Day-21 bone marrow findings incorrectly designate residual leukaemia in FLT3-mutated acute myeloid leukaemia treated with intensive induction plus midostaurin: a morphology-focused study

Early induction response assessment with day-21 bone marrow (D21-BM) is commonly performed in patients with FLT3-mutated acute myeloid leukaemia (AML), where detection of residual leukaemia (RL; blasts ≥5%) typically results in the administration of a second induction course. However, whether D21-BM results predict for RL at the end of first induction has not been systematically assessed. This study evaluates the predictive role of D21-BM morphology in detecting RL following first induction. Between August 2018 and March 2022, all patients with FLT3-AML receiving 7+3 plus midostaurin, with D21-BM performed, were identified. Correlation between D21-BM morphology vs D21-BM ancillary flow/molecular results, as well as vs D28-BM end of first induction response, were retrospectively reviewed. Subsequently, D21-BMs were subjected to anonymised morphological re-assessments by independent haematopathologists (total in triplicate per patient). Of nine patients included in this study, three (33%) were designated to have RL at D21-BM, all of whom entered complete remission at D28-BM. Furthermore, only low-level measurable residual disease was detected in all three cases by flow or molecular methods at D21-BM, hence none proceeded to a second induction. Independent re-evaluations of these cases failed to correctly reassign D21-BM responses, yielding a final false positive rate of 33%. In summary, based on morphology alone, D21-BM assessment following 7+3 intensive induction plus midostaurin for FLT3-AML incorrectly designates RL in some patients; thus correlating with associated flow and molecular results is essential before concluding RL following first induction. Where remission status is unclear, repeat D28-BMs should be performed.

Phase 1 study of azacitidine in combination with quizartinib in patients with FLT3 or CBL mutated MDS and MDS/MPN

We conducted a phase 1 study evaluating 3 dose levels of quizartinib (30 mg, 40 mg or 60 mg) in combination with azacitidine for HMA-naïve or relapsed/refractory MDS or MDS/MPN with FLT3 or CBL mutations. Overall, 12 patients (HMA naïve: n=9, HMA failure: n=3) were enrolled; 7 (58 %) patients had FLT3 mutations and 5 (42 %) had CBL mutations. The maximum tolerated dose was not reached. Most common grade 3-4 treatment-emergent adverse events were thrombocytopenia (n=5, 42 %), anemia (n=4, 33 %), lung infection (n=2, 17 %), skin infection (n=2, 17 %), hyponatremia (n=2, 17 %) and sepsis (n=2, 17 %). The overall response rate was 83 % with median relapse-free and overall survivals of 15.1 months (95 % CI 0.0-38.4 months) and 17.5 months (95 % CI NC-NC), respectively. FLT3 mutation clearance was observed in 57 % (n=4) patients. These data suggest quizartinib is safe and shows encouraging activity in FLT3-mutated MDS and MDS/MPN. This study is registered at Clinicaltrials.gov as NCT04493138.

FLT3L governs the development of partially overlapping hematopoietic lineages in humans and mice

FMS-related tyrosine kinase 3 ligand (FLT3L), encoded by FLT3LG, is a hematopoietic factor essential for the development of natural killer (NK) cells, B cells, and dendritic cells (DCs) in mice. We describe three humans homozygous for a loss-of-function FLT3LG variant with a history of various recurrent infections, including severe cutaneous warts. The patients' bone marrow (BM) was hypoplastic, with low levels of hematopoietic progenitors, particularly myeloid and B cell precursors. Counts of B cells, monocytes, and DCs were low in the patients' blood, whereas the other blood subsets, including NK cells, were affected only moderately, if at all. The patients had normal counts of Langerhans cells (LCs) and dermal macrophages in the skin but lacked dermal DCs. Thus, FLT3L is required for B cell and DC development in mice and humans. However, unlike its murine counterpart, human FLT3L is required for the development of monocytes but not NK cells.

A case report of secondary B-cell acute lymphoblastic leukemia treated with a combination of FLT3 inhibitor and decitabine

Secondary acute lymphoblastic leukemia (s-ALL) refers to acute lymphoblastic leukemia that occurs after a previous malignant tumor, including therapy-related acute lymphoblastic leukemia (t-ALL) and prior malignant tumor acute lymphoblastic leukemia (pm-ALL). We report a case of a 51-year-old female patient who developed acute lymphoblastic leukemia 14 years after being diagnosed with diffuse large B-cell lymphoma (DLBCL). The patient was unresponsive to conventional chemotherapy for acute lymphoblastic leukemia (ALL) and achieved remission with a combination of sorafenib and decitabine based on the molecular biology characteristics of her B-ALL.

A systematic review of second-generation FLT3 inhibitors for treatment of patients with relapsed/refractory acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia (AML) is a complex disease with diverse mutations, including prevalent mutations in the FMS-like receptor tyrosine kinase 3 (FLT3) gene that lead to poor prognosis. Recent advancements have introduced FLT3 inhibitors that have improved outcomes for FLT3-mutated AML patients, however, questions remain on their application in complex conditions such as relapsed/refractory (R/R) disease. Therefore, we aimed to evaluate the clinical effectiveness of second-generation FLT3 inhibitors in treating patients with R/R AML.

METHODS

A systematic literature search of PubMed, MEDLINE, SCOPUS and Google Scholar databases was made to identify relevant studies up to January 30, 2024. This study was conducted following the guidelines of the PRISMA.

RESULTS

The ADMIRAL trial revealed significantly improved overall survival and complete remission rates with gilteritinib compared to salvage chemotherapy, with manageable adverse effects. Ongoing research explores its potential in combination therapies, showing synergistic effects with venetoclax and promising outcomes in various clinical trials. The QuANTUM-R trial suggested longer overall survival with quizartinib compared to standard chemotherapy, although concerns were raised regarding trial design and cardiotoxicity. Ongoing research explores combination therapies involving quizartinib, such as doublet or triplet regimens with venetoclax, showing promising outcomes in FLT3-mutated AML patients.

CONCLUSION

These targeted therapies offer promise for managing this subgroup of AML patients, but further research is needed to optimize their use. This study underscores the importance of personalized treatment based on genetic mutations in AML, paving the way for more effective and tailored approaches to combat the disease.

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.

Gilteritinib in combination with venetoclax, low-dose cytarabine and actinomycin D for relapsed or refractory FLT3-mutated acute myeloid leukaemia

We have conducted a retrospective, single-centre analysis of 20 patients with relapsed or refractory FLT3-mutated acute myeloid leukaemia (FLT3m AML) who received a salvage quadruplet regimen consisting of gilteritinib, venetoclax, low-dose cytarabine and actinomycin D (G-ACTIVE). G-ACTIVE resulted in a 95% (19/20) overall response rate and 75% (15/20) complete remission and complete remission with an incomplete platelet recovery (CR + CRp) rate. Out of 13 transplant-eligible patients, 11 (86%) proceeded to an allogeneic stem cell transplantation. The median overall survival and relapse-free survival after G-ACTIVE were 32 and 12.9 months respectively. The Day 60 mortality rate was 15%.

Durable responses in acute lymphoblastic leukaemia with the use of FLT3 and IDH inhibitors

Data regarding the use of FMS-like tyrosine kinase 3 (FLT3) and isocitrate dehydrogenase 1/2 (IDH1/2) inhibitors in acute lymphoblastic leukaemia (ALL) are lacking. We identified 14 patients with FLT3- or IDH1/2-mutated ALL. Three early T-cell precursor-ALL patients received FLT3 or IDH2 inhibitors. Patient 1 maintains a complete remission (CR) with enasidenib after intolerance to chemotherapy. Patient 2 maintained a CR for 27 months after treatment with enasidenib for relapsed disease. Patient 3 was treated with venetoclax and gilteritinib at the time of relapse and maintained a CR with gilteritinib for 8 months. These cases suggest that FLT3 and IDH inhibitors could represent a viable therapeutic option for ALL patients with these mutations.

