N822 mutation of KIT gene was frequent in pediatric acute myeloid leukemia patients with t(8;21) in Japan: a study of the Japanese childhood AML cooperative study group

New C3H KitN824K/WT cancer mouse model develops late-onset malignant mammary tumors with high penetrance

Gastro-intestinal stromal tumors and acute myeloid leukemia induced by activating stem cell factor receptor tyrosine kinase (KIT) mutations are highly malignant. Less clear is the role of KIT mutations in the context of breast cancer. Treatment success of KIT-induced cancers is still unsatisfactory because of primary or secondary resistance to therapy. Mouse models offer essential platforms for studies on molecular disease mechanisms in basic cancer research. In the course of the Munich N-ethyl-N-nitrosourea (ENU) mutagenesis program a mouse line with inherited polycythemia was established. It carries a base-pair exchange in the Kit gene leading to an amino acid exchange at position 824 in the activation loop of KIT. This KIT variant corresponds to the N822K mutation found in human cancers, which is associated with imatinib-resistance. C3H Kit^N824K/WT mice develop hyperplasia of interstitial cells of Cajal and retention of ingesta in the cecum. In contrast to previous Kit-mutant models, we observe a benign course of gastrointestinal pathology associated with prolonged survival. Female mutants develop mammary carcinomas at late onset and subsequent lung metastasis. The disease model complements existing oncology research platforms. It allows for addressing the role of KIT mutations in breast cancer and identifying genetic and environmental modifiers of disease progression.

Prospective evaluation of prognostic impact of KIT mutations on acute myeloid leukemia with RUNX1-RUNX1T1 and CBFB-MYH11

The prognostic impact of KIT mutation on core-binding factor acute myeloid leukemia (CBF-AML) remains controversial. We registered 199 newly diagnosed de novo CBF-AML patients, aged 16 to 64 years, who achieved complete remission. They received 3 courses of high-dose cytarabine therapy and no further treatment until hematological relapse. Mutations in exons 8, 10-11, and 17 of the KIT gene were analyzed. Furthermore, we analyzed mutations in 56 genes that are frequently identified in myeloid malignancies and evaluated minimal residual disease (MRD). The primary end point was relapse-free survival (RFS) according to KIT mutations. The RFS in KIT-mutated patients was inferior to that in unmutated patients (hazard ratio, 1.92; 95% confidence interval, 1.23-3.00; P = .003). Based on subgroup analysis, KIT mutations had a prognostic impact in patients with RUNX1-RUNX1T1, but not in those with CBFB-MYH11, and only exon 17 mutation had a significant prognostic impact. Multivariate Cox regression analysis with stepwise selection revealed that the KIT exon 17 mutation and the presence of extramedullary tumors in patients with RUNX1-RUNX1T1, and loss of chromosome X or Y and NRAS mutation in patients with CBFB-MYH11 were poor prognostic factors for RFS. MRD was evaluated in 112 patients, and it was associated with a poorer RFS in the patients with CBFB-MYH11, but not in those with RUNX1-RUNX1T1. These results suggested that it is necessary to separately evaluate AML with RUNX1-RUNX1T1 or CBFB-MYH11 according to appropriate prognostic factors. This study was registered at www.umin.ac.jp/ctr/ as #UMIN000003434.

Core binding factor acute myeloid leukemia: Advances in the heterogeneity of KIT, FLT3, and RAS mutations (Review)

Core binding factor (CBF) is a heterodimer protein complex involved in the transcriptional regulation of normal hematopoietic process. In addition, CBF molecular aberrations represent approximately 20% of all adult Acute Myeloid Leukemia (AML) patients. Treated with standard therapy, adult CBF AML has higher complete remission (CR) rate, longer CR duration, and better prognosis than that of AML patients with normal karyotype or other chromosomal aberrations. Although the prognosis of CBF AML is better than other subtypes of adult AML, it is still a group of heterogeneous diseases, and the prognosis is often different. Recurrence and relapse-related death are the main challenges to be faced following treatment. Mounting research shows the gene heterogeneity of CBF AML. Therefore, to achieve an improved clinical outcome, the differences in clinical and genotypic characteristics should be taken into account in the evaluation and management of such patients, so as to further improve the risk stratification of prognosis and develop targeted therapy. The present article is a comprehensive review of the differences in some common mutant genes between two subtypes of CBF AML.

