More on prognostic significance of FLT3/ITD size in acute myeloid leukemia (AML)

Genomic Alterations, Gene Expression Profiles and Functional Enrichment of Normal-Karyotype Acute Myeloid Leukaemia Based on Targeted Next-Generation Sequencing

Characterising genomic variants is paramount in understanding the pathogenesis and heterogeneity of normal-karyotype acute myeloid leukaemia (AML-NK). In this study, clinically significant genomic biomarkers were ascertained using targeted DNA sequencing and RNA sequencing on eight AML-NK patients' samples collected at disease presentation and after complete remission. In silico and Sanger sequencing validations were performed to validate variants of interest, and they were followed by the performance of functional and pathway enrichment analyses for overrepresentation analysis of genes with somatic variants. Somatic variants involving 26 genes were identified and classified as follows: 18/42 (42.9%) as pathogenic, 4/42 (9.5%) as likely pathogenic, 4/42 (9.5%) as variants of unknown significance, 7/42 (16.7%) as likely benign and 9/42 (21.4%) as benign. Nine novel somatic variants were discovered, of which three were likely pathogenic, in the CEBPA gene with significant association with its upregulation. Transcription misregulation in cancer tops the affected pathways involving upstream genes (CEBPA and RUNX1) that were deregulated in most patients during disease presentation and were closely related to the most enriched molecular function gene ontology category, DNA-binding transcription activator activity RNA polymerase II-specific (GO:0001228). In summary, this study elucidated putative variants and their gene expression profiles along with functional and pathway enrichment in AML-NK patients.

Impact of FLT3-ITD Insertion Length on Outcomes in Acute Myeloid Leukemia: A Propensity Score-Adjusted Cohort Study

The prognostic significance of the length of internal tandem duplication (ITD) insertions in mutant FLT3 genes in acute myeloid leukemia (AML) is controversial. We conducted a retrospective study to evaluate the correlation between the ITD base-pair (bp) insertion length and clinical outcomes. The mutational status of the FLT3 gene was evaluated in 402 of 467 consecutive AML patients treated at the University of Maryland Greenebaum Comprehensive Cancer Center between 2013 and 2020; 77 had FLT3-ITD mutations. Patients were divided into three cohorts based on bp insertion length (<30 (0−33rd percentile), 30−53 (34th−66th percentile),and >53 (>66th percentile)). The median overall survival (OS) of patients was 16.5 months (confidence interval (CI) 7.3-NA), 18.5 months (CI 7.3-NA), and 21.9 months (CI 19.1-NA) (p = 0.03) for the <30, 30−53, and >53 bp insertion length cohorts, respectively. The adjusted median event-free survival (EFS) for the ITD insertion lengths >30, 30−53, and >53 bp was 11.1 months (CI 2.8−16.5), 5.2 months (CI 2.9−12.6), and 9.1 months (CI 5.4-NA) (p = 0.5), respectively. Complete remission (CR) rates were 64% (<30 inserted bp), 55% (30−53 inserted bp), and 79% (>53 inserted bp) (p = 0.23). For patients treated with gilteritinib and midostaurin, the unadjusted median OS was not statistically significantly different between cohorts.

Prognostic significance of FLT3-ITD length in AML patients treated with intensive regimens

FLT3-ITD mutations are detected in approximately 25% of newly diagnosed adult acute myeloid leukemia (AML) patients and confer an adverse prognosis. The FLT3-ITD allelic ratio has clear prognostic value. Nevertheless, there are numerous manuscripts with contradictory results regarding the prognostic relevance of the length and insertion site (IS) of the FLT3-ITD fragment. We aimed to assess the prognostic impact of these variables on the complete remission (CR) rates, overall survival (OS) and relapse-free survival (RFS) of AML patients with FLT3-ITDmutations. We studied the FLT3-ITD length of 362 adult AML patients included in the PETHEMA AML registry. We tried to validate the thresholds of ITD length previously published (i.e., 39 bp and 70 bp) in intensively treated AML patients (n = 161). We also analyzed the mutational profile of 118 FLT3-ITD AML patients with an NGS panel of 39 genes and correlated mutational status with the length and IS of ITD. The AUC of the ROC curve of the ITD length for OS prediction was 0.504, and no differences were found when applying any of the thresholds for OS, RFS or CR rate. Only four out of 106 patients had ITD IS in the TKD1 domain. Our results, alongside previous publications, confirm that FLT3-ITD length lacks prognostic value and clinical applicability.

