A novel c-abl protein product in Philadelphia-positive acute lymphoblastic leukaemia

Navigating between Scylla and Charybdis: A roadmap to do better than Pola-RCHP in DLBCL

In treating diffuse large B-cell lymphoma (DLBCL), oncologists have traditionally relied on the chemotherapy backbone of R-CHOP as standard of care. The two dangers that the hematologist must navigate between are the aggressive disease (Charybdis that in the absence of therapy systematically destroys all the ships) and the toxicity of the therapies (Scylla with its six monstrous heads that devours six crew members at a time), and hematologists have to navigate very carefully between both. Therefore, three different strategies were employed with the goal of improving cure rates: de-escalating regimens, escalating regimens, and replacement strategies. With a replacement strategy, a breakthrough in treatment was identified with polatuzumab vedotin (anti-CD79B antibody/drug conjugate) plus R-CHP. However, this regimen still did not achieve the elusive universal cure rate. Fortunately, advances in genomic and molecular technologies have allowed for an improved understanding of the heterogenous molecular nature of the disease to help develop and guide more targeted, precise, and individualized therapies. Additionally, new pharmaceutical technologies have led to the development of novel cellular therapies, such as chimeric antigen receptor (CAR) T-cell therapy, that could be more effective, while maintaining an acceptable safety profile. Thus, we aim to highlight the challenges of DLBCL therapy as well as the need to address therapeutic regimens eventually no longer tethered to a chemotherapy backbone. In the intersection of artificial intelligence and multi-omics (genomics, epigenomics, transcriptomics, proteomics, metabolomics), we propose the need to analyze multidimensional biologic datato launch a decisive attack against DLBCL in a targeted and individualized fashion.

The EMA Assessment of Asciminib for the Treatment of Adult Patients With Philadelphia Chromosome-Positive Chronic Myeloid Leukemia in Chronic Phase Who Were Previously Treated With At Least 2 Tyrosine Kinase Inhibitors

Asciminib is an allosteric high-affinity tyrosine kinase inhibitor (TKI) of the BCR-ABL1 protein kinase. This kinase is translated from the Philadelphia chromosome in chronic myeloid leukemia (CML). Marketing authorization for asciminib was granted on August 25, 2022 by the European Commission. The approved indication was for patients with Philadelphia chromosome-positive CML in the chronic phase which have previously been treated with at least 2 TKIs. Clinical efficacy and safety of asciminib were evaluated in the open-label, randomized, phase III ASCEMBL study. The primary endpoint of this trial was major molecular response (MMR) rate at 24 weeks. A significant difference in MRR rate was shown between the asciminib treated population and the bosutinib control group (25.5% vs. 13.2%, respectively, P = .029). In the asciminib cohort, adverse reactions of at least grade 3 with an incidence ≥ 5% were thrombocytopenia, neutropenia, increased pancreatic enzymes, hypertension, and anemia. The aim of this article is to summarize the scientific review of the application which led to the positive opinion by the European Medicines Agency's Committee for Medicinal Products for Human Use.

Molecular basis and clinical application of targeted therapy in oncology

Targeted therapy and precision oncology aim to improve efficacy and minimize side effects by targeting specific molecules involved in cancer growth and spread. With the advancements in genomics, proteomics, and transcriptomics with the accessible modalities such as next-generation sequencing, circulating tumor cells, and tumor Deoxyribonucleic Acid (DNA), more number of patients are being offered the targeted therapy in form of monoclonal antibodies and various intracellular targets, specific for their tumor. The harnessing of host immunity against the cancer cells by utilizing immune-oncology agents and chimeric antigen receptor T-cell therapy has further revolutionized the management of various cancers. These agents, however, have the challenge of managing the adverse effects that are peculiar to the class of drugs and very different from the conventional chemotherapy. This review article discusses the molecular basis, diagnostics, and use of targeted therapy in oncology.

The coming decade in precision oncology: six riddles

High-throughput methods to investigate tumour omic landscapes have quickly catapulted cancer specialists into the precision oncology era. The singular lesson of precision oncology might be that, for it to be precise, treatment must be personalized, as each cancer's complex molecular and immune landscape differs from patient to patient. Transformative therapies include those that are targeted at the sequelae of molecular abnormalities or at immune mechanisms, and, increasingly, pathways previously thought to be undruggable have become druggable. Critical to applying precision medicine is the concept that the right combination of drugs must be chosen for each patient and used at the right stage of the disease. Multiple puzzles remain that complicate therapy choice, including evidence that deleterious mutations are common in normal tissues and non-malignant conditions. The host's role is also likely to be key in determining treatment response, especially for immunotherapy. Indeed, maximizing the impact of immunotherapy will require omic analyses to match the right immune-targeted drugs to the individualized patient and tumour setting. In this Perspective, we discuss six key riddles that must be solved to optimize the application of precision oncology to otherwise lethal malignancies.

Insights into the prenatal origin of childhood acute lymphoblastic leukemia

Pediatric acute lymphoblastic leukemia (ALL) is defined by recurrent chromosomal aberrations including hyperdiploidy and chromosomal translocations. Many of these aberrations originate in utero and the cells transform in early childhood through acquired secondary mutations. In this review, we will discuss the most common prenatal lesions that can lead to childhood ALL, with a special emphasis on the most common translocation in childhood ALL, t(12;21), which results in the ETV6-RUNX1 gene fusion. The ETV6-RUNX1 fusion arises prenatally and at a 500-fold higher frequency than the corresponding ALL. Even though the findings regarding the frequency of ETV6-RUNX1 were originally challenged, newer studies have confirmed the higher frequency. The prenatal origin has also been proven for other gene fusions, including KMT2A, the translocations t(1;19) and t(9;22) leading to TCF3-PBX1 and BCR-ABL1, respectively, as well as high hyperdiploidy. For most of these aberrations, there is evidence for more frequent occurrence than the corresponding leukemia incidences. We will briefly discuss what is known about the cells of origin, the mechanisms of leukemic transformation through lack of immunosurveillance, and why only a part of the carriers develops ALL.

Review of precision cancer medicine: Evolution of the treatment paradigm

In recent years, biotechnological breakthroughs have led to identification of complex and unique biologic features associated with carcinogenesis. Tumor and cell-free DNA profiling, immune markers, and proteomic and RNA analyses are used to identify these characteristics for optimization of anticancer therapy in individual patients. Consequently, clinical trials have evolved, shifting from tumor type-centered to gene-directed, histology-agnostic, with innovative adaptive design tailored to biomarker profiling with the goal to improve treatment outcomes. A plethora of precision medicine trials have been conducted. The majority of these trials demonstrated that matched therapy is associated with superior outcomes compared to non-matched therapy across tumor types and in specific cancers. To improve the implementation of precision medicine, this approach should be used early in the course of the disease, and patients should have complete tumor profiling and access to effective matched therapy. To overcome the complexity of tumor biology, clinical trials with combinations of gene-targeted therapy with immune-targeted approaches (e.g., checkpoint blockade, personalized vaccines and/or chimeric antigen receptor T-cells), hormonal therapy, chemotherapy and/or novel agents should be considered. These studies should target dynamic changes in tumor biologic abnormalities, eliminating minimal residual disease, and eradicating significant subclones that confer resistance to treatment. Mining and expansion of real-world data, facilitated by the use of advanced computer data processing capabilities, may contribute to validation of information to predict new applications for medicines. In this review, we summarize the clinical trials and discuss challenges and opportunities to accelerate the implementation of precision oncology.

