FLT3 internal tandem duplication during myelodysplastic syndrome follow-up: a marker of transformation to acute myeloid leukemia

Induction of cytotoxicity and apoptosis in FLT3 mutant expressing cells using novel pyrimido cyanoacrylates and quinoline derivatives

BACKGROUND

Aberrant activation of FMS-like tyrosine kinase 3 (FLT3) is associated with acute myeloid leukemia (AML). Leukemic cells expressing constitutively active FLT3 mutants are resistance to the current cancer therapies (radiotherapy and chemotherapy); hence, there is an increased interest to identify new agents for the treatment of AML. The main aim of this study was evaluating cytotoxic effects of novel pyrimidocyanoacrylates and quinoline derivatives on FLT3 overexpressing cells.

MATERIALS AND METHODS

Five novel pyrimidocyanoacrylates & 2-chloro 3-carbaldehyde quinolone derivative compounds, E1QAC1, E1QAC2, E1QAC3, E1QAC4, and E1QAC5 were designed and synthesized at the Department of Chemistry, Faculty of Sciences, Ferdowsi University, Mashhad, Iran. FDC-P1 cells expressing human wild-type FLT3 (FD-FLT3-WT) and internal tandem duplication (ITD) mutants (FD-FLT3-ITD) used in this study. The cells maintained in DMEM medium supplemented with 10% fetal calf serum (FCS) and murine granulocyte-macrophage colony stimulating factor (mGM-CSF). Potency for induction of cytotoxicity (IC₅₀ value) and apoptosis was determined after treating the cells with concentration of the compounds by resazurin assay. Bax and Bcl2 activation status was also investigated by Western blot analysis.

RESULTS

All the compounds had concentration-dependent effects on inhibition of cell proliferation and induction of apoptosis in both cell lines. E1QAC4 was the most potent compound for inhibition of cell proliferation (with IC50 value of 19 μM) and apoptosis induction in the FLT3-WT cells. However, FD-FLT3-ITD cells were nearly five-times more resistant to all the compounds (except than E1QAC2) that the FLT3-WT expressing cells. Western blotting results also showed that FD-FLT3-ITD cells had lower levels of Bax and higher levels of Bcl2 than the FD-FLT3-WT cells.

CONCLUSION

The five novel heterocyclic compounds (E1QAC1-5) had cytotoxic effects and induced apoptosis in FD-FLT3 cells. Therefore, it is worthwhile to consider them as potential lead compound for development of new therapeutic agents for AML patients.

Molecular and Cellular Mechanisms of Myelodysplastic Syndrome: Implications on Targeted Therapy

Myelodysplastic syndrome (MDS) is a group of heterogeneous clonal hematopoietic stem cell disorders characterized by cytopenia, ineffective hematopoiesis, and progression to secondary acute myeloid leukemia in high-risk cases. Conventional prognostication relies on clinicopathological parameters supplemented by cytogenetic information. However, recent studies have shown that genetic aberrations also have critical impacts on treatment outcome. Moreover, these genetic alterations may themselves be a target for treatment. The mutation landscape in MDS is shaped by gene aberrations involved in DNA methylation (TET2, DNMT3A, IDH1/2), histone modification (ASXL1, EZH2), the RNA splicing machinery (SF3B1, SRSF2, ZRSR2, U2AF1/2), transcription (RUNX1, TP53, BCOR, PHF6, NCOR, CEBPA, GATA2), tyrosine kinase receptor signaling (JAK2, MPL, FLT3, GNAS, KIT), RAS pathways (KRAS, NRAS, CBL, NF1, PTPN11), DNA repair (ATM, BRCC3, DLRE1C, FANCL), and cohesion complexes (STAG2, CTCF, SMC1A, RAD21). A detailed understanding of the pathogenetic mechanisms leading to transformation is critical for designing single-agent or combinatorial approaches in target therapy of MDS.

