Outcome of patients with FLT3-mutated acute myeloid leukemia in first relapse

Quizartinib, an FLT3 inhibitor, as monotherapy in patients with relapsed or refractory acute myeloid leukaemia: an open-label, multicentre, single-arm, phase 2 trial

BACKGROUND

Old age and FMS-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) mutations in patients with acute myeloid leukaemia are associated with early relapse and poor survival. Quizartinib is an oral, highly potent, and selective next-generation FLT3 inhibitor with clinical antileukaemic activity in relapsed or refractory acute myeloid leukaemia. We aimed to assess the efficacy and safety of single-agent quizartinib in patients with relapsed or refractory acute myeloid leukaemia.

METHODS

We did an open-label, multicentre, single-arm, phase 2 trial at 76 hospitals and cancer centres in the USA, Europe, and Canada. We enrolled patients with morphologically documented primary acute myeloid leukaemia or acute myeloid leukaemia secondary to myelodysplastic syndromes and an Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 into two predefined, independent cohorts: patients who were aged 60 years or older with relapsed or refractory acute myeloid leukaemia within 1 year after first-line therapy (cohort 1), and those who were 18 years or older with relapsed or refractory disease following salvage chemotherapy or haemopoietic stem cell transplantation (cohort 2). Patients with an FLT3-ITD allelic frequency of more than 10% were considered as FLT3-ITD positive, whereas all other patients were considered as FLT3-ITD negative. Patients received quizartinib once daily as an oral solution; the initial 17 patients received 200 mg per day but the QTcF interval was prolonged for more than 60 ms above baseline in some of these patients. Subsequently, doses were amended for all patients to 135 mg per day for men and 90 mg per day for women. The co-primary endpoints were the proportion of patients who achieved a composite complete remission (defined as complete remission + complete remission with incomplete platelet recovery + complete remission with incomplete haematological recovery) and the proportion of patients who achieved a complete remission. Efficacy and safety analyses included all patients who received at least one dose of quizartinib (ie, the intention-to-treat population). Patients with a locally assessed post-treatment bone marrow aspirate or biopsy were included in efficacy analyses by response; all other patients were considered to have an unknown response. This study is registered with ClinicalTrials.gov, number NCT00989261, and with the European Clinical Trials Database, EudraCT 2009-013093-41, and is completed.

FINDINGS

Between Nov 19, 2009, and Oct 31, 2011, a total of 333 patients were enrolled (157 in cohort 1 and 176 in cohort 2). In cohort 1, 63 (56%) of 112 FLT3-ITD-positive patients and 16 (36%) of 44 FLT3-ITD-negative patients achieved composite complete remission, with three (3%) FLT3-ITD-positive patients and two (5%) FLT3-ITD-negative patients achieving complete remission. In cohort 2, 62 (46%) of 136 FLT3-ITD-positive patients achieved composite complete remission with five (4%) achieving complete remission, whereas 12 (30%) of 40 FLT3-ITD-negative patients achieved composite complete remission with one (3%) achieving complete remission. Across both cohorts (ie, the intention-to-treat population of 333 patients), grade 3 or worse treatment-related treatment-emergent adverse events in 5% or more of patients were febrile neutropenia (76 [23%] of 333), anaemia (75 [23%]), thrombocytopenia (39 [12%]), QT interval corrected using Fridericia's formula (QTcF) prolongation (33 [10%]), neutropenia (31 [9%]), leucopenia (22 [7%]), decreased platelet count (20 [6%]), and pneumonia (17 [5%]). Serious adverse events occurring in 5% or more of patients were febrile neutropenia (126 [38%] of 333; 76 treatment related), acute myeloid leukaemia progression (73 [22%]), pneumonia (40 [12%]; 14 treatment related), QTcF prolongation (33 [10%]; 32 treatment related), sepsis (25 [8%]; eight treatment related), and pyrexia (18 [5%]; nine treatment related). Notable serious adverse events occurring in less than 5% of patients were torsades de pointes (one [<1%]) and hepatic failure (two [1%]). In total, 125 (38%) of 333 patients died within the study treatment period, including the 30-day follow-up. 18 (5%) patients died because of an adverse event considered by the investigator to be treatment related (ten [6%] of 157 patients in cohort 1 and eight [5%] of 176 in cohort 2.

INTERPRETATION

Single-agent quizartinib was shown to be highly active and generally well tolerated in patients with relapsed or refractory acute myeloid leukaemia, particularly those with FLT3-ITD mutations. These findings confirm that targeting the FLT3-ITD driver mutation with a highly potent and selective FLT3 inhibitor is a promising clinical strategy to help improve clinical outcomes in patients with very few options. Phase 3 studies (NCT02039726; NCT02668653) will examine quizartinib at lower starting doses.

FUNDING

Ambit Biosciences/Daiichi Sankyo.

NT1721, a novel epidithiodiketopiperazine, exhibits potent in vitro and in vivo efficacy against acute myeloid leukemia

Acute myeloid leukemia (AML) is an aggressive malignancy characterized by heterogeneous genetic and epigenetic changes in hematopoietic progenitors that lead to abnormal self-renewal and proliferation. Despite high initial remission rates, prognosis remains poor for most AML patients, especially for those harboring internal tandem duplication (ITD) mutations in the fms-related tyrosine kinase-3 (FLT3). Here, we report that a novel epidithiodiketopiperazine, NT1721, potently decreased the cell viability of FLT3-ITD+ AML cell lines, displaying IC50 values in the low nanomolar range, while leaving normal CD34+ bone marrow cells largely unaffected. The IC50 values for NT1721 were significantly lower than those for clinically used AML drugs (i.e. cytarabine, sorafenib) in all tested AML cell lines regardless of their FLT3 mutation status. Moreover, combinations of NT1721 with sorafenib or cytarabine showed better antileukemic effects than the single agents in vitro. Combining cytarabine with NT1721 also attenuated the cytarabine-induced FLT3 ligand surge that has been linked to resistance to tyrosine kinase inhibitors. Mechanistically, NT1721 depleted DNA methyltransferase 1 (DNMT1) protein levels, leading to the re-expression of silenced tumor suppressor genes and apoptosis induction. NT1721 concomitantly decreased the expression of EZH2 and BMI1, two genes that are associated with the maintenance of leukemic stem/progenitor cells. In a systemic FLT3-ITD+ AML mouse model, treatment with NT1721 reduced tumor burdens by > 95% compared to the control and significantly increased survival times. Taken together, our results suggest that NT1721 may represent a promising novel agent for the treatment of AML.

