Chronic Myeloid Leukemia: Beyond BCR-ABL1

Purpose of review

In this review, we emphasize up-to-date practical cytogenetic and molecular aspects of chronic myeloid leukemia (CML) and summarize current knowledge on tyrosine kinase inhibitor (TKI) resistance and treatment response monitoring of CML.

Recent findings

The introduction of TKIs has changed the natural course of CML and markedly improved patient survival. Over the past decades, many research efforts were devoted to elucidating the leukemogenic mechanisms of BCR-ABL1 and developing novel TKIs. More recent studies have attempted to answer new questions that have emerged in the TKI era, such as the cytogenetic and molecular bases of treatment failure and disease progression, the clinical impact of genetic aberrations in Philadelphia chromosome (Ph)-positive and Ph-negative cells, and the biological significance of Ph secondarily acquired during therapy of other hematological neoplasms.

Summary

Recent progresses in the understanding of the cytogenetic and molecular mechanisms underlying therapeutic failure and disease progression have improved the risk stratification of CML and will be helpful in the design of novel therapeutic strategies.

     

Tumor Necrosis Factor as Marker for Monocyte Function in Chronic Myeloid Leukemia

The intactness of monocyte function in chronic myeloid leukemia (CML) patients as assessed by their ability to secrete tumor necrosis factor was evaluated. Monocytes from CML patients continued to respond to lipopolysaccharide (LPS) stimulation even during the refractory period, suggesting different pathways for stimulation by LPS and malignant processes.     

MDR1 RNA Expression as a Prognostic Factor in Acute Myeloid Leukemia: An Update

In order to confirm our initial report on the negative impact of MDR1 gene expression on the outcome of de novo acute myeloid leukemia (AML), we present an update of our prospective study with a larger number of patients and a longer duration of follow-up. At diagnosis, MDR1 RNA expression of the leukemic cells was negative in 37% and positive in 63% of the patients (N = 79). The complete remission rate of induction chemotherapy was 76% for MDR1 RNA negative and 54% for MDR1 RNA positive patients (p = 0.05). At a median observation duration of 33 months, the duration of overall survival was 19 months for the MDR1 RNA negative patients but only 8 months for the patients with MDR1 gene expression (p = 0.02). Thus the long-term data also indicate that MDR1 gene expression is an unfavourable prognostic factor in AML.     

Prevalence of BCR-ABL T315I Mutation in Malaysian Patients with Imatinib-Resistant Chronic Myeloid Leukemia

Objective: Chronic Myeloid Leukemia (CML) is caused by a reciprocal translocation between chromosomes 9and 22, t(9;22) (q34;q11) which encodes for the BCR-ABL fusion protein. Discovery of Imatinib Mesylate (IM) asfirst line therapy has brought tremendous improvement in the management of CML. However, emergence of pointmutations within the BCR-ABL gene particularly T315I mutation, affects a common BCR-ABL kinase contact residuewhich impairs drug binding thus contribute to treatment resistance. This study aims to investigate the BCR-ABL T315Imutation in Malaysian patients with CML. Methods: A total of 285 patients diagnosed with CML were included in thisstudy. Mutation detection was performed using qualitative real-time PCR (qPCR). Results: Fifteen out of 285 samples(5.26%) were positive for T315I mutations after amplification with real-time PCR assay. From the total number ofpositive samples, six patients were in accelerated phase (AP), four in chronic phase (CP) and five in blast crisis (BC).Conclusion: Mutation testing is recommended for choosing various tyrosine kinase inhibitors (TKIs) to optimizeoutcomes for both cases of treatment failure or suboptimal response to imatinib. Therefore, detection of T315I mutationin CML patients are clinically useful in the selection of appropriate treatment strategies to prevent disease progression.     

