Chronic Myeloid Leukemia, Version 1.2019, NCCN Clinical Practice Guidelines in Oncology

Chronic myeloid leukemia (CML) is defined by the presence of Philadelphia chromosome (Ph), resulting from a reciprocal translocation between chromosomes 9 and 22 [t(9;22] that gives rise to a BCR-ABL1 fusion gene. CML occurs in 3 different phases (chronic, accelerated, and blast phase) and is usually diagnosed in the chronic phase. Tyrosine kinase inhibitor (TKI) therapy is a highly effective first-line treatment option for all patients with newly diagnosed chronic phase CML (CP-CML). The selection TKI therapy should be based on the risk score, toxicity profile of TKI, patient's age, ability to tolerate therapy, and the presence of comorbid conditions. This manuscript discusses the recommendations outlined in the NCCN Guidelines for the diagnosis and management of patients with CP-CML.

Flow Cytometric Immunobead Assay for Detection of BCR-ABL1 Fusion Proteins in Chronic Myleoid Leukemia: Comparison with FISH and PCR Techniques

Chronic Myeloid Leukemia (CML) is characterized by a balanced translocation juxtaposing the Abelson (ABL) and breakpoint cluster region (BCR) genes. The resulting BCR-ABL1 oncogene leads to increased proliferation and survival of leukemic cells. Successful treatment of CML has been accompanied by steady improvements in our capacity to accurately and sensitively monitor therapy response. Currently, measurement of BCR-ABL1 mRNA transcript levels by real-time quantitative PCR (RQ-PCR) defines critical response endpoints. An antibody-based technique for BCR-ABL1 protein recognition could be an attractive alternative to RQ-PCR. To date, there have been no studies evaluating whether flow-cytometry based assays could be of clinical utility in evaluating residual disease in CML patients. Here we describe a flow-cytometry assay that detects the presence of BCR-ABL1 fusion proteins in CML lysates to determine the applicability, reliability, and specificity of this method for both diagnosis and monitoring of CML patients for initial response to therapy. We show that: i) CML can be properly diagnosed at onset, (ii) follow-up assessments show detectable fusion protein (i.e. relative mean fluorescent intensity, rMFI%>1) when BCR-ABL1IS transcripts are between 1-10%, and (iii) rMFI% levels predict CCyR as defined by FISH analysis. Overall, the FCBA assay is a rapid technique, fully translatable to the routine management of CML patients.

[A multicenter comparison study on the quantitative detection of bcr-abl (P210) transcript levels in China]

OBJECTIVE

To investigate the comparability of bcr-abl (P210) transcript levels detected in different hospitals.

METHODS

Ten hospitals in China took part in the four times of sample exchange and comparisons from April, 2010 to August, 2011. The exchange samples were prepared by Peking University People's Hospital. Firstly, the BCR-ABL (P210)(+) cells from a newly diagnosed chronic myeloid leukemia patient were 10-fold serially diluted by BCR-ABL (P210)(-) cells and they covered 4 magnitudes. Then, TRIzol reagents were thoroughly mixed with cells in each tube. Every 12 samples (three samples per magnitude) were sent to the other 9 hospitals. The cell number of each sample was 8×10(6). The detection of bcr-abl transcript levels by real-time quantitative PCR were performed in every hospital according to their own protocols. Conversion factors (CF) were calculated using regression equation.

RESULTS

Differences in bcr-abl transcript levels did exist among results of 10 hospitals in each comparison. In general, the results of the most of hospitals were in line with the dilutions of cells. CF of every hospital fluctuated. Three hospitals had relatively stable CF, and their ranges were 2.8 - 5.2, 1.2 - 2.8 and 2.2 - 6.8, respectively; two hospitals had unstable CF with ranges 0.76 - 7.0 and 2.1 - 18.7; three hospitals couldn't be calculated CF one or two times because of the significant deviation of the results from the actually bcr-abl transcript levels, and their ranges of CF which could be calculated were 1.9 - 19.2, 3.6 - 7.6 and 0.18 - 14.7; One hospital only had two CF (3.3 and 5.0) because of the replacement of an important reagent during the period of comparisons.