FLT3-ITD mutations in acute myeloid leukaemia - molecular characteristics, distribution and numerical variation

Recurrent somatic internal tandem duplications (ITD) in the FMS-like tyrosine kinase 3 (FLT3) gene characterise approximately one third of patients with acute myeloid leukaemia (AML), and FLT3-ITD mutation status guides risk-adapted treatment strategies. The aim of this work was to characterise FLT3-ITD variant distribution in relation to molecular and clinical features, and overall survival in adult AML patients. We performed two parallel retrospective cohort studies investigating FLT3-ITD length and expression by cDNA fragment analysis, followed by Sanger sequencing in a subset of samples. In the two cohorts, a total of 139 and 172 mutant alleles were identified in 111 and 123 patients, respectively, with 22% and 28% of patients presenting with more than one mutated allele. Further, 15% and 32% of samples had a FLT3-ITD total variant allele frequency (VAF) < 0.3, while 24% and 16% had a total VAF ≥ 0.7. Most of the assessed clinical features did not significantly correlate to FLT3-ITD numerical variation nor VAF. Low VAF was, however, associated with lower white blood cell count, while increasing VAF correlated with inferior overall survival in one of the cohorts. In the other cohort, ITD length above 50 bp was identified to correlate with inferior overall survival. Our report corroborates the poor prognostic association with high FLT3-ITD disease burden, as well as extensive inter- and intrapatient heterogeneity in the molecular features of FLT3-ITD. We suggest that future use of FLT3-targeted therapy could be accompanied with thorough molecular diagnostics and follow-up to better predict optimal therapy responders.

De novo adult acute myeloid leukemia with two new mutations in juxtatransmembrane domain of the FLT3 gene: a case report

Background

Approximately 30% of adult acute myeloid leukemia (AML) acquire within fms-like tyrosine kinase 3 gene (FLT3) internal tandem duplications (FLT3/ITDs) in their juxtamembrane domain (JMD). FLT3/ITDs range in size from three to hundreds of nucleotides, and confer an adverse prognosis. Studies on a possible relationship between of FLT3/ITDs length and clinical outcomes in those AML patients were inconclusive, yet.

Case presentation

Here we report a 54-year-old Arab male diagnosed with AML who had two FLT3-ITD mutations in addition to NPM1 mutation. Cytogenetic approaches (banding cytogenetics) and fluorescence in situ hybridization (FISH) using specific probes to detect translocations t(8;21), t(15;17), t(16;16), t(12;21), and deletion del(13q)) were applied to exclude chromosomal abnormalities. Molecular genetic approaches (polymerase chain reaction (PCR) and the Sanger sequencing) identified a yet unreported combination of two new mutations in FLT3-ITDs. The first mutation induced a frameshift in JMD, and the second led to a homozygous substitution of c.1836T>A (p.F612L) also in JMD. Additionally a NPM1 type A mutation was detected. The first chemotherapeutic treatment was successful, but 1 month after the initial diagnosis, the patient experienced a relapse and unfortunately died.

Conclusions

To the best of our knowledge, a combination of two FLT3-ITD mutations in JMD together with an NPM1 type A mutation were not previously reported in adult AML. Further studies are necessary to prove or rule out whether the size of these FLT3-ITDs mutations and potential other double mutations in FLT3-ITD are correlated with the observed adverse outcome.

Impact of numerical variation, allele burden, mutation length and co-occurring mutations on the efficacy of tyrosine kinase inhibitors in newly diagnosed FLT3- mutant acute myeloid leukemia

FLT3-ITD mutations in newly diagnosed acute myeloid leukemia (AML) are associated with worse overall survival (OS). FLT3-ITD diversity can further influence clinical outcomes. Addition of FLT3 inhibitors to standard chemotherapy has improved OS. The aim of this study is to evaluate the prognostic impact of FLT3 diversity and identify predictors of efficacy of FLT3 inhibitors. We reviewed prospectively collected data from 395 patients with newly diagnosed FLT3-ITD mutant AML. 156 (39%) patients received FLT3 inhibitors combined with either high or low intensity chemotherapy. There was no statistically significant difference in clinical outcomes among patients treated with FLT3 inhibitors based on FLT3 numerical variation (p = 0.85), mutation length (p = 0.67). Overall, the addition of FLT3 inhibitor to intensive chemotherapy was associated with an improved OS (HR = 0.35, 95% CI: 0.24-0.5, p = 0.0005), but not in combination with lower intensity chemotherapy (HR = 0.98, 95%CI: 0.7-1.36, p = 0.85). A differential effect of FLT3 inhibitor on OS was more pronounced in younger patients with FLT3 allelic ratio ≥0.5 (HR = 0.41, 95% CI: 0.25-0.66, p < 0.001), single ITD mutation (HR = 0.55, 95% CI: 0.34-0.88, p = 0.01), diploid cytogenetics (HR = 0.52, 95% CI: 0.35-0.76, p = 0.001), NPM1 co-mutation (HR = 0.35, 95% CI: 0.19-0.67, p = 0.001). Our analysis identifies predictors of survival among diverse FLT3 related variables in patients treated with FLT3 inhibitor.

