ASP2215 in the treatment of relapsed/refractory acute myeloid leukemia with FLT3 mutation: background and design of the ADMIRAL trial

An Expedition on Synthetic Methodology of FDA-approved Anticancer Drugs (2018-2021)

New drugs being established in the market every year produce specified structures for selective biological targeting. With medicinal insights into molecular recognition, these begot molecules open new rooms for designing potential new drug molecules. In this review, we report the compilation and analysis of a total of 56 drugs including 33 organic small molecules (Mobocertinib, Infigratinib, Sotorasib, Trilaciclib, Umbralisib, Tepotinib, Relugolix, Pralsetinib, Decitabine, Ripretinib, Selpercatinib, Capmatinib, Pemigatinib, Tucatinib, Selumetinib, Tazemetostat, Avapritinib, Zanubrutinib, Entrectinib, Pexidartinib, Darolutamide, Selinexor, Alpelisib, Erdafitinib, Gilteritinib, Larotrectinib, Glasdegib, Lorlatinib, Talazoparib, Dacomitinib, Duvelisib, Ivosidenib, Apalutamide), 6 metal complexes (Edotreotide Gallium Ga-68, fluoroestradiol F-18, Cu 64 dotatate, Gallium 68 PSMA-11, Piflufolastat F-18, 177Lu (lutetium)), 16 macromolecules as monoclonal antibody conjugates (Brentuximabvedotin, Amivantamab-vmjw, Loncastuximabtesirine, Dostarlimab, Margetuximab, Naxitamab, Belantamabmafodotin, Tafasitamab, Inebilizumab, SacituzumabGovitecan, Isatuximab, Trastuzumab, Enfortumabvedotin, Polatuzumab, Cemiplimab, Mogamulizumab) and 1 peptide enzyme (Erwiniachrysanthemi-derived asparaginase) approved by the U.S. FDA between 2018 to 2021. These drugs act as anticancer agents against various cancer types, especially non-small cell lung, lymphoma, breast, prostate, multiple myeloma, neuroendocrine tumor, cervical, bladder, cholangiocarcinoma, myeloid leukemia, gastrointestinal, neuroblastoma, thyroid, epithelioid and cutaneous squamous cell carcinoma. The review comprises the key structural features, approval times, target selectivity, mechanisms of action, therapeutic indication, formulations, and possible synthetic approaches of these approved drugs. These crucial details will benefit the scientific community for futuristic new developments in this arena.

Repurposing Axl Kinase Inhibitors for the Treatment of Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) infection persists as a common pathogen of pulmonary infection in infants and in the elderly with high morbidity and mortality. However, no specific therapeutics are available. Axl, a member of the TAM (Tyro3, Axl, and Mertk) family receptor kinases, is a pleiotropic inhibitor of the innate immune response and functions as a negative regulator of interferon pathway activation. In this report, we investigated Axl inhibitors for their effects against RSV infection. Axl inhibition with kinase inhibitors, including BMS-777607, R428, and TP-0903, or Axl ablation resulted in a significant reduction of RSV infection in cell-based assays. In an animal model of pulmonary RSV infection, treatment with BMS-777607, R428, or TP-0903 ameliorated pulmonary pathology with a significant reduction of RSV titers in the lung tissues and, consequently, decreased the expression of proinflammatory genes. The host promotes ISG expression for the antiviral response and for viral clearance. We found that Axl inhibition led to more robust IFN-β expression and antiviral gene induction. Thus, the results of this study imply that Axl kinase inhibitors may possess a broad spectrum of antiviral effects by promoting ISG expression.