Results of a phase 1 study of quizartinib as maintenance therapy in subjects with acute myeloid leukemia in remission following allogeneic hematopoietic stem cell transplant

FLT3-ITD-mutated acute myeloid leukemia (AML) has very high risk of relapse and is associated with poor outcome following allogeneic hematopoietic-cell transplant (allo-HCT). This two-part, phase 1, multicenter, open-label, sequential-group, dose-escalation study aimed to determine dose-limiting toxicities (DLTs), maximum tolerated dose (MTD), and safety/tolerability of quizartinib, a selective and highly potent FLT3 inhibitor, when administered as maintenance therapy after allo-HCT. Thirteen subjects with documented FLT3-ITD-mutated AML in morphological remission following allo-HCT received one of two quizartinib dihydrochloride dose levels (DL): 40 mg/d (DL1; n = 7) and 60 mg/d (DL2; n = 6), administered orally in 28-day cycles for up to 24 cycles. Median age of participants was 43 years. All subjects received human leukocyte antigen (HLA)-matched allo-HCT. One subject treated at DL1 and 1 treated at DL2 had DLTs that required drug interruption (grade 3 gastric hemorrhage and grade 3 anemia, respectively). Ten subjects (77%) received quizartinib for >1 year; 5 (38%) completed 24 cycles. Four subjects (31%) discontinued quizartinib due to adverse events. One subject (8%) experienced relapse during cycle 1 and discontinued treatment. Most common grade 3/4 adverse events were neutropenia (23%), anemia (15%), leukopenia (15%), lymphopenia (15%), and thrombocytopenia (15%). This study demonstrated acceptable tolerability and early evidence of reduced relapse rate following allo-HCT with quizartinib maintenance compared to historical cohorts. No MTD was identified, but 60 mg daily was selected as highest dose for continuous daily administration based on randomized comparison of daily 30 and 60 mg doses in relapsed/refractory AML.

The combination effect of homoharringtonine and ibrutinib on FLT3-ITD mutant acute myeloid leukemia

Acute myeloid leukemia (AML) is a highly heterogeneous disease and internal tandem duplication mutation in FMS-like tyrosine-kinase-3 (FLT3-ITD) has a negative impact on outcome. Finding effective treatment regimens is desperately needed. In this study, we explored the inhibitory effect and mechanism of homoharringtonine (HHT) in combination with ibrutinib on FLT3-ITD mutant AML cells. Consequently, we observed a synergistic inhibitory effect when ibrutinib was combined with HHT to inhibit cell proliferation, induce apoptosis and arrest cell cycle at G0/G1 phase in MV4-11 and MOLM-13 leukemia cells. Our results indicate that the mechanisms of the combination effect are mainly via regulating the STAT5/Pim-2/C-Myc pathway, AKT pathway and Bcl-2 family, activating p21WAF1/CIP1 and inhibiting CCND/CDK complex protein. Interestingly, synergistic cytotoxicity of ibrutinib and HHT was dependent on both FLT3 and BTK. Here we provide a novel effective therapeutic approach for the treatment of AML patients with FLT3-ITD mutation.

'Did He Who Made the Lamb Make Thee?' New Developments in Treating the 'Fearful Symmetry' of Acute Myeloid Leukemia

Malignant cells must circumvent endogenous cell death pathways to survive and develop into cancers. Acquired cell death resistance also sets up malignant cells to survive anticancer therapies. Acute Myeloid Leukemia (AML) is an aggressive blood cancer characterized by high relapse rate and resistance to cytotoxic therapies. Recent collaborative profiling projects have led to a greater understanding of the 'fearful symmetry' of the genomic landscape of AML, and point to the development of novel potential therapies that can overcome factors linked to chemoresistance. We review here the most recent research in the genetics of AML and how these discoveries have led, or might lead, to therapies that specifically activate cell death pathways to substantially challenge this 'fearful' disease.

Mutations in AML: prognostic and therapeutic implications

Acute myeloid leukemia (AML) is a heterogeneous hematologic malignancy characterized by the proliferation and aberrant differentiation of immature clonal myeloid cells. The prognosis of AML is variable, based on clinical features such as patient age, performance status, and comorbidities, as well as leukemia-specific genetic features including cytogenetics and molecular classification. The modern application of next-generation sequencing technology has uncovered marked heterogeneity and genomic complexity within AML, based on the presence or absence of cooperating mutations within functional categories such as epigenetic regulators, cell signaling and proliferation pathways, and master hematopoietic transcription factors. Although the treatment of AML has hitherto changed little in the past 40 years, the enhanced scientific understanding of AML pathophysiology and leukemogenesis has led to the recent development of multiple targeted and selective treatment approaches, and our increasing awareness of functional AML subsets will be evermore used to inform rational and personalized treatment strategies.

How I treat FLT3-mutated AML

FLT3-mutated acute myeloid leukemia (AML), despite not being recognized as a distinct entity in the World Health Organization (WHO) classification system, is readily recognized as a particular challenge by clinical specialists who treat acute leukemia. This is especially true with regards to the patients harboring the most common type of FLT3 mutation, the internal tandem duplication (FLT3-ITD) mutation. Here we present 4 patient cases from our institution and discuss how our management reflects what we have learned about this subtype of the disease. We also reflect on how we anticipate the management might change in the near future, with the emergence of clinically useful tyrosine kinase inhibitors.

Inhibition of FLT3 in AML: a focus on sorafenib

FMS-like tyrosine kinase 3 (FLT3) is one of the most commonly mutated genes in AML. FLT3 is mutated in ~30% of patients with AML, either by internal tandem duplications (FLT3-ITD) of the juxta-membrane domain or by a point mutation, usually involving the tyrosine kinase domain. Several FLT3 tyrosine kinase inhibitors are being evaluated in multiple studies aiming at improving outcomes. The most widely used is sorafenib, a potent multikinase inhibitor approved for hepatocellular carcinoma and renal cell carcinoma. Sorafenib monotherapy or in combination with conventional chemotherapy, has been evaluated in various settings in AML, including front-line, relapsed or refractory disease including post-allograft failures and, more recently, as post-transplant maintenance therapy. Encouraging data have emerged with several other agents like lestaurtinib, midostaurin, crenolanib, gilteritinib and quizartinib. Although transient responses to FLT3 inhibitors are often observed in case of disease relapse, the most promising approach is the use of FLT3 inhibitors either in combination with induction chemotherapy or as consolidation/maintenance therapy after allogeneic hematopoietic cell transplantation. In this review, we summarize the clinical data on sorafenib and other FLT3 inhibitors in AML.

