Dasatinib [BMS 354825] is an orally active, small molecule, dual inhibitor of both SRC and ABL kinases that is under development with Bristol-Myers Squibb for the treatment of patients with chronic myelogenous leukaemia (CML) and imatinib-acquired resistance/intolerance. While imatinib remains a frontline therapy for CML, patients with advanced disease frequently develop resistance to imatinib therapy through multiple mechanisms. These mechanisms include insufficient potency at therapeutic doses, activation of alternate oncogenic pathways, and overexpression of the multidrug-resistant gene. One of the possible causes of imatinib-acquired resistance is associated with increased expression of the SRC-related kinase Lyn and loss of BCR-ABL dependence arising from sequence mutations. In December 2005, Bristol-Myers Squibb announced that it has completed the rolling NDA submission to the US FDA for dasatinib in the treatment of CML in chronic, accelerated or blast phases, as well as Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukaemia (ALL) in patients with resistance or intolerance to prior treatment. At the Bristol-Myers Squibb R&D Day in May 2005, the company stated that it plans to evaluate dasatinib in solid tumours. In in vitro assays, dasatinib induced apoptosis and had potent activity in the imatinib-resistant tumour cells lines and CML patient specimens. It effectively inhibited the proliferation of cells expressing nearly all imatinib-resistant isoforms. In vivo, dasatinib has shown efficacy, with no apparent toxicity, when administered orally in SCID mice with xenografts of imatinib-sensitive and resistant human CML cells lines. Dasatinib is also undergoing preclinical evaluation for its potential as a therapy against multiple myeloma. Bristol-Myers Squibb has a composition-of-matter patent covering this research approach that will expire in 2020.