-therapy

Background

Malignant pericardial effusion (MPE) is a common complication of advanced breast cancer (BRCA) and plays an important role in BRCA. This study is aims to construct a prognostic model based on MPE-related genes for predicting the prognosis of breast cancer.

Methods

The BRCA samples are analyzed based on the expression of MPE-related genes by using an unsupervised cluster analysis method. This study processes the data by least absolute shrinkage and selection operator and multivariate Cox analysis, and uses machine learning algorithms to construct BRCA prognostic model and develop web tool.

Results

BRCA patients are classified into three clusters and a BRCA prognostic model is constructed containing 9 MPE-related genes. There are significant differences in signature pathways, immune infiltration, immunotherapy response and drug sensitivity testing between the high and low-risk groups. Of note, a web-based tool (http://wys.helyly.top/cox.html) is developed to predict overall survival as well as drug-therapy response of BRCA patients quickly and conveniently, which can provide a basis for clinicians to formulate individualized treatment plans.

Conclusion

The MPE-related prognostic model developed in this study can be used as an effective tool for predicting the prognosis of BRCA and provides new insights for the diagnosis and treatment of BRCA patients.

Design and synthesis 1H-Pyrrolo[2,3-b]pyridine derivatives as FLT3 inhibitors for the treatment of Acute myeloid Leukemia

Acute myeloid leukemia (AML) is the most common type of blood cancer and has been strongly correlated with the overexpression of Fms-like tyrosine kinase 3 (FLT3), a member of the class III receptor tyrosine kinase family. With the emergence of FLT3 internal tandem duplication alteration (ITD) and tyrosine kinase domain (TKD) mutations, the development of FLT3 small molecule inhibitors has become an effective medicinal chemistry strategy for AML. Herein, we have designed and synthesized two series of 1H-pyrrolo[2,3-b]pyridine derivatives CM1-CM24, as FLT3 inhibitors based on F14, which we previously reported, that can target the hydrophobic FLT3 back pocket. Among these derivates, CM5 showed significant inhibition of FLT3 and FLT3-ITD, with inhibitory percentages of 57.72 % and 53.77 % respectively at the concentration of 1 μΜ. Furthermore, CM5 demonstrated potent inhibition against FLT3-dependent human AML cell lines MOLM-13 and MV4-11 (both harboring FLT3-ITD mutant), with IC50 values of 0.75 μM and 0.64 μM respectively. In our cellular mechanistic studies, CM5 also effectively induces apoptosis by arresting cell cycle progression in the G0/G1 phase. In addition, the amide and urea linker function were discussed in detail based on computational simulations studies. CM5 will serve as a novel lead compound for further structural modification and development of FLT3 inhibitors specifically targeting AML with FLT3-ITD mutations.

Acute myeloid leukemia: Current understanding and management

ABSTRACT

Although relatively rare, acute myeloid leukemia (AML) is the most common type of acute leukemia in adults. AML is associated with poor 5-year overall survival and prompt treatment is critical. Classifying AML based on World Health Organization criteria is important for determining prognosis and applying a risk-adapted treatment approach. Throughout therapy, patients require comprehensive supportive care measures with blood product transfusions, antimicrobial treatment, and frequent monitoring for chemotherapy-related complications. This article provides an overview of AML and its treatments. Clinicians in all specialties must be able to recognize the early signs of AML and ensure their patients seek appropriate expert medical care with a hematologist/oncologist.

The Clinical Utility of FLT3 Mutation Testing in Acute Leukemia: A Canadian Consensus

FMS-like tyrosine kinase 3 (FLT3) mutations are detected in approximately 20-30% of patients with acute myeloid leukemia (AML), with the presence of a FLT3 internal tandem duplication (FLT3-ITD) mutation being associated with an inferior outcome. Assessment of FLT3 mutational status is now essential to define optimal upfront treatment in both newly diagnosed and relapsed AML, to support post-induction allogeneic hematopoietic stem cell transplantation (alloSCT) decision-making, and to evaluate treatment response via measurable (minimal) residual disease (MRD) evaluation. In view of its importance in AML diagnosis and management, the Canadian Leukemia Study Group/Groupe canadien d'étude sur la leucémie (CLSG/GCEL) undertook the development of a consensus statement on the clinical utility of FLT3 mutation testing, as members reported considerable inter-center variability across Canada with respect to testing availability and timing of use, methodology, and interpretation. The CLSG/GCEL panel identified key clinical and hematopathological questions, including: (1) which patients should be tested for FLT3 mutations, and when?; (2) which is the preferred method for FLT3 mutation testing?; (3) what is the clinical relevance of FLT3-ITD size, insertion site, and number of distinct FLT3-ITDs?; (4) is there a role for FLT3 analysis in MRD assessment?; (5) what is the clinical relevance of the FLT3-ITD allelic burden?; and (6) how should results of FLT3 mutation testing be reported? The panel followed an evidence-based approach, taken together with Canadian clinical and laboratory experience and expertise, to create a consensus document to facilitate a more uniform approach to AML diagnosis and treatment across Canada.