Pleural Effusion in Dasatinib-Treated Patients With Chronic Myeloid Leukemia in Chronic Phase: Identification and Management

Dasatinib has demonstrated durable clinical responses in patients, both as first-line and subsequent lines of therapy. Dasatinib use can result in pleural effusion in some patients, occurring any time during treatment and commonly characterized as mild to moderate in severity. Early identification of symptoms is essential in the proper management of pleural effusion. Prompt confirmation of diagnosis and management of pleural effusion can minimize morbidity and maximize the ability to preserve long-term clinical benefits with dasatinib. Here, we provide guidance on early identification and management of dasatinib-related pleural effusion.     

Optimal Time Points for BCR-ABL1 Tyrosine Kinase Domain Mutation Analysis on the Basis of European LeukemiaNet Recommendations in Chronic Myeloid Leukemia

BackgroundIn this study we aimed to evaluate appropriate time points for mutation analysis of chronic myeloid leukemia.Patients and MethodsIn total, 961 blood samples obtained from 605 chronic-phase chronic myeloid leukemia patients treated with imatinib were subjected to Sanger sequencing to detect BCR-ABL1 mutations. Mutation frequencies at landmark time points (3, 6, and 12 months) were assessed with 16 landmark responses defined by European LeukemiaNet and 2 additional responses, including a complete hematologic response (CHR) at 3 months and a complete cytogenetic response (CCyR) at 12 months.ResultsAfter 12 months of imatinib treatment of 605 patients, 28 (4.6%) patients harbored 33 mutations, including 23 (69.7%) highly resistant T315I and P-loop mutations. Sequencing data from 650 samples were compared with cytogenetic responses. The mutation frequencies in optimal, warning, and failure groups were 0.5% (2/430), 1.8% (2/110), and 19.1% (21/110), respectively. The molecular response was assessed using 956 samples, and the mutation frequencies were 0.7% (3/425), 3.4% (12/358), and 7.6% (14/173) for the optimal, warning, and failure groups, respectively. For the 2 additional responses, the mutation frequencies in patients with CHR at 3 months and with CCyR at 12 months were 0% (0/160) and 1.7% (4/242), respectively. Overall, mutations were frequently detected at 3-month cytogenetic failure (25.0%), 12-month cytogenetic failure (23.2%), and 6-month cytogenetic failure (10.5%) using response–mutation association analysis.ConclusionIrrespective of mutation frequency, failure of achievement of a cytogenetic response should be conducted with appropriate mutation analysis.     

A Critical Review of Trials of First-Line BCR-ABL Inhibitor Treatment in Patients With Newly Diagnosed Chronic Myeloid Leukemia in Chronic Phase

BackgroundThe characteristic expression of the constitutively active oncoprotein, BCR-ABL tyrosine kinase, in chronic myeloid leukemia (CML) was the basis for the development of BCR-ABL tyrosine kinase inhibitors for treatment. Three BCR-ABL inhibitors, imatinib, nilotinib, and dasatinib, have been approved by the US Food and Drug Administration for first-line treatment of patients with newly diagnosed CML in chronic phase (CML-CP).MethodsThis article reviews the key phase III clinical trials supporting the use of first-line imatinib, nilotinib, and dasatinib in patients with CML-CP, as well as findings of supportive phase II studies.ResultsAt the time of its approval in 2001, imatinib induced unprecedented response rates in patients with CML-CP; however, resistance and intolerance to imatinib prevent 20% to 30% of patients from deriving full therapeutic benefit. Nilotinib and dasatinib, both approved in 2010 for first-line CML-CP treatment, are more potent than imatinib and less susceptible to imatinib resistance mechanisms. Comparative clinical trials of each agent with imatinib have shown that they are associated with significantly deeper and more rapid responses than standard-dose imatinib, without compromising safety.ConclusionsGiven that evidence suggests achievement of an early response is predictive of improved long-term outcomes, earlier use of these compounds may lead to more rapid, deeper responses corresponding with improvements in patient outcome. Although future studies will benefit from more uniform definitions of end points and methods of analysis, data from published studies of first-line BCR-ABL inhibitor treatment for patients with newly diagnosed CML-CP support the use of dasatinib or nilotinib in place of imatinib.     

