BCR-ABL tyrosine kinase inhibitors in chronic myeloid leukemia: using guidelines to make rational treatment choices

The success of the BCR-ABL tyrosine kinase inhibitor (TKI) imatinib in improving prognosis in chronic myeloid leukemia (CML) has led to its wide use as first-line therapy at a standard dose of 400 mg daily. As more patients have undergone therapy, the development of molecular and clinical resistance to imatinib has raised further therapeutic challenges. The 2 main approaches to overcoming resistance are imatinib dose escalation and the use of alternative more potent TKIs, such as dasatinib or nilotinib. The phase II SRC/ABL Tyrosine Kinase Inhibition Activity Research Trials (START) of dasatinib have established dasatinib as potent and effective in overcoming imatinib resistance or intolerance in all phases of CML. The most recent treatment guidelines by the National Comprehensive Cancer Network now contain recommendations for using dasatinib in this setting. The issue of when to change from imatinib to an alternative agent in preference to imatinib dose escalation is keenly debated, particularly as new clinical evidence emerges, which highlights the importance of achieving early cytogenetic and molecular responses for a good long-term outcome. Identifying patients in whom a change to dasatinib or nilotinib is more appropriate than imatinib dose escalation is therefore important.     

Evolution of therapies for chronic myelogenous leukemia

The clinical outcome for patients with chronic myelogenous leukemia (CML) has changed dramatically in the past 15 years. This has been due to the development of tyrosine kinase inhibitors (TKIs), compounds that inhibit the activity of the oncogenic BCR-ABL1 protein. Imatinib was the first TKI developed for CML, and it led to high rates of complete cytogenetic responses and improved survival for patients with this disease. However, approximately 35% of patients in chronic phase treated with imatinib will develop resistance or intolerance to this drug. The recognition of the problem of imatinib failure led to the design of second-generation TKI (dasatinib, nilotinib, and bosutinib). These drugs are highly active in the scenario of imatinib resistance or intolerance. More recently, both nilotinib and dasatinib were approved for frontline use in patients with chronic phase CML. Ponatinib represents the last generation of TKI, and this drug has been developed with the aim of targeting a specific BCR-ABL1 mutation (T315I), which arises in the setting of prolonged TKI therapy and leads to resistance to all commercially available TKI. Parallel to the development of specific drugs for treating CML, major advances were made in the field of disease monitoring and standardization of response criteria. In this review, we summarize how therapy with TKI for CML has evolved during the last decade.     

Extending the duration of response in chronic myelogenous leukemia: targeted therapy with sequential tyrosine kinase inhibitors

Tyrosine kinase inhibitors (TKIs) are the mainstay for treatment of chronic myelogenous leukemia (CML). Imatinib was the first TKI approved for use in CML, but resistance to this therapy has emerged as a significant issue, and second-line options are often necessary. Increased-dose imatinib may elicit responses in some patients, but clinical evidence suggests only a minority experience sustained benefit. The second-generation TKIs, dasatinib and nilotinib, have demonstrated efficacy in patients resistant or intolerant to imatinib. Changes in therapy, with the aim of inducing durable response, should occur promptly after imatinib failure is identified as all agents are more effective in chronic phase disease than in later stages. Selection of second-line agents should be driven by efficacy and safety: dasatinib may be more effective in patients with P-loop or F359C mutations; nilotinib may be more effective in those with F317L mutations.     

Tailoring tyrosine kinase inhibitor therapy to tackle specific BCR-ABL1 mutant clones

Several tyrosine kinase inhibitors (TKIs) are currently under development for the treatment of patients with chronic myelogenous leukemia (CML) resistant or intolerant of imatinib therapy, including nilotinib, dasatinib, and bosutinib. The current paradigm of TKI therapy involves a sequential use of these compounds, with imatinib invariably used as frontline therapy followed by either dasatinib or nilotinib on an empiric basis. A more sensible approach to this sequence is the selection of the TKI best suited to overcome the resistance conferred by BCR-ABL1 mutations detected at each time-point. As more TKIs are becoming available, the management of patients with CML will require degree of “finesse” to better match each patient with the best TKI available. This match is best made based on available in vitro data regarding the activity of each agent against each specific mutation. The case herein reported supports such strategy.     