Targeting fusions for improved outcomes in oncology treatment

BACKGROUND

Fusions are increasingly pursued as oncology therapeutic targets. The current study evaluated differences in outcomes for fusion versus nonfusion targets.

METHODS

Outcomes were compared for patients with fusions versus those with other alterations for US Food and Drug Administration-approved single agents (from package inserts) and for patients treated at the University of California at San Diego.

RESULTS

A total of 28 drugs approved by the US Food and Drug Administration (6189 patients) were included in the analysis. The median response rate was 68% versus 50% for fusions versus nonfusion matches (odds ratio [OR], 1.67; P < .0001); solid tumor therapies had an OR of 2.07 (P < .0001) and hematologic therapies had an OR of 3.35 (P < .0001) for fusion versus nonfusion targets. The University of California at San Diego analysis included 79 patients in whom fusions were treated of the 2455 patients screened. Patients matched to fusions were found to have a longer median progression-free survival (PFS) (11.6 months; 95% CI, 4.0-35.4 months) compared with those unmatched to fusions (4.9 months; 95% CI, 3.5-8.8 months) (P = .034). Patients with fusions matched to other alterations present in the tumor had a median PFS that was indistinguishable from that of those patients with fusions who were treated with unmatched therapy (4.0 months vs 5.0 months; P = .75).

CONCLUSIONS

Significantly higher response rates and a longer PFS were observed when targeting fusions compared with nonfusions. The observations reported in the current study suggest that fusions are important targets and that additional studies are needed to confirm that optimized therapy may require targeting fusions, even in the presence of other alterations.

A rare e14a3 BCR/ABL fusion transcript in acute lymphoblastic leukemia patient treated with CAR-modified T-cell therapy

E14a3 breakpoint cluster region (BCR)/ABL proto-oncogene 1, non-receptor tyrosine kinase (ABL) fusion transcript is rare in Philadelphia chromosome positive disease, particularly in acute lymphoblastic leukemia (ALL). Recently an e14a3 fusion transcript was detected by multiple laboratory examinations, and the patient was suffering from ALL. Except for the BCR/ABL fusion gene, in the present study the patient additionally had an IKAROS family zinc finger 1 deletion which, has been confirmed as a significant adverse prognosis factor. Following 2 rounds of chemotherapy, the patient presented cytological remission; however, the patient then relapsed 2 months later. They then received chimeric antigen receptor modified (CAR-modified) T-cell therapy and achieved complete remission. CAR-modified T-cell therapy is a powerful novel therapy which, exhibited great potential for treating refractory ALL, regardless of the existence and form of the BCR/ABL fusion transcript.

The Conundrum of Genetic "Drivers" in Benign Conditions

Advances in deep genomic sequencing have identified a spectrum of cancer-specific passenger and driver aberrations. Clones with driver anomalies are believed to be positively selected during carcinogenesis. Accumulating evidence, however, shows that genomic alterations, such as those in BRAF, RAS, EGFR, HER2, FGFR3, PIK3CA, TP53, CDKN2A, and NF1/2, all of which are considered hallmark drivers of specific cancers, can also be identified in benign and premalignant conditions, occasionally at frequencies higher than in their malignant counterparts. Targeting these genomic drivers can produce dramatic responses in advanced cancer, but the effects on their benign counterparts are less clear. This benign-malignant phenomenon is well illustrated in studies of BRAF V600E mutations, which are paradoxically more frequent in benign nevi (∼80%) than in dysplastic nevi (∼60%) or melanoma (∼40%-45%). Similarly, human epidermal growth factor receptor 2 is more commonly overexpressed in ductal carcinoma in situ (∼27%-56%) when compared with invasive breast cancer (∼11%-20%). FGFR3 mutations in bladder cancer also decrease with tumor grade (low-grade tumors, ∼61%; high-grade, ∼11%). “Driver” mutations also occur in nonmalignant settings: TP53 mutations in synovial tissue from rheumatoid arthritis and FGFR3 mutations in seborrheic keratosis. The latter observations suggest that the oncogenicity of these alterations may be tissue context–dependent. The conversion of benign conditions to premalignant disease may involve other genetic events and/or epigenetic reprogramming. Putative driver mutations can also be germline and associated with increased cancer risk (eg, germline RAS or TP53 alterations), but germline FGFR3 or NF2 abnormalities do not predispose to malignancy. We discuss the enigma of genetic “drivers” in benign and premalignant conditions and the implications for prevention strategies and theories of tumorigenesis.

Bosutinib for the Treatment of Philadelphia Chromosome-Positive Leukemias

Introduction

Bosutinib is a dual ABL1 and SRC third generation tyrosine kinase inhibitor (TKI) indicated for the treatment of patients with chronic myelogenous leukemia (CML) resistant to or intolerant of other BCR-ABL1 inhibitors. Bosutinib is active against leukemia cells expressing imatinib-resistant BCR-ABL1 mutations. Mechanistically, this agent may also be beneficial for Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) because in preclinical animal models, SRC accelerates ALL disease development.

Areas Covered

Here we review the current scientific and medical literature on the role of bosutinib for the treatment of CML. We address the unique therapeutic advantages of this agent, specifically its ability to inhibit mutant BCR-ABL1 kinases conferring resistance to other TKIs and its unique safety profile consisting of mainly manageable self-limited diarrhea, not cardiovascular, side effects. Long-term toxicities reported with dasatinib, nilotinib and ponatinib have not been described with bosutinib. Lastly, we present preclinical data demonstrating that bosutinib inhibits a broader range of tyrosine kinases than any other TKI, including those implicated in acute leukemia.

Expert Opinion

We propose that future studies should explore the use of bosutinib in Ph+ ALL due to its multi-kinase inhibitory activity and its relatively long-term safety compared to other second and third generation TKIs.

Targeting paediatric acute lymphoblastic leukaemia: novel therapies currently in development

Modifications to the treatment of acute lymphoblastic leukaemia (ALL) in children have led to a dramatic increase in survival in the past 40 years. Despite this success, a significant subset of paediatric leukaemia patients either relapse or fail to ever achieve a complete remission. Additionally, some patients necessitate treatment with intensified chemotherapy regimens due to clinical or laboratory findings which identify them as high risk. These patients are unlikely to respond to further minor adjustments to the dosing or timing of administration of the same chemotherapy medications. Many novel targeted therapies for the treatment of childhood ALL provide potential mechanisms to further improve cure rates, and provide the possibility of minimizing toxicity to non-malignant cells, given their specificity to malignant cell phenotypes. This article explores many of the potential targeted therapies in varying stages of development, from those currently in clinical trials to those still being refined in the research laboratory.

FAK silencing inhibits leukemogenesis in BCR/ABL-transformed hematopoietic cells

Focal adhesion kinase (FAK) is constitutively activated and tyrosine phosphorylated in BCR/ABL-transformed hematopoietic cells, but the role it plays during leukemogenesis remains unclear. Here, we examined the effects of RNA interference-mediated FAK silencing on leukemogenesis induced by a BCR/ABL-transformed cell line. Transduction of BCR/ABL-BaF3 cells with FAK shRNA inhibited FAK expression and reduced STAT5 phosphorylation, but induced caspase-3 activation. In vitro studies showed that treatment with FAK shRNA resulted in impaired cell proliferation and colony formation, while increasing cell apoptosis. Mice that received transplants of BCR/ABL-BaF3 cells with FAK shRNA displayed significantly prolonged survival time and diminished leukemia progression. In addition, FAK silencing enhanced in vitro and in vivo efficacy of ABL tyrosine kinase inhibitor imatinib in BCR/ABL-BaF3 cells. Our results suggest that FAK is critical for leukemogenesis and might be a potential target for leukemia therapy.

