BMS-354825 Is a SRC/ABL Inhibitor with High Nanomolar Activity Against the Kit D816v Mutation, Which Drives Systemic Mastocytosis and Is Imatinib-Resistant.

The vast majority of systemic mastocytosis cases are associated with a somatic KIT oncoprotein point mutation which substitutes a valine for aspartic acid (D816V), resulting in KIT receptor auto-phosphorylation in a ligand-independent manner. Previous reports have demonstrated that this mutation is inherently imatinib-resistant. Although interferon-alpha has some activity against aggressive systemic mastocytosis, major responses are uncommon, and the drug is associated with significant toxicity. To date, there remains no effective therapy for systemic mastocytosis. We recently described BMS-354825, a novel orally bioavailable SRC/ABL inhibitor that has activity against multiple imatinib-resistant BCR-ABL isoforms in vitro (Shah et al, Science 305:399, 2004). BMS-354825 is presently undergoing evaluation in a phase I clinical trial of imatinib-resistant CML patients, and is showing signs of clinical efficacy. Pharmacokinetic analysis suggests that high nanomolar concentrations of the compound can be safely achieved in humans (see Sawyers et al, Talpaz et al, abstracts submitted for this meeting). To determine if this compound warrants study in other human hematologic conditions, we tested BMS-354825 for activity against human mastocytosis cell lines HMC-1⁵⁶⁰ and HMC-1^560,816, carrying an activating c-kit mutation in juxtamembrane domain (codon 560) with or without a second mutation in tyrosine kinase domain (codon 816), respectively. While 1 um imatinib failed to inhibit the growth of HMC-1^560,816 cells carrying the tyrosine kinase domain c-kit mutation, BMS-354825 led to an almost complete growth inhibition at the same concentration, with an IC50 of 0.1–1 uM. In addition, growth of HMC-1560 cells carrying the juxtamembrane c-kit mutation alone was more effectively inhibited by BMS-354825 as compared to imatinib (IC50 of <0.01 vs 0.01–0.1 micromolars respectively). Significantly, detection of phospho-KIT by Western blot analysis was significantly reduced in the presence of BMS-354825 at nanomolar concentrations. An ex vivo assessment of D816V-harboring mast cell sensitivity using a flow cytometric method in systemic mastocytosis bone marrow samples is ongoing. Our findings suggest that studies to evaluate BMS-354825 for the treatment of systemic mastocytosis are warranted. Additionally, the compound may harbor activity in other disease settings that contain activating KIT mutations.