How Much and How Long: Tyrosine Kinase Inhibitor Therapy in Chronic Myeloid Leukemia

As the first clinically successful tyrosine kinase inhibitor (TKI), imatinib pioneered a new approach to treating patients with cancer. Dramatic results from chronic myeloid leukemia (CML) clinical trials spurred the development of TKIs for other malignancies such as acute myeloid leukemia as well as kidney and lung cancer. In CML, imatinib resistance led to the rapid development of dasatinib and nilotinib, more potent second-generation ABL kinase inhibitors that can often overcome imatinib resistance. While the clinical efficacy of TKIs in CML is well established, a number of important questions remain about the optimal dose and duration of therapy. Even the best initial dose for imatinib is still under investigation. Although laboratory and clinical studies had led to the prevailing view that continual inhibition of the BCR-ABL kinase was required for optimal efficacy, recent data on dasatinib have upended this notion and have led to a change in the recommended dosing schedule. The availability of dasatinib and nilotinib also begs the question of whether they might be superior to imatinib as first-line agents. Finally, the question of whether it may be possible to stop TKI therapy at least in some patients with CML has attracted considerable attention. More than 10 years after the introduction of imatinib, optimization of TKI therapy for CML continues.     

How to choose frontline therapy for chronic myelogenous leukemia: so many drugs, not so many patients

With the development of tyrosine kinase inhibitors (TKIs), the management and outlook for patients with chronic myelogenous leukemia (CML) have completely changed over the past 10 years. Imatinib was the first TKI approved to treat CML in the chronic phase. After their initial approval as second-line agents, dasatinib and nilotinib were compared with imatinib in the first-line setting in 2 randomized trials. Both trials showed that therapeutic milestones (complete cytogenetic remission and major molecular remission) occurred earlier with these newer agents, leading to their approval for the treatment of newly diagnosed CML. Therefore, 3 different TKIs are now available for treating CML. Long-term follow-up of patients treated with imatinib shows that the attainment of therapeutic milestones by 12 months of therapy leads to better long-term outcomes. Most patients who experience disease progression on imatinib do so within the first 3 years of therapy. Therefore, one can argue that dasatinib or nilotinib should be chosen to treat patients with newly diagnosed CML. However, these agents do not have the long-term track record of imatinib. This article summarizes the published data and reviews the rationale in choosing the appropriate TKI for first-line treatment of CML in the chronic phase.     

Advanced CML: therapeutic options for patients in accelerated and blast phases

Tyrosine kinase inhibitor (TKI) therapy has impacted the natural course of chronic myelogenous leukemia (CML), because patients diagnosed as having chronic-phase disease can experience long-lasting responses. However, for patients with advanced CML (accelerated and blast phases), the efficacy of all current therapies is reduced. For these patients, allogeneic stem cell transplantation remains the preferred treatment if a donor is available, although TKIs play a valuable role as a bridging therapy. For patients with accelerated-phase CML, imatinib, dasatinib, and nilotinib have been shown to produce meaningful rates of hematologic and cytogenetic response. Imatinib and dasatinib are also approved for blast-phase CML. Studies with the newer agents have involved heavily pretreated patients; however, response rates have been at least comparable to those achieved with imatinib in previous studies. Therefore, these newer, more potent TKIs will probably be more likely to induce a deep response in previously untreated patients. Moreover, because fewer mechanisms appear to exist for secondary resistance to dasatinib and nilotinib, reducing the potential for disease to escape TKI therapy, these agents may result in improved longer-term outcomes. However, BCR-ABL-independent pathways may also become more important, indicating that other therapeutic targets may also have a future role in managing patients with advanced CML.     

All tyrosine kinase inhibitor-resistant chronic myelogenous cells are highly sensitive to Ponatinib

The advent of tyrosine kinase inhibitor (TKI) therapy has considerably improved the survival of patients suffering chronic myelogenous leukemia (CML). Indeed, inhibition of BCR-ABL by imatinib, dasatinib or nilotinib triggers durable responses in most patients suffering from this disease. Moreover, resistance to imatinib due to kinase domain mutations can be generally circumvented using dasatinib or nilotinib, but the multi-resistant T315I mutation that is insensitive to these TKIs, remains to date a major clinical problem. In this line, ponatinib (AP24534) has emerged as a promising therapeutic option in patients with all kinds of BCR-ABL mutations, especially the T315I one. However and surprisingly, the effect of ponatinib has not been extensively studied on imatinib-resistant CML cell lines. Therefore, in the present study, we used several CML cell lines with different mechanisms of resistance to TKI to evaluate the effect of ponatinib on cell viability, apoptosis and signaling. Our results show that ponatinib is highly effective on both sensitive and resistant CML cell lines, whatever the mode of resistance and also on BaF3 murine B cells carrying native BCR-ABL or T315I mutation. We conclude that ponatinib could be effectively used for all types of TKI-resistant patients.     

