Molecular drug targets in myeloproliferative neoplasms: mutant ABL1, JAK2, MPL, KIT, PDGFRA, PDGFRB and FGFR1

Exploring hematological alterations and genetics linked to SNV rs10974944 in myeloproliferative neoplasms among Amazon patients

BCR::ABL1-negative myeloproliferative neoplasms are hematopoietic disorders characterized by panmyelosis. JAK2 V617F is a frequent variant in these diseases and often occurs in the 46/1 haplotype. The G allele of rs10974944 has been shown to be associated with this variant, specifically its acquisition, correlations with familial cases, and laboratory alterations. This study evaluated the association between the 46/1 haplotype and JAK2 V617F in patients with myeloproliferative neoplasms in a population from the Brazilian Amazon. Clinical, laboratory and molecular sequencing analyses were considered. Carriers of the G allele of rs10974944 with polycythemia vera showed an increase in mean corpuscular volume and mean corpuscular hemoglobin, while in those with essential thrombocythemia, there was an elevation in red blood cells, hematocrit, and hemoglobin. Associations were observed between rs10974944 and the JAK2 V617F, in which the G allele (OR 3.4; p < 0.0001) and GG genotype (OR 4.9; p = 0.0016) were associated with JAK2 V617F + and an increase in variant allele frequency (GG: OR 15.8; p =  < 0.0001; G: OR 6.0; p = 0.0002). These results suggest an association between rs10974944 (G) and a status for JAK2 V617F, JAK2 V617F + _VAF ≥ 50%, and laboratory alterations in the erythroid lineage.

Protein kinases: drug targets for immunological disorders

Protein kinases play a major role in cellular activation processes, including signal transduction by diverse immunoreceptors. Given their roles in cell growth and death and in the production of inflammatory mediators, targeting kinases has proven to be an effective treatment strategy, initially as anticancer therapies, but shortly thereafter in immune-mediated diseases. Herein, we provide an overview of the status of small molecule inhibitors specifically generated to target protein kinases relevant to immune cell function, with an emphasis on those approved for the treatment of immune-mediated diseases. The development of inhibitors of Janus kinases that target cytokine receptor signalling has been a particularly active area, with Janus kinase inhibitors being approved for the treatment of multiple autoimmune and allergic diseases as well as COVID-19. In addition, TEC family kinase inhibitors (including Bruton's tyrosine kinase inhibitors) targeting antigen receptor signalling have been approved for haematological malignancies and graft versus host disease. This experience provides multiple important lessons regarding the importance (or not) of selectivity and the limits to which genetic information informs efficacy and safety. Many new agents are being generated, along with new approaches for targeting kinases.

The differences of hemogram, myelogram, and driver gene mutations in classic myeloproliferative neoplasms

The aim of this study was to explore and compare routine blood features and pathological characteristics of bone marrow tissues in essential thrombocythemia (ET), polycythemia vera (PV), primary myelofibrosis, prefibrotic stage (prePMF) and overt fibrotic stage (overtPMF), and the correlation between common driver gene mutations and clinical manifestations of myeloproliferative neoplasms (MPN). Methods: We analyzed 259 MPN patients treated at Tongji Hospital of Huazhong University of Science and Technology from January 2016 to December 2020. Results: Among ET, PV, prePMF, and overtPMF, the median leukocyte counts of PV and prePMF were significantly higher than those of ET. The average hemoglobin level of overtPMF was significantly lower than that of ET, PV, and prePMF. ET and prePMF had higher platelet counts than PV and overtPMF, whereas ET had the lowest platelet distribution width. Regarding hematopoietic tissues in the bone marrow, enlarged megakaryocytes were easily found in ET, PV, and prePMF, whereas the average diameter of megakaryocytes in prePMF was smaller than in ET, and PV showed various sizes of megakaryocytes. An increased M/E ratio and dilation of sinus were seen more frequently in PMF. Additionally, JAK2-positive patients tended to have significantly higher leukocyte counts than CALR-positive patients in ET and PMF.

An optimized targeted Next-Generation Sequencing approach for sensitive detection of single nucleotide variants

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NGS based detection of low-level SNVs is feasible with sensitivities up to 10⁻⁴.

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PCR-induced bias could be significantly reduced by the choice of adequate enzymes.

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The prevalent transition vs. transversion bias affects site-specific detection limits.

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Results from clinical data validated the feasibility of NGS-based MRD detection.

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Results help to select suitable biomarkers for MRD quantification.

Monitoring of minimal residual disease (MRD) has become an important clinical aspect for early relapse detection during follow-up care after cancer treatment. Still, the sensitive detection of single base pair point mutations via Next-Generation Sequencing (NGS) is hampered mainly due to high substitution error rates. We evaluated the use of NGS for the detection of low-level variants on an Ion Torrent PGM system. As a model case we used the c.1849G > T (p.Val617Phe) mutation of the JAK2-gene. Several reaction parameters (e.g. choice of DNA-polymerase) were evaluated and a comprehensive analysis of substitution errors was performed. Using optimized conditions, we reliably detected JAK2 c.1849G > T VAFs in the range of 0.01–0.0015% which, in combination with results obtained from clinical data, validated the feasibility of NGS-based MRD detection. Particularly, PCR-induced transitions (mainly G > A and C > T) were the major source of error, which could be significantly reduced by the application of proofreading enzymes. The integration of NGS results for several common point mutations in various oncogenes (i.e. IDH1 and 2, c-KIT, DNMT3A, NRAS, KRAS, BRAF) revealed that the prevalent transition vs. transversion bias (3.57:1) has an impact on site-specific detection limits of low-level mutations. These results may help to select suitable markers for MRD detection and to identify individual cut-offs for detection and quantification.