CONCLUSIONS

Comparability of bcr-abl (P210) transcript levels between different hospitals could be achieved through CF which acquired by sample exchange and comparison. The stable and reliable detection system is the premise to acquire correct CF.

[Real-time PCR quantification of bcr/abl chimera and WT1 genes in chronic myeloid leukemia]

Quantification of mRNAs deriving from malignant cells is useful for estimating leukemic states. In this study, we have developed RT-PCR methods using real-time PCR detection system, a LightCycler, for quantification of bcr/abl chimerical genes in peripheral blood and bone marrow of chronic myeloid leukemia patients. Total amounts of RNA extracted were corrected using beta-actin gene as an internal standard. The coefficients of variation of intra-assay variation and inter-assay variation for each gene were within a range of 1.7-26.0% which showed more precise quantification than the competitive PCR method. The coefficients of variation of assay are within a range of 7.7-27.6% in the case of using three samples of normal subjects from blood collecting to quantification of bcr gene. Bcr/abl and WT1 genes could be measured from 10(2) to 10(8) copies and 10 to 10(5) copies with linearity, respectively. Using real-time PCR detection with LightCycler system, 2 x 10(3) K562 cells among 2 x 10(6) total cells demonstrated the bcr/abl gene, while 2 x 10(1) K562 cells among 2 x 10(6) total cells could be detected using the nested PCR method. In tests of seven clinical samples, five samples demonstrated bcr/abl and WT1 genes, while those in two other patients after bone marrow transplantation and a normal subject could not detected. This result suggests that our quantitative method reflect the clinical stages of CML patients.

Polarized distribution of Bcr-Abl in migrating myeloid cells and co-localization of Bcr-Abl and its target proteins

Bcr-Abl plays a critical role in the pathogenesis of Philadelphia chromosome-positive leukemia. Although a large number of substrates and interacting proteins of Bcr-Abl have been identified, it remains unclear whether Bcr-Abl assembles multi-protein complexes and if it does where these complexes are within cells. We have investigated the localization of Bcr-Abl in 32D myeloid cells attached to the extracellular matrix. We have found that Bcr-Abl displays a polarized distribution, colocalizing with a subset of filamentous actin at trailing portions of migrating 32D cells, and localizes on the cortical F-actin and on vesicle-like structures in resting 32D cells. Deletion of the actin binding domain of Bcr-Abl (Bcr-AbI-AD) dramatically enhances the localization of Bcr-Abl on the vesicle-like structures. These distinct localization patterns of Bcr-Abl and Bcr-Abl-AD enabled us to examine the localization of Bcr-Abl substrate and interacting proteins in relation to Bcr-Abl. We found that a subset of biochemically defined target proteins of Bcr-Abl redistributed and co-localized with Bcr-Abl on F-actin and on vesicle-like structures. The co-localization of signaling proteins with Bcr-Abl at its sites of localization supports the idea that Bcr-Abl forms a multi-protein signaling complex, while the polarized distribution and vesicle-like localization of Bcr-Abl may play a role in leukemogenesis.

A new method for the detection of bcr/abl sequences amplified by polymerase chain reaction (PCR) following bone marrow transplantation

Disease recurrence is a major problem in patients receiving bone marrow transplantation for chronic myeloid leukemia. Residual malignant cells are the most likely source of recurrence. Detection of minimal residual disease early during therapy may provide an additional prognostic value and help in identifying patients who are at high risk of relapse. PCR followed by hybridization is the most sensitive method to investigate the persistence of leukemic cells. However, more reproducible methods suitable to standardization and quantification are required in clinical practice. In this study, we describe a novel PCR assay combined with immunological and colorimetric detection of the bcr-rearrangement. Residual bcr/abl rearranged cells were observed in 7 patients. Our results show that the assay is equally sensitive as RT-PCR, more versatile in terms of standardization and easily adaptable as a diagnostic test.