A combinatorial therapeutic approach to enhance FLT3-ITD AML treatment

Internal tandem duplication mutations of the FMS-like tyrosine kinase-3 (FLT3-ITDs) occur in 25%-30% of patients with acute myeloid leukemia (AML) and are associated with dismal prognosis. Although FLT3 inhibitors have demonstrated initial clinical efficacy, the overall outcome of patients with FLT3-ITD AML remains poor, highlighting the urgency to develop more effective treatment strategies. In this study, we reveal that FLT3 inhibitors reduced protein stability of the anti-cancer protein p53, resulting in drug resistance. Blocking p53 degradation with proteasome inhibitors restores intracellular p53 protein levels and, in combination with FLT3-ITD inhibitors, shows superior therapeutic effects against FLT3-ITD AML in cells, mouse models, and patients. These data suggest that this combinatorial therapeutic approach may represent a promising strategy to target FLT3-ITD AML.

CPX-351 in FLT3-mutated acute myeloid leukemia

CPX-351, a dual-drug liposomal encapsulation of daunorubicin and cytarabine in a 1:5 molar ratio, is approved for the treatment of newly diagnosed therapy-related acute myeloid leukemia (AML) or AML with myelodysplasia-related changes. In a pivotal phase III trial, CPX-351 significantly improved overall survival compared with standard-of-care 7 + 3 chemotherapy (7 days cytarabine; 3 days daunorubicin) in adults aged 60-75 years with newly diagnosed high-risk or secondary AML (median = 9.56 months vs. 5.95 months; hazard ratio = 0.69; 95% confidence interval = 0.52-0.90; p = 0.003). Approximately 30% of patients with newly diagnosed AML have mutations in the FLT3 gene, which may be associated with poor outcomes. Here, we review the current in vitro, clinical, and real-world evidence on the use of CPX-351 in patients with AML and mutations in FLT3. Additionally, we review preliminary data from clinical trials and patient case reports that suggest the combination of CPX-351 with FLT3 inhibitors may represent another treatment option for patients with FLT3 mutation-positive AML.

Rational discovery of dual FLT3/HDAC inhibitors as a potential AML therapy

Acute myeloid leukemia (AML) patients often experience poor therapeutic outcomes and relapse after treatment with single-target drugs, representing the urgent need of new therapies. Simultaneous inhibition of multiple oncogenic signals is a promising strategy for tumor therapy. Previous studies have reported that concomitant inhibition of Fms-like tyrosine kinase 3 (FLT3) and histone deacetylases (HDACs) can significantly improve the therapeutic efficacy for AML. Herein, a series of novel dual FLT3/HDAC inhibitors were developed through a rational structure-based drug design strategy for the first time. Among them, multiple compounds showed potent and equivalent inhibitory activities against FLT3-ITD and HDAC1, with the representative compound 63 selectively inhibiting HDAC class I (HDAC1/2/3/8) and IIB isoforms (HDAC6) related to tumorigenesis, and intensively blocking proliferation of MV4-11 cells. The antiproliferation activity was proven to depend on the dual inhibition of FLT3 and HDAC1. Mechanism assays demonstrated that 63 prohibited both FLT3 and HDAC pathways, induced apoptosis and arrested cell cycle in MV4-11 cells in a dose-dependent manner. In summary, this study validated the therapeutic potential of a kind of dual FLT3/HDAC inhibitors for AML and provided novel compounds for further biological investigation on concomitant inhibition of FLT3/HDAC pathways. Additionally, the structure-based drug design strategy described herein may provide profound enlightenment for developing superior anti-AML drugs.

Design, synthesis and biological evaluation of 2-aminopyrimidine derivatives as potent FLT3 inhibitors

Acute myeloid leukemia (AML) is an aggressive cancer, which is characterized by clonal expansion of myeloid progenitors in the bone marrow and peripheral blood. FMS-like tyrosine kinase 3 (FLT3) mutations are the most frequently identified mutations, present in approximately 25-30 % AML patients, making FLT3 inhibitors a crucial treatment option for AML. In this study, we described the design, synthesis and biological evaluation of a series of 2-aminopyrimidine derivatives as potent FLT3 inhibitors. Notably, compound 15 displayed potent kinase inhibitory activities against FLT3 (FLT3-WT IC50 = 7.42 ± 1.23 nM; FLT3-D835Y IC50 = 9.21 ± 0.04 nM) and robust antiproliferative activities against MV4-11 cells (IC50 = 0.83 ± 0.15 nM) and MOLM-13 cells (IC50 = 10.55 ± 1.70 nM). Compound 15 also possessed potent antiproliferative activities against BaF3 cells carrying various FLT3-TKD and FLT3-ITD-TKD mutations, indicating its potential to overcome on-target resistance caused by FLT3 mutations. In summary, compound 15 showed promising potential for further exploration as a treatment of AML.

Prognostic value of the mutation types and dynamics of FLT3-ITD in acute myeloid leukemia

OBJECTIVE

The prognostic value of the mutation types and dynamics of FLT3-ITD in acute myeloid leukemia (AML) and other known factors were studied.

METHODS

Initial and follow-up samples from 45 AML patients with FLT3-ITD mutations were analyzed by fragment length analysis, Sanger sequencing, and next-generation sequencing.