Molecular imaging of Bcr-Abl phosphokinase in a xenograft model

The purpose of this study was to determine whether the Bcr-Abl tyrosine kinase can be assessed by gamma-imaging using an 111In-labeled anti-phosphotyrosine (APT) antibody, and if the response to treatment with imatinib could be detected using this imaging technique. APT antibody was labeled with 111In using ethylenedicysteine (EC) as a chelator. To determine if 111In-EC-APT could assess a nonreceptor tyrosine kinase, xenografts of the human chronic myelogenous leukemia cell line K562 were used. gamma-Scintigraphy of the tumor-bearing mice, before and after imatinib treatment, was obtained 1, 24, and 48 h after they were given 111In-EC-APT (100 microCi/mouse i.v.). 111In-EC-APT is preferentially taken up by Bcr-Abl-bearing tumor cells when compared with 111In-EC-BSA or 111In-EC-IgG1 controls and comparable with the level of uptake of 111In-EC-Bcr-Abl. Imatinib treatment resulted in decreased expression of phospho-Bcr-Abl by Western blot analysis, which correlated with early (4 days after starting imatinib) kinase down-regulation as assessed by imaging using 111In-EC-APT. The optimal time to imaging was 24 and 48 h after injection of 111In-EC-APT. Although tumor regression was insignificant on day 4 after starting imatinib treatment, it was marked by day 14. 111In-EC-APT can assess intracellular phosphokinase activity, and down-regulation of phosphokinase activity predates tumor regression. This technique may therefore be useful in the clinic to detect the presence of phosphokinase activity and for early prediction of response.

The drug development crisis: efficiency and safety

Despite advancements in genetics, chemistry, and protein engineering, recent years have seen fewer approvals of new drugs, increases in development costs, and high-profile drug withdrawals. This article focuses on technologic methods for improving drug development efficiency. These technologies include high-content cell screening, expression profiling, mass spectroscopy, mouse models of disease, and a post-launch screening program that enables investigations of adverse drug effects. Implementation of these new technologies promises to improve performance in drug development and safety.

Sustained leukaemic phenotype after inactivation of BCR-ABLp190 in mice

Pharmacological inactivation of cancer genes or products is being used as a strategy for therapy in oncology. To investigate the potential role of BCR-ABLp190 cessation in leukaemia development, we generated mice carrying a tetracycline-repressible BCR-ABLp190 transgene. These mice were morphologically normal at birth, and developed leukaemias. Disease was characterized by the presence of B-cell blasts co-expressing myeloid markers, reminiscent of the human counterpart. BCR-ABLp190 activation can initiate leukaemia in both young and adult mice. Transitory expression of BCR-ABLp190 is enough to develop leukaemia. Suppression of the BCR-ABLp190 transgene in leukaemic CombitTA-p190 mice did not rescue the malignant phenotype, indicating that BCR-ABLp190 is not required to maintain the disease in mice. Similar results were obtained by inactivation of BCR-ABLp190 with STI571 (Gleevec; Novartis, East Hanover, NJ, USA) in leukaemic CombitTA-p190 mice. However, gradual suppression of BCR-ABLp190 in leukaemic CombitTA-p190 mice identified a minimum level of BCR-ABLp190 expression necessary to revert the specific block in B-cell differentiation in the leukaemic cells. Overall, the findings indicate that BCR-ABLp190 appears to cause epigenetic and/or genetic changes in tumour-maintaining cells that render them insensitive to BCR-ABLp190 inactivation.

Targeting mutated tyrosine kinases in the therapy of myeloid leukaemias

Myeloid leukaemias are frequently associated with translocations and mutations of tyrosine kinase genes. The products of these oncogenes, including BCR-ABL, TEL-PDGFR, Flt3 and c-Kit, have elevated tyrosine kinase activity and transform haematopoietic cells, mainly by augmentation of proliferation and enhanced viability. Activated ABL kinases are associated with chronic myeloid leukaemia. Mutations in platelet-derived growth factor receptor beta are associated with chronic myelomonocytic leukaemia. Flt3 or c-Kit cooperate with other types of oncogenes to create fully transformed acute leukaemias. Elevated activity of these tyrosine kinases is crucial for transformation, thus making the kinase domain an ideal target for therapeutic intervention. Tyrosine kinase inhibitors for various kinases are currently being evaluated in clinical trials and are potentially useful therapeutic agents in myeloid leukaemias. Here, the authors review the signalling activities, mechanism of transformation and therapeutic targeting of several tyrosine kinase oncogenes important in myeloid leukaemias.

Chronic Myelogenous Leukemia: From Molecular Biology to Clinical Aspects and Novel Targeted Therapies

The critical causative event in chronic myelogenous leukemia (CML) is the fusion of the head of the bcr gene with the body of the abl gene, named bcr/abl gene. This chimeric BCR/ABL molecule transforms primary myeloid cells to leukemic cells and induces a CML-like disease in mice. The mouse CML model expressing the BCR/ABL molecule has provided important new insights into the molecular pathophysiology of CML and has directly answered many questions regarding this disease. Furthermore, numerous clinical studies have demonstrated a correlation between leukemic clinical features and the position of the breakpoint in the BCR gene of the chimeric BCR/ABL gene. Understanding of the molecular pathogenesis of CML has led to the development of several novel therapies. The BCR/ABL molecule is unique oncogeneiety, having ABL tyrosine kinase activity, making it an ideal target for drug development. Subsequent clinical studies now realize the hypothesis that selective inhibition of the abl tyrosine kinase activity using imatinib mesylate might be useful for the treatment of CML. This article reviews the history of BCR/ABL molecular biology, including the CML model mouse, clinical molecular studies and the recent findings of imatinib mesylate and more potent tyrosine kinase inhibitors developed for the treatment of CML.

Distinct patterns of hematopoietic stem cell involvement in acute lymphoblastic leukemia

The cellular targets of primary mutations and malignant transformation remain elusive in most cancers. Here, we show that clinically and genetically different subtypes of acute lymphoblastic leukemia (ALL) originate and transform at distinct stages of hematopoietic development. Primary ETV6-RUNX1 (also known as TEL-AML1) fusions and subsequent leukemic transformations were targeted to committed B-cell progenitors. Major breakpoint BCR-ABL1 fusions (encoding P210 BCR-ABL1) originated in hematopoietic stem cells (HSCs), whereas minor BCR-ABL1 fusions (encoding P190 BCR-ABL1) had a B-cell progenitor origin, suggesting that P190 and P210 BCR-ABL1 ALLs represent largely distinct tumor biological and clinical entities. The transformed leukemia-initiating stem cells in both P190 and P210 BCR-ABL1 ALLs had, as in ETV6-RUNX1 ALLs, a committed B progenitor phenotype. In all patients, normal and leukemic repopulating stem cells could successfully be separated prospectively, and notably, the size of the normal HSC compartment in ETV6-RUNX1 and P190 BCR-ABL1 ALLs was found to be unaffected by the expansive leukemic stem cell population.

