The mutational spectrum of FLT3 gene in acute lymphoblastic leukemia is different from acute myeloid leukemia

Deep Learning Techniques to Characterize the RPS28P7 Pseudogene and the Metazoa-SRP Gene as Drug Potential Targets in Pancreatic Cancer Patients

The molecular explanation about why some pancreatic cancer (PaCa) patients die early and others die later is poorly understood. This study aimed to discover potential novel markers and drug targets that could be useful to stratify and extend expected survival in prospective early-death patients. We deployed a deep learning algorithm and analyzed the gene copy number, gene expression, and protein expression data of death versus alive PaCa patients from the GDC cohort. The genes with higher relative amplification (copy number >4 times in the dead compared with the alive group) were EWSR1, FLT3, GPC3, HIF1A, HLF, and MEN1. The most highly up-regulated genes (>8.5-fold change) in the death group were RPL30, RPL37, RPS28P7, RPS11, Metazoa_SRP, CAPNS1, FN1, H3-3B, LCN2, and OAZ1. None of their corresponding proteins were up or down-regulated in the death group. The mRNA of the RPS28P7 pseudogene could act as ceRNA sponging the miRNA that was originally directed to the parental gene RPS28. We propose RPS28P7 mRNA as the most druggable target that can be modulated with small molecules or the RNA technology approach. These markers could be added as criteria to patient stratification in future PaCa drug trials, but further validation in the target populations is encouraged.

Deep Learning Techniques to Characterize the RPS28P7 Pseudogene and the Metazoa-SRP Gene as Drug Potential Targets in Pancreatic Cancer Patients

The molecular explanation about why some pancreatic cancer (PaCa) patients die early and others die later is poorly understood. This study aimed to discover potential novel markers and drug targets that could be useful to stratify and extend expected survival in prospective early-death patients. We deployed a deep learning algorithm and analyzed the gene copy number, gene expression, and protein expression data of death versus alive PaCa patients from the GDC cohort. The genes with higher relative amplification (copy number >4 times in the dead compared with the alive group) were EWSR1, FLT3, GPC3, HIF1A, HLF, and MEN1. The most highly up-regulated genes (>8.5-fold change) in the death group were RPL30, RPL37, RPS28P7, RPS11, Metazoa_SRP, CAPNS1, FN1, H3−3B, LCN2, and OAZ1. None of their corresponding proteins were up or down-regulated in the death group. The mRNA of the RPS28P7 pseudogene could act as ceRNA sponging the miRNA that was originally directed to the parental gene RPS28. We propose RPS28P7 mRNA as the most druggable target that can be modulated with small molecules or the RNA technology approach. These markers could be added as criteria to patient stratification in future PaCa drug trials, but further validation in the target populations is encouraged.

Human and mouse early B cell development: So similar but so different

Early B cell development in the bone marrow ensures the replenishment of the peripheral B cell pool. Immature B cells continuously develop from hematopoietic stem cells, in a process guided by an intricate network of transcription factors as well as chemokine and cytokine signals. Humans and mice possess somewhat similar regulatory mechanisms of B lymphopoiesis. The continuous discovery of monogenetic defects that impact early B cell development in humans substantiates the similarities and differences with B cell development in mice. These differences become relevant when targeted therapeutic approaches are used in patients; therefore, predicting potential immunological adverse events is crucial. In this review, we have provided a phenotypical classification of human and murine early progenitors and B cell stages, based on surface and intracellular protein expression. Further, we have critically compared the role of key transcription factors (Ikaros, E2A, EBF1, PAX5, and Aiolos) and chemo- or cytokine signals (FLT3, c-kit, IL-7R, and CXCR4) during homeostatic and aberrant B lymphopoiesis in both humans and mice.

In vivo activity of the dual SYK/FLT3 inhibitor TAK-659 against pediatric acute lymphoblastic leukemia xenografts

BACKGROUND

While children with acute lymphoblastic leukemia (ALL) experience close to a 90% likelihood of cure, the outcome for certain high-risk pediatric ALL subtypes remains dismal. Spleen tyrosine kinase (SYK) is a prominent cytosolic nonreceptor tyrosine kinase in pediatric B-lineage ALL (B-ALL). Activating mutations or overexpression of Fms-related receptor tyrosine kinase 3 (FLT3) are associated with poor outcome in hematological malignancies. TAK-659 (mivavotinib) is a dual SYK/FLT3 reversible inhibitor, which has been clinically evaluated in several other hematological malignancies. Here, we investigate the in vivo efficacy of TAK-659 against pediatric ALL patient-derived xenografts (PDXs).

