Molecular pathogenesis of chronic myeloid leukemia: implications for new therapeutic strategies

Corneal Infantile Myofibromatosis Caused by Novel Activating Imatinib-Responsive Variants in PDGFRB

Purpose

To investigate the genetic cause, clinical characteristics, and potential therapeutic targets of infantile corneal myofibromatosis.

Design

Case series with genetic and functional in vitro analyses.

Participants

Four individuals from 2 unrelated families with clinical signs of corneal myofibromatosis were investigated.

Methods

Exome-based panel sequencing for platelet-derived growth factor receptor beta gene (PDGFRB) and notch homolog protein 3 gene (NOTCH3) was performed in the respective index patients. One clinically affected member of each family was tested for the pathogenic variant detected in the respective index by Sanger sequencing. Immunohistochemical staining on excised corneal tissue was conducted. Functional analysis of the individual PDGFRB variants was performed in vitro by luciferase reporter assays on transfected porcine aortic endothelial cells using tyrosine kinase inhibitors. Protein expression analysis of mutated PDGFRB was analyzed by Western blot.

Main Outcome Measures

Sequencing data, immunohistochemical stainings, functional analysis of PDGFRB variants, and protein expression analysis.

Results

We identified 2 novel, heterozygous gain-of-function variants in PDGFRB in 4 individuals from 2 unrelated families with corneal myofibromatosis. Immunohistochemistry demonstrated positivity for alpha-smooth muscle actin and β-catenin, a low proliferation rate in Ki-67 (< 5%), marginal positivity for Desmin, and negative staining for Caldesmon and CD34. In all patients, recurrence of disease occurred after corneal surgery. When transfected in cultured cells, the PDGFRB variants conferred a constitutive activity to the receptor in the absence of its ligand and were sensitive to the tyrosine kinase inhibitor imatinib. The variants can both be classified as likely pathogenic regarding the American College of Medical Genetics and Genomics classification criteria.

Conclusions

We describe 4 cases of corneal myofibromatosis caused by novel PDGFRB variants with autosomal dominant transmission. Imatinib sensitivity in vitro suggests perspectives for targeted therapy preventing recurrences in the future.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Clinical Cytogenetics: Current Practices and Beyond

BACKGROUND

Throughout history, the field of cytogenetics has witnessed significant changes due to the constant evolution of technologies used to assess chromosome number and structure. Similar to the evolution of single nucleotide variant detection from Sanger sequencing to next-generation sequencing, the identification of chromosome alterations has progressed from banding to fluorescence in situ hybridization (FISH) to chromosomal microarrays. More recently, emerging technologies such as optical genome mapping and genome sequencing have made noteworthy contributions to clinical laboratory testing in the field of cytogenetics.

CONTENT

In this review, we journey through some of the most pivotal discoveries that have shaped the development of clinical cytogenetics testing. We also explore the current test offerings, their uses and limitations, and future directions in technology advancements.

SUMMARY

Cytogenetics methods, including banding and targeted assessments like FISH, continue to hold crucial roles in cytogenetic testing. These methods offer a rapid turnaround time, especially for conditions with a known etiology involving recognized cytogenetic aberrations. Additionally, laboratories have the flexibility to now employ higher-throughput methodologies to enhance resolution for cases with greater complexity.

The Transforming Growth Factor Beta 1/SMAD Signaling Pathway Involved in Human Chronic Myeloid Leukemia

Transforming growth factor beta 1 (TGF-β1) is the prototypic member of a large family of structurally related pleiotropic-secretedcytokines. The TGF-β1/SMAD signaling pathway usually participates in a wide range of cellular processes such as growth, proliferation, differentiation and apoptosis. Upon binding onTGF-β1, the dimerized TGF-β type II receptors recruit and phosphorylate the TGF-β type I receptors, which phosphorylate the receptor-regulated SMAD (SMAD2 and SMAD3) presented by the SMAD anchor for receptor activation.

The phosphorylated receptor-regulated SMAD form heterologous complexes with the common-mediator SMAD (SMAD4) and subsequently translocate into the nucleus, where they interact with other transcription factors to regulate the expression of target genes. This multi-functional signaling pathway modulated by various elements with complex mechanisms at different levels is also inevitably involved in cancer. We herein present data on the role of the TGF-β1/SMAD signaling pathway in human chronic myeloid leukemia and explain the potent biological effects of TGF-β1 on leukemia cells. The paper is based on a review of articles selected from Cancerline and Medline data bases.

The constitutively active tyrosine kinase produced by the specific Bcr-Abl fusion gene on the Philadelphia chromosome can enhance the resistance of malignant cells to TGF-β1-induced growth inhibition and apoptosis, which contributes to enhancement of proteasomal degradation of p27. However, overexpression of the EVI1 gene, which is also caused by Bcr-Abl, can recruit the C-terminal binding protein and histone deacetylase to prevent the MH2 domain on SMAD3. The later is essential for transcription activation on target genes and leads to blockage of the TGF-β1/SMAD signaling pathway.

Some studies have indicated that certain therapeutic agents applied in clinical treatment can inhibit proliferation and promote differentiation of leukemia cells by way of modulation of the TGF-β1/SMAD signal pathway. For example, arsenic trioxide can promote specific degradation of the AML1/MDS1/EVI1 oncoprotein and inhibit the proliferation of leukemia cells. However, specific histone deacetylase inhibitors can interrupt the effect of histone deacetylase to alleviate EVI1-mediated suppression of TGF-β1/SMAD signaling. The tyrosine kinase inhibitor in the target therapy of chronic myeloid leukemia can effectively inhibit the tyrosine kinase activity of Bcr-Abl and induce suppression on the TGF-β1/SMAD signaling pathway.

The TGF-β1/SMAD signaling pathway plays an important role in chronic myeloid leukemia cells and leads the leukemia cells to growth inhibition, differentiation and apoptosis. The positive influence of the TGF-β1/SMAD signaling pathway in chronic myeloid leukemia is fairly significant, and its potential effects in clinical treatment will bring about definite benefits.

Since it is a complex signaling pathway widely involved in many aspects of cellular activities, further study and comprehensive analysis of the TGF-β1/SMAD signaling pathway are imperative and will have a guiding significance in research and clinical applications. It is an exciting area for future research. Free full text available at www.tumorionline.it

Adiponectin enhances Imatinib anti-tumour activity in human chronic myeloid leukaemia cells with serum levels associated with Imatinib efficacy in early chronic phase patients

OBJECTIVES

Adiponectin, a functional ligand of adiponectin receptor-1 (AdipoR1) and adiponectin receptor-2 (AdipoR2), has been found to be linked to risk of development of chronic myeloid leukaemia (CML). Imatinib, as its first-line therapy, exhibits striking activity in both chronic and accelerated phases of the condition. However, numerous clinical trials have shown that many patients become refractory or experience relapses. Thus, development of new, hopefully effective Imatinib-based treatment strategies, are still needed.

MATERIALS AND METHODS

Effects of recombinant adiponectin protein, in enhancing Imatinib anti-tumour activities, in K562 and MEG-01 CML cells, were examined in vitro and in vivo. Forty-eight consecutive newly diagnosed adult patients with Bcr-Abl-positive CML, in the early chronic phase (ECP), were enrolled in the study. Imatinib efficacy, plasma adiponectin levels and their correlations were analysed.

RESULTS

Data presented here indicate that adiponectin enhanced Imatinib efficacy in vitro and in vivo. Furthermore, this augmented effect was due to inhibition of Bcr-Abl tyrosine kinase activity in an AdipoR1-dependent way, while AdipoR2 was not involved. Most importantly, additional clinical data revealed that adiponectin plasma levels in CML ECP patients, correlated with Imatinib efficacy.

CONCLUSIONS

Adiponectin enhanced Imatinib anti-tumour activity in human chronic myeloid leukaemia cells and its serum levels were associated with Imatinib efficacy, in early chronic phase patients.