SOHO State of the Art Updates and Next Questions: Pre-emptive Therapy at Molecular Measurable Residual Disease Failure in Acute Myeloid Leukemia

Molecular measurable residual disease (MRD, eg, by real-time quantitative polymerase chain reaction, RT-qPCR), is an integral part of response assessment in acute myeloid leukemia (AML) with established prognostic and evolving therapeutic significance. MRD failure can occur through several pathways (namely MRD persistence at the end of treatment at a high level, MRD progression from a low level or MRD re-emergence during follow up; the latter two constitute MRD relapse as defined by the European Leukemia Net) and is clinically actionable, with survival benefit reported in AML subgroups. Selection of pre-emptive therapy at MRD failure relies upon an integrated clinico-molecular assessment and is subset-specific. In acute promyelocytic leukemia, arsenic trioxide-based regimen for MRD failure following frontline treatment with all-trans-retinoic acid plus chemotherapy represents standard of care, while hypomethylating agents (eg, azacitidine), salvage chemotherapy (eg, FLAG-IDA) and venetoclax-based regimens are effective in NPM1-mutated AML. Specific inhibitors of FLT3 have emerging use in FLT3-mutated AML and are associated with minimal toxicity. Furthermore, immunotherapeutic approaches such as donor lymphocyte infusions and interferon-⍺ are efficacious options in the post-allogeneic-HSCT settings. Enrollment into clinical trials with genomic-guided assignment of pre-emptive therapy at MRD failure should be prioritized. Finally, with the emergence of novel agents (eg, menin inhibitors) and approaches (eg, adoptive cellular and immunological therapy), an exciting future lies ahead where a broad array of highly active pre-emptive therapeutic options will likely be clinically applicable to a wide range of AML subsets.

Leukemic mutation FLT3-ITD is retained in dendritic cells and disrupts their homeostasis leading to expanded Th17 frequency

Dendritic cells (DC) are mediators between innate and adaptive immune responses to pathogens and tumors. DC development is determined by signaling through the receptor tyrosine kinase Fms-like tyrosine kinase 3 (FLT3) in bone marrow myeloid progenitors. Recently the naming conventions for DC phenotypes have been updated to distinguish between "Conventional" DCs (cDCs) and plasmacytoid DCs (pDCs). Activating mutations of FLT3, including Internal Tandem Duplication (FLT3-ITD), are associated with poor prognosis for acute myeloid leukemia (AML) patients. Having a shared myeloid lineage it can be difficult to distinguish bone fide DCs from AML tumor cells. To date, there is little information on the effects of FLT3-ITD in DC biology. To further elucidate this relationship we utilized CITE-seq technology in combination with flow cytometry and multiplex immunoassays to measure changes to DCs in human and mouse tissues. We examined the cDC phenotype and frequency in bone marrow aspirates from patients with AML to understand the changes to cDCs associated with FLT3-ITD. When compared to healthy donor (HD) we found that a subset of FLT3-ITD+ AML patient samples have overrepresented populations of cDCs and disrupted phenotypes. Using a mouse model of FLT3-ITD+ AML, we found that cDCs were increased in percentage and number compared to control wild-type (WT) mice. Single cell RNA-seq identified FLT3-ITD+ cDCs as skewed towards a cDC2 T-bet- phenotype, previously shown to promote Th17 T cells. We assessed the phenotypes of CD4+ T cells in the AML mice and found significant enrichment of both Treg and Th17 CD4+ T cells in the bone marrow and spleen compartments. Ex vivo stimulation of CD4+ T cells also showed increased Th17 phenotype in AML mice. Moreover, co-culture of AML mouse-derived DCs and naïve OT-II cells preferentially skewed T cells into a Th17 phenotype. Together, our data suggests that FLT3-ITD+ leukemia-associated cDCs polarize CD4+ T cells into Th17 subsets, a population that has been shown to be negatively associated with survival in solid tumor contexts. This illustrates the complex tumor microenvironment of AML and highlights the need for further investigation into the effects of FLT3-ITD mutations on DC phenotypes and their downstream effects on Th polarization.

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.

Blasts with folded nuclei: A histopathologic finding in myeloid leukemia cutis with NPM1 and FLT3 mutations

Leukemia cutis is a term used to describe cutaneous manifestations of leukemic infiltration of the skin and portends a poor prognosis. Cutaneous involvement by hematopoietic/lymphoid tumors can occur before, concurrently, or after the initial diagnosis. Early involvement of dermatologists and timely biopsies play a crucial role in achieving a prompt diagnosis. Prior reports of acute myeloid leukemia have revealed a strong association between the cup-like nuclear morphology observed in bone marrow specimens and concurrent mutations of NPM1 and FLT3-ITD. In cutaneous tissue sections of leukemia cutis, folded or indented nuclei may represent the "cup-like" counterpart previously described in bone marrow specimens. Recognizing this morphological feature could aid in identifying this molecular subtype of leukemia cutis. In this study, we present a case of leukemia cutis in a 63-year-old female with AML and NPM1 and FLT3-ITD mutations, demonstrating scattered indented/folded nuclei.

Discovery of LWY713 as a potent and selective FLT3 PROTAC degrader with in vivo activity against acute myeloid leukemia

Fms-like tyrosine kinase 3 (FLT3) has been validated as a therapeutic target for acute myeloid leukemia (AML). While a number of FLT3 kinase inhibitors have been approved for AML treatment, the clinical data revealed that they cannot achieve complete and sustained suppression of FLT3 signaling at the tolerated dose. Here we report a series of new, potent and selective FLT3 proteolysis targeting chimera degraders. The optimal compound LWY713 potently induced the degradation of FLT3 with a DC50 value of 0.64 nM and a Dmax value of 94.8% in AML MV4-11 cells with FLT3-internal tandem duplication (ITD) mutation. Mechanistic studies demonstrated that LWY713 selectively induced FLT3 degradation in a cereblon- and proteasome-dependent manner. LWY713 potently inhibited FLT3 signaling, suppressed cell proliferation, and induced cell G0/G1-phase arrest and apoptosis in MV4-11 cells. Importantly, LWY713 displayed potent in vivo antitumor activity in MV4-11 xenograft models.

Developments of Fms-like Tyrosine Kinase 3 Inhibitors as Anticancer Agents for AML Treatment

BACKGROUND

FMS-like tyrosine kinase 3 (FLT3) is a commonly mutated gene in acute myeloid leukemia. As a receptor tyrosine kinase (RTK), FLT3 plays a role in the proliferation and differentiation of hematopoietic stem cells. As the most frequent molecular alteration in AML, FLT3 has drawn the attention of many researchers, and a lot of small molecule inhibitors targeting FLT3 have been intensively investigated as potential drugs for AML therapy.

METHODS

In this paper, PubMed and SciFinder® were used as a tool; the publications about "FLT3 inhibitor" and "Acute myeloid leukemia" were surveyed from 2014 to the present with an exclusion of those published as patents.

RESULTS

In this study, the structural characterization and biological activities of representative FLT3 inhibitors were summarized. The major challenges and future directions for further research are discussed.

CONCLUSION

Recently, numerous FLT3 inhibitors have been discovered and employed in FLT3-mutated AML treatment. In order to overcome the drug resistance caused by FLT3 mutations, screening multitargets FLT3 inhibitors has become the main research direction. In addition, the emergence of irreversible FLT3 inhibitors also provides new ideas for discovering new FLT3 inhibitors.

Application of Newly Customized Myeloid NGS Panel in the Diagnosis of Myeloid Malignancies

Purpose

Genetic mutations are major factors in the diagnosis and prognosis of leukemia, and it is difficult to assess these variants using single-gene analysis. Therefore, this study aimed to develop a fast and cost-effective method for genetic screening of myeloid malignancies using a customized next-generation sequencing (NGS) panel.