METHODS

SYK and FLT3 mRNA expression was quantified by RNA-seq. PDX engraftment and drug responses in NSG mice were evaluated by enumerating the proportion of human CD45+ cells (%huCD45+ ) in the peripheral blood. TAK-659 was administered per oral at 60 mg/kg daily for 21 days. Events were defined as %huCD45+ ≥ 25%. In addition, mice were humanely killed to assess leukemia infiltration in the spleen and bone marrow (BM). Drug efficacy was assessed by event-free survival and stringent objective response measures.

RESULTS

FLT3 and SYK mRNA expression was significantly higher in B-lineage compared with T-lineage PDXs. TAK-659 was well tolerated and significantly prolonged the time to event in six out of eight PDXs tested. However, only one PDX achieved an objective response. The minimum mean %huCD45+ was significantly reduced in five out of eight PDXs in TAK-659-treated mice compared with vehicle controls.

CONCLUSIONS

TAK-659 exhibited low to moderate single-agent in vivo activity against pediatric ALL PDXs representative of diverse subtypes.

Mutation spectrum of FLT3 and significance of non-canonical FLT3 mutations in haematological malignancy

Fms-like tyrosine kinase 3 (FLT3) is frequently mutated in haematological malignancies. Although canonical FLT3 mutations including internal tandem duplications (ITDs) and tyrosine kinase domains (TKDs) have been extensively studied, little is known about the clinical significance of non-canonical FLT3 mutations. Here, we first profiled the spectrum of FLT3 mutations in 869 consecutively newly diagnosed acute myeloid leukaemia (AML), myelodysplastic syndrome and acute lymphoblastic leukaemia patients. Our results showed four types of non-canonical FLT3 mutations depending on the affected protein structure: namely non-canonical point mutations (NCPMs) (19.2%), deletion (0.7%), frameshift (0.8%) and ITD outside the juxtamembrane domain (JMD) and TKD1 regions (0.5%). Furthermore, we found that the survival of patients with high-frequency (>1%) FLT3-NCPM in AML was comparable to those with canonical TKD. In vitro studies using seven representative FLT3-deletion or frameshift mutant constructs showed that the deletion mutants of TKD1 and the FLT3-ITD mutant of TKD2 had significantly higher kinase activity than wild-type FLT3, whereas the deletion mutants of JMD had phosphorylation levels comparable with wild-type FLT3. All tested deletion mutations and ITD were sensitive to AC220 and sorafenib. Collectively, these data enrich our understanding of FLT3 non-canonical mutations in haematological malignancies. Our results may also facilitate prognostic stratification and targeted therapy of AML with FLT3 non-canonical mutations.

Targeting Proliferation Signals and the Cell Cycle Machinery in Acute Leukemias: Novel Molecules on the Horizon

Uncontrolled proliferative signals and cell cycle dysregulation due to genomic or functional alterations are important drivers of the expansion of undifferentiated blast cells in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) cells. Therefore, they are largely studied as potential therapeutic targets in the field. We here present the most recent advancements in the evaluation of novel compounds targeting cell cycle proteins or oncogenic mechanisms, including those showing an antiproliferative effect in acute leukemia, independently of the identification of a specific target. Several new kinase inhibitors have been synthesized that showed effectiveness in a nanomolar to micromolar concentration range as inhibitors of FLT3 and its mutant forms, a highly attractive therapeutic target due to its driver role in a significant fraction of AML cases. Moreover, we introduce novel molecules functioning as microtubule-depolymerizing or P53-restoring agents, G-quadruplex-stabilizing molecules and CDK2, CHK1, PI3Kδ, STAT5, BRD4 and BRPF1 inhibitors. We here discuss their mechanisms of action, including the downstream intracellular changes induced by in vitro treatment, hematopoietic toxicity, in vivo bio-availability and efficacy in murine xenograft models. The promising activity profile demonstrated by some of these candidates deserves further development towards clinical investigation.

PAX5 and TDT-Negative B-Acute Lymphoblastic Leukemia with Unusual Genetic Mutations: A Case Report

B-acute lymphoblastic leukemia (B-ALL) is commonly encountered in clinical practice. Patients present with increased percentage of lymphoblasts in bone marrow and/or peripheral blood. Immunophenotypic study by flow cytometry or immunohistochemistry is essential to establish the diagnosis. Paired box-5 (PAX5) is a B cell lineage protein and terminal deoxynucleotidyl transferase (TDT) is an immature marker, both of which are routinely tested in the pathologic workup of acute leukemia. In this report, we describe a case of B-ALL in a 37-year-old woman in which both PAX5 and TDT were negative. Next-generation sequencing test detected mutations in DNA methyltransferase 3 α and Fms related receptor tyrosine kinase 3 genes, which are frequently mutated in acute myeloid leukemia rather than B-ALL. The constellation of these rare findings in a single case signifies the importance of examining a wide panel of markers when the diagnosis of ALL is suspected.