Pattern and prognostic value of FLT3-ITD mutations in Chinese de novo adult acute myeloid leukemia

FMS‐like tyrosine kinase 3 (FLT3) is one of the most frequently mutated genes in hematological malignancies. FLT3 internal tandem duplication (FLT3‐ITD) mutations located in juxtamembrane domain (JMD) and tyrosine kinase domain 1 (TKD1) regions account for two‐thirds of all FLT3 mutations. The outcome of patients remains unsatisfactory, with low survival rates. It is not yet known whether the different mutations within the FLT3 gene are all associated with patient outcome. In addition, the cause of FLT3‐ITD in‐frame duplication events remains unknown. Although there are some published studies investigating the FLT3‐ITD mutation and its clinical implications in Chinese acute myeloid leukemia (AML) patients, sample sizes tend to be small and detailed molecular profiles of FLT3 mutations are lacking in these studies. In our study, 227 FLT3‐ITD sequences were analyzed from 227 Chinese de novo AML patients. ITD were next classified into 3 types based on molecular profiles of insertion DNA sequences: DNA complete duplication (type I), DNA partial duplication (type II) and complete random sequence (type III). From the 154 patients, we confirmed that high ITD allelic ratio (≥.5) and allogeneic stem cell transplant treatment under CR1 are independent prognostic factors. We also presented evidence that ITD integration sites in the hinge region or beta1‐sheet region are an unfavorable prognostic factor in adult AML patients with FLT3‐ITD mutations. These findings may help to decipher the mechanisms of FLT3‐ITD in‐frame duplication events and stratify patients when considering different therapeutic combinations.

Clinical implications of molecular markers in acute myeloid leukemia

The recently updated World Health Organization (WHO) Classification of myeloid neoplasms and leukemia reflects the fact that research in the underlying pathogenic mechanisms of acute myeloid leukemia (AML) has led to remarkable advances in our understanding of the disease. Gene mutations now allow us to explore the enormous diversity among cytogenetically defined subsets of AML, particularly the large subset of cytogenetically normal AML. Despite the progress in unraveling the tumor genome, only a small number of recurrent mutations have been incorporated into risk-stratification schemes and have been proven to be clinically relevant, targetable lesions. We here discuss the utility of molecular markers in AML in prognostication and treatment decision making, specifically highlighting the aberrations included in the current WHO classification.

Clonal heterogeneity of FLT3-ITD detected by high-throughput amplicon sequencing correlates with adverse prognosis in acute myeloid leukemia

In acute myeloid leukemia (AML), internal tandem duplications (ITDs) of FLT3 are frequent mutations associated with unfavorable prognosis. At diagnosis, the FLT3-ITD status is routinely assessed by fragment analysis, providing information about the length but not the position and sequence of the ITD. To overcome this limitation, we performed cDNA-based high-throughput amplicon sequencing (HTAS) in 250 FLT3-ITD positive AML patients, treated on German AML Cooperative Group (AMLCG) trials. FLT3-ITD status determined by routine diagnostics was confirmed by HTAS in 242 out of 250 patients (97%). The total number of ITDs detected by HTAS was higher than in routine diagnostics (n = 312 vs. n = 274). In particular, HTAS detected a higher number of ITDs per patient compared to fragment analysis, indicating higher sensitivity for subclonal ITDs. Patients with more than one ITD according to HTAS had a significantly shorter overall and relapse free survival. There was a close correlation between FLT3-ITD mRNA levels in fragment analysis and variant allele frequency in HTAS. However, the abundance of long ITDs (≥75nt) was underestimated by HTAS, as the size of the ITD affected the mappability of the corresponding sequence reads. In summary, this study demonstrates that HTAS is a feasible approach for FLT3-ITD detection in AML patients, delivering length, position, sequence and mutational burden of this alteration in a single assay with high sensitivity. Our findings provide insights into the clonal architecture of FLT3-ITD positive AML and have clinical implications.

RNA-based FLT3-ITD allelic ratio is associated with outcome and ex vivo response to FLT3 inhibitors in pediatric AML

Controversy exists whether internal tandem duplication of FMS-like tyrosine kinase 3 (FLT3-internal tandem duplication [ITD]) allelic ratio (AR) and/or length of the ITD should be taken into account for risk stratification of pediatric acute myeloid leukemia (AML) and whether it should be measured on RNA or DNA. Moreover, the ITD status may be of relevance for selecting patients eligible for FLT3 inhibitors. Here, we included 172 pediatric AML patients, of whom 36 (21%) harbored FLT3-ITD as determined on both RNA and DNA. Although there was a good correlation between both parameters AR_spearman = 0.62 (95% confidence interval, 0.22-0.87) and ITDlength_spearman = 0.98 (95% confidence interval, 0.90-1.00), only AR ≥ 0.5 and length ≥48 base pairs (bps) based on RNA measurements were significantly associated with overall survival (AR: P_logrank = .008; ITDlength: P_logrank = .011). In large ITDs (>156 bp on DNA) a remarkable 90-bp difference exists between DNA and RNA, including intron 14, which is spliced out in RNA. Ex vivo exposure (n = 30) to FLT3 inhibitors, in particular to the FLT3-specific inhibitor gilteritinib, showed that colony-forming capacity was significantly more reduced in FLT3-ITD-AR ≥ 0.5 compared with ITD-AR-low and ITD^- patient samples (P < .001). RNA-based FLT3-ITD measurements are recommended for risk stratification, and the relevance of AR regarding eligibility for FLT3-targeted therapy warrants further study.

Pathology Consultation on Gene Mutations in Acute Myeloid Leukemia

OBJECTIVES

Acute myeloid leukemia (AML) is a rapidly fatal disease without the use of aggressive chemotherapy regimens. Cytogenetic and molecular studies are commonly used to classify types of AML based on prognosis, as well as to determine therapeutic regimens.