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

BACKGROUND AND AIMS

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.

METHODS

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.

RESULTS

Mutations were present in 28 patients indicating a prevalence of 20.28%. Median age was 47 years (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 4.9 months vs. 20.4 months, 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).

CONCLUSION

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.

FLT3 Inhibitors for Treating Acute Myeloid Leukemia

FLT3 (Fms-like tyrosine kinase 3) inhibitors are tyrosine kinase inhibitors. The first-generation FLT3 inhibitors were developed several years ago and include midostaurin, lestaurtinib, sunitinib, and sorafenib. They are relatively nonspecific for FLT3, with other potential targets that include platelet-derived growth factor receptor, vascular endothelial growth factor receptor, KIT, and Janus kinase 2. The second-generation inhibitors, including quizartinib, crenolanib, PLX3397, and ASP2215, are more potent and selective than the first-generation inhibitors. The greater potency and selectivity promises greater efficacy in FLT3-mutated acute myelogenous leukemia (AML) (particularly in patients with a greater allele burden) and less toxicity. A number of receptor tyrosine kinase inhibitors are being studied across virtually all disease settings, including frontline, relapsed and refractory, and maintenance, mainly in patients with FLT3-mutated AML. The future of FLT3 inhibitors in the treatment of AML, in combination with chemotherapy or stem cell transplant, appears bright. The present report reviews the current data on FLT3 inhibitors.

Does FLT3 mutation impact survival after hematopoietic stem cell transplantation for acute myeloid leukemia? A Center for International Blood and Marrow Transplant Research (CIBMTR) analysis

BACKGROUND

Patients with FMS like tyrosine kinase 3 (FLT3)-mutated acute myeloid leukemia (AML) have a poor prognosis and are referred for early allogeneic hematopoietic stem cell transplantation (HCT).

METHODS

Data from the Center for International Blood and Marrow Transplant Research (CIBMTR) were used to evaluate 511 adult patients with de novo AML who underwent HCT during 2008 through 2011 to determine whether FLT3 mutations had an impact on HCT outcomes.

RESULTS

In total, 158 patients (31%) had FLT3 mutations. Univariate and multivariate analyses revealed an increased risk of relapse at 3 years in the FLT3 mutated group compared with the wild-type (WT) group (38% [95% confidence interval (CI), 30%-45%] vs 28% [95% CI, 24%-33%]; P = .04; relative risk, 1.60 [95% CI, 1.15-2.22]; P = .0048). However, FLT3 mutation status was not significantly associated with nonrelapse mortality, leukemia-free survival, or overall survival. Although more patients in the FLT3 mutated group died from relapsed primary disease compared with those in the WT group (60% vs 46%), the 3-year overall survival rate was comparable for the 2 groups (mutated group: 49%; 95% CI, 40%-57%; WT group: 55%, 95% CI, 50%-60%; P = .20).

CONCLUSIONS

The current data indicate that FLT3 mutation status did not adversely impact overall survival after HCT, and about 50% of patients with this mutation who underwent HCT were long-term survivors. Cancer 2016;122:3005-3014. © 2016 American Cancer Society.

Relapsed Acute Myeloid Leukemia: Need for Innovative Treatment Strategies to Improve Outcome

Relapse continues to be a major hurdle in achieving cure in patients with acute myeloid leukemia (AML). The outcome after relapse is not uniform in all patients with AML and is dependent on several prognostic variables, including age, cytogenetics at initial diagnosis, duration of first complete remission, whether an allogeneic stem cell transplant was performed during first complete remission, and the presence of a number of molecular aberrations. Despite extensive research over the past several decades, there is no standard of care for treating patients with relapsed AML. This is possibly due to the accrual of patients with widely different disease profiles in most trials for relapsed AML. With increasing insights into the disease biology based on identification of pathogenic and aberrant molecular and cellular pathways, novel therapeutic strategies are emerging. Hopefully in the near future, we can improve the outcome of patients with relapsed AML with treatment strategies based on identification of specific targets and methods to overcome these aberrant processes.

Considerations and challenges for patients with refractory and relapsed acute myeloid leukaemia

Despite advances in understanding the complexities of acute myeloid leukaemia (AML), the treatment of refractory or relapsed AML (rrAML) remains a daunting clinical challenge. Numerous clinical trials have failed to identify new treatments or combinations of existing therapies that substantially improve outcomes and survival. This may be due, at least in part, to heterogeneity among study patients with respect to multiple inter-related factors that have been shown to affect treatment outcomes for patients with rrAML; such factors include age, cytogenetics, immunophenotypic changes, and (in the case of relapsed AML) duration of first complete remission, or if the patient has had a previous blood and marrow transplant (BMT). A clear understanding of disease characteristics and patient-related factors that influence treatment response, as well as expected outcomes with existing and emerging therapies, can aid clinicians in helping their patients navigate through this complex disease state.

Acute myeloid leukemia--major progress over four decades and glimpses into the future

In this Review, the progress in research and therapy of acute myeloid leukemia is detailed.

Improvement in clinical outcome of FLT3 ITD mutated acute myeloid leukemia patients over the last one and a half decade

AML with FLT3 ITD mutations are associated with poor outcome. We reviewed outcomes of patients with FLT3 ITD mutated AML to investigate trends over time. We analyzed 224 AML patients (excluding patients with core binding factor and acute promyelocytic leukemia) referred to our institution between 2000 and 2014. Patients were divided into five cohorts by era: 2000-2002 (Era 1, n = 19), 2003-2005 (Era 2, n = 41), 2006-2008 (Era 3, n = 53), 2009-2011 (Era 4, n = 55), and 2012-2014 (Era 5, n = 56) to analyze differences in outcome. The baseline characteristics were not statistically different across Eras. The response rate (CR/CRp) from Era 1-5 was 68%, 49%, 72%, 73%, and 75%, respectively. The overall response rate (all Eras) with chemotherapy alone versus chemotherapy plus FLT3 inhibitor was 67% and 72.5%, respectively (P = 0.4). The median time to relapse was 6, 3.6, 7.9, 8.1 months and not reached from Eras 1 through 5, respectively (P = 0.001). The median OS has improved: 9.6, 7.6, 14.4, 15.7, and 17.8 month from Eras 1-5, respectively (P = <0.001). Stem cell transplant as a time-dependent variable, showed better OS in the univariate analysis (HR: 0.57, 95% CI: 0.39-0.84, P = 0.004) but did not retained its significance in multivariate analysis (HR: 0.75, 95% CI: 0.50-1.13, P = 0.16). Our data suggest improvement in outcome of FLT3 ITD mutated AML patients over the last 15 years. This is probably due to improvement in treatment strategies, including but not limited to integration of FLT3 inhibitors and increased use of SCT.