Molecular mechanisms of the progression of myelodysplastic syndrome to secondary acute myeloid leukaemia and implication for therapy

Myelodysplastic syndrome (MDS) includes a heterogeneous group of clonal haematological stem cell disorders characterized by dysplasia, cytopenias, ineffective haematopoiesis, and an increased risk of progression to acute myeloid leukaemia (AML), which is also called secondary AML (sAML). Approximately one-third of patients with MDS will progress to sAML within a few months to a few years, and this type of transformation is more common and rapid in patients with high-risk MDS (HR-MDS). However, the precise mechanisms underlying the evolution of MDS to sAML remain unclear. Currently, chemotherapy for sAML has minimal efficacy. The only method of curing patients with sAML is allogeneic haematopoietic stem cell transplantation (Allo-HSCT). Unfortunately, only a few patients are appropriate for transplantation because this disease primarily affects older adult patients. Additionally, compared to de novo AML, sAML is more difficult to cure, and the prognosis is often worse. Therefore, it is important to clarify the molecular mechanisms of the progression of MDS to sAML and to explore the potent drugs for clinical use. This review will highlight several molecular mechanisms of the progression of MDS to sAML and new therapeutic strategies of this disease.

Engineering mouse models with myelodysplastic syndrome human candidate genes; how relevant are they?

Myelodysplastic syndromes represent particularly challenging hematologic malignancies that arise from a large spectrum of genetic events resulting in a disease characterized by a range of different presentations and outcomes. Despite efforts to classify and identify the key genetic events, little improvement has been made in therapies that will increase patient survival. Animal models represent powerful tools to model and study human diseases and are useful pre-clinical platforms. In addition to enforced expression of candidate oncogenes, gene inactivation has allowed the consequences of the genetic effects of human myelodysplastic syndrome to be studied in mice. This review aims to examine the animal models expressing myelodysplastic syndrome-associated genes that are currently available and to highlight the most appropriate model to phenocopy myelodysplastic syndrome disease and its risk of transformation to acute myelogenous leukemia.

FLT3-ITD knockin impairs hematopoietic stem cell quiescence/homeostasis, leading to myeloproliferative neoplasm

Internal tandem duplication (ITD) mutations within the FMS-like tyrosine kinase-3 (FLT3) render the receptor constitutively active driving proliferation and survival in leukemic blasts. Expression of FLT3-ITD from the endogenous promoter in a murine knockin model results in progenitor expansion and a myeloproliferative neoplasm. In this study, we show that this expansion begins with overproliferation within a compartment of normally quiescent long-term hematopoietic stem cells (LT-HSCs), which become rapidly depleted. This depletion is reversible upon treatment with the small molecule inhibitor Sorafenib, which also ablates the disease. Although the normal LT-HSC has been defined as FLT3(-) by flow cytometric detection, we demonstrate that FLT3 is capable of playing a role within this compartment by examining the effects of constitutively activated FLT3-ITD. This indicates an important link between stem cell quiescence/homeostasis and myeloproliferative disease while also giving novel insight into the emergence of FLT3-ITD mutations in the evolution of leukemic transformation.

FLT3/ITD AML and the law of unintended consequences

Acute myeloid leukemia with a FLT3 internal tandem duplication (FLT3/ITD) mutation is an aggressive hematologic malignancy with a generally poor prognosis. It can be successfully treated into remission with intensive chemotherapy, but it routinely relapses. At relapse, the blasts tend to have higher mutant allelic ratios and, in vitro, are more addicted to the aberrant signaling from the FLT3/ITD oncoprotein. They remain highly responsive to FLT3 ligand, the levels of which rise several-fold during the course of chemotherapy. The question now arises as to whether these high levels of FLT3 ligand are actually promoting relapse, and, if so, how we can use this information to adjust our therapeutic approach and improve the cure rate for acute myeloid leukemia with FLT3/ITD.