Patients and Methods

A customized myeloid panel was designed and investigated in 15 acute myeloid leukemia patients. The panel included 11 genes that were most commonly mutated in myeloid malignancies. This panel was designed to sequence the complete genome of CALR, IDH1, IDH2, JAK2, FLT3, NPM1, MPL, TET2, SF3B1, TP53, and MLL.

Results

Among the 15 patients, 14 actual pathogenic variants were identified in nine samples, and negative results were found in six samples. Positive findings were observed for JAK2, FLT3, SF3B1, and TET2. Interestingly, non-classical FLT3 mutations (c.1715A>C, c.2513delG, and c.2507dupT) were detected in patients who were negative for FLT3-ITD and TKD by routine molecular results. All identified variants were pathogenic, and the high coverage of the assay allowed us to predict variants at a low frequency (1%) with 1000x coverage.

Conclusion

Utilizing a custom panel allowed us to identify variants that were not detected by routine tests or those that were not routinely investigated. Using the costuming panel will enable us to sequence all genes and discover new potential pathogenic variants that are not possible with other commercially available panels that focus only on hotspot regions. This study's strength in utilizing NGS and implanting a customized panel to identify new pathogenic variants that might be common in our population and important in routine diagnosis for providing optimal healthcare for personalized medicine.

Identifying novel therapeutic inhibitors to target FMS-like tyrosine kinase-3 (FLT3) against acute myeloid leukemia: a molecular docking, molecular dynamics, and DFT study

Around 30% of acute myeloid leukemia (AML) patients have triggering mutations in Feline McDonough Sarcoma (FMS)-like tyrosine kinase 3 (FLT3), which has been suggested as a possible therapeutic candidate for AML therapy. Many tyrosine kinase inhibitors are available and have a wide variety of applications in the treatment of cancer by inhibiting subsequent steps of cell proliferation. Therefore, our study aims to identify effective antileukemic agents against FLT3 gene. Initially, well-known antileukemic drug candidates have been chosen to generate a structure-based pharmacophore model to assist the virtual screening of 217,77,093 compounds from the Zinc database. The final hits compounds were retrieved and evaluated by docking against the target protein, where the top four compounds have been selected for the analysis of ADMET. Based on the density functional theory (DFT), the geometry optimization, frontier molecular orbital (FMO), HOMO-LUMO, and global reactivity descriptor values have been evaluated that confirming a satisfactory profile and reactivity order for the selected candidates. In comparison to control compounds, the docking results revealed that the four compounds had substantial binding energies (-11.1 to -11.5 kcal/mol) with FLT3. The physicochemical and ADMET (adsorption, distribution, metabolism, excretion, toxicity) prediction results corresponded to the bioactive and safe candidates. Molecular dynamics (MD) confirmed the better binding affinity and stability compared to gilteritinib as a potential FLT3 inhibitor. In this study, a computational approach has been performed that found a better docking and dynamics score against target proteins, indicating potent and safe antileukemic agents, furthermore in-vivo and in-vitro investigations are recommended.Communicated by Ramaswamy H. Sarma.

BCG immunotherapy promotes tumor-derived T-cell activation through the FLT3/FLT3LG pathway in bladder cancer

Bladder instillation therapy is a common treatment for superficial or nonmuscle invasive bladder cancer. After surgery or reresection, chemotherapy drugs (epirubicin) or medications such as Bacillus Calmette-Guérin (BCG) are used for bladder instillation therapy, which can reduce the risk of bladder cancer recurrence and progression. However, the specific mechanism by which BCG stimulates the antitumor response has not been thoroughly elucidated. Additionally, although BCG immunotherapy is effective, it is difficult to predict which patients will have a positive response. In this study, we explored the BCG-induced immune response and found that high levels of Fms-related receptor tyrosine kinase 3 ligand (FLT3LG) were expressed after BCG treatment. This FLT3LG can directly act on CD8+ T cells and promote their proliferation and activation. The use of FLT3 inhibitors can neutralize the antitumor effects of BCG. In vitro experiments showed that FLT3LG can synergize with T-cell receptor activators to promote the activation of tumor-derived T cells. This study partially elucidates the mechanism of CD8+ T-cell activation in BCG immunotherapy and provides a theoretical basis for optimizing BCG instillation therapy in bladder cancer.

Preclinical characterization of danatinib as a novel FLT3 inhibitor with excellent efficacy against resistant acute myeloid leukemia

The therapeutic benefits of available FLT3 inhibitors for AML are limited by drug resistance, which is related to mutations, as well toxicity caused by off-target effects. In this study, we introduce a new small molecule FLT3 inhibitor called danatinib, which was designed to overcome the limitations of currently approved agents. Danatinib demonstrated greater potency and selectivity, resulting in cytotoxic activity specific to FLT3-ITD and/or FLT3-TKD mutated models. It also showed a superior kinome inhibition profile compared to several currently approved FLT3 inhibitors. In diverse FLT3-TKD models, danatinib exhibited substantially improved activity at clinically relevant doses, outperforming approved FLT3 inhibitors. In vivo safety evaluations performed on the granulopoiesis of transgenic myeloperoxidase (MPO) zebrafish and mice models proved danatinib to have an acceptable safety profile. Danatinib holds promise as a new and improved FLT3 inhibitor for the treatment of AML, offering long-lasting remissions and improved overall survival rates.

FLT3 targeting in the modern era: from clonal selection to combination therapies

Fms-like tyrosine kinase 3 (FLT3) is the most frequently mutated gene in acute myeloid leukemia (AML). Modern targeting of FLT3 with inhibitors has improved clinical outcomes and FLT3 inhibitors have been incorporated into the treatment of AML in all phases of the disease, including the upfront, relapsed/refractory and maintenance settings. This review will discuss the current understanding of FLT3 biology, the clinical use of FLT3 inhibitors, resistance mechanisms and emerging combination treatment strategies.

Clinical features and prognostic significance of DNMT3A, FLT3, and NPM1 mutations in de novo acute myeloid leukemia patients

OBJECTIVE

Different co-mutation patterns are associated with varied clinical manifestations and prognosis. The purpose of this research was to explore the clinical characteristics and prognosis of individuals with AML who had DNMT3A, FLT3, and NPM1 mutations.

MATERIALS AND METHODS

A total of 259 newly diagnosed AML patients were investigated in this study, including 148 AMLFLT3mutDNMT3Awt , 48 AMLFLT3wtDNMT3Amut , and 63 AMLFLT3mutDNMT3Amut patients. Mutations were detected by targeted next-generation sequencing and Sanger sequencing. In addition, we utilized the publicly available data to analyze the expression profiles of AML.

RESULTS

Correlation analysis showed NPM1 mutations were positively associated with FLT3-ITD and DNMT3A, but negatively with CEBPA and RUNX1 mutations. In the presence of both DNMT3A and FLT3 mutations, patients were associated with typical clinical manifestations such as heavy disease burden and old age. Patients with both FLT3 and DNMT3A mutations had lower complete remission rates and poorer clinical outcomes than those with FLT3 or DNMT3A mutation alone. Univariate analysis showed that age, response to treatment, DNMT3A R882 mutation, NPM1 mutation, and consolidation treatment options were associated with OS. According to multivariate analysis, only consolidation treatment options could be considered as an independent prognostic factor. In addition, the percentage of AMLFLT3mutDNMT3AmutNPM1mut patients in our study was about 5.9%. Interestingly, the expression profile of this subgroup was significantly related to HOX family and histone H1 family, and enriched pathways associated with transcriptional misregulation.

CONCLUSION

We comprehensively evaluated the clinical and genetic characteristics, and expression profiles of AML patients with common mutations, and found that AML patients with triple mutations might be a distinct AML subtype, which should be redefined.