Tyrosine kinases in KMT2A/MLL-rearranged acute leukemias as potential therapeutic targets to overcome cancer drug resistance

Aim: The main goal of this study was to elucidate at the transcript level the tyrosine kinase expression profiles of primary leukemia cells from mixed lineage leukemia 1 gene rearranged (KMT2A/MLL-R⁺) acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) patients. Methods: We evaluated protein tyrosine kinase (PTK) gene expression profiles of primary leukemic cells in KMT2A/MLL-R⁺ AML and ALL patients using publicly available archived datasets. Results: Our studies provided unprecedented evidence that the genetic signatures of KMT2A/MLL-R⁺ AML and ALL cells are characterized by transcript-level overexpression of specific PTK. In infants, children and adults with KMT2A/MLL-R⁺ ALL, as well as pediatric patients with KMT2A/MLL-R⁺ AML, the gene expression levels for FLT3, BTK, SYK, JAK2/JAK3, as well as several SRC family PTK were differentially amplified. In adults with KMT2A/MLL-R⁺ AML, the gene expression levels for SYK, JAK family kinase TYK2, and the SRC family kinases FGR and HCK were differentially amplified. Conclusion: These results provide new insights regarding the clinical potential of small molecule inhibitors of these PTK, many of which are already FDA/EMA-approved for other indications, as components of innovative multi-modality treatment platforms against KMT2A/MLL-R⁺ acute leukemias.

Developments and challenges of FLT3 inhibitors in acute myeloid leukemia

FLT3 mutations are one of the most common genetic alterations in acute myeloid leukemia (AML) and are identified in approximately one-third of newly diagnosed patients. Aberrant FLT3 receptor signaling has important implications for the biology and clinical management of AML. In recent years, targeting FLT3 has been a part of every course of treatment in FLT3-ITD/TKD-mutated AML and contributes to substantially prolonged survival. At the same time, wide application of next-generation sequencing (NGS) technology has revealed a series of non-canonical FLT3 mutations, including point mutations and small insertions/deletions. Some of these mutations may be able to influence downstream phosphorylation and sensitivity to FLT3 inhibitors, while the correlation with clinical outcomes remains unclear. Exploration of FLT3-targeted therapy has made substantial progress, but resistance to FLT3 inhibitors has become a pressing issue. The mechanisms underlying FLT3 inhibitor tolerance can be roughly divided into primary resistance and secondary resistance. Primary resistance is related to abnormalities in signaling factors, such as FL, CXCL12, and FGF2, and secondary resistance mainly involves on-target mutations and off-target aberrations. To overcome this problem, novel agents such as FF-10101 have shown promising potential. Multitarget strategies directed at FLT3 and anomalous signaling factors simultaneously are in active clinical development and show promising results.

Point Mutations in the FLT3-ITD Region Are Rare but Recurrent Alterations in Adult AML and Associated With Concomitant KMT2A-PTD

FLT3-ITD mutations are common druggable alterations in patients with acute myeloid leukemia (AML) and associated with poor prognosis. Beside typical ITD mutations, point mutations and deletions in the juxtamembrane domain (JMD) have been observed. However, due to the low frequency of these alterations, there is only limited information on molecular and clinical associations. To evaluate the prognostic impact of non-ITD mutations in the FLT3 JMD region, we analyzed a large cohort of 1,539 adult AML patients treated in different protocols of the Study Alliance Leukemia, using next-generation sequencing. Non-ITD point mutations and deletions within the FLT3 JMD were identified with a prevalence of ~1.23% (n = 19). Both FLT3-ITD and non-ITD mutations were associated with a higher rate of NPM1 (42%-61%; p < 0.001) and DNMT3A mutations (37%-43%; p < 0.001), as well as an increased percentage of peripheral blood (54%-65%) and bone marrow blast cells (74%; p < 0.001), compared to FLT3-wild-type patients. Most significantly, AML patients with FLT3 non-ITD mutations had a higher rate of concomitant KMT2A-PTD mutations (37.5%; p < 0.001) as compared to FLT3-ITD (7%) or FLT3-wild-type cases (4.5%). In a multivariable analysis, FLT3 non-ITD mutations were not an independent prognostic factor. However, patients with dual FLT3 non-ITD and KMT2A-PTD mutations showed a trend for inferior outcome, which points at a functional interaction in this subset of AML.

