Synthesis, kinase inhibition and anti-leukemic activities of diversely substituted indolopyrazolocarbazoles

Pyrazole analogues of the staurosporine aglycone K252c, in which the lactam ring was replaced by a pyrazole moiety, were synthesized. In this series, one or the other nitrogen atoms of the indolocarbazole scaffold was substituted by aminoalkyl chains, aiming at improving protein kinase inhibition as well as cellular potency toward acute myeloid leukemia (AML) cell lines. Compound 19a, substituted at the N12-position by a 3-(methylamino)propyl group, showed high cellular activity in the low micromolar range toward three AML cell lines (MOLM-13, OCI-AML3 and MV4-11) with selectivity over non-cancerous cells (NRK, H9c2). 19a is also a highly potent inhibitor of the three Pim kinase isoforms, Pim-3 being the most inhibited with an IC50 value in the nanomolar range. A selectivity screening toward a panel of 50 protein kinases showed that 19a also potently inhibited PRK2 and to a lower extent AMPK, MARK3, GSK3β and JAK3. Our results enhance the understanding of the structural characteristics of indolopyrazolocarbazoles essential for potent protein kinase inhibition with therapeutic potential against AML.

FLT3 signaling augments macrophage production from human pluripotent stem cells

Recent advances in cell engineering technologies enable immune cells to be utilized for adoptive cell transfer (ACT) immunotherapy against cancers. Macrophages have the potential to directly and indirectly exterminate cancers and are therefore an attractive option for therapies. To develop new ACT therapies using macrophages, a great number of macrophages are required. Human induced pluripotent stem cells (iPSCs) are expected to be a source of macrophages; therefore, a system to efficiently produce macrophages from human iPSCs is needed. Here, we demonstrated that human iPSCs were robustly differentiated into macrophages by enforced FMS-like tyrosine kinase-3 (FLT3) signaling via the introduction of exogenous FLT3 into iPSCs and the addition of its ligand FLT3L to the macrophage induction culture. These iPSC-derived macrophages were identical to those obtained by standard differentiation induction methods. Thus, our novel system enables the preparation of scalable macrophages from human iPSCs. We believe that this system will be useful to develop a novel ACT therapy using macrophages.

The CSF-1R inhibitor pexidartinib affects FLT3-dependent DC differentiation and may antagonize durvalumab effect in patients with advanced cancers

Tumor-associated macrophages (TAMs) are a critical determinant of resistance to PD-1/PD-L1 blockade. This phase 1 study (MEDIPLEX, NCT02777710) investigated the safety and efficacy of pexidartinib, a CSF-1R-directed tyrosine kinase inhibitor (TKI), and durvalumab (anti-PD-L1) in patients with advanced colorectal and pancreatic carcinoma with the aim to enhance responses to PD-L1 blockade by eliminating CSF-1-dependent suppressive TAM. Forty-seven patients were enrolled. No unexpected toxicities were observed, one (2%) high microsatellite instability CRC patient had a partial response, and seven (15%) patients experienced stable disease as their best response. Increase of CSF-1 concentrations and decrease of CD14lowCD16high monocytes in peripheral blood mononuclear cells (PBMCs) confirmed CSF-1R engagement. Treatment decreased blood dendritic cell (DC) subsets and impaired IFN-λ/IL-29 production by type 1 conventional DCs in ex vivo TLR3-stimulated PBMCs. Pexidartinib also targets c-KIT and FLT3, both key growth factor receptors of DC development and maturation. In patients, FLT3-L concentrations increased with pexidartinib treatment, and AKT phosphorylation induced by FLT3-L ex vivo stimulation was abrogated by pexidartinib in human blood DC subsets. In addition, pexidartinib impaired the FLT3-L- but not GM-CSF-dependent generation of DC subsets from murine bone marrow (BM) progenitors in vitro and decreased DC frequency in BM and tumor-draining lymph node in vivo. Our results demonstrate that pexidartinib, through the inhibition of FLT3 signaling, has a deleterious effect on DC differentiation, which may explain the limited antitumor clinical activity observed in this study. This work suggests that inhibition of FLT3 should be considered when combining TKIs with immune checkpoint inhibitors.

Bayesian Optimization in the Latent Space of a Variational Autoencoder for the Generation of Selective FLT3 Inhibitors

The process of drug design requires the initial identification of compounds that bind their targets with high affinity and selectivity. Advances in generative modeling of small molecules based on deep learning are offering novel opportunities for making this process faster and cheaper. Here, we propose an approach to achieve this goal, where predictions of binding affinity are used in conjunction with the Junction Tree Variational Autoencoder (JTVAE) whose latent space is used to facilitate the efficient exploration of the chemical space using a Bayesian optimization strategy. The exploration identifies small molecules predicted to have both high affinity and high selectivity by using an objective function that optimizes the binding to the target while penalizing the binding to off-targets. The framework is demonstrated for FMS-like tyrosine kinase 3 (FLT3) and shown to predict small molecules with predicted affinity and selectivity comparable to those of clinically approved drugs for this target.

[Fulminant Clostridioides difficile infection during treatment with FLT3 inhibitor for acute myeloid leukemia]

An 80-year-old man with FLT3-TKD mutation-positive acute myeloid leukemia (AML) relapsed during consolidation therapy with venetoclax/azacitidine and was started on gilteritinib as salvage therapy. On the day after treatment initiation, febrile neutropenia was observed, but the fever resolved promptly after initiation of antimicrobial therapy. On the fifth day after completion of antimicrobial therapy, the patient experienced fever and watery diarrhea over 10 times a day, and a diagnosis of Clostridioides difficile infection (CDI) was made based on stool examination. The patient was treated with intravenous metronidazole, but renal dysfunction, hypotension, and hypoxemia developed, and a CT scan showed pleural and intraperitoneal effusion, significant intestinal wall thickening, and intestinal dilatation. Fidaxomicin was started under general monitoring in the intensive care unit and response was achieved. The patient was discharged from the intensive care unit on the 18th day after the onset of CDI. We report this case not only due to the rarity of fulminant CDI during AML treatment, but also because it is a valuable example of effective treatment of fulminant CDI with fidaxomicin.

[Acute myeloid leukemia with central nervous system involvement successfully treated with gilteritinib]

A 69-year-old woman was referred to our hospital due to hyperleukocytosis. We diagnosed acute myeloid leukemia and started induction therapy with the CAG regimen (aclarubicin, cytarabine and filgrastim). However, the patient was refractory to the initial treatment and developed quadriplegia, and a cerebrospinal fluid (CSF) test showed elevated blasts. We then performed intrathecal chemotherapy, and the number of blasts in CSF gradually decreased. But only two cycles of intrathecal therapy were possible due to severe methotrexate-induced mucositis. The leukemia cells had fms-like kinase 3-internal tandem duplication (FLT3-ITD), so we started treatment with oral gilteritinib. The patient then achieved hematological complete remission. Her paralysis was also resolving, and the CSF was clear of blasts for more than 6 months. Some reports show that gilteritinib may penetrate the CNS, and this case also supports the effectiveness of gilteritinib on CNS leukemia.

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.