Tyrosine kinase inhibitors and the dawn of molecular cancer therapeutics

The clinical application of tyrosine kinase inhibitors for cancer treatment represents a therapeutic breakthrough. The rationale for developing these compounds rests on the observation that tyrosine kinase enzymes are critical components of the cellular signaling apparatus and are regularly mutated or otherwise deregulated in human malignancies. Novel tyrosine kinase inhibitors are designed to exploit the molecular differences between tumor cells and normal tissues. Herein, we will review the current state-of-the-art using agents that target as prototypes Bcr-Abl, platelet-derived growth factor receptor (PDGFR), KIT (stem cell factor receptor), and epidermal growth factor receptor (EGFR). These compounds are remarkably effective in treating diverse cancers that are highly resistant to conventional treatment, including various forms of leukemia, hypereosinophilic syndrome, mast cell disease, sarcomas, and lung cancer. It is now clear that the molecular defects underlying cancer can be targeted with designer drugs that yield striking salutary effects with minimal toxicity.

Cytogenetics in acute leukemia

Cytogenetic analyses in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) have revealed a great number of non-random chromosome abnormalities. In many instances, molecular studies of these abnormalities identified specific genes implicated in the process of leukemogenesis. The more common chromosome aberrations have been associated with specific laboratory and clinical characteristics, and are now being used as diagnostic and prognostic markers guiding the clinician in selecting the most effective therapies. Specific chromosome aberrations and their molecular counterparts have been included in the World Health Organization classification of hematologic malignancies, and together with morphology, immunophenotype and clinical features are used to define distinct disease entities. However, the prognostic importance of less frequent recurrent aberrations in AML and ALL, both primary and secondary, is still to be determined. This review summarizes current views on clinical relevance of major cytogenetic findings in adult AML and ALL.

The BCR-ABL story: bench to bedside and back

The twenty-first century is beginning with a sharp turn in the field of cancer therapy. Molecular targeted therapies against specific oncogenic events are now possible. The BCR-ABL story represents a notable example of how research from the fields of cytogenetics, retroviral oncology, protein phosphorylation, and small molecule chemical inhibitors can lead to the development of a successful molecular targeted therapy. Imatinib mesylate (Gleevec, STI571, or CP57148B) is a direct inhibitor of ABL (ABL1), ARG (ABL2), KIT, and PDGFR tyrosine kinases. This drug has had a major impact on the treatment of chronic myelogenous leukemia (CML) as well as other blood neoplasias and solid tumors with etiologies based on activation of these tyrosine kinases. Analysis of CML patients resistant to BCR-ABL suppression by Imatinib mesylate coupled with the crystallographic structure of ABL complexed to this inhibitor have shown how structural mutations in ABL can circumvent an otherwise potent anticancer drug. The successes and limitations of Imatinib mesylate hold general lessons for the development of alternative molecular targeted therapies in oncology.

Mutated tyrosine kinases as therapeutic targets in myeloid leukemias

Tyrosine kinases are commonly mutated and activated in both acute and chronic myeloid leukemias. Here, we review the functions, signaling activities, mechanism of transformation, and therapeutic targeting of two prototypic tyrosine kinase oncogenes, BCR-ABL and FLT3, associated with chronic myeloid leukemia (CML) and acute myeloid leukemia (AML), respectively. BCR-ABL is generated by the Philadelphia chromosome translocation between chromosomes 9 and 22, creating a chimeric oncogene in which the BCR and c-ABL genes are fused. The product of this oncogene, BCR-ABL, has elevated ABL tyrosine kinase activity and transforms hematopoietic cells by exerting a wide variety of biological effects, including reduction in growth factor dependence, enhanced viability, and altered adhesion of chronic myelocytic leukemia (CML) cells. Elevated tyrosine kinase activity of BCR-ABL is critical for activating downstream signalling cascades and for all aspects of transformation, explaining the remarkable clinical efficacy of the tyrosine kinase inhibitor, imatinib mesylate (STI571). By comparison, FLT3 is mutated in about one third of all cases of AML, most often through a mechanism that involves an internal tandem duplication (ITD) of a small number of amino acid residues in the juxtamembrane domain of the receptor. As is the case for BCR-ABL, these mutations activate the kinase activity constitutively, activate multiple signaling pathways, and result in an augmentation of proliferation and viability. Transformation by FLT3-ITD can readily be observed in murine models, and FLT3 cooperates with other types of oncogenes to create a fully transformed acute leukemia. FLT3 tyrosine kinase inhibitors are currently being evaluated in clinical trials and may be very useful therapeutic agents in AML.

Bcr: a negative regulator of the Bcr-Abl oncoprotein in leukemia

The fusion of 5' parts of the BCR gene to the ABL gene at the second exon yields several forms of an oncogenic Bcr-Abl oncoprotein observed in several types of Philadelphia chromosome positive leukemia patients. The first exon of the BCR gene is a critical part of this fusion, as the coiled-coil domain at the amino terminal domain of the Bcr protein causes oligomerization of the Bcr-Abl oncoprotein forming tetramers, thereby activating the tyrosine kinase activity of the normally silent c-Abl protein. Another consequence of this Bcr-Abl fusion is the extensive autophosphorylation of the cis Bcr protein sequences on tyrosine residues. This review will summarize the effects of Bcr-Abl autophosphorylation on tyrosines as they relate to the oncogenic activity of Bcr-Abl, and as a means to inactivate the serine/threonine kinase activity of the Bcr protein. The review also discusses our findings that show that phosphoserine Bcr by means of a unique structure, binds to the Abl SH2 domain of the Bcr-Abl oncoprotein, and as a result this SH2 binding inhibits the oncogenic effects of the oncoprotein. Our results indicate that one effect of this binding is inhibition of the Bcr-Abl tyrosine kinase. Serine 354 of Bcr plays a major role in this inhibition. In the case of Bcr(64-413), serine 354 is required for the formation of the unique Bcr structure that binds to the Abl SH2 domain.

Increased circulating normal and BCR-ABL+Ve progenitor numbers in Philadelphia chromosome-positive acute myeloid leukaemia

We recorded elevated numbers of circulating myeloid and erythroid colony-forming cells in 15 adult patients with acute myeloid leukaemia (AML) who presented with high blood white cell counts. Since leukaemic blasts from three of these patients were Philadelphia chromosome-positive (Ph+), we were able to determine if blood progenitors from these particular patients arose from the leukaemic clone or from residual normal progenitors. Blasts and colonies were intensively investigated using a combination of cell surface marker analysis by flow cytometry, RT-PCR and interphase fluorescence in situ hybridization (FISH). FISH detected rearrangements within the major breakpoint BCR (M-BCR) region in blasts and in some myeloid and erythroid colonies from patients 1 and 2. The minor breakpoint (m-BCR) region was detected in blasts and in some myeloid and erythroid colonies from patient 3. RT-PCR detected long b2a2 BCR-ABL transcripts in blasts from patients 1 and 2, although misspliced short e1a2 transcripts were also seen in patient 1. Only e1a2 transcripts were found in blasts from patient 3. Flow sorting demonstrated the B-cell marker CD19 on blasts and on a proportion of myeloid and erythroid progenitors from patients 1 and 3. RT-PCR also detected IgH rearrangements, further evidence of B-cell differentiation, in blasts from these two patients. We conclude that both normal and clonal circulating progenitor numbers can be raised in both M-BCR and m-BCR Ph+ AML. The underlying cause, perhaps efflux from a congested marrow, may be common to AML patients with a high blood white cell count.

