FLT3 inhibitors in acute myeloid leukemia: Current and future

Quizartinib: a new hope in acute myeloid leukemia, an applied comprehensive review

Acute myeloid leukemia (AML) is caused by a defective precursor leading to malignant clonal expansion, often with FMS-like tyrosine kinase-3 receptor (FLT3) mutations, particularly internal tandem duplication (ITD), which has a poor prognosis. Quizartinib, a second-generation FLT3 inhibitor, has FDA approval for relapsed/refractory AML with FLT3/ITD mutation. It has shown promise in clinical studies since 2013 due to its excellent oral absorption and potent activity on FLT3. This review explores Quizartinib's mechanism of action, efficacy in monotherapy or combination with chemotherapy, drug interactions, adverse events, resistance mechanisms and future research directions.

Inhibition of FLT3-ITD Kinase in Acute Myeloid Leukemia by New Imidazo[1,2-b]pyridazine Derivatives Identified by Scaffold Hopping

FLT3 kinase is a potential drug target in acute myeloid leukemia (AML). Patients with FLT3 mutations typically have higher relapse rates and worse outcomes than patients without FLT3 mutations. In this study, we investigated the suitability of various heterocycles as central cores of FLT3 inhibitors, including thieno[3,2-d]pyrimidine, pyrazolo[1,5-a]pyrimidine, imidazo[4,5-b]pyridine, pyrido[4,3-d]pyrimidine, and imidazo[1,2-b]pyridazine. Our assays revealed a series of imidazo[1,2-b]pyridazines with high potency against FLT3. Compound 34f showed nanomolar inhibitory activity against recombinant FLT3-ITD and FLT3-D835Y (IC50 values 4 and 1 nM, respectively) as well as in the FLT3-ITD-positive AML cell lines MV4-11, MOLM-13, and MOLM-13 expressing the FLT3-ITD-D835Y mutant (GI50 values of 7, 9, and 4 nM, respectively). In contrast, FLT3-independent cell lines were much less sensitive. In vitro experiments confirmed suppression of FLT3 downstream signaling pathways. Finally, the treatment of MV4-11 xenograft-bearing mice with 34f at doses of 5 and 10 mg/kg markedly blocked tumor growth without any adverse effects.

The Therapeutic Potential of a Strategy to Prevent Acute Myeloid Leukemia Stem Cell Reprogramming in Older Patients

Acute myeloid leukemia (AML) is the most common and incurable leukemia subtype. Despite extensive research into the disease's intricate molecular mechanisms, effective treatments or expanded diagnostic or prognostic markers for AML have not yet been identified. The morphological, immunophenotypic, cytogenetic, biomolecular, and clinical characteristics of AML patients are extensive and complex. Leukemia stem cells (LSCs) consist of hematopoietic stem cells (HSCs) and cancer cells transformed by a complex, finely-tuned interaction that causes the complexity of AML. Microenvironmental regulation of LSCs dormancy and the diagnostic and therapeutic implications for identifying and targeting LSCs due to their significance in the pathogenesis of AML are discussed in this review. It is essential to perceive the relationship between the niche for LSCs and HSCs, which together cause the progression of AML. Notably, methylation is a well-known epigenetic change that is significant in AML, and our data also reveal that microRNAs are a unique factor for LSCs. Multiple-targeted approaches to reduce the risk of epigenetic factors, such as the administration of natural compounds for the elimination of local LSCs, may prevent potentially fatal relapses. Furthermore, the survival analysis of overlapping genes revealed that specific targets had significant effects on the survival and prognosis of patients. We predict that the multiple-targeted effects of herbal products on epigenetic modification are governed by different mechanisms in AML and could prevent potentially fatal relapses. Thus, these strategies can facilitate the incorporation of herbal medicine and natural compounds into the advanced drug discovery and development processes achievable with Network Pharmacology research.

Incidence and clinical significance of FLT3 and nucleophosmin mutation in childhood acute myeloid leukemia in Chile

INTRODUCTION

Acute myeloid leukemia (AML) is a heterogeneous disease and approximately one-third of its carriers do not have evident genetic abnormalities. The mutation of specific molecular markers, such as fms-like tyrosine kinase 3 (FTL3) internal tandem duplication (ITD), FLT3 tyrosine kinase domain (TKD) and nucleophosmin (NPM1), are associated with an adverse and favorable prognosis, respectively.

OBJECTIVE

The objective was to determine the prevalence of FLT3/ITD and NPM1 in Chilean patients and their association with clinical data and prognosis.

