Mechanisms of apoptosis by the tyrphostin AG957 in hematopoietic cells

Abstract

AG957 (NSC 654705) is a tyrphostin tyrosine kinase inhibitor that has been demonstrated previously to induce growth arrest in chronic myelogenous leukemia cells by inhibiting p210 bcr–abl kinase activity and by stabilizing the association of p210 bcr–abl kinase with its signaling adaptor molecules, Shc and Grb2. In previous studies, it has been demonstrated that AG957-associated down-regulation of bcr–abl activates the cytochrome c/Apaf-1/caspase-9 pathway and induces apoptosis in chronic myelogenous leukemia blasts and progenitor cells. While AG957 has been purported to have specificity for the p210 bcr–abl kinase, antiproliferative effects of AG957 in normal T-lymphocytes and bcr–abl negative leukemia cells suggest that other targets, such as c-CBL, may be substrates. In this study, we explored the mechanisms of AG957-mediated growth inhibition and apoptosis in the p210 bcr–abl negative leukemia cell lines Nalm-6 and Jurkat, and demonstrate that AG957-mediated apoptosis is associated with altered phosphorylation of Akt and BAD, which destabilizes the Bcl-xL/BAD complex and releases the block to apoptosis. We, therefore, propose that AG957 induces apoptosis in bcr–abl negative hematopoietic cells by affecting the phosphorylation state of phosphatidylinositol-3 kinase/Akt.