Correlation of blood cell counts with mutant subtypes and impact prognosis in acute myeloid leukemia patients with FLT3 mutations

OBJECTIVES

Acute myeloid leukemia (AML) often presents with abnormal blood cell counts and gene mutations at diagnosis. But, the correlation between blood cell counts and gene mutations and the clinical effects on AML is unclear.

METHODS

279 AML patients with FMS-like tyrosine kinase 3(FLT3) mutations were selected. Patients with FLT3 mutations were counted by PCR amplification products direct sequencing and second-generation sequencing (NGS), and blood cell counts at the time of initial diagnosis. The relapse-free survival (RFS) and overall survival (OS) and the influence of the clinical characteristics of patients on the prognosis in different groups were analyzed.

RESULTS

The median of platelet (PLT) count was higher in the TET2 non-mutation group than mutation group and higher in the IDH1/2 mutation group than non-mutation group. The median of white blood cell (WBC) count was reduced in the poor prognosis group. The differences in levels of WBC and PLT count varied among the four groups binding sequence (JM-B), switching sequence (JM-S), zipper sequence (JM-Z), and high chain region (JM-H). The differences in PLT count varied between the insertion length ≥39 bp and <39 bp, and between ≥ 50 bp and <50 bp; The OS and RFS in 10 < WBC (×10⁹/L) < 100 group and in the 30 ≤ PLT (×109/L)<80 group were better.

CONCLUSIONS

In AML patients with FLT3 mutations, the location of FLT3 mutations and the type of co-mutated genes may be correlated with blood cell counts, and different blood cell counts may have an impact on the prognosis.

Frequency and Prognostic Impact of Aberrant Antigens Expression among Egyptian Adult Acute Leukemia

OBJECTIVE

Aberrant antigen expression was reported to be due to genetic and epigenetic dysregulation. This study aimed to address aberrant antigen expression and its link to poor prognostic genetic markers in acute leukemia patients.

METHODS

This study included 432 newly diagnosed acute leukemia patients (AML, B-ALL). For all included patients blast cells expression for line assignment CD33 CD13 on B-All and CD7 on cytogenetically normal-AML blasts was assessed by flow cytometry in parallel to FLT3 and Philadelphia and philadelphia like chromosome in B-ALL.

RESULTS

From the total 432 cases of acute leukemia, the most frequent aberrant antigen expressed in B acute lymphoid leukemia (ALL) was CD33 (23.3%) followed by CD13(16.7%); while the most frequent one in AML was CD7 (16.7%). Aberrant myeloid phenotype in B-ALL was associated with lower mean total leukocytes count (TLC), low platelets count, positive Philadelphia like chromosome, shorter overall survival compared to the B-ALL without. Aberrant lymphoid phenotype (CD7) in AML was associated with a higher platelets count, FLT3 mutation, shorter disease-free and overall survival compared to those patients without.

CONCLUSION

CD7 aberrant antigen expression is frequently detected in patients with CN-AML and frequently associated with FLT3 mutation. While in patients with B-ALL the most frequently detected ones are CD33 and CD13 which are frequently associated with Philadelphia like chromosome.

Allosteric SHP2 inhibition increases apoptotic dependency on BCL2 and synergizes with venetoclax in FLT3- and KIT-mutant AML

Mutations in the receptor tyrosine kinases (RTKs) FLT3 and KIT are frequent and associated with poor outcomes in acute myeloid leukemia (AML). Although selective FLT3 inhibitors (FLT3i) are clinically effective, remissions are short-lived due to secondary resistance characterized by acquired mutations constitutively activating the RAS/MAPK pathway. Hereby, we report the pre-clinical efficacy of co-targeting SHP2, a critical node in MAPK signaling, and BCL2 in RTK-driven AML. The allosteric SHP2 inhibitor RMC-4550 suppresses proliferation of AML cell lines with FLT3 and KIT mutations, including cell lines with acquired resistance to FLT3i. We demonstrate that pharmacologic SHP2 inhibition unveils an Achilles' heel of RTK-driven AML, increasing apoptotic dependency on BCL2 via MAPK-dependent mechanisms, including upregulation of BMF and downregulation of MCL1. Consequently, RMC-4550 and venetoclax are synergistically lethal in AML cell lines and in clinically relevant xenograft models. Our results provide mechanistic rationale and pre-clinical evidence for co-targeting SHP2 and BCL2 in RTK-driven AML.

Perspectives and challenges of small molecule inhibitor therapy for FLT3-mutated acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous clonal disease characterized overall by an aggressive clinical course. The underlying genetic abnormalities present in leukemic cells contribute significantly to the AML phenotype. Mutations in FMS-like tyrosine kinase 3 (FLT3) are one of the most common genetic abnormalities identified in AML, and the presence of these mutations strongly influences disease presentation and negatively impacts prognosis. Since mutations in FLT3 were identified in AML, they have been recognized as a valid therapeutic target resulting in decades of research to develop effective small molecule inhibitor treatment that could improve outcome for these patients. Despite the approval of several FLT3 inhibitors over the last couple of years, the treatment of patients with FLT3-mutated AML remains challenging and many questions still need to be addressed. This review will provide an up-to-date overview of our current understanding of FLT3-mutated AML and discuss what the current status is of the available FLT3 inhibitors for the day-to-day management of this aggressive disease.

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.

Targeting FLT3-TAZ signaling to suppress drug resistance in blast phase chronic myeloid leukemia

BACKGROUND

Although the development of BCR::ABL1 tyrosine kinase inhibitors (TKIs) rendered chronic myeloid leukemia (CML) a manageable condition, acquisition of drug resistance during blast phase (BP) progression remains a critical challenge. Here, we reposition FLT3, one of the most frequently mutated drivers of acute myeloid leukemia (AML), as a prognostic marker and therapeutic target of BP-CML.

METHODS

We generated FLT3 expressing BCR::ABL1 TKI-resistant CML cells and enrolled phase-specific CML patient cohort to obtain unpaired and paired serial specimens and verify the role of FLT3 signaling in BP-CML patients. We performed multi-omics approaches in animal and patient studies to demonstrate the clinical feasibility of FLT3 as a viable target of BP-CML by establishing the (1) molecular mechanisms of FLT3-driven drug resistance, (2) diagnostic methods of FLT3 protein expression and localization, (3) association between FLT3 signaling and CML prognosis, and (4) therapeutic strategies to tackle FLT3+ CML patients.

RESULTS

We reposition the significance of FLT3 in the acquisition of drug resistance in BP-CML, thereby, newly classify a FLT3+ BP-CML subgroup. Mechanistically, FLT3 expression in CML cells activated the FLT3-JAK-STAT3-TAZ-TEAD-CD36 signaling pathway, which conferred resistance to a wide range of BCR::ABL1 TKIs that was independent of recurrent BCR::ABL1 mutations. Notably, FLT3+ BP-CML patients had significantly less favorable prognosis than FLT3- patients. Remarkably, we demonstrate that repurposing FLT3 inhibitors combined with BCR::ABL1 targeted therapies or the single treatment with ponatinib alone can overcome drug resistance and promote BP-CML cell death in patient-derived FLT3+ BCR::ABL1 cells and mouse xenograft models.

CONCLUSION

Here, we reposition FLT3 as a critical determinant of CML progression via FLT3-JAK-STAT3-TAZ-TEAD-CD36 signaling pathway that promotes TKI resistance and predicts worse prognosis in BP-CML patients. Our findings open novel therapeutic opportunities that exploit the undescribed link between distinct types of malignancies.