Gata2 deficiency delays leukemogenesis while contributing to aggressive leukemia phenotype in Cbfb-MYH11 knockin mice

Inversion of chromosome 16 (inv(16)) generates a fusion gene CBFB-MYH11, which is a driver mutation for acute myeloid leukemia (AML). Gene expression profiling suggests that Gata2, a hematopoietic transcription factor, is a top upregulated gene in preleukemic Cbfb-MYH11 knockin mice and is expressed in human inv(16) AML. On the other hand, we have also identified recurrent monoallelic deletions of GATA2 in relapsed human CBF-AML patients. To clarify the role of Gata2 in leukemogenesis by Cbfb-MYH11, we generated conditional Cbfb-MYH11 knockin mice with Gata2 heterozygous knockout. Gata2 heterozygous knockout reduced abnormal myeloid progenitors, which are capable of inducing leukemia in the Cbfb-MYH11 mice. Consequently, Cbfb-MYH11 mice with Gata2 heterozygous knockout developed leukemia with longer latencies than those with intact Gata2. Interestingly, leukemic cells with Gata2 heterozygous knockout gained higher number of mutations and showed more aggressive phenotype in both primary and transplanted mice. Moreover, leukemic cells with Gata2 heterozygous knockout showed higher repopulating capacity in competitive transplantation experiments. In summary, reduction of Gata2 activity affects mutational dynamics of leukemia with delayed leukemia onset in Cbfb-MYH11 knockin mice, but paradoxically results in a more aggressive leukemia phenotype, which may be correlated with leukemia relapse or poor prognosis in human patients.

Long-term Remission of Acute Myeloid Leukemia Developed From Systemic Mastocytosis by Conventional Chemotherapy

Systemic mastocytosis (SM) is a disorder characterized by abnormal proliferation of mast cells with KIT mutations, especially in codon 816. The prognosis of patients developing acute myeloid leukemia (AML) from SM is extremely poor, and hematopoietic cell transplantation is recommended. Herein, we describe a case of an 8-year-old female diagnosed with SM developing AML. A KIT M541L variant in SM was identified in leukemic cells, normal hematopoietic cells, and buccal mucosal cells, suggesting a germline polymorphism. The patient has remained in complete remission for 39 months after completion of chemotherapy. SM developing AML without a KIT D816 mutation may be not necessarily associated with a poor prognosis.

Prevalence and prognostic significance of c-KIT mutations in core binding factor acute myeloid leukemia: a comprehensive large-scale study from a single Chinese center

To clarify the prevalence and prognostic significance of c-KIT mutations in patients with core binding factor acute myeloid leukemia (CBF-AML), a total of 351 patients who were categorized as pediatric t(8;21), adult t(8;21), pediatric inv(16), or adult inv(16) were screened at diagnosis for c-KIT mutations in exons 17 and 8 using direct sequencing. A total of 250 patients underwent follow-up. Overall, 36.5% of the patients had a c-KIT mutation. Adult t(8;21) and inv(16) patients had mutations predominantly in exons 17 and 8, respectively. Higher White blood cell (WBC) count, WBC index, and AML1-ETO transcript levels in adult t(8;21) patients were significantly associated with c-KIT mutations and mutations in exon 17 (P≤0.030). c-KIT mutations in adult t(8;21) patients were significantly correlated with a high cumulative incidence of relapse (CIR, P=0.0070) at 2 years and a low 2-year disease-free survival (DFS, P=0.013) and overall survival (OS, P=0.0055). However, no significant difference was revealed in the effect of c-KIT mutations on outcome of adult inv(16) and pediatric t(8;21) patients (all P>0.05). Multivariate analysis revealed that c-KIT mutation is an independent prognostic factor for relapse, DFS, and OS (P≤0.016) in adult t(8;21) AML patients. Therefore, with regard to c-KIT mutation, CBF-AML is a heterogeneous disease. c-KIT mutations have a strong adverse effect on the relapse and survival of adult t(8;21) AML patients.

NPM1, FLT3, and c-KIT mutations in pediatric acute myeloid leukemia in Russian population

We evaluated frequencies of NPM1, FLT3, c-KIT mutations in childhood acute myeloid leukemia (AML) in Russia and assessed prognostic relevance of the mutations. RNA and DNA were extracted from bone marrow samples of 186 (106 male and 80 female) pediatric patients younger than 17 year with de novo AML. Mutations and chromosomal rearrangements were detected by sequencing of a corresponding gene. NPM1 mutations were found in 5.2%, FLT3 mutations in 12.1%, c-KIT mutations in 3.7% of the patients. NPM1 mutations were associated with the absence of chromosomal aberrations (P=0.007) and FLT3/ITD (P=0.018). New data on incidence of c-KIT mutations in various AML subtypes as well as new variations of c-KIT mutations in the exon 8 are presented. The results are compared to previously published studies on NPM1, FLT3, c-KIT mutations in various populations. No statistically significant differences in survival rates between groups with or without of FLT3, NPM1, c-KIT mutations were found (P>0.05). Meanwhile, 4-year overall survival rates were higher in patients having NPM1 mutations comparing with NPM1/WT patients (100% vs. 50%) and in patients having FLT3 mutations comparing with FLT3/WT patients (70% vs. 50%). The data presented contribute to knowledge on incidence and prognostic significance of the mutations in pediatric AML.