Gilteritinib Enhances Anti-Tumor Efficacy of CDK4/6 Inhibitor, Abemaciclib in Lung Cancer Cells

Abemaciclib is a cyclin-dependent kinases 4/6 (CDK4/6) inhibitor approved for the treatment of metastatic breast cancer. Preclinical studies suggest that abemaciclib has the potential for lung cancer treatment. However, several clinical trials demonstrate that monotherapy with abemaciclib has no obvious superiority than erlotinib to treat lung cancer patients, limiting its therapeutic options for lung cancer treatment. Here, we show that the US Food and Drug Administration (FDA)-approved drug, gilteritinib, enhances the cytotoxicity of abemaciclib through inducing apoptosis and senescence in lung cancer cells. Interestingly, abemaciclib in combination with gilteritinib leads to excessive accumulation of vacuoles in lung cancer cells. Mechanistically, combined abemaciclib and gilteritinib induces complete inactivation of AKT and retinoblastoma (Rb) pathways in lung cancer cells. In addition, RNA-sequencing data demonstrate that combination of abemaciclib and gilteritinib treatment induces G2 phase cell-cycle arrest, inhibits DNA replication, and leads to reduction in homologous recombination associated gene expressions. Of note, abemaciclib-resistant lung cancer cells are more sensitive to gilteritinib treatment. In a mouse xenograft model, combined abemaciclib and gilteritinib is more effective than either drug alone in suppressing tumor growth and appears to be well tolerated. Together, our findings support the combination of abemaciclib with gilteritinib as an effective strategy for the treatment of lung cancer, suggesting further evaluation of their efficacy is needed in a clinical trial.

Cost-effectiveness of gilteritinib for relapsed/refractory FLT3mut+ acute myeloid leukemia

BACKGROUND: Patients with relapsed or refractory (R/R) acute myeloid leukemia (AML) and confirmed feline McDonough sarcoma (FMS)-like tyrosine kinase 3 gene mutations (FLT3^mut+) have a poor prognosis and limited effective treatment options. Gilteritinib is the first targeted therapy approved in the United States and Europe for R/R FLT3^mut+ AML with significantly improved efficacy compared with existing treatments. OBJECTIVE: To evaluate gilteritinib against salvage chemotherapy (SC) and best supportive care (BSC) over a lifetime horizon among adult patients with R/R FLT3^mut+ AML from a US third-party payer's perspective. METHODS: The model structure of this cost-effectiveness analysis included a decision tree to stratify patients based on their hematopoietic stem cell transplantation (HSCT) status, followed by 2 separate 3-state partitioned survival models to predict the long-term health status conditional on HSCT status. The ADMIRAL trial data and literature were used to predict probabilities of patients being in different health states until a conservative cure point at year 3. Afterwards, living patients followed the survival outcomes of long-term survivors with AML. Model inputs for utilities, medical resource use, and costs were based on the ADMIRAL trial, published literature, and public sources. All costs were inflated to 2019 US dollars (USD). Total incremental costs (in 2019 USD), life-years (LYs), quality-adjusted LYs (QALYs), and incremental cost-effectiveness ratios (ICERs) were calculated. Deterministic sensitivity analyses and probabilistic sensitivity analyses were performed. RESULTS: Over a lifetime horizon with a 3.0% annual discount rate, the base-case model estimated that gilteritinib led to an increase of 1.29 discounted QALYs at an additional cost of $148,106 vs SC, corresponding to an ICER of $115,192 per QALY; for BSC, results were an increase of 2.32 discounted QALYs, $249,674, and $107,435, respectively. The base-case findings were robust in sensitivity analyses. The estimated probabilities of gilteritinib being cost-effective vs SC and BSC were 90.5% and 99.8%, respectively, in the probabilistic sensitivity analyses, based on a willingness-to-pay threshold of $150,000 per QALY. CONCLUSIONS: Gilteritinib is a cost-effective novel treatment for patients with R/R FLT3^mut+ AML in the United States. DISCLOSURES: This work was supported by Astellas Pharma, Inc., which was involved in all stages of the research and manuscript development. Garnham, Pandya, and Shah are employees of Astellas and hold stock/stock options. Zeidan consulted and received personal fees/honoraria and research funding from Astellas. Zeidan also has received research funding from Celgene/BMS, Abbvie, Astex, Pfizer, Medimmune/AstraZeneca, Boehringer-Ingelheim, Trovagene/Cardiff Oncology, Incyte, Takeda, Novartis, Amgen, Aprea, and ADC Therapeutics; has participated in advisory boards; has consulted with and/or received honoraria from AbbVie, Otsuka, Pfizer, Celgene/BMS, Jazz, Incyte, Agios, Boehringer-Ingelheim, Novartis, Acceleron, Daiichi Sankyo, Taiho, Seattle Genetics, BeyondSpring, Cardiff Oncology, Takeda, Ionis, Amgen, Janssen, Syndax, Gilead, Kura, Aprea, Lox Oncology, Genentech, Servier, Jasper, Tyme, and Epizyme; has served on clinical trial committees for Novartis, Abbvie, Geron, Gilead, Kura, Lox Oncology, BioCryst, and Celgene/BMS; and has received travel support for meetings from Pfizer, Novartis, and Cardiff Oncology. Qi and Yang are employees of Analysis Group, Inc., which received consulting fees from Astellas for work on this study. Part of this material was presented at the American Society of Hematology (ASH) Annual Meeting; December 7-10, 2019; Orlando, FL.