Design, synthesis, and biological evaluation of 3, 5-disubsituted-1H-pyrazolo[3,4-b]pyridines as multiacting inhibitors against microtubule and kinases

Combination therapy of kinases inhibitors and chemotherapeutics targeting tubulin dynamics is an important strategy to improve therapeutic efficacy and overcome the resistance to single-target drug therapies. Inspired by this, we report herein the rational design of 3,5-disubsituted-1H-pyrazolo[3,4-b]pyridines as multiacting molecules that are capable of inhibiting tubulin and kinases simultaneously. Among them, 8g showed excellent antiproliferative activities toward a panel of cancer cell lines. 8g strongly inhibited tubulin assembly and demonstrated a potent inhibition toward FLT3 and Abl1 in both enzymatic and cellular assays. 8g caused a cell cycle arrest at G2/M phase, and significantly disrupted HUVEC tube formation. In vivo efficacy studies showed that 8g significantly inhibited tumor growth on the K562 leukemia xenograft model at 10 mg/kg. Collectively our studies suggest that the excellent antiproliferative potency of 8g may be attributed to its potent inhibitory activity against both microtubule and kinases.

Gilteritinib and the risk of intracranial hemorrhage: a case series of a possible, under-reported side effect

Gilteritinib is currently approved for patients with relapsed/refractory AML with FLT3 mutations, based on the positive results of the pivotal ADMIRAL study. In ADMIRAL trial, no increased risk of bleeding was reported, but in the previous dose finding study, a single event of intracranial hemorrhage (ICH) was registered after exposure to subtherapeutic doses of gilteritinib. Here, we report the first case series on five ICHs diagnosed in patients with FLT3-mutated AML, occurred within the first month of exposure to gilteritinib. Our cohort included 24 patients treated in three Italian centers. Most of these ICH cases were non-severe and self-limiting, while one was fatal. This link with ICHs remains in any case uncertain for the presence of active AML. We further reported that an analysis of the post-marketing surveillance data (EudraVigilance) retrieved other 11 cases of ICHs present in the database after gilteritinib treatment. A causality assessment was performed according to the Dx3 method to evaluate the possibility that ICHs might be an actual side effect of gilteritinib. In conclusion, further research is needed to elucidate the potential role of gilteritinib in the pathogenesis of ICHs.

Mechanisms of Resistance to Small Molecules in Acute Myeloid Leukemia

In recent years, great progress has been made in the therapy of AML by targeting cellular processes associated with specific molecular features of the disease. Various small molecules inhibiting FLT3, IDH1/IDH2, and BCL2 have already gained approval from the respective authorities and are essential parts of personalized therapeutic regimens in modern therapy of AML. Unfortunately, primary and secondary resistance to these inhibitors is a frequent problem. Here, we comprehensively review the current state of knowledge regarding molecular processes involved in primary and secondary resistance to these agents, covering both genetic and nongenetic mechanisms. In addition, we introduce concepts and strategies for how these resistance mechanisms might be overcome.

Characteristics and Outcome of FLT3-ITD-Positive Pediatric Acute Myeloid Leukemia-Experience of Polish Pediatric Leukemia and Lymphoma Study Group from 2005 to 2022

BACKGROUND

The FMS-like tyrosine kinase 3 (FLT3) gene mutated in 10-15% of pediatric acute myeloid leukemia (AML) is associated with an inferior outcome. The aim of the study was to analyze the outcome and characteristics of FLT3-ITD-positive pediatric AML.

METHODS

We retrospectively analyzed the nationwide pediatric AML database from between 2005 and 2022. FLT3-ITD was found in 54/497 (10.7%) patients with available analysis. Three consecutive treatment protocols were used (AML-BFM 2004 Interim, AML-BFM 2012 Registry, AML-BFM 2019 recommendations).

RESULTS

Probabilities of 5-year overall (OS), event-free (EFS) and relapse-free survival were significantly lower in the FLT3-ITD-positive patients compared to FLT3-ITD-negative (0.54 vs. 0.71, p = 0.041; 0.36 vs. 0.59, p = 0.0004; 0.47 vs. 0.70, p = 0.0029, accordingly). An improvement in the outcome was found in the analyzed period of time, with a trend of better survival in patients treated under the AML-BFM 2012 and AML-BFM 2019 protocols compared to the AML-BFM 2004 protocol (5-year EFS 0.52 vs. 0.27, p = 0.069). There was a trend of improved outcomes in patients treated with FLT3 inhibitors (n = 9, 2-year EFS 0.67 vs. 0.33, p = 0.053) and those who received stem cell transplantation (SCT) (n = 26; 5-year EFS 0.70 vs. 0.27, p = 0.059). The co-occurrence of the WT1 mutation had a dismal impact on the prognosis (5-year EFS 0.23 vs. 0.69, p = 0.002), while the NPM1 mutation improved survival (5-year OS 1.0 vs. 0.44, p = 0.036).

CONCLUSIONS

It seems that SCT and FLT3 inhibitors have a beneficial impact on the prognosis. Additional genetic alterations, like the WT1 and NPM1 mutations, significantly influence the outcome.

FLT3-directed UniCAR T-cell therapy of acute myeloid leukaemia

Adaptor chimeric antigen receptor (CAR) T-cell therapy offers solutions for improved safety and antigen escape, which represent main obstacles for the clinical translation of CAR T-cell therapy in myeloid malignancies. The adaptor CAR T-cell platform 'UniCAR' is currently under early clinical investigation. Recently, the first proof of concept of a well-tolerated, rapidly switchable, CD123-directed UniCAR T-cell product treating patients with acute myeloid leukaemia (AML) was reported. Relapsed and refractory AML is prone to high plasticity under therapy pressure targeting one single tumour antigen. Thus, targeting of multiple tumour antigens seems to be required to achieve durable anti-tumour responses, underlining the need to further design alternative AML-specific target modules (TM) for the UniCAR platform. We here present the preclinical development of a novel FMS-like tyrosine kinase 3 (FLT3)-directed UniCAR T-cell therapy, which is highly effective for in vitro killing of both AML cell lines and primary AML samples. Furthermore, we show in vivo functionality in a murine xenograft model. PET analyses further demonstrate a short serum half-life of FLT3 TMs, which will enable a rapid on/off switch of UniCAR T cells. Overall, the presented preclinical data encourage the further development and clinical translation of FLT3-specific UniCAR T cells for the therapy of AML.

Gilteritinib in peritransplant period for relapsed or refractory FLT3-mutated acute myeloid leukemia: A case report of three patients

Patients with relapsed or refractory acute myeloid leukemia (RR-AML) with mutations of FMS-like tyrosine kinase 3 (FLT3) have a poor prognosis even after allogeneic hematopoietic cell transplantation (allo-HCT). Multiple FLT3 inhibitors, including gilteritinib, have been developed and serve as treatment options for RR-AML. Here, we describe three cases of FLT3 mutated RR-AML that were successfully treated with gilteritinib administration before and after allo-HCT. Gilteritinib treatment before HCT was helpful in achieving remission. However, HCT often resulted in mild liver damage, and careful introduction of gilteritinib after HCT at a lower dose may be helpful for its safe usage. The three cases discussed had a successful clinical outcome in terms of disease control as well as the management of side effects associated with gilteritinib treatment.

Phase I study evaluating the Fc-optimized FLT3 antibody FLYSYN in AML patients with measurable residual disease

BACKGROUND

About half of AML patients achieving complete remission (CR) display measurable residual disease (MRD) and eventually relapse. FLYSYN is an Fc-optimized antibody for eradication of MRD directed to FLT3/CD135, which is abundantly expressed on AML cells.

METHODS

This first-in-human, open-label, single-arm, multicenter trial included AML patients in CR with persisting or increasing MRD and evaluated safety/tolerability, pharmacokinetics and preliminary efficacy of FLYSYN at different dose levels administered intravenously (cohort 1-5: single dose of 0.5 mg/m2, 1.5 mg/m2, 5 mg/m2, 15 mg/m2, 45 mg/m2; cohort 6: 15 mg/m2 on day 1, 15 and 29). Three patients were treated per cohort except for cohorts 4 and 6, which were expanded to nine and ten patients, respectively. Primary objective was safety, and secondary efficacy objective was ≥ 1 log MRD reduction or negativity in bone marrow.

