Experimental non-ATP-competitive therapies for chronic myelogenous leukemia

How I treat CML blast crisis

Blast crisis (BC) remains the major challenge in the management of chronic myeloid leukemia (CML). It is now generally accepted that BC is the consequence of continued BCR-ABL activity leading to genetic instability, DNA damage, and impaired DNA repair. Most patients with BC carry multiple mutations, and up to 80% show additional chromosomal aberrations in a nonrandom pattern. Treatment with tyrosine kinase inhibitors has improved survival in BC modestly, but most long-term survivors are those who have been transplanted. Patients in BC should be treated with a tyrosine kinase inhibitor according to mutation profile, with or without chemotherapy, with the goal of achieving a second chronic phase and proceeding to allogeneic stem cell transplantation as quickly as possible. Although long-term remissions are rare, allogeneic stem cell transplantation provides the best chance of a cure in BC. Investigational agents are not likely to provide an alternative in the near future. In view of these limited options, prevention of BC by a rigorous and early elimination of BCR-ABL is recommended. Early response indicators should be used to select patients for alternative therapies and early transplantation. Every attempt should be made to reduce or eliminate BCR-ABL consistent with good patient care as far as possible.

Predictive value of in vitro mutation data to guide second-generation tyrosine kinase inhibitor selection: ready for prime time?

Significant advances in treatment and monitoring for patients with chronic myeloid leukemia have occurred over the last decade. With the introduction of the tyrosine kinase inhibitor imatinib, long-term outcomes have improved and new challenges, such as resistance, including mutations, have emerged. Research efforts into mutational analysis have intensified, with emphasis on the potential of using this technique to guide second-generation tyrosine kinase inhibitor selection. Although some data suggest that a small number of mutations may be associated with a less favorable response to treatment with one second-generation tyrosine kinase inhibitor versus another, these data need to be interpreted cautiously because they are derived primarily retrospectively from single-institution studies and a small number of patients. More research and clinical experience and a better understanding of the implications of in vitro data are needed before these data can be routinely incorporated into therapeutic decisions. Currently, there is no consensus on when to screen patients for mutations, what technique should be used, or how values should be reported. Selection of a second-generation tyrosine kinase inhibitor should therefore be based upon its toxicity profile in conjunction with the patient's comorbidities and the practitioner's experience.

Advances in treatment of chronic myelogenous leukemia--new treatment options with tyrosine kinase inhibitors

Imatinib is considered standard therapy for patients with chronic myelogenous leukemia (CML), inducing a high rate of hematologic and cytogenetic responses. Despite these excellent results, several patients develop resistance to imatinib. Mechanisms of resistance are varied and include BCR-ABL1 kinase domain mutations, decreased entry of imatinib into cells, acquisition of secondary genetic changes and activation of alternate signaling pathways. Second-generation tyrosine kinase inhibitors (TKI) (dasatinib, nilotinib) were developed as an alternative for patients that develop resistance or are intolerant to imatinib. Dasatinib is a dual Abl/Src kinase TKI that is structurally unrelated to imatinib and is approved for therapy of all phases of CML in patients who are resistant or intolerant to imatinib. Nilotinib is a compound related to imatinib that has greater specificity and improved binding characteristics, and has clinical activity in the setting of imatinib failure. Resistance to multiple TKIs does occur, particularly in patients with the T315I mutation. Several new agents are in development including new TKIs, aurora kinase inhibitors and homoharringtonine.