Healthcare resource utilization and costs during first salvage therapy for relapsed or refractory acute myeloid leukemia in the United States

Real-world US healthcare resource utilization (HRU) and costs during first salvage therapy for relapsed/refractory (R/R) acute myeloid leukemia (AML) are described using IBM MarketScan® data (1/1/2007-6/30/2020). Treatments included high- (HIC) and low-intensity chemotherapy (LIC) alone, and gilteritinib, other FLT3 tyrosine kinase inhibitors (TKIs), and venetoclax with or without chemotherapy. Patients were diagnosed with R/R AML at ≥18 years of age between 1/1/2017-12/31/2019. Patient monthly all-cause HRU and costs were analyzed using a fixed-effects model. Data from 399 patients were analyzed (HIC, n = 104; LIC, n = 133; gilteritinib, n = 14; other FLT3 TKIs, n = 68; venetoclax, n = 80). Inpatient HRU was generally highest with HIC, whereas outpatient HRU was generally highest with LIC and venetoclax. Total all-cause incremental monthly costs appeared to be highest with HIC ($171,982) and similar for LIC ($60,512), gilteritinib ($47,218), other FLT3 TKIs ($43,218), and venetoclax ($77,566). Results highlight HRU and cost differences for R/R AML during first salvage therapy.

Meta-analysis of the effect of FLT3 inhibitor maintenance therapy on survival and chronic graft-versus-host disease in allogeneic hematopoietic stem cell transplantation for malignant hematologic disease

This study aimed to investigate the effect of FLT3 inhibitor maintenance therapy on survival and chronic graft-versus-host diseases (cGVHD) in allogeneic hematopoietic stem cell transplantation (allo-HSCT) for malignant hematologic disease (MHD) by meta-analysis. For this purpose, Pubmed, Web of Science, Embase, and The Cochrane Library were searched for studies published up to April 2023. The search term was set as "FLT3 inhibitor". "allogeneic hematopoietic stem cell transplantation"; "malignant hematologic disease"; "chronic graft-versus-host disease". The literature was screened according to the inclusion and exclusion criteria, and then the data were extracted and analyzed by Revman5.3 software. Results showed that 9 eligible studies involving 964 patients were obtained. The relapse-free survival (RFS) of patients after treatment was analyzed by comprehensive model, odds ratio=3.28, 95% confidence interval (CI) = 1.76-6.11, Z=3.75, P=0.0002; Comprehensive model analysis of overall survival (OS), odds ratio=2.85, 95% CI= 2.12-3.83, Z=6.95, P <0.00001; Comprehensive model analysis of cGVHD, odds ratio=1.06, 95%CI = 0.37-2.98, Z=0.11, P=0.92. It was concluded that FLT3 inhibitor maintenance therapy could improve the RFS and OS of MHD patients treated with allo-HSCT but did not markedly affect the occurrence of cGVHD.

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).

Mannose metabolism inhibition sensitizes acute myeloid leukaemia cells to therapy by driving ferroptotic cell death

Resistance to standard and novel therapies remains the main obstacle to cure in acute myeloid leukaemia (AML) and is often driven by metabolic adaptations which are therapeutically actionable. Here we identify inhibition of mannose-6-phosphate isomerase (MPI), the first enzyme in the mannose metabolism pathway, as a sensitizer to both cytarabine and FLT3 inhibitors across multiple AML models. Mechanistically, we identify a connection between mannose metabolism and fatty acid metabolism, that is mediated via preferential activation of the ATF6 arm of the unfolded protein response (UPR). This in turn leads to cellular accumulation of polyunsaturated fatty acids, lipid peroxidation and ferroptotic cell death in AML cells. Our findings provide further support to the role of rewired metabolism in AML therapy resistance, unveil a connection between two apparently independent metabolic pathways and support further efforts to achieve eradication of therapy-resistant AML cells by sensitizing them to ferroptotic cell death.

Population Pharmacokinetics of Mivavotinib (TAK-659), a Dual Spleen Tyrosine Kinase and FMS-Like Tyrosine Kinase 3 Inhibitor, in Patients With Advanced Solid Tumors or Hematologic Malignancies

Mivavotinib (TAK-659), an orally administered, small-molecule, dual inhibitor of spleen tyrosine kinase and FMS-like tyrosine kinase 3 (SYK/FLT3), is under development for the treatment of patients with advanced malignancies. In this analysis, we evaluated the population pharmacokinetics (PK) of mivavotinib and its sources of variability (covariates) in adult patients with advanced solid tumors, or relapsed/refractory B-cell lymphomas or acute myeloid leukemia, using pooled data from 159 patients enrolled in 2 phase 1/2 clinical studies. A 2-compartment model with first-order linear elimination and a first-order absorption rate (and associated lag time) adequately described the PK of mivavotinib in this patient population. The population estimates of apparent clearance (CL/F) and apparent central compartment volume (V_c /F) were 31.6 L/h and 893 L, respectively, resulting in a half-life of ≈20 hours. In the final model, creatinine clearance was included as a covariate of CL/F, and sex as a covariate of V_c /F. Simulations showed that steady-state exposure to mivavotinib increased with decreasing renal function. Expanding eligibility by enrolling patients with moderate renal impairment in phase 1 increased the diversity of patients in early trials and allowed the model to inform dose adjustment in patients with moderate renal impairment in future trials. In addition, simulations showed median steady-state trough concentration of mivavotinib following 70 mg twice daily and 160 mg daily dosing to be commensurate with 100 ng/mL, the level leading to >90% FLT3 inhibition per ex vivo plasma immune assays and considered a potential exposure threshold required for FLT3-driven efficacy.

Pacritinib inhibits glucose consumption in squamous cell lung cancer cells by targeting FLT3

Squamous cell lung cancer maintains its growth through elevated glucose consumption, but selective glucose consumption inhibitors are lacking. Here, we discovered using a high-throughput screen new compounds that block glucose consumption in three squamous cell lung cancer cell lines and identified 79 compounds that block glucose consumption in one or more of these cell lines. Based on its ability to block glucose consumption in all three cell lines, pacritinib, an inhibitor of FMS Related Receptor Tyrosine Kinase 3 (FLT3) and Janus Kinase 2 (JAK2), was further studied. Pacritinib decreased glucose consumption in squamous cell lung cancer cells in cell culture and in vivo without affecting glucose consumption in healthy tissues. Pacritinib blocked hexokinase activity, and Hexokinase 1 and 2 mRNA and protein expression. Overexpression of Hexokinase 1 blocked the ability of pacritinib to inhibit glucose consumption in squamous cell lung cancer cells. Overexpression of FLT3 but not JAK2 significantly increased glucose consumption and blocked the ability of pacritinib to inhibit glucose consumption in squamous cell lung cancer cells. Additional FLT3 inhibitors blocked glucose consumption in squamous cell lung cancer cells. Our study identifies FLT3 inhibitors as a new class of inhibitors that can block glucose consumption in squamous cell lung cancer.

Synthesis and Structural Optimization of 2,7,9-Trisubstituted purin-8-ones as FLT3-ITD Inhibitors

Therapy of FLT3-positive acute myeloid leukemia still remains complicated, despite the availability of newly approved kinase inhibitors. Various strategies to avoid the reduced efficacy of therapy have been explored, including the development of dual targeting compounds, which inhibit FLT3 and another kinase necessary for the survival and proliferation of AML cells. We have designed new 2,7,9-trisubstituted 8-oxopurines as FLT3 inhibitors and report here the structure-activity relationship studies. We demonstrated that substituents at positions 7 and 9 modulate activity between CDK4 and FLT3 kinase, and the isopropyl group at position 7 substantially increased the selectivity toward FLT3 kinase, which led to the discovery of compound 15a (9-cyclopentyl-7-isopropyl-2-((4-(piperazin-1-yl)phenyl)amino)-7,9-dihydro-8H-purin-8-one). Cellular analyses in MV4-11 cells revealed inhibition of autophosphorylation of FLT3 kinase in nanomolar doses, including the suppression of downstream STAT5 and ERK1/2 phosphorylation. We also describe mechanistic studies in cell lines and activity in a mouse xenograft model in vivo.

