Evolution of therapies for chronic myelogenous leukemia

Abstract

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.

Figure 1

Three Generations of Tyrosine Kinase Inhibitors. First-generation: Imatinib; Second-generation: Nilotinib, Dasatinib and Bosutinib; Third-generation: Ponatinib

Figure 2

Timeline of Development of Therapy for Chronic Myelogenous Leukemia

Figure 3

Mechanism of action of Imatinib and other TKI. A. The BCR-ABL1 oncogenic TK phosphorylates protein targets leading to activation of intracellular pathways associated with increased cellular proliferation and apoptosis resistance. ATP binds to BCR-ABL1 and supplies phosphate groups for the phosphorylation reaction. B. Current available TKI are ATP-mimetic compounds, competing with ATP for the ATP-binding site at BCR-ABL1. Binding of the TKI to BCR-ABL1 prevents phosphorylation of protein substrates, since no phosphate group is available for the reaction to occur. As a consequence, oncogenic signaling pathways are no longer activated and the cell undergoes apoptosis.