A novel somatic mutation in ACD induces telomere lengthening and apoptosis resistance in leukemia cells

BACKGROUND

The identification of oncogenic driver mutations has largely relied on the assumption that genes that exhibit more mutations than expected by chance are more likely to play an active role in tumorigenesis. Major cancer sequencing initiatives have therefore focused on recurrent mutations that are more likely to be drivers. However, in specific genetic contexts, low frequency mutations may also be capable of participating in oncogenic processes. Reliable strategies for identifying these rare or even patient-specific (private) mutations are needed in order to elucidate more personalized approaches to cancer diagnosis and treatment.

METHODS

Here we performed whole-exome sequencing on three cases of childhood pre-B acute lymphoblastic leukemia (cALL), representing three cytogenetically-defined subgroups (high hyperdiploid, t(12;21) translocation, and cytogenetically normal). We applied a data reduction strategy to identify both common and rare/private somatic events with high functional potential. Top-ranked candidate mutations were subsequently validated at high sequencing depth on an independent platform and in vitro expression assays were performed to evaluate the impact of identified mutations on cell growth and survival.

RESULTS

We identified 6 putatively damaging non-synonymous somatic mutations among the three cALL patients. Three of these mutations were well-characterized common cALL mutations involved in constitutive activation of the mitogen-activated protein kinase pathway (FLT3 p.D835Y, NRAS p.G13D, BRAF p.G466A). The remaining three patient-specific mutations (ACD p.G223V, DOT1L p.V114F, HCFC1 p.Y103H) were novel mutations previously undescribed in public cancer databases. Cytotoxicity assays demonstrated a protective effect of the ACD p.G223V mutation against apoptosis in leukemia cells. ACD plays a key role in protecting telomeres and recruiting telomerase. Using a telomere restriction fragment assay, we also showed that this novel mutation in ACD leads to increased telomere length in leukemia cells.

CONCLUSION

This study identified ACD as a novel gene involved in cALL and points to a functional role for ACD in enhancing leukemia cell survival. These results highlight the importance of rare/private somatic mutations in understanding cALL etiology, even within well-characterized molecular subgroups.

Phase I/II trial of the combination of midostaurin (PKC412) and 5-azacytidine for patients with acute myeloid leukemia and myelodysplastic syndrome

We investigated the combination of midostaurin and azacitidine (AZA) in patients with acute myeloid leukemia (AML) and high risk myelodysplastic syndrome (MDS). Patients received AZA 75 mg m(-2) on days 1-7 and midostaurin 25 mg bid (in cohort 1 of phase I) or 50 mg bid (in cohort 2 of Phase I and in Phase II) orally on day 8-21 during the first cycle and continuously thereafter. Fourteen patients were enrolled in the phase I and 40 in the phase II. Overall response rate was 26%. The median remission duration (RD) was 20 weeks and was significantly longer in patients with FLT3 mutations not previously exposed to other FLT3 inhibitors (P = 0.05) and in patients not previously transplanted (P = 0.01). Thirty-two (59%) patients have died, all of complications related to disease progression. G3-4 nonhematological toxicity was reported in 38 (70%) patients, most frequently infections (56%), ejection fraction reduction (11%), and diarrhea or nausea/vomiting (9% each). The combination of midostaurin and AZA is an effective and safe regimen in patients with AML and high-risk MDS. Patients with FLT3 mutations but not previously exposed to other FLT3 inhibitors and patients not previously transplanted derived the greatest benefit. Further studies with this combination are warranted.

Synergistic effect of all‑trans retinoic acid in combination with protein kinase C 412 in FMS-like tyrosine kinase 3-mutated acute myeloid leukemia cells

Acute myeloid leukemia (AML) is a heterogeneous disease. Numerous molecular abnormalities have been identified in AML and, amongst these, FMS‑like tyrosine kinase 3 (FLT3) mutations are one of the most common somatic alterations detected. In the present study, an in vitro investigation was performed to evaluate the effects of all‑trans retinoic acid (ATRA) and PKC412, alone and in combination, in FLT3‑mutated AML cell lines. Trypan blue exclusion test, as well as morphological, western blot and isobologram analyses were conducted. The results indicated that the combined ATRA and PKC412 treatment exhibited additive or synergistic effects in FLT3‑mutated AML cell lines. These results provided in vitro evidence for the future clinical trials evaluating the effects of a combination treatment using PKC412 and ATRA on AML patients with FLT3‑mutations.

Advances in treating acute myeloid leukemia

Acute myeloid leukemia (AML) arises within the bone marrow from a malignant hematopoietic progenitor cell. Though AML is still often fatal, cure rates overall continue to improve incrementally yet steadily, primarily for two reasons: first, insights into the pathogenesis of AML over the last several decades have led to the development of a relatively sophisticated classification scheme that allows more nuanced risk stratification to guide treatment choices; second, improvements in stem cell transplantation have allowed many more patients to take advantage of this highly effective therapeutic technique. Improvements in overall survival for patients with AML are expected to continue rising because of the anticipated introduction of targeted therapies into this treatment platform.

Targeting FLT3 to treat leukemia

INTRODUCTION

Approximately 23% of acute myeloid leukemia (AML) patients younger than 60 years of age carry a mutation in the transmembrane domain of the FMS-like tyrosine kinase-3 (FLT3) gene (FLT3/internal tandem duplications [ITD]). In normal karyotype AML, the presence of a FLT3/ITD mutation is associated with poor prognosis, as mirrored by a high risk of relapse even after allogeneic stem cell transplantation. The poor prognostic impact along with the observation that FLT3 is frequently overexpressed in the majority of AML cases has formed the platform for the development of FLT3-targeted strategies. To date, several FLT3 kinase inhibitors have been investigated in preclinical and clinical studies. However, as of yet, none of the studied FLT3 inhibitors has received FDA approval for routine clinical use in AML. This is in part due to the 'off target' effects observed with most inhibitors when administered at concentrations needed to achieve sustained levels of FLT3 inhibition, which are required to exhibit substantial cytotoxic effects against leukemic blasts. Furthermore, the development of resistance mutations has emerged as a clinical issue posing a threat to successful FLT3 inhibitor therapy.