RESULTS

Overall, 31 patients were treated, of whom seven patients (22.6%) experienced a transient decrease in neutrophil count (two grade 3, others ≤ grade 2). No infusion-related reaction or dose-limiting toxicity was observed. Adverse events (AEs) were mostly mild to moderate, with the most frequent AEs being hematologic events and laboratory abnormalities. Response per predefined criteria was documented in 35% of patients, and two patients maintained MRD negativity until end of study. Application of 45 mg/m2 FLYSYN as single or cumulative dose achieved objective responses in 46% of patients, whereas 28% responded at lower doses.

CONCLUSIONS

FLYSYN monotherapy is safe and well-tolerated in AML patients with MRD. Early efficacy data are promising and warrant further evaluation in an up-coming phase II trial. Trial registration This clinical is registered on clinicaltrials.gov (NCT02789254).

Elevated FAM134B expression induces radiation-sensitive in hepatocellular carcinoma

BACKGROUND

Previous studies have shown that Family with sequence similarity 134 member B (FAM134B) was involved in the occurrence and development of malignancy, however, the function and molecular mechanism of FAM134B in Hepatocellular Carcinoma (HCC) radiotherapy resistance remain unclear. Therefore, it may clinical effective to clarify the molecular mechanism and identify novel biomarker to overcome radiotherapy resistance in HCC.

METHODS

The protein and mRNA expression of FAM134B were determined using Real-time PCR and Western blot, respectively. IHC assay was performed to investigate the association between FAM134B expression and the clinicopathological characteristics of 132 HCC patients. Functional assays, such as in situ model, colon formation, FACS, and Tunel assay were used to determine the oncogenic role of FAM134B in human HCC progression. Furthermore, western blotting and luciferase assay were used to determine the mechanism of FAM134B promotes radiation-sensitive in HCC cells.

RESULTS

We noted that FAM134B was downregulated in HCC, which was correlated with the radiation resistance in patients with HCC. Overexpression of FAM134B contribute to radiation sensitive in HCC; however, inhibition of FAM134B confers HCC cell lines to radiation resistance both in vitro and in vivo. Moreover, we found that FAM134B interacts with FMS related receptor tyrosine kinase 3 (FLT3) and downregulation of FAM134B activated JAK/Stat3 signaling pathway. Importantly, pharmacological inhibition of JAK/Stat3 signaling pathway significantly counteracted downregulation of FAM134B-induced radiation resistance and enhanced radiation therapeutic efficacy in HCC.

CONCLUSIONS

Our findings suggest that FAM134B may be a potential therapeutic biomarker for the treatment of HCC patients with radiotherapy tolerance.

Combination of an Oxindole Derivative with (-)-β-Elemene Alters Cell Death Pathways in FLT3/ITD+ Acute Myeloid Leukemia Cells

Acute myeloid leukemia (AML) is one of the cancers that grow most aggressively. The challenges in AML management are huge, despite many treatment options. Mutations in FLT3 tyrosine kinase receptors make the currently available therapies less responsive. Therefore, there is a need to find new lead molecules that can specifically target mutated FLT3 to block growth factor signaling and inhibit AML cell proliferation. Our previous studies on FLT3-mutated AML cells demonstrated that β-elemene and compound 5a showed strong inhibition of proliferation by blocking the mutated FLT3 receptor and altering the key apoptotic genes responsible for apoptosis. Furthermore, we hypothesized that both β-elemene and compound 5a could be therapeutically effective. Therefore, combining these drugs against mutated FLT3 cells could be promising. In this context, dose-matrix combination-based cellular inhibition analyses, cell morphology studies and profiling of 43 different apoptotic protein targets via combinatorial treatment were performed. Our studies provide strong evidence for the hypothesis that β-elemene and compound 5a combination considerably increased the therapeutic potential of both compounds by enhancing the activation of several key targets implicated in AML cell death.

Promising Cytotoxic butenolides from the Soybean endophytic fungus Aspergillus terreus: a combined molecular docking and in-vitro studies

AIM

This study aimed to use one strain many compounds approach (OSMAC) to investigate the cytotoxic potential of Aspergillus terreus associated with soybean versus several cancer cell lines, by means of in-silico and in vitro approaches.

METHODS AND RESULTS

Fermentation of the isolated strain was done on five media. The derived extracts were investigated for their inhibitory activities against three human cancer cell lines; mammary gland breast cancer (MCF-7), colorectal adenocarcinoma (Caco-2) and hepatocellular carcinoma (HepG2) using MTT Assay. The fungal mycelia fermented in Modified Potato Dextrose Broth (MPDB) was the most cytotoxic extract against HepG2, MCF-7 and Caco-2 cell lines with IC50 4.2 ± 0.13, 5.9 ± 0.013 and 7.3 ± 0.004 µg.mL-1, respectively. MPDB extract was scaled up resulting in the isolation of six metabolites; three fatty acids (1, 2 and 4), one sterol (3) and two butenolides (5 and 6) by column chromatography. The isolated compounds (1-6) were screened through a molecular docking approach for their binding aptitude to various active sites. butyrolactone-I (5) revealed a significant interaction within the CDK2 active site, while aspulvinone E (6) showed promising binding affinity to FLT3 and EGFR active sites that was confirmed by in vitro CDK2, FLT3 and EGFR inhibitory activity. Finally, the in vitro cytotoxic activities of butyrolactone-I (5) and aspulvinone E (6) revealed the antiproliferative activity of butyrolactone-I (5), against HepG2 cell line (IC50 = 17.85 ± 0.32 µM).

CONCLUSION

Molecular docking analysis and in vitro assays suggested the CDK2/A2 inhibitory potential of butyrolactone-I (5) in addition to the promising interaction abilities of aspulvinone E (6) with EGFR and FLT3 active sites as a possible mechanism of their biological activities.

Ferroptosis vulnerability in FLT3-mutant leukemia

Resistance to FLT3 inhibition is a prevalent challenge in managing FLT3-mutant acute myeloid leukemia (AML). A recent study by Sabatier et al. discovered ferroptosis vulnerability in FLT3-mutant AML and they propose a promising therapeutic approach of combining FLT3 inhibitors with ferroptosis inducers for treating this type of cancer.

High GLI-1 Expression is a Reliable Indicator of Bad Prognosis in Newly Diagnosed Acute Leukemia Patients

PURPOSE

To explore the expression and prognostic significance of Hedgehog signaling transcription factor GLI-1 in newly diagnosed acute myeloid leukemia (AML) patients.

METHODS

Clinical specimens were obtained from 46 recently diagnosed AML patients. Real-time qPCR was used to measure the GLI-1 mRNA expression in bone marrow mononuclear cells.Also, the relationship between GLI-1 mRNA levels and clinical variables and prognostic variables was assessed.

RESULTS

GLI-1 was overexpressed in the bone marrow samples of our patients. GLI-1mRNA expression did not differ significantly across different age groups, between both sexes, or between different FAB subtypes (P = 0.882, P = 0.246, and P = 0.890, respectively). GLI-1 expression varied significantly in different risk categories, with the greatest levels observed in 11 patients with poor risk (24.6 versus 22.7) compared to intermediate risk (5.2 versus 3.9; P = 0.006) and favorable risk (4.2 versus 3; P = 0.001). Comparing patients with the wild FLT3 allele to those with the mutant one, GLI-1 gene levels were considerably greater in those with the mutant allele of FLT3.Following induction chemotherapy, the levels of GLI-1 mRNA were significantly higher in 22 patients who did not experience complete remission (CR) diagnosed with de novo non-acute promyelocytic leukemia (APL) compared to 17 patients who did (P = 0.017). Significantly greater levels of expression were observed in each category of the patients with favorable risk; wild FLT3 allele (P = 0.033) and CR failure P = 0.005).

CONCLUSION

GLI-1 overexpression is a risk factor for poor prognosis and could be a novel therapeutic target for AML.

