Recent advances in FLT3 inhibitors for acute myeloid leukemia

Fms-like tyrosine kinase-3 (FLT3) mutations occur in approximately 30% of acute myeloid leukemia (AML) cases, suggesting FLT3 as an attractive target for AML treatment. Early FLT3 inhibitors enhance antileukemia efficacy by inhibiting multiple targets, and thus had stronger off-target activity, increasing their toxicity. Recently, a number of potent and selective FLT3 inhibitors have been developed, many of which are effective against multiple mutations. This review outlines the evolution of AML-targeting FLT3 inhibitors by focusing on their chemotypes, selectivity and activity over FLT3 wild-type and FLT3 mutations as well as new techniques related to FLT3. Compounds that currently enter the late clinical stage or have entered the market are also briefly reported.

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Emerging treatment paradigms with FLT3 inhibitors in acute myeloid leukemia

Therapeutic Advances in Hematology ◽

10.1177/2040620719827310 ◽

2019 ◽

Vol 10 ◽

pp. 204062071982731 ◽

Cited By ~ 40

Author(s):

Nicholas J. Short ◽

Hagop Kantarjian ◽

Farhad Ravandi ◽

Naval Daver

Keyword(s):

Acute Myeloid Leukemia ◽

Tyrosine Kinase ◽

Myeloid Leukemia ◽

The United States ◽

Efficacy Data ◽

Increased Risk ◽

Flt3 Mutations ◽

Flt3 Inhibitors ◽

Us Fda ◽

Acute Myeloid

Mutations in the fms-like tyrosine kinase 3 ( FLT3) gene are detected in approximately one-third of patients with newly diagnosed acute myeloid leukemia (AML). These consist of the more common FLT3-internal tandem duplication (ITD) in approximately 20–25% of AML cases, and point mutations in the tyrosine kinase domain (TKD) in approximately 5–10%. FLT3 mutations, especially FLT3-ITD, are associated with proliferative disease, increased risk of relapse, and inferior overall survival when treated with conventional regimens. However, the recent development of well tolerated and active FLT3 inhibitors has significantly improved the outcomes of this aggressive subtype of AML. The multikinase inhibitor midostaurin was approved by the United States Food and Drug Administration (US FDA) in April 2017 for the frontline treatment of patients with FLT3-mutated (either ITD or TKD) AML in combination with induction chemotherapy, representing the first new drug approval in AML in nearly two decades. In November 2018, the US FDA also approved the second-generation FLT3 inhibitor gilteritinib as a single agent for patients with relapsed or refractory FLT3-mutated AML. Promising phase I and II efficacy data for quizartinib is likely to lead to a third regulatory approval in relapsed/refractory AML in the near future. However, despite the significant progress made in managing FLT3-mutated AML, many questions remain regarding the best approach to integrate these inhibitors into combination regimens, and also the optimal sequencing of different FLT3 inhibitors in various clinical settings. This review comprehensively examines the FLT3 inhibitors currently in clinical development, with an emphasis on their spectra of activity against different FLT3 mutations and other kinases, clinical safety and efficacy data, and their current and future roles in the management of AML. The mechanisms of resistance to FLT3 inhibitors and potential combination strategies to overcome such resistance pathways are also discussed.

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Prevalence and Prognostic Significance of FLT3 Mutations in Acute Myeloid Leukemia: Association of ITDs with Poor Outcome in Patients with Normal Cytogenetics.

Blood ◽

10.1182/blood.v108.11.2017.2017 ◽

2006 ◽

Vol 108 (11) ◽

pp. 2017-2017

Author(s):

Michela Palmisano ◽

Emanuela Ottaviani ◽

Tiziana Grafone ◽

Nicoletta Testoni ◽

Stefania Paolini ◽

...