Recent advances of targeted therapy in relapsed/refractory acute myeloid leukemia

Despite advances in the understanding of disease pathobiology, treatment for relapsed or refractory acute myeloid leukemia (R/R AML) remains challenging. The prognosis of R/R AML remains extremely poor despite chemotherapy and bone marrow transplants. Discoveries on recurrent and novel genetic mutations, such as FLT3-ITD and IDH1/IDH2, critical signaling pathways, and unique molecular markers expressed on the surface of leukemic cells have been under investigation for the management of R/R AML. Other than monoclonal antibodies, diabodies, and triabodies are new targeted therapies developed in recent years and will be the new direction of immunotherapy. Targeted agents combined intensive regimens can be viable options for salvage therapy and as bridges to allogeneic transplant. Future directions will focus on novel, efficient and targeted combinations, low-toxicity maintenance, and individualized precision strategies. Here, we review the major recent advances of targeted therapies in the treatment of R/R AML.

The combination of CUDC-907 and gilteritinib shows promising in vitro and in vivo antileukemic activity against FLT3-ITD AML

About 25% of patients with acute myeloid leukemia (AML) harbor FMS-like tyrosine kinase 3 (FLT3) internal tandem duplication (ITD) mutations and their prognosis remains poor. Gilteritinib is a FLT3 inhibitor approved by the US FDA for use in adult FLT3-mutated relapsed or refractory AML patients. Monotherapy, while efficacious, shows short-lived responses, highlighting the need for combination therapies. Here we show that gilteritinib and CUDC-907, a dual inhibitor of PI3K and histone deacetylases, synergistically induce apoptosis in FLT3-ITD AML cell lines and primary patient samples and have striking in vivo efficacy. Upregulation of FLT3 and activation of ERK are mechanisms of resistance to gilteritinib, while activation of JAK2/STAT5 is a mechanism of resistance to CUDC-907. Gilteritinib and CUDC-907 reciprocally overcome these mechanisms of resistance. In addition, the combined treatment results in cooperative downregulation of cellular metabolites and persisting antileukemic effects. CUDC-907 plus gilteritinib shows synergistic antileukemic activity against FLT3-ITD AML in vitro and in vivo, demonstrating strong translational therapeutic potential.

Discovery of pyrrolo[2,3-d]pyrimidine derivatives as potent Axl inhibitors: Design, synthesis and biological evaluation

Axl has emerged as an attractive target for cancer therapy due to its strong correlation with tumor growth, metastasis, poor survival, and drug resistance. Herein, we report the design, synthesis and structure-activity relationship (SAR) investigation of a series of pyrrolo[2,3-d]pyrimidine derivatives as new Axl inhibitors. Among them, the most promising compound 13b showed high enzymatic and cellular Axl potencies. Furthermore, 13b possessed preferable pharmacokinetic properties and displayed promising therapeutic effect in BaF3/TEL-Axl xenograft tumor model. Compound 13b may serve as a lead compound for new antitumor drug discovery.