AREAS COVERED

In this review, the authors provide a brief summary of FLT3 inhibitors investigated thus far, and discuss current treatment approaches and strategies how to best incorporate FLT3 tyrosine kinase inhibitors (TKIs) into therapy.

EXPERT OPINION

The combination of a FLT3 inhibitor with conventional chemotherapeutic regimens, epigenetic modifiers or inhibitors of FLT3 downstream and collateral effectors has emerged as a promising strategy to improve treatment outcome. The future of a tailored, molecular-based treatment approach for FLT3-mutated AML demands novel clinical trial concepts based on harmonized and aligned research goals between clinical and research centers and industry.

Recent advances and novel agents for FLT3 mutated acute myeloid leukemia

Acute myeloid leukemia (AML) is a devastating hematologic malignancy that affects both older adults as well as children. Treatments available for AML largely depend on cytotoxic agents and often the only curative option is an allogeneic bone marrow transplant, an option limited to young persons and associated with high morbidity and mortality. There is an urgent need for the identification of new myeloid targets and an understanding of the key genetic mutations involved in disease progression and prognosis. One such mutation is the internal tandem duplication (ITD) in the FMS-like tyrosine kinase receptor-3 (FLT3) gene which confers an inferior outcome that is attributed to a higher relapse rate. In this review, we evaluate the FLT3-ITD mutation and discuss the recent data regarding emerging approaches using FLT3 inhibitors for the treatment of AML.

Relapsed acute myeloid leukemia: why is there no standard of care?

Relapse after achieving a prior response remains one of the most important obstacles to improving the outcome of patients with acute myeloid leukemia (AML). Although overall, the majority of patients with disease relapse do poorly, this is by no means uniform and a number of predictors of outcome have been identified. Previously, most trials of investigational agents in the setting of disease relapse in AML have accrued a wide range of patients with widely different patient and disease characteristics. With increased understanding of the biology of the neoplastic change in AML, and better identification of disease subsets based on their molecular characterization, target-specific novel agents are being developed that will hopefully lead to better strategies, not only for treating relapsed disease, but also for the initial induction treatment.

CD123 immunohistochemical expression in acute myeloid leukemia is associated with underlying FLT3-ITD and NPM1 mutations

FLT3-ITD and NPM1 mutation testing in acute myeloid leukemia (AML) plays an important role in prognostic risk stratification, especially within the intermediate cytogenetic risk group. Molecular studies require adequate fresh material and are typically performed on a dedicated aspirate specimen, which may not be available in all cases. Prior flow cytometric studies have suggested an association between CD123 overexpression in AML and FLT3-ITD and/or NPM1 mutations; however, the immunohistochemical (IHC) correlate is unknown. We assessed CD123 IHC expression in 157 AML bone marrow biopsies and/or marrow particle preparations, and correlated with the morphologic, immunophenotypic, and cytogenetic features and with the presence of FLT3-ITD and NPM1 mutations. We found that CD123 IHC expression, seen in 40% of AML, occurred across a wide spectrum of 2008 World Health Organization subtypes and was most frequent within the intermediate risk group. As compared with CD123 IHC-AML, CD123 IHC+AML demonstrated higher marrow blast percentages (median 69%), monocytic differentiation (33/63 cases), and CD34 negativity (29/63 cases). Eighty-three percent (25/30) FLT3-ITD-mutated AML were CD123+ (P<0.0001) and 62% (18/29) NPM1-mutated cases were CD123 IHC+ (P=0.0052) with negative predictive values of 95% for FLT3-ITD and 88% for NPM1. CD123 IHC+AML presents with characteristic pathologic features, some of which may be related to underlying FLT3-ITD and/or NPM1 mutations.

Outcome of older patients with acute myeloid leukemia in first relapse

To provide data for future drug evaluation, we analyzed the outcome of 393 patients aged 50 years or older (median, 64 years) with AML in first relapse after treatment in recent ALFA trials. Salvage options were retrospectively classified as follows: best supportive care (BSC), low-dose cytarabine (LDAC), gemtuzumab ozogamicin (GO), intensive chemotherapy (ICT), or ICT combined with GO. Second complete remission (CR2) rate was 31% and median post-relapse survival was 6.8 months (0, 17, 42.5, 53, and 80% and 3.2, 5.6, 8.9, 9, and 19.8 months in BSC, LDAC, GO, ICT, and ICT + GO subsets, respectively). Age, performance status, WBC, CR1 duration, and favorable AML karyotype, but not other cytogenetic or molecular features, influenced post-relapse outcome. Multivariate adjustment and propensity score matching showed that intensive salvage (ICT/ICT+GO/GO versus LDAC/BSC) was associated with longer post-relapse survival, at least in patients with CR1 duration ≥12 months (P = 0.001 and 0.0005, respectively). Of interest, GO appeared to be as effective as standard ICT, and ICT + GO combination more effective than standard ICT. In conclusion, older patients with CR1 duration ≥12 months appeared to benefit from intensive salvage and results observed with GO-containing salvage suggest that GO combination studies should be actively pursued in this setting.

Clinical characteristics and outcomes of therapy-related chronic myelomonocytic leukemia

We sought to describe the clinical features and outcomes of therapy-related chronic myelomonocytic leukemia (t-CMML) and compare with those of de novo CMML. We identified 358 CMML patients, of whom 39 (11%) had t-CMML. Although the groups had similar demographic, hematologic, and molecular alteration profiles, the proportion of patients with intermediate or high CMML-specific cytogenetic risk in the t-CMML was significantly higher than that in the de novo CMML (P = .011). The median latency to develop t-CMML was 6 years. The median overall and leukemia-free survival duration of the t-CMML were shorter than those of the de novo CMML; however, t-CMML itself was not prognostic after adjusting for the effects of other covariates including cytogenetics. These results suggest that compared with de novo CMML, t-CMML is associated with more high-risk cytogenetics that manifest as poor outcomes. We propose that t-CMML be recognized as one of the therapy-related myeloid neoplasms.

