STI 571 (formerly known as CGP 57148B), a 2-phenylaminopyrimidine derivative, is a known inhibitor of the the c-abl, bcr-abl, and platelet-derived growth factor receptor tyrosine kinases. This compound is currently being evaluated in clinical trials for the treatment of CML. We sought to extend the activity profile of STI 571 by testing its ability to inhibit the tyrosine kinase activity of mutant c-kit molecules associated with mastocytosis. We treated a human myeloid leukemia cell line (MO7e) that expresses wild-type c-kit protein with increasing doses of STI 571 prior to stimulation by Steel factor (SLF), the ligand for c-kit. SLF-induced c-kit autophosphorylation was effectively inhibited by STI 571 at concentrations of 0.1-10 u.M. The IC50 for inhibition of proliferation was 0.1-0.2 u.M. Additionally, we found that STI 571 blocked the anti-apoptotic activity of SLF. In contrast, the compound had no effect on cellular proliferation in response to GM-CSF. We also tested the activity of the compound using a human mast cell leukemia cell line (V560G HMC-1) that has an activating mutation of the juxtamembrane domain of c-kit (V560G). In V560G HMC-1 cells, STI 571 inhibited c-kit autophosphorylation, MAP kinase activation and Akt activation without altering total protein levels of c-kit, MAP kinase or Akt. The IC!0 for these effects was 0.01-0.1 U.M. The compound potently induced apoptosis (96.5% apoptosis at l U.M STI 571 vs. 8.5% in control cells). These results suggest that malignant mast cells are likely to be dependent upon the kinase activity of mutant c-kit molecules for proliferation and survival. However, most cases of human mastocytosis are associated with the activating mutations of the TK2 domain (D816V) rather than the juxtamembrane domain. In contrast to the results with wild type or V560G c-kit isoforms, STI 571 was unable to inhibit the kinase activity of the D816V mutant ckit (ICSO>5 U.M). Based on these studies, STI 571 would be predicted to be ineffective in the treatment of most patients with mastocytosis.
|Original language||English (US)|
|Issue number||11 PART II|
|State||Published - Dec 1 2000|
ASJC Scopus subject areas
- Cell Biology