Keyword(s):

Acute Myeloid Leukemia ◽

Tyrosine Kinase ◽

Myeloid Leukemia ◽

Prognostic Impact ◽

Wild Type ◽

Poor Prognostic Factor ◽

Flt3 Mutations ◽

Blast Cells ◽

Normal Cytogenetics ◽

Acute Myeloid

Abstract Acute Myeloid Leukemia (AML) is a difficult disease to treat, and better treatments are needed. Molecular targeted therapy represents a novel therapeutic approach. Activating mutations of FMS-like tyrosine kinase 3 (FLT3) are present in approximately one third of patients with de novo AML and have been implicated in its pathogenesis. The leukemic blasts of most AML patients have the internal tandem duplications (ITDs) in the juxtamembrane region or point mutations in Asp835 and Iso836 codons in the activation loop of the kinase domain (TKD) of the FLT3 receptor. Both mutations result in constitutive FLT3 receptor activity and may play a significant role in leukemogenesis. In this study we have analyzed the incidence and type of FLT3 mutations in a large series of newly diagnosed AML patients. Furthermore, we have evaluated the prognostic impact of FLT3 mutations. The FLT3/ITD was determined by polymerase chain reaction (PCR). The mutations of D835 and I836 codons were determined by PCR followed by restriction enzyme digestion (PCR-RFLP). For the estimation of the statistic significance of the differences in the clinical-biological characteristics, between the mutated patients and wild-type patients, it has been used the Student’s test t for independent data. The probabilities of overall survival (OS) and disease free survival (DFS) were analysed by Kaplan-Meier method; the differences of OS and DFS, between the mutated patients and wild-type patients, were assessed using the log-rank test. Both FLT3/ITD and FLT3/TKD mutations were found in 15%. Dual mutations were found in 2% of 126 patients. Among the FAB subtypes of AML, the rate of FLT3 aberrations was higher in M4 (27%) and M5 (26%). FLT3/ITD was associated to leukocytosis (106.8x10(e)9/l vs 30x10(e)9/l in FLT3-wt, p=0.015) and high percentage of circulating blast cells (82% vs 42% in FLT3-wt, p<0.0001). Differently, FLT3/TKD mutations were not associated with high white blood cells count and blast cells percentage. FLT3 mutations were more prevalent in patients with normal karyotype (51%). In this group, DFS and OS were significantly inferior for patients with FLT3/ITD than patients withouth mutations (0 vs 5, p=0.0032; 5 vs 9, p=0.049, respectively). We have identified the FLT3/ITD as an independent poor prognostic factor in AML patients with normal cytogenetics. Therefore, targeting FLT3 mutations represents a potential therapeutic target for AML. These results suggest that new treatment modalities, such as therapy with a FLT3 tyrosine kinase inhibitor, are clearly needed for this group of patients with “standard risk” profile.

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FLT3 inhibitors in acute myeloid leukemia: Current and future

Journal of Oncology Pharmacy Practice ◽

10.1177/1078155218802620 ◽

2018 ◽

Vol 25 (1) ◽

pp. 163-171 ◽

Cited By ~ 7

Author(s):

Christan M Thomas ◽

Peter Campbell

Keyword(s):

Acute Myeloid Leukemia ◽

Tyrosine Kinase ◽

Myeloid Leukemia ◽

Kinase Inhibitors ◽

Disease Free Survival ◽

Hematopoietic Stem ◽

Significant Toxicity ◽

Flt3 Mutations ◽

Flt3 Inhibitors ◽

Acute Myeloid

FMS-like tyrosine kinase 3 (FLT3) is a receptor tyrosine kinase that is responsible for the proliferation and survival of hematopoietic stem cells in acute myeloid leukemia. Although patients with FLT3 mutations have similar rates of remission following induction chemotherapy, relapse rates are significantly higher and patients with FLT3 mutations have significantly worse outcomes for overall survival and disease-free survival. Early FLT3 inhibitors, such as sorafenib, were non-selective and inhibited several tyrosine kinase receptors resulting in significant toxicity. The treatment of FLT3-positive acute myeloid leukemia has advanced recently with the development of a several FLT3-targeting agents that are either approved or in development. Midostaurin represents the first FDA-approved treatment targeted against FLT3, and there are several promising agents currently undergoing clinical trials. Although certain mutations confer resistance to earlier generation FLT3-targeted tyrosine kinase inhibitors, newer agents show activity in the presence of these mutations.

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Genome-wide CRISPR screen identifies regulators of MAPK and MTOR pathways mediating sorafenib resistance in acute myeloid leukemia

Haematologica ◽

10.3324/haematol.2020.257964 ◽

2020 ◽

Author(s):

Alisa Damnernsawad ◽

Daniel Bottomly ◽

Stephen E. Kurtz ◽

Christopher A. Eide ◽

Shannon K. McWeeney ◽

...