Core-binding factor acute myeloid leukemia: can we improve on HiDAC consolidation?

Acute myeloid leukemia (AML) with t(8;21) or inv(16) is commonly referred to as core-binding factor AML (CBF-AML). The incorporation of high-dose cytarabine for postremission therapy has substantially improved the outcome of CBF-AML patients, especially when administered in the setting of repetitive cycles. For many years, high-dose cytarabine was the standard treatment in CBF-AML resulting in favorable long-term outcome in approximately half of the patients. Therefore, CBF-AML patients are generally considered to be a favorable AML group. However, a substantial proportion of patients cannot be cured by the current treatment. Additional genetic alterations discovered in CBF-AML help in our understanding of the process of leukemogenesis and some of them may refine the risk assessment in CBF-AML and, importantly, also serve as targets for novel therapeutic approaches. We discuss the clinical and genetic heterogeneity of CBF-AML, with a particular focus on the role of KIT mutations as a prognosticator, and also discuss recent efforts to target the KIT kinase in the context of existing therapeutic regimens.

Systemic mastocytosis associated with t(8;21) acute myeloid leukemia in a child: detection of the D816A mutation of KIT

Systemic mastocytosis (SM) associated with t(8;21) acute myeloid leukemia (AML) is very rare, and the D816 mutation of the KIT gene has previously been detected only in adult patients. We herein report the case of a 5-year-old female presenting with AML harboring t(8;21)(q22;q22). Her AML was refractory to chemotherapy, and bone marrow mastocytosis developed simultaneously at the initial diagnosis and during chemotherapy. The D816A mutation of KIT was detected. SM associated with t(8;21) AML, accompanied by a KIT mutation in children may result in a poor prognosis, despite the fact that t(8;21) AML are generally considered to have a favorable risk.

Integrative analysis of prognostic factors in Chinese core binding factor leukemia

The characteristics of core binding factor (CBF) leukemia appear to differ between Chinese and Caucasian patients. In this study, we analyzed the biological and clinical characteristics of 76 Chinese CBF leukemia patients out of 425 newly diagnosed acute myeloid leukemia (AML) patients. The frequency of CBF AML was 17.9%. Patients harboring t(8;21) were predominant in CBF AML. The incidence of c-kit mutation in CBF AML was 28.9%. The N822K mutation appeared to be more prevalent in Chinese CBF AML patients. Multivariate analysis showed that c-kit mutation and high white blood cell count could negatively impact overall survival (OS) (HR=2.74 and 6.24, P=0.007 and 0.022, respectively) but did not affect relapse-free survival (RFS). Kaplan-Meier analysis showed a significant difference in both OS and RFS between wild-type and mutated c-kit patients. Although we had included recently reported prognostic indicators in our analysis, our results demonstrated that only c-kit mutation and high white blood cell count had prognostic impact on Chinese CBF AML patients.

Diagnosis and management of acute myeloid leukemia in children and adolescents: recommendations from an international expert panel

Despite major improvements in outcome over the past decades, acute myeloid leukemia (AML) remains a life-threatening malignancy in children, with current survival rates of ∼70%. State-of-the-art recommendations in adult AML have recently been published in this journal by Döhner et al. The primary goal of an international expert panel of the International BFM Study Group AML Committee was to set standards for the management, diagnosis, response assessment, and treatment in childhood AML. This paper aims to discuss differences between childhood and adult AML, and to highlight recommendations that are specific to children. The particular relevance of new diagnostic and prognostic molecular markers in pediatric AML is presented. The general management of pediatric AML, the management of specific pediatric AML cohorts (such as infants) or subtypes of the disease occurring in children (such as Down syndrome related AML), as well as new therapeutic approaches, and the role of supportive care are discussed.