Reliability Evaluation of Fluorescence In Situ Hybridization (FISH) and G-Banding on Bone Marrow and Peripheral Blood Cells in Chronic Myelogenous Leukemia Patients

Chronic myeloid leukemia (CML) is a myeloproliferative disease. The cytogenetic hallmark of CML is Philadelphia (Ph) chromosome. This study aimed to diagnose suspected CML patients, to monitor CML patients under therapy using cytogenetic and fluorescence in situ hybridization (FISH) techniques to analyze their bone marrow (BM) and peripheral blood (PB) samples, and finally to compare their obtained results for both specimens. This study was conducted during one-year period (2012-2013). The participants were recruited from the Hematology and Oncology Clinic of Shahid Gazi (Emam Reza) Hospital of Tabriz University of Medical Sciences, Tabriz, East Azerbaijan Province, Iran. We analyzed 90 samples from 60 suspected CML patients (30 BM and 60 PB samples). All samples were analyzed using G-banding, 5 samples using dual fusion FISH (DF-FISH) probes, as well as 30 samples using both FISH and G-banding. Among the 90 analyzed samples of 60 patients, 25 (41.66%) were Ph+ using karyotyping, whereas five cases were not analyzable, so FISH was applied and the results confirmed that only two individuals were BCR-ABL+. In the comparison between 25 BM and 25 PB samples using karyotyping, 15 (60%) and 10 (40%) were ph+, respectively. The comparison of FISH and karyotyping on 30 samples showed that 9 (30%) and 8 (26.66%) were Ph+, respectively, and only 18.18% of Ph+ patients showed atypical patterns. In the comparison between BM-cytogenetic and PB- interphase-FISH (I-FISH), BM-cytogenetic was more reliable than PB-I-FISH in detecting Ph. Our data demonstrate that FISH analysis is a rapid, reliable and sensitive technique. The comparison between BM and PB showed that PB can not be replaced by BM, even in detecting by FISH.

Assessment of interleukin 1β serum level in different responder groups and stages of chronic myeloid leukemia patients on imatinb mesylate therapy

Chronic myeloid leukemia (CML) is a myeloproliferative disorder characterized by the presence of an acquired mutation which affects the hematopoietic stem cell, leading to a striking overproduction of immature granulocytes. The first important clue to its pathogenesis the Philadelphia chromosome created by a reciprocal translocation between chromosomes 9 and 22 (t [9; 22] [q34; q11]). The development of the BCR-ABL-targeted imatinib mesylate represents a paradigm shift in the treatment of CML. Imatinib displays inhibitory activity against other kinase(s) that play a role in monocyte/macrophage development. Accordingly many studies revealed the role of cytokines in pathophysiology of myeloid neoplasia including participation of IL-1β in the pathogenesis of CML. This study designed to assess the behavior of IL-1β through newly diagnosed patients, different responders groups (optimal, suboptimal and failure cytogenetic response) and advanced stages (acceleration and crisis groups) of CML Iraqi patients whom receiving Imatinib mesylate (tyrosine kinase inhibitor), trying to elucidate the role of immunity in pathophysiology of CML disease development and treatments. In this study 96 Iraqi CML patients under imatinib mesylate treatment categorized by complete blood picture and fluorescent in situ hybridization analysis into different response groups and stages, then used an enzyme linked immunosorbent assay technique to assess serum level of IL-1β in each response group and advance stage (acceleration and transformed) of CML patients, in comparison to level in 32 healthy control subjects and 32 newly diagnosed CML. Out of 128 patients the mean serum of interleukin 1β level (pg/ml) for the newly diagnosed, optimal responded, suboptimal responded, failure cytogenetic and advance stage of CML were 6.53 ± 3.81, 18.47 ± 4.29, 18.69 ± 3.03, 5.73 ± 2.44, and 18.10 ± 3.10, respectively. While healthy was 12.17 ± 3.44. The measurement of IL-1β before and during treatment of CML patients may contribute to the early identification of responder and non responder patients, and help in the earlier choice and/or design of alternative therapeutic strategies.

Sequence and structural basis for chromosomal fragility during translocations in cancer

Chromosomal aberration is considered to be one of the major characteristic features in many cancers. Chromosomal translocation, one type of genomic abnormality, can lead to deregulation of critical genes involved in regulating important physiological functions such as cell proliferation and DNA repair. Although chromosomal translocations were thought to be random events, recent findings suggest that certain regions in the human genome are more susceptible to breakage than others. The possibility of deviation from the usual B-DNA conformation in such fragile regions has been an active area of investigation. This review summarizes the factors that contribute towards the fragility of these regions in the chromosomes, such as DNA sequences and the role of different forms of DNA structures. Proteins responsible for chromosomal fragility, and their mechanism of action are also discussed. The effect of positioning of chromosomes within the nucleus favoring chromosomal translocations and the role of repair mechanisms are also addressed.

Critical appraisal of nilotinib in frontline treatment of chronic myeloid leukemia

The development of imatinib has revolutionized the treatment of chronic myeloid leukemia. Follow-up analysis of IRIS trial participants continues to demonstrate durable responses for imatinib at 400 mg/day. However, 10%-15% of patients with chronic myeloid leukemia will become imatinib-resistant or intolerant of adverse events. Phase II studies have shown that most of these patients will respond to second-generation tyrosine kinase inhibitors, such as nilotinib, dasatinib, and bosutinib. Both nilotinib and dasatinib have recently demonstrated clinical efficacy as frontline therapy in Phase III studies. In the ENESTnd trial, nilotinib 600-800 mg/day produced significantly higher major molecular rates and complete cytogenetic response rates in comparison with imatinib at 12 months. Recently, 18-month follow-up analysis of this trial continues to demonstrate superiority for nilotinib. It is unknown whether this will ultimately translate into improved long-term outcomes, such as event-free survival or overall survival. Nilotinib continues to be generally well tolerated and tends to produce less Grade 3/4 toxicity in frontline therapy when compared with its use following imatinib failure. With three tyrosine kinase inhibitors for potential frontline therapy and an active drug discovery pipeline, treatment for chronic myeloid leukemia is still subject to change with time as clinical algorithms continue to evolve.

Photocleavable peptide-conjugated magnetic beads for protein kinase assays by MALDI-TOF MS

Peptides were immobilized onto superparamagnetic beads via photocleavable linkers. This enabled simple, rapid, and label-free protein kinase assays via MALDI-TOF MS detection of substrate peptide phosphorylation. Abltide, a model substrate for the Abl protein tyrosine kinase model, was coupled onto amine-terminated beads, incubated with ATP and recombinant c-Abl kinase, and released and further detected to determine phosphorylation. Abltide phosphorylation was found to depend significantly on the length and composition of linkers to the bead surface. Inserting a diblock spacer of poly(glycine) and poly(ethylene glycol) segments markedly enhanced phosphorylation. To validate the assay, the activity of two small-molecule kinase inhibitors, imatinib and dasatinib, which target the oncogenic mutant tyrosine kinase Bcr-Abl to treat chronic myeloid leukemia (CML), was tested. Examining inhibition of the purified c-Abl or Bcr-Abl in K562 CML cell extracts, IC(50) values were determined to be consistent with the literature. This simple, label-free, MALDI-based protein kinase assay can be readily adapted to allow multiplexed assays of multiple peptide substrates and/or analysis of alternative post-translational modifications as a tool for drug discovery and clinical testing.

Design and synthesis of novel 2-phenylaminopyrimidine (PAP) derivatives and their antiproliferative effects in human chronic myeloid leukemia cells

A series of novel 2-phenylaminopyrimidine (PAP) derivatives structurally related to STI-571 were designed and synthesized. The abilities of these compounds to inhibit proliferation were tested in human chronic myeloid leukemia K562 cells. (E)-3-(2-bromophenyl)-N-[4-methyl-3-(4-pyridin-3-yl-pyrimidin-2-ylamino)phenyl]acrylamide(12d) was the most effective cell growth inhibitor and was 3-fold more potent than STI-571.

A solid-phase Bcr-Abl kinase assay in 96-well hydrogel plates

Regulated phosphorylation by protein tyrosine kinases (PTKs), such as c-Abl, is critical to cellular homeostasis. In turn, once deregulated as in the chronic myeloid leukemia (CML) fusion protein Bcr-Abl, PTKs can promote cancer onset and progression. The dramatic success of the Bcr-Abl inhibitor imatinib as therapy for CML has inspired interest in other PTKs as targets for cancer drug discovery. Here we report a novel PTK activity and inhibition screening method using hydrogel-immobilized peptide substrates. Using acrylate crosslinkers, we tether peptides via terminal cysteines to thiol-presenting hydrogels in 96-well plates. These surfaces display low background and high reproducibility, allowing semiquantitative detection of peptide phosphorylation by recombinant c-Abl or by Bcr-Abl activity in cell extracts using traditional anti-phosphotyrosine immunodetection and chemifluorescence. The capabilities of this assay are demonstrated by performing model screens for inhibition with several commercially available PTK inhibitors and a collection of pyridopyrimidine Src/Abl dual inhibitors. This assay provides a practical method to measure the activity of a single kinase present in a whole cell lysate with high sensitivity and specificity as a valuable means for efficient small molecule screening.