Spotlight on midostaurin in the treatment of FLT3-mutated acute myeloid leukemia and systemic mastocytosis: design, development, and potential place in therapy

The Fms-like tyrosine kinase-3 (FLT3; fetal liver kinase-2; human stem cell tyrosine kinase-1; CD135) is a class III receptor tyrosine kinase that is normally involved in regulating the proliferation, differentiation, and survival of both hematopoietic cells and dendritic cells. Mutations leading it to be constitutively activated make it an oncogenic driver in ~30% of acute myeloid leukemia (AML) patients where it is associated with poor prognosis. The prevalence of oncogenic FLT3 and the dependency on its constitutively activated kinase activity for leukemia growth make this protein an attractive target for therapeutic intervention. Of the numerous small molecule inhibitors under clinical investigation for the treatment of oncogenic FLT3-positive AML, the N-benzoyl-staurosporine, midostaurin (CGP41251; PKC412; Rydapt^®; Novartis Pharma AG, Basel, Switzerland), is the first to be approved by the US Food and Drug Administration for the treatment, in combination with standard chemotherapy, of newly diagnosed adult AML patients who harbor mutations in FLT3. Here, we describe the early design of midostaurin, the preclinical discovery of its activity against oncogenic FLT3, and its subsequent clinical development as a therapeutic agent for FLT3 mutant-positive AML.

[The study of 4 cases of myeloid neoplasm with t (5;12) (q33;p13) and the literatures review]

OBJECTIVE

To report clinical and laboratory features of 4 cases of myeloid neoplasm with t (5;12) (q33;p13).

METHODS

Cytogenetic examination of bone marrow cells obtained from patients was performed by 24 h culture method. R banding technical was used for karyotype analysis. PDGFRβ gene rearrangement was detected by FISH using dual color break apart PDGFRβ probe. ETV6-PDGFRβ fusion genes were detected by multiple-reverse transcription polymerase chain reaction (RT-PCR). Direct sequencing analysis was performed on the PCR products in case 1. Immunophenotype analysis was carried out by flow cytometry. Four cases were treated with imatinib (IM) and followed up.

RESULTS

The diagnoses included 3 MPN and 1 AML-M2. The t (5;12) (q33;p13) was a primary abnormality in 3 cases of MPN and a secondary abnormality in 1 case of AML-M2. PDGFRβ gene rearrangement and ETV6-PDGFRβ fusion genes were detected by FISH and multiple-RT-PCR in 4 cases, respectively. The immunophenotypical analysis of leukemia cells showed positive for CD13, CD33 and CD34. Two cases obtained MMR after the treatment of IM, one case complete hematologic and complete cytogenetic response. ETV6-PDGFRβ was negative detected by multiple-RT-PCR after the treatment of IM, but relapsed and died soon in case 4.

CONCLUSIONS

The t (5;12) myeloid neoplasm was a subtype with unique features. The t (5;12) maybe a primary chromosome abnormality in MPN and a secondary in AML. MPN with t (5;12) could benefit from IM, but not for AML. Dual-FISH was a reliable tool for detecting PDGFRβ rearrangement.

The Burden of JAK2V617F Mutated Allele in Turkish Patients With Myeloproliferative Neoplasms

BACKGROUND

Studies regarding the impact of JAK2V617F allele burden on phenotypic properties and clinical course in Philadelphia-negative myeloproliferative neoplasms (Ph-negative MPNs) have reported variable results. We aimed to analyze the association of mutated JAK2V617F allele burden with laboratory characteristics and clinical phenotype in Turkish patients (107 essential thrombocythemia (ET) and 77 primary myelofibrosis (PMF)).

METHODS

Peripheral blood samples of 184 patients with Ph-negative MPNs were analyzed for JAK2V617F allele status and burden. JAK2 MutaScreen assay (Ipsogen, Luminy Biotech, Marseille, France) was used to detect the JAK2V617F status and quantitative JAK2V617F allele burdens in genomic DNA using TaqMan allelic discrimination.

RESULTS

Frequency of JAK2V617F-positive patients with high mutation load (allele burden > 50%) was higher in PMF compared to ET (23.4% and 4.7%, respectively; P = 0.001). We found significant association between ET patients with high JAK2V617F allele burden and lower hemoglobin (Hgb) and hematocrit (Hct), higher LDH levels and more prevalent massive splenomegaly (P = 0.001, P = 0.001, P = 0.012 and P = 0.015, respectively). ET patients with high mutation load displayed higher prevalence of bleeding compared to low mutation load and wild-type mutational status (P = 0.003). Rate of DVT was significantly higher in ET patients with mutant allele burden in upper half compared to lower half and wild-type (P = 0.029). We observed significant association between PMF patients with high JAK2V617F allele burden and higher Hgb, Hct levels and leukocyte counts (P = 0.003, P = 0.021 and P = 0.001, respectively).

