Dasatinib: a new step in molecular target therapy.

The chimeric BCR-ABL gene, originated by the Philadelphia chromosome, encodes a fusion protein, BCR-ABL, bearing unregulated tyrosine kinase activity, the pivotal pathogenetic step of chronic myeloid leukemia (CML). Imatinib, an inhibitor of the BCR-ABL tyrosine kinase, significantly improves the outcome of patients with CML. Although the majority of CML patients are responsive to imatinib, a subset of patients loses the response and some progress to accelerated- or blast-phase CML. The understanding of mechanisms of imatinib resistance has led to the development of novel BCR-ABL inhibitors; among these, dasatinib emerged as the most promising, being approximately 300-fold more potent than imatinib; it also inhibits SRC family kinases. Preliminary data, after the introduction of dasatinib in clinical trials, in patients with CML, suggest that this drug is safe and well tolerated; furthermore, the majority of patients with imatinib-resistant disease achieved objective responses, although the durability of responses remains to be defined. Recently, dasatinib emerged as a potent inhibitor of imatinib-resistant protein tyrosine kinase (KIT) activation loop mutants and it is able to induce apoptosis in mast cell and leukemic cell lines expressing these mutations. The preclinical data concerning its activity on several human solid tumor lines widen new opportunities for their use outside CML.