Initial testing of dasatinib by the pediatric preclinical testing program

Background. Dasatinib, a dual inhibitor of the src and abl tyrosine kinases, was recently approved by the Federal Drug Administration for the treatment of imatinib mesylate-resistant chronic myeloid leukemia. Procedures. Dasatinib was tested against the Pediatric Preclinical Testing Program (PPTP) in vitro panel at concentrations ranging from 0.1 nM to 1.0 μM and was tested in vivo at a dose of 50 mg/kg administered orally twice daily 5 days per week for 4 weeks for the solid tumor xenografts and once daily for the acute lymphoblastic leukemia (ALL) xenografts. Results. Dasatinib was selectively active against the cell lines of the PPTP in vitro panel, reaching an IC ₅₀ in 6 of the 22 lines. The most sensitive were the AML line Kasumi-1, which has a gain-of-function c-Kit mutation (Asn822Lys), and the rhabdoid tumor line CHLA-266 (IC₅₀ approximately 10 nM for each). In the in vivo panel, dasatinib induced significant differences in EFS distribution in 8 of 32 (25%) solid tumor models and 3 of 7 ALL models. Using the time to event activity measure, dasatinib had intermediate activity against 1 of 27 (4%) evaluable solid tumor xenografts and 3 of 7 ALL xenografts. One xenograft in the ALL panel, a Philadelphia chromosome positive (Ph⁺) ALL xenograft, demonstrated a complete response. Conclusions. Dasatinib was active at low nanomolar concentrations against a small subset of the PPTP's in vitro panel. Dasatinib had limited in vivo activity against the PPTP solid tumor xenografts, but was highly active against a Ph⁺ ALL xenograft and also had anti-leukemia activity against two other xenografts.