CONCLUSIONS

Our study demonstrated JAK2V617F allele burden correlates with clinical features in ET and PMF. We conclude quantification of JAK2V617F mutation contributes to the workup of Ph-negative MPNs.

JAK-STAT pathway activation in malignant and nonmalignant cells contributes to MPN pathogenesis and therapeutic response

The identification of JAK2/MPL mutations in patients with myeloproliferative neoplasms (MPN) has led to the clinical development of JAK kinase inhibitors, including ruxolitinib. Ruxolitinib reduces splenomegaly and systemic symptoms in myelofibrosis and improves overall survival; however, the mechanism by which JAK inhibitors achieve efficacy has not been delineated. Patients with MPN present with increased levels of circulating proinflammatory cytokines, which are mitigated by JAK inhibitor therapy. We sought to elucidate mechanisms by which JAK inhibitors attenuate cytokine-mediated pathophysiology. Single-cell profiling demonstrated that hematopoietic cells from myelofibrosis models and patient samples aberrantly secrete inflammatory cytokines. Pan-hematopoietic Stat3 deletion reduced disease severity and attenuated cytokine secretion, with similar efficacy as observed with ruxolitinib therapy. In contrast, Stat3 deletion restricted to MPN cells did not reduce disease severity or cytokine production. Consistent with these observations, we found that malignant and nonmalignant cells aberrantly secrete cytokines and JAK inhibition reduces cytokine production from both populations.

SIGNIFICANCE

Our results demonstrate that JAK-STAT3-mediated cytokine production from malignant and nonmalignant cells contributes to MPN pathogenesis and that JAK inhibition in both populations is required for therapeutic efficacy. These findings provide novel insight into the mechanisms by which JAK kinase inhibition achieves therapeutic efficacy in MPNs.

STAT signaling in the pathogenesis and treatment of myeloid malignancies

STAT transcription factors play a critical role in mediating the effects of cytokines on myeloid cells. As STAT target genes control key processes such as survival, proliferation and self-renewal, it is not surprising that constitutive activation of STATs, particularly STAT3 and STAT5, are common events in many myeloid tumors. STATs are activated both by mutant tyrosine kinases as well as other pathogenic events, and continued activation of STATs is common in the setting of resistance to kinase inhibitors. Thus, the targeting of STATs, alone or in combination with other drugs, will likely have increasing importance for cancer therapy.

Cytogenetics, JAK2 and MPL mutations in polycythemia vera, primary myelofibrosis and essential thrombocythemia

Background

The detection of molecular and cytogenetic alterations is important for the diagnosis, prognosis and classification of myeloproliferative neoplasms.

Objectives

The aim of this study was to detect the following mutations: JAK2 V617F, JAK2 exon 12 and MPL W515K/L, besides chromosomal abnormalities. Furthermore, molecular and cytogenetic alterations were correlated with the leukocyte and platelet counts, hemoglobin levels and age in all patients and with the degree of fibrosis in primary myelofibrosis cases.

Methods

Twenty cases of polycythemia vera, 17 of essential thrombocythemia and 21 of primary myelofibrosis were selected in the Hematology Department of the Universidade Federal de São Paulo (UNIFESP) between February 2008 and December 2009. The JAK2 V617F, JAK2 exon 12 mutations, MPL W515K and MPL W515L mutations were investigated by real-time PCR and direct sequencing. G-band karyotyping and fluorescence in situ hybridization were used to detect chromosomal abnormalities.

Results

Chromosomal abnormalities were observed only in polycythemia vera (11.8%) and primary myelofibrosis cases (17.6%), without correlation to clinical data. Chromosomal abnormalities were not detected by fluorescence in situ hybridization. The JAK2 V617F mutation was observed in polycythemia vera (90%), primary myelofibrosis (42.8%) and essential thrombocythemia (47%). Patients with JAK2 V617F-negative polycythemia vera had lower platelet and leukocyte counts compared to V617F-positive polycythemia vera (p-value = 0.0001 and p-value = 0.023, respectively). JAK2 V617F-positive and MPL W515L-positive primary myelofibrosis cases had a higher degree of fibrosis than V617F-negative cases (p-value = 0.022). JAK2 exon 12 mutations were not detected in polycythemia vera patients. The MPL W515L mutation was observed in one case of primary myelofibrosis and in one of essential thrombocythemia. The MPL W515K mutation was not found in patients with essential thrombocythemia or primary myelofibrosis. The MPL W515L-positive patient with primary myelofibrosis had more severe anemia than other patients with primary myelofibrosis.

Conclusions

This study demonstrates that karyotyping for JAK2 and MPL mutations is useful in the diagnosis of myeloproliferative neoplasms. The precise pathogenetic contribution of these alterations is still unclear. However, this study adds more information about the pathophysiology of polycythemia vera, essential thrombocythemia and primary myelofibrosis.

Targeting self-renewal pathways in myeloid malignancies

A fundamental property of hematopoietic stem cells (HSCs) is the ability to self-renew. This is a complex process involving multiple signal transduction cascades which control the fine balance between self-renewal and differentiation through transcriptional networks. Key activators/regulators of self-renewal include chemokines, cytokines and morphogens which are expressed in the bone marrow niche, either in a paracrine or autocrine fashion, and modulate stem cell behaviour. Increasing evidence suggests that the downstream signaling pathways induced by these ligands converge at multiple levels providing a degree of redundancy in steady state hematopoiesis. Here we will focus on how these pathways cross-talk to regulate HSC self-renewal highlighting potential therapeutic windows which could be targeted to prevent leukemic stem cell self-renewal in myeloid malignancies.