Emerging small molecular inhibitors as targeted therapies for high-risk acute myeloid leukemias

INTRODUCTION

Acute myeloid leukemia (AML) is an aggressive disease which has traditionally been treated with intensive chemotherapy. Survival in patients with high-risk cytogenetic and molecular subsets has been poor with this approach due to suboptimal responses seen with intensive chemotherapy and due to many patients with higher risk disease being older and unable to tolerate intensive therapies. In recent years, several targeted therapies have been under investigation for patients with high-risk AML subsets.

AREAS COVERED

This review covers four different subsets of high-risk AML including TP53-mutated, KMT2A-rearranged, FLT3-mutated, and secondary AML developing after prior hypomethylating agent exposure. The research discussed in this review focuses on small molecule inhibitors that have been studied in the treatment of these high-risk AML subsets.

EXPERT OPINION

There are several small molecule inhibitors that have demonstrated promise in these high-risk AML subsets. Longer follow-up and ongoing investigation are needed to continue to optimize therapy for patients with high-risk AML.

RUNX1/ETO regulates reactive oxygen species (ROS) levels in t(8,21) acute myeloid leukaemia via FLT3 and RAC1

Reactive oxygen species (ROS) homeostasis is crucial for leukaemogenesisand deregulation would hamper leukaemic progression. Although the regulatory effects of RUNX1/ETO has been extensively studied, its underlying molecular mechanims in ROS production in t(8,21) AML is yet to be fully elucidated. Here, we report that RUNX1/ETO could directly control FLT3 by occupying several DNA elements on FLT3 locus. The possible hijacking mechanism by RUNX1/ETO over FLT3 mediated ROS modulation in AML t(8;21) was made apparent when suppression of RUNX1/ETO led to decrement in ROS levels and the direct oxidative marker FOXO3 but not in FLT3 and RAC1 suppressed t(8,21) AML cell line Furthermore, nuclear import of RUNX1/ETO was aberrated following RUNX1/ETO and RAC1 suppression suggesting association in ROS control. A different picture was depicted in non t(8;21) cells where suppression of RAC1 and FLT3 led to decreased levels of FOXO3a and ROS. Results alltogether indicate a possible dysregulation of ROS levels by RUNX1/ETO in t(8,21) AML.

In vivo activity of the dual SYK/FLT3 inhibitor TAK-659 against pediatric acute lymphoblastic leukemia xenografts

BACKGROUND

While children with acute lymphoblastic leukemia (ALL) experience close to a 90% likelihood of cure, the outcome for certain high-risk pediatric ALL subtypes remains dismal. Spleen tyrosine kinase (SYK) is a prominent cytosolic nonreceptor tyrosine kinase in pediatric B-lineage ALL (B-ALL). Activating mutations or overexpression of Fms-related receptor tyrosine kinase 3 (FLT3) are associated with poor outcome in hematological malignancies. TAK-659 (mivavotinib) is a dual SYK/FLT3 reversible inhibitor, which has been clinically evaluated in several other hematological malignancies. Here, we investigate the in vivo efficacy of TAK-659 against pediatric ALL patient-derived xenografts (PDXs).

METHODS

SYK and FLT3 mRNA expression was quantified by RNA-seq. PDX engraftment and drug responses in NSG mice were evaluated by enumerating the proportion of human CD45+ cells (%huCD45+ ) in the peripheral blood. TAK-659 was administered per oral at 60 mg/kg daily for 21 days. Events were defined as %huCD45+ ≥ 25%. In addition, mice were humanely killed to assess leukemia infiltration in the spleen and bone marrow (BM). Drug efficacy was assessed by event-free survival and stringent objective response measures.

RESULTS

FLT3 and SYK mRNA expression was significantly higher in B-lineage compared with T-lineage PDXs. TAK-659 was well tolerated and significantly prolonged the time to event in six out of eight PDXs tested. However, only one PDX achieved an objective response. The minimum mean %huCD45+ was significantly reduced in five out of eight PDXs in TAK-659-treated mice compared with vehicle controls.

CONCLUSIONS

TAK-659 exhibited low to moderate single-agent in vivo activity against pediatric ALL PDXs representative of diverse subtypes.

Novel spiroindoline quinazolinedione derivatives as anticancer agents and potential FLT3 kinase inhibitors

Despite considerable recent progress in therapeutic strategies, cancer still remains one of the leading causes of death. Molecularly targeted therapies, in particular those focused on blocking receptor tyrosine kinases have produced promising outcomes in recent years. In this study, a new series of spiro[indoline-3,2'-quinazoline]-2,4'(3'H)-dione derivatives (5a-5l) were synthesized and evaluated as potential kinase inhibitors with anticancereffects. The anti-proliferative activity was measured by MTT assay, while the cell cycle was studied using flow cytometry. Moreover, kinase inhibition profiles of the most promising compounds were assessed against a panel of 25 oncogenic kinases. Compounds 5f,5g,5i, and 5jshowed anti-proliferative effect against EBC-1, A549, and HT-29 solid tumor models in addition to leukemia cell line K562. In particular, compound 5f, bearing 4-methylphenyl pendant on the isatin ring displayed considerable potency with IC₅₀ values of 2.4 to 13.4 μM against cancer cells. The most potent derivatives also altered the distribution of cells in different phases of cell cycle and increased the sub-G1 phase cells in K562 cells. Moreover, kinase inhibition assays identified FLT3 kinase was as the primary targetof these derivatives. Compound 5f at 25 μM concentration showed inhibitory activities of 55% and 62% against wild-type FLT3 and its mutant, D835Y, respectively. Finally, the docking and simulation studies revealed the important interactions of compound 5f with wild type and mutant FLT3. The results of this study showed that some novel spiroindoline quinazolinedione compounds could be potential candidates for further development as novel targeted anticancer agents.

Mutation spectrum of FLT3 and significance of non-canonical FLT3 mutations in haematological malignancy

Fms-like tyrosine kinase 3 (FLT3) is frequently mutated in haematological malignancies. Although canonical FLT3 mutations including internal tandem duplications (ITDs) and tyrosine kinase domains (TKDs) have been extensively studied, little is known about the clinical significance of non-canonical FLT3 mutations. Here, we first profiled the spectrum of FLT3 mutations in 869 consecutively newly diagnosed acute myeloid leukaemia (AML), myelodysplastic syndrome and acute lymphoblastic leukaemia patients. Our results showed four types of non-canonical FLT3 mutations depending on the affected protein structure: namely non-canonical point mutations (NCPMs) (19.2%), deletion (0.7%), frameshift (0.8%) and ITD outside the juxtamembrane domain (JMD) and TKD1 regions (0.5%). Furthermore, we found that the survival of patients with high-frequency (>1%) FLT3-NCPM in AML was comparable to those with canonical TKD. In vitro studies using seven representative FLT3-deletion or frameshift mutant constructs showed that the deletion mutants of TKD1 and the FLT3-ITD mutant of TKD2 had significantly higher kinase activity than wild-type FLT3, whereas the deletion mutants of JMD had phosphorylation levels comparable with wild-type FLT3. All tested deletion mutations and ITD were sensitive to AC220 and sorafenib. Collectively, these data enrich our understanding of FLT3 non-canonical mutations in haematological malignancies. Our results may also facilitate prognostic stratification and targeted therapy of AML with FLT3 non-canonical mutations.