[Effect of Dihydroartemisinin and Arsenic Trioxide on Apoptosis of Acute Myeloid Leukemia Cells]

OBJECTIVE

To investigate the effect of dihydroartemisinin (DHA) combined with arsenic trioxide (ATO) on the viability and apoptosis of acute myeloid leukemia (AML) FLT3-ITD mutant cell line MOLM13 and its mechanism.

METHODS

MOLM13 cells were treated with DHA or ATO alone or in combination. The viability of MOLM13 cells was detected by CCK-8 assay, cell proliferation was observed by colony formation assay, cell apoptosis and reactive oxygen species (ROS) level were measured by flow cytometry, and the expression levels of proteins related to apoptosis were detected by Western blot.

RESULTS

Compared with the control group, treatment with DHA and ATO alone or in combination could inhibit cell proliferation, activate ROS formation, and finally induce cell apoptosis. DHA in combination with ATO produced a synergistic effect. Western blot analysis showed that DHA combined with ATO could significantly upregulate the level of c-PARP and activate apoptosis via inhibition of Mcl-1 and FLT3-ITD.

CONCLUSION

DHA combined with ATO induces the apoptosis of FLT3-ITD AML cell line MOLM13 by inhibiting Mcl-1 pathway and activating FLT3-ITD protein degradation.

Evolution of Graves' Disease during Immune Reconstitution following Nonmyeloablative Haploidentical Peripheral Blood Stem Cell Transplantation in a Boy Carrying Germline SAMD9L and FLT3 Variants

Graves’ disease, characterized by hyperthyroidism resulting from loss of immune tolerance to thyroid autoantigens, may be attributable to both genetic and environmental factors. Allogeneic hematopoietic stem cell transplantation (HSCT) represents a means to induce immunotolerance via an artificial immune environment. We present a male patient with severe aplastic anemia arising from a germline SAMD9L missense mutation who successfully underwent HSCT from his HLA-haploidentical SAMD9L non-mutated father together with nonmyeloablative conditioning and post-transplant cyclophosphamide at 8 years of age. He did not suffer graft-versus-host disease, but Graves’ disease evolved 10 months post-transplant when cyclosporine was discontinued for one month. Reconstitution of peripheral lymphocyte subsets was found to be transiently downregulated shortly after Graves’ disease onset but recovered upon antithyroid treatment. Our investigation revealed the presence of genetic factors associated with Graves’ disease, including HLA-B*46:01 and HLA-DRB1*09:01 haplotypes carried by the asymptomatic donor and germline FLT3 c.2500C>T mutation carried by both the patient and the donor. Given his current euthyroid state with normal hematopoiesis, the patient has returned to normal school life. This rare event of Graves’ disease in a young boy arising from special HSCT circumstances indicates that both the genetic background and the HSCT environment can prompt the evolution of Graves’ disease.

[Predictive Value of Acute Phase Proteins on the Prognosis of Patients with Acute Myeloid Leukemia]

OBJECTIVE

To analyze the predictive value of acute phase proteins (APPs) on the prognosis of patients with acute myeloid leukemia (AML).

METHODS

293 AML patients who met the study requirements from January 2015 to April 2021 were collected, their clinical characteristics and pre-treatment APPs levels ［including albumin (ALB), fibrinogen (FIB), C-reactive protein (CRP), Ferritin (FER)］ were followed up and investigated. Pearson correlation coefficient was used to analyze the correlation between APPs. Logistic regression was used to analyze the risk factors for mortality in AML patients. ROC curve was used to analyze the predictive value of APP for mortality in AML patients, and Kaplan-Meier survival analysis was used to compare the effect of APPs on complete remission (CR) rate, overall survival (OS), disease-free survival (DFS), and progression-free survival rate (PFS) of AML patients.

RESULTS

Pearson correlation analysis showed that there were negative correlations between ALB and CRP (r=-0.134, P=0002), as well as ALB and FER (r=-0.148, P=0.001). There were correlations between FER and CRP (r=0361, P＜0.001), as well as FER and FIB (r=0.293, P＜0.001). Logistic regression analysis showed that advanced age (>50 years) (OR=1.87, 95% CI=1.25-2.15, P＜0.001), relapse after treatment (OR=2.11, 95% CI=111-3.18, P=0.003), FLT3-ITD mutation (OR=2.59, 95% CI=1.10-4.12, P＜0.001), CRP≥524 mg/L (OR=1.21, 95% CI=1.02-2.14, P=0.024), CFA (CFA=CRP*FIB/ ALB)≥3 (OR=2.41, 95% CI=1.65-6.47, P＜0.001), and FER≥1145.58 mg/ml (OR=1.67, 95% CI=1.15-3.75, P＜0.001) were the risk factors for the survival of AML patients. ROC curve analysis showed that FER (AUC=0.752, 95% CI=0.681-0823, P＜0.001, the best cut-off value=1220.56 mg/ml) and CFA (AUC=0.804, 95% CI=0.741-0.868, P＜0.001, the best cut-off value=3.00) had higher predictive value for the survival of AML patients. The remission rate, PFS, DFS, and OS in the low CFA group (CFA≤3) were significantly higher than those in the high CFA group (CFA＞3), and the overall mortality rate was lower than that in the high CFA group; the remission rate, PFS, DFS, and OS in the low FER group (FER≤1220.56 mg/ml) were significantly higher than those in the high FER group (FER＞1220.56 mg/ml), while the overall mortality rate was lower than that in the high FER group, and the difference is statistically significant.

CONCLUSION

The CFA value and FER level before treatment in AML patients can independently predict the prognosis of patients, and high levels of CFA and FER are associated with poor prognosis of AML patients.

[Analysis of Gene Mutation Characteristics and Prognosis of Elderly Patients with Acute Myeloid Leukemia]

OBJECTIVE

To investigate the characteristics of gene mutation in elderly patients with acute myeloid leukemia (AML) and its effect on prognosis.

METHODS

The clinical and laboratorial characteristics of 54 AML patients (≥60 years old) in Department of Hematology, Tangdu Hospital were analyzed retrospectively during April 2016 to October 2019. Thirty-four AML/myelodysplastic syndrome/myeloproliferative neoplasm related mutant genes were detected by second-generation sequencing technology, and their clinical characteristics, treatment effect, and influence on prognosis were analyzed.

RESULTS

All the patients received DAC+CAG induction treatment, after 1-2 couses of treatment, 36 cases (66.7%) achieved complete response, with a total effective rate of 75.9%, and the median survival time was 17 months. The most frequent mutant genes were TET2 (33.3%), CEBPA (31.5%), DNMT3A (18.5%), ASXL1 (16.7%), NRAS (14.8%), RUNX1 (14.8%), FLT3-ITD (12.9%), TP53 (12.9%), NPM1 (12.9%), and IDH2 (12.9%). Among 7 patients with TP53 mutation, 6 cases obtained complete response after 1-2 courses of induction treatment, but there was no statistically significant difference in the effect on prognosis. Patients with FLT3-ITD and NRAS mutations had shorter overall survival time compared with who had no mutation (P=0.47, P=0.48). Multivariate analysis showed that FLT3-ITD and NRAS mutations were poor prognostic factors.

CONCLUSION

The incidence of TET2 gene mutation is high in elderly AML patients. AML patients with TET2 and TP53 mutations may benefit from Decitabine-based chemotherapy. However, patients with FLT3-ITD and NRAS mutations have a short survival time, and may have a poor prognosis.