METHOD AND RESULTS

Two hundred and thirty-two children were studied between 2011 and 2017, the median being 8.6 years (ranging from 1 to 18 months). Acute promyelocytic leukemia (APL) was diagnosed in 29%. The FLT3/ITD-mutated in non-promyelocytic AML was at 10% (14/133) and the FLT3/TKD, at 3.7% (2/54). In APL, it was at 25.4% (16/63). In non-promyelocytic AML, the FLT3/ITD-mutated was associated with a high leucocyte count, the median being 28.5 x mm³ (n = 14) versus 19.4 x mm³ (n = 119), (p = 0.25), in non-mutated cases. In APL, the median was 33.6 x mm3 (n = 15) versus 2.8 x mm3 (n = 47), (p < 0.001). The five-year overall survival (OS) in non-promyelocytic AML with non-mutated and mutated FLT3/ITD were 62.7% and 21.4%, respectively, (p < 0.001); the 5-year event-free survival (EFS) were 79.5% and 50%, respectively, (p < 0.01). The five-year OS in APL with non-mutated and mutated FLT3/ITD was 84.7% and 62.5%, respectively, (p = 0.05); the 5-year EFS was 84.7% and 68.8%, respectively, (p = 0.122). The NPM1 mutation was observed in 3.2% (5/155), all non-promyelocytic AML with the normal karyotype.

CONCLUSION

The FLT3/ITD mutation was observed more frequently in APL and associated with a higher white cell count at diagnosis. However, the most important finding was that the FLT3/ITD mutation was associated with a shorter survival in non-promyelocytic AML.

Molecular Systems Architecture of Interactome in the Acute Myeloid Leukemia Microenvironment

A molecular systems architecture is presented for acute myeloid leukemia (AML) to provide a framework for organizing the complexity of biomolecular interactions. AML is a multifactorial disease resulting from impaired differentiation and increased proliferation of hematopoietic precursor cells involving genetic mutations, signaling pathways related to the cancer cell genetics, and molecular interactions between the cancer cell and the tumor microenvironment, including endothelial cells, fibroblasts, myeloid-derived suppressor cells, bone marrow stromal cells, and immune cells (e.g., T-regs, T-helper 1 cells, T-helper 17 cells, T-effector cells, natural killer cells, and dendritic cells). This molecular systems architecture provides a layered understanding of intra- and inter-cellular interactions in the AML cancer cell and the cells in the stromal microenvironment. The molecular systems architecture may be utilized for target identification and the discovery of single and combination therapeutics and strategies to treat AML.

Haematologic malignancies with unfavourable gene mutations benefit from donor lymphocyte infusion with/without decitabine for prophylaxis of relapse after allogeneic HSCT: A pilot study

Relapse is the main cause of treatment failure for leukaemia patients with unfavourable gene mutations who receive allogeneic haematopoietic stem cell transplantation (allo‐HSCT). There is no consensus on the indication of donor lymphocyte infusion (DLI) for prophylaxis of relapse after allo‐HSCT. To evaluate the tolerance and efficacy of prophylactic DLI in patients with unfavourable gene mutations such as FLT3‐ITD, TP53, ASXL1, DNMT3A or TET2, we performed a prospective, single‐arm study. Prophylactic use of decitabine followed by DLI was planned in patients with TP53 or epigenetic modifier gene mutations. The prophylaxis was planned in 46 recipients: it was administered in 28 patients and it was not administered in 18 patients due to contraindications. No DLI‐associated pancytopenia was observed. The cumulative incidences of grade II–IV and III–IV acute graft‐versus‐host disease (GVHD) at 100 days post‐DLI were 25.8% and 11.0%, respectively. The rates of chronic GVHD, non‐relapse mortality and relapse at 3 years post‐DLI were 21.6%, 25.0% and 26.1%, respectively. The 3‐year relapse‐free survival and overall survival (OS) rates were 48.9% and 48.2%, respectively. Acute GVHD (HR: 2.30, p = 0.016) and relapse (HR: 2.46, p = 0.003) after DLI were independently associated with inferior OS. Data in the current study showed the feasibility of prophylactic DLI with/without decitabine in the early stage after allo‐HSCT in patients with unfavourable gene mutations.