METHODS

Although there are several AML classifications determined by particular translocations, cytogenetically normal AML represents a molecularly, as well as clinically, heterogeneous group of diseases. Laboratory evaluation of AML will become increasingly important as new mutations with both prognostic and therapeutic implications are being recognized. Moreover, because many patients with AML are being treated more effectively, these mutations may become increasingly useful as markers of minimal residual disease, which can be interpreted in an individualized approach.

RESULTS

Current laboratory studies of gene mutations in AML include analysis of NPM1, FLT3, CEBPA, and KIT. In addition to these genes, many other genes are emerging as potentially useful in determining patients' prognosis, therapy, and disease course.

CONCLUSIONS

This article briefly reviews the current most clinically relevant gene mutations and their clinical and immunophenotypic features, prognostic information, and methods used for detection.

[ITD mutation burden for the prognosis in FLT3-ITD positive acute myeloid leukemia patients]

OBJECTIVE

To explore the impact of ITD mutation characteristics on the overall survival (OS) and complete remission duration (CRD) in FLT3-ITD positive non-M3 acute myeloid leukemia (AML).

METHODS

Capillary electrophoresis was used to detect the FLT3-ITD characteristics after PCR amplication. Single or multiple mutations were identified by the numbers of peak. FLT3-ITD mutation burden was calculated by the peak area of mutant divided by the wild-type and mutant peak areas. Clinical data was collected and followed up in the FLT3-ITD mutation patients.

RESULTS

Multiple ITD mutations were common in patients aged 60 and above. Patients with single ITD mutation had higher percentage of blasts in bone marrow than multiple ITD mutations (0.758 vs 0.638, P=0.028). The numbers and length of FLT3-ITD mutation had no impact on prognosis. Patients with less than 10% of ITD mutation burden showed no difference with the intermediate-risk c-kit group in OS and CRD, but the two groups had longer OS and CRD than ITD mutation burden above 10% (OS: undefined, undefined, 9.9 months, P<0.05; CRD: undefined, undefined, 6.7 months, P<0.05). In patients with ITD mutation burden above 10%, cases with NPM1 or CEBPA mutation alone had markedly longer CRD than ITD mutation alone (25.0 vs 5.1 months, P=0.003), while OS were similar (11.4 vs 8.0 months, P>0.05).

CONCLUSION

Non-M3 AML patients with less than 10% FLT3-ITD mutation burden had a better prognosis than those above 10%.

Differential impact of allelic ratio and insertion site in FLT3-ITD-positive AML with respect to allogeneic transplantation

The objective was to evaluate the prognostic and predictive impact of allelic ratio and insertion site (IS) of internal tandem duplications (ITDs), as well as concurrent gene mutations, with regard to postremission therapy in 323 patients with FLT3-ITD-positive acute myeloid leukemia (AML). Increasing FLT3-ITD allelic ratio (P = .004) and IS in the tyrosine kinase domain 1 (TKD1, P = .06) were associated with low complete remission (CR) rates. After postremission therapy including intensive chemotherapy (n = 121) or autologous hematopoietic stem cell transplantation (HSCT, n = 17), an allelic ratio ≥ 0.51 was associated with an unfavorable relapse-free (RFS, P = .0008) and overall survival (OS, P = .004); after allogeneic HSCT (n = 93), outcome was significantly improved in patients with a high allelic ratio (RFS, P = .02; OS, P = .03), whereas no benefit was seen in patients with a low allelic ratio (RFS, P = .38; OS, P = .64). Multivariable analyses revealed a high allelic ratio as a predictive factor for the beneficial effect of allogeneic HSCT; ITD IS in TKD1 remained an unfavorable factor, whereas no prognostic impact of concurrent gene mutations was observed. The clinical trials described herein were previously published or are registered as follows: AMLHD93 and AMLHD98A, previously published; AML SG 07-04, ClinicalTrials.gov identifier #NCT00151242.

The Biology and Targeting of FLT3 in Pediatric Leukemia

Despite remarkable improvement in treatment outcomes in pediatric leukemia over the past several decades, the prognosis for high-risk groups of acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL), as well as for relapsed leukemia, remains poor. Intensification of chemotherapy regimens for those at highest risk has improved success rates, but at the cost of significantly increased morbidity and long-term adverse effects. With the success of imatinib in Philadelphia-chromosome-positive leukemia and all-trans retinoic acid in acute promyelocytic leukemia, the quest to find additional molecularly targeted therapies has generated much excitement over recent years. Another such possible target in pediatric acute leukemia is FMS-like tyrosine kinase 3 (FLT3). FLT3 aberrations are among the most frequently identified transforming events in AML, and have significant clinical implications in both high-risk pediatric AML and in certain high-risk groups of pediatric ALL. Therefore, the successful targeting of FLT3 has tremendous potential to improve outcomes in these subsets of patients. This article will give an overview of the molecular function and signaling of the FLT3 receptor, as well as its pathogenic role in leukemia. We review the discovery of targeting FLT3, discuss currently available FLT3 inhibitors in pediatric leukemia and results of clinical trials to date, and finally, consider the future promise and challenges of FLT3 inhibitor therapy.