[Effects of Paclitaxel and Quizartinib Alone and in Combination on AML Cell Line MV4-11 and Its STAT5 Signal Pathway]

OBJECTIVE

To investigate the effects of paclitaxel, quizartinib and their combination on proliferation, apoptosis and FLT3/STAT5 pathway of human leukemia cell line MV4-11 (FLT3-ITD+).

METHODS

MV4-11 cells were treated with paclitaxel and quizartinib at different concentrations for 24 h, 48 h and 72 h, respectively, and then the two drugs were combined at 48 h to compare the inhibition of proliferation, the apoptosis rate was detected by flow cytometry, the expression of FLT3 and STAT5 mRNA was determined by fluorescence quantitative PCR, and the protein expression of FLT3, p-FLT3, STAT5 and p-STAT5 was determined by Western blot.

RESULTS

Different combination groups of paclitaxel and quizartinib had synergistic inhibitory effect. The cell survival rate in the combination group was significantly lower than that in the single drug group (P<0.05). The cell apoptosis rate in the combination group was significantly higher than that in the single drug group (P<0.001). The expression of FLT3 mRNA in combination group was significantly higher than that in two single drugs (P<0.01). The expression of STAT5 mRNA in combination group was significantly higher than that in quizartinib group (P<0.001); increased compared with paclitaxel group, but there was no statistical significance. The expression level of p-FLT3、p-STAT5 protein in the combination group was significantly lower than that in the single drug group (P<0.05, P<0.05).

CONCLUSION

Paclitaxel combined with quizartinib can synergistically inhibit the proliferation of MV4-11 cell line and promote the apoptosis of MV4-11 cell line by inhibiting the activity of FLT3/STAT5 pathway.

[Analysis of Coexisting Gene with NRAS in Acute Myeloid Leukemia]

OBJECTIVE

To investigate the coexisting mutations and clinical significance of Homo sapiens neuroblastoma RAS viral oncogene homolog (NRAS) gene in acute myeloid leukemia (AML) patients.

METHODS

High-throughput DNA sequencing and Sanger sequencing were used to detect 51 gene mutations. The occurrence, clinical characteristics and treatment efficacy of coexisting genes with NRAS were investigated.

RESULTS

A total of 57 NRAS mutations (17.5%) were detected in 326 patients with AML. Compared with the patients in NRAS non-mutation group, patients in the mutant group were younger (P=0.018) and showed lower platelet count (P=0.033), but there was no significant difference in peripheral leukocyte count, hemoglobin, and sex. For FAB classification, NRAS mutation and M2 subtype showed mutually exclusive (P=0.038). Among 57 patients carried with NRAS mutation, 51 (89.5%) patients carried with other gene mutations, 25 (43.9%) carried with double gene mutations, 10 (17.5%) carried with 3 gene mutations, and 16 (28.1%) corried with ≥ 4 gene mutations. The most common coexisting gene mutation was KRAS (24.6%, 14/57), followed by FLT3-ITD (14.0%, 8/57), RUNX1 (12.3%, 7/57), NPM1 (10.5%, 6/57), PTPN11 (10.5%, 6/57), DNMT3A (10.5%, 6/57) and so on. The age (P=0.013, P=0.005) and peripheral platelet count (P=0.007, P=0.021) of patients with NPM1 or DNMT3A mutations were higher than those of the patients with wild type, but there was no significant difference in peripheral leukocyte count and hemoglobin. Also, there was no significant difference in age, peripheral leukocyte count, hemoglobin, and peripheral platelet count between the patients in KRAS, FLT3-ITD, RUNX1 or PTPN11 mutant group and the wild group. Patients with FLT3-ITD mutations showed a lower complete remission (CR) rate (P=0.044). However, there was no significant difference in CR rate between the patients with KRAS, NPM1, RUNX1, PTPN11 or DNMT3A mutations and the wild group. The CR rate of the patents with single gene mutation, double gene mutations, 3 gene mutations, and≥ 4 gene mutations were decreased gradually, and there was no significant difference in CR rate between pairwise comparisons.

CONCLUSION

The mutation rate of NRAS mutation is 17.5%, 89.5% of AML patients with NRAS mutation coexist with additional gene mutations. The type of coexisting mutations has a certain impact on clinical characteristics and CR rate of patients with AML.

[Effect of Age on the Time of Neutropenia after Initial Induction Therapy for Patients with Newly Diagnosed Acute Myeloid Leukemia]

OBJECTIVE

To explore the effect of age on the time of neutropenia after initial induction therapy for newly diagnosed acute myeloid leukemia (AML) patients.

METHODS

Data of 18-65 years old AML patients treated in our hospital from Junuary 2015 to July 2020 were retrospectively analyzed. The clinical characteristics, time of neutropenia after initial induction treatment, early responses, and related influencing factors for the time of neutropenia were analyzed and compared between 18-40 years old group and 41-65 years old group.

RESULTS

There were 112 patients enrolled in this study, including 66 (58.9%) males, and their median age was 46 years old. Compared with 18-40 years old group, the incidence of FLT3-ITD gene mutation increased (P=0.039) but core binding factor (CBF) decreased (P=0.003) significantly in 41-65 years old group. The incidence of neutropenia was 97.3%, and the average time was (18.70±1.192) days. The time of neutropenia was (21.43±1.736) days in 41-65 years old group, which was longer than (14.91±1.356) days in 18-40 years old group (P=0.006). The time of neutropenia in CBF positive group was shorter than that in negative group (P=0.012), as well as in patients with remission (CR+CRi) (≤ 2 courses) than those with non-remission (NR) (P=0.024), while in high-risk group was longer than that in low-risk group (P=0.040). Multivariate analysis showed that age, FLT3-ITD gene mutation positive, and non-remission (NR) after two courses of treatment were independent risk factors for the time of neutropenia.

CONCLUSION

In non-elderly patients with newly diagnosed AML, age is an influencing factor for the time of neutropenia. Key words　　;

[Treatment stratification by fitness for chemotherapy in acute myeloid leukemia]

Acute myelogenous leukemia (AML) is a hematopoietic malignancy that is characterized by clonal autonomous proliferation of myeloid cells with impaired differentiation and maturation. Recent advances in next-generation sequencing technology have elucidated the pathogenesis of AML at the genetic level. Furthermore, the molecular targeted therapy to efficiently eradicate leukemic cells has been rapidly expanding since 2017. In Japan, gilteritinib and quizartinib, which target FMS-like tyrosine kinase 3, and venetoclax, which targets B-cell lymphoma 2, have finally become available after resolving the drug launch lag between Japan and the United States. The combination of venetoclax and azacitidine, which was simultaneously approved with venetoclax for AML, is expected to be more effective than conventional therapy in patients who are ineligible for transplantation. Herein, we review the National Comprehensive Cancer Network guidelines for intensive chemotherapy in Japan and the United States and discuss the future of AML treatment, including the development of novel agents.

Hypomethylating Agents and FLT3 Inhibitors As Maintenance Treatment for Acute Myeloid Leukemia and Myelodysplastic Syndrome After Allogeneic Hematopoietic Stem Cell Transplantation-A Systematic Review and Meta-Analysis

BACKGROUND

Disease relapse remains the major cause of death among patients with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) who receive an allogeneic hematopoietic cell transplant (allo-HCT). Maintenance treatment with FLT3 inhibitors and hypomethylating agents (HMA) has been studied in various clinical trials with mixed results.

OBJECTIVE

To synthesize the current evidence on the efficacy and safety of FLT3 inhibitors and HMA for maintenance therapy after allo-HCT in AML and MDS.