Prevalence and prognostic significance of KIT mutations in pediatric patients with core binding factor AML enrolled on serial pediatric cooperative trials for de novo AML

KIT receptor tyrosine kinase mutations are implicated as a prognostic factor in adults with core binding factor (CBF) acute myeloid leukemia (AML). However, their prevalence and prognostic significance in pediatric CBF AML is not well established. We performed KIT mutational analysis (exon 8 and exon 17) on diagnostic specimens from 203 pediatric patients with CBF AML enrolled on 4 pediatric AML protocols. KIT mutations were detected in 38 (19%) of 203 (95% CI, 14%-25%) patient samples of which 20 (52.5%) of 38 (95% CI, 36%-69%) involved exon 8, 17 (45%) of 38 (95% CI, 29%-62%) involved exon 17, and 1 (2.5%; 95% CI, 0%-14%) involved both locations. Patients with KIT mutations had a 5-year event-free survival of 55% (+/- 17%) compared with 59% (+/- 9%) for patients with wild-type KIT (P = .86). Rates of complete remission, overall survival, disease-free survival, or relapse were not significantly different for patients with or without KIT mutations. Location of the KIT mutation and analysis by cytogenetic subtype [t(8;21) vs inv(16)] also lacked prognostic significance. Our study shows that KIT mutations lack prognostic significance in a large series of pediatric patients with CBF AML. This finding, which differs from adult series and a previously published pediatric study, may reflect variations in therapeutic approaches and/or biologic heterogeneity within CBF AML. Two of 4 studies included in this analysis are registered at http://clinicaltrials.gov as NCT00002798 (CCG-2961) and NCT00070174 (COG AAML03P1).

RAS, FLT3, and C-KIT mutations in immunophenotyped canine leukemias

OBJECTIVE

To determine the frequency of FLT3, C-KIT, and RAS mutations in canine leukemia patients.

MATERIALS AND METHODS

Ethylenediamine tetra-acetic acid blood samples were recruited from dogs with suspected leukemia, categorized by quantitative and cytological evaluation and immunophenotyping. Flow cytometry was carried out using antibodies against CD3; CD3e; CD4; CD5; CD8; CD11a, b, c, and d; CD14; CD21; CD34; CD45 and 45RA; CD79a; CD90 (THY-1); major histocompatibility complex II; myeloperoxidase; MAC387; and neutrophil-specific antibody. Genomic DNA was extracted from whole blood and analyzed for mutations in N, H, and K-RAS, FLT3, and C-KIT genes by polymerase chain reaction and sequencing.

RESULTS

Fifty-seven (77.0%) of 74 samples submitted from dogs with suspected leukemia had cytologically and immunophenotypically confirmed leukemia. There were 36 (63.2%) acute leukemias, 16 (28.1%) chronic, 3 (5.3%) prolymphocytic, 1 natural killer cell, and 1 chronic leukemia undergoing blast transformation. N-RAS mis-sense mutations were identified in 14 (25%) dogs with acute myeloid (AML) or lymphoid (ALL) leukemia, and also in one dog in the leukemic phase of lymphoma. Mutations in K-RAS were found in two dogs with AML. There were no H-RAS mutations. FLT3 internal tandem duplications were identified in three dogs with ALL, and a mis-sense mutation was found in one dog with ALL. C-KIT mutations were identified in three dogs with AML. Sixty-one percent of dogs with acute leukemia harbored mutations in N/K-RAS, FLT3, or C-KIT.

CONCLUSION

RAS, FLT3, and C-KIT mutations, analogous to those found in human leukemia, occur commonly in acute canine leukemia.

Comparison of antitumor effects of multitargeted tyrosine kinase inhibitors in acute myelogenous leukemia

We compared the antitumor activities of the multitargeted tyrosine kinase inhibitors imatinib, sorafenib, and sunitinib to determine which inhibitor is best suited to be used for the treatment of acute myelogenous leukemia (AML). In nine human AML cell lines, sorafenib and sunitinib were more potent inhibitors of cellular proliferation than imatinib (IC50, 0.27 to >40, 0.002-9.1, and 0.007-13 micromol/L for imatinib, sorafenib, and sunitinib, respectively). Sorafenib and sunitinib were potent inhibitors of cells with fms-like tyrosine kinase 3 internal tandem duplication (IC50, 2 and 7 nmol/L) and c-KIT N822K mutations (IC50, 23 and 40 nmol/L). In four cell lines (MV4-11, Kasumi-1, KG-1, and U937) that spanned a range of drug sensitivities, sorafenib and sunitinib had similar activity in apoptosis and cell cycle assays, except that sunitinib did not promote apoptosis in U937 cells. Both drugs inhibited mitogen-activated protein kinase signaling but had no effect on AKT signaling in most of the cell lines tested. Sorafenib was substantially more bound than sunitinib in human plasma (unbound fraction, 0.59% versus 8.4%) and cell culture medium (unbound fraction, 1.3% versus 39%), indicating that sorafenib was more potent than sunitinib and that unbound sorafenib concentrations with activity against most AML cell lines are achievable in vivo. There was more intracellular accumulation of sorafenib than of sunitinib and imatinib in AML cells. Between 1 and 10 micromol/L, sorafenib inhibited the proliferation of six of nine primary AML blast samples by > or =50%. Our results highlight the pharmacologic features of sorafenib that may provide it an advantage in the treatment of AML.