Characterization of NPM1-mutated AML with a history of myelodysplastic syndromes or myeloproliferative neoplasms

The role of the nucleophosmin (NPM1) mutations in de novo acute myeloid leukemia (AML) is well analyzed, but the impact in secondary AML (s-AML) following myelodysplastic syndromes (MDS) or transformed myeloproliferative neoplasms (MPNs) remains unclear. We investigated 350 patients-283 s-AML after MDS and 67 transformed MPNs-for NPM1mut. NPM1mut was detected in 43/350 patients (12.3%) at diagnosis of s-AML (transformed MDS: 37/283; 13.1%; transformed MPNs: 6/67; 9.0%). Cytogenetic alterations were present in 12/40 cases (30.0%) with available karyotypes. Additional molecular mutations were found in 23/43 NPM1mut s-AML after MDS (53.5%) and in transformed MPN in 18/37 (48.6%): FLT3-ITD: 14/37 (37.8%); FLT3-TKD: 3/28 (10.7%); NRASmut: 4/37 (10.8%), RUNX1mut: 1/16 (6.3%). In NPM1mut-transformed MPNs, five out of six cases showed 1-2 additional molecular mutations (2 × KITD816V, ETV6-PDGFRB, 2 × JAK2V617F, 2 × FLT3-ITD). Backtracking of nine of these cases by quantitative real time PCR showed the NPM1mut already at diagnosis of MDS/MPN, at variable levels and up to 14 months before diagnosis of AML, and at transformation often being preceded or accompanied by other genetic alterations. Thus, NPM1 mutations are involved in the transformation from MDS to AML or MPN to blast phase in single cases, which should be further confirmed in larger studies.

Screening for hotspot mutations in PI3K, JAK2, FLT3 and NPM1 in patients with myelodysplastic syndromes

INTRODUCTION

Myelodysplastic syndromes encompass a heterogeneous group of clonal hematopoietic stem cell disorders characterized by ineffective hematopoiesis, refractory cytopenia and a tendency to progress toward acute myeloid leukemia. The accumulation of genetic alterations is closely associated with the progression of myelodysplastic syndromes toward acute myeloid leukemia.

OBJECTIVE

To investigate the presence of mutations in the points most frequent for mutations (hotspot mutations) in phosphatidylinositol-3-kinase (PI3K), Janus kinase 2 (JAK2), FMS-like tyrosine kinase 3 (FLT3) and nucleophosmin (NPM1), which are involved in leukemia and other cancers, in a population of Brazilian MDS patients.

METHODS

Fifty-one myelodysplastic syndromes patients were included in the study. According to French-American-British classification, the patients were distributed as follows: 31 with refractory anemia, 8 with refractory anemia with ringed sideroblasts, 7 with refractory anemia with excess blasts, 3 with refractory anemia with excess blasts in transformation and 2 with chronic myelomonocytic leukemia. Bone marrow samples were obtained and screened for the presence of hotspot mutations using analysis based on amplification with the polymerase chain reaction, sequencing, fragment size polymorphisms or restriction enzyme digestion. All patients were screened for mutations at the time of diagnosis, and 5 patients were also screened at the time of disease progression.

RESULTS

These results show that hotspot mutations in the PI3K, JAK2, FLT3 and NPM1 genes are not common in MDS patients; nevertheless, JAK2 mutations may be present in myelodysplasia during disease progression.

CONCLUSIONS

These results show that hotspot mutations in the PI3K, JAK2, FLT3 and NPM1 genes are not common in MDS patients; nevertheless, JAK2 mutations may be present in myelodysplasia during disease progression.