METHODS

For this systematic review and meta-analysis Cochrane Library, Google Scholar, Ovid Medline, Ovid Embase, PubMed, Scopus, and Web of Science Core Collection were searched from inception to March 2021 for studies on maintenance therapies after allo-HCT in AML and MDS. Studies were excluded if they were reviews, commentaries, case series with <5 patients, or basic research articles, not published in English, not on post-allo-HCT maintenance with FLT3 inhibitors or HMA in AML or MDS, or if they were clinical trials without published results or duplicate publications from the same patient cohort. Studies with insufficient reporting of the primary endpoint (2-year overall survival [OS]) and studies using FLT3 inhibitors or HMA for pre-emptive treatment of imminent relapse based on positive measurable residual disease testing were excluded. Random-effects models were used to pool response rates for the primary outcome of 2-year OS. Hazard ratios (HR) for death and relapse were calculated for studies that included a control group. Rates of relapse-free survival (RFS), non-relapse mortality, and acute and chronic graft-versus-host-disease (GVHD) were studied as secondary endpoints. Downs and Black checklist and risk of bias assessments were used to gauge the quality of individual studies. The study protocol has been registered on PROSPERO (CRD42020187298).

RESULTS

Our search strategy identified 5559 studies. Twenty-one studies with a total of 809 patients were included in the meta-analysis. The 2-year OS rates were 81.7% (95% confidence interval [CI], 73.8%-87.7%) and 65.7% (95% CI, 55.1%-74.9%) among patients treated with FLT3 inhibitors and HMA, respectively. In sensitivity analyses restricted to studies that included a control group, maintenance therapy with FLT3 inhibitors (HR for death = 0.41; 95% CI, 0.26-0.62) or HMA (HR = 0.45; 95% CI, 0.31-0.66) appeared superior to no maintenance therapy. The 2-year RFS rates were 79.8% (95% CI, 75.0%-83.9%) and 62.4% (95% CI, 50.6%-72.9%) among patients treated with FLT3 inhibitors and HMA, respectively. Rates of any grade acute and chronic GVHD were 33.1% (95% CI, 25.4%-41.8%; grade 3/4: 16.5%) and 42.5% (95% CI, 26.3%-60.4%) among FLT3 inhibitor and 42.7% (95% CI, 33.5%-52.4%; grade 3/4: 8.1%) and 41.5% (95% CI, 32.0%-51.6%) among HMA-treated patients, respectively.

CONCLUSION

Maintenance therapy with either FLT3 inhibitors or HMA after allo-HCT can lead to prolonged and improved OS and RFS with a favorable safety profile. Additional studies are needed to define the optimal duration of treatment, the role of measurable residual disease status, and transplant characteristics in patient selection.

ScanITD: Detecting internal tandem duplication with robust variant allele frequency estimation

BACKGROUND

Internal tandem duplications (ITDs) are tandem duplications within coding exons and are important prognostic markers and drug targets for acute myeloid leukemia (AML). Next-generation sequencing has enabled the discovery of ITD at single-nucleotide resolution. ITD allele frequency is used in the risk stratification of patients with AML; higher ITD allele frequency is associated with poorer clinical outcomes. However, the ITD allele frequency data are often unavailable to treating physicians and the detection of ITDs with accurate variant allele frequency (VAF) estimation remains challenging for short-read sequencing.

RESULTS

Here we present the ScanITD approach, which performs a stepwise seed-and-realignment procedure for ITD detection with accurate VAF prediction. The evaluations on simulated and real data demonstrate that ScanITD outperforms 3 state-of-the-art ITD detectors, especially for VAF estimation. Importantly, ScanITD yields better accuracy than general-purpose structural variation callers for predicting ITD size range duplications.

CONCLUSIONS

ScanITD enables the accurate identification of ITDs with robust VAF estimation. ScanITD is written in Python and is open-source software that is freely accessible at https://github.com/ylab-hi/ScanITD.

[The prognostic value of cloned genetic mutations detected by second-generation sequencing in RUNX1-RUNX1T1 positive acute myeloid leukemia patients receiving intensive consolidation therapy]

Objective: To investigate the prognostic value of clonal gene mutations detected by second-generation sequencing in patients with positive RUNX1-RUNX1T1 acute myeloid leukemia (AML) who received high-dose chemotherapy or autologous transplantation (intensive consolidation therapy) in the first complete remission (CR(1)) state. Methods: 79 AML patients with positive RUNX1-RUNX1T1 who received intensive consolidation therapy in CR(1) state from July 2011 to August 2017 were analyzed retrospectively. Kaplan-Meier curve and Cox regression model were used to figure out the effect of leukocyte counts at onset and gene mutations for prognosis. Results: C-KIT, FLT3, CEBPA and DNMT3A gene mutations were found in 25 (31.6%) , 6 (7.6%) , 7 (8.9%) and 1 (1.3%) patient among the population. Mutations in C-KIT exon17 and C-KIT exon8 were detected in 19 (24.1%) and 5 (6.3%) cases, respectively, and mutations of FLT3-ITD were confirmed in 5 (6.3%) cases. The higher leukocyte counts presented at onset of leukemia, the shorter overall survival (OS) was seen in these patients (P=0.03) . Patients with C-KIT exon17 mutation had significantly shorter OS (P=0.01) and disease free survival (DFS) (P=0.006) compared with those without gene mutations, and patients with FLT3-ITD gene mutation got the inferior OS (P=0.048) and DFS (P=0.071) . Conclusion: In AML patients with positive RUNX1-RUNX1T1 receiving intensive consolidation therapy, the white blood cell counts at onset of leukemia, C-KIT mutations in exon 17, and FLT3-ITD gene mutations suggest poor prognosis, which would contribute to elaborate risk stratification, personalized treatment and predict prognosis for these patients.

Design and Synthesis of 4-(Heterocyclic Substituted Amino)-1H-Pyrazole-3-Carboxamide Derivatives and Their Potent Activity against Acute Myeloid Leukemia (AML)

Fms-like receptor tyrosine kinase 3 (FLT3) has been emerging as an attractive target for the treatment of acute myeloid leukemia (AML). By modifying the structure of FN-1501, a potent FLT3 inhibitor, 24 novel 1H-pyrazole-3-carboxamide derivatives were designed and synthesized. Compound 8t showed strong activity against FLT3 (IC₅₀: 0.089 nM) and CDK2/4 (IC₅₀: 0.719/0.770 nM), which is more efficient than FN-1501(FLT3, IC₅₀: 2.33 nM; CDK2/4, IC₅₀: 1.02/0.39 nM). Compound 8t also showed excellent inhibitory activity against a variety of FLT3 mutants (IC₅₀ < 5 nM), and potent anti-proliferative effect within the nanomolar range on acute myeloid leukemia (MV4-11, IC₅₀: 1.22 nM). In addition, compound 8t significantly inhibited the proliferation of most human cell lines of NCI60 (GI₅₀ < 1 μM for most cell lines). Taken together, these results demonstrated the potential of 8t as a novel compound for further development into a kinase inhibitor applied in cancer therapeutics.