Keyword(s):

Acute Myeloid Leukemia ◽

Myeloid Leukemia ◽

Ex Vivo ◽

Mek Inhibitors ◽

Genome Wide ◽

A Genome ◽

Flt3 Mutations ◽

Flt3 Inhibitors ◽

Crispr Screen ◽

Acute Myeloid

Drug resistance impedes the long-term effect of targeted therapies in acute myeloid leukemia (AML), necessitating the identification of mechanisms underlying resistance. Approximately 25% of AML patients carry FLT3 mutations and develop post-treatment insensitivity to FLT3 inhibitors, including sorafenib. Using a genome-wide CRISPR screen, we identified LZTR1, NF1, TSC1 or TSC2, negative regulators of the MAPK and MTOR pathways, as mediators of sorafenib resistance. Analyses of ex vivo drug sensitivity assays in FLT3-ITD AML patient samples revealed lower expression of LZTR1, NF1, and TSC2 correlated with sorafenib sensitivity. Importantly, MAPK and/or MTOR complex1 (MTORC1) activity were upregulated in AML cells made resistant to several FLT3 inhibitors, including crenolanib, quizartinib, or sorafenib. These cells were sensitive to MEK inhibitors, and the combination of FLT3 and MEK inhibitors showed enhanced efficacy, suggesting its effectiveness in AML patients with FLT3 mutations and those with resistance to FLT3 inhibitors.

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Molecular Mechanisms of Resistance to FLT3 Inhibitors in Acute Myeloid Leukemia: Ongoing Challenges and Future Treatments

Cells ◽

10.3390/cells9112493 ◽

2020 ◽

Vol 9 (11) ◽

pp. 2493

Author(s):

Sebastian Scholl ◽

Maximilian Fleischmann ◽

Ulf Schnetzke ◽

Florian H. Heidel

Keyword(s):

Acute Myeloid Leukemia ◽

Tyrosine Kinase ◽

Myeloid Leukemia ◽

Molecular Mechanisms ◽

Continuous Treatment ◽

Next Generation ◽

Secondary Resistance ◽

Development Of Resistance ◽

Flt3 Inhibitors ◽

Acute Myeloid

Treatment of FMS-like tyrosine kinase 3 (FLT3)-internal tandem duplication (ITD)-positive acute myeloid leukemia (AML) remains a challenge despite the development of novel FLT3-directed tyrosine kinase inhibitors (TKI); the relapse rate is still high even after allogeneic stem cell transplantation. In the era of next-generation FLT3-inhibitors, such as midostaurin and gilteritinib, we still observe primary and secondary resistance to TKI both in monotherapy and in combination with chemotherapy. Moreover, remissions are frequently short-lived even in the presence of continuous treatment with next-generation FLT3 inhibitors. In this comprehensive review, we focus on molecular mechanisms underlying the development of resistance to relevant FLT3 inhibitors and elucidate how this knowledge might help to develop new concepts for improving the response to FLT3-inhibitors and reducing the development of resistance in AML. Tailored treatment approaches that address additional molecular targets beyond FLT3 could overcome resistance and facilitate molecular responses in AML.

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Monocytic Maturation Induced by FLT3 Inhibitor Therapy of Acute Myeloid Leukemia: Morphologic and Immunophenotypic Characteristics

Laboratory Medicine ◽

10.1093/labmed/lmz094 ◽

2019 ◽

Vol 51 (5) ◽

pp. 478-483

Author(s):

Cade D Arries ◽

Sophia L Yohe

Keyword(s):