RESULTS

Some patients (13%) had multiple FLT3-ITD mutations, and many of them had acute promyelocytic leukemia (APL). FLT3-ITD mutations were classified according to mutation types, including duplication-only FLT3-ITD (52%) and FLT3-ITD with duplications and insertions (dup + ins) (48%). The dup + ins FLT3-ITD variant was independently associated with poor prognosis among non-APL patients (odds ratio, 2.92) in addition to FLT3-ITD with ≥50% variant allele frequency (VAF). The VAFs of FLT3-ITD were low (median 2.2%) when detected during morphologic complete remission (CR) after conventional chemotherapy; however, in two patients treated with gilteritinib after relapse, the VAFs of FLT3-ITD were much higher (>95% and 8.1%) in the morphologic CR state.

CONCLUSIONS

The type of FLT3-ITD mutation is important in prognosis, and the dup + ins type of FLT3-ITD can be an indicator of poor prognosis. In addition, the FLT3-ITD mutation status may unexpectedly not match the morphologic examination results after gilteritinib treatment.

Gilteritinib in Combination With Induction and Consolidation Chemotherapy and as Maintenance Therapy: A Phase IB Study in Patients With Newly Diagnosed AML

PURPOSE

Gilteritinib is a type 1 FLT3 inhibitor active as monotherapy for relapsed or refractory FLT3-mutated AML. We investigated the safety, tolerability, and efficacy of gilteritinib incorporated into intensive induction and consolidation chemotherapy, and as maintenance therapy for adult patients with newly diagnosed, non-favorable-risk AML.

METHODS

In this phase IB study (2215-CL-0103; ClinicalTrials.gov identifier: NCT02236013), 103 participants were screened and 80 were allocated to treatment. The study was divided into four parts: dose escalation, dose expansion, investigation of alternate anthracycline and gilteritinib schedule, and continuous gilteritinib during consolidation.

RESULTS

After dose escalation, 120 mg gilteritinib once daily was chosen for further study. There were 58 participants evaluable for response at this dose, 36 of whom harbored FLT3 mutations. For participants with FLT3-mutated AML, the composite complete response (CRc) rate was 89% (83% were conventional complete responses), all achieved after a single induction cycle. The median overall survival time was 46.1 months. Gilteritinib was well-tolerated in this context although the median time to count recovery during induction was approximately 40 days. Longer time-to-count recovery was associated with higher trough levels of gilteritinib, which, in turn, were associated with azole use. The recommended regimen is gilteritinib at a dose of 120 mg once daily from days 4 to 17 or 8 to 21 of a 7 + 3 induction with either idarubicin or daunorubicin and from day 1 continuously with high-dose cytarabine consolidation. Maintenance therapy with gilteritinib was well-tolerated.

CONCLUSION

These results demonstrated the safety and tolerability of gilteritinib incorporated into an induction and consolidation chemotherapy regimen, and as single-agent maintenance therapy for patients with newly diagnosed FLT3-mutant AML. The data herein provide an important framework for the design of randomized trials comparing gilteritinib with other FLT3 inhibitors.

Acute Myeloid Leukemia Stem Cells in Minimal/Measurable Residual Disease Detection

Acute myeloid leukemia (AML) is a hematological malignancy characterized by an abundance of incompletely matured or immature clonally derived hematopoietic precursors called leukemic blasts. Rare leukemia stem cells (LSCs) that can self-renew as well as give rise to leukemic progenitors comprising the bulk of leukemic blasts are considered the cellular reservoir of disease initiation and maintenance. LSCs are widely thought to be relatively resistant as well as adaptive to chemotherapy and can cause disease relapse. Therefore, it is imperative to understand the molecular bases of LSC forms and functions during different stages of disease progression, so we can more accurately identify these cells and design therapies to target them. Irrespective of the morphological, cytogenetic, and cellular heterogeneity of AML, the uniform, singularly important and independently significant prognosticator of disease response to therapy and patient outcome is measurable or minimal residual disease (MRD) detection, defined by residual disease detection below the morphology-based 5% blast threshold. The importance of LSC identification and frequency estimation during MRD detection, in order to make MRD more effective in predicting disease relapse and modifying therapeutic regimen is becoming increasingly apparent. This review focuses on summarizing functional and cellular composition-based LSC identification and linking those studies to current techniques of MRD detection to suggest LSC-inclusive MRD detection as well as outline outstanding questions that need to be addressed to improve the future of AML clinical management and treatment outcomes.

Single-Cell Next-Generation Sequencing to Monitor Hematopoietic Stem-Cell Transplantation: Current Applications and Future Perspectives

Acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) are genetically complex and diverse diseases. Such complexity makes challenging the monitoring of response to treatment. Measurable residual disease (MRD) assessment is a powerful tool for monitoring response and guiding therapeutic interventions. This is accomplished through targeted next-generation sequencing (NGS), as well as polymerase chain reaction and multiparameter flow cytometry, to detect genomic aberrations at a previously challenging leukemic cell concentration. A major shortcoming of NGS techniques is the inability to discriminate nonleukemic clonal hematopoiesis. In addition, risk assessment and prognostication become more complicated after hematopoietic stem-cell transplantation (HSCT) due to genotypic drift. To address this, newer sequencing techniques have been developed, leading to more prospective and randomized clinical trials aiming to demonstrate the prognostic utility of single-cell next-generation sequencing in predicting patient outcomes following HSCT. This review discusses the use of single-cell DNA genomics in MRD assessment for AML/MDS, with an emphasis on the HSCT time period, including the challenges with current technologies. We also touch on the potential benefits of single-cell RNA sequencing and analysis of accessible chromatin, which generate high-dimensional data at the cellular resolution for investigational purposes, but not currently used in the clinical setting.