P210 Bcr-Abl interacts with the interleukin-3 beta c subunit and constitutively activates Jak2

Chronic myelogenous leukemia is a neoplasm of pluripotent hematopoietic cells. Cytokines such as interleukin-3 and granulocyte-macrophage colony-stimulating factor regulate the growth and differentiation of hematopoietic precursors. These cytokines activate two distinct signals to the nucleus. One signal is through the Ras pathway, and the second involves activation of Jak2. We demonstrated that Bcr-Abl co-immunoprecipitates with and constitutively phosphorylates the common beta c chain of the interleukin-3 (IL-3) and granulocyte-macrophage-macrophage colony-stimulating factor (GM-CSF) receptors. Our data show that formation of this complex leads to the constitutive activation of Jak2. Previously, it has been demonstrated that Bcr-Abl interacts with Grb2 and Shc, which in turn activates the Ras pathway. Thus, Bcr-Abl can activate signalling through both pathways in a factor-independent fashion.

[Fluorescent in-situ hybridization technique (FISH) in the diagnosis of Philadelphia translocation in chronic myeloid leukemia]

The Philadelphia chromosome (Ph) resulting from translocation t(9;22)(q34;q11) is observed in more than 90% of patients with chronic myeloid leukemia (CML). Its molecular consequence is the genesis of a fusion gene BCR-ABL between the 5' sequences of the BCR gene (chromosome 22) and the 3' end of the ABL gene (chromosome 9). Fluorescence in situ hybridization (FISH) using specific DNA probes provides a useful tool for the detection of t(9;22) and BCR-ABL rearrangement. We report our results using the FISH technique for t(9;22) assessment in the hematopoietic cells of patients with Ph-positive CML. The DNA libraries pBS 9 and pBS 22 containing multiple sequences derived from chromosomes 9 and 22 have been used to identify t(9;22) in metaphase cells. The cos bcr-51 and cos abl-18 probes that hybridize to unique sequences specific to the BCR and ABL genes have the ability to detect the BCR-ABL rearrangement in metaphase cells as well as in interphase nuclei. FISH is a sensitive and specific technique that represents a valuable complement to conventional cytogenetics. The BCR-ABL rearrangement can be detected in metaphase spreads of insufficient quality or from interphase nuclei in the case of terminally differentiated cells or of cells which do not divide in vitro. When the efficiency of hybridization and detection is good, a large number of cells can be analyzed. This is of major significance in assessment of response to treatment and definition of a cytogenetic remission. However, interphase cytogenetics may be difficult due to variations in signal resolution and background level. The FISH technique can also be used to detect the BCR-ABL rearrangement in cases of Ph negative BCR-ABL positive CML.

Tyrosine phosphorylation and activation of focal adhesion kinase (p125FAK) by BCR-ABL oncoprotein

Focal adhesion kinase (p125FAK; FAK) is a protein tyrosine kinase that is tyrosine-phosphorylated in response to v-src-mediated transformation, cell adhesion, and stimulation with neuropeptides. To elucidate a possible functional relationship between FAK and BCR-ABL oncoprotein detected in Philadelphia chromosome-positive (Ph+) leukemias, we investigated the tyrosine phosphorylation state of FAK in a murine growth factor-dependent cell line and in its stable human bcr-abl cDNA transfectant. In interleukin-3 (IL-3)-dependent NFS/N1.H7 cells, tyrosine phosphorylation of FAK was not detected after stimulation with either IL-3 or Steel factor (SLF), both of which involve Ras-mediated signaling pathways. However, stable gene transfection with p210bcr-abl cDNA into H7 cells made these cells growth factor-independent for proliferation and resulted in constitutive tyrosine phosphorylation and kinase activation of FAK. Constitutive phosphorylation and activation of FAK was also observed in all Ph+ leukemia cell lines examined--that is, K562, TS9;22, and YS9;22, which express p210BCR-ABL, and NALM-21 and OM9;22, which express p185BCR-ABL. Ph-negative (Ph-) cell lines, such as MO7e and JM, did not show any detectable tyrosine phosphorylation of FAK. FAK phosphorylation in BCR-ABL-expressing cells was inhibited in a dose-dependent manner by cytochalasin D, a reagent that disrupts the intracellular network of actin filaments. However, no suppression of kinase activity or protein expression of BCR-ABL was observed after treatment with cytochalasin D. A physical association between BCR-ABL and FAK was not apparent. These data suggest that BCR-ABL may be involved in the activation of FAK. Moreover, FAK may be distinct from components in Ras-mediated signaling cascades that are activated by stimulation of myeloid cells with various cytokines.