A budget impact analysis of gilteritinib for the treatment of relapsed or refractory FLT3 mut+ acute myeloid leukemia in a US health plan

AIMS

To estimate the economic impact of the introduction of gilteritinib for the treatment of relapsed/refractory (R/R) FLT3 mutation-positive (FLT3 ^mut+) acute myeloid leukemia (AML) from a US payer's perspective.

METHODS

A budget impact model (BIM) was developed to evaluate the 3-year total budgetary impact of treating adults with R/R FLT3 ^mut+ AML eligible for gilteritinib in a hypothetical US health plan. Total costs (drugs/administration, hospitalization, monitoring, adverse events, transfusions, subsequent hematopoietic stem cell transplantation, post-progression, and FLT3 testing) were estimated before and after gilteritinib entry. The budget impact was the total cost difference between the two scenarios. The target population size and cost inputs were based on public data or published literature, drug market share was informed by market research data, and the model included recommended treatments for R/R FLT3 ^mut+ AML per clinical guidelines. Deterministic sensitivity analyses (DSAs) and scenario analyses varying key model inputs and assumptions were conducted to test for robustness.

RESULTS

In a hypothetical health plan with 1 million members, 20.9 adults with R/R FLT3 ^mut+ AML were estimated to be eligible for gilteritinib. Of these, it was assumed 30.0% would be treated with gilteritinib in Year 1 following gilteritinib entry, increasing the total plan budget by $663,795 and the per-member-per-month (PMPM) cost by $0.055. In Years 2-3, the market share of gilteritinib increased to 45.0%, increasing the total plan budget impact by $1,078,371 and $1,087,230, and the PMPM cost by $0.090 and $0.091, respectively. The model results remained robust in DSAs and scenario analyses, with the largest impact observed when the projected uptake of gilteritinib was changed.

LIMITATIONS

The results of this BIM are contingent upon the model's assumptions and inputs.

CONCLUSIONS

Adding gilteritinib to the formulary for the treatment of adults with R/R FLT3 ^mut+ AML had a minimal budget impact from a US payer's perspective.

Dual Kinase Targeting in Leukemia

Simple Summary

A new option to treat cancer is based on the use of so-called multi-targeting drugs. This strategy can replace the standard treatment based on the co-administration of several drugs. An increased and uncontrolled activity of kinases (enzymes devoted to the regulation of several cell pathways) is often seen in hematological malignancies. The development of multi-kinase inhibitors is having a great impact on the treatment of this kind of cancer. Here, we review the most recent findings on this novel class of drugs.

Abstract

Pharmacological cancer therapy is often based on the concurrent inhibition of different survival pathways to improve treatment outcomes and to reduce the risk of relapses. While this strategy is traditionally pursued only through the co-administration of several drugs, the recent development of multi-targeting drugs (i.e., compounds intrinsically able to simultaneously target several macromolecules involved in cancer onset) has had a dramatic impact on cancer treatment. This review focuses on the most recent developments in dual-kinase inhibitors used in acute myeloid leukemia (AML), chronic myelogenous leukemia (CML), and lymphoid tumors, giving details on preclinical studies as well as ongoing clinical trials. A brief overview of dual-targeting inhibitors (kinase/histone deacetylase (HDAC) and kinase/tubulin polymerization inhibitors) applied to leukemia is also given. Finally, the very recently developed Proteolysis Targeting Chimeras (PROTAC)-based kinase inhibitors are presented.