New strategies in controlling drug resistance in chronic myeloid leukemia

PURPOSE

Imatinib has been quite effective in maintaining patients with CML in the chronic phase (CP); however, some patients develop imatinib resistance. This review addresses the mechanisms underlying imatinib resistance and the strategies currently being used to overcome that resistance.

SUMMARY

Chronic myeloid leukemia (CML) is a stem cell cancer caused by BCR-ABL. Imatinib, a BCR-ABL inhibitor, has significantly decreased CML mortality by stopping disease progression in CP. This success has been tempered by the appearance of imatinib-resistant clones. These clones allow CML to progress to advanced stages of disease where the prognosis is poor. Mechanisms of imatinib resistance include plasma protein binding, drug efflux, mutation of BCR-ABL, gene amplification of BCR-ABL, and activation of BCR-ABL independent proliferative pathways. The first four of these mechanisms could potentially be addressed by increasing the imatinib dose and recent clinical trials have shown this to be the case. Pharmacokinetic analysis demonstrated that patients with low imatinib plasma concentrations fared more poorly then patients with high plasma concentrations. Doubling the standard dose of 400 mg per day increased patient responses while decreasing the time to response. Toxicity was also increased resulting in approximately 50% of patients decreasing the dose. The strategy of waiting to see who failed imatinib at 400 mg per day and then increasing the dose of that subpopulation was unsuccessful. The interpretation of these data is that it is beneficial to treat CML as aggressively as possible as early as possible. Dasatinib is the second BCR-ABL inhibitor to become available. It binds with a 350-fold greater affinity to BCR-ABL and shows efficacy against a number of imatinib-resistant mutations. Dasatinib also inhibits SRC kinase, which may play a role in both maintaining BCR-ABL activity and in BCR-ABL independent signaling pathways. Clinical trials with dasatinib have had favorable results and are comparable with high-dose imatinib. Imatinib also compares favorably with stem cell transplant (SCT). Economic analysis shows imatinib and dasatinib therapies, while quite expensive, are on par with dialysis in terms of cost of quality adjusted life years.

CONCLUSION

A better understanding of imatinib resistance mechanisms has resulted in the development of useful strategies both to predict responders and nonresponders and to minimize imatinib resistance and prolong the life of the patient.

Synthesis and Cytotoxic Evaluation of Substituted Urea Derivatives as Inhibitors of Human-Leukemia K562 Cells

A series of substituted urea derivatives, compounds 1-14, were synthesized and evaluated for their cytotoxic activities against the human-leukemia K562 cell line. Two structurally simple compounds, 7 and 12, both incorporating a morpholine ring, were found to be highly active, with IC50 values of ca. 0.25 microM.

Curcumin synergistically augments bcr/abl phosphorothioate antisense oligonucleotides to inhibit growth of chronic myelogenous leukemia cells

AIM

To investigate the growth inhibition effect of the combination of bcr/abl phosphorothioate antisense oligonucleotides (PS-ASODN) and curcumin (cur), and the possible mechanisms of cur on the chronic myelogenous leukemia cell line K562.

METHODS

The K562 cell line was used as a P210( bcr/abl )-positive cell model in vitro and was exposed to different concentrations of PS-ASODN (0-20 micromol/L), cur (0-20 micromol/L), or a combination of both. Growth inhibition and apoptosis of K562 cells were assessed by MTT assay and AO/EB fluorescent staining, respectively. The expression levels of P210( bcr/abl ), NF-kappaB and heat shock protein 90 (Hsp90) were assessed by Western blot.

RESULTS

Exposure to cur (5-20 micromol/L) and PSASODN (5-20 micromol/L) resulted in a synergistic inhibitory effect on cell growth. Growth inhibition was associated with the inhibition of the proliferation and induction of apoptosis. Western blot analysis showed that the drugs synergistically downregulated the level of P210( bcr/abl ) and NF-kappaB. Cur downregulated Hsp90, whereas no synergism was observed when cur was combined with PS-ASODN.

CONCLUSION

PS-ASODN and cur exhibited a synergistic inhibitory effect on the cell growth of K562. The synergistic growth inhibition was mediated through different mechanisms that involved the inhibition of P210( bcr/abl ).

Identification of NVP-TAE684, a potent, selective, and efficacious inhibitor of NPM-ALK

Constitutive overexpression and activation of NPM-ALK fusion protein [t(2:5)(p23;q35)] is a key oncogenic event that drives the survival and proliferation of anaplastic large-cell lymphomas (ALCLs). We have identified a highly potent and selective small-molecule ALK inhibitor, NVP-TAE684, which blocked the growth of ALCL-derived and ALK-dependent cell lines with IC(50) values between 2 and 10 nM. NVP-TAE684 treatment resulted in a rapid and sustained inhibition of phosphorylation of NPM-ALK and its downstream effectors and subsequent induction of apoptosis and cell cycle arrest. In vivo, NVP-TAE684 suppressed lymphomagenesis in two independent models of ALK-positive ALCL and induced regression of established Karpas-299 lymphomas. NVP-TAE684 also induced down-regulation of CD30 expression, suggesting that CD30 may be used as a biomarker of therapeutic NPM-ALK kinase activity inhibition.

Pyrrolo[1,2-b][1,2,5]benzothiadiazepines (PBTDs): A New Class of Agents with High Apoptotic Activity in Chronic Myelogenous Leukemia K562 Cells and in Cells from Patients at Onset and Who Were Imatinib-Resistant

Pyrrolo[1,2-b][1,2,5]benzothiadiazepine 5,5-dioxides (PBTDs) induced apoptosis in human BCR-ABL-expressing leukemia cells. The apoptotic activity was also observed in primary leukemic blasts, obtained from chronic myelogenous leukemia (CML) patients at onset or from patients in blast crisis and who were imatinib-resistant. Compounds 5 and 14 induced apoptosis before BCR-ABL protein expression and tyrosin phosphorylation were affected and activated different caspases in the apoptotic pathway. PBTDs are a new class of valid candidates for the treatment of CML.

Blastic phase of chronic myelogenous leukemia

Chronic myelogenous leukemia (CML), also known as chronic myelocytic or chronic myeloid leukemia, is a clonal disorder of hematopoiesis that arises in a hematopoietic stem cell or early progenitor cell. This is characterized by the dysregulated production of mature nonlymphoid cells with normal differentiation. Eventually, in spite of the term chronic, there is progression to acute leukemia, usually of the myeloid variety, which is highly resistant to current therapies. Despite recent improvements in the treatment of early-stage disease, CML blast crisis (CMLBC) remains a therapeutic challenge. CMLBC is highly refractory to standard induction chemotherapy, with a response rate in myeloid blast crisis of less than 30%. Conventional chemotherapy has been much less successful in this disease compared with de novo acute leukemia, with a mean survival after diagnosis of blast crisis of only 2 to 4 months for nonresponders. Many regimens of chemotherapies have been tried in CMLBC, with minor success. Although imatinib was evaluated in patients with CMLBC, most CMLBC cases today arise in patients already on imatinib-based therapy and developing blastic phase on that therapy; thus there is no standard therapy for patients with CMLBC. Further studies of the mechanisms of transformation of chronic-phase CMLBC at a molecular level, and methods to target these molecular abnormalities, will determine the future direction of new treatment modalities. The prognosis of CML in blast crisis remains disappointing, despite great efforts. Currently, the most successful strategy for improving survival in CML is by prolonging the chronic phase and delaying the onset of blast crisis.

Identification of Differentially Expressed Proteins in Imatinib Mesylate-resistant Chronic Myelogenous Cells

Resistance to imatinib mesylate (also known as Gleevec, Glivec, and STI571) often becomes a barrier to the treatment of chronic myelogenous leukemia (CML). In order to identify markers of the action of imatinib mesylate, we used a mass spectrometry approach to compare protein expression profiles in human leukemia cells (K562) and in imatinib mesylate-resistant human leukemia cells (K562-R) in the presence and absence of imatinib mesylate. We identified 118 differentially regulated proteins in these two leukemia cell-lines, with and without a 1 microM imatinib mesylate challenge. Nine proteins of unknown function were discovered. This is the first comprehensive report regarding differential protein expression in imatinib mesylate-treated CML cells.