[Factors associated with early treatment response in adults with acute myeloid leukemia]

Objective: To explore the factors influencing early treatment responses in adult with de novo acute myeloid leukemia (AML) . Methods: Data of consecutive newly-diagnosed AML (non-acute promyelocytic leukemia) adults were analyzed retrospectively. To assess the impact of clinical characteristics at diagnosis and induction regimen on achieving morphologic leukemia-free state (MLFS) , blood counts and minimal residual leukemia (MRD, positive MRD defined as RQ-PCR WT1 mRNA ≥0.6% and/or any level of abnormal blast population detected by flow cytometry) at the time of achieving MLFS. Results: 739 patients were included in this study. 406 (54.9%) patients were male, with a median age of 42 years (range, 18-65 years) . In the 721 evaluable patients, MLFS was achieved in 477 (66.2%) patients after the first induction regimen and 592 (82.1%) within two cycles. A total of 634 patients (87.9%) achieved MLFS, including 534 (84.2%) achieving a complete remission (CR, defined as MLFS with ANC ≥ 1×10(9)/L and PLT ≥ 100×10(9)/L) , 100 (15.8%) achieving a CRi (defined as MLFS with incomplete ANC or PLT recovery) , respectively. 260 (45.9%) patients of 566 (89.3%) who detected MRD at the time of achieving MLFS had positive MRD. Multivariate analyses showed that female gender, favorable-risk of SWOG criteria, IA10 and HAA/HAD as induction regimen were factors associated with achieving early MLFS. In addition, low bone marrow blasts, HGB ≥ 80 g/L, PLT counts<30×10(9)/L and mutated NPM1 without FLT3-ITD were factors associated with achieving MLFS after the first induction regimen; Negative FLT3-ITD mutation was factor associated with achieving MLFS within two cycles. PLT counts ≥30×10(9)/L and IA10, IA8 or HAA/HAD as induction chemotherapy were factors associated with achieving CR. Female gender, favorable-risk of SWOG criteria, FLT3-ITD mutation negative, mutated NPM1 without FLT3-ITD were factors associated with negative MRD. Conclusions: Female gender, favorable molecular markers or cytogenetics, and standard-dose induction regimen were key factors associated with higher probability of early and deep responses in adults with AML.

[Sorafenib in combination with chemotherapy as first-line therapy for FLT3-ITD positive acute myeloid leukemia]

Objective: To analyze the clinical features of acute myeloid leukemia patients with Fms-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) mutation and the therapeutic effect of sorafenib in combination with chemotherapy as first-line therapy for these patients. Methods: Clinical features and therapeutic effect were retrospectively analyzed in 53 AML patients with FLT3-ITD mutation diagnosed in Henan Cancer Hospital from January 2013 to August 2016. The biological characteristics and clinical efficacy of chemotherapy in combination with or without Sorafeinb were analyzed. Results: FLT3-ITD mutation was identified in 53 AML patients, 22 cases (41.5%) were M(5) subtype. The median of the peripheral WBC was 61.00 (0.98-920.00) ×10(9)/L, and there were 50 (94.3%) patients with WBC>10×10(9)/L. The median of blast cell in bone marrow was 0.730 (0.234-0.966) . The total remission rate of all these 53 patients was 56.6% (30/53) . The complete remission (CR) rates in patients treated with chemotherapy in combination with sorafenib and patients with chemotherapy alone were 86.4% (19/22) and 35.5% (11/31) , respectively. The 1-year overall survival rates of the two groups were 78.3%% and 50.0% (P=0.041) , and 1-year progression free survival rates were 75.9% and 42.4% (P=0.044) , respectively. Conclusion: AML patients with FLT3-ITD mutation have the characteristics of high peripheral WBC, high blast cells in bone marrow and accompanying with M(5) subtype. Sorafeinb combined with chemotherapy can significantly improve CR rate and short term survival.

[Efficacy and safety of Sorafenib as monotherapy to FLT3-ITD positive acute myeloid leukemia]

Objective: To explore the efficacy and safety of Sorafenib as monotherapy to FLT3 positive acute myeloid leukemia (AML). Methods: From April 2014 to December 2015, fourteen AML patients with FLT3 positive, 7 males and 7 females with a median age of 42 (range: 14-81) years old, were enrolled in this study. Of the 14 cases, 4 were de novo cases, 9 refractory cases and 1 relapsed case, including 78.6% patients with severe complications and 57.1% patients with KPS score less than 60 [the median KPS score was 45 (20-70) ]. The administration of Sorafenib was 400 mg twice daily and Sorafenib was continued if tolerated. The treatment response was evaluated by MICM and the data were analyzed by paired samples t test before and after Sorafenib treatment. Results: The peripheral blood WBC count [4.2 (0.9-11.8) ×109/L vs 39.6 (2.3-209.5) ×109/L, P<0.001 ], the percentage of peripheral blast cell [0.07 (0-0.54) vs 0.53 (0-0.94), P<0.001] and the percentage of bone marrow blast cell [0.266 (0.020-0.880) vs 0.604 (0.180-0.900), P=0.003] were significantly decreased after Sorafenib monotherapy compared with before. The overall response rate was 57.1% (8/14), including 5 cases (35.7%) with complete remission (CR). Of 4 de novo cases, 2 achieved CR, 1 with PR, 1 with NR; 3 of 10 refractory and relapsed patients achieved CR and 2 cases achieved PR, 5 cases NR. The median duration of achieving molecular remission (FLT3-ITD negative) after Sorafenib was 46(33-72) days, and the median progression free survival (PFS) was 53 (28-175) days. Conclusion: Sorafenib shows activity in FLT3-ITD mutation positive AML patients. Sorafenib monotherapy could be used as a treatment option for elderly patients or patients with severe complications, and refractory and relapsed patients with not suitable for intensive chemotherapy.

[Biological characteristics of mesenchymal stem cell and hematopoietic stem cell in the co-culture system]

The aim of the present study was to obtain the qualified hematopoietic stem/progenitor cells (HSC/HPC) and human umbilical cord-mesenchymal stem cells (MSC) in vitro in the co-culture system. Cord blood mononuclear cells were separated from umbilical cord blood by Ficoll lymphocyte separation medium, and then CD34⁺ HSC was collected by MACS immunomagnetic beads. The selected CD34⁺ HSC/HPC and MSC were transferred into culture flask. IMDM culture medium with 15% AB-type cord plasma supplemented with interleukin-3 (IL-3), IL-6, thrombopoietin (TPO), stem cell factor (SCF) and FMS-like tyrosine kinase 3 ligand (Flt-3L) factors were used as the co-culture system for the amplification of HSC/HPC and MSC. The cellular growth status and proliferation on day 6 and 10 after co-culture were observed by using inverted microscope. The percentage of positive expression of CD34 in HSC/HPC, as well as the percentages of positive expressions of CD105, CD90, CD73, CD45, CD34 and HLA-DR in the 4^th generation MSC, was tested by flow cytometry. Semisolid colony culture was used to test the HSC/HPC colony forming ability. The osteogenic, chondrogenesis and adipogenic ability of the 4^th generation MSC were assessed. The karyotype analysis of MSC was conducted by colchicines. The results demonstrated that the HSC/HPC of co-culture group showed higher ability of amplification, CFU-GM and higher CD34⁺ percentage compared with the control group. The co-cultured MSC maintained the ability to differentiate into bone cells, fat cells and chondrocytes. And the karyotype stability of MSC remained normal. These results reveal that the appropriate co-culture system for MSC and HSC is developed, and via this co-culture system we could gain both two kinds of these cells. The MSCs under the co-culture system maintain the biological characteristics. The CFU-GM ability, cell counting and the flow cytometry results of HSC/HPC under the co-culture system are conform to the criterion, showing that the biological functions of HSC/HPC are maintained.

[ITD mutation burden for the prognosis in FLT3-ITD positive acute myeloid leukemia patients]

OBJECTIVE

To explore the impact of ITD mutation characteristics on the overall survival (OS) and complete remission duration (CRD) in FLT3-ITD positive non-M3 acute myeloid leukemia (AML).

METHODS

Capillary electrophoresis was used to detect the FLT3-ITD characteristics after PCR amplication. Single or multiple mutations were identified by the numbers of peak. FLT3-ITD mutation burden was calculated by the peak area of mutant divided by the wild-type and mutant peak areas. Clinical data was collected and followed up in the FLT3-ITD mutation patients.