CAR-T Cells Immunotherapies for the Treatment of Acute Myeloid Leukemia-Recent Advances

In order to increase the effectiveness of cancer therapies and extend the long-term survival of patients, more and more often, in addition to standard treatment, oncological patients receive also targeted therapy, i.e., CAR-T cells. These cells express a chimeric receptor (CAR) that specifically binds an antigen present on tumor cells, resulting in tumor cell lysis. The use of CAR-T cells in the therapy of relapsed and refractory B-type acute lymphoblastic leukemia (ALL) resulted in complete remission in many patients, which prompted researchers to conduct tests on the use of CAR-T cells in the treatment of other hematological malignancies, including acute myeloid leukemia (AML). AML is associated with a poorer prognosis compared to ALL due to a higher risk of relapse caused by the development of resistance to standard treatment. The 5-year relative survival rate in AML patients was estimated at 31.7%. The objective of the following review is to present the mechanism of action of CAR-T cells, and discuss the latest findings on the results of anti-CD33, -CD123, -FLT3 and -CLL-1 CAR-T cell therapy, the emerging challenges as well as the prospects for the future.

How acute myeloid leukemia (AML) escapes from FMS-related tyrosine kinase 3 (FLT3) inhibitors? Still an overrated complication?

FMS-related tyrosine kinase 3 (FLT3) mutations, present in about 25%-30% of acute myeloid leukemia (AML) patients, constitute one of the most frequently detected mutations in these patients. The binding of FLT3L to FLT3 activates the phosphatidylinositol 3-kinase (PI3K) and RAS pathways, producing increased cell proliferation and the inhibition of apoptosis. Two types of FLT3 mutations exist: FLT3-ITD and FLT3-TKD (point mutations in D835 and I836 or deletion of codon I836). A class of drugs, tyrosine-kinase inhibitors (TKI), targeting mutated FLT3, is already available with 1^st and 2^nd generation molecules, but only midostaurin and gilteritinib are currently approved. However, the emergence of resistance or the selection of clones not responding to FLT3 inhibitors has become an important clinical dilemma, as the duration of clinical responses is generally limited to a few months. This review analyzes the insights into mechanisms of resistance to TKI and poses a particular view on the clinical relevance of this phenomenon. Has resistance been overlooked? Indeed, FLT3 inhibitors have significantly contributed to reducing the negative impact of FLT3 mutations on the prognosis of AML patients who are no longer considered at high risk by the European LeukemiaNet (ELN) 2022. Finally, several ongoing efforts to overcome resistance to FLT3-inhibitors will be presented: new generation FLT3 inhibitors in monotherapy or combined with standard chemotherapy, hypomethylating drugs, or IDH1/2 inhibitors, Bcl2 inhibitors; novel anti-human FLT3 monoclonal antibodies (e.g., FLT3/CD3 bispecific antibodies); FLT3-CAR T-cells; CDK4/6 kinase inhibitor (e.g., palbociclib).

Revisiting the prognostic role of FLT3 mutations in acute myelogenous leukemia

INTRODUCTION

Approximately one-third of patients with acute myelogenous leukemia (AML) harbor mutations in the fms-like tyrosine kinase 3 (FLT3) gene. The features regarding prognostic impact of FLT3 mutated AML have been widely investigated and debated in the last decades, and the significance of this mutation is constantly evolving.

AREAS COVERED

In this article, the significance of the FLT3 mutation and various aspects of this mutation are discussed in the light of new understanding and research progress in past years. The recently updated European Leukemia Net (ELN) guidelines are reviewed and discussed, special emphasis given to the the improvement in therapeutic approaches for FLT3 mutated AML.

EXPERT OPINION

Aspects related to FLT3 mutated AML include the type of mutation in addition to FLT3-internal tandem duplication (ITD) length, location, and allelic ratio. Furthermore, the coexistence of cytogenetic variants and molecular genetic mutations utterly complicate the evaluation of the prognostic impact. In addition, introduction of FLT3 inhibitors and establishment of measurable residual disease (MRD) monitoring have entered the treatment and evaluation armamentarium in the handling of AML patients, resulting in improved prognosis for these patients. However, future research to optimize the treatment of FLT3 mutated AML is highly desired.

Set Protein Is Involved in FLT3 Membrane Trafficking

The in-frame internal tandem duplication (ITD) of the FLT3 gene is an important negative prognostic factor in acute myeloid leukemia (AML). FLT3-ITD is constitutive active and partially retained in the endoplasmic reticulum (ER). Recent reports show that 3'UTRs function as scaffolds that can regulate the localization of plasma membrane proteins by recruiting the HuR-interacting protein SET to the site of translation. Therefore, we hypothesized that SET could mediate the FLT3 membrane location and that the FLT3-ITD mutation could somehow disrupt the model, impairing its membrane translocation. Immunofluorescence and immunoprecipitation assays demonstrated that SET and FLT3 co-localize and interact in FLT3-WT cells but hardly in FLT3-ITD. SET/FLT3 interaction occurs before FLT3 glycosylation. Furthermore, RNA immunoprecipitation in FLT3-WT cells confirmed that this interaction occurs through the binding of HuR to the 3'UTR of FLT3. HuR inhibition and SET nuclear retention reduced FLT3 in the membrane of FLT3-WT cells, indicating that both proteins are involved in FLT3 membrane trafficking. Interestingly, the FLT3 inhibitor midostaurin increases FLT3 in the membrane and SET/FLT3 binding. Therefore, our results show that SET is involved in the transport of FLT3-WT to the membrane; however, SET barely binds FLT3 in FLT3-ITD cells, contributing to its retention in the ER.

Targeting FLT3-specific chimeric antigen receptor T cells for acute lymphoblastic leukemia with KMT2A rearrangement

CD19-specific chimeric antigen receptor T (CAR T) immunotherapy is used to treat B-cell malignancies. However, antigen-escape mediated relapse following CAR T therapy has emerged as a major concern. In some relapsed cases, especially KMT2A rearrangement-positive B-acute lymphoblastic leukemia (KMT2A-r B-ALL), most of the B-cell antigens are lost via lineage conversion to the myeloid phenotype, rendering multi-B-cell-antigen-targeted CAR T cell therapy ineffective. Fms-related tyrosine kinase-3 (FLT3) is highly expressed in KMT2A-r B-ALL; therefore, in this study, we aimed to evaluate the antitumor efficacy of CAR T cells targeting both CD19 and FLT3 in KMT2A-r B-ALL cells. We developed piggyBac transposon-mediated CAR T cells targeting CD19, FLT3, or both (dual) and generated CD19-negative KMT2A-r B-ALL models through CRISPR-induced CD19 gene-knockout (KO). FLT3 CAR T cells showed antitumor efficacy against CD19-KO KMT2A-r B-ALL cells both in vitro and in vivo; dual-targeted CAR T cells showed cytotoxicity against wild-type (WT) and CD19-KO KMT2A-r B-ALL cells, whereas CD19 CAR T cells demonstrated cytotoxicity only against WT KMT2A-r B-ALL cells in vitro. Therefore, targeting FLT3-specific CAR T cells would be a promising strategy for KMT2A-r B-ALL cells even with CD19-negative relapsed cases.

Higher mTOR Expression: A Marker of Poor Outcome in Patients with de Novo AML

Acute myeloid leukemia (AML) displays significant clinical diversity mainly due to the variation in the underlying molecular defects, which is now recognized as the main driver for leukemogenesis. mTOR deregulation is thought to promote the proliferation and survival of leukemic blasts. This work aimed to study mTOR gene expression as a prognostic marker and a potential therapeutic target in AML. Quantitative real-time PCR evaluated mTOR expression in 45 new AML cases in relation to disease characteristics and outcome. mTOR was overexpressed in AML patients and higher levels were seen in the group that was not in complete remission (CR), at the end of induction, compared to those who achieved remission (17.03 ± 16.44 vs 3.91 ± 2.55 respectively, p < 0.001). In addition, mTOR expression inversely correlated with survival (p < 0.001). Patients with mTOR expression > 5.2 had a median overall survival of 10 months as opposed to 23 months in those with an expression of ≤ 5.2, p < 0.001. mTOR was an independent risk factor for failure of response in our patient group (p 0.007 and OR 1.54). mTOR has prognostic implications as it predicted the response and survival in our patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12288-022-01569-3.