The Structural Effect of FLT3 Mutations at 835th Position and Their Interaction with Acute Myeloid Leukemia Inhibitors: In Silico Approach

FMS-like tyrosine kinase 3 (FLT3) gene mutations have been found in more than one-third of Acute Myeloid Leukemia (AML) cases. The most common point mutation in FLT3 occurs at the 835th residue (D835A/E/F/G/H/I/N/V/Y), in the activation loop region. The D835 residue is critical in maintaining FLT3 inactive conformation; these mutations might influence the interaction with clinically approved AML inhibitors used to treat the AML. The molecular mechanism of each of these mutations and their interactions with AML inhibitors at the atomic level is still unknown. In this manuscript, we have investigated the structural consequence of native and mutant FLT-3 proteins and their molecular mechanisms at the atomic level, using molecular dynamics simulations (MDS). In addition, we use the molecular docking method to investigate the binding pattern between the FLT-3 protein and AML inhibitors upon mutations. This study apparently elucidates that, due to mutations in the D835, the FLT-3 structure loses its conformation and becomes more flexible compared to the native FLT3 protein. These structural changes are suggested to contribute to the relapse and resistance responses to AML inhibitors. Identifying the effects of FLT3 at the molecular level will aid in developing a personalized therapeutic strategy for treating patients with FLT-3-associated AML.

Targeting Leukemia-Initiating Cells in Acute Lymphoblastic Leukemia

The concept that different leukemias are developmentally distinct and, like in normal hematopoiesis, generated by restricted populations of cells named leukemia-initiating cells (LIC), is becoming more established. These cancer stem-like cells have been assumed to have unique properties, including the capability of self-renewing and giving rise to "differentiated" or non-LICs that make up the whole tumor. Cell populations enriched with LIC activity have been characterized in different hematopoietic malignancies, including human acute lymphoblastic leukemia (ALL). Related studies have also demonstrated that LICs are functionally distinct from bulk cells and modulated by distinct molecular signaling pathways and epigenetic mechanisms. Here we review several biological and clinical aspects related to LICs in ALL, including (i) immunophenotypic characterization of LIC-enriched subsets in human and mouse models of ALL, (ii) emerging therapeutics against regulatory signaling pathways involved in LIC progression and maintenance in T- and B-cell leukemias, (iii) novel epigenetic and age-related mechanisms of LIC propagation, and (iv) ongoing efforts in immunotherapy to eradicate LIC-enriched cell subsets in relapsed and refractory ALL cases. Current conventional treatments do not efficiently eliminate LICs. Therefore, innovative therapeutics that exclusively target LICs hold great promise for developing an effective cure for ALL.

Protein Tyrosine Kinases: Their Roles and Their Targeting in Leukemia

Simple Summary

Protein phosphorylation is a key regulatory mechanism that controls a wide variety of cellular responses. This process is catalysed by the members of the protein kinase superfamily that are classified into two main families based on their ability to phosphorylate either tyrosine or serine and threonine residues in their substrates. Massive research efforts have been invested in dissecting the functions of tyrosine kinases, revealing their importance in the initiation and progression of human malignancies. Based on these investigations, numerous tyrosine kinase inhibitors have been included in clinical protocols and proved to be effective in targeted therapies for various haematological malignancies. In this review, we provide insights into the role of tyrosine kinases in leukaemia and discuss their targeting for therapeutic purposes with the currently available inhibitory compounds.