Quantitative threefold allele-specific PCR (QuanTAS-PCR) for highly sensitive JAK2 V617F mutant allele detection

Background

The JAK2 V617F mutation is the most frequent somatic change in myeloproliferative neoplasms, making it an important tumour-specific marker for diagnostic purposes and for the detection of minimal residual disease. Sensitive quantitative assays are required for both applications, particularly for the monitoring of minimal residual disease, which requires not only high sensitivity but also very high specificity.

Methods

We developed a highly sensitive probe-free quantitative mutant-allele detection method, Quantitative Threefold Allele-Specific PCR (QuanTAS-PCR), that is performed in a closed-tube system, thus eliminating the manipulation of PCR products. QuantTAS-PCR uses a threefold approach to ensure allele-specific amplification of the mutant sequence: (i) a mutant allele-specific primer, (ii) a 3′dideoxy blocker to suppress false-positive amplification from the wild-type template and (iii) a PCR specificity enhancer, also to suppress false-positive amplification from the wild-type template. Mutant alleles were quantified relative to exon 9 of JAK2.

Results

We showed that the addition of the 3′dideoxy blocker suppressed but did not eliminate false-positive amplification from the wild-type template. However, the addition of the PCR specificity enhancer near eliminated false-positive amplification from the wild-type allele. Further discrimination between true and false positives was enabled by using the quantification cycle (Cq) value of a single mutant template as a cut-off point, thus enabling robust distinction between true and false positives. As 10,000 JAK2 templates were used per replicate, the assay had a sensitivity of 1/10^-4 per replicate. Greater sensitivity could be reached by increasing the number of replicates analysed. Variation in replicates when low mutant-allele templates were present necessitated the use of a statistics-based approach to estimate the load of mutant JAK2 copies. QuanTAS-PCR showed comparable quantitative results when validated against a commercial assay.

Conclusions

QuanTAS-PCR is a simple, cost-efficient, closed-tube method for JAK2 V617F mutation quantification that can detect very low levels of the mutant allele, thus enabling analysis of minimal residual disease. The approach can be extended to the detection of other recurrent single nucleotide somatic changes in cancer.

Incidence and clinical characteristics of myeloproliferative neoplasms displaying a PDGFRB rearrangement

OBJECTIVES

The myeloproliferative neoplasms displaying a PDGFRB rearrangement are rare diseases derived from a haematopoietic stem cell. The goals of the study were to assess the incidence of these disorders and to define the clinical and biological characteristics as well as the response to the imatinib therapy.

METHODS

A total of 556 patients with myeloproliferative neoplasms were studied by means of molecular cytogenetics.

RESULTS

The incidence of myeloproliferative neoplasms (MPN) with PDGFRB rearrangement was low (10 cases, 1.8% of all MPN). Most of the patients showed moderate anaemia (median Hb was 10.0 gr/dL; range from 7.5 to 13 g/dL), leukocytosis (median white blood cells was 21.7 × 10(9) /L with a range from 4 to 43 × 10(9) /L) and eosinophilia (median circulating eosinophils was 2.4 × 10(9) /L with a range of 1.1-5.7 × 10(9) /L) with a median of bone marrow infiltration cells displaying PDGFRB rearrangement of 55% (range, 37-85%). In three cases, a t(5;12) was observed while two patients showed rearrangements of 17q21 region. In two cases, a del(5)(q31) was observed. Most of the patients responded to standard dosage of imatinib, and the response was maintained in the time in those patients with a follow-up higher than 9 years.

CONCLUSIONS

The incidence of patients with PDGFRB rearrangement is low. These patients showed leukocytosis with eosinophilia and anaemia. The efficacy of imatinib therapy in patients showing PDGFRB rearrangement is high. For this reason, in all patients with MPN without any other molecular aberration, PDGFRB rearrangement should be ascertained.

Crenolanib inhibits the drug-resistant PDGFRA D842V mutation associated with imatinib-resistant gastrointestinal stromal tumors

PURPOSE

To determine the potential of crenolanib, a potent inhibitor of PDGFRA, to treat malignancies driven by mutant PDGFRA.

EXPERIMENTAL DESIGN

The biochemical activity of crenolanib was compared with imatinib using a panel of PDGFRA-mutant kinases expressed in several different cell line models, including primary gastrointestinal stromal tumors (GIST) cells. The antiproliferative activity of crenolanib was also studied in several cell lines with PDGFRA-dependent growth.

RESULTS

Crenolanib was significantly more potent than imatinib in inhibiting the kinase activity of imatinib-resistant PDGFRA kinases (D842I, D842V, D842Y, DI842-843IM, and deletion I843). For example, crenolanib was 135-fold more potent than imatinib against D842V in our isogenic model system, with an IC(50) of approximately 10 nmol/L. The relative potency of crenolanib was further confirmed in BaF3 and primary GIST cells expressing PDGFRA D842V. In contrast, imatinib was at least 10-fold more potent than crenolanib in inhibiting the V561D mutation. For all other tested PDGFRA mutations, crenolanib and imatinib had comparable potency.