Current and emerging molecular and epigenetic disease entities in acute myeloid leukemia and a critical assessment of their therapeutic modalities

Acute myeloid leukemia (AML) is the most frequently diagnosed acute leukemia, and its incidence increases with age. Although the etiology of AML remains unknown, exposure to genotoxic agents or some prior hematologic disorders could lead to the development of this condition. The pathogenesis of AML involves the development of malignant transformation of hematopoietic stem cells that undergo successive genomic alterations, ultimately giving rise to a full-blown disease. From the disease biology perspective, AML is considered to be extremely complex with significant genetic, epigenetic, and phenotypic variations. Molecular and cytogenetic alterations in AML include mutations in those subsets of genes that are involved in normal cell proliferation, maturation and survival, thus posing significant challenge to targeting these pathways without attendant toxicity. In addition, multiple malignant cells co-exist in the majority of AML patients. Individual subclones are characterized by unique genetic and epigenetic abnormalities, which contribute to the differences in their response to treatment. As a result, despite a dramatic progress in our understanding of the pathobiology of AML, not much has changed in therapeutic approaches to treat AML in the past four decades. Dose and regimen modifications with improved supportive care have contributed to improved outcomes by reducing toxicity-related side effects. Several drug candidates are currently being developed, including targeted small-molecule inhibitors, cytotoxic chemotherapies, monoclonal antibodies and epigenetic drugs. This review summarizes the current state of affairs in the pathobiological and therapeutic aspects of AML.

Optimization of pyrazolo[1,5-a]pyrimidines lead to the identification of a highly selective casein kinase 2 inhibitor

Casein kinase 2 (CK2) is a constitutively expressed serine/threonine kinase that has a large diversity of cellular substrates. Thus, CK2 has been associated with a plethora of regulatory functions and dysregulation of CK2 has been linked to disease development in particular to cancer. The broad implications in disease pathology makes CK2 an attractive target. To date, the most advanced CK2 inhibitor is silmitasertib, which has been investigated in clinical trials for treatment of various cancers, albeit several off-targets for silmitasertib have been described. To ascertain the role of CK2 inhibition in cancer, other disease and normal physiology the development of a selective CK2 inhibitor would be highly desirable. In this study we explored the pyrazolo [1,5-a]pyrimidine hinge-binding moiety for the development of selective CK2 inhibitors. Optimization of this scaffold, which included macrocyclization, led to IC20 (31) a compound that displayed high in vitro potency for CK2 (K_D = 12 nM) and exclusive selectivity for CK2. X-ray analysis revealed a canonical type-I binding mode for IC20 (31). However, the polar carboxylic acid moiety that is shared by many CK2 inhibitors including silmitasertib was required for potency but limits the cellular activity of IC20 (31) and the cellular IC₅₀ dropped to the low micromolar range. In summary, IC20 (31) represents a highly selective and potent inhibitor of CK2, which can be used as a tool compound to study CK2 biology and potential new applications for the treatment of diseases.

Fentanyl inhibits acute myeloid leukemia differentiated cells and committed progenitors via opioid receptor-independent suppression of Ras and STAT5 pathways

Fentanyl is a common sedative/analgesic used for intrathecal chemotherapy injection in children with acute leukemia. Given the contradictory findings that fentanyl has both inhibitory and stimulatory activities in cancer cells, we investigated the biological effects of fentanyl alone and its combination with standard of care in acute myeloid leukemia (AML) cells at all stages of development. We showed that fentanyl at clinically relevant concentration inhibited growth and colony formation of AML differentiated cells and committed progenitors without affecting their survival. Compared to AML cells without FLT3 mutation, cells harboring FLT3-ITD mutation are likely to be more sensitive to fentanyl. However, fentanyl did not affect the most primitive AML stem cells. Fentanyl significantly augmented the efficacy of cytarabine but not midostaurin in AML differentiated cells and committed progenitors. We further demonstrated that fentanyl inhibited AML cells via suppressing Ras/Raf/MEK/ERK and STAT5 pathway, and this was not dependent on opioid receptor system. Our findings demonstrate the anti-leukemia activity of fentanyl and synergistic effects between fentanyl and cytarabine in AML, via opioid receptor-independent suppression of Ras and STAT5 pathways. Our work is the first to suggest the beneficial effects of fentanyl in children with leukemia.