4-Hydroxyphenyl Retinamide Preferentially Targets FLT3 Mutated Acute Myeloid Leukemia via ROS Induction and NF-κB Inhibition

FMS-like tyrosine kinase 3 (FLT3) mutation is strongly associated with poor prognosis in acute myeloid leukemia (AML). Though many FLT3 inhibitors have been developed for clinical application with 34%-56% complete remission rate, patients would develop resistance sooner or later after initial response to tyrosine kinase inhibitors (TKIs), such as gilteritinib. And increasing studies have shown that several resistance related mutations of FLT3 emerged during the AML progression. Thus, further investigation is warranted for these FLT3^mut AML patients to achieve a better treatment outcome. 4-Hydroxyphenyl retinamide (4-HPR) has been investigated extensively in animal models and clinical trials as an anticancer/chemopreventive agent and is currently used for protection against cancer development/recurrence, with minimal side effects. In this study, we performed gene-set enrichment analysis and found that down-regulated genes induced by 4-HPR were associated with FLT3-ITD gene sets. CD34⁺ AML stem/progenitor cells separated from 32 AML samples were treated with 4-HPR. Correlation analysis showed that AML cells with FLT3-ITD genetic alteration were more sensitive to 4-HPR treatment than those without FLT3-ITD. Next, we treated 22 primary AML cells with 4-HPR and found that 4-HPR was more toxic to AML cells with FLT3-ITD. These results indicated that 4-HPR was preferentially cytotoxic to all FLT3-ITD AML⁺ cells irrespective of stem/progenitor cells or blast cells. 4-HPR-induced reactive oxygen species (ROS) production and NF-κB inhibition might be the reason of 4-HPR selectivity on FLT3 mutated AML cells.

Arsenic trioxide potentiates Gilteritinib-induced apoptosis in FLT3-ITD positive leukemic cells via IRE1a-JNK-mediated endoplasmic reticulum stress

Background

Acute myeloid leukemia (AML) patients with FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD) have a high relapse rate and poor prognosis. This study aims to explore the underlying mechanism of combining Gilteritinib with ATO at low concentration in the treatment of FLT3-ITD positive leukemias.

Methods

We used both in vitro and in vivo studies to investigate the effects of combination of Gilteritinib with ATO at low concentration on FLT3-ITD positive leukemias, together with the underlying molecular mechanisms of these processes.

Results

Combination of Gilteritinib with ATO showed synergistic effects on inhibiting proliferation, increasing apoptosis and attenuating invasive ability in FLT3-ITD-mutated cells and reducing tumor growth in nude mice. Results of western blot indicated that Gilteritinib increased a 160KD form of FLT3 protein on the surface of cell membrane. Detection of endoplasmic reticulum stress marker protein revealed that IRE1a and its downstream signal phosphorylated JNK were suppressed in Gilteritinib-treated FLT3-ITD positive cells. The downregulation of IRE1a induced by Gilteritinib was reversed with addition of ATO. Knockdown of IRE1a diminished the combinatorial effects of Gilteritinib plus ATO treatment and combination of tunicamycin (an endoplasmic reticulum pathway activator) with Gilteritinib achieved the similar effect as treatment with Gilteritinib plus ATO.

Conclusions

Thus, ATO at low concentration potentiates Gilteritinib-induced apoptosis in FLT3-ITD positive leukemic cells via IRE1a-JNK signal pathway, targeting IRE1a to cooperate with Gilteritinib may serve as a new theoretical basis on FLT3-ITD mutant AML treatment.

Successful treatment with gilteritinib for isolated extramedullary relapse of acute myeloid leukemia with FLT3-ITD mutation after allogeneic stem cell transplantation

Acute myeloid leukemia (AML) harboring Fms-like tyrosine kinase 3 (FLT3) internal tandem duplication (ITD) mutation is associated with shorter remission and higher relapse risk. Several FLT3 inhibitors have been used in clinical trials, but their efficacy in extramedullary disease remains unclear. In the present case, a 56-year-old man was diagnosed with FLT3-ITD mutated AML. Due to bone marrow relapse during consolidation therapy, he underwent salvage therapy and a myeloablative conditioning regimen, followed by peripheral blood stem cell transplantation (PBSCT) from a HLA-matched related donor. Acute graft-versus-host disease (GVHD) did not develop, and complete donor chimerism was confirmed on days 27 and 96 after PBSCT. On day 180, he experienced extensive chronic GVHD and had several subcutaneous tumors in his body, which were diagnosed as myeloid sarcoma by pathological examination. We considered this to be a case of isolated extramedullary relapse, as his bone marrow had maintained complete donor chimerism. Treatment with etoposide and ranimustine produced no effect, and tumor progression continued. We started administration of gilteritinib, a FLT3/AXL inhibitor, after identifying the FLT3-ITD mutation in the tumor. Subsequently, there has been a remarkable regression of the tumors. Gilteritinib can be effective in isolated extramedullary relapse after allogeneic stem cell transplantation.