Molecular cytogenetic aspects of hematological malignancies: clinical implications

The field of molecular cytogenetics has had a great impact on many aspects of medical and basic sciences. During the past 30 years, the application of molecular cytogenetic methodologies has resulted in remarkable advances in the field of cancer genetics and cytogenetics. These advances have led to the establishment of chromosome patterns as diagnostic and prognostic indexes in an array of acute and chronic leukemias and lymphomas, as key information in BMT, and as guides for the localization of oncogenes and tumor suppressor genes that are apparently responsible for the development of neoplastic states. With such information, the physician is in a more favorable position to devise therapy, appraise diagnosis, and plan follow-up.

Ectopic expression of protein-tyrosine kinase Bcr-Abl suppresses tumor necrosis factor (TNF)-induced NF-kappa B activation and IkappaBalpha phosphorylation. Relationship with down-regulation of TNF receptors

Bcr-Abl, the product of the protooncogene bcr-abl, is a constitutively active protein-tyrosine kinase that is highly expressed in chronic myelogenous leukemia and in acute myeloid leukemia cells. Because Bcr-Abl is known to provide mitogenic signals through suppression of apoptosis, we investigated the effect of this oncogene product on signaling by tumor necrosis factor (TNF), a proapoptotic cytokine. We used a bcr-abl-deficient human megakaryocytic leukemia cell line MO7E and an isogenic MBA cell line stably transfected with bcr-abl. Electrophoretic mobility shift assay revealed that TNF activated the nuclear transcription factor NF-kappaB in MO7E cells but not in MBA cells. The impaired NF-kappaB activation in Bcr-Abl-expressing cells was not due to absence of the NF-kappaB proteins p65, p50, or p100 or of IkappaBalpha or IkappaBbeta. Okadaic acid-induced NF-kappaB activation was unaffected by Bcr-Abl expression. TNF induced IkappaBalpha phosphorylation and degradation in MO7E cells but not in MBA cells. The suppression of TNF-induced NF-kappaB activation by Bcr-Abl was not restricted to MBA cells, because ectopic expression of Bcr-Abl in human acute myeloid leukemia HL-60 cells also blocked TNF-induced NF-kappaB activation. When examined for the TNF receptors by the radioreceptor assay, flow cytometry, or Western blot analysis, we found that Bcr-Abl expression down-regulated the expression of the TNF receptors. The RNase protection assay and Northern blot analysis revealed the transcriptional down-regulation of the TNF receptor by Bcr-Abl protein. Overall, these results indicate that ectopic expression of Bcr-Abl interferes with the TNF signaling pathway through the down-regulation of TNF receptors.

Bcr-Abl variants: biological and clinical aspects

Bcr-Abl is an oncogene that arises from fusion of the Bcr gene with the c-Abl proto-oncogene. Three different Bcr-Abl variants can be formed, depending on the amount of Bcr gene included: p185, p210, and p230. The three variants are associated with distinct types of human leukemias. Examination of the signaling pathways differentially regulated by the Bcr-Abl proteins will help us gain better insight into Bcr-Abl mediated leukemogenesis.

p38 MAPK-mediated activation of NF-kappaB by the RhoGEF domain of Bcr

The oncogenic fusion protein p210 Bcr-Abl is causally associated with virtually all cases of chronic myelogenous leukemia. The wild-type Bcr product has several recognizable structural and functional motifs including a domain that contains guanine nucleotide exchange activity for Rho family GTPases (DH/PH domain). Although this domain is retained within p210 Bcr-Abl, it has no known signaling activities in vivo. Here we report that a fragment of Bcr that encodes the isolated DH/PH domain is a potent activator of the NF-kappaB transcription factor. Within the context of full length Bcr, this activity is regulated by proximal flanking sequences that suppress the DH/PH domain encoded guanine nucleotide exchange activity. NF-kappaB activation by Bcr is not mediated by nuclear translocation, but rather by p38 mitogen-activated protein kinase (MAPK)-dependent modification of the RelA/p65 transactivation domain. Although we were able to demonstrate that Bcr can function as an exchange factor for Cdc42 in vivo, NF-kappaB activation appears to occur via a Cdc42-independent mechanism. These studies constitute direct evidence that the Bcr RhoGEF domain can function in vivo, and identify a new signaling activity that may contribute to the transforming potential of p210 Bcr-Abl.

Quantification of minimal residual disease in patients with e1a2 BCR-ABL-positive acute lymphoblastic leukemia using a real-time RT-PCR assay

Using a real-time RT-PCR method, we analyzed the expression of e1a2 BCR-ABL mRNA in bone marrow samples from 13 patients with e1a2 BCR-ABL-positive acute lymphoblastic leukemia (ALL) at different time points during chemotherapy and after bone marrow transplantation (BMT). The detection limit of the method, assessed using serial dilutions of ALL/MIK cells, was found to be 1:10(5), similar to what is observed for the conventional RT-nested PCR method. The e1a2 BCR-ABL values were normalized with respect to those of the housekeeping gene GAPDH. The decrease in the e1a2 BCR-ABL/GAPDH ratio after remission induction chemotherapy reflects well the response to chemotherapy and consequently correlates with the prognosis. Although molecular remission was achieved by chemotherapy alone, some patients relapsed, and the e1a2 BCR-ABL/GAPDH ratios in these cases progressively increased to the levels seen prior to hematological relapse. Long-term hematological complete remission (more than 30 months) could be achieved in cases in which a more than 4.0 log decrease in the e1a2 BCR-ABL/GAPDH ratio was obtained by chemotherapy alone, and BMT was then performed. In conclusion, real-time RT-PCR allows for an evaluation of the kinetics of e1a2 BCR-ABL/GAPDH expression during the various phases of chemotherapy or after BMT and may be effective for the indication and control of disease relapse in Ph-positive ALL patients.

Philadelphia chromosome-positive acute lymphoblastic leukemia- current concepts and future perspectives

Philadelphia chromosome (Ph)-positive acute lymphoblastic leukemia (ALL) is diagnosed rarely in children, but constitutes the most frequent cytogenetic abnormality in adults with ALL. In contrast to chronic myeloid leukemia (CML), patients with Ph-positive ALL usually demonstrate expression of a truncated version of the BCR-ABL protein called p190bcr-abl. Irrespective of age and breakpoint location, Ph-positive ALL carries a poor prognosis. Although remission rates are identical to those of Ph-negative ALL, relapse is almost universal and long-term survival remains rare. Given the poor outcome with current chemotherapy consolidation programs, stem cell transplantation is usually recommended for these patients in first remission or as soon as feasible. Even with transplantation the impact on outcome is limited and new therapeutic concepts are urgently needed. One of the most promising developments in recent years has been the introduction of the tyrosine kinase inhibitors such as STI571. An overview of current treatment modalities in Ph-positive ALL will be provided and the rationale for new therapies will be discussed.

