FLT3-ITD Mutations In Acute Myeloid Leukemia Research Articles

GATM-Mediated Creatine Biosynthesis Enables Maintenance of FLT3-ITD-Mutant Acute Myeloid Leukemia.

FMS-like tyrosine kinase 3 (FLT3) is one of the most frequently mutated genes in acute myeloid leukemia (AML), with the most common mutation being internal tandem duplications (ITD). The presence of FLT3-ITD in AML carries a particularly poor prognosis and renders therapeutic resistance. New druggable targets are thus needed in this disease. In this study, we demonstrate the effects of de novo creatine biosynthesis upregulation by FLT3-ITD on AML sustainability. Our data show that FLT3-ITD constitutively activates the STAT5 signaling pathway, which upregulates the expression of glycine amidinotransferase (GATM), the first rate-limiting enzyme of de novo creatine biosynthesis. Pharmacologic FLT3-ITD inhibition reduces intracellular creatinine levels through transcriptional downregulation of genes in the de novo creatine biosynthesis pathway. The same reduction can be achieved by cyclocreatine or genetic GATM knockdown with shRNA and is reflected in significant decrease of cell proliferation and moderate increase of cell apoptosis in FLT3-ITD-mutant cell lines. Those effects are at least partially mediated through the AMPK/mTOR signaling pathway. This study uncovers a previously uncharacterized role of creatine metabolic pathway in the maintenance of FLT3-ITD-mutant AML and suggests that targeting this pathway may serve as a promising therapeutic strategy for FLT3-ITD-positive AML. IMPLICATIONS: FLT3-ITD mutation in AML upregulates de novo creatine biosynthesis that we show can be suppressed to diminish the proliferation and survival of blast cells.

Terminal deoxynucleotidyl transferase (TdT) expression is associated with FLT3-ITD mutations in Acute Myeloid Leukemia

The terminal deoxynucleotidyl transferase (TdT) is a DNA polymerase expressed in acute myeloid leukemias (AMLs), where it may be involved in the generation of NPM1 and FLT3-ITD mutations. We studied the correlations between TdT expression and FLT3-ITD or NPM1 mutations in primary AML samples, and the impact on patients’ survival. TdT expression was analyzed in 143 adult AML patients by flow cytometry as percentage of positivity and mean fluorescence intensity (MFI) on blasts. TdT was positive in 49 samples (34.2%), with a median of 48% TdT-positivity (range 7-98) and a median MFI of 2.70 (range 1.23-30.54). FLT3-ITD and NPM1 mutations were present in 24 (16.7%) and 34 (23.7%) cases, respectively. Median TdT expression on blasts was significantly higher in FLT3-ITD+, as compared with FLT3-ITD- AMLs (median 8% vs 0% respectively, p = 0.035). NPM1 mutational status, FLT3-ITD allelic ratio, karyotype, and ELN risk groups, did not correlate with TdT expression or MFI on blasts. TdT + patients had poorer survival as compared to TdT-, but this result was not confirmed by the multivariable analysis, where ELN risk stratification as well as age and type of treatment remained independent prognostic factors for OS. In summary, our results support the possible implication of TdT enzyme in the generation of FLT3-ITD mutations in AML.

Prevalence and Clinical Significance of FLT3 Mutation Status in Acute Myeloid Leukemia Patients: A Multicenter Study

FLT3-ITD mutations in acute myeloid leukemia (AML) are associated with a poor prognosis. In Latin America, little epidemiological data exist about these mutations and their influence on clinical evolution and prognosis. Standardization and well-established clinical correlation make FLT3 mutational analysis by molecular methods an invaluable tool to decide among treatment options and to determine AML prognosis. We assessed the prevalence of FLT3-ITD mutations in 138 patients with AML at four hematology referral centers from Mexico and Colombia. Molecular methods based on polymerase chain reaction (PCR) were employed for determining FLT3-ITD status. Mutations were present in 28 patients indicating a prevalence of 20.28%. Median age was 47years (5-96). The FLT3 mutation positive group was older, had higher WBC and hemoglobin values and lower platelet counts but without statistical significance. A not previously described mutation in the FLT3 gene was found in one patient involving a nucleotide exchange of timine for cytosine at the 66608 position. A high mortality was found in the FLT3-mutated group, 67.8 vs. 42.72% in the non-mutated group and median survival was 4.9months vs. 20.4months, p=0.009. A mutated FLT3 did not confer poor prognosis to those with M3 AML. The mutated FLT3 population had poor overall survival (OS) despite hematoprogenitor stem cell transplantation (HSCT). Prevalence of FLT3-ITD mutation in AML was present in a proportion comparable to other populations and, when present, was associated with a very poor prognosis.

