Chronic myelogenous leukemia blast cell proliferation is inhibited by peptides that disrupt Grb2-SoS complexes

Chronic myelogenous leukemia (CML) is commonly characterized by the presenc e of the p210(Bcr-Abl) oncoprotein. Many downstream effectors of Bcr-Abl ha ve been described, including activation of the Grb2-SoS-Ras-MAP kinase (Erk ) pathway. The precise contributions of these signal-transduction proteins in CML blast cells in human patients are not yet well defined. To gain furt her insight into the importance of Grb2 for CML, peptides that disrupt Grb2 -SoS complexes were tested. These high-affinity Grb2-binding peptides (HAGB Ps) can autonomously shuttle into cells and function by binding to the N-te rminal SH3 domain of Grb2. The HAGBPs were analyzed for their effects on Bc r-Abl-expressing cell lines and freshly isolated CML blast cells from patie nts. They induced a dramatic decrease in the proliferation of CML cell line s. This was not observed with point-mutated control peptides with abolished Grb2SH3(N) binding. As expected, Grb2-SoS complexes were greatly diminishe d in the HAGBP-treated cells, and MAP kinase activity was significantly red uced as determined by an activation-specific phospho-MAPK antibody. Further more, cell fractions that are enriched for blast cells from CIVIL patients with active disease were also incubated with the Grb2 blocker peptides. The HAGBPs led to a significant proliferation reduction of these cells in the majority of the isolates, but not in all patients' cells. These results sho w that, in addition to the direct targeting of Bcr-Abl, selective inhibitio n of Grb2 protein complexes may be a therapeutic option for a significant n umber of CIVIL patients. (C) 2001 by The American Society of Hematology.