New drugs approved for acute myeloid leukaemia in 2018

Acute myeloid leukaemia (AML) is a haematopoietic stem cell disorder, that is characterized by the clonal expansion of myeloid blasts and suppression of normal haematopoiesis. The 3 + 7 regimen is the backbone of standard first-line induction therapy among young/fit patients. However, in elderly and/or unfit patients with newly diagnosed AML, who cannot receive intensive chemotherapy, low-dose cytarabine or hypomethylating agents (azacitidine or decitabine) are the treatment options, which generally cannot induce durable responses. Among young/fit patients, for high-risk disease in first remission, or in cases with relapsed/refractory AML, allogeneic stem cell transplantation should be performed when complete remission is achieved. However, since AML is primarily a disease of the elderly, neither intensive chemotherapy nor allogeneic stem cell transplantation can be generally tolerated in most cases. There is clearly a need for new treatment options in elderly and young/unfit patients who cannot receive intensive chemotherapy. The discovery of novel molecular genetic markers (e.g. FMS-like tyrosine kinase 3, isocitrate dehydrogenase 1 and 2) resulted in the development of new therapeutic options in AML. This review mainly focuses on 4 targeted therapy agents; glasdegib and venetoclax used in combination treatment with low-dose cytarabine or hypomethylating agents among newly diagnosed cases with AML; and ivosidenib and gilteritinib as monotherapy in the treatment of relapsed/refractory AML, which were all approved by the US Food and Drug Administration in 2018.

Targeting Apoptotic Pathways in Acute Myeloid Leukaemia

Acute Myeloid Leukaemia is a devastating disease that continues to have a poor outcome for the majority of patients. In recent years, however, a number of drugs have received FDA approval, following on from successful clinical trial results. This parallels the characterization of the molecular landscape of Acute Myeloid Leukaemia (AML) over the last decade, which has led to the development of drugs targeting newly identified recurring mutations. In addition, basic biological research into the pathobiology of AML has identified aberrant programmed cell death pathways in AML. Following on from successful outcomes in lymphoid malignancies, drugs targeting the B Cell Lymphoma 2 (BCL-2) family of anti-apoptotic proteins have been explored in AML. In this review, we will outline the preclinical and clinical work to date supporting the role of drugs targeting BCL-2, with Venetoclax being the most advanced to date. We will also highlight rationale combinations using Venetoclax, ongoing clinical trials and biomarkers of response identified from the early phase clinical trials performed.

Effect of Fms-like tyrosine kinase 3 (FLT3) ligand (FL) on antitumor activity of gilteritinib, a FLT3 inhibitor, in mice xenografted with FL-overexpressing cells

Therapeutic effects of FLT3 inhibitors have been reported in acute myeloid leukemia (AML) with constitutively activating FLT3 mutations, including internal tandem duplication (ITD) and point mutation, which are found in approximately one-third of AML patients. One of the critical issues of treatment with FLT3 inhibitors in FLT3-mutated AML is drug resistance. FLT3 ligand (FL) represents a mechanism of resistance to FLT3 inhibitors, including quizartinib, midostaurin, and sorafenib, in AML cells harboring both wild-type and mutant FLT3 (FLT3^wt/FLT3^mut). Here, we investigated the effect of FL on the efficacy of gilteritinib, a FLT3 inhibitor, in AML-derived cells in vitro and in mice. In contrast to other FLT3 inhibitors, FL stimulation had little effect on growth inhibition or apoptosis induction by gilteritinib. The antitumor activity of gilteritinib was also comparable between xenograft mouse models injected with FL-expressing and mock MOLM-13 cells. In the FLT3 signaling analyses, gilteritinib inhibited FLT3^wt and FLT3-ITD to a similar degree in HEK293 and Ba/F3 cells, and similarly suppressed FLT3 downstream signaling molecules (including ERK1/2 and STAT5) in both the presence and absence of FL in MOLM-13 cells. Co-crystal structure analysis showed that gilteritinib bound to the ATP-binding pocket of FLT3. These results suggest that gilteritinib has therapeutic potential in FLT3-mutated AML patients with FL overexpression.