A phase Ib trial of mivavotinib (TAK-659), a dual SYK/FLT3 inhibitor, in patients with relapsed/refractory acute myeloid leukemia

Mivavotinib (TAK-659) is an investigational type 1 tyrosine kinase inhibitor with dual activity against spleen tyrosine kinase (SYK) and FMS-like tyrosine kinase 3 (FLT3). We conducted a phase Ib study to investigate the safety, tolerability, and efficacy of mivavotinib in patients with refractory and/or relapsed (R/R) acute myeloid leukemia (AML). Both daily (QD) and twice daily (BID) dosing regimens were evaluated. A total of 43 patients were enrolled, and there were 5 complete responses (4 with incomplete count recovery). In the QD dosing regimen, the maximum tolerated dose (MTD) was not reached up to 160 mg QD per protocol; 140 mg QD was identified as the recommended phase II dose. In the BID dosing regimen, the MTD was 60 mg BID. Thirty patients (70%) experienced a bleeding event on study; the majority were grades 1 or 2, were resolved without mivavotinib modification, and were not considered related to study treatment. Eleven patients (26%) experienced grade ≥3 bleeding events, which were observed most frequently with the 80 mg BID dose. We conducted platelet aggregation studies to investigate the potential role of mivavotinib-mediated SYK inhibition on platelet function. The bleeding events observed may have been the result of several confounding factors, including AML disease status, associated thrombocytopenia, and high doses of mivavotinib. Overall, these findings indicate that the activity of mivavotinib in R/R AML is modest. Furthermore, any future clinical investigation of this agent should be undertaken with caution, particularly in thrombocytopenic patients, due to the potential bleeding risk of SYK inhibition. ClinicalTrials.gov: NCT02323113.

An Update on FLT3 in Acute Myeloid Leukemia: Pathophysiology and Therapeutic Landscape

PURPOSE OF REVIEW

This review aims to summarize the pathophysiology, clinical presentation, and management of acute myeloid leukemia (AML) with FMS-like tyrosine kinase-3 (FLT3) mutations.

RECENT FINDINGS

The recent European Leukemia Net (ELN2022) recommendations re-classified AML with FLT3 internal tandem duplications (FLT3-ITD) as intermediate risk regardless of Nucleophosmin 1 (NPM1) co-mutation or the FLT3 allelic ratio. Allogeneic hematopoietic cell transplantation (alloHCT) is now recommended for all eligible patients with FLT3-ITD AML. This review outlines the role of FLT3 inhibitors in induction and consolidation, as well as for post-alloHCT maintenance. It outlines the unique challenges and advantages of assessing FLT3 measurable residual disease (MRD) and discusses the pre-clinical basis for the combination of FLT3 and menin inhibitors. And, for the older or unfit patient ineligible for upfront intensive chemotherapy, it discusses the recent clinical trials incorporating FLT3 inhibitors into azacytidine- and venetoclax-based regimens. Finally, it proposes a rational sequential approach for integrating FLT3 inhibitors into less intensive regimens, with a focus on improved tolerability in the older and unfit patient population. The management of AML with FLT3 mutation remains a challenge in clinical practice. This review provides an update on the pathophysiology and therapeutic landscape of FLT3 AML, as well as a clinical management framework for managing the older or unfit patient ineligible for intensive chemotherapy.

The clinical impact of the molecular landscape of acute myeloid leukemia

Research into the underlying pathogenic mechanisms of acute myeloid leukemia (AML) has led to remarkable advances in our understanding of the disease. Mutations now allow us to explore the enormous diversity among cytogenetically defined subsets of AML, particularly the large subset of cytogenetically normal AML. Despite the progress in unraveling the tumor genome, only a small number of recurrent mutations have been incorporated into risk-stratification schemes and have been proven to be clinically relevant, targetable lesions. The current World Health Organization Classification of myeloid neoplasms and leukemia includes eight AML categories defined by recurrent genetic abnormalities as well as three categories defined by gene mutations. We here discuss the utility of molecular markers in AML in prognostication and treatment decision-making. New therapies based on targetable markers include IDH inhibitors (ivosidenib, enasidenib), venetoclax-based therapy, FLT3 inhibitors (midostaurin, gilteritinib, and quizartinib), gemtuzumab ozogamicin, magrolimab and menin inhibitors.

The Cup Runneth Over: Treatment Strategies for Newly Diagnosed Acute Myeloid Leukemia

Since 2017, the number of agents for acute myeloid leukemia (AML) has rapidly expanded. Given the increased therapeutic options, better identification of high-risk subsets of AML and more refined approaches to patient fitness assessment, the decisions surrounding selection of intensive chemotherapy versus lower-intensity treatment have grown increasingly more nuanced. In this review, we present available data for both standard and investigational approaches in the initial treatment of AML using an intensive chemotherapy backbone or a lower-intensity approach. We summarize management strategies in newly diagnosed secondary AML, considerations around allogeneic stem-cell transplantation, and the role of maintenance therapy. Finally, we highlight important areas of future investigation and novel agents that may hold promise in combination with standard therapies.