Role of p21 RAS in p210 bcr-abl transformation of murine myeloid cells

The p21 RAS product has been implicated as part of the downstream signaling of certain nonreceptor tyrosine kinase oncogenes and several growth factor receptor-ligand interactions. We have reported that the chronic myelogenous leukemia oncogene p210 bcr-abl transforms a growth-factor-dependent myeloid cell line NFS/N1.H7 to interleukin-3 (IL-3) independence. In these p210 bcr-abl-transformed cells (H7 bcr-abl.A54) and in two other murine myeloid cell lines transformed to IL-3 independence by p210 bcr-abl, endogenous p21 RAS is activated as determined by an elevated ratio of associated guanosine triphosphate (GTP)/guanosine diphosphate (GDP), assayed by thin-layer chromatography of the nucleotides eluted from p21 RAS after immunoprecipitation with the Y13-259 antibody. Treatment of p210 bcr-abl-transformed cells with a specific tyrosine kinase inhibitor herbimycin A resulted in diminished tyrosine phosphorylation of p210 bcr-abl and associated proteins, without major reduction in expression of the p210 bcr-abl protein itself. Inhibition of p210 bcr-abl-dependent tyrosine phosphorylation resulted in a reduction of active p21RAS-GTP complexes in the transformed cells, in diminished expression of the nuclear early response genes c-jun and c-fos, and in lower cellular proliferation rate. To further implicate p21 RAS in these functional events downstream of p210 bcr-abl tyrosine phosphorylation, we targeted G-protein function directly by limiting the availability of GTP with the inosine monophosphate dehydrogenase inhibitor, tiazofurin (TR). In p210 bcr-abl-transformed cells treated for 4 hours with TR, in which the levels of GTP were reduced by 50%, but GDP, guanosine monophosphate, and adenosine triphosphate (ATP) were unaffected, p210 bcr-abl tyrosine phosphorylation was at control levels. However, expression of c-fos and c-jun nuclear proto-oncogenes were strongly inhibited and p21 RAS activity was downregulated. These findings show that p210 bcr-abl transduces proliferative signals, in part, through downstream activation of p21 RAS. Furthermore, p21 RAS activity is linked to pathways that regulate c-jun and c-fos expression.

Comparison of baculovirus-expressed c-Abl and BCR/ABL protein tyrosine kinases

Mouse c-Abl type IV and human BCR/ABL proteins have been expressed in insect cells using the baculovirus system. The proteins were expressed as full-length polypeptides as judged by electrophoresis in denaturing gels. They were identified by immunoprecipitation and immunoblotting with antibodies against ABL peptides and, for BCR/ABL, against a BCR peptide. In these immunoprecipitates both proteins gave autophosphorylation principally on tyrosine. Both proteins were active tyrosine kinases, phosphorylating a variety of tyrosine-containing substrates. In fresh extracts both proteins contained phosphotyrosine as shown by Western blots with antiphosphotyrosine antibodies. Partial purification could be achieved readily using ion exchange columns, and the BCR/ABL protein, p210BCR/ABL, could be further purified to near-homogeneity using an antiphosphotyrosine column. Both enzymes required a divalent metal ion for activity. At low concentrations of ATP (2 microM) and with angiotensin II as substrate both enzymes were activated by Mn2+ or by Mg2+. No major differences in catalytic properties were found between the two isolated enzymes in solution. The oncogenic properties of p210BCR/ABL may be due to its different subcellular location, or to the presence of an intracellular inhibitor of c-Abl that does not inhibit BCR/ABL, or to altered substrate-specificity such that it can phosphorylate a unique substrate which is not recognised by c-Abl.