Bone Marrow ◽

Acute Myeloid Leukemia ◽

Tyrosine Kinase ◽

Cell Population ◽

Myeloid Leukemia ◽

Inhibitor Therapy ◽

Molecular Abnormalities ◽

Flt3 Inhibitor ◽

Flt3 Inhibitors ◽

Acute Myeloid

Abstract Background FMS-like tyrosine kinase-3 (FLT3-ITD) mutations are some of the most common mutations in acute myeloid leukemia (AML), and patient outcomes have improved since the advent of tyrosine kinase inhibitors. First, granulocytic differentiation was described in FLT3-positive AML treated with FLT3 inhibitors, and more recently, monocytic differentiation was reported. Methods Two patients with myelomonocytic cells in their bone marrow were identified during routine follow-up after AML treatment that included FLT3 inhibitors. The bone marrow study was done as standard of care. Results Both patients had FLT3-ITD+ AML and showed an atypical maturing monocytic cell population and a decrease in the leukemic blast cell population after FLT3 inhibitor therapy. Concurrent genetic testing revealed persistent genetic abnormalities. Conclusions These cases illustrate monocytic maturation in FLT3+ AML after FLT3 inhibitor treatment. It is critical for pathologists and clinicians to be aware of the differentiation phenomenon, as these patients have persistent molecular abnormalities despite response to treatment and normalization of blast counts.

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Go6976, a Potent FLT3 Kinase Inhibitor, Exerts Antiproliferative Activity Against Acute Myeloid Leukemia Via Inhibition Of Survivin and Mcl-1 In The Presence Of Human Serum

Blood ◽

10.1182/blood.v122.21.3839.3839 ◽

2013 ◽

Vol 122 (21) ◽

pp. 3839-3839

Author(s):

Akira Yoshida ◽

Kouichi Zokumasu ◽

Takanori Ueda

Keyword(s):

Acute Myeloid Leukemia ◽

Tyrosine Kinase ◽

Human Serum ◽

Inhibitory Activity ◽

Myeloid Leukemia ◽

Human Leukemia ◽

Acid Glycoprotein ◽

Flt3 Inhibitors ◽

Ic50 Values ◽

Acute Myeloid

Abstract The FMS-like tyrosine kinase 3 (FLT3) is a class III receptor tyrosine kinase involved in hematopoietic progenitor cell development. Mutations of FLT3 have been reported in about a third of patients with acute myeloid leukemia (AML). The presence of FLT3 mutations confers a poor prognosis, and thus recent studies are directed at developing and testing novel FLT3 inhibitors for the treatment of AML. Go6976 is an indolocarbazole with a simillar structural backbone to staurosporine. In the present study, we demonstrated that Go6976 displays a potent inhibitory activity against recombinant FLT3 using in vitro kinase assay. Its IC50 value is 0.7nM. We also tested the effect of Go6976 on several kinds of other kinases. Go6976 inhibited the kinase activity of Aurora-A, Aurora-B and JAK2 with IC50 values of 118.2 nM, 77.7 nM and 92.7 nM, respectively. Go6976 did not show the inhibitory activity against the FGFR3 even at 1 microM. These data indicated Go6976 preferentially and potently inhibit the FLT3. Go6976 significantly inhibited the proliferation of human leukemia cells having FLT3-ITD. The IC50 values of Go6976 against MV4-11 and MOLM-13 were 0.044 and 0.008 microM, respectively. In contrast, human leukemia HL-60 and U937 cells which lack FLT3-ITD showed strong resistance to Go6976 treatment. Furthermore, we observed that Go6976 shows minimal toxicity for purified human normal CD34(+) cells. Go6976 suppressed the phosphorylation of FLT3 in MV4-11 and MOLM13 cells. Consistent with FLT3 inhibition, Go6976 potently inhibited phosphorylation of constitutively activated STAT3/5, Erk1/2, and Akt. Western blotting analysis revealed that MV4-11 and MOLM13 cells possess abundant survivin and Mcl-1 protein. We hypothesized that the expression of survivin and Mcl-1 may be regulated by constitutive activation of FLT3. In order to test this hypothesis, the effect of siRNA for FLT3-ITD was examined. Indeed, we observed that siRNA-induced down-regulation of FLT3 decreased survivin and Mcl-1 expression in MOLM13 cells, suggesting that up-regulated survivin and Mcl-1 may be closely associated with FLT3 signaling. Interestingly, we found that both survivin mRNA and protein were rapidly downregulated by Go6976 treatment in MOLM13 and MV4-11 cells. It was also observed that Go6976 significantly suppressed Mcl-1 mRNA and protein. It has been reported that STAT-3 and STAT-5 signaling play a pivotal role in the regulation of survivin and Mcl-1, respectively. Thus, inhibitory effects of Go6976 on the expression Survivin and Mcl-1 may be a consequence of the suppression of phosphorylation of STAT-3 and STAT-5 by Go6976 in FLT3-ITD cells. This inhibition of anti-apoptotic proteins by Go6976 may be critical for its antiproliferative effect in FLT3-ITD cells. It has been known that previous FLT3 inhibitors such as PKC412 and CEP-701 bind to the human plasma protein, alpha1-acid glycoprotein, resulting in significantly diminished inhibitory activity against FLT3. Indeed, inhibitory effect of PKC412 on FLT3 was significantly decreased, when MOLM13 cells were treated with PKC412 in the presence of human serum. In contrast, we found that Go6976 potently inhibits phosphorylation of FLT3 and exerts cytotoxicity even in the presence of human serum or human alpha1-acid glycoprotein. In conclusion, our data indicate that Go6976 may have a unique therapeutic potential for FLT3-driven acute myeloid leukemia. Disclosures: No relevant conflicts of interest to declare.