Design and synthesis of selective FLT3 inhibitors via exploration of back pocket II

Aim: The clinical benefits of FLT3 inhibitors against acute myeloid leukemia (AML) have been limited by selectivity and resistance mutations. Thus, to identify FLT3 inhibitors possessing high selectivity and potency is of necessity. Methods & results: The authors used computational methods to systematically compare pocket similarity with 269 kinases. Subsequently, based on these investigations and beginning with in-house compound 10, they synthesized a series of 6-methyl-isoxazol[3,4-b]pyridine-3-amino derivatives and identified that compound 45 (IC₅₀: 103 nM) displayed gratifying potency in human AML cell lines with FLT3-internal tandem duplications mutation as well as FLT3-internal tandem duplications-tyrosine kinase domain-transformed BaF3 cells. Conclusion: The integrated biological activity results indicated that compound 45 deserves further development for therapeutic remedies for AML.

The signature based on seven genomic instability-related genes could predict the prognosis of acute myeloid leukemia patients

BACKGROUND

Acute myeloid leukemia (AML) is the most common acute blood malignancy in adults. The complicated and dynamic genomic instability (GI) is the most prominent feature of AML. Our study aimed to explore the prognostic value of GI-related genes in AML patients.

METHODS

The mRNA data and mutation data were downloaded from the TCGA and GEO databases. Differential expression analyses were completed in limma package. GO and KEGG functional enrichment was conducted using clusterProfiler function of R. Univariate Cox and LASSO Cox regression analyses were performed to screen key genes for Risk score model construction. Nomogram was built with rms package.

RESULTS

We identified 114 DEGs between high TMB patients and low TMB AML patients, which were significantly enriched in 429 GO terms and 13 KEGG pathways. Based on the univariate Cox and LASSO Cox regression analyses, seven optimal genes were finally applied for Risk score model construction, including SELE, LGALS1, ITGAX, TMEM200A, SLC25A21, S100A4 and CRIP1. The Risk score could reliably predict the prognosis of AML patients. Age and Risk score were both independent prognostic indicators for AML, and the Nomogram based on them could also reliably predict the OS of AML patients.

CONCLUSIONS

A prognostic signature based on seven GI-related genes and a predictive Nomogram for AML patients are finally successfully constructed.

Therapeutic Targeting of FLT3 in Acute Myeloid Leukemia: Current Status and Novel Approaches

FMS-like tyrosine kinase 3 (FLT3) is mutated in approximately 30% of acute myeloid leukemia (AML) patients. The presence of FLT3-ITD (internal tandem duplication, 20-25%) mutation and, to a lesser extent, FLT3-TKD (tyrosine kinase domain, 5-10%) mutation is associated with poorer diagnosis and therapy response since the leukemic cells become hyperproliferative and resistant to apoptosis after continuous activation of FLT3 signaling. Targeting FLT3 has been the focus of many pre-clinical and clinical studies. Hence, many small-molecule FLT3 inhibitors (FLT3is) have been developed, some of which are approved such as midostaurin and gilteritinib to be used in different clinical settings, either in combination with chemotherapy or alone. However, many questions regarding the best treatment strategy remain to be answered. On the other hand, various FLT3-dependent and -independent resistance mechanisms could be evolved during FLT3i therapy which limit their clinical impact. Therefore, identifying molecular mechanisms of resistance and developing novel strategies to overcome this obstacle is a current interest in the field. In this review, recent studies of approved FLT3i and knowledge about major resistance mechanisms of clinically approved FLT3i's will be discussed together with novel treatment approaches such as designing novel FLT3i and dual FLT3i and combination strategies including approved FLT3i plus small-molecule agents targeting altered molecules in the resistant cells to abrogate resistance. Moreover, how to choose an appropriate FLT3i for the patients will be summarized based on what is currently known from available clinical data. In addition, strategies beyond FLT3i's including immunotherapeutics, small-molecule FLT3 degraders, and flavonoids will be summarized to highlight potential alternatives in FLT3-mutated AML therapy.

PCW-A1001, AI-assisted de novo design approach to design a selective inhibitor for FLT-3(D835Y) in acute myeloid leukemia

Treating acute myeloid leukemia (AML) by targeting FMS-like tyrosine kinase 3 (FLT-3) is considered an effective treatment strategy. By using AI-assisted hit optimization, we discovered a novel and highly selective compound with desired drug-like properties with which to target the FLT-3 (D835Y) mutant. In the current study, we applied an AI-assisted de novo design approach to identify a novel inhibitor of FLT-3 (D835Y). A recurrent neural network containing long short-term memory cells (LSTM) was implemented to generate potential candidates related to our in-house hit compound (PCW-1001). Approximately 10,416 hits were generated from 20 epochs, and the generated hits were further filtered using various toxicity and synthetic feasibility filters. Based on the docking and free energy ranking, the top compound was selected for synthesis and screening. Of these three compounds, PCW-A1001 proved to be highly selective for the FLT-3 (D835Y) mutant, with an IC50 of 764 nM, whereas the IC50 of FLT-3 WT was 2.54 μM.