Development of UHPLC-MS/MS Method for Indirubin-3'-Oxime Derivative as a Novel FLT3 Inhibitor and Pharmacokinetic Study in Rats

This study aimed to develop and validate a sensitive liquid chromatography-coupled tandem mass spectrometry method for the quantification of LDD-2614, an indirubin derivative and novel FLT3 inhibitor, in rat plasma. In addition, the developed analytical method was applied to observe the pharmacokinetic properties of LDD-2614. Chromatographic separation was achieved on a Luna omega C₁₈ column using a mixture of water and acetonitrile, both containing 0.1% formic acid. Quantitation was performed using positive electrospray ionization in a multiple reaction monitoring (MRM) mode. The MRM transitions were optimized as m/z 426.2→113.1 for LDD-2614 and m/z 390.2→113.1 for LDD-2633 (internal standard), and the lower limit of quantification (LLOQ) for LDD-2614 was determined as 0.1 ng/mL. Including the LLOQ, the nine-point calibration curve was linear with a correlation coefficient greater than 0.9991. Inter- and intraday accuracies (RE) ranged from -3.19% to 8.72%, and the precision was within 9.02%. All validation results (accuracy, precision, matrix effect, recovery, stability, and dilution integrity) met the acceptance criteria of the U.S. Food and Drug Administration and the Korea Ministry of Food and Drug Safety guidelines. The proposed method was validated and demonstrated to be suitable for the quantification of LDD-2614 for pharmacokinetics studies.

Midostaurin In Acute Myeloid Leukemia: An Evidence-Based Review And Patient Selection

Fms-related-tyrosine kinase 3 (FLT3) mutations occur in approximately a third of acute myeloid leukemia (AML) patients and confer an adverse prognosis. Numerous studies have evaluated FLT3 targeting as single agent and in combination approaches in frontline and relapsed AML. At this time, midostaurin, a multikinase inhibitor, is the only FLT3-inhibitor that is US FDA approved to be used in combination with induction therapy in the frontline FLT3-mutated AML setting based on improved overall survival noted in the RATIFY Phase III trial. The utility of midostaurin in maintenance post stem cell transplantation has shown promising results and further studies are still ongoing. In this review, we discuss the studies that led to the inception of midostaurin as a targeted kinase inhibitor, its evaluation in AML, the early clinical trials and the large Phase III clinical trial that led to its eventual US FDA-approval in FLT3-mutated AML. Our review also discusses data on midostaurin adverse effects, mechanisms of resistance and limitations of its utility. We further discuss emerging second-generation FLT3 inhibitors, with a focus on quizartinib and gilteritinib and future directions to enhance FLT3-inhibitor efficacy and overcome mechanisms of resistance.

The Impact of Flt3 Gene Mutations in Acute Promyelocytic Leukemia: A Meta-Analysis

The association of FLT3 mutations with white blood cell (WBC) counts at diagnosis and early death was studied in patients with acute promyelocytic leukemia (APL). Publications indexed in databases of biomedical literature were analyzed. Potential publication bias was evaluated by analyzing the standard error in funnel plots using the estimated relative risk (RR). Mixed-effect models were used to obtain the consolidated RR. All analyses were conducted using the R statistical software package. We used 24 publications in the final meta-analysis. Of 1005 males and 1376 females included in these 24 publications, 645 had FLT3-ITD (internal tandem duplication) mutations. Information on FLT3-D835 mutations was available in 10 publications for 175 patients. Concurrent occurrence of the two mutations was rare. WBC count at diagnosis was ≥10 × 109/L in 351 patients. For patients with the FLT3-ITD mutation, RR was 0.59 for overall survival (OS) and 1.62 for death during induction. For those with FLT3-D835 mutations, the RR was 0.50 for OS and 1.77 for death during induction. RR for WBC count ≥10 × 109/L was 3.29 and 1.48 for patients with FLT3-ITD and FLT3-D835, respectively. APL patients with FLT3-ITD or FLT3-D835 are more likely to present with elevated WBC counts and poorer prognosis than those without these mutations.

Molecular Approaches to Treating Pediatric Leukemias

Over the past decades, striking progress has been made in the treatment of pediatric leukemia, approaching 90% overall survival in children with acute lymphoblastic leukemia (ALL) and 75% in children with acute myeloid leukemia (AML). This has mainly been achieved through multiagent chemotherapy including CNS prophylaxis and risk-adapted therapy within collaborative clinical trials. However, prognosis in children with refractory or relapsed leukemia remains poor and has not significantly improved despite great efforts. Hence, more effective and less toxic therapies are urgently needed. Our understanding of disease biology, molecular drivers, drug resistance and, thus, the possibility to identify children at high-risk for treatment failure has significantly improved in recent years. Moreover, several new drugs targeting key molecular pathways involved in leukemia development, cell growth, and proliferation have been developed and approved. These striking achievements are linked to the great hope to further improve survival in children with refractory and relapsed leukemia. This review gives an overview on current molecularly targeted therapies in children with leukemia, including kinase, and proteasome inhibitors, epigenetic and enzyme targeting, as well as apoptosis regulators among others.