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Early Results Of a Phase I/II Trial Of Midostaurin (PKC412) and 5-Azacytidine (5-AZA) For Patients (Pts) With Acute Myeloid Leukemia and Myelodysplastic Syndrome

Blood ◽

10.1182/blood.v122.21.3949.3949 ◽

2013 ◽

Vol 122 (21) ◽

pp. 3949-3949

Author(s):

Paolo Strati ◽

Hagop M Kantarjian ◽

Aziz Nazha ◽

Gautam Borthakur ◽

Naval G. Daver ◽

...

Keyword(s):

Acute Myeloid Leukemia ◽

Myelodysplastic Syndrome ◽

Phase I ◽

Phase Ii ◽

Myeloid Leukemia ◽

Research Funding ◽

Flt3 Mutations ◽

Flt3 Inhibitors ◽

Grade 3 ◽

Acute Myeloid

Abstract Background Acute Myeloid Leukemia (AML) and Myelodysplastic Syndrome (MDS) affect primarily elderly pts. Their treatment with aggressive chemotherapy is frequently challenging. Moreover, pts with FLT3 mutations have very poor prognosis. We hypothesized that the combination of midostaurin, a FLT3 inhibitor, and 5-AZA, a hypomethylating agent, may be an effective and safe regimen. Methods Both untreated (8) and previously treated (36) pts with AML or MDS were eligible for this study, regardless of FLT3 mutation and prior exposure to FLT3 inhibitors. Pts received 5-AZA 75 mg/mq subcutaneously or intravenously on day 1-7 and midostaurin 25 mg bid (in cohort 1 of phase I) or 50 mg bid (in cohort 2 of Phase I and in Phase II) orally on day 8-21 during the first cycle and continuously thereafter, for 12 cycles of 28 days duration. Cytogenetic risk was defined according to MRC criteria. Differences between categorical variables were compared by the chi2 test. CR duration (CRD) was calculated from the time of CR achievement until relapse and estimated by the Kaplan-Meier method and compared by the log-rank test. Results Fourty-four pts were enrolled, 13 included in Phase I and 31 in Phase II. Baseline pts’ characteristics are shown in the Table. Thirty-eight pts (86%) received 50 mg bid of midostaurin, and 6 (14%; Phase I) received 25 mg bid. The median number of administered cycles was 2 (1-9). Grade 3-4 hematological toxicities consisted of 95% neutropenia, 64% anemia and 93% thrombocytopenia. Grade 3-4 non-hematological toxicities consisted of 45% infections, 23% hypokalemia, 16% hyponatremia, 7% reduction in ejection fraction, 7% hyperuricemia, 4% hyperglycemia, 4% nausea/vomiting, 4% QTc prolongation, 4% hyperbilirubinemia, and 4% elevated AST. Eleven pts (25%) achieved a CR, 9 with incomplete platelet recovery (20%), after a median time of 13 (10-16) weeks from treatment start. Five (11%) of these pts relapsed after achieving CR. Two pts (5%) received an allogeneic stem cell transplant while on study, one in CR and one primary refractory (after a blast count drop from 27 to 7%), and they are both still in CR and alive. Among 26 pts with FLT3 ITD and no D835 mutation, 9 (35%) achieved CR/CRp. Six of 18 (33%) pts not previously exposed to FLT3 inhibitors responded. There was no significant correlation of dose with response (24% with 50 mg bid vs 33% with 25 mg bid, p=0.63). After a median follow-up of 15 (3-72) weeks, 20 pts (64%) died, 3 (7%) while on study (2 died of sepsis, 1 of unknown causes with progressive disease). The median CRD was 16 (9-23) months. Factors significantly associated with a longer CRD were male sex (p=0.04), age older than 65 years (0.03) and use of 50 mg bid of midostaurin (p=0.02). Conclusions The combination of midostaurin and 5-AZA is safe and well tolerated. Its efficacy is most noticeable among pts with FLT3 mutations. A longer response duration is observed using midostaurin at 50 mg bid dose and in elderly male pts. Disclosures: Ravandi: CELGENE: Honoraria; NOVARTIS: Honoraria. Cortes:ARIAD: Consultancy, Research Funding; ASTELLAS: Research Funding; AMBIT: Research Funding; AROG: Research Funding; NOVARTIS: Research Funding.