Small molecule inhibitors in acute myeloid leukemia: from the bench to the clinic

Many patients with acute myeloid leukemia will eventually develop refractory or relapsed disease. In the absence of standard therapy for this population, there is currently an urgent unmet need for novel therapeutic agents. Targeted therapy with small molecule inhibitors represents a new therapeutic intervention that has been successful for the treatment of multiple tumors (e.g., gastrointestinal stromal tumors, chronic myelogenous leukemia). Hence, there has been great interest in generating selective small molecule inhibitors targeting critical pathways of proliferation and survival in acute myeloid leukemia. This review highlights a selective group of intriguing therapeutic agents and their presumed targets in both preclinical models and in early human clinical trials.

Detection of minor clones with internal tandem duplication mutations of FLT3 gene in acute myeloid leukemia using delta-PCR

Internal tandem duplication (ITD) mutations of the FLT3 gene have been associated with inferior prognosis of acute myeloid leukemia. Detection of minor clones or minimal residual clones with ITD mutations is desirable, but is challenging when the mutant signal determined by polymerase chain reaction (PCR) and capillary electrophoresis is weak. In this study, we applied delta-PCR, which is a triple-primer strategy, to ensure PCR specificity and improve the sensitivity to 0.1% leukemic cells with ITD mutation. We also applied a reference peak to calculate ITD allelic burdens of <2% threshold of technical limitation for evaluating the relative ratio of 2 signals by capillary electrophoresis. Delta-PCR was able to detect single or multiple ITD mutations with an allelic burden (peak height ratio of mutant allele and wild-type allele) ranging from 0.4% to >100% among all 31 cases with previous documented ITD mutations. In one of the 3 cases with previously reported negative ITD mutation in the initial diagnostic specimen and ITD-positive results in the follow-up specimens, an ITD of 0.04% allele burden was retrospectively detected in the initial diagnosis specimen using delta-PCR. We also demonstrated that minor ITD mutant clones with an allelic burden of <1% present at diagnosis may become a dominant clone at the later refractory status, suggesting that detection of leukemic clones with allelic burdens of <1% may be clinically significant. Delta-PCR can detect ITD mutations with improved sensitivity and specificity and may be useful for the detection of minimal residual leukemia.

FLT3 tyrosine kinase inhibitors in acute myeloid leukemia: clinical implications and limitations

Internal tandem duplications of the FMS-like tyrosine kinase 3 (FLT3) gene are one of the most frequent gene mutations in acute myeloid leukemia (AML) and are associated with poor clinical outcome. The remission rate is high with intensive chemotherapy, but most patients eventually relapse. During the last decade, FLT3 mutations have emerged as an attractive target for a molecularly specific treatment strategy. Targeting FLT3 receptor tyrosine kinases in AML has shown encouraging results in the treatment of FLT3 mutated AML, but in most patients responses are incomplete and not sustained. Newer, more specific compounds seem to have a higher potency and selectivity against FLT3. During therapy with FLT3 tyrosine kinase inhibitors (TKIs) the induction of acquired resistance has emerged as a clinical problem. Therefore, optimization of the targeted therapy and potential treatment options to overcome resistance is currently the focus of clinical research. In this review we discuss the use and limitations of TKIs as a therapeutic strategy for the treatment of FLT3 mutated AML, including mechanisms of resistance to TKIs as well as possible novel strategies to improve FLT3 inhibitor therapy.

Molecular analysis of different FLT3-ITD mutations in acute myeloid leukemia

Mutation of the FMS-like tyrosine kinase-3 (FLT3) gene occurs with a frequency of 20-25% in acute myeloid leukemia (AML). Different studies have reported conflicting results, stating the importance of the length, position and number of internal tandem duplications (ITDs) for prognostic significance. In the present study, FLT3-ITD mutations were found in 51 (23%) of 218 patients with AML. Using sequence analysis we categorized ITD integration sites according to functional regions of the FLT3 receptor. Median ITD size was 61 bp. The insertion site was strongly correlated with ITD size: more C-terminal located inserted fragments were significantly bigger. Our data confirm that FLT3-ITD mutations identify a subset of young patients with AML with normal cytogenetics but with inferior outcome. Patients with AML with mutation localization outside the juxtamembrane domain showed no correlation with worse prognosis. A high mutant/wild-type ratio appears to have a major impact on the prognostic relevance.

FLT3 as a therapeutic target in AML: still challenging after all these years

Mutations within the FMS-like tyrosine kinase 3 (FLT3) gene on chromosome 13q12 have been detected in up to 35% of acute myeloid leukemia (AML) patients and represent one of the most frequently identified genetic alterations in AML. Over the last years, FLT3 has emerged as a promising molecular target in therapy of AML. Here, we review results of clinical trials and of correlative laboratory studies using small molecule FLT3 tyrosine kinase inhibitors (TKIs) in AML patients. We also review mechanisms of primary and secondary drug resistance to FLT3-TKI, and from the data currently available we summarize lessons learned from FLT3-TKI monotherapy. Finally, for using FLT3 as a molecular target, we discuss novel strategies to overcome treatment failure and to improve FLT3 inhibitor therapy.