Differential tyrosine phosphorylation of leukemic cells during apoptosis as a result of treatment with imatinib mesylate

Bcr-Abl fusion tyrosine kinase contributes to leukemic transformation. Imatinib mesylate inhibits Bcr-Abl tyrosine kinase, resulting in a blockage of tyrosine phosphorylation in its downstream pathways. We analyzed the alteration of tyrosine phosphorylation, on BCR/ABL+ chronic myelogenous leukemia cells, after treatment with imatinib mesylate. Data were collected using a two-dimensional gel electrophoresis followed by Western blot and mass spectrometry. The inhibition of Bcr-Abl tyrosine kinase by 2.5 microM imatinib mesylate caused both cell cycle arrest in the G0/G1 phase and increased the portion of apoptotic cells. As a result, the population of leukemic cells decreased by 30% and 70% compared to controls at 24 and 72 h, respectively. Furthermore, treatment with imatinib mesylate altered tyrosine phosphorylation of 24 protein spots as the incubation time proceeded from 0 to 24 and 72 h. Ten of the 24 protein spots are visible at all three times. Four are detectable at both the 0 and 24 h points in time. Eight were detectable only at time 0.

BCR-ABL induces the expression of Skp2 through the PI3K pathway to promote p27Kip1 degradation and proliferation of chronic myelogenous leukemia cells

Chronic myelogenous leukemia (CML) is characterized by the expression of the BCR-ABL tyrosine kinase, which results in increased cell proliferation and inhibition of apoptosis. In this study, we show in both BCR-ABL cells (Mo7e-p210 and BaF/3-p210) and primary CML CD34+ cells that STI571 inhibition of BCR-ABL tyrosine kinase activity results in a G(1) cell cycle arrest mediated by the PI3K pathway. This arrest is associated with a nuclear accumulation of p27(Kip1) and down-regulation of cyclins D and E. As a result, there is a reduction of the cyclin E/Cdk2 kinase activity and of the retinoblastoma protein phosphorylation. By quantitative reverse transcription-PCR we show that BCR-ABL/PI3K regulates the expression of p27(Kip1) at the level of transcription. We further show that BCR-ABL also regulates p27(Kip1) protein levels by increasing its degradation by the proteasome. This degradation depends on the ubiquitinylation of p27(Kip1) by Skp2-containing SFC complexes: silencing the expression of Skp2 with a small interfering RNA results in the accumulation of p27(Kip1). We also demonstrate that BCR-ABL cells show transcriptional up-regulation of Skp2. Finally, expression of a p27(Kip1) mutant unable of being recognized by Skp2 results in inhibition of proliferation of BCR-ABL cells, indicating that the degradation of p27(Kip1) contributes to the pathogenesis of CML. In conclusion, these results suggest that BCR-ABL regulates cell cycle in CML cells at least in part by inducing proteasome-mediated degradation of the cell cycle inhibitor p27(Kip1) and provide a rationale for the use of inhibitors of the proteasome in patients with BCR-ABL leukemias.

CD34+CD7+ Leukemic Progenitor Cells May Be Involved in Maintenance and Clonal Evolution of Chronic Myeloid Leukemia

Purpose: We analyzed CD34+ cells coexpressing CD7 in chronic myeloid leukemia (CML) in chronic phase (CP) or accelerated phase (AP) to clarify their role in progression or regression of the disease during treatment.

Experimental Design: Enumeration of CD34+CD7+ cells was done on bone marrow nucleated cells from normal donors and CML patients. Fluorescence in situ hybridization analysis was done on sorted CD34+CD7+ and CD34+CD7− cells to examine the occupancy rate of each fraction by BCR-ABL+ cells with or without additional cytogenetic abnormalities.

Results: The proportion of CD34+CD7+ cells was significantly affected by the treatment outcome and/or the disease status as follows: 20.5 ± 10.4% in normal donors (n = 22), 18.1 ± 10.2% in CP with major cytogenetic response (n = 14), 53.0 ± 12.9% in CP at diagnosis (n = 18), 55.0 ± 15.8% in CP with minor or no cytogenetic response (n = 28), and 70.2 ± 18.1% in AP (n = 6). The proportion of CD34+CD7+ cells decreased in parallel with cytogenetic improvement in individual patients. In six untreated CP patients, the ratio of BCR-ABL+ cells was comparable between each fraction. In three patients with major cytogenetic response, the ratio of BCR-ABL+ cells was remarkably lower in CD34+CD7− cells than in CD34+CD7+ cells. In three AP patients with additional cytogenetic abnormalities, extra signals were detected at a much higher rate in CD34+CD7+ cells than in CD34+CD7− cells.

Conclusions: Our results suggest that CD34+CD7+ cells may be involved in maintenance and clonal evolution of BCR-ABL+ cells in CML.

Denbinobin-mediated anticancer effect in human K562 leukemia cells: role in tubulin polymerization and Bcr-Abl activity

Denbinobin (5-hydroxy-3,7-dimethoxy-1,4-phenanthraquinone) has been reported to exhibit anti-tumor and anti-inflammatory activity. Nevertheless, the anti-tumor mechanism of denbinobin remains unclear. In the present study, we evaluated the anticancer activity of denbinobin in human myelogenous K562 leukemia cells. In accordance with the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay, we demonstrated that denbinobin inhibited cell viability in a concentration-dependent manner with an IC50 value of 1.84 microM. Cell cycle analysis illustrated that exposure of denbinobin caused a G2/M phase accumulation in a time-dependent manner. Tubulin polymerization in cells was apparently enhanced by denbinobin, implying that denbinobin might have a regulatory role in tubulin/microtubule. Furthermore, denbinobin significantly suppressed the expression of Bcr-Abl and phosphorylation of CrkL, a crucial tyrosine kinase and an adaptor protein in chronic myeloid leukemia, respectively. Denbinobin also markedly enhanced CD11b expression after a long-term treatment, suggesting that denbinobin might play a role in facilitating differentiation in K562 cells. In summary, we have demonstrated that denbinobin displays anticancer effects in K562 cells through the increase of levels of tubulin polymerization and deregulation of Bcr-Abl signaling. Our data demonstrate that denbinobin could be a potential anticancer lead compound for further development.

Efficient Silencing of bcr/abl Oncogene by Single- and Double-Stranded siRNAs Targeted against b2a2 Transcripts

In this work, double- and single-stranded small-interference RNAs (siRNAs) were designed to knock down the bcr/abl oncogene in leukaemia KYO-1 cells. The siRNA molecules were targeted against two distinct sites encompassing the b2a2 junction of the bcr/abl transcripts. The siRNAs were able to reduce the levels of both bcr/abl mRNA and protein p210(BCR/ABL). Conversely, control siRNAs bearing 3 or 4 base-pair substitutions did not produce any inhibitory effect. The designed siRNAs were also found to be active in KCl22 cells, which harbor the b2a2 junction, but not in K562 cells, which, by contrast, harbor the b3a2 junction. The anti-b2a2 siRNAs promoted biological effects on KYO-1 cells, because the bcr/abl suppression resulted in the inhibition of cell growth and colony formation in agar and activation of apoptosis and upregulation of the cell-cycle inhibitor p27 protein. The bioactivity of the designed siRNAs is discussed in terms of internal stability of the RNA duplexes. Our data suggest that siRNAs can be considered strong tools for functional analysis of bcr/abl and for developing molecular therapeutic approaches to leukaemia.

Chronic myeloid leukemia: pathophysiology, diagnostic parameters, and current treatment concepts

Chronic myeloid leukemia (CML) is a stem cell disease characterized by excessive accumulation of clonal myeloid (precursor) cells in hematopoietic tissues. CML cells display the translocation t(9; 22) that creates the bcr/abl oncogene. The respective oncoprotein (= BCR/ABL) exhibits constitutive tyrosine kinase activity and promotes growth and survival in CML cells. Clinically, CML can be divided into three phases: the chronic phase (CP), the accelerated phase (AP), and the blast phase (BP) that resembles acute leukemia. Progression to AP and BP is associated with occurrence of additional genetic defects that cooperate with bcr/abl in leukemogenesis and lead to resistance against antileukemic drugs. The prognosis in CML is variable depending on the phase of disease, age, and response to therapy. The only curative approach available to date is stem cell transplantation. For those who cannot be transplanted, the BCR/ABL tyrosine kinase inhibitor STI571 (Glivec, Imatinib), interferon-alpha (with or without ARAC), or other cytoreductive drugs are prescribed. Currently available data show that STI571 is a superior compound compared to other drugs in producing complete cytogenetic and molecular responses. However, despite superior initial data and high expectations for an effect on survival, long term results are not available so far, and resistance against STI571 has been reported. Forthcoming strategies are therefore attempting to prevent or counteract STI571 resistance by co-administration of other antileukemic drugs. Whether these strategies will lead to curative drug therapy in CML in the future remains at present unknown.