Incidence, Characteristics, and Outcome of FLT3-ITD Mutations in AML Arising from an Antecedent Hematologic Disorder

Abstract 2522Internal tandem duplication (ITD) mutations in FLT3 (fms-like tyrosine kinase III) are common in acute myeloid leukemia (AML) and are associated with increased relapse risk and adverse outcome. A subset of AML, arising from an antecedent hematologic disorder (AHD) such as myelodysplastic syndrome (MDS), is also associated with an adverse outcome. We sought to review our experience and define the incidence, characteristics, and outcome of FLT3-ITD in AML arising from AHD. We reviewed all cases of newly diagnosed AML, excluding acute promyelocytic leukemia from 2001–2010 at our institution. FLT3-ITD mutational analysis was performed using PCR-based DNA sequencing on 1254 cases. Overall, 187 (15%) patients (pts) had FLT3-ITD mutations. Of the 1254 pts, 545 (43%) were classified as having an AHD and 709 (57%) were not. The incidence of FLT3-ITD in pts with and without AHD was 11% (125/709) and 18% (62/545), respectively (p=0.002). As a separate analysis, among pts who had received any prior chemotherapy or radiation, the incidence of FLT3-ITD was 8% (17/201) vs. 16% (170/1053) in those who had not (p=0.005). Baseline characteristics of the patients with FLT3-ITD positive AML with or without AHD are shown in table 1. The 187 pts with FLT3-ITD were treated with several different therapies as their initial treatment for AML. These included: high dose cytarabine-based (HiDAC) in 131 (70%), conventional dose cytarabine-based in 28 (15%), hypomethylating agents (HMA) in 12 (6%), and other in 16 (9%). The response rates to HiDAC and HMA in each of the two cohorts is shown in table 1. The median overall survival of patients with FLT3-ITD and AHD was 40 weeks vs. 54 weeks in those without AHD (p=0.046, Figure 1). In conclusion, FLT3-ITD is relatively less common in AML arising from AHD and in therapy-related AML compared to de novo AML. AML pts with FLT3-ITD and AHD tend to be older, have a lower bone marrow and peripheral blasts, a lower serum LDH, and significantly shorter overall survival. Compared to those without AHD, the response rate to HiDAC-based therapy in patients with FLT3-ITD and AHD are similar, but the response rates to HMA-based therapy are higher. The role of HMA in the treatment of FLT3-ITD patients with and without AHD should be investigated further. [Display omitted] [Display omitted] Disclosures:No relevant conflicts of interest to declare.

RGS2 is an important target gene of Flt3-ITD mutations in AML and functions in myeloid differentiation and leukemic transformation

AbstractActivating fetal liver tyrosine kinase 3 (Flt3) mutations represent the most common genetic aberrations in acute myeloid leukemia (AML). Most commonly, they occur as internal tandem duplications in the juxtamembrane domain (Flt3-ITD) that transform myeloid cells in vitro and in vivo and that induce aberrant signaling and biologic functions. We identified RGS2, a regulator of G-protein signaling, as a gene specifically repressed by Flt3-ITD. Here we demonstrate an important role of RGS2 in Flt3-ITD–mediated transformation. RGS2 was repressed after forced expression of activating Flt3 mutations in 2 myeloid cell lines (32Dcl3 and NB4). Furthermore, RGS2 was repressed in Flt3-mutation–positive AML cases in comparison to Flt3-mutation–negative cases, especially in Flt3-ITD–positive cases with a high ITD-to–wild-type (WT) ratio. Coexpression of RGS2 with Flt3-ITD inhibited Flt3-ITD–induced autonomous proliferation and clonal growth of 32D cells. RGS2 also inhibited Flt3-ITD–induced phosphorylation of Akt and glycogen synthase kinase β (Gsk3-β) without influencing signal transducer and activator of transcription 5 (STAT5) activation. In addition, RGS2 reinduced the expression of Flt3-ITD–repressed CCAAT/enhancer-binding protein α (c/EBPα) and antagonized the Flt3-ITD–induced differentiation block in 32D cells. Expression analyses in myeloid cell lines revealed induction of RGS2 during granulocytic but not during monocytic differentiation. Taken together, RGS2 is a novel mediator of myeloid differentiation, and its repression is an important event in Flt3-ITD–induced transformation.