FLT3 and KIT mutated pediatric acute myeloid leukemia (AML) samples are sensitive in vitro to the tyrosine kinase inhibitor SU11657

New treatment strategies to improve the outcome of pediatric acute myeloid leukemia (AML) are required as 40% of children diagnosed with AML do not survive. Around 30% of pediatric AML patients harbour a mutation in the tyrosine kinases FLT3 (+/-20%) or KIT (+/-10%). In this study we investigated whether pediatric AML samples (N=61) were sensitive to the tyrosine kinase inhibitor SU11657 (similar to the clinically available drug sunitinib) in vitro, and whether sensitivity was related to expression of, and mutations in, FLT3 and KIT. Overall, SU11657 showed only moderate cytotoxicity. A FLT3 mutation was detected in 35% and a KIT mutation in 8% of the samples. FLT3 and KIT mutated samples were significantly more sensitive to SU11657 than WT KIT and FLT3 samples. Samples without KIT or FLT3 mutations, but with a high wild-type (WT) KIT expression were significantly more sensitive to SU11657 than samples with low KIT expression. Further clinical evaluation of SU11657 and sunitinib combined with chemotherapy would be of interest. Inclusion in clinical trials should not be restricted to patients with FLT3 or KIT mutations.

Phase I/II study of combination therapy with sorafenib, idarubicin, and cytarabine in younger patients with acute myeloid leukemia

PURPOSE To determine the efficacy and toxicity of the combination of sorafenib, cytarabine, and idarubicin in patients with acute myeloid leukemia (AML) younger than age 65 years. PATIENTS AND METHODS In the phase I part of the study, 10 patients with relapsed AML were treated with escalating doses of sorafenib with chemotherapy to establish the feasibility of the combination. We then treated 51 patients (median age, 53 years; range, 18 to 65 years) who had previously untreated AML with cytarabine at 1.5 g/m(2) by continuous intravenous (IV) infusion daily for 4 days (3 days if > 60 years of age), idarubicin at 12 mg/m(2) IV daily for 3 days, and sorafenib at 400 mg orally twice daily for 7 days. RESULTS Overall, 38 (75%) patients have achieved a complete remission (CR), including 14 (93%) of 15 patients with mutated FMS-like tyrosine kinase-3 (FLT3; the 15th patient had complete remission with incomplete platelet recovery [CRp]) and 24 (66%) of 36 patients with FLT3 wild-type (WT) disease (three additional FLT3-WT patients had CRp). FLT3-mutated patients were more likely to achieve a CR than FLT3-WT patients (P = .033). With a median follow-up of 54 weeks (range, 8 to 87 weeks), the probability of survival at 1 year is 74%. Among the FLT3-mutated patients, 10 have relapsed and five remain in CR with a median follow-up of 62 weeks (range, 10 to 76 weeks). Plasma inhibitory assay demonstrated an on-target effect on FLT3 kinase activity. CONCLUSION Sorafenib can be safely combined with chemotherapy, produces a high CR rate in FLT3-mutated patients, and inhibits FLT3 signaling.

FLT3-ITD expression levels and their effect on STAT5 in AML with and without NPM mutations

FLT3-internal tandem duplication (ITD) mutations are heterogeneous with regards to length and proportion of DNA harbouring the mutation and the expression level of FLT3 also varies widely, however very little is known about the biological effects of these variables. We studied FLT3-associated biological parameters in 322 acute myeloid leukaemia samples to establish their importance. Expression of total FLT3 transcripts was shown to be significantly higher in the FLT3-ITD cohort (n = 121) compared to the wild-type cohort (P = 0.004). Whilst phosphorylated signal transducer and activator of transcription 5 (phospho-STAT5) was not confined to FLT3-ITD samples, within the FLT3-ITD group phosphorylation correlated with adjusted FLT3-ITD levels assessed by determining the total transcripts and proportion of FLT3-ITD within a sample. Expression of the STAT5 downstream target Bcl-xl (an isoform of BCL2L1) was strongly correlated with FLT3 total and adjusted FLT3-ITD levels in FLT3-ITD samples (P < 0.001), however there was no association between Bcl-xl and phospho-STAT5 levels suggesting that STAT5 is not the sole regulator of Bcl-xl in FLT3-ITD cells. We further stratified our cohort by the presence/absence of a cytoplasmic nucleophosmin NPMc+ mutation. Samples co-expressing NPMc+ had longer FLT3-ITD mutations (P = 0.01) and there was a high occurrence of NPMc+ in samples that had >1 FLT3-ITD mutation. Phospho-STAT5 levels were reduced in the FLT3-ITD/NPMc+ group (P = 0.04) suggesting that NPMc+ may oppose the FLT3-ITD-dependent activation of STAT5.