Ever-advancing chronic myeloid leukemia treatment

Treatment of chronic myeloid leukemia (CML) has been drastically changed by the emergence of the ABL tyrosine kinase inhibitor (TKI), imatinib mesylate. However, resistance and intolerance have frequently been reported, particularly in patients with advanced-stage disease. Point mutations within the ABL kinase domain that interfere with imatinib binding are the most critical cause of imatinib resistance. To overcome this resistance, four second-generation ATP competitive ABL TKIs, dasatinib, nilotinib, bosutinib and bafetinib, have been developed. Dasatinib and nilotinib also demonstrated higher efficacy than imatinib in previously untreated CML patients in chronic phase. Despite promising clinical results, the frequently observed mutant T315I is not effectively targeted by any of the second-generation ABL TKIs. Thus, a third-generation ABL TKI, ponatinib, was developed to inhibit all mutated BCR-ABL and showed clinical efficacy in CML cells harbouring T315I. CML treatment is rapidly progressing and further evolution is surely expected. Moreover, it was recently reported that some CML patients who achieved sustained complete molecular response could stop TKI. CML may become the first human cancer to be conquered solely with oral medicines.     

Clinical Trials in Chronic Myeloid Leukemia

The introduction of the tyrosine kinase inhibitor (TKI) imatinib in the treatment of Philadelphia chromosome-positive chronic myeloid leukemia (CML) has substantially improved the outcome of CML patients. Despite the positive results, problems and questions remained. This was the rationale to setup trials for treatment optimization, where imatinib was administered in higher dose and/or in combination with other therapy but where also new and potentially more efficacious second-generation TKI, nilotinib and dasatinib, were investigated. This review summarizes data of recently published first-line studies with the standard treatment imatinib 400 mg as one study arm. Results of randomized comparisons to higher-dose imatinib treatment, nilotinib or dasatinib are discussed. With regard to outcome interpretation, general aspects on statistical issues and endpoint definitions are put into focus. Considering decidedly increased longevity thanks to TKI treatment, future research should include the evaluation of the quality of life (QoL). Relating also to QoL, safe ways of drug discontinuation need to be investigated.     

Long-term outcomes in the second-line treatment of chronic myeloid leukemia: a review of tyrosine kinase inhibitors

Chronic myeloid leukemia (CML) is a progressive and often fatal myeloproliferative neoplasm. The hallmark of CML is an acquired chromosomal translocation known as the Philadelphia chromosome (Ph), which results in the synthesis of the breakpoint cluster region-Abelson murine leukemia (BCR-ABL) fusion oncoprotein, a constitutively active tyrosine kinase. The introduction of imatinib, a tyrosine kinase inhibitor (TKI) that is specific for BCR-ABL, was a major breakthrough in CML therapy. Although most patients respond to first-line imatinib therapy, some experience loss of response (resistance) or require treatment discontinuation because of toxicity (intolerance). For patients with CML, failure on standard-dose imatinib therapy (400 mg daily), imatinib dose escalation (600-800 mg daily) is a second-line option. However, high-dose imatinib is not an appropriate approach for patients who experience drug toxicity, and there remain questions over the durability of responses achieved with this strategy. Alternative second-line options include the TKIs dasatinib and nilotinib. A substantial amount of long-term data for these agents is available. Although both are potent and specific BCR-ABL TKIs, dasatinib and nilotinib exhibit unique pharmacologic profiles and response patterns relative to different patient characteristics, such as disease stage and BCR-ABL mutation status. To optimize therapeutic benefit, clinicians should select treatment based on each patient's historic response, adverse-event tolerance, and risk factors.     

Clinical Algorithms for the Treatment of Patients With Chronic Myeloid Leukemia: The 2010 Perspective

Chronic myeloid leukemia (CML) is a progressive and often fatal myeloproliferative disorder. The hallmark of CML is an acquired chromosomal translocation known as the Philadelphia chromosome (Ph) that results in the synthesis of the BCR-ABL fusion protein, a constitutively active tyrosine kinase (TK). The introduction of imatinib, a TK inhibitor (TKI) specific for BCR-ABL, was a major breakthrough in CML therapy. Although most patients respond to first-line imatinib therapy, some experience a loss of response (resistance) or require treatment discontinuation because of toxicity (intolerance). In patients for whom standard-dose imatinib therapy (400 mg/day) fails, imatinib dose escalation (600-800 mg/day) is a second-line option. However, high-dose imatinib is not an appropriate approach for patients experiencing drug toxicity, and there remain questions over the durability of responses achieved with this strategy. Alternative second-line options include the newer TKIs dasatinib and nilotinib. A substantial amount of long-term data for these agents is available. Although both are potent and specific BCR-ABL TKIs, dasatinib and nilotinib exhibit unique pharmacologic profiles and response patterns relative to different patient characteristics, such as disease stage and BCR-ABL mutational status. To optimize therapeutic benefit, clinicians should select treatment based on each patient's historical response, adverse event tolerance level, and risk factors.     