Mechanisms of Bcr-Abl-mediated NF-kappaB/Rel activation

Bcr-Abl constitutes a deregulated tyrosine kinase involved in the pathogenesis of chronic myeloid leukemia (CML) and a subset of acute lymphoblastic leukemia (ALL). Although activation of the transcription factor NF-kappaB/Rel has been demonstrated, mechanisms of NF-kappaB/Rel activation by Bcr-Abl remain obscure. In this paper we demonstrate activation of NF-kappaB/Rel by Bcr-Abl and for the first time by v-Abl. Furthermore, we investigated mechanisms of NF-kappaB/Rel induction by Bcr-Abl and v-Abl. Both Bcr-Abl and v-Abl induced NF-kappaB/Rel DNA binding in Ba/F3 cells. DNA binding was a result of nuclear translocation of p65/RelA, whereas p65/RelA expression was unaffected. Nuclear translocation of p65/RelA is at least partially due to increased IkappaBalpha degradation, which is independent of IkappaB kinase (IKK) activity. IKK activity is not deregulated by Bcr-Abl and v-Abl. NF-kappaB/Rel transactivation was dependent on abl kinase activity but independent of Grb2 and Grb10 binding tobcr sequences. In addition, NF-kappaB/Rel activation was dependent on Ras activity. Primary CML blasts showed constitutive p65/RelA NF-kappaB/Rel DNA binding activity. Thus NF-kappaB/Rel represents a potential target for molecular therapies in CML.

High affinity molecules disrupting GRB2 protein complexes as a therapeutic strategy for chronic myelogenous leukaemia

Chronic myelogenous leukaemia (CML) is one of the most intensively studied human malignancies. It has been the focus of major efforts to develop potent drugs for several decades, but until recently cure rates remained low. A breakthrough in CML therapy was very likely accomplished with the clinical introduction of STI-571 [imatinib mesylate; Gleevec (USA); Glivec (other countries)] in 2000/2001. Despite the hope that STI-571 has generated for many CML patients, development of resistance to this drug is already apparent in some cases, especially if the CML is diagnosed in its later stages. Therefore, novel drugs which can be used alone or in combination with STI-571 are highly desirable. This review briefly summarises the current understanding and therapy of CML and then discusses in more detail basic laboratory research that attempts to target Grb2, an adaptor protein known to directly interact with the Bcr portion of the Bcr-Abl fusion protein. Blocking the binding of Grb2 to the GDP-releasing protein SoS is well known to abrogate the activation of the GTPase Ras, a major driving force of the central mitogenic (MAP kinase) pathway. Additional Grb2 effector proteins may also contribute to the proliferation-inhibiting effects observed upon uncoupling Grb2 from its downstream signalling system. Since Grb2 is a known signal transducer for several major human oncogenes, this approach may have applications for a wider range of human cancers.

Inverse relationship between myeloid maturation and leukotriene C4 synthase expression in normal and leukemic myelopoiesis-consistent overexpression of the enzyme in myeloid cells from patients with chronic myeloid leukemia

OBJECTIVE

Leukotriene (LT) C(4) synthase (LTC(4)S) is the key enzyme in the biosynthesis of LTC(4), which has been reported to stimulate the growth of human myeloid progenitor cells and is specifically overproduced in chronic myeloid leukemia (CML). The aim of this study was to clarify the expression of LTC(4)S during normal and leukemic myelopoiesis and to investigate the correlation between abnormal LTC(4)S expression in CML myeloid cells and the activity of the disease-specific tyrosine kinase p210 BCR-ABL.

MATERIALS AND METHODS

Immature and mature myeloid cell subpopulations were isolated with magnetic cell sorting from healthy volunteer bone marrow (n = 11) and CML patient peripheral blood (n = 8), respectively. The cells were subjected to analysis of LTC(4)S protein expression and activity. Expression of LTC(4)S was investigated in CD16(+) neutrophils from CML patients before and after 1 month of medication with imatinib mesylate (STI571), which is a specific inhibitor of p210 BCR-ABL.

RESULTS

Among normal cells, the highest enzyme activity was observed in the most immature, CD34(+) progenitor cell-enriched and CD15(+) myelocyte-enriched fractions. Subsequently, LTC(4)S activity decreased with increasing maturity, with only negligible amounts of LTC(4) produced in CD16(+) neutrophils. LTC(4)S was expressed at the protein level in the immature myeloid cell fractions but not in CD16(+) cells. In CML cells, LTC(4)S activity and expression were consistently elevated. Thus, the CML CD34(+) and CD15(+) cell fractions, as well as the CD11b(+) myelocyte/metamyelocyte-enriched fractions, produced 6 to 10 times as much LTC(4) as the corresponding normal cells. Again, enzyme expression was highest in the most immature cells, although evident LTC(4)S expression and activity remained in CML CD16(+) neutrophils. Interestingly, treatment of five CML patients with imatinib mesylate down-regulated the abnormal neutrophil LTC(4)S expression and activity.

CONCLUSIONS

Expression of LTC(4)S in immature myelopoid cells is in line with a role for this enzyme in myelopoiesis. In addition, consistent overexpression of LTC(4)S in CML and the correlation to p210 BCR-ABL activity suggests that LTC(4)S may be involved in leukemic pathogenesis.

The interaction of the Bcr-Abl tyrosine kinase with the Src kinase Hck is mediated by multiple binding domains

Bcr-Abl is found in more than 95% of cases with CML. The mechanism of Bcr-Abl-induced transformation is not fully understood. Bcr-Abl is a constitutively active tyrosine kinase with transforming capacity for hematopoietic cells. We demonstrated recently that the Src kinase Hck interacts directly with Bcr-Abl by a kinase-independent mechanism. Moreover, the inhibition of the Hck kinase seems to block some of the transforming effects of Bcr-Abl. To identify the binding domains mediating this interaction of Hck with Bcr-Abl, we co-expressed different plasmid and baculovirus vectors containing mutants or single domains of Bcr-Abl and/or Hck in COS7 and Sf9 cells. At least four independent binding regions for Hck were identified in Bcr-Abl, one in Bcr, one in the region comprising the SH3 and SH2 domain of Abl, one in the SH1 domain of Abl, and one in the C-terminal domain of Abl. In the Hck kinase, deletion of the SH2 and/or the SH3 region abolished binding to Bcr-Abl. In contrast, deletion of the Hck SH1 domain enhanced binding of Hck to Abl and Bcr-Abl. In conclusion, the results indicate that the interaction of Bcr-Abl with Hck is mediated by a novel, complex mechanism that involves multiple domains of Bcr-Abl and the SH2 and SH3 domains of Hck.

Dual-specific Src and Abl kinase inhibitors, PP1 and CGP76030, inhibit growth and survival of cells expressing imatinib mesylate-resistant Bcr-Abl kinases

The leukemogenic tyrosine kinase Bcr-Abl contains a highly conserved inhibitor-binding pocket (IBP), which serves as a binding site for imatinib mesylate. Mutations at the IBP may lead to resistance of the Abl kinase against imatinib mesylate. To examine the mechanisms of imatinib mesylate binding and resistance in more detail, we created several point mutations at amino acid positions 315 and 380 of Abl, blocking the access to the IBP and rendering Bcr-Abl imatinib mesylate-resistant. Moreover, introduction of a mutation destabilizing the inactive conformation of Abl (Asp276Ser/Glu279Ser) also led to imatinib mesylate resistance, suggesting that the inhibitor required inactivation of the kinase prior to binding. These Bcr-Abl mutants were then used to evaluate the binding mode and specificity of 2 compounds, PP1 and CGP76030, originally characterized as Src kinase inhibitors. Both compounds inhibited Bcr-Abl in a concentration-dependent manner by overlapping binding modes. However, in contrast to imatinib mesylate, PP1 and CGP76030 blocked cell growth and survival in cells expressing various inhibitor-resistant Abl mutants. Studies on the potential signaling mechanisms demonstrated that in cells expressing inhibitor-resistant Bcr-Abl mutants, PP1 and CGP76030 inhibited the activity of Src family tyrosine kinases and Akt but not signal transducer and activator of transcription-5 (STAT5) and JUN kinase (Jnk). The results suggest that the use of Src kinase inhibitors is a potential strategy to prevent or overcome clonal evolution of imatinib mesylate resistance in Bcr-Abl(+) leukemia.