Insertion of FLT3 internal tandem duplication in the tyrosine kinase domain-1 is associated with resistance to chemotherapy and inferior outcome

To evaluate internal tandem duplication (ITD) insertion sites and length as well as their clinical impact in younger adult patients with FLT3-ITD-positive acute myeloid leukemia (AML), sequencing after DNA-based amplification was performed in diagnostic samples from 241 FLT3-ITD-mutated patients. All patients were treated on 3 German-Austrian AML Study Group protocols. Thirty-four of the 241 patients had more than 1 ITD, leading to a total of 282 ITDs; the median ITD length was 48 nucleotides (range, 15-180 nucleotides). ITD integration sites were categorized according to functional regions of the FLT3 receptor: juxtamembrane domain (JMD), n = 148; JMD hinge region, n = 48; beta1-sheet of the tyrosine kinase domain-1 (TKD1), n = 73; remaining TKD1 region, n = 13. ITD length was strongly correlated with functional regions (P < .001). In multivariable analyses, ITD integration site in the beta1-sheet was identified as an unfavorable prognostic factor for achievement of a complete remission (odds ratio, 0.22; P = .01), relapse-free survival (hazard ratio, 1.86; P < .001), and overall survival (hazard ratio, 1.59; P = .008). ITD insertion site in the beta1-sheet appears to be an important unfavorable prognostic factor in young adult patients with FLT3-ITD-positive AML. The clinical trials described herein have been registered as follows: AML HD93 (already published in 2003), AML HD98A (NCT00146120; http://www.ClinicalTrials.gov), and AMLSG 07-04 (NCT00151242; http://www.ClinicalTrials.gov).

Thalidomide and lenalidomide: Mechanism-based potential drug combinations

Thalidomide and its analogue lenalidomide are potent anti-inflammatory, anti-angiogenic and immunomodulatory drugs, successfully used for the treatment of hematological cancers, in particular multiple myeloma (MM). Both drugs reveal a dual mechanism of action: they target tumour cells by direct cytotoxicity and, indirectly, by interfering with several components of the bone marrow microenvironment. Lenalidomide and thalidomide are versatile drugs with a broad range of activities that potentiate the anti-MM effects of conventional and novel agents. Here, we review the mechanism of action of these drugs, providing a rationale for combination studies in order to improve patient outcome and reduce side effects.

VTD combination therapy with bortezomib-thalidomide-dexamethasone is highly effective in advanced and refractory multiple myeloma

Bortezomib (V) was combined with thalidomide (T) and dexamethasone (D) in a phase I/II trial to determine dose-limiting toxicities (DLT's) and clinical activity of the VTD regimen in 85 patients with advanced and refractory myeloma. The starting dose of V was 1.0 mg/m(2) (days 1, 4, 8, 11, every 21 day) with T added from cycle 2 at 50 mg/day, with 50 mg increments per 10 patient cohorts, to a maximum dose of 200 mg. In the absence of DLT's, the same reiteration of T dose increases was applied with a higher dose of V=1.3 mg/m(2). D was added with cycle 4 in the absence of partial response (PR). Ninety-two percent had prior autotransplants, 74% had prior T and 76% abnormal cytogenetics. MTD was reached at V=1.3 mg/m(2) and T=150 mg. Minor response (MR) was recorded in 79%, and 63% achieved PR including 22% who qualified for near-complete remission. At 4 years, 6% remain event-free and 23% alive. Both OS and EFS were significantly longer in the absence of prior T exposure and when at least MR status was attained. The MMSET/FGFR3 molecular subtype was prognostically favorable, a finding since reported for a VTD-incorporating tandem transplant trial (Total Therapy 3) for untreated patients with myeloma (BJH 2008).

The impact of FLT3 internal tandem duplication mutant level, number, size, and interaction with NPM1 mutations in a large cohort of young adult patients with acute myeloid leukemia

An internal tandem duplication in the fms-like tyrosine kinase 3 gene (FLT3/ITD) is associated with poor prognosis in acute myeloid leukemia (AML), but the impact of mutant level, size, and interaction with nucleophosmin 1 (NPM1) mutations remains controversial. We evaluated these characteristics in a large cohort of young adult AML patients. There was a highly significant trend for worsening in relapse risk (RR) and overall survival (OS) with increasing FLT3/ITD mutant level (P < .001 for both), and even in the low level mutant group (1%-24% of total FLT3 alleles), RR was significantly worse than in the FLT3 wild-type (WT) group (P < .001). In multivariate analysis, mutant level was the most powerful prognostic factor for RR. Mutant size and number had no significant impact on outcome. The beneficial impact of an NPM1 mutation on RR and OS was seen in FLT3/ITD+ as well as FLT3/WT patients; both markers were highly significant independent predictors of outcome (P < .001). Stratification using both markers identified 3 prognostic groups: good (FLT3/ITD−NPM1+), intermediate (FLT3/ITD−NPM1− or FLT3/ITD+NPM1+), and poor (FLT3/ITD+NPM1−). Patients with high FLT3/ITD mutant level (greater than 50%) or FLT3/ITD+ in the absence of an NPM1 mutation may be good candidates for more experimental therapeutic approaches.