CONCLUSIONS

Crenolanib is a potent inhibitor of imatinib-resistant PDGFRA kinases associated with GIST, including the PDGFRA D842V mutation found in approximately 5% of GISTs. The spectrum of activity of crenolanib suggests that this drug is a type I inhibitor (inhibitor of activated conformation of kinase). Based in part on these results, a phase II clinical study of this agent to treat GIST with the PDGFRA D842V mutation has been initiated.

Pathogenesis and classification of eosinophil disorders: a review of recent developments in the field

Eosinophils and their products play an essential role in the pathogenesis of various reactive and neoplastic disorders. Depending on the underlying disease, molecular defect and involved cytokines, hypereosinophilia may develop and may lead to organ damage. In other patients, persistent eosinophilia is accompanied by typical clinical findings, but the causative role and impact of eosinophilia remain uncertain. For patients with eosinophil-mediated organ pathology, early therapeutic intervention with agents reducing eosinophil counts can be effective in limiting or preventing irreversible organ damage. Therefore, it is important to approach eosinophil disorders and related syndromes early by using established criteria, to perform all appropriate staging investigations, and to search for molecular targets of therapy. In this article, we review current concepts in the pathogenesis and evolution of eosinophilia and eosinophil-related organ damage in neoplastic and non-neoplastic conditions. In addition, we discuss classifications of eosinophil disorders and related syndromes as well as diagnostic algorithms and standard treatment for various eosinophil-related disorders.

New pieces of a puzzle: the current biological picture of MPN

Over the last years, we have witnessed significant improvement in our ability to elucidate the genetic events, which contribute to the pathogenesis of acute and chronic leukemias, and also in patients with myeloproliferative neoplasms (MPN). However, despite significant insight into the role of specific mutations, including the JAK2V617F mutation, in MPN pathogenesis, the precise mechanisms by which specific disease alleles contribute to leukemic transformation in MPN remain elusive. Here we review recent studies aimed at understanding the role of downstream signaling pathways in MPN initiation and phenotype, and discuss how these studies have begun to lead to novel insights with biologic, clinical, and therapeutic relevance.

Mutations in the transmembrane and juxtamembrane domains enhance IL27R transforming activity

Cytokines and their receptors regulate haemopoiesis by controlling cellular growth, survival and differentiation. Thus it is not surprising that mutations of cytokine receptors contribute to the formation of haemopoietic disorders, including cancer. We recently identified transforming properties of IL27R, the ligand-binding component of the receptor for interleukin-27. Although wild-type IL27R exhibits transforming properties in haemopoietic cells, in the present study we set out to determine if the transforming activity of IL27R could be enhanced by mutation. We identified three mutations of IL27R that enhance its transforming activity. One of these mutations is a phenylalanine to cysteine mutation at residue 523 (F523C) in the transmembrane domain of the receptor. The two other mutations identified involve deletions of amino acids in the cytoplasmic juxtamembrane region of the receptor. Expression of each of these mutant IL27R proteins led to rapid cytokine-independent transformation in haemopoietic cells. Moreover, the rate of transformation induced by these mutants was significantly greater than that induced by wild-type IL27R. Expression of these IL27R mutants also induced enhanced activation of JAK (Janus kinase)/STAT (signal transducer and activator of transcription) signalling compared with wild-type. An activating deletion mutation of IL27R enhanced homodimerization of the receptor by a mechanism that may involve disulfide bonding. These transforming IL27R mutants displayed equal or greater transforming activity than bona fide haemopoietic oncogenes such as BCR-ABL (breakpoint cluster region-Abelson murine leukaemia viral oncogene homologue) and JAK2-V617F. Since IL27R is expressed on haemopoietic stem cells, lymphoid cells and myeloid cells, including acute myeloid leukaemia blast cells, mutation of this receptor has the potential to contribute to a variety of haemopoietic neoplasms.

Part 4: pharmacogenetic variability in anticancer pharmacodynamic drug effects

Response to treatment with anticancer drugs is subject to wide interindividual variability. This variability is expressed not only as differences in severity and type of toxicity, but also as differences in effectiveness. Variability in the constitution of genes involved in the pharmacokinetic and pharmacodynamic pathways of anticancer drugs has been shown to possibly translate into differences in treatment outcome. The overall knowledge in the field of pharmacogenetics has tremendously increased over the last couple of years, and has thereby provided opportunities for patient-tailored anticancer therapy. In previous parts of this series, we described pharmacogenetic variability in anticancer phase I and phase II drug metabolism and drug transport. This fourth part of a four-part series of reviews is focused on pharmacodynamic variability and encompasses genetic variation in drug target genes such as those encoding thymidylate synthase, methylene tetrahydrofolate reductase, and ribonucleotide reductase. Furthermore, genetic variability in other pharmacodynamic candidate genes involved in response to anticancer drugs is discussed, including genes involved in DNA repair such as those encoding excision repair crosscomplementing group 1 and group 2, x-ray crosscomplementing group 1 and group 3, and breast cancer genes 1 and 2. Finally, somatic mutations in KRAS and the gene encoding epidermal growth factor receptor (EGFR) and implications for EGFR-targeted drugs are discussed. Potential implications and opportunities for patient and drug selection for genotype-driven anticancer therapy are outlined.