Abstract

Protein kinases constitute a large group of enzymes catalysing protein phosphorylation and controlling multiple signalling events. The human protein kinase superfamily consists of 518 members and represents a complicated system with intricate internal and external interactions. Protein kinases are classified into two main families based on the ability to phosphorylate either tyrosine or serine and threonine residues. Among the 90 tyrosine kinase genes, 58 are receptor types classified into 20 groups and 32 are of the nonreceptor types distributed into 10 groups. Tyrosine kinases execute their biological functions by controlling a variety of cellular responses, such as cell division, metabolism, migration, cell–cell and cell matrix adhesion, cell survival and apoptosis. Over the last 30 years, a major focus of research has been directed towards cancer-associated tyrosine kinases owing to their critical contributions to the development and aggressiveness of human malignancies through the pathological effects on cell behaviour. Leukaemia represents a heterogeneous group of haematological malignancies, characterised by an uncontrolled proliferation of undifferentiated hematopoietic cells or leukaemia blasts, mostly derived from bone marrow. They are usually classified as chronic or acute, depending on the rates of their progression, as well as myeloid or lymphoblastic, according to the type of blood cells involved. Overall, these malignancies are relatively common amongst both children and adults. In malignant haematopoiesis, multiple tyrosine kinases of both receptor and nonreceptor types, including AXL receptor tyrosine kinase (AXL), Discoidin domain receptor 1 (DDR1), Vascular endothelial growth factor receptor (VEGFR), Fibroblast growth factor receptor (FGFR), Mesenchymal–epithelial transition factor (MET), proto-oncogene c-Src (SRC), Spleen tyrosine kinase (SYK) and pro-oncogenic Abelson tyrosine-protein kinase 1 (ABL1) mutants, are implicated in the pathogenesis and drug resistance of practically all types of leukaemia. The role of ABL1 kinase mutants and their therapeutic inhibitors have been extensively analysed in scientific literature, and therefore, in this review, we provide insights into the impact and mechanism of action of other tyrosine kinases involved in the development and progression of human leukaemia and discuss the currently available and emerging treatment options based on targeting these molecules.

FLT3-ITD and CD135 Over-Expression are Frequent Findings of Poor Survival in Adult Patients with Acute Leukemias

BACKGROUND

Fms-like tyrosine kinase 3 (FLT3) expression and mutation have been considered a poor prognostic factor in acute myeloid leukemia (AML). FLT3-ITD mutation is present in 30% of adult patients with AML and 2-5% in childhood acute lymphoblastic leukemia (ALL). The impact of these mutations on the prognosis of ALL patients, has not yet been established. Moreover, a limited number of publications regarding the level of expression of the FLT3 receptor (CD135) in both leukemias exist. This study aimed to analyze the clinical outcomes associated to the presence of FLT3-ITD mutation and the expression of CD135.

METHODS

82 adult patients with newly diagnosed acute leukemia (39 with AML and 43 with ALL) were included. Flow cytometry and RT-PCR were done to analyze the expression of CD135 and the presence of FLT3 ITD mutation, respectively.

RESULTS

FLT3-ITD was present in 14 (36%) of AML and 15 (35%) of ALL patients. Disease free survival (DFS) and overall survival (OS) were lower in ALL patients having a CD135 expression >3000 cells/μL. There was a trend for poor OS in AML patients expressing FLT3 ITD. OS was worse in AML patients with high expression of CD135.

CONCLUSION

A higher (35%) frequency of FLT3-ITD was found in adult ALL patients. The presence of FLT3-ITD was associated with a trend of poor OS in AML cases, and overexpression of CD135 was correlated with poor DFS in ALL cases and poor OS in both acute leukemias.

Profiling FLT3 Mutations in Mexican Acute Myeloid Leukemia Pediatric Patients: Impact on Overall Survival

Background: Acute myeloid leukemia (AML) is the second most frequent leukemia in childhood. The FLT3 gene participates in hematopoietic stem cell proliferation. FLT3 mutations are recurrent in AML and influence prognosis. In Mexican pediatric AML patients, FLT3 mutational profile, and their clinical impact have not been evaluated. Aim of the study: This study aimed to identify the profile of FLT3 mutations in pediatric patients with de novo AML and to assess their possible influence on overall survival (OS) and other clinical features. Methods: Massive parallel target sequencing of FLT3 was performed in 80 patients. Results: FLT3 mutations [internal tandem duplication (ITD) or tyrosine kinase domain (TKD)] were identified in 24% of them. OS was significantly lower in FLT3 POS cases than in FLT3 NEG (p = 0.03). The average OS for FLT3 POS was 1.2 vs. 2.2 years in FLT3 NEG. There were no significant differences in the children's sex, age, percentage of blasts in bone marrow aspirate, or white blood cell count in peripheral blood at diagnosis between both groups. No differences were identified stratifying by the mutational load (high > 0.4) or type of mutation. The negative effect of FLT3 mutations was also observed in patients with acute promyelocytic leukemia (APL). Conclusions: FLT3 mutational profile is described in Mexican pediatric AML patients for the first time. Mutated FLT3 negatively impacts the outcome of AML patients, even considering the APL group. The clinical benefit from treatment with tyrosine kinase inhibitors in the FLT3 POS pediatric patients needs to be assessed in clinical trials. FLT3 testing may contribute to better risk stratification in our pediatric AML patients.