Cooperating gene mutations in acute myeloid leukemia: a review of the literature

Acute myeloid leukemia (AML) is a heterogeneous group of neoplastic disorders with great variability in clinical course and response to therapy, as well as in the genetic and molecular basis of the pathology. Major advances in the understanding of leukemogenesis have been made by the characterization and the study of acquired cytogenetic abnormalities, particularly reciprocal translocations observed in AML. Besides these major cytogenetic abnormalities, gene mutations also constitute key events in AML pathogenesis. In this review, we describe the contribution of known gene mutations to the understanding of AML pathogenesis and their clinical significance. To gain more insight in this understanding, we clustered these alterations in three groups: (1) mutations affecting genes that contribute to cell proliferation (FLT3, c-KIT, RAS, protein tyrosine standard phosphatase nonreceptor 11); (2) mutations affecting genes involved in myeloid differentiation (AML1 and CEBPA) and (3) mutations affecting genes implicated in cell cycle regulation or apoptosis (P53, NPM1). This nonexhaustive review aims to show how gene mutations interact with each other, how they contribute to refine prognosis and how they can be useful for risk-adapted therapeutic management of AML patients.

An update on drug combinations for treatment of myeloma

Multiple myeloma is the second most common haematological malignancy. It is becoming increasingly manageable with conventional and high-dose chemotherapy but there remains a critical need to develop both new drugs and combinations to improve long-term outcomes. Novel biological therapies that specifically target myeloma cells and/or their microenvironmental interactions are being developed that are highly effective, both as single agents and as combinations. Chief among these new agents are the proteasome inhibitor, bortezomib, and the immunomodulatory agents, thalidomide and lenalidomide. These drugs show improved single agent activity that is enhanced in combination. However, many drugs that are being developed in this setting may only have limited single agent activity, but combination use with these and other agents represents a very exciting way of targeting important pathogenic pathways crucial in myeloma development. This represents a challenge for both drug development and clinical trial evaluation, which has the potential to revolutionise the clinical management of myeloma and a paradigm for drug development in other diseases.

Lenalidomide in the treatment of multiple myeloma

PURPOSE

The pharmacology, clinical use, adverse effects, dosage and administration, and cost of lenalidomide in the treatment of multiple myeloma (MM) are reviewed.

SUMMARY

Lenalidomide is an analogue of thalidomide and has been shown to be more potent than thalidomide in the stimulation of T-cell, interleukin-2, and interferon-gamma production. Both drugs have direct cytotoxic effects on myeloma cells and are capable of inducing apoptosis. They are also capable of reducing angiogenesis through the inhibition of the secretion of vascular endothelial growth factor (VEGF). Inhibition of VEGF leads to alterations in the microvasculature of the bone marrow environment and inhibits myeloma cell growth and proliferation. Unlike thalidomide, lenalidomide has almost no sedative or constipative properties and induces only minimal neurotoxicity; however, there is concern about lenalidomide's teratogenic potential. Phase I, II, and III trials have been carried out with lenalidomide in patients with relapsed or refractory MM, and the drug has shown impressive response rates in relapsed disease. The combination of lenalidomide and dexamethasone has shown superior patient survival. Lenalidomide's efficacy in newly diagnosed MM is currently being studied. Neutropenia and thrombocytopenia were found to be the most common grade 3 or higher toxicities. Rates of these toxicities varied among trials and may have been affected by the setting in which lenalidomide was used (i.e., relapsed or refractory disease versus newly diagnosed MM).

CONCLUSION

Lenalidomide, a thalidomide analogue, has produced good results when used with dexamethasone in patients with relapsed or refractory MM. Lenalidomide is associated with hematologic toxicities, and participation in a restricted-distribution program is required of prescribers, pharmacies, and patients because of the drug's teratogenic potential.

Arginine 595 is duplicated in patients with acute leukemias carrying internal tandem duplications of FLT3 and modulates its transforming potential

FLT3–internal tandem duplications (FLT3-ITDs) comprise a heterogeneous group of mutations in patients with acute leukemias that are prognostically important. To characterize the mechanism of transformation by FLT3-ITDs, we sequenced the juxtamembrane region (JM) of FLT3 from 284 patients with acute leukemias. The length of FLT3-ITDs varied from 2 to 42 amino acids (AAs) with a median of 17 AAs. The analysis of duplicated AAs showed that in the majority of patients, the duplications localize between AAs 591 to 599 (YVDFREYEY). Arginine 595 (R595) within this region is duplicated in 77% of patients. Single duplication of R595 in FLT3 conferred factor-independent growth to Ba/F3 cells and activated STAT5. Moreover, deletion or substitution of the duplicated R595 in 2 FLT3-ITD constructs as well as the deletion of wild-type R595 in FLT3-ITD substantially reduced the transforming potential and STAT5 activation, pointing to a critical role of the positive charge of R595 in stabilizing the active confirmation of FLT3-ITDs. Deletion of R595 in FLT3-WT nearly abrogated the ligand-dependent activation of FLT3-WT. Our data provide important insights into the molecular mechanism of transformation by FLT3-ITDs and show that duplication of R595 is important for the leukemic potential of FLT3-ITDs.