RESULTS

Multiple ITD mutations were common in patients aged 60 and above. Patients with single ITD mutation had higher percentage of blasts in bone marrow than multiple ITD mutations (0.758 vs 0.638, P=0.028). The numbers and length of FLT3-ITD mutation had no impact on prognosis. Patients with less than 10% of ITD mutation burden showed no difference with the intermediate-risk c-kit group in OS and CRD, but the two groups had longer OS and CRD than ITD mutation burden above 10% (OS: undefined, undefined, 9.9 months, P<0.05; CRD: undefined, undefined, 6.7 months, P<0.05). In patients with ITD mutation burden above 10%, cases with NPM1 or CEBPA mutation alone had markedly longer CRD than ITD mutation alone (25.0 vs 5.1 months, P=0.003), while OS were similar (11.4 vs 8.0 months, P>0.05).

CONCLUSION

Non-M3 AML patients with less than 10% FLT3-ITD mutation burden had a better prognosis than those above 10%.

CD47 is upregulated on circulating hematopoietic stem cells and leukemia cells to avoid phagocytosis

Macrophages clear pathogens and damaged or aged cells from the blood stream via phagocytosis. Cell-surface CD47 interacts with its receptor on macrophages, SIRPalpha, to inhibit phagocytosis of normal, healthy cells. We find that mobilizing cytokines and inflammatory stimuli cause CD47 to be transiently upregulated on mouse hematopoietic stem cells (HSCs) and progenitors just prior to and during their migratory phase, and that the level of CD47 on these cells determines the probability that they are engulfed in vivo. CD47 is also constitutively upregulated on mouse and human myeloid leukemias, and overexpression of CD47 on a myeloid leukemia line increases its pathogenicity by allowing it to evade phagocytosis. We conclude that CD47 upregulation is an important mechanism that provides protection to normal HSCs during inflammation-mediated mobilization, and that leukemic progenitors co-opt this ability in order to evade macrophage killing.

High-throughput sequence analysis of the tyrosine kinome in acute myeloid leukemia

To determine whether aberrantly activated tyrosine kinases other than FLT3 and c-KIT contribute to acute myeloid leukemia (AML) pathogenesis, we used high-throughput (HT) DNA sequence ana-lysis to screen exons encoding the activation loop and juxtamembrane domains of 85 tyrosine kinase genes in 188 AML patients without FLT3 or c-KIT mutations. The screen identified 30 nonsynonymous sequence variations in 22 different kinases not previously reported in single-nucleotide polymorphism (SNP) databases. These included a novel FLT3 activating allele and a previously described activating mutation in MET (METT1010I). The majority of novel sequence variants were stably expressed in factor-dependent Ba/F3 cells. Apart from one FLT3 allele, none of the novel variants showed constitutive phosphorylation by immunoblot analysis and none transformed Ba/F3 cells to factor-independent growth. These findings indicate the majority of these alleles are not potent tyrosine kinase activators in this cellular context and that a significant proportion of nonsynonymous sequence variants identified in HT DNA sequencing screens may not have functional significance. Although some sequence variants may represent SNPs, these data are consistent with recent reports that a significant fraction of such sequence variants are "passenger" rather than "driver" alleles and underscore the importance of functional assessment of candidate disease alleles.

Mutations of genes in the receptor tyrosine kinase (RTK)/RAS-BRAF signal transduction pathway in therapy-related myelodysplasia and acute myeloid leukemia

Mutations of the FLT3, c-KIT, c-FMS, KRAS, NRAS, BRAF and CEBPA genes in the receptor tyrosine kinase (RTK)/RAS-BRAF signal-transduction pathway are frequent in acute myeloid leukemia (AML). We examined 140 patients with therapy-related myelodysplasia or AML (t-MDS/t-AML) for point mutations of these seven genes. In all, 11 FLT3, two c-KIT, seven KRAS, eight NRAS and three BRAF mutations were identified in 29 patients (21%). All but one patient with a FLT3 mutation presented with t-AML (P=0.0002). Furthermore, FLT3 mutations were significantly associated with previous radiotherapy without chemotherapy (P=0.03), and with a normal karyotype (P=0.004), but inversely associated with previous therapy with alkylating agents (P=0.003) and with -7/7q- (P=0.001). RAS mutations were associated with AML1 point mutations (P=0.046) and with progression from t-MDS to t-AML (P=0.008). Noteworthy, all three patients with BRAF mutations presented as t-AML of M5 subtype with t(9;11)(p22;q23) and MLL-rearrangement (P=0.01). In t-AML RAS/BRAF mutations were significantly associated with a very short survival (P=0.017). Half of the patients with a mutation in the RTK/RAS-BRAF signal-transduction pathway (denoted 'class-I' mutations) simultaneously disclosed mutation of a hematopoietic transcription factor (denoted 'class-II' mutations) (P=0.046) suggesting their cooperation in leukemogenesis.

Acute myeloid leukaemia with FLT3 gene mutations of both internal tandem duplication and point mutation type

FLT3 gene mutations, either internal tandem duplication or point mutation type, are common in acute myeloid leukaemia (AML). We describe 21 AML cases with both types of gene mutations, so-called dual mutations, representing approximately 1% of all cases. Most newly diagnosed AML with FLT3 dual mutations had monocytic differentiation and a normal karyotype. Over the disease course, changes in FLT3 mutation status were seen in 89% of cases, and were associated with cytogenetic changes. We conclude that FLT3 dual mutations occur rarely in AML, and appear to be related to clonal evolution.

Mutations in KIT and RAS are frequent events in pediatric core-binding factor acute myeloid leukemia

Activating mutations in RAS and receptor tyrosine kinases such as KIT and FLT3 are hypothesized to cooperate with chimeric transcription factors in the pathogenesis of acute myeloid leukemia (AML). To test this hypothesis, we genotyped 150 pediatric AML samples for mutations in KIT (exons 8, 17), NRAS and KRAS (exons 1, 2) and FLT3/ITD. This is the largest cohort of pediatric AML patients reported thus far screened for all four mutations. Of the children with AML, 40% had a mutation in KIT (11.3%), RAS (18%) or FLT3/ITD (11.1%), and 70% of cases of core-binding factor (CBF) leukemia were associated with a mutation of KIT or RAS. Mutations in RAS or FLT3/ITD were frequently found in association with a normal karyotype. Patients with a FLT3/ITD mutation had a significantly worse clinical outcome. However, the presence of a KIT or RAS mutation did not significantly influence clinical outcome. We demonstrate that KIT exon 8 mutations result in constitutive ligand-independent kinase activation that can be inhibited by clinically relevant concentrations of imatinib. Our results demonstrate that abnormalities of signal transduction pathways are frequent in pediatric AML. Future clinical studies are needed to determine whether selective targeting of these abnormalities will improve treatment results.