Emergence of Chronic Myelogenous Leukemia From a Background of Myeloproliferative Disorder: JAK2V617F as a Potential Risk Factor for BCR-ABL Translocation

We report the emergence of chronic myelogenous leukemia (CML) in a patient with JAK2V617F-positive polycythemia vera after 15 years of phlebotomy. The polycythemia vera clinical and molecular findings were suppressed at the time of CML diagnosis, only to re-emerge after the leukemia was successfully treated with imatinib. We explored the potential association between myeloproliferative disorders and CML in the context of the current literature and found a higher-than-expected coincidence based on known epidemiologic data for each specific condition. We hypothesize that myeloproliferative disorder (JAK2V617F or molecular events that cause JAK2V617F) is a risk factor for CML (BCR-ABL translocation). Because of therapeutic implications, clinicians should be aware that the conditions co-occur more frequently than once thought.     

Chronic Myeloid Leukemia: State of the Art in 2012

The prognosis of Philadelphia positive (Ph+) chronic myeloid leukemia (CML) has been revolutionized since the discovery of the pathogenetic role of BCR-ABL and the invention of tyrosine kinase inhibitors (TKIs). With a follow-up of 8?years, patients had an OS of 85?% and, with second generation TKIs, dasatinib and nilotinib, almost 50?% of the resistant patients gained a remission with an OS over 90?% at 2?years. Currently the challenge is preventing resistance leading to progression to advance phases that have still few chances of effective treatment. Another objective, derived from the needs of our patients, beside the pride of the scientist, is the discontinuation of the treatment. Second generations TKIs applied to the first line setting seem to be a good option either to avoid progression and to achieve deeper rates of molecular response, necessary for the cure.     

Biochemical Characterization of a Novel Autocrine Transferrin-Like Growth Factor in Acute Myeloblastic Leukemia

Serum-free conditioned media (CM) of acute myelogenous leukemia cell lines induce growth stimulation of other leukemic cell lines. A transferrin (Tf)-like iron binding kD 50 protein was found to be the main growth factor of these CM's. Purification and further characterization of this protein was performed by chromatographic methods, SDS-PAGE, peptide mapping and amino acid analysis. In addition m-RNA of leukemic cell lines was analysed by Northern blot analysis with oligonucleotide probes specific for human serum Tf and melano-transferrin (p97) respectively. No hybridization signals for these probes have been detected. Biochemical results show significant differences between human serum Tf and the kD 50 growth factor with respect to retention time on reversed phase FPLC, pattern of digestion peptides in SDS-PAGE and amino acid composition, which suggests, that this protein is an additional tumor associated member of the transferrin superfamily.     

Tyrosine Kinase Inhibitors in Ph Chronic Myeloid Leukemia Therapy: a Review

Chronic myeloid leukaemia (CML) is a clonal myeloproliferative hematopoietic stem cell disorder. Deregulated BCRABL fusion tyrosine kinase activity is the main cause of CML disease pathogenesis, making BCRABL an ideal target for inhibition. Current tyrosine kinase inhibitors (TKIs) designed to inhibit BCRABL oncoprotein activity, have completely transformed the prognosis of CML. Interruption of TKI treatment leads to minimal residual disease reside (MRD), thought to reside in TKIinsensitive leukaemia stem cells which remain a potential reservoir for disease relapse. This highlights the need to develop new therapeutic strategies for CML either as small molecule master TKIs or phytopharmaceuticals derived from nature to achieve chronic molecular remission. This review outlines the past, present and future therapeutic approaches for CML including coverage of relevant mechanisms, whether ABL dependent or independent, and epigenetic factors responsible for developing resistance against TKIs. Appearance of mutant clones along the course of therapy either preexisting or induced due to therapy is still a challenge for the clinician. A proposed invitro model of generating colony forming units from CML stem cells derived from diagnostic samples seems to be achievable in the era of high throughput technology which can take care of single cell genomic profiling.     