Selective pyrrolo-pyrimidine inhibitors reveal a necessary role for Src family kinases in Bcr-Abl signal transduction and oncogenesis

Chronic myelogenous leukemia (CML) is defined by the presence of the Philadelphia (Ph) chromosome, which results in the expression of the 210 kDa Bcr-Abl tyrosine kinase. Bcr-Abl constitutively activates several signaling proteins important for the proliferation and survival of myeloid progenitors, including the Src family kinases Hck and Lyn, the Stat5 transcription factor and upstream components of the Ras/Erk pathway. Recently, we found that kinase-defective Hck blocks Bcr-Abl-induced transformation of DAGM myeloid leukemia cells to cytokine independence, suggesting that activation of the Src kinase family may be essential to oncogenic signaling by Bcr-Abl. To investigate the contribution of Src kinases to Bcr-Abl signaling in vivo, we used the pyrrolo-pyrimidine Src kinase inhibitors PP2 and A-419259. Treatment of the Ph+ CML cell lines K-562 and Meg-01 with either compound resulted in growth arrest and induction of apoptosis, while the Ph- leukemia cell lines TF-1 and HEL were unaffected over the same concentration ranges. Suppression of Ph+ cell growth by PP2 and A-419259 correlated with a decrease in Src kinase autophosphorylation. Both inhibitors blocked Stat5 and Erk activation, consistent with the suppressive effects of the compounds on survival and proliferation. In contrast, the phosphotyrosine content of Bcr-Abl and its endogenous substrate CrkL was unchanged at inhibitor concentrations that induced apoptosis, blocked oncogenic signaling and inhibited Src kinases. These data implicate the Src kinase family in Stat5 and Erk activation downstream of Bcr-Abl, and identify myeloid-specific Src kinases as potential drug targets in CML.

Antiproliferative effect in chronic myeloid leukaemia cells by antisense peptide nucleic acids

Peptide nucleic acid (PNA) is a synthetic DNA analogue that is resistant to nucleases and proteases and binds with exceptional affinity to RNA. Because of these properties PNA has the potential to become a powerful therapeutic agent to be used in vivo. Until now, however, the use of PNA in vivo has not been much investigated. Here, we have attempted to reduce the expression of the bcr/abl oncogene in chronic myeloid leukaemia KYO-1 cells using a 13mer PNA sequence (asPNA) designed to hybridise to the b2a2 junction of bcr/abl mRNA. To enhance cellular uptake asPNA was covalently linked to the basic peptide VKRKKKP (NLS-asPNA). Moreover, to investigate the cellular uptake by confocal microscopy, both PNAs were linked by their N-terminus to fluorescein (FL). Studies of uptake, carried out at 4 and 37 degrees C on living KYO-1 cells stained with hexidium iodide, showed that both NLS-asPNA-FL and asPNA-FL were taken up by the cells, through a receptor-independent mechanism. The intracellular amount of NLS-asPNA-FL was about two to three times higher than that of asPNA-FL. Using a semi-quantitative RT- PCR technique we found that 10 micro M asPNA and NLS-asPNA reduced the level of b2a2 mRNA in KYO-1 cells to 20 +/- 5% and 60 +/- 10% of the control, respectively. Western blot analysis showed that asPNA promoted a significant inhibition of p210(BCR/ABL) protein: residual protein measured in cells exposed for 48 h to asPNA was approximately 35% of the control. Additionally, asPNA impaired cell growth to 50 +/- 5% of the control and inhibited completion of the cell cycle. In summary, these results demonstrate that a PNA 13mer is taken up by KYO-1 cells and is capable of producing a significant and specific down-regulation of the bcr/abl oncogene involved in leukaemogenesis.

Isolation of differentially expressed genes in NPM-ALK-positive anaplastic large cell lymphoma

In this study, we used subtractive suppression hybridization to compare gene expression between an ALK-positive anaplastic large cell lymphoma (ALCL)-derived cell line and a clinical case of ALK-negative ALCL. Construction and screening of a subtracted library resulted in the cloning of 29 cDNAs which were differentially expressed. Most of these clones corresponded to novel genes with unknown function (EST) or to genes implicated in the differentiation, activation or signalling of T cells such as Ran/TC4, interleukin 1-receptor, thymosin beta4, thymosin beta10, moesin and cytohesin-1. Other genes involved in the regulation of apoptosis, such as human inhibitor of apoptosis-1 (HIAP-1), Bax inhibitor-1 and MCL-1, or DNA repair, such as poly (ADP-ribose) polymerase 1 (PARP-1), X-associated protein-1 (XAP-1), SUMO-1 (sentrin-1) and RanGTPase-activating protein 1 (RanGAP-1), were isolated. Interestingly, we found that both RNA and protein levels of human sterol isomerase (hSI), also referred to as emopamil binding protein (EBP), were overexpressed in ALK+ tumours. This protein is involved in the biosynthesis of cholesterol and may be activated by NPM-ALK. Overall, our results suggest that all the genes described above are upregulated in the NPM-ALK-driven transformation process, and that moesin and cytohesin-1 may be more specifically implicated in a signalling pathway involving PLCgamma and PI3K.

Cytokine signaling and hematopoietic homeostasis are disrupted in Lnk-deficient mice

The adaptor protein Lnk, and the closely related proteins APS and SH2B, form a subfamily of SH2 domain-containing proteins implicated in growth factor, cytokine, and immunoreceptor signaling. To elucidate the physiological function of Lnk, we derived Lnk-deficient mice. Lnk(-/-) mice are viable, but display marked changes in the hematopoietic compartment, including splenomegaly and abnormal lymphoid and myeloid homeostasis. The in vitro proliferative capacity and absolute numbers of hematopoietic progenitors from Lnk(-/-) mice are greatly increased, in part due to hypersensitivity to several cytokines. Moreover, an increased synergy between stem cell factor and either interleukin (IL)-3 or IL-7 was observed in Lnk(-/-) cells. Furthermore, Lnk inactivation causes abnormal modulation of IL-3 and stem cell factor-mediated signaling pathways. Consistent with these results, we also show that Lnk is highly expressed in multipotent cells and committed precursors in the erythroid, megakaryocyte, and myeloid lineages. These data implicate Lnk as playing an important role in hematopoiesis and in the regulation of growth factor and cytokine receptor-mediated signaling.

A randomized study of interferon-alpha versus interferon-alpha and low-dose arabinosyl cytosine in chronic myeloid leukemia

Interferon-alpha (IFN-alpha) has significantly prolonged survival in chronic myeloid leukemia (CML), but some patients do not respond and many responses are not durable. To improve the results, IFN-alpha has been combined with other treatments, but so far only the association with low-dose arabinosyl cytosine (LDAC) has been shown to increase the response rate and to prolong survival. Here are reported the results of a study of 538 Philadelphia chromosome-positive CML patients who were assigned at random to treatment with IFN-alpha 2a alone or in combination with LDAC. The scheduled dose of IFN-alpha 2a was 5(6) IU/m(2)/d. The scheduled dose of AC was 40 mg/d for the first 10 days of each month of treatment. The efficacy endpoints were a complete hematologic response rate at 6 months (62% in the IFN-alpha-plus-LDAC arm versus 55% in the IFN-alpha arm; P =.11), major cytogenetic response (MCgR) rate at 24 months (28% versus 18%; P =.003), and overall survival (5-year survival, 68% versus 65%; P =.77). Treatment did not affect overall survival within different prognostic risk groups: low, intermediate, or high. Also the duration of MCgR was identical. The results of this study confirm the results of a similar French study only for the response rate, not for survival, suggesting that the relationship between cytogenetic response and survival may be extremely variable and that a meta-analysis of these and other studies of IFN-alpha versus IFN-alpha plus LDAC is required to settle the issue of the role of LDAC in the treatment of CML.