Critical role for Gab2 in transformation by BCR/ABL

The BCR/ABL oncogene causes chronic myelogenous leukemia (CML) in humans and a CML-like disease, as well as lymphoid leukemia, in mice. p210 BCR/ABL is an activated tyrosine kinase that phosphorylates itself and several cellular signaling proteins. The autophosphorylation site tyrosine 177 binds the adaptor Grb2 and helps determine the lineage and severity of BCR/ABL disease: Tyr177 mutation (BCR/ABL-Y177F) dramatically impairs myeloid leukemogenesis, while diminishing lymphoid leukemogenesis. The critical signal(s) from Tyr177 has remained unclear. We report that Tyr177 recruits the scaffolding adaptor Gab2 via a Grb2/Gab2 complex. Compared to BCR/ABL-expressing Ba/F3 cells, BCR/ABL-Y177F cells exhibit markedly reduced Gab2 tyrosine phosphorylation and association of phosphatidylinositol-3 kinase (PI3K) and Shp2 with Gab2 and BCR/ABL, and decreased PI3K/Akt and Ras/Erk activation, cell proliferation, and spontaneous migration. Remarkably, bone marrow myeloid progenitors from Gab2 (-/-) mice are resistant to transformation by BCR/ABL, whereas lymphoid transformation is diminished as a consequence of markedly increased apoptosis. BCR/ABL-evoked PI3K/Akt and Ras/Erk activation also are impaired in Gab2 (-/-) primary myeloid and lymphoid cells. Our results identify Gab2 and its associated proteins as key determinants of the lineage and severity of BCR/ABL transformation.

Modelling haematopoietic malignancies in the mouse and therapeutical implications

Modelling human disease in the mouse has become an essential activity in biomedical research in order to unravel molecular mechanisms underlying pathological conditions as well as to determine in vivo the consequences of aberrant gene function. The mouse is by far the most accessible mammalian system physiologically similar to humans. Furthermore, the development of novel techniques for manipulating the murine genome, which allow the in vivo modification of virtually any genomic region in a time and/or tissue specific manner, renders the mouse an ideal model system to study human pathological conditions. Modelling human diseases in mice has reached an even greater relevance in the field of haematological malignancies, due to the already advanced characterization of the molecular basis of many haematological disorders. In this review, we describe the most important technological developments that made it possible to reproduce in the mouse the genetic lesions that characterize human haematological malignancies, thus often generating faithful mouse models of the human condition. We provide specific examples of the advantages and limitations of the various genetic approaches utilized to model leukaemia and lymphoma in the mouse. Finally, we discuss the power of mouse modelling in developing and testing novel therapeutic modalities in pre-clinical studies.

Progress with chronic myelogenous leukemia: a personal perspective over four decades

Our understanding and treatment of chronic myelogenous leukemia (CML) has progressed since 1960 in parallel with work on cancer in general. CML provided the first evidence of a specific genetic change associated with a human cancer (the Philadelphia chromosome) and the clonal nature of these disorders. With improved cytogenetic and molecular techniques over subsequent decades, the specific genetic rearrangements of CML and many other tumors were defined and the complex mechanisms of carcinogenesis gradually unraveled. During this period, improved treatments for CML (chemotherapy, interferon, bone marrow transplantation) were implemented, and therapy targeted to the specific genetic change in the leukemic cells has recently been brought to promising clinical trials. Similar efforts are under way for other human cancers, and although the problem is enormously complex, there is real hope for major improvements in controlling these disorders.

BCR-ABL as a target for novel therapeutic interventions

The BCR-ABL oncogene is the result of a reciprocal translocation between the long arms of chromosome 9 and 22 t(9; 22). There is good experimental evidence demonstrating that BCR-ABL is the single causative abnormality in chronic myeloid leukaemia (CML), making it a unique model for the development of molecular targets. In addition to CML, BCR-ABL transcripts can be found in a minority of acute lymphoblastic leukaemias and very rarely in acute myeloid leukaemia (AML). Elucidating the molecular mechanisms and downstream pathways of BCR-ABL has led to the design of several novel therapeutic approaches. In this review, molecular targeting of BCR-ABL will be discussed based on the inhibition of protein tyrosine kinase activity, antisense strategies and immunomodulation.

Detection of minimal residual disease

A high percentage of patients with leukemia, lymphoma, and solid tumors achieve a complete clinical remission after initial treatment, but the majority of these patients will finally relapse from residual tumor cells detectable in clinical remission only by the most sensitive methods. The in vitro amplification of tumor-specific DNA or RNA sequences by polymerase chain reaction (PCR) allows identification of a few neoplastic cells in 10(4) to 10(6) normal cells. Depending on the underlying malignant disease and therapeutic treatment, the presence of residual tumor cells in an individual patient may herald relapse, but a long-term stable situation or slowly vanishing tumor cells are also possible. Molecular monitoring of residual leukemia and lymphoma cells by quantitative PCR techniques has provided important information about the effectiveness of treatment and the risk of recurrent disease as shown by minimal residual disease (MRD) analysis in patients with various malignant diseases. Such diseases include childhood acute lymphoblastic leukemia, after induction therapy; acute promyelocytic leukemia, during and after chemotherapy; and chronic myelogenous leukemia, during treatment with alpha-interferon and after allogeneic bone marrow transplantation. Evaluation of the predictive value of the detection of MRD has to take into account its evolution and course, the pathogenesis, biology, and natural course of the underlying malignant disease, the molecular genetic lesion, and finally, the type of treatment. Quantification of minimal residual cells by the recently developed real-time quantitative PCR technique will surely have a major impact on our therapeutic strategies for patients with leukemia, lymphomas, and solid tumors. Based on quantitative PCR data, the terms molecular remission and molecular relapse have to be exactly defined and validated in prospective clinical trials to assess the biological and clinical significance of MRD in various types of malignancies.

Erythropoiesis in the absence of janus-kinase 2: BCR-ABL induces red cell formation in JAK2(-/-) hematopoietic progenitors

The receptor-associated protein tyrosine kinase janus-kinase 2 (JAK2) is essential for normal red cell development and for erythropoietin receptor (EpoR) signaling. JAK2(-/-) embryos are severely deficient in erythropoiesis and die at an early stage of development from fetal anemia. The binding of erythropoietin (Epo) to the EpoR triggers the activation of JAK2, the phosphorylation of the EpoR, and the initiation of the EpoR signaling cascade. In addition to Epo binding to its receptor, signaling pathways downstream of the EpoR can also be stimulated by the BCR-ABL oncoprotein. This study explored whether JAK2 is required for BCR-ABL-mediated stimulation of erythropoiesis. Here, it is shown that JAK2 is constitutively tyrosine phosphorylated in cultured and primary erythroid cells expressing BCR-ABL. However, BCR-ABL effectively supports normal erythroid proliferation, differentiation, and maturation in JAK2-deficient fetal liver cells. Using mutants of BCR-ABL, this study shows that certain signaling pathways activated by BCR-ABL segments distinct from its tyrosine kinase domain are essential for rescue of erythropoiesis in JAK2(-/-) progenitors. The consequences of these multiple signaling pathways for normal erythroid development are discussed.

The proteasome in cancer biology and treatment

During the last 30 years, investigation of the transcriptional and translational mechanisms of gene regulation has been a major focus of molecular cancer biology. More recently, it has become evident that cancer-related mutations and cancer-related therapies also can affect post-translational processing of cellular proteins and that control exerted at this level can be critical in defining both the cancer phenotype and the response to therapeutic intervention. One post-translational mechanism that is receiving considerable attention is degradation of intracellular proteins through the multicatalytic 26S proteasome. This follows growing recognition of the fact that protein degradation is a well-regulated and selective process that can differentially control intracellular protein expression levels. The proteasome is responsible for the degradation of all short-lived proteins and 70-90% of all long-lived proteins, thereby regulating signal transduction through pathways involving factors such as AP1 and NFKB, and processes such as cell cycle progression and arrest, DNA transcription, DNA repair/misrepair, angiogenesis, apoptosis/survival, growth and development, and inflammation and immunity, as well as muscle wasting (e.g. in cachexia and sepsis). In this review, we discuss the potential involvement of the proteasome in both cancer biology and cancer treatment.

