Use of tyrosine kinase inhibitors for chronic myeloid leukemia: management of patients and practical applications for pharmacy practitioners

OBJECTIVE

To summarize the use of tyrosine kinase inhibitors (TKIs) for treatment of patients with chronic myeloid leukemia (CML) and provide practical information for patient management.

DATA SOURCES

Literature was retrieved from PubMed (2000-January 2011), using the search terms chronic myeloid leukemia and tyrosine kinase inhibitor. Abstracts presented at the 2008-2010 annual meetings of the American Society of Hematology and the American Society of Clinical Oncology, reference citations from identified publications, as well as the manufacturers' full prescribing information for cited drugs, also were reviewed.

STUDY SELECTION AND DATA EXTRACTION

Articles evaluating the efficacy and safety of the TKIs imatinib, nilotinib, and dasatinib were evaluated. Focus was placed on publications supporting management of patients with CML in the chronic phase. Reports presenting clinical trial information of TKIs in development also were included.

DATA SYNTHESIS

The discovery of targeted tyrosine kinase inhibition of BCR-ABL kinase dramatically changed the treatment of CML. Imatinib, the first TKI approved for treatment of patients with Philadelphia chromosome--positive CML, demonstrated significant superiority over the previous standard of care: interferon plus cytarabine. The newer, more potent TKIs, nilotinib and dasatinib, have demonstrated improved efficacy over imatinib as first-line therapy and provide an effective option for patients with resistance or intolerance to imatinib.

CONCLUSIONS

To maximize efficacy of TKI therapy, close patient management, involving frequent monitoring of patient response, is essential. Given the importance of continuing TKI therapy, early recognition and management of adverse events are critical to optimizing outcomes in patients with CML. In addition to the safety profile and considerations of comorbidities, additional factors can affect therapeutic selection, including drug-drug and drug-food interactions. Research investigating new therapies, particularly for patients harboring the T315I mutation-which remains refractory to current TKIs-continues in the quest to improve outcomes in patients with CML.

Targeted therapy in haematological malignancies

The recent and rapid development of molecularly targeted therapy is best illustrated by advances in the management of haematological malignancy. In myeloid diseases we have seen dramatic improvements in the overall survival and quality of life for patients with chronic myeloid leukaemia treated with ABL and Src/ABL kinase inhibitors and we are poised to discover whether JAK2 inhibitors may offer similar benefit in myeloproliferative diseases. For acute myeloid leukaemia, the introduction of ATRA and myelotarg have had major impacts on the design of therapy regimens and many novel targeted agents, including farnesyl transferase, FLT3 and histone deacetylase inhibitors, are now in clinical trial. In lymphoid malignancies the highlight has been the introduction of rituximab, with significant improvements in the management of non-Hodgkin lymphoma and chronic lymphocytic leukaemia. The last 10 years has experienced a rapidly expanding interest and acceptance that leukaemic stem cells, including an improved ability to target them, may hold the key to improved response and reduced relapse rates across both myeloid and lymphoid disease. We now eagerly anticipate an era in which a wealth of preclinical discoveries are progressed to the clinic.

Second-line therapy and beyond resistance for the treatment of patients with chronic myeloid leukemia post imatinib failure

Chronic myeloid leukemia (CML) is characterized at the molecular level by the presence of the Philadelphia chromosome (Ph) and the resultant oncogenic signaling by the BCR-ABL fusion protein. The treatment and outlook for CML were revolutionized by the introduction of imatinib, but resistance is a substantial barrier to successful treatment in many patients. Introduction of the second-generation tyrosine kinase inhibitors (TKI) dasatinib and nilotinib has provided effective therapeutic options for many patients with resistance to front-line imatinib. However, the T315I mutation remains a significant clinical issue because it is insensitive to all currently available agents. A number of new agents are in development and many hold the promise of activity in T315I-mutated disease. Successful treatment of patients with disease harboring T315I might lie in the effective combination or sequencing of these new agents with existing TKI therapies.

Class effects of tyrosine kinase inhibitors in the treatment of chronic myeloid leukemia

Tyrosine kinase inhibitors have revolutionized the treatment of chronic myeloid leukemia (CML), offering patients several targeted therapeutic options that provide the possibility of sustained remissions and prolonged survival. With the availability of imatinib, nilotinib and dasatinib, physicians must weigh the efficacy and safety profile of each agent when choosing the best therapeutic option for individual patients. Each agent targets tyrosine kinases within the cell uniquely to cause the desired antiproliferative effect. In addition to inhibiting the BCR-ABL kinase, imatinib and nilotinib target the same array of other tyrosine kinases, including c-KIT and platelet-derived growth factor receptor (PDGFR), albeit with differing potencies. While targeting BCR-ABL with the highest potency among approved agents in CML, dasatinib also targets a broad array of off-target kinases, including SRC family members, PDGFR and EPHB4. The differences in kinase inhibition profiles among these agents in vitro probably account for the differing clinical safety profiles of these agents. This paper reviews the various kinases inhibited by imatinib, nilotinib and dasatinib, and describes the potential impact of kinase inhibition on the efficacy and safety of each agent.

