Efficacy of Dasatinib in Patients with Chronic Phase Philadelphia Chromosome-Positive CML Resistant or Intolerant to Imatinib: First Results of the CA180013 ‘START-C’ Phase II Study.

After 3 years of imatinib (IM) therapy, hematologic relapse occurred in 7% of newly diagnosed chronic myeloid leukemia (CML) pts, and 20% of chronic phase (CP)-CML pts after failure to interferon alpha (IFN), which was mostly associated with BCR-ABL mutations and/or clonal evolution. Dasatinib (BMS-354825) is a novel, oral, multi-targeted kinase inhibitor of BCR-ABL and SRC kinases. Dasatinib has been shown to have 325-fold greater potency compared with imatinib in cells transduced with BCR-ABL and is active against 18/19 BCR-ABL mutants tested that confer imatinib resistance. A Phase I dose-escalating study provided early evidence for the safety and efficacy of dasatinib in imatinib-resistant (IM-R) or -intolerant (IM-I) patients in CP-CML, which was followed by ‘START-C’ (CA180013), the first Phase II open-label study in dasatinib in CP IM-R or IM-I CML pts. Between February-May 2005, 186 pts (86 male, median age 60 yrs [range 25–82]) were recruited from 40 institutions. Data from 30 pts accrued prior to March 20, 2005, are available for the initial analysis. The definition of IM-R required a failure of IM doses >600 mg/d or the occurrence of BCR-ABL mutations associated with virtual insensitivity to IM. Dasatinib was administered at 70 mg twice daily (BID), based on phase I data and optimal inhibition of BCR-ABL activity from biomarker analysis. Dose escalation to 90 mg BID was permitted in pts lacking response, and dose reductions to 50 and 40 mg BID were allowed in the event of intolerance. Complete blood counts were obtained weekly for the first 12 weeks; bone marrow cytology and cytogenetics every 3 months. In the group of 30 evaluable pts, median age was 59 yrs (range 25–78), 50% were male. Median time from diagnosis of CML was 70.8 months (range 7.9–202.1). Prior therapy included IFN in 77% and stem cell transplantation in 10% of pts. 60% of pts were considered IM-R, with the maximum prior IM dose of >600 mg in 60% of pts. 60% of pts received IM for >3 yrs. Best response to prior IM therapy was a complete hematologic response in 83%, and complete (CCyR) and partial (PCyR) cytogenetic responses in 17% and 13% of pts, respectively. Median (range) baseline hematologic parameters were: white blood cells 16.1/nl (4.3–84.3); platelets 437/nl (173–960). IM-R BCR-ABL mutations were documented in 6/12 pts with currently available data. Within the first 3 months, 2 pts required dose escalations and 6 had a dose reduction, mostly due to thrombocytopenia. Hematologic responses were documented in 21/24 pts with available data. From 16 pts evaluable for 3-month cytogenetic analysis, 7 cytogenetic responses were observed, including CCyR (n=4) and PCyR (n=1). Analysis of molecular response is in progress. Grade 3/4 neutropenia or thrombocytopenia were reported in 6 pts each. Most common non-hematologic toxicities were diarrhea (6 pts, 1 grade 3), rash (5 pts, all grade 1), edema (3 pts, all grade 1) and pleural effusion (1 pt, grade 2). In conclusion, despite the short follow up, major hematologic and cytogenetic responses were seen in a group of pretreated CP-CML pts, which further supports the activity of dasatinib in this disease. An updated analysis based on 186 pts with 6-month follow up will be presented.