Human leukemias with mutated FLT3 kinase are synergistically sensitive to FLT3 and Hsp90 inhibitors: the key role of the STAT5 signal transduction pathway

17-allylamino-17-demethoxygeldanamycin (17-AAG), an inhibitor of the molecular chaperone heat shock protein 90, results in cell type-specific inhibition of proliferation of leukemic cells. GTP14564 is a tyrosine kinase inhibitor actively against FLT3. The current study evaluated the single and combined effects of 17-AAG and GTP14564, and the role of FLT3 in their inhibitory effects. The importance of FLT3 mutations was demonstrated using small interfering RNA (siRNA) targeted to FLT3. Similar to FLT3 siRNA, GTP14564 inhibited FLT3 internal tandem duplication (ITD) cells (MV4;11) and FLT3 amplified wild-type cells (SEMK2-M1), but not wild-type FLT3 cells (RS4;11). However, when RS4;11 cells were stimulated with FLT3-ligand, phosphorylation of STAT5 and GTP14564 inhibition were observed. Responses to GTP14564 in all cell types were directly related to the level of STAT5 phosphorylation in the cells. We observed synergistic effects of combined 17-AAG and GTP14564 in cell lines with FLT3-ITD and amplified wild-type FLT3. Combined treatment with 17-AAG and GTP14564 reduced the levels of p-FLT3 and p-STAT5, enhanced G0/G1 arrest and apoptosis in FLT3-ITD and amplified wild-type FLT3. The combination of 17-AAG with FLT3 kinase inhibitors can enhance targeted therapy in leukemias with FLT3 mutations, such as MLL fusion gene leukemias.

Neurotrophin-3 and FLT3 tyrosine kinase receptor in perinatal life

Our aim is to determine—in 30 healthy full-term infants and their mothers—circulating levels of neurotrophin-3 (NT-3) (important for antenatal and postnatal brain development and implicated in the immune response) and FLT3 tyrosine kinase receptor (FLT3) (controlling hematopoiesis and found in the nervous tissue), in the fetal and neonatal life. NT-3 levels, in contrast to FLT3 ones, increased significantly on the fourth postnatal day in relation to the low levels found in the mother, fetus, and day 1 neonate (P = .03, respectively). Maternal and umbilical NT3 levels positively correlated with respective FLT3 levels (P = .003 and P = .03). Circulating NT-3 levels increased in early neonatal life, possibly due to exposure to various stimuli soon after birth. FLT3 levels do not seem to behave accordingly, although these two substances probably synergize.

Delineation and molecular characterization of acute myeloid leukemia patients with coduplication of FLT3 and MLL

Partial tandem (PTD) and internal tandem duplications (ITD) of the MLL or FLT3 genes respectively, have been demonstrated in acute myeloid leukemia (AML). While occurrence of each of these PTD/ITD seem to confer an unfavorable prognosis, the literature contains only sparse information of the occurrence and the prognosis of simultaneous PTD/ITD of these genes. We have therefore attempted to determine the presence and its consequence in AML and with the further aim of characterizing such patients with respect to other genetic aberrations and to prototype variables in this disease. We analyzed blast cells from 250 adult patients treated at the same institution during a 15-year period for FLT3 ITD and MLL PTD and the duplications were found in 24% and 4%, respectively. The four co-duplicated cases (2%) did not differ with respect to sex, age, FAB-type, or immunophenotype, promoter methylation of p15, E-cadherin (CDH1), Estrogen receptor, MDR1, expression of apoptosis-related or multidrug resistance-related genes, though a trend toward decreased gene expression of MDR1 was observed. Two of the patients had a normal karyotypic analysis, while the remaining two showed aberrations in chromosome 11, one with trisomy 11 and the other with a der (11). The extensive molecular characterization of FLT3/MLL coduplicated patients presented here indicates that, even though they do not differ molecularly from the groups of patients with single ITDs, their prognosis and overall survival is universally poor. More patients are needed to determine whether coduplication has independent clinical implications compared to patients with single ITD/PTD.

AML1B transcriptional repressor function is impaired by the Flt3-internal tandem duplication

Fms-like tyrosine kinase 3 (Flt3) is a type III receptor tyrosine kinase. The internal tandem duplication (ITD) of the juxtamembrane region of this receptor is the most prevalent mutation in acute myeloid leukaemia (AML). The silencing mediator of retinoic and thyroid hormone receptors (SMRT) co-repressor recruits histone deacetylases (HDAC) and mediates transcriptional repression by interacting with various transcription factors. We recently reported that Flt3-ITD interferes with the transcriptional and biological action of promyelocytic leukaemia zinc finger transcriptional repressor by dissociating it from SMRT. In this study, we aimed to clarify whether the repressional activity of other well-known oncoproteins, such as AML1/Runx1 (AML1), is also affected by Flt3-ITD. We verified that the repression activity of AML1B, the isoform of AML1, is dependent on HDAC activity by using HDAC inbitor trichostatin A in GAL4 reporter assays. Mammalian two-hybrid assays demonstrated that this protein interacts with SMRT. Furthermore, this AML1B-SMRT interaction was disrupted by the overexpression of Flt3-ITD, leading to the reduction of AML1B repression activity. Additionally, we showed AML1B repression target, p21 (WAF1/CIP1), was aberrantly expressed in Flt3-ITD stably expressed BaF3 cells. Taken together, Flt3-ITD disrupts transcriptional repressor functions resulting in aberrant gene regulation in leukaemic cells.

RAS mutation in acute myeloid leukemia is associated with distinct cytogenetic subgroups but does not influence outcome in patients younger than 60 years

The pathogenesis of acute myeloid leukemia (AML) involves the cooperation of mutations promoting proliferation/survival and those impairing differentiation. The RAS pathway has been implicated as a key component of the proliferative drive in AML. We have screened AML patients, predominantly younger than 60 years and treated within 2 clinical trials, for NRAS (n = 1106), KRAS (n = 739), and HRAS (n = 200) hot-spot mutations using denaturing high-performance liquid chromatography or restriction fragment length polymorphism (RFLP) analysis. NRAS mutations were confirmed in 11% of patients (126/1106) and KRAS mutations in 5% (39/739). No HRAS mutations were detected in 200 randomly selected samples. Codons most frequently mutated were N12 (43%), N13 (21%), and K12 (21%). KRAS mutations were relatively overrepresented in French-American-British (FAB) type M4 (P < .001). NRAS mutation was over-represented in the t(3;5)(q21 approximately 25;q31 approximately q35) subgroup (P < .001) and underrepresented in t(15;17)(q22;q21) (P < .001). KRAS mutation was overrepresented in inv(16)(p13q22) (P = .004). Twenty-three percent of KRAS mutations were within the inv(16) subgroup. RAS mutation and FLT3 ITD were rarely coexistent (14/768; P < .001). Median percentage of RAS mutant allele assayed by quantitative RFLP analysis was 28% (N12), 19% (N13), 25% (N61), and 21% (K12). RAS mutation did not influence clinical outcome (overall/disease-free survival, complete remission, relapse rate) either for the entire cohort or within cytogenetic risk groups.

Mutations in the receptor tyrosine kinase pathway are associated with clinical outcome in patients with acute myeloblastic leukemia harboring t(8;21)(q22;q22)

AML1-MTG8 generated by t(8;21) contributes to leukemic transformation, but additional events are required for full leukemogenesis. We examined whether mutations in the receptor tyrosine kinase (RTK) pathway could be the genetic events that cause acute myeloblastic leukemia (AML) harboring t(8;21). Mutations in the second tyrosine kinase domain, juxtamembrane (JM) domain and exon 8 of the C-KIT gene were observed in 10, one and three of 37 AML patients with t(8;21), respectively. Three patients showed an internal tandem duplication in the JM domain of the FLT3 gene. One patient had a mutation in the K-Ras gene at codon 12. As the occurrence of these mutations was mutually exclusive, a total of 18 (49%) patients showed mutations in the RTK pathway. These results suggest that activating mutations in the RTK pathway play a role in part as an additional event leading to the development of t(8;21) AML. The 6-year cumulative incidence of relapse in patients with RTK pathway mutations was 79.8%, compared with 13.5% in patients lacking such mutations (P=0.0029). Furthermore, the 6-year relapse-free survival in patients with mutations was 18% compared to 60% in those without mutations (P=0.0340), indicating that RTK mutations are associated with the clinical outcome in t(8;21) AML.