Comparison of the clinical outcomes of nilotinib and dasatinib therapies in newly diagnosed patients in the chronic phase of chronic myeloid leukemia: a retrospective analysis

Treatment with a tyrosine kinase inhibitor (TKI) is the standard of care for patients with chronic myeloid leukemia (CML). The new-generation TKIs, nilotinib and dasatinib, are found to have deeper and faster treatment response rates compared to imatinib in the first-line setting. However, a direct comparison between nilotinib and dasatinib has never been reported previously. Our study aims to compare the outcomes and molecular responses achieved following the first-line use of these two agents in patients with CML-CP. The database of the CML Cooperative Study Group was reviewed and patients with CML in the chronic phase (CP) who were given nilotinib or dasatinib as first-line therapy were identified. Out of 361 patients with CML-CP enrolled in our database, 58 and 63 had been treated with conventional doses of nilotinib (300 mg twice daily) and dasatinib (100 mg once daily), respectively, as first-line therapy. The patient demographics did not show significant differences between the groups. The event-free survival rates did not differ between these two groups. The major molecular response (MMR) and the deep molecular response (DMR) rates by 6, 12, 18, and 24 months did not differ between groups. Among the three scoring systems, only the Hasford score could predict the achievement of DMR, and all of them failed to predict the achievement of MMR in the entire cohort. Our data suggest that both nilotinib and dasatinib have comparable efficacies and promising outcomes.     

Tyrosine Kinase Inhibitors: The First Decade

The treatment of chronic myeloid leukemia (CML) drastically changed with the introduction of imatinib mesylate, a Bcr-Abl1 tyrosine kinase inhibitor (TKI), in 1998. By directly targeting this leukemogenic protein kinase, imatinib affords patients with CML sustained chromosomal remissions, which translate into prolonged survival. However, there has been concern over the emergence of resistance to imatinib, and some patients fail to respond or are intolerant of imatinib therapy because of untoward toxicity. This has spurred interest in developing novel TKIs to overcome the mechanisms of resistance that lead to treatment failure—most importantly, Bcr-Abl1 kinase domain mutations. Two of these second-generation TKIs, nilotinib and dasatinib, are approved worldwide for the treatment of CML after imatinib failure or intolerance. Although these agents are active, they fail in many patients because of the development of highly resistant mutations such as the T315I, against which several novel agents are currently being tested in clinical trials. This review provides an account of the progress made in the field of TKI therapy for CML over the past decade.     

Practical advice for determining the role of BCR-ABL mutations in guiding tyrosine kinase inhibitor therapy in patients with chronic myeloid leukemia

Data demonstrating the superiority of nilotinib over imatinib in the frontline treatment of chronic myeloid leukemia (CML) and ongoing studies with dasatinib and bosutinib are rapidly changing the treatment landscape for CML. In this review, the authors discuss currently available therapies for CML, focusing on mechanisms of resistance to imatinib and treatment strategies to overcome resistance. Relevant articles were identified through searches of PubMed and abstracts from international hematology/oncology congresses. Additional information sources were identified from the bibliographies of these references and from the authors' own libraries and expertise. In vitro 50% inhibitory concentration (IC(50) ) data alone are not sufficient to guide the choice of a tyrosine kinase inhibitor (TKI) in the presence of a mutant breakpoint cluster region-v-abl Abelson murine leukemia viral oncogene homolog (BCR-ABL) clone, because there is a lack of data regarding how well such IC(50) values correlate with clinical response. A small subset of BCR-ABL mutant clones have been associated with impaired responses to second-generation TKIs (tyrosine to histidine mutation at codon 253 [Y253H], glutamic acid to lysine or valine mutation at codon 255 [E255K/V], and phenylalanine to cysteine or valine mutation at codon 359 [F359C/V] for nilotinib; valine to leucine mutation at codon 299 [V299L] and F317L for dasatinib); neither nilotinib nor dasatinib is active against the threonine to isoleucine mutation at codon 315 (T315I). For each second-generation TKI, the detection of 1 of a small subset of mutations at the time of resistance may be helpful in the selection of second-line therapy. For the majority of patients, comorbidities and drug safety profiles should be the basis for choosing a second-line agent. Clinical trial data from an evaluation of the response of specific mutant BCR-ABL clones to TKIs is needed to establish the role of mutation testing in the management of CML.     