Protein kinases as targets for anticancer agents: from inhibitors to useful drugs

Many components of mitogenic signaling pathways in normal and neoplastic cells have been identified, including the large family of protein kinases, which function as components of signal transduction pathways, playing a central role in diverse biological processes, such as control of cell growth, metabolism, differentiation, and apoptosis. The development of selective protein kinase inhibitors that can block or modulate diseases caused by abnormalities in these signaling pathways is widely considered a promising approach for drug development. Because of their deregulation in human cancers, protein kinases, such as Bcr-Abl, those in the epidermal growth factor-receptor (HER) family, the cell cycle regulating kinases such as the cyclin-dependent kinases, as well as the vascular endothelial growth factor-receptor kinases involved in the neo-vascularization of tumors, are among the protein kinases considered as prime targets for the development of selective inhibitors. These drug-discovery efforts have generated inhibitors and low-molecular weight therapeutics directed against the ATP-binding site of various protein kinases that are in various stages of development (up to Phase II/III clinical trials). Three examples of inhibitors of protein kinases are reviewed, including low-molecular weight compounds targeting the cell cycle kinases; a potent and selective inhibitor of the HER1/HER2 receptor tyrosine kinase, the pyrollopyrimidine PKI166; and the 2-phenyl-aminopyrimidine STI571 (Glivec(R), Gleevec) a targeted drug therapy directed toward Bcr-Abl, the key player in chronic leukemia (CML). Some members of the HER family of receptor tyrosine kinases, in particular HER1 and HER2, have been found to be overexpressed in a variety of human tumors, suggesting that inhibition of HER signaling would be a viable antiproliferative strategy. The pyrrolo-pyrimidine PKI166 was developed as an HER1/HER2 inhibitor with potent in vitro antiproliferative and in vivo antitumor activity. Based upon its clear association with disease, the Bcr-Abl tyrosine kinase in CML represents the ideal target to validate the clinical utility of protein kinase inhibitors as therapeutic agents. In a preclinical model, STI571 (Glivec(R), Gleevec) showed potent in vitro and in vivo antitumor activity that was selective for Abl, c-Kit, and the platelet-derived growth factor-receptor. Phase I/II studies demonstrated that STI571 is well tolerated, and that it showed promising hematological and cytogenetic responses in CML and clinical responses in the c-Kit-driven gastrointestinal tumors.

Antigene effect in K562 cells of a PEG-conjugated triplex-forming oligonucleotide targeted to the bcr/abl oncogene

Triplex-forming oligonucleotides are able to modulate gene expression by site-specific binding to genomic DNA. Their use as therapeutic agents is limited by inefficient cellular uptake, scarce nuclear internalization, and oligonucleotide self-aggregation. In this study, we demonstrate that a 13-mer AG motif oligonucleotide covalently linked to a high-molecular mass (9000 Da) polyethylene glycol (PEG ODN(13)) exhibits uptake and biological properties that are superior to those of the nonconjugated isosequence analogue (free ODN(13)). Band-shift and footprinting experiments showed that PEG ODN(13) forms a stable triple helix (apparent K(d) between 10(-6) and 10(-7) M in 50 mM Tris-acetate, 10 mM MgCl(2), pH 7.4, 37 degrees C) with a natural polypurine-polypyrimidine target located in the 5' flanking region of the human bcr/abl oncogene. Confocal laser microscopy performed on unfixed live cells stained with hexidium iodide as well as on glass-fixed cells stained with propidium iodide showed that fluorescein-labeled PEG ODN(13) is far more efficiently taken up and internalized in the nucleus by K562 and HeLa cells than the nonconjugated free ODN(13). It was found that PEG ODN(13) specifically downregulated the transcription of bcr/abl mRNA at 65 +/- 5% with respect to control and inhibited cell growth by 32 +/- 3% in a 3 day liquid culture assay. Moreover, PEG ODN(13) was more resistant against S1 and fetal bovine serum nucleases than free ODN(13), and less inclined to self-associate into multistrand structures in solution. Taken together, these results provide useful elements for designing artificial transcription repressors with enhanced potency in vivo.

Cytokine signalling and disease

Cytokines mediate their response via cell surface receptors that in turn activate intracellular signalling pathways and lead to gene activation, cell proliferation and differentiation. Many recent studies have shown that cytokine and cytokine receptor pathways are frequently mutated in disease, thus shedding light on the generation of the inflammatory response, specific immunity and mechanisms of haematopoiesis. Many approaches are being used to translate this basic research into successful therapies and although host immune responses involve many different cells and crucial pathways, modulation of therapeutic responses can be induced or inhibited by, targeting a single cytokine. This review summarises current knowledge of cytokine pathways in disease and the use of cytokine- or receptor-directed therapy to exploit the immune response to disease.

Expression of the oncogenic NPM-ALK chimeric protein in human lymphoid T-cells inhibits drug-induced, but not Fas-induced apoptosis

Anaplastic large cell lymphomas (ALCLs) are frequently associated with the t(2;5)(p23;q35) translocation, leading to the expression of NPM-ALK, a fusion protein linking nucleophosmin and anaplastic lymphoma kinase, a receptor tyrosine kinase. In ALCLs, dimerization of NPM-ALK leads to constitutive autophosphorylation and activation of the kinase, necessary for NPM-ALK oncogenicity. To investigate whether NPM-ALK, like other oncogenic tyrosine kinases, can inhibit drug-induced apoptosis, we permanently transfected NPM-ALK into Jurkat T-cells. As in ALCLs, NPM-ALK was expressed as a constitutively kinase-active 80 kDa protein, and could be detected by immunocytochemistry in nucleoli, nuclei and cytoplasm. Doxorubicin-induced apoptosis (assessed by cell morphology and annexin V-FITC binding) was significantly inhibited in two independent NPM-ALK-expressing clones (5.2+/-1.8 and 7.5+/-0.8% apoptosis), compared to control vector-transduced cells (36+/-6.7%). Similar results were observed with etoposide. In contrast, Fas-induced apoptosis was not inhibited. Cytochrome c release into the cytosol was delayed in doxorubicin-, but not anti-Fas-treated transfectant cells, indicating that apoptosis inhibition occurred upstream of mitochondrial events. Using NPM-ALK mutants, we demonstrated that inhibition of drug-induced apoptosis: (1) requires functional kinase activity, (2) does not involve phospholipase C-gamma, essential for NPM-ALK-mediated mitogenicity and (3) appears to be phosphoinositide 3-kinase independent, despite a strong Akt/PKB activation observed in wild type NPM-ALK-expressing cells. These results suggest that the NPM-ALK antiapoptotic and mitogenic pathways are distinct.

Chronic myelogenous leukemia: laboratory diagnosis and monitoring

Rapid developments have occurred both in laboratory medicine and in therapeutic interventions for the management of patients with chronic myelogenous leukemia (CML). With a wide array of laboratory tests available, selecting the appropriate test for a specific diagnostic or therapeutic setting has become increasingly difficult. In this review, we first discuss, from the point of view of laboratory medicine, the advantages and disadvantages of several commonly used laboratory assays, including cytogenetics, fluorescence in situ hybridization (FISH), and qualitative and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). We then discuss, from the point of view of clinical care, the test(s) of choice for the most common clinical scenarios, including diagnosis and monitoring of the therapeutic response and minimal residual disease in patients treated with different therapies. The purpose of this review is to help clinicians and laboratory physicians select appropriate tests for the diagnosis and monitoring of CML, with the ultimate goal of improving the cost-effective usage of clinical laboratories and improving patient care.

Results of therapy with interferon alpha and cyclic combination chemotherapy in patients with philadelphia chromosome positive chronic myelogenous leukemia in early chronic phase

The objective of the study was to investigate the toxicity and efficacy of cyclic combination therapy offered to patients with Ph-positive CML having a sub-optimal response to IFN-alpha. Patients in early chronic phase CML were treated with IFN-alpha at 5MU/m(2) daily. Patients who did not achieve cytogenetic response after 6 months of IFN-alpha therapy, or Ph-suppression to less than 35% Ph-positive cells (partial cytogenetic response) after 12 months of therapy were offered cyclic intensive chemotherapy every 6 months, with IFN-alpha maintenance between cycles. The initial 3 cycles included daunorubicin, vincristine, cytosine arabinoside (ara-C) and prednisone (DOAP). Later cycles were given with cyclophosphamide replacing daunorubicin (COAP). Of 74 patients treated, 61 (82%) achieved complete hematologic response (CHR): 51 (69%) had a cytogenetic response, which was major (Ph < 35%) in 31 (42%), and complete in 23 (31%). Fifty-five patients (74%) achieved CHR by 6 months of therapy, 38 (69%; 51% of total) with a cytogenetic response - 13 (24%) had a major cytogenetic response. Seventeen patients received at least 1 course of DOAP therapy. Median survival of the overall cohort of patients was 120 months. With a median follow-up of 145 months (103+ to 155+ months), 40 patients (54%) have died. The median duration of cytogenetic response was 35 months (range 3 to 149+ months) and the estimated 10-year cytogenetic response rate was 37%. A durable complete cytogenetic response was observed in 16 patients (20%) with a median duration of 139+ months (range 12+ to 149+ months), 11 of them (15%) are now off IFN-alpha therapy for a median of 57+ months (range 12+ to 128+ months). The projected 10-year survival was 50% for the study group versus 35% for 208 patients who received other IFN-alpha based regimens at the MD Anderson Cancer Center (p<.01). In conclusion, the addition of intensive chemotherapy may improve survival in patients with CML who have not obtained an adequate cytogenetic response on an IFN-alpha-based regimen.