Hematopoietic transplantation for acute myeloid leukemia with internal tandem duplication of FLT3 gene (FLT3/ITD)

PURPOSE OF REVIEW

Patients with acute myeloid leukemia (AML) traditionally classified as having an intermediate cytogenetic risk [mostly cytogenetically normal AML (CN-AML)] really include a significant proportion of cases with a poor outcome. This is based on the molecular findings at diagnosis, mainly the presence of internal tandem duplication in the FMS-like tyrosine kinase 3 gene(s) (FLT3/ITD). Optimal postremission therapy for these high-risk molecular cases is not well established; as the prognosis is adverse hematopoietic cell transplantation (HCT), mainly allogeneic HCT (allo-HCT), is the most widely accepted strategy.

RECENT FINDINGS

As a rule, patients with FLT3/ITD have a poor outcome with conventional chemotherapy alone. Only patients with an associated nucleophosmin 1 (NPM1) mutation and those with a low mutated-to-wild-type allelic ratio of FLT3/ITD have less unfavorable outcome. Most studies show an advantage of allo-HCT in first complete remission (CR1), with higher 3-5 year disease-free survival and lower relapse risk than with chemotherapy or autologous transplantation (auto-HCT). Regarding allo-HCT proceeding early after reaching CR1 seems to improve survival, rather than after several courses of consolidation chemotherapy.

SUMMARY

Patients with intermediate-risk cytogenetics AML and FLT3/ITD, especially NPM1-wild cases and those NPM1 mutated with a high allelic ratio, should proceed to allo-HCT if possible early after achieving CR1.

Inhibition of FLT3 expression by green tea catechins in FLT3 mutated-AML cells

Acute myeloid leukemia (AML) is a heterogeneous disease characterized by a block in differentiation and uncontrolled proliferation. FLT3 is a commonly mutated gene found in AML patients. In clinical trials, the presence of a FLT3-ITD mutation significantly correlates with an increased risk of relapse and dismal overall survival. Therefore, activated FLT3 is a promising molecular target for AML therapies. In this study, we have shown that green tea polyphenols including (-)-epigallocatechin-3-gallate (EGCG), (-)-epigallocatechin (EGC), and (-)-epicatechin-3-gallate (ECG) suppress the proliferation of AML cells. Interestingly, EGCG, EGC and ECG showed the inhibition of FLT3 expression in cell lines harboring FLT3 mutations. In the THP-1 cells harboring FLT3 wild-type, EGCG showed the suppression of cell proliferation but did not suppress the expression of FLT3 even at the concentration that suppress 100% cell proliferation. Moreover, EGCG-, EGC-and ECG-treated cells showed the suppression of MAPK, AKT and STAT5 phosphorylation. Altogether, we suggest that green tea polyphenols could serve as reagents for treatment or prevention of leukemia harboring FLT3 mutations.

Salvage therapy using FLT3 inhibitors may improve long-term outcome of relapsed or refractory AML in patients with FLT3-ITD

To determine the long-term efficacy of FLT3 inhibitors (FLT3i) in the salvage setting for relapsed and refractory (rel/ref) acute myeloid leukemia (AML) with FLT3 internal tandem duplication (AML FLT3-ITD), we conducted a retrospective study of 120 patients with rel/ref AML FLT3-ITD who received salvage therapy with either FLT3i-containing regimen (FLT3i group, N = 45) or conventional cytotoxic regimen (conventional group, N = 75). The median overall survival (OS) after the first salvage in the FLT3i group was 6·9 vs. 4·6 months in the conventional group (P = 0·17). The OS was better in the FLT3i group among patients with initial complete remission (CR) duration ≤12 months or with primary refractory disease (6·9 vs. 3·7 months; P < 0·01). The OS was better when FLT3i was combined with cytotoxic agents versus monotherapy (17 vs. 4·8 months; P = 0·017). Multivariate analysis revealed that the use of FLT3i was an independent predictor of OS (hazard ratio 0·58; 95% confidence interval, 0·38-0·88). Incorporating FLT3i into salvage strategies may improve long-term outcome of patients with AML FLT3-ITD. Prospective studies to validate this conclusion are warranted.

Effect of FLT3 ligand on survival and disease phenotype in murine models harboring a FLT3 internal tandem duplication mutation

Many of the mutations contributing to leukemogenesis in acute myeloid leukemia have been identified. A common activating mutation is an internal tandem duplication (ITD) mutation in the FLT3 gene that is found in approximately 25% of patients and confers a poor prognosis. FLT3 inhibitors have been developed and have some efficacy, but patients often relapse. Levels of FLT3 ligand (FL) are significantly elevated in patients during chemotherapy and may be an important component contributing to relapse. We used a mouse model to investigate the possible effect of FL expression on leukemogenesis involving FLT3-ITD mutations in an in vivo system. FLT3(ITD/ITD) FL(-/-) (knockout) mice had a statistically significant increase in survival compared with FLT3(ITD/ITD) FL(+/+) (wildtype) mice, most of which developed a fatal myeloproliferative neoplasm. These findings suggest that FL levels may have prognostic significance in human patients. We also studied the effect of FL expression on survival in a FLT3-ITD NUP98-HOX13 (NHD13) fusion mouse model. These mice develop an aggressive leukemia with short latency. We asked whether FL expression played a similar role in this context. The NUP98-HOX13 FLT3(ITD/wt) FL(-/-) mice did not have a survival advantage, compared with NUP98-HOX13 FLT3(ITD/wt) FL(+/+) mice (normal FL levels). The loss of the survival advantage of the FL knockout group in the NUP98-HOX13 model suggests that adding a second mutation changes the effect of FL expression in the context of more aggressive disease.

The prognostic impact of FLT3-ITD and NPM1 mutations in patients with relapsed acute myeloid leukemia and intermediate-risk cytogenetics

Internal tandem duplication of the fms-like tyrosine kinase-3 gene (FLT3-ITD) and nucleophosmin-1 (NPM1) mutations have prognostic importance in acute myeloid leukemia (AML) patients with intermediate-risk karyotype at diagnosis, but less is known about their utility to predict outcomes at relapse. We retrospectively analysed outcomes of 70 patients with relapsed, intermediate-risk karyotype AML who received a uniform reinduction regimen, with respect to FLT3-ITD and NPM1 mutation status and first complete remission (CR1) duration. CR1 duration, but not molecular status, was significantly correlated with CR2 rate. On univariate analysis, patients with mutated FLT3-ITD (FLT3+) had significantly worse overall survival (OS) compared with those with neither an NPM1 nor FLT3-ITD mutation (NPM1-/FLT3-). On multivariate analysis, shorter CR1 duration was significantly correlated with inferior OS at relapse (P<0.0001), while FLT3 and NPM1 mutation status and age were not significantly correlated with OS. Patients who subsequently underwent allogeneic stem cell transplant (alloSCT) had a superior OS regardless of CR1 duration, but outcomes were better in patients with CR1 duration>12 months. In intermediate-risk karyotype AML patients receiving reinduction, CR1 duration remains the most important predictor of OS at relapse; FLT3-ITD and NPM1 status are not independent predictors of survival.