19S Proteasome Subunits as Oncogenes and Prognostic Biomarkers in FLT3-Mutated Acute Myeloid Leukemia (AML)

26S proteasome non-ATPase subunits 1 (PSMD1) and 3 (PSMD3) were recently identified as prognostic biomarkers and potential therapeutic targets in chronic myeloid leukemia (CML) and multiple solid tumors. In the present study, we analyzed the expression of 19S proteasome subunits in acute myeloid leukemia (AML) patients with mutations in the FMS-like tyrosine kinase 3 (FLT3) gene and assessed their impact on overall survival (OS). High levels of PSMD3 but not PSMD1 expression correlated with a worse OS in FLT3-mutated AML. Consistent with an oncogenic role for PSMD3 in AML, shRNA-mediated PSMD3 knockdown impaired colony formation of FLT3+ AML cell lines, which correlated with increased OS in xenograft models. While PSMD3 regulated nuclear factor-kappa B (NF-κB) transcriptional activity in CML, we did not observe similar effects in FLT3+ AML cells. Rather, proteomics analyses suggested a role for PSMD3 in neutrophil degranulation and energy metabolism. Finally, we identified additional PSMD subunits that are upregulated in AML patients with mutated versus wild-type FLT3, which correlated with worse outcomes. These findings suggest that different components of the 19S regulatory complex of the 26S proteasome can have indications for OS and may serve as prognostic biomarkers in AML and other types of cancers.

Developments and challenges of FLT3 inhibitors in acute myeloid leukemia

FLT3 mutations are one of the most common genetic alterations in acute myeloid leukemia (AML) and are identified in approximately one-third of newly diagnosed patients. Aberrant FLT3 receptor signaling has important implications for the biology and clinical management of AML. In recent years, targeting FLT3 has been a part of every course of treatment in FLT3-ITD/TKD-mutated AML and contributes to substantially prolonged survival. At the same time, wide application of next-generation sequencing (NGS) technology has revealed a series of non-canonical FLT3 mutations, including point mutations and small insertions/deletions. Some of these mutations may be able to influence downstream phosphorylation and sensitivity to FLT3 inhibitors, while the correlation with clinical outcomes remains unclear. Exploration of FLT3-targeted therapy has made substantial progress, but resistance to FLT3 inhibitors has become a pressing issue. The mechanisms underlying FLT3 inhibitor tolerance can be roughly divided into primary resistance and secondary resistance. Primary resistance is related to abnormalities in signaling factors, such as FL, CXCL12, and FGF2, and secondary resistance mainly involves on-target mutations and off-target aberrations. To overcome this problem, novel agents such as FF-10101 have shown promising potential. Multitarget strategies directed at FLT3 and anomalous signaling factors simultaneously are in active clinical development and show promising results.

Clinical Impact of Measurable Residual Disease in Acute Myeloid Leukemia

Simple Summary

Advances in immunophenotyping and molecular techniques have allowed for the development of more sensitive diagnostic tests in acute leukemia. These techniques can identify low levels of leukemic cells (quantified as 10⁻⁴ to 10⁻⁶ ratio to white blood cells) in patient samples. The presence of such low levels of leukemic cells, termed “measurable/minimal residual disease” (MRD), has been shown to be a marker of disease burden and patient outcomes. In acute lymphoblastic leukemia, new agents are highly effective at eliminating MRD for patients whose leukemia progressed despite first line therapies. By comparison, the role of MRD in acute myeloid leukemia is less clear. This commentary reviews select data and remaining questions about the clinical application of MRD to the treatment of patients with acute myeloid leukemia.

Abstract

Measurable residual disease (MRD) has emerged as a primary marker of risk severity and prognosis in acute myeloid leukemia (AML). There is, however, ongoing debate about MRD-based surveillance and treatment. A literature review was performed using the PubMed database with the keywords MRD or residual disease in recently published journals. Identified articles describe the prognostic value of pre-transplant MRD and suggest optimal timing and techniques to quantify MRD. Several studies address the implications of MRD on treatment selection and hematopoietic stem cell transplant, including patient candidacy, conditioning regimen, and transplant type. More prospective, randomized studies are needed to guide the application of MRD in the treatment of AML, particularly in transplant.

A Novel BRD Family PROTAC Inhibitor dBET1 Exerts Great Anti-Cancer Effects by Targeting c-MYC in Acute Myeloid Leukemia Cells

Acute myeloid leukemia (AML) represents an aggressive hematopoietic malignancy with a prognosis inferior to that of other leukemias. Recent targeted therapies offer new opportunities to achieve better treatment outcomes. However, due to the complex heterogeneity of AML, its prognosis remains dismal. In this study, we first identified the correlation between high expression of BRD4 and overall survival of patients with AML. Targeted degradation of BRD2, BRD3, and BRD4 proteins by dBET1, a proteolysis-targeting chimera (PROTAC) against the bromodomain and extra-terminal domain (BET) family members, showed cytotoxic effects on Kasumi (AML1-ETO), NB4 (PML-RARa), THP-1 (MLL-AF9), and MV4-11 (MLL-AF4) AML cell lines representing different molecular subtypes of AML. Furthermore, we determined that dBET1 treatment arrested cell cycling and enhanced apoptosis and c-MYC was identified as the downstream target. Collectively, our results indicated that dBET1 had broad anti-cancer effects on AML cell lines with different molecular lesions and provided more benefits to patients with AML.