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FLT3 mutations in acute myeloid leukemia: what is the best approach in 2013?

Hematology ◽

10.1182/asheducation-2013.1.220 ◽

2013 ◽

Vol 2013 (1) ◽

pp. 220-226 ◽

Cited By ~ 129

Author(s):

Mark Levis

Keyword(s):

Acute Myeloid Leukemia ◽

Myeloid Leukemia ◽

Allogeneic Transplantation ◽

Current Treatment ◽

Flt3 Mutation ◽

Flt3 Mutations ◽

Flt3 Inhibitors ◽

First Remission ◽

Acute Myeloid

Abstract Patients with acute myeloid leukemia who harbor an FMS-like tyrosine kinase 3 (FLT3) mutation present several dilemmas for the clinician. The results of an FLT3 mutation test, which can be influenced by several variables, need to be interpreted according to the clinical setting and there is a need for internationally standardized FLT3 mutation assays. Because of the lack of prospective studies, the role of allogeneic transplantation as consolidation therapy is still somewhat controversial, but the preponderance of evidence suggests that transplantation in first remission, if possible, is probably the best option. Clinically useful FLT3 inhibitors are hopefully on the near horizon and are being studied in the context of current treatment paradigms.

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Dual Mechanism Inhibitor Control and Pharmacological Utility of Drug Resistance FLT3-ITD in Acute Myeloid Leukemia Cells

10.54137/ijotr111 ◽

2021 ◽

Vol 1 (1) ◽

Author(s):

Maria Rogdaki ◽

Xinhua Xiao

Keyword(s):

Acute Myeloid Leukemia ◽

Myeloid Leukemia ◽

Point Mutations ◽

Kinase Domain ◽

Genetic Alterations ◽

Tyrosine Kinase Domain ◽

Tubulin Inhibitor ◽

Flt3 Mutations ◽

Flt3 Inhibitors ◽

Acute Myeloid

FLT3 mutations are among the most common genetic alterations in acute-myeloid leukemia (AML). They are associated with poor prognosis. Multiple FLT3 inhibitors have been in clinical evaluation at various stages. Resistance to FLT3 inhibitors due to acquired point mutations in the tyrosine-kinase domain (TKD), have limited the effectiveness of treatments. A “gatekeeper” mutation (F691L), is also resistant to most FLT3 inhibitors. New therapies are therefore needed. FLT3 inhibitors are needed to protect against FLT3-TKD mutations and FLT3 internal tandem duplicate (FLT3–ITD). We identified KX2-391, a dual FLT3/tubulin inhibitor, and examined its efficacy and mechanisms for overcoming drug-resistant FLT3ITD-TKD mutations. KX2-391 had potent growth inhibitory effects and apoptosis promoting effects on AML cell lines that harbor FLT3-ITD mutations. KX2-391 orally administered significantly prolonged the survival time of a murine model with leukemia caused by FLT3ITD-F691L. KX2-391 also inhibited growth of primary AML cells that express FLT3ITD-F691L and 2 primary cells that are FLT3ITD-D835Y. Preclinical data suggest that KX2-391 is a promising FLT3 inhibitor. The treatment of AML patients with FLT3 mutations, particularly refractory/relapsed patients suffering from F691L or other FLT3TKD mutations.

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