Model mice for BCR/ABL-positive leukemias

p210bcr/abl is detected in almost all chronic myelogenous leukemia (CML) patients and a significant number of acute lymphoblastic leukemia (ALL) cases. It is generated by a reciprocal chromosomal translocation, t(9;22) (q34;q11), and the enhanced kinase activity of the protein is believed to be implicated in the pathogenesis of the diseases. To examine its oncogenicity in vivo and to create an animal model for BCR/ABL-positive leukemias, we generated transgenic mice expressing p210bcr/abl driven by the promoter of the mouse tec gene, a cytoplasmic tyrosine kinase preferentially expressed in early hematopoietic progenitors. While the founder mice showed excessive proliferation of lymphoblasts shortly after birth and were diagnosed as ALL, the transgenic progeny reproducibly exhibited marked granulocyte hyperplasia with thrombocytosis after a long latent period, which closely resembles the clinical course of human CML. In addition, to investigate whether loss of p53 would play a role in the transition from chronic phase to blast crisis of CML, we crossmated p210bcr/abl transgenic (BCR/ABLtg/-) mice with p53 heterozygous (p53+/-) mice and generated p210bcr/abl transgenic, p53 heterozygous (BCR/ABLtg/- p53+/-) mice, in which a somatic alteration in the residual p53 allele directly abrogates p53 function. The BCR/ABLtg/- p53+/- mice exhibited rapid proliferation of blast cells and died in a short period compared with their wild-type (BCR/ABL-/- p53+/+), p53 heterozygous (BCR/ABL-/- p53+/-), and p210bcr/abl transgenic (BCR/ABLtg/- p53+/+) littermates. Interestingly, the normal p53 allele was frequently and preferentially lost in the tumor tissues, providing in vivo evidence that acquired loss of p53 contributes to the blastic transformation of p210bcr/abl-expressing hematopoietic cells. Our transgenic mice will be a useful model for investigating oncogenic properties of p210bcr/abl in vivo and will provide insights into the molecular mechanism(s) underlying the progression from chronic phase to blast crisis of CML.

BCR rearrangement-negative chronic myelogenous leukemia revisited

PURPOSE

To document the characteristics of patients with major breakpoint cluster region (M-bcr) rearrangement-negative chronic myelogenous leukemia (CML).

PATIENTS AND METHODS

The hematopathologist, who was blinded to patients' molecular status, reviewed the referral bone marrows and peripheral-blood smears from 26 patients with Philadelphia (Ph) translocation-negative CML who lacked Bcr rearrangement (and other evidence of a Bcr-Abl anomaly) and 14 patients (controls) with chronic-phase Ph-positive CML. Clinical data was ascertained by chart review.

RESULTS

Among the 26 M-bcr rearrangement-negative CML patients, three pathologic subtypes emerged: (1) patients indistinguishable from classic CML (n = 9), (2) patients with atypical CML (n = 8), and (3) patients with chronic neutrophilic leukemia (n = 9). Among the 14 patients with Ph-positive CML who were included in the blinded review, 13 were classified as classic CML, and one was classified as atypical CML. The only statistically significant difference between M-bcr rearrangement-negative subgroups was in the proportion of patients having karyotypic abnormalities, an observation common only in patients with atypical CML (P = 0.008). However, the small number of patients in each subgroup limited our ability to differentiate between them. Interferon alfa induced complete hematologic remission in five of 14 patients; four of these remissions lasted more than 5 years. Only one of 26 patients developed blast crisis. The median survival of the 26 patients was 37 months.

CONCLUSION

Patients with M-bcr rearrangement-negative CML fall into three morphologic subgroups. Disease evolution does not generally involve blastic transformation. Instead, patients show progressive organomegaly, leukocytosis, anemia, and thrombocytosis. Some patients in each subgroup can respond to interferon alfa.

ABL1 methylation in Ph-positive ALL is exclusively associated with the P210 form of BCR-ABL

In human Ph-positive leukemia there is a clear association of different forms of the BCR-ABL oncogene with distinct types of leukemia. The P190 form of BCR-ABL is rarely observed in chronic myeloid leukemia (CML) but is present in 50% of Ph-positive acute lymphoblastic leukemia (ALL). In contrast, the P210 form is observed both in CML and 50% of Ph-positive ALL. Methylation of the proximal promoter of the ABL1 gene has been shown to be a nearly universal event associated with clinical progression of CML. This raises the question of whether methylation of the ABL1 promoter is an epigenetic modification also associated with Ph-positive ALL. To study this issue, we used methylation-specific PCR and bisulfite sequencing to determine the methylation status of the ABL1 promoter in 18 Ph-positive ALL samples. We report here that gene-specific ABL1 promoter methylation is associated mainly with the P210 form of BCR-ABL and not the P190 form. While six out of the seven P210-positive ALL samples had ABL1 promoter methylation, none of the 11 P190-positive ALL samples demonstrated ABL1 promoter methylation. In addition, we estimated the extent and relative abundance of ABL1 promoter methylation in several Ph-positive ALL samples and compared it to the methylation pattern in chronic, accelerated and blastic crisis phases of CML. We put forth a model that correlates the different types of leukemias with the different levels of ABL1 promoter methylation.

Mechanisms of transformation by the BCR/ABL oncogene

The Philadelphia chromosome generates a chimeric oncogene in which the BCR and c-ABL genes are fused. The product of this oncogene, BCR/ABL, has elevated ABL tyrosine kinase activity, relocates to the cytoskeleton, and phosphorylates multiple cellular substrates. BCR/ABL transforms hematopoietic cells and exerts a wide variety of biological effects, including reduction in growth factor dependence, enhanced viability, and altered adhesion of chronic myelocytic leukemia (CML) cells. Elevated tyrosine kinase activity of BCR/ABL is critical for activating downstream signal transduction and for all aspects of transformation. This review will describe mechanisms of transformation by the BCR/ABL oncogene and opportunities for clinical intervention with specific signal transduction inhibitors such as STI-571 in CML.

Insights into the biologic and molecular abnormalities in adult acute lymphocytic leukemia

The last 3 decades have seen much progress in the treatment and outcome of patients with ALL. Unfortunately, the success that has been achieved in children with ALL has not yet been translated into adult patients. Insight into the biologic and molecular abnormalities in ALL may, however, provide the necessary clues that allow a clearer understanding of the crucial differences in the behavior of ALL in different groups of patients. As the molecular basis of the disease is deciphered, new targets are discovered that may prove useful for therapeutic interventions in the future.