FLT3 and NPM1 mutations in myelodysplastic syndromes: Frequency and potential value for predicting progression to acute myeloid leukemia

We reviewed FLT3 and NPM1 mutation data in a large cohort of patients with myelodysplastic syndrome (MDS). The frequencies of FLT3 and NPM1 mutation were 2.0% and 4.4%, respectively, and mutations were restricted to cases of intermediate- and high-risk MDS. Cytogenetic abnormalities were identified in 46.9% of cases. FLT3 mutations were associated with a complex karyotype (P = .009), whereas NPM1 mutations were associated with a diploid karyotype (P < .001). FLT3 mutation (P < .001) was associated with progression to acute myeloid leukemia (AML), as were a higher bone marrow (BM) blast count (P < .001) and complex cytogenetics (P = .039). No patient with an NPM1 mutation alone had disease that progressed to AML. Cox proportional regression multivariate analysis indicated that FLT3 mutation, NPM1 mutation, complex cytogenetics, BM blast count, pancytopenia, and age were independent factors that correlated with progression-free survival. We conclude that FLT3 and NPM1 mutations are rare in MDS, but assessment of mutation status is potentially useful for predicting progression to AML.

Prognostic molecular markers in myelodysplastic syndromes

Cytogenetic findings in myelodysplastic syndromes play an important role in diagnosis, prognostication and clinical decision making. Therefore, they became an important aspect in scoring systems such as the International Prognostic Scoring System (IPSS) and the WHO-adapted Prognostic Scoring System (WPSS). Ongoing efforts to refine the categorization of karyotypes with regard to prognosis and therapeutic options will change scoring systems in the near future. In order to learn more about the pathophysiology of myelodysplastic syndromes, various molecular genetic aberrations are identified and their impact on prognosis discussed. New screening methods such as gene expression or single nucleotide polymorphism analysis are good candidates to find entrance in clinical practice in the future as they are useful tools in further elucidation of the underlying defects in myelodysplastic syndromes and the development of more specific classifications of the disease concerning risk assessment.

Comparison of I-FISH and G-banding for the detection of chromosomal abnormalities during the evolution of myelodysplastic syndrome

Myelodysplastic syndrome (MDS) patients with a normal karyotype constitute a heterogeneous group from a biological standpoint and their outcome is often unpredictable. Interphase fluorescence in situ hybridization (I-FISH) studies could increase the rate of detection of abnormalities, but previous reports in the literature have been contradictory. We performed I-FISH and conventional karyotyping (G-banding) on 50 MDS patients at diagnosis, after 6 and 12 months or at any time if a transformation to acute myeloid leukemia (AML) was detected. Applying a probe-panel targeting the centromere of chromosomes 7 and 8, 5q31, 5p15.2 and 7q31, we observed one case with 5q deletion not identified by G-banding. I-FISH at 6 and 12 months confirmed the karyotype results. Eight cases transformed to AML during follow-up, but no hidden clone was detected by I-FISH in any of them. The inclusion of I-FISH during follow-up of MDS resulted in a small improvement in abnormality detection when compared with conventional G-banding.

Suppression of farnesyltransferase activity in acute myeloid leukemia and myelodysplastic syndrome: current understanding and recommended use of tipifarnib

IMPORTANCE OF THE FIELD

Acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) incidence in the United States increases with age. Given the progressive ageing of the general population, incidence of these diseases is likely to continue to rise in the future. There is an acute need for therapeutic developments because of the poor prognosis of these diseases. Since the knowledge of molecular genetics in AML and MDS has expanded recently, targeted therapeutics should offer an exciting new frontier for advancement. Of all the targeted inhibitors developed, tipifarnib represents one of the few compounds with some activity as a single agent.

AREAS COVERED IN THIS REVIEW

Described in this review are the molecular targets of tipifarnib, safety and tolerability of the drug, chemistry, and clinical efficacy in AML.

WHAT THE READER WILL GAIN

The reader will gain a thorough understanding of tipifarnib as it relates to the current and future use of the drug in AML.

TAKE HOME MESSAGE

The future of tipifarnib, along with other molecularly-targeted drugs, lies in achieving a better understanding of leukemia biology and harnessing the activity of this agent using predictive biomarkers for improved patient selection.