Phase 2 study of azacytidine plus sorafenib in patients with acute myeloid leukemia and FLT-3 internal tandem duplication mutation

Patients received 5-azacytidine (AZA) 75 mg/m(2) intravenously daily for 7 days and sorafenib 400 mg orally twice daily continuously; cycles were repeated at ~1-month intervals. Forty-three acute myeloid leukemia (AML) patients with a median age of 64 years (range, 24-87 years) were enrolled; 37 were evaluable for response. FMS-like tyrosine kinase-3 (FLT3)-internal tandem duplication (ITD) mutation was detected in 40 (93%) patients, with a median allelic ratio of 0.32 (range, 0.009-0.93). They had received a median of 2 prior treatment regimens (range, 0-7); 9 had failed prior therapy with a FLT3 kinase inhibitor. The response rate was 46%, including 10 (27%) complete response with incomplete count recovery (CRi), 6 (16%) complete responses (CR), and 1 (3%) partial response. The median time to achieve CR/CRi was 2 cycles (range, 1-4), and the median duration of CR/CRi was 2.3 months (range, 1-14.3 months). Sixty-four percent of patients achieved adequate (defined as >85%) FLT3 inhibition during their first cycle of therapy. The degree of FLT3 inhibition correlated with plasma sorafenib concentrations. FLT3 ligand levels did not rise to levels seen in prior studies of patients receiving cytotoxic chemotherapy. The combination of AZA and sorafenib is effective for patients with relapsed AML and FLT-3-ITD. This trial was registered at clinicaltrials.gov as #NCT01254890.

Salvage therapy for relapsed or refractory acute myeloid leukemia

There are a significant number of patients diagnosed with acute leukemia who either fail to achieve remission or who relapse thereafter. Challenges in treating this patient population include accurately assessing prognosis of disease and whether remission can be achieved; assessing the ability of patients to tolerate aggressive salvage therapies; choosing a salvage therapy that is most likely to succeed; and identifying suitable patients for hematopoietic stem cell transplantation. Despite the development of a variety of new investigational therapies, relapsed or refractory acute myeloid Leukemia remains a difficult clinical problem. Clinicians will need to consider all currently available approaches, including cytotoxic chemotherapy, targeted agents, and allogeneic stem cell transplantation, to optimize outcomes.

The prevalent predicament of relapsed acute myeloid leukemia

A majority of patients with acute myeloid leukemia (AML) will relapse after achieving complete remission. At relapse, patients should be risk stratified and a decision made about the appropriateness of intensive therapy and whether a potentially curative allogeneic stem cell transplantation (allo-SCT) is possible. Risk factors include duration of first complete remission and adverse cytogenetics, as well as age and FLT3 mutation status. Available therapies are steadily increasing, but for the most part should be regarded as either best palliation or as a bridge to allo-SCT. Simple symptomatic therapies for patients with extreme age or the worst prognosis should also be considered. Newer therapeutic options include novel cytotoxic chemotherapies including clofarabine, immunomodulatory agents, targeted therapies against FLT3 and mTOR, and immunoconjugates. All patients with relapsed AML should be considered for an appropriate clinical trial.

Clinical impact of change of FLT3 mutation status in acute myeloid leukemia patients

FMS-like tyrosine kinase 3 (FLT3) is one of the most frequently mutated genes in acute myeloid leukemia and is associated with worse clinical outcome. Changes in FLT3 mutation status can occur during the course of disease, but the clinical impact of a change is unclear. We retrospectively reviewed 3555 acute myeloid leukemia patients, who have been assessed for FLT3 mutation at our institution between May 2002 and January 2011. We found that 42 (6.2%) out of 680 patients with FLT3 mutation experienced a change of FLT3 mutation status. In all, 36 patients with wild-type FLT3 at the time of initial diagnosis gained mutation (Negative/Positive) and six initially FLT3-mutated patients became wild type during their following relapses (Positive/Negative). The 5-year survival of these patients was similar to that of patients with persistently wild-type FLT3 (Negative/Negative; P=0.464), and significantly better than patients who had stable FLT3 mutation during their disease course (Positive/Positive; P<0.001). However, after mutations became detectable in the Negative/Positive group, the forward survival of these patients tracked that of the Positive/Positive group after relapse (P=0.761). In addition, we did not find a significant difference in survival between patients with internal tandem duplications and those with point mutations in the tyrosine kinase domain of the FLT3 gene. These results suggest that FLT3 mutations are unstable and that there is potential clinical value in continuously monitoring FLT3 mutation status.

Potential of whole-genome sequencing for determining risk and personalizing therapy: focus on AML

In spite of recent advances in molecular diagnostic techniques and expanded indications for allogeneic hematopoietic stem cell transplantation, treatment of acute myeloid leukemia (AML) remains a major challenge. In the last decade, several recurrent genetic abnormalities and gene mutations with prognostic implications have been identified. This has led to improved informed treatment decisions. However, there has been limited change in the use of nonspecific cytotoxic chemotherapy and mortality rates continue to be unacceptably high, with 5 year overall survival rates of older AML patients at 30% or less. Whole-genome sequencing offers hope for greater diagnostic accuracy and is likely to lead to further characterization of disease subsets with differential outcome and response to treatment. The holy grail of personalized targeted therapy for the individual AML patient, while minimizing toxicity and prolonging survival, appears closer than ever.

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.

Targeting the FMS-like tyrosine kinase 3 in acute myeloid leukemia

Acute myeloid leukemia (AML) is a highly heterogenous disease with multiple signaling pathways contributing to its pathogenesis. A key driver of AML is the FMS-like tyrosine kinase receptor-3 (FLT3). Activating mutations in FLT3, primarily the FLT3-internal tandem duplication (FLT3-ITD), are associated with decreased progression-free and overall survival. Identification of the importance of FLT3-ITD and the FLT3 pathway in the prognosis of patients with AML has stimulated efforts to develop therapeutic inhibitors of FLT3. Although these inhibitors have shown promising antileukemic activity, they have had limited efficacy to date as single agents and may require use in combination with cytotoxic chemotherapies. Here, we review clinical and preclinical results for the clinically mature FLT3 inhibitors currently in development. We conclude that multitargeted FLT3 inhibitors may have more utility earlier in the course of disease, when in vitro evidence suggests that AML cells are less dependent on FLT3 signaling, perhaps because of upregulation of multiple other signaling pathways. More potent agents may have greater utility in relapsed and heavily pretreated patients, in whom high levels of circulating FLT3 ligand may necessitate use of an agent with a very favorable pharmacokinetic/pharmacodynamic profile. Novel combination regimens are also discussed.