Cytoplasmic and nuclear localization of the 130 and 160 kDa Bcr proteins

Formation of the Bcr-Abl chimeric protein is the molecular hallmark of Philadelphia-positive leukemia. Normal Bcr is a complex protein which has been found in the cytoplasm, has serine kinase activity, and has been implicated in cellular signal transduction. However, we have recently demonstrated that Bcr can also associate with condensed chromatin. Since two major Bcr proteins have been characterized (p160Bcr and p130Bcr), we sought to determine if different forms of Bcr localized to the nucleus vs the cytoplasm. Metabolic labeling and Western blotting experiments were performed using nuclear and cytoplasmic extracts of three human Philadelphia-negative leukemia/lymphoma cell lines (KG-1, HL-60, and Jurkat). Both methodologies showed that p160Bcr and p130Bcr localized to the cytoplasm, but the p130 form predominated in the nucleus. These results suggest that Bcr serves both nuclear and cytoplasmic functions, and that different forms of Bcr may be preferentially involved in these distinct activities.

Novel oxime derivatives of radicicol induce erythroid differentiation associated with preferential G1 phase accumulation against chronic myelogenous leukemia cells through destabilization of Bcr-Abl with Hsp90 complex

Chronic myelogenous leukemia (CML) is a clonal disorder of a pluripotent hematopoietic stem cells characterized by a chimericbcr-abl gene giving rise to a p210Bcr-Ablprotein with dysregulated tyrosine kinase activity. Radicicol, a macrocyclic antifungal antibiotic, binds to the N-terminal of heat shock protein 90 (Hsp90) and destabilizes Hsp90-associated proteins such as Raf-1. This study investigated the effect of radicicol, novel oxime derivatives of radicicol (KF25706 and KF58333), and herbimycin A (HA), a benzoquinoid ansamycin antibiotic, on the growth and differentiation of human K562 CML cells. Although KF25706 and KF58333 induced the expression of glycophorin A in K562 cells, radicicol and HA caused erythroid differentiation transiently. Cell cycle analysis showed that G1 phase accumulation was observed in K562 cells treated with KF58333. KF58333 treatment depleted p210Bcr-Abl, Raf-1, and cellular tyrosine phosphorylated proteins in K562 cells, whereas radicicol and HA showed transient depletion of these proteins. KF58333 also down-regulated the level of cell cycle–dependent kinases 4 and 6 and up-regulated cell cycle–dependent kinase inhibitor p27Kip1protein without an effect on the level of Erk and Hsp90 proteins. Immunoprecipitation analysis showed that p210Bcr-Abl formed multiple complexes with Hsp90, some containing p23 and others Hsp70; KF58333 treatment dissociated p210Bcr-Abl from Hsp90/p23 chaperone complexes. Furthermore, KF58333 induced apoptosis in K562 cells and administration of KF58333 prolonged the survival time of SCID mice inoculated with K562 cells. These results suggest that KF58333 may have therapeutic potential for the treatment of CML that involves abnormal cellular proliferation induced by p210Bcr-Abl.

Novel oxime derivatives of radicicol induce erythroid differentiation associated with preferential G1 phase accumulation against chronic myelogenous leukemia cells through destabilization of Bcr-Abl with Hsp90 complex

Chronic myelogenous leukemia (CML) is a clonal disorder of a pluripotent hematopoietic stem cells characterized by a chimericbcr-abl gene giving rise to a p210Bcr-Ablprotein with dysregulated tyrosine kinase activity. Radicicol, a macrocyclic antifungal antibiotic, binds to the N-terminal of heat shock protein 90 (Hsp90) and destabilizes Hsp90-associated proteins such as Raf-1. This study investigated the effect of radicicol, novel oxime derivatives of radicicol (KF25706 and KF58333), and herbimycin A (HA), a benzoquinoid ansamycin antibiotic, on the growth and differentiation of human K562 CML cells. Although KF25706 and KF58333 induced the expression of glycophorin A in K562 cells, radicicol and HA caused erythroid differentiation transiently. Cell cycle analysis showed that G1 phase accumulation was observed in K562 cells treated with KF58333. KF58333 treatment depleted p210Bcr-Abl, Raf-1, and cellular tyrosine phosphorylated proteins in K562 cells, whereas radicicol and HA showed transient depletion of these proteins. KF58333 also down-regulated the level of cell cycle–dependent kinases 4 and 6 and up-regulated cell cycle–dependent kinase inhibitor p27Kip1protein without an effect on the level of Erk and Hsp90 proteins. Immunoprecipitation analysis showed that p210Bcr-Abl formed multiple complexes with Hsp90, some containing p23 and others Hsp70; KF58333 treatment dissociated p210Bcr-Abl from Hsp90/p23 chaperone complexes. Furthermore, KF58333 induced apoptosis in K562 cells and administration of KF58333 prolonged the survival time of SCID mice inoculated with K562 cells. These results suggest that KF58333 may have therapeutic potential for the treatment of CML that involves abnormal cellular proliferation induced by p210Bcr-Abl.

Autoantibodies to Abl and Bcr proteins

Formation of an aberrant, chimeric Bcr-Abl protein is the hallmark of Philadelphia (Ph) chromosome-positive leukemias. The Bcr-Abl protein, as well as its normal cellular counterparts--Abl and Bcr--are intracellular molecules with postulated roles in a variety of critical biologic functions. In this study, we demonstrate the existence of autoantibodies against these proteins. Plasma from 18 of 31 individuals (58%), including 14 of 20 Ph-positive CML patients (70%), two of four normal volunteers (50%), and two of seven patients with Ph-negative leukemia (29%) recognized p210Bcr-Abl when used in immunoprecipitation followed by immunoblotting experiments. In all 18 patients, plasma was able to recognize baculovirus-expressed Abl protein; in four patients, recognition of baculovirus-expressed Bcr protein was also demonstrated. These observations suggest that a humoral immune response to p210Bcr-Abl is discernible in both Ph-positive and -negative leukemias and in healthy individuals, and is most likely due to autoantibodies which recognize normal Abl and, to a lesser extent, normal Bcr proteins.

Analysis of the biologic properties of p230 Bcr-Abl reveals unique and overlapping properties with the oncogenic p185 and p210 Bcr-Abl tyrosine kinases

The reciprocal translocation between chromosomes 9 and 22 that fuses coding sequences of the Bcr and Abl genes is responsible for a remarkably diverse group of hematologic malignancies. A newly described 230-kd form of Bcr-Abl has been associated with an indolent myeloproliferative syndrome referred to as chronic neutrophilic leukemia. We have cloned the corresponding gene and examined the biologic and biochemical properties of p230 Bcr-Abl after retroviral-mediated gene transfer into hematopoietic cell lines and primary bone marrow cells. p230 Bcr-Abl–expressing 32D myeloid cells were fully growth factor-independent and activated similar signal transduction pathways as the well-characterized p210 and p185 forms of Bcr-Abl. In contrast, primary mouse bone marrow cells expressing p230 required exogenous hematopoietic growth factors for optimal growth, whereas p185- and p210-expressing cells were independent of growth factors. The 3 Bcr-Abl proteins exerted different effects on differentiation of bone marrow cells. p185 induced outgrowth of lymphoid precursors capable of tumor formation in immunodeficient mice. In contrast, p210- and p230-expressing bone marrow cells caused limited outgrowth of lymphoid precursors that failed to form tumors in immunodeficient mice. Removal of cytokines and autologous stroma from Bcr-Abl–expressing bone marrow cultures produced the expansion of distinct lineages by the various Bcr-Abl proteins. p185 drove expansion of cytokine-independent lymphoid progenitors, while p210 and p230 generated cytokine-independent monocyte/myeloid cells. These findings suggest that the different Bcr-Abl fusion proteins drive the expansion of different hematopoietic populations, which may explain the association of the various Bcr-Abl oncoproteins with different spectra of human leukemias.