The FLT3 Y842D mutation may be highly sensitive to midostaurin: a case report

A Y842D mutation within the activation loop of fms-like tyrosine kinase 3 (FLT3) has been shown to confer strong resistance to sorafenib in vitro. Whether this type of mutation exerts clinically significant effects in patients with acute myeloid leukaemia (AML) remains unclear. Here, a novel Y842D activating mutation within the kinase domain of FLT3, in a pregnant patient with de novo hyperleucocyte acute myeloid leukaemia, is described. Following induction failure with standard dose idarubicin and cytarabine (IA), the patient received re-induction combined with midostaurin, a promising agent targeting mutant-FLT3, and IA regimen. Fortunately, morphological remission was achieved. During the period of midostaurin treatment, the patient exhibited a symptom that was characteristic of differentiation syndrome, which disappeared following treatment with methylprednisolone. The present case revealed that Y842D, an uncommon activating mutation in the activation loop of FLT3, may be a midostaurin-sensitive mutation type in patients with acute myeloid leukaemia.

Fast in-vitro screening of FLT3-ITD inhibitors using silkworm-baculovirus protein expression system

We report expression and purification of a FLT3 protein with ITD mutation (FLT3-ITD) with a steady tyrosine kinase activity using a silkworm-baculovirus system, and its application as a fast screening system of tyrosine kinase inhibitors. The FLT3-ITD protein was expressed in Bombyx mori L. pupae infected by gene-modified nucleopolyhedrovirus, and was purified as an active state. We performed an inhibition assay using 17 kinase inhibitors, and succeeded in screening two inhibitors for FLT3-ITD. The result has paved the way for screening FLT3-ITD inhibitors in a fast and easy manner, and also for structural studies.

Small Molecule Compounds of Natural Origin Target Cellular Receptors to Inhibit Cancer Development and Progression

Receptors are macromolecules that transmit information regulating cell proliferation, differentiation, migration and apoptosis, play key roles in oncogenic processes and correlate with the prognoses of cancer patients. Thus, targeting receptors to constrain cancer development and progression has gained widespread interest. Small molecule compounds of natural origin have been widely used as drugs or adjuvant chemotherapeutic agents in cancer therapies due to their activities of selectively killing cancer cells, alleviating drug resistance and mitigating side effects. Meanwhile, many natural compounds, including those targeting receptors, are still under laboratory investigation for their anti-cancer activities and mechanisms. In this review, we classify the receptors by their structures and functions, illustrate the natural compounds targeting these receptors and discuss the mechanisms of their anti-cancer activities. We aim to provide primary knowledge of mechanistic regulation and clinical applications of cancer therapies through targeting deregulated receptors.

Differential in vitro anti-leukemic activity of resveratrol combined with serine palmitoyltransferase inhibitor myriocin in FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD) carrying AML cells

Treatment of FMS-like tyrosine kinase 3 (FLT3)-internal tandem duplication (ITD) AML is restricted due to toxicity, drug resistance and relapse eventhough targeted therapies are clinically available. Resveratrol with its multi-targeted nature is a promising chemopreventive remaining limitedly studied in FLT3-ITD AML regarding to ceramide metabolism. Here, its cytotoxic, cytostatic and apoptotic effects are investigated in combination with serine palmitoyltransferase (SPT), the first enzyme of de novo pathway of ceramide production, inhibitor myriocin on MOLM-13 and MV4-11 cells. We assessed dose-dependent cell viability, flow cytometric cell death and cell cycle profiles of resveratrol in combination with myriocin by MTT assay, annexin-V/PI staining and PI staining respectively. Resveratrol's dose-dependent effect on SPT protein expression was also checked by western blot. Resveratrol decreased cell viability in a dose- dependent manner whereas myriocin did not affect cell proliferation effectively in both cell lines after 48h treatments. Although resveratrol induced both apoptosis and a significant S phase arrest in MV4-11 cells, it triggered apoptosis and non-significant S phase accumulation in MOLM-13 cells. Co-administrations reduced cell viability. Increased cytotoxic effect of co-treatments was further proved mechanistically through induction of apoptosis via phosphatidylserine relocalization. The cell cycle alteration in co-treatment was significant with an S phase arrest in MV4-11 cells, however, it was not effective on cell cycle progression of MOLM-13 cells. Resveratrol also increased SPT expression. Overall, modulation of SPT together with resveratrol might be the possible explanation for resveratrol's action. It could be an integrative medicine for FLT3-ITD AML after investigating its detailed mechanism of action in relation to de novo pathway of ceramide production.