Pathogenesis, classification and treatment of mastocytosis: state of the art in 2010 and future perspectives

Mastocytosis is a myeloid neoplasm characterized by abnormal accumulation and frequent activation of mast cells (MCs) in various organs. Organ systems typically involved are the bone marrow, skin, liver and gastrointestinal tract. In most adult patients, the systemic form of mastocytosis (SM) is diagnosed, which includes an indolent subvariant, an aggressive subvariant and a leukemic subvariant, also termed MC leukemia. Whereas in pediatric mastocytosis, which is usually confined to the skin, a number of different KIT mutations and other defects may be detected, the KIT mutation D816V is detectable in most (adult) patients with SM. In a subset of these patients, additional oncogenic factors may lead to enhanced survival and growth of MCs and, thus, to advanced SM. Other factors may lead to MC activation, with consecutive anaphylactic reactions that can be severe or even fatal. Treatment of SM usually focuses on symptom relief by histamine receptor antagonists and other supportive therapy. However, in aggressive and leukemic variants, cytoreductive and targeted drugs must be applied. Unfortunately, the prognosis in these patients remains poor, even when treated with novel KIT-targeting agents, polychemotherapy or stem cell transplantation. This article provides a summary of our knowledge on the pathogenesis and on treatment options in SM.

Frequency of heterozygous TET2 deletions in myeloproliferative neoplasms

The Philadelphia chromosome (Ph)-negative myeloproliferative neoplasms (MPNs), including polycythemia vera, essential thrombocythemia, and primary myelofibrosis, are a group of clonal hematopoietic stem cell disorders with overlapping clinical and cytogenetic features and a variable tendency to evolve into acute leukemia. These diseases not only share overlapping chromosomal abnormalities but also a number of acquired somatic mutations. Recently, mutations in a putative tumor suppressor gene, ten-eleven translocation 2 (TET2) on chromosome 4q24 have been identified in 12% of patients with MPN. Additionally 4q24 chromosomal rearrangements in MPN, including TET2 deletions, have also been observed using conventional cytogenetics. The goal of this study was to investigate the frequency of genomic TET2 rearrangements in MPN using fluorescence in situ hybridization as a more sensitive method for screening and identifying genomic deletions. Among 146 MPN patients, we identified two patients (1.4%) who showed a common 4q24 deletion, including TET2. Our observations also indicated that the frequency of TET2 deletion is increased in patients with an abnormal karyotype (5%).

Mutational analysis in BCR-ABL-negative classic myeloproliferative neoplasms: impact on prognosis and therapeutic choices

The diagnostic value of JAK2 mutational analysis in myeloproliferative neoplasms (MPN) is now well established and endorsed by the World Health Organization classification system for hematologic malignancies. The current review is focused on the prognostic impact and therapeutic relevance of JAK2 and other MPN-associated mutations in polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). Mutations involving JAK2, MPL, TET2, and ASXL1 are discussed. In general, within a specific disease category, the mere presence or absence of any one of these mutations does not appear to correlate with survival or development of blast phase disease, myelofibrosis, or thrombosis. In contrast, interesting associations between JAK2V617F allele burden and clinical outcome (e.g. lower quartile range allele burden and shorter survival in PMF and higher allele burden and fibrotic transformation in PV) have been made, but require further validation, and their impact on treatment choices is not clear. Similarly, although detection of JAK2V617F status post allogeneic hematopoietic cell transplant indicates minimal residual disease, the general use of mutant allele burden for monitoring treatment response has not been systematically studied. Current information on mutational status and response to JAK2 inhibitor drug therapy is too preliminary to draw any conclusions.

Cancer-associated myeloproliferation: old association, new therapeutic target

The association between malignancy and development of a paraneoplastic leukocytosis, the so-called leukemoid reaction, has long been appreciated. Although a leukemoid reaction has conventionally been defined as a peripheral blood leukocytosis composed of both mature and immature granulocytes that exceeds 50,000/microL, a less profound leukocytosis may be appreciated in many patients harboring a malignant disease. More recent insights have shed new light on this long-recognized association, because research performed in both murine models and cancer patients has uncovered multiple mechanisms by which tumors both drive myelopoiesis, sometimes leading to a clinically apparent leukocytosis, and inhibit the differentiation of myeloid cells, resulting in a qualitative change in myelopoiesis. This qualitative change leads to the accumulation of immature myeloid cells, which due to their immune suppressive effects have been collectively called myeloid-derived suppressor cells. More recently, myeloid cells have been shown to promote tumor angiogenesis. Cancer-associated myeloproliferation is not merely a paraneoplastic phenomenon of questionable importance but leads to the suppression of host immunity and promotion of tumor angiogenesis, both of which play an integral part in tumorigenesis and metastasis. Therefore, cancer-associated myeloproliferation represents a novel therapeutic target in cancer that, decades after its recognition, is only now being translated into clinical practice.