Development of PH Positive Chronic Myeloid Leukemia in a Patient with Chronic Lymphocytic Leukemia Treated with Total Body Irradiation: A Rare Association

Philadelphia (ph) chromosome positive chronic myeloid leukemia developed in a patient treated for chronic lymphocytic leukemia after treatment with total body irradiation. The role of radiation in the development of CML is discussed.     

达沙替尼二线治疗儿童慢性髓性白血病临床分析

摘 要：［目的］探讨达沙替尼（dasatinib,DAS）二线治疗儿童慢性髓性白血病（chronic myeloid leukemia,CML）的疗效、安全性及不良反应。［方法］ 回顾性分析一线伊马替尼（imatinib,IM）治疗未获得满意疗效或因不耐受更换为国产DAS（依尼舒）二线治疗的CML慢性期（CML-CP）9例儿童患者的临床资料,分析其临床特征、治疗效果及不良反应。［结果］ 9例患者确诊患病时中位年龄10（3~14）岁,更换DAS时中位年龄14岁（5~16）岁,换药后中位随访时间28（12~38）个月。3个月、6个月、12个月获得主要分子学反应（MMR）的比例分别为44.4%、44.4%和55.6%。22.2%患者出现1级白细胞减少;22.2%患者出现贫血,1例为轻度,1例为中度;33.3%患者出现血小板减少,其中1~2级2例,3级1例。11.1%患者出现头痛、头晕,11.1%患者出现肌肉骨骼酸痛;11.1%患者出现轻度腹泻;33.3%患者出现皮疹;无肺动脉高压、胸腔积液、心包积液、肺水肿发生,定期肝肾功能检测未见明显异常。［结论］ DAS治疗儿童CML安全、有效,IM耐药或不耐受的儿童可考虑更换为DAS治疗。     

Parameters Involved in Autophosphorylation in Chronic Myeloid Leukemia: a Systems Biology Approach

Background: Chronic myeloid leukemia (CML) is a stem cell disorder characterized by the fusion of twooncogenes namely BCR and ABL with their aberrant expression. Autophosphorylation of BCR-ABL oncogenesresults in proliferation of CML. The study deals with estimation of rate constant involved in each step of thecellular autophosphorylation process, which are consequently playing important roles in the proliferation ofcancerous cells. Materials and Methods: A mathematical model was proposed for autophosphorylation of BCRABLoncogenes utilizing ordinary differential equations to enumerate the rate of change of each responsiblesystem component. The major difficulty to model this process is the lack of experimental data, which areneeded to estimate unknown model parameters. Initial concentration data of each substrate and product forBCR-ABL systems were collected from the reported literature. All parameters were optimized through timeinterval simulation using the fminsearch algorithm. Results: The rate of change versus time was estimated toindicate the role of each state variable that are crucial for the systems. The time wise change in concentration ofsubstrate shows the convergence of each parameter in autophosphorylation process. Conclusions: The role ofeach constituent parameter and their relative time dependent variations in autophosphorylation process couldbe inferred.     

Longer Hydroxyurea Administration Prior to Imatinib Mesylate is Risk Factor for Unsuccessful Major Molecular Response in Chronic-Phase Chronic Myeloid Leukemia: Possibility of P-Glycoprotein Role