Inhibition of Bcl-2 Synergistically Enhances the Antileukemic Activity of Midostaurin and Gilteritinib in Preclinical Models of FLT3-Mutated Acute Myeloid Leukemia

PURPOSE

To investigate the efficacy of the combination of the FLT3 inhibitors midostaurin or gilteritinib with the Bcl-2 inhibitor venetoclax in FLT3-internal tandem duplication (ITD) acute myeloid leukemia (AML) and the underlying molecular mechanism.

EXPERIMENTAL DESIGN

Using both FLT3-ITD cell lines and primary patient samples, Annexin V-FITC/propidium iodide staining and flow cytometry analysis were used to quantify cell death induced by midostaurin or gilteritinib, alone or in combination with venetoclax. Western blot analysis was performed to assess changes in protein expression levels of members of the JAK/STAT, MAPK/ERK, and PI3K/AKT pathways, and members of the Bcl-2 family of proteins. The MV4-11-derived xenograft mouse model was used to assess in vivo efficacy of the combination of gilteritinib and venetoclax. Lentiviral overexpression of Mcl-1 was used to confirm its role in cell death induced by midostaurin or gilteritinib with venetoclax. Changes of Mcl-1 transcript levels were assessed by RT-PCR.

RESULTS

The combination of midostaurin or gilteritinib with venetoclax potently and synergistically induces apoptosis in FLT3-ITD AML cell lines and primary patient samples. The FLT3 inhibitors induced downregulation of Mcl-1, enhancing venetoclax activity. Phosphorylated-ERK expression is induced by venetoclax but abolished by the combination of venetoclax with midostaurin or gilteritinib. Simultaneous downregulation of Mcl-1 by midostaurin or gilteritinib and inhibition of Bcl-2 by venetoclax results in "free" Bim, leading to synergistic induction of apoptosis. In vivo results show that gilteritinib in combination with venetoclax has therapeutic potential.

CONCLUSIONS

Inhibition of Bcl-2 via venetoclax synergistically enhances the efficacy of midostaurin and gilteritinib in FLT3-mutated AML.See related commentary by Perl, p. 6567.

Pediatric Acute Myeloid Leukemia (AML): From Genes to Models Toward Targeted Therapeutic Intervention

This review aims to provide an overview of the current knowledge of the genetic lesions driving pediatric acute myeloid leukemia (AML), emerging biological concepts, and strategies for therapeutic intervention. Hereby, we focus on lesions that preferentially or exclusively occur in pediatric patients and molecular markers of aggressive disease with often poor outcome including fusion oncogenes that involve epigenetic regulators like KMT2A, NUP98, or CBFA2T3, respectively. Functional studies were able to demonstrate cooperation with signaling mutations leading to constitutive activation of FLT3 or the RAS signal transduction pathways. We discuss the issues faced to faithfully model pediatric acute leukemia in mice. Emerging experimental evidence suggests that the disease phenotype is dependent on the appropriate expression and activity of the driver fusion oncogenes during a particular window of opportunity during fetal development. We also highlight biochemical studies that deciphered some molecular mechanisms of malignant transformation by KMT2A, NUP98, and CBFA2T3 fusions, which, in some instances, allowed the development of small molecules with potent anti-leukemic activities in preclinical models (e.g., inhibitors of the KMT2A-MENIN interaction). Finally, we discuss other potential therapeutic strategies that not only target driver fusion-controlled signals but also interfere with the transformed cell state either by exploiting the primed apoptosis or vulnerable metabolic states or by increasing tumor cell recognition and elimination by the immune system.