New insights into the mechanisms of hematopoietic cell transformation by activated receptor tyrosine kinases

A large number of alterations in genes encoding receptor tyrosine kinase (RTK), namely FLT3, c-KIT, platelet-derived growth factor (PDGF) receptors, fibroblast growth factor (FGF) receptors, and the anaplastic large cell lymphoma kinase (ALK), have been found in hematopoietic malignancies. They have drawn much attention after the development of tyrosine kinase inhibitors. RTK gene alterations include point mutations and gene fusions that result from chromosomal rearrangements. In both cases, they activate the kinase domain in the absence of ligand, producing a permanent signal for cell proliferation. Recently, this simple model has been refined. First, by contrast to wild-type RTK, many mutated RTK do not seem to signal from the plasma membrane, but from various locations inside the cell. Second, their signal transduction properties are altered: the pathways that are crucial for cell transformation, such as signal transducer and activator of transcription (STAT) factors, do not necessarily contribute to the physiologic functions of these receptors. Finally, different mechanisms prevent the termination of the signal, which normally occurs through receptor ubiquitination and degradation. Several mutations inactivating CBL, a key RTK E3 ubiquitin ligase, have been recently described. In this review, we discuss the possible links among RTK trafficking, signaling, and degradation in leukemic cells.

Novel mutations and their functional and clinical relevance in myeloproliferative neoplasms: JAK2, MPL, TET2, ASXL1, CBL, IDH and IKZF1

Myeloproliferative neoplasms (MPNs) originate from genetically transformed hematopoietic stem cells that retain the capacity for multilineage differentiation and effective myelopoiesis. Beginning in early 2005, a number of novel mutations involving Janus kinase 2 (JAK2), Myeloproliferative Leukemia Virus (MPL), TET oncogene family member 2 (TET2), Additional Sex Combs-Like 1 (ASXL1), Casitas B-lineage lymphoma proto-oncogene (CBL), Isocitrate dehydrogenase (IDH) and IKAROS family zinc finger 1 (IKZF1) have been described in BCR-ABL1-negative MPNs. However, none of these mutations were MPN specific, displayed mutual exclusivity or could be traced back to a common ancestral clone. JAK2 and MPL mutations appear to exert a phenotype-modifying effect and are distinctly associated with polycythemia vera, essential thrombocythemia and primary myelofibrosis; the corresponding mutational frequencies are approximately 99, 55 and 65% for JAK2 and 0, 3 and 10% for MPL mutations. The incidence of TET2, ASXL1, CBL, IDH or IKZF1 mutations in these disorders ranges from 0 to 17%; these latter mutations are more common in chronic (TET2, ASXL1, CBL) or juvenile (CBL) myelomonocytic leukemias, mastocytosis (TET2), myelodysplastic syndromes (TET2, ASXL1) and secondary acute myeloid leukemia, including blast-phase MPN (IDH, ASXL1, IKZF1). The functional consequences of MPN-associated mutations include unregulated JAK-STAT (Janus kinase/signal transducer and activator of transcription) signaling, epigenetic modulation of transcription and abnormal accumulation of oncoproteins. However, it is not clear as to whether and how these abnormalities contribute to disease initiation, clonal evolution or blastic transformation.

Hypereosinophilic syndrome and clonal eosinophilia: point-of-care diagnostic algorithm and treatment update

Acquired eosinophilia is operationally categorized into secondary, clonal, and idiopathic types. Causes of secondary eosinophilia include parasite infections, allergic or vasculitis conditions, drugs, and lymphoma. Clonal eosinophilia is distinguished from idiopathic eosinophilia by the presence of histologic, cytogenetic, or molecular evidence of an underlying myeloid malignancy. The World Health Organization classification system for hematologic malignancies recognizes 2 distinct subcategories of clonal eosinophilia: chronic eosinophilic leukemia, not otherwise specified and myeloid/lymphoid neoplasms with eosinophilia and mutations involving platelet-derived growth factor receptor alpha/beta or fibroblast growth factor receptor 1. Clonal eosinophilia might also accompany other World Health Organization-defined myeloid malignancies, including chronic myelogenous leukemia, myelodysplastic syndromes, chronic myelomonocytic leukemia, and systemic mastocytosis. Hypereosinophilic syndrome, a subcategory of idiopathic eosinophilia, is defined by the presence of a peripheral blood eosinophil count of 1.5 x 10(9)/L or greater for at least 6 months (a shorter duration is acceptable in the presence of symptoms that require eosinophil-lowering therapy), exclusion of both secondary and clonal eosinophilia, evidence of organ involvement, and absence of phenotypically abnormal and/or clonal T lymphocytes. The presence of the latter defines lymphocytic variant hyper eosinophilia, which is best classified under secondary eosinophilia. In the current review, we provide a simplified algorithm for distinguishing the various causes of clonal and idiopathic eosinophilia and discuss current therapy, including new drugs (imatinib mesylate, alemtuzumab, and mepolizumab).

Perspectives for the use of structural information and chemical genetics to develop inhibitors of Janus kinases

Gain-of-function mutations in the genes encoding Janus kinases have been discovered in various haematologic diseases. Jaks are composed of a FERM domain, an SH2 domain, a pseudokinase domain and a kinase domain, and a complex interplay of the Jak domains is involved in regulation of catalytic activity and association to cytokine receptors. Most activating mutations are found in the pseudokinase domain. Here we present recently discovered mutations in the context of our structural models of the respective domains. We describe two structural hotspots in the pseudokinase domain of Jak2 that seem to be associated either to myeloproliferation or to lymphoblastic leukaemia, pointing at the involvement of distinct signalling complexes in these disease settings. The different domains of Jaks are discussed as potential drug targets. We present currently available inhibitors targeting Jaks and indicate structural differences in the kinase domains of the different Jaks that may be exploited in the development of specific inhibitors. Moreover, we discuss recent chemical genetic approaches which can be applied to Jaks to better understand the role of these kinases in their biological settings and as drug targets.