Detection of internal tandem duplications in the FLT3 gene by different electrophoretic methods

BACKGROUND

In acute myeloid leukemia (AML), the internal tandem duplication (ITD) in the juxtamembrane domain of the FLT3 (Fms-like tyrosine kinase 3) gene is one of the most frequent genetic alterations associated with poor prognosis.

METHODS

A complex evaluation of the analytical properties of the three most frequently used detection methods--PCR followed by agarose (AGE), polyacrylamide (PAGE) or capillary electrophoresis (CE)--was performed on 95 DNA samples obtained from 73 AML patients.

RESULTS

All the three methods verified the presence of a mutant allele in 20 samples from 18 patients. AGE and PAGE could detect the presence of 1%-2% mutant allele, while the detection limit of CE was 0.28%. However, acceptable reproducibility (inter-assay CV <25%) of the mutant allele rate determination was only achievable above 1.5% mutant/total allele rate. The reproducibility of the ITD size determination by CE was much better, but the ITD size calculated by PeakScanner or GeneScan analysis was 7% lower as compared to values obtained by DNA sequencing. The presence of multiple ITD was over-estimated by PAGE and AGE due to the formation of heteroduplexes.

CONCLUSIONS

This study suggests the use of PCR+CE in the diagnostics and the follow-up of AML patients. The data further supports the importance of proper analytical evaluation of home-made molecular biological diagnostic tests.

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.

Emerging FMS-like tyrosine kinase 3 inhibitors for the treatment of acute myelogenous leukemia

INTRODUCTION

The FMS-like tyrosine kinase 3 (FLT3) is highly expressed in acute leukemias. Mutations involving FLT3 are among the most common molecular abnormalities in acute myelogenous leukemia (AML). Available evidence suggests that these molecular lesions confer a shorter disease-free survival and overall survival in patients with intermediate-risk cytogenetics. Therefore, substantial interest in FLT3 as a therapeutic target has led to the development of several promising inhibitors that target this tyrosine kinase.

AREAS COVERED

This review covers the molecular pathways associated with FLT3 activation in patients with AML, the biological rationale for inhibiting FLT3 and recent clinical progress with FLT3 inhibitors for the treatment of AML. Six FLT3 inhibitors undergoing clinical evaluation are discussed. A review of selected published manuscripts on the subject of FLT3 inhibition in AML and a search of the English language manuscripts in PubMed using the index words FLT3 and AML were conducted and articles of interest selected.

EXPERT OPINION

Mutated forms of FLT3, specifically FLT3-internal tandem duplication, have a significant impact on the prognosis of AML patients, particularly those with a normal karyotype. Inhibiting FLT3 may lead to clinical benefit for patients with AML. Newly developed FLT3 inhibitors have shown encouraging activity as monotherapy and in combination with other therapeutic agents.

FLT3-internal tandem duplication and age are the major prognostic factors in patients with relapsed acute myeloid leukemia with normal karyotype

BACKGROUND

Several genetic aberrations with prognostic impact in first-line therapy have been described in patients with acute myeloid leukemia and normal karyotype. However, little is known about the influence of these aberrations on outcome after relapse. This study aimed to identify clinical and molecular risk factors for patients with relapsed acute myeloid leukemia with normal karyotype.

DESIGN AND METHODS

We analyzed 94 patients with acute myeloid leukemia and normal karyotype after first relapse for clinical and molecular risk factors for survival. All patients had received first-line treatment and follow-up within two prospective, multicenter trials. Leukemic blasts were analyzed at diagnosis for genetic aberrations in the FLT3, NPM1, CEBPA, WT1, IDH1 and IDH2 genes by polymerase chain reaction and/or direct sequencing.

RESULTS

A second complete remission was achieved in 52% of patients who received re-induction therapy. The presence of an FLT3-internal tandem duplication, duration of first complete remission less than 6 months and age above the median of 47 years were associated with a significantly lower rate of second complete remission. The median survival after relapse was 11 months and the 6-year survival rate was 28%. In multivariate analysis, FLT3-internal tandem duplication and age above the median were the only independent negative prognostic factors for survival. The 6-year survival rate of patients with none of these factors was 56%, whereas it was significantly inferior in patients with one or both of these factors (15% and 6%, respectively). This was also true for patients who underwent allogeneic stem cell transplantation after relapse.

CONCLUSIONS

FLT3-internal tandem duplication and age are the major prognostic factors in patients with relapsed acute myeloid leukemia with a normal karyotype. Patients with at least one of these risk factors have a dismal outcome and might be considered for investigational treatment approaches after relapse. (ClinicalTrials.gov Identifier: NCT00209833).

Molecular genetics in acute myeloid leukemia

PURPOSE OF REVIEW

Acute myeloid leukemia (AML) is a highly heterogeneous disorder being composed of various genetically defined subtypes. In recent years, molecular research provided the basis for a more differentiated characterization of AML patients, for example, of the large subgroup with normal karyotypes. This review summarizes the current status of molecular diagnostics in AML and refers to the diagnostic techniques being most suitable for the individual markers.

RECENT FINDINGS

A molecular data set based on mutations of the NPM1, FLT3, and CEBPA genes and the MLL-PTD provides a prognostically relevant risk stratification that can support the decision pro or con an allogeneic hematopoietic stem cell transplantation in first remission. The panel of known molecular markers is continuously increasing, for example, considering the recently described TET2 and IDH1 mutations. The introduction of next generation sequencing will certainly catalyze the molecular characterization of AML. Monitoring of the minimal residual disease load with quantitative real-time PCR can be performed for NPM1 and MLL-PTD-mutated cases.

SUMMARY

Targeted therapy studies with FLT3 inhibitors for patients with FLT3-mutated AML as single agents or combined with chemotherapy illustrate the translation of the molecular techniques into clinical practice already being realized in distinct subgroups of AML.