Gab2 deficiency prevents Flt3-ITD driven acute myeloid leukemia in vivo

Internal tandem duplications (ITD) of the FMS-like tyrosine kinase 3 (FLT3) predict poor prognosis in acute myeloid leukemia (AML) and often co-exist with inactivating DNMT3A mutations. In vitro studies implicated Grb2-associated binder 2 (GAB2) as FLT3-ITD effector. Utilizing a Flt3-ITD knock-in, Dnmt3a haploinsufficient mouse model, we demonstrate that Gab2 is essential for the development of Flt3-ITD driven AML in vivo, as Gab2 deficient mice displayed prolonged survival, presented with attenuated liver and spleen pathology and reduced blast counts. Furthermore, leukemic bone marrow from Gab2 deficient mice exhibited reduced colony-forming unit capacity and increased FLT3 inhibitor sensitivity. Using transcriptomics, we identify the genes encoding for Axl and the Ret co-receptor Gfra2 as targets of the Flt3-ITD/Gab2/Stat5 axis. We propose a pathomechanism in which Gab2 increases signaling of these receptors by inducing their expression and by serving as downstream effector. Thereby, Gab2 promotes AML aggressiveness and drug resistance as it incorporates these receptor tyrosine kinases into the Flt3-ITD signaling network. Consequently, our data identify GAB2 as a promising biomarker and therapeutic target in human AML.

The beginning of a new therapeutic era in acute myeloid leukemia

In the field of AML, the early 2000s were shaped by the advent of novel molecular biology technologies including high-throughput sequencing that improved prognostic classification, response evaluation through the quantification of minimal residual disease, and the launch of research on targeted therapies. Our knowledge of leukemogenesis, AML genetic diversity, gene-gene interactions, clonal evolution, and treatment response assessment has also greatly improved. New classifications based on chromosomal abnormalities and gene mutations are now integrated on a routine basis. These considerable efforts contributed to the discovery and development of promising drugs which specifically target gene mutations, apoptotic pathways and cell surface antigens as well as reformulate classical cytotoxic agents. In less than 2 years, nine novels drugs have been approved for the treatment of AML patients, and many others are being intensively investigated, in particular immune therapies. There are now numerous clinical research opportunities offered to clinicians, thanks to these new treatment options. We are only at the start of a new era which should see major disruptions in the way we understand, treat, and monitor patients with AML.

Clinical values of gene alterations as marker of minimal residual disease in non-M3 acute myeloid leukemia

Acute myeloid leukemia (AML) is a malignant disease of the hematopoietic system. Residual leukemic cells after treatment are associated with relapse. Thus, detecting minimal residual disease (MRD) is significant. Major techniques for MRD assessment include multiparameter flow cytometry (MFC), polymerase chain reaction (PCR), and next-generation sequencing (NGS). At a molecular level, AML is the consequence of collaboration of several gene alterations. Some of these gene alterations can also be used as MRD markers to evaluate the level of residual leukemic cells by PCR and NGS. However, when as MRD markers, different gene alterations have different clinical values. This paper aims to summarize the characteristics of various MRD markers, so as to better predict the clinical outcome of AML patients and guide the treatment.

Effective Immunosurveillance After Allogeneic Hematopoietic Stem Cell Transplantation in Acute Myeloid Leukemia

The number of patients receiving allogeneic hematopoietic stem cell transplantation (alloHCT) has increased constantly over the last years due to advances in transplant technology development, supportive care, transplant safety, and donor availability. Currently, acute myeloid leukemia (AML) is the most frequent indication for alloHCT. However, disease relapse remains the main cause of therapy failure. Therefore, concepts of maintaining and, if necessary, reinforcing a strong graft-versus-leukemia (GvL) effect is crucial for the prognosis and long-term survival of the patients. Over the last decades, it has become evident that effective immunosurveillance after alloHCT is an entangled complex of donor-specific characteristics, leukemia-associated geno- and phenotypes, and acquired resistance mechanisms. Furthermore, adoption of effector cells such as natural killer (NK) cells, alloreactive and regulatory T-cells with their accompanying receptor repertoire, and cell–cell interactions driven by messenger molecules within the stem cell and the bone marrow niche have important impact. In this review of pre- and posttransplant elements and mechanisms of immunosurveillance, we highlight the most important mechanisms after alloHCT.

Strategies targeting FLT3 beyond the kinase inhibitors

Acute myeloid leukemia (AML) is a hematological malignancy characterized by clonal expansion and differentiation arrest of the myeloid progenitor cells, which leads to the accumulation of immature cells called blasts in the bone marrow and peripheral blood. Mutations in the receptor tyrosine kinase FLT3 occur in 30% of normal karyotype patients with AML and are associated with a higher incidence of relapse and worse survival. Targeted therapies against FLT3 mutations using small-molecule FLT3 tyrosine kinase inhibitors (TKIs) have long been investigated, with some showing favorable clinical outcomes. However, major setbacks such as limited clinical efficacy and the high risk of acquired resistance remain unresolved. FLT3 signaling, mutations, and FLT3 inhibitors are topics that have been extensively reviewed in recent years. Strategies to target FLT3 beyond the small molecule kinase inhibitors are expanding, nevertheless they are not receiving enough attention. These modalities include antibody-based FLT3 targeted therapies, immune cells mediated targeting strategies, and approaches targeting downstream signaling pathways and FLT3 translation. Here, we review the most recent advances and the challenges associated with the development of therapeutic modalities targeting FLT3 beyond the kinase inhibitors.