Objective: This study aimed to identify the association between duration of HU administration prior to IM treatment and MMR achievement in chronic-phase CML while evaluating the role of MDA, HIF-1α and P-gp. Methods: The study was conducted at Dr. Cipto Mangunkusumo National General Hospital and Dharmais Cancer Hospital, Jakarta using retrospective cohort design to analyse the association between the duration of HU before IM and its MMR achievement and cross-sectional design to analyse the association between MDA, HIF-1α and P-gp expressions with MMR achievement. Main subjects were chronic-phase CML patients treated by HU prior to IM for ≥ 12 months and HU only. The subjects were divided into four main groups: (1) chronic-phase CML patients treated with HU ≤ 6 months + IM ≥ 12 months and (2) HU > 6 months + IM ≥ 12 months (3) HU only (≤ 6 months), (4) HU only ( >6 months). Subjects were obtained from January 2015 to May 2016. Data were gathered through history taking, physical examination, medical record evaluation, and blood sample analysis. Bivariate analysis was conducted using chi square, independent T-test, and Mann-Whitney according to the variables. Results: Administration of HU for more than 6 months prior to IM was associated with unsuccessful MMR achievement (RR 1.60; 95%CI 1.29-2.00). MDA level, HIF-1α, P-glycoprotein expression were not associated with MMR achievement but the mean MDA level (0.63±0.31 vs 0.75±0.41 p=0.461) and median P-glycoprotein expressions {16,92 (0,04 – 43,86) vs. 5,15 (0,02–39,64); p=0.311} were found to be higher in patients receiving HU for > 6 months group than in HU ≤ 6 months group consecutively. Conclusion: Administration of HU for more than 6 months prior to IM was associated with unsuccessful MMR achievement in chronic-phase CML. The study suggested that P-glycoprotein overexpression as the predictor for unsuccessful MMR achievement.     

Generic Imatinib in Chronic Myeloid Leukemia: Survival of the Cheapest

IntroductionThe patent expiration of imatinib mesylate (Gleevec; Novartis) on February 1, 2016, has brought the focus back on generic versions of the drug, and an opportunity to provide a safe and cost-effective alternative. The objective of our study was to determine the molecular and cytogenetic responses, survival endpoints (event-free survival, failure-free survival, transformation-free survival, overall survival), and safety of innovator and generic brands of imatinib.Materials and MethodsIn this retrospective analysis, data from 1812 patients with chronic myeloid leukemia treated with frontline imatinib mesylate (innovator/generic) at a single institution between 2008 and 2014 is included. Of these, 445 were excluded owing to inadequate data and follow-up, and a further 156 were excluded as they were in either the accelerated phase or blast crisis at diagnosis. Thus, data from 1067 patients who were treated with Gleevec (Novartis), and 144 patients with Veenat (NATCO) were available for analysis, and included in the study.ResultsThere was no significant difference in event-free survival (P = .05), failure-free survival (P = .07), transformation-free survival (P = .12), or overall survival (P = .24) between the 2 groups. The frequency of reported nonhematologic adverse events and hematologic adverse events was comparable between the study groups.ConclusionThe findings of the present study showed comparable efficacy and safety of the generic and innovator versions of imatinib in the treatment of patients with chronic myeloid leukemia.     

Ph-Negative Chronic Myeloid Leukemia: The Nature of the Breakpoint Junctions and Mechanism of ABL Transposition

CML is a well-defined hematological and clinical entity which sooner or later progresses to blast crisis and death of the patient. Leukemic cells of about 95% of patients show the Ph chromosome which is evidence of the t(9;22)(q34;q11), the cytogenetic rearrangement whereby the BCR gene on chromosome 22 and the ABL gene on chromosome 9 are joined together. The juxtaposition of these genes deregulates the usual function of ABL and causes leukemia. Leukemic cells of the remaining 5% (approximate) of CML patients show complex translocations or have a normal karyotype. Complex translocations achieve the same juxtaposition of BCR and ABL as the standard t(9;22). The Ph chromosome is usually present but may be masked. The final result of a complex translocation can be an apparently normal karyotype and, although BCR and ABL are juxtaposed, there is no Ph chromosome. This is the origin of some cases of Ph-negative CML, in others, part of chromosome 9 including ABL is inserted within the BCR gene. We believe that simple and complex recombinations and insertions are each caused by a single concerted event which breaks a number of adjacent DNA strands at the same time, followed by their mismatched joining and consequent recombination.

The association of BCR-ABL is the essential etiological feature of CML and can be explained, in all cases investigated, by chromosomal rearrangement which takes the form of simple or complex translocations or chromosome insertion. Events that initiate chromosome rearrangement are therefore important in the etiology of CML. Chromosome rearrangement is the result of abnormal DNA recombination which may be caused by an error in normal recombination processes or by endogenous and exogenous mutagens such as chemicals or radiation. These can be regarded as the prime causes of CML.