Disease relapse in CML patients treated with imatinib is often associated with mutations in the BCR-ABL gene that interfere with the ability of imatinib to block BCR-ABL kinase activity. BMS-354825 is a novel, orally available, dual SRC/ABL kinase inhibitor with more than 100-fold greater potency than imatinib that has in vitro and in vivo preclinical activity against 14 of 15 imatinib resistant BCR-ABL mutants (Shah et al, Science, 305:399, 2004). Here we report the phase I clinical results of BMS-354825 in Philadelphia chromosome positive (Ph+) CML patients in chronic phase with hematologic progression or intolerance while being treated with imatinib. To date (Aug 6, 2004), 29 patients have been treated on 9 cohorts with doses ranging from 15 to 180 mg of BMS-354825 per day given in single or divided doses for 5–7 days per week, for up to 9 months. Similar to imatinib, BMS-354825 has been well tolerated in all patients, with a single episode of grade 4 thrombocytopenia as the only potential drug related adverse event. BMS-354825 is rapidly absorbed with peak concentrations achieved within 2 hours and a terminal phase half-life of about 5 hours. Serum levels well above the concentration required to block CML cell proliferation in vitro have been readily achieved without side effects. Pharmacodynamic studies demonstrate greater than 50 percent inhibition of phosphorylation of the BCR-ABL substrate CRKL and the SRC kinase Lyn, consistent with the serum concentrations observed in pharmacokinetic studies. Patients not receiving optimal clinical benefit were escalated to the next higher dose for which safety parameters were available, thereby allowing a preliminary assessment of clinical activity. To date, 26 patients (22 with imatinib resistance, 4 with imatinib intolerance; average CML duration 6.1 years) have been followed for greater than 4 weeks and are eligible for assessment of hematologic benefit. 22 patients had detectable BCR-ABL kinase domain mutations prior to starting BMS-354825. All 26 patients have been treated with doses of 35 mg per day or greater and have had clinical benefit, including 19 with complete hematologic responses (73%). Of the 7 partial responders, two subsequently had disease progression, one of whom had expansion of a CML subclone containing the imatinib-resistant T315I mutation in BCR-ABL, which also confers resistance to BMS-354825 in preclinical studies. The other 5 partial responders are now being treated with higher doses to attempt conversion to complete hematologic response. 11 of 21 patients (52%) treated for greater than 3 months have cytogenetic benefit, including 6 major (1–35% Ph+), 1 minor (36–65% Ph+) and 4 minimal (66–95% Ph+) cytogenetic responses. One patient has achieved complete cytogenetic response. Dose escalation continues, and phase II studies in chronic, accelerated and blast crisis CML are currently being initiated. These data provide compelling evidence supporting the safety and efficacy of BMS-354825 in imatinib-resistant chronic phase CML.