Once-Daily Dasatinib for Treatment of Patients with Chronic Myeloid Leukemia

Objective

To discuss the new dasatinib dosing regimen for the treatment of chronic phase chronic myelogenous leukemia (CP CML) in patients who failed or were intolerant to imatinib therapy.

Data Sources

Literature published between July 2008 and December 2008 was accessed via MEDLINE, the Proceedings of the American Society of Hematology, and the Proceedings of the American Society of Clinical Oncology using the key words chronic myelogenous leukemia, chronic myeloid leukemia, dasatinib, imatinib, nilotinib, pharmacokinetics, and regimen.

Study Selection And Data Extraction

Meeting abstracts and reports of major Phase 1–3 studies published in English are included.

Data Synthesis

Imatinib is the standard first-line therapy for CML; however, some patients develop resistance or are intolerant to the drug. Dasatinib was approved for the treatment of imatinib-resistant/intolerant patients with CML or Philadelphia chromosome–positive acute lymphoblastic leukemia at the dosage of 70 mg twice daily. A Phase 3 dose-optimization study was performed to compare this regimen with others, including dasatinib 100 mg once daily, in patients with CP CML. Results of this study showed that there was no significant difference in efficacy between these 2 regimens. The safety profile was improved in the 100-mg once-daily dasatinib arm with significantly reduced frequencies of grade 3–4 thrombocytopenia and all-grade pleural effusions. The number of patients who had to discontinue, reduce, or interrupt their dosage was also less among patients taking dasatinib 100 mg once daily.

Conclusions

Dasatinib 100 mg once daily has a more favorable risk to benefit assessment compared with the previous 70 mg twice-daily regimen and is now the recommended schedule for patients with CP CML.

Treatment selection after imatinib resistance in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a progressive and often fatal malignancy of the blood. The harbinger of CML is a chromosomal translocation that results in the synthesis of the BCR-ABL fusion protein, a constitutively active tyrosine kinase. The advent of imatinib, an inhibitor targeted specifically for BCR-ABL, represented a significant medical advance in CML therapy. However, patients with CML can exhibit varying responses to first-line treatment with imatinib. While most patients respond to treatment, some may experience a loss of response or require treatment discontinuation due to toxicity. Frequent monitoring for resistance or intolerance is a requirement for recognition of suboptimal response. Mutational analysis of the patient's BCR-ABL alleles is also informative and may be predictive of a response to therapy. Published physician guidelines have highlighted these recommendations, but it is not clear if these guidelines are universally followed. One option in patients showing poor response to standard-dose imatinib of 400 mg is to escalate the dose. However, this option should be reserved for patients with minimal disease burden. Clinically available options mainly include second-generation tyrosine kinase inhibitors, such as dasatinib and nilotinib. Allogenic stem cell transplantations (for eligible patients) also should be considered. The disease and patient characteristics at the time of imatinib failure should be evaluated before choosing second-line therapy to optimize the therapeutic benefit without unnecessary delay.

Novel agents in CML therapy: tyrosine kinase inhibitors and beyond

The emergence of resistance to imatinib has become a significant problem despite the remarkable clinical results achieved with this tyrosine kinase inhibitor in the treatment of chronic myeloid leukaemia. The most common cause of imatinib resistance is the selection of leukemic clones with point mutations in the Abl kinase domain. These mutations lead to amino acid substitutions and prevent the appropriate binding of imatinib. Genomic amplification of BCR-ABL, modulation of drug efflux or influx transporters, and Bcr-Abl-independent mechanisms also play important roles in the development of resistance. Persistent disease is another therapeutic challenge and may in part, be due to the inability of imatinib to eradicate primitive stem cell progenitors. A multitude of novel agents have been developed and have shown in vitro and in vivo efficacy in overcoming imatinib resistance. In this review, we will discuss the current status of the ATP-competitive and non-ATP-competitive Bcr-Abl tyrosine kinase inhibitors. We will also describe inhibitors acting on targets found in signaling pathways downstream of Bcr-Abl, such as the Ras-Raf-mitogen-activated protein kinase and phosphatidylinositol-3 kinase-Akt-mammalian target of rapamycin pathways, and targets without established links with Bcr-Abl.