Improving Outcomes in Chronic Myeloid Leukemia Over Time in the Era of Tyrosine Kinase Inhibitors

Most patients with chronic myeloid leukemia (CML) receiving treatment with BCR-ABL1 tyrosine kinase inhibitors (TKIs) will achieve favorable responses. Moreover, TKI therapy enables patients to experience long-term survival, with survival rates similar to those of individuals without CML. This enhanced survival has resulted from the availability of multiple BCR-ABL1 TKIs with efficacy, not only in frontline treatment, but, importantly, also in second- and third-line treatment. We have reviewed the changes in long-term outcomes in the era of TKI therapy and how these changes have affected treatment practices. We discuss the development of imatinib, the first BCR-ABL1 TKI, followed by newer TKIs, including nilotinib, dasatinib, bosutinib, and ponatinib. We consider the key studies that led to their development as frontline or later-line therapies, their safety profiles, and their effect on improving patient outcomes. With these improved outcomes, the definition of an optimal response has become more stringent, and treatment monitoring strategies have changed. Second-line patient populations have evolved from those with resistance to, or intolerance of, imatinib to those with moderate responses to, or low-grade adverse events with, imatinib. Although all TKIs are associated with high survival rates, newer TKIs have been associated with lower disease progression rates and, importantly, deeper treatment responses and, potentially, a greater chance of future treatment-free remission. Finally, we consider the unmet needs of patients with CML, including the challenges remaining for those without optimal responses during TKI therapy and new therapies and strategies to identify such patients at diagnosis.     

Chronic Myeloid Leukemia in the Tyrosine Kinase Inhibitor Era: What Is the “Best” Therapy?

The introduction of imatinib mesylate, a Bcr-Abl1 tyrosine kinase inhibitor (TKI), has revolutionized the treatment of chronic myeloid leukemia (CML). By directly targeting the Bcr-Abl kinase, imatinib leads to durable cytogenetic remissions and in turn improved survival. However, many patients with CML develop resistance, fail to respond, or become intolerant to imatinib due to side effects. This has spurred interest in developing second-generation TKIs to overcome the mechanisms of resistance that lead to treatment failure, specifically Bcr-Abl1 kinase domain mutations. Two second-generation TKIs, nilotinib and dasatinib, are approved for the treatment of CML after imatinib failure or intolerance. Unfortunately, many patients fail subsequent treatment with these agents, as they can develop highly resistant mutations such as T315I. Various other strategies are now in use to optimize the treatment of CML, including dose optimization of imatinib, combination therapy, upfront use of second-generation TKIs, and use of maintenance therapy with interferon-α and vaccines. This review highlights progress made in the treatment of CML in the past year.     

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.     

Practical Management of Toxicities Associated with Tyrosine Kinase Inhibitors in Chronic Myeloid Leukemia

The tyrosine kinase inhibitor (TKI) imatinib constitutes the current first-line therapeutic approach for patients with chronic myeloid leukemia. The success of imatinib relies on its potent inhibitory activity against the Bcr-Abl kinase that drives the pathogenesis of this disorder. The vast majority of patients treated with imatinib as a single agent will achieve a complete cytogenetic response. However, a subset of patients will develop imatinib resistance, frequently associated with mutations within the Abl kinase domain. In this setting, treatment with the second-generation TKIs nilotinib and dasatinib has proved highly efficacious. While therapy with these Bcr-Abl TKIs is generally well tolerated, adverse events are common and can result in treatment interruptions that compromise clinical responses. Herein, we discuss some of the toxicities characteristically associated with TKI therapy and provide practical approaches to the clinical management of these adverse effects.     

Current and emerging treatment options in chronic myeloid leukemia

Treatments for chronic myeloid leukemia (CML) represent a success story in molecular medicine. The development of imatinib, a tyrosine kinase inhibitor (TKI) targeted against the causative Bcr-Abl oncoprotein in CML, has resulted in hematologic and cytogenetic remissions in all phases of CML. A significant proportion of patients are resistant to imatinib or develop resistance during treatment. This is often a result of mutated forms of the Bcr-Abl oncoprotein to which imatinib is unable to bind. Several strategies have been developed to overcome the problem of imatinib resistance, including high-dose imatinib, novel targeted agents, and combination treatments. Novel agents include dasatinib, a potent TKI that inhibits several critical oncogenic proteins and which has recently been approved for patients with CML who are resistant or intolerant to imatinib; and nilotinib, a potent selective Bcr-Abl kinase inhibitor currently in clinical development. Other agents in development include SKI-606 and INNO-406. Stem cell transplantation remains a useful option, although it is not generally used as first-line treatment. Overall, there are an increasing number of treatment options available for patients with CML.