Screening for diverse PDGFRA or PDGFRB fusion genes is facilitated by generic quantitative reverse transcriptase polymerase chain reaction analysis

BACKGROUND

Rapid identification of diverse fusion genes with involvement of PDGFRA or PDGFRB in eosinophilia-associated myeloproliferative neoplasms is essential for adequate clinical management but is complicated by the multitude and heterogeneity of partner genes and breakpoints.

DESIGN AND METHODS

We established a generic quantitative reverse transcriptase polymerase chain reaction to detect overexpression of the 3'-regions of PDGFRA or PDGFRB as a possible indicator of an underlying fusion.

RESULTS

At diagnosis, all patients with known fusion genes involving PDGFRA (n=5; 51 patients) or PDGFRB (n=5; 7 patients) showed significantly increased normalized expression levels compared to 191 patients with fusion gene-negative eosinophilia or healthy individuals (PDGFRA/ABL: 0.73 versus 0.0066 versus 0.0064, P<0.0001; PDGFRB/ABL: 196 versus 3.8 versus 5.85, P<0.0001). The sensitivity and specificity of the activation screening test were, respectively, 100% and 88.4% for PDGFRA and 100% and 94% for PDGFRB. Furthermore, significant overexpression of PDGFRB was found in a patient with an eosinophilia-associated myeloproliferative neoplasm with uninformative cytogenetics and an excellent response to imatinib. Subsequently, a new SART3-PDGFRB fusion gene was identified by 5'-rapid amplification of cDNA ends polymerase chain reaction (5'-RACE-PCR).

CONCLUSIONS

Quantitative reverse transcriptase polymerase chain reaction analysis is a simple and useful adjunct to standard diagnostic assays to detect clinically significant overexpression of PDGFRA and PDGFRB in eosinophilia-associated myeloproliferative neoplasms or related disorders.

Mature survival data for 176 patients younger than 60 years with primary myelofibrosis diagnosed between 1976 and 2005: evidence for survival gains in recent years

In the past 20 years, management of primary myelofibrosis (PMF) has incorporated new treatment approaches, but survival benefits have not been confirmed in controlled studies. This retrospective study includes 176 consecutive patients younger than age 60 years in whom PMF was diagnosed during a 30-year period (1976-2005). Median age at diagnosis was 50 years (range, 18-59 years), and 98 patients (55%) were men. At the time of this report, 99 patients (56%) had died; the 77 surviving patients were followed up for a median of 8 years (range, 4-24 years). Overall median survival was 9.2 years, and 15- and 20-year survival rates were 32% and 20%, respectively. According to the Dupriez Prognostic Scoring System (PSS), median survivals were 12.7, 4.8, and 2.4 years in low- (n=117), intermediate- (n=44) and high- (n=15) risk patients (P<.001). According to the International PSS, median survivals were 13.4, 9.7, 3.3, and 2.4 years in low- (n=76), intermediate-1 (n=50), intermediate-2 (n=29), and high-risk patients (n=8; P<.001). To examine the effect of decade of diagnosis on survival, we divided study patients into 3 groups by year of diagnosis: 1976-1985 (n=36), 1986-1995 (n=45), and 1996-2005 (n=95). The corresponding median survivals were 4.8, 7.3, and "not reached" (P=.003), and the difference in survival was significant during multivariable analysis that included risk scores according to the aforementioned PSSs and age as covariates. The improvement in survival in recent years was most apparent in patients with high/intermediate-risk disease (P<.002), not in those with low-risk disease (P=.42). These observations are encouraging and suggest a salutary effect from modern therapeutic approaches in PMF.

International Prognostic Scoring System-independent cytogenetic risk categorization in primary myelofibrosis

Among 200 patients with primary myelofibrosis, karyotype at diagnosis was abnormal in 83 (42%). To assess their individual prognostic impact, specific cytogenetic abnormalities with more than or equal to 5 informative cases were identified and the rest grouped separately as "other abnormalities." Median survival in patients with sole +9 (n = 6), sole 20q- (n = 21), sole 13q- (n = 8), normal karyotype (n = 117), "other abnormalities" (n = 28), complex karyotype (n = 13), and sole +8 (n = 7) were "not reached," 112, 105, 80, 46, 34, and 28 months, respectively (P = .01). Accordingly, 4 cytogenetic risk groups were considered: (1) favorable (sole +9, 20q-, or 13q-), (2) normal, (3) unfavorable (complex karyotype or sole +8), and (4) "other abnormalities." Multivariable analysis confirmed the International Prognostic Scoring System (IPSS)-independent prognostic value of both 4-way and 2-way (ie, favorable/normal vs unfavorable/other abnormalities; IPSS-adjusted hazard ratio = 0.37; 95% confidence interval, 0.24-0.58) cytogenetic risk categorization (P < .01). The ability to prognostically dissect a specific IPSS category has major therapeutic implications.