Synergistic activity of the new ABL-specific tyrosine kinase inhibitor STI571 and chemotherapeutic drugs on BCR-ABL-positive chronic myelogenous leukemia cells

The ABL-specific tyrosine kinase inhibitor STI571 (formerly CGP57148B) induced cytogenetic remissions in 33% of chronic myelogenous leukemia (CML) patients in a phase I trial (Druker et al 1999). Combination therapy may increase this proportion. We tested whether combinations of STI571 and cytarabine or other chemotherapeutic agents such as hydroxyurea, mafosfamide or etoposide would display synergistic activity in BCR-ABL-positive chronic myelogenous leukemia (CML) cell lines derived from patients in blast crisis. In addition, the toxicity of these combinations on BCR-ABL-negative cells was investigated. A tetrazolium-based MTT assay was used to quantity growth inhibition after 48 h of exposure to cytotoxic agents alone and in simultaneous combination with STI571. The drug interactions were analyzed using the median-effect method of Chou and Talalay. The combination index (CI) was calculated according to the classic isobologram equation. At growth inhibition levels of over 50%, STI571 + cytarabine as well as STI571 + etoposide were significantly synergistic (CI < 1, P < 0.05) in the BCR-ABL-positive cell lines evaluated. At 60% inhibition or higher, a similar synergistic pattern became apparent for STI571 + mafosfamide (P < 0.05), while STI571 + hydroxyurea showed ambiguous, cell line-dependent synergism (BV173), additivity (EM-3) or antagonism (K562) in CML cell lines. Furthermore, the BCR-ABL-negative HL-60, KG1a and normal CD34+ progenitor cells were not affected by 0.8 microM STI571, a concentration which produced more than 50% growth inhibition in all BCR-ABL-positive cells tested, and no potentiation of growth inhibition was observed in these BCR-ABL-negative cells when STI571 was combined with chemotherapeutic agents. Our in vitro data with CML blast crisis cell lines strongly suggest that combinations of STI571 with cytarabine or etoposide be rapidly considered for clinical testing.

Cytarabine added to interferon improves the cost-effectiveness of initial therapy for patients with early chronic phase chronic myelogenous leukemia

The French Chronic Myeloid Leukemia Study Group prospective randomized study results indicate that the addition of cytarabine to alpha interferon (IFN-alpha) increases the rate of major cytogenetic response and prolongs survival in patients with early chronic phase chronic myelogenous leukemia (CML). The French group study design permitted a single crossover to include or discontinue cytarabine or interferon. Endpoints were overall survival, complete hematologic remission (CHR) at six months, and major cytogenetic response at 12 months. We modified a published Markov model that compared IFN-alpha alone to IFN-alpha plus cytarabine and included the possibility of crossover as in the French study. The model permits allogeneic and autologous stem cell transplantation (SCT), and follows cytogenetic response and acceleration of CML through death. Treatment response, toxicity, and survival are drawn from the French Chronic Myeloid Leukemia Study Group population of 810 patients on an intention-to-treat model. Survivals are extended to 62 months based on currently available follow-up. Costs from a United States oncology specialty institution, and state utilities from previous research and a quality-adjusted Time Without Symptoms or Toxicity analysis of the subject study were discounted at 3% per annum. At the median cohort age of 50, cytarabine offers 21 months of added median survival to IFN-alpha, which itself is superior to conventional chemotherapy by 21 months. Cost-effectiveness estimates for cytarabine added to IFN-alpha range from $7,000 per quality-adjusted life year (QALY) to $35,000 per QALY, under all plausible assumptions superior to IFN-alpha alone. The model is sensitive to the quality of life on therapy, as well as to remission rate with additive cytarabine, although the cost-effectiveness calculations are robust over the entire range of clinical assumptions. Based on data from the French study, cytarabine added to IFN-alpha substantially improves the cost-effectiveness of initial therapy for early chronic phase CML.

Induction of apoptosis in chronic myelogenous leukemia cells through nuclear entrapment of BCR-ABL tyrosine kinase

The chimeric BCR-ABL oncoprotein is the molecular hallmark of chronic myelogenous leukemia (CML). BCR-ABL contains nuclear import and export signals but it is localized only in the cytoplasm where it activates mitogenic and anti-apoptotic pathways. We have found that inhibition of the BCR-ABL tyrosine kinase, either by mutation or by the drug STI571, can stimulate its nuclear entry. By combining STI571 with leptomycin B (LMB) to block nuclear export, we trapped BCR-ABL in the nucleus and the nuclear BCR-ABL tyrosine kinase activates apoptosis. As a result, the combined treatment with STI571 and LMB causes the irreversible and complete killing of BCR-ABL transformed cells, whereas the effect of either drug alone is fully reversible. The combined treatment with STI571 and LMB also preferentially eliminates mouse bone marrow cells that express BCR-ABL. These results indicate that nuclear entrapment of BCR-ABL can be used as a therapeutic strategy to selectively kill chronic myelogenous leukemia cells.

Interferon-alpha and the pathogenesis of myeloproliferative disorders

Interferon-alpha (IFN-alpha), a molecule with multiple biological actions, is widely used in the treatment of chronic myelogenous leukemia (CML) and the other myeloproliferative disorders. This glycoprotein belonging to the type I subfamily of interferons has been recombinantly manufactured and has been approved for the biotherapy of CML, now becoming the first line of treatment for CML patients in chronic phase who are not candidates for allogeneic hematopoietic stem cell or bone marrowtransplantation. Interferon-alpha action involves binding to its cell membrane receptor and initiation of an intracellular signal transduction cascade. Two major pathways mediate the biologic actions of IFN-alpha. The JAK-STAT pathway leads to phosphorylation and activation of STAT 1 and STAT 2 molecules and transcription of genes like p21 and caspase-1 resulting in cycle arrest and apoptosis. The PKR (protein kinase dsRNA-induced) kinase phosphorylates and inhibits the eukaryotic initiator of translation eIF-2alpha leading again to apoptosis. The PKR kinase cascade also leads to activation of the transcription factor NF-kappaB. The relevance of this activation is unclearand it is possiblethat NF-kappaB has not had the opportunity to transcribe its target genes as it is a substrate of effector caspases and is maybe cleaved by them before exerting any transcription activity. Through the JAK-STAT and the PKR kinase pathways IFN-alpha is able to modify the proliferative and antiapoptotic actions of the constitutively activated kinase bcr-abl, the product of the t(9;22) translocation present in CML, and has therapeutic effects in this disease.

Reduced oncogenicity of p190 Bcr/Abl F-actin–binding domain mutants

The deregulated Bcr/Abl tyrosine kinase is responsible for the development of Philadelphia (Ph)-positive leukemia in humans. To investigate the significance of the C-terminal Abl actin-binding domain within Bcr/Abl p190 in the development of leukemia/lymphoma in vivo, mutant p190 DNA constructs were used to generate transgenic mice. Eight founder and progeny mice of 5 different lines were monitored for leukemogenesis. Latency was markedly increased and occurrence decreased in the p190 del C lines as compared with nonmutated p190BCR/ABL transgenics. Western blot analysis of involved hematologic tissues of the p190 del C transgenics with end-stage disease showed high-level expression of the transgene and tyrosine phosphorylation of Cbl and Hef1/Cas, proteins previously shown to be affected by Bcr/Abl. These results show that the actin-binding domain of Abl enhances leukemia development but does not appear to be an absolute requirement for leukemogenesis.