Effects of the Bcr/abl kinase inhibitors STI571 and adaphostin (NSC 680410) on chronic myelogenous leukemia cells in vitro

Abstract

IntroductionApproximately 4500 new cases of chronic myelogenous leukemia (CML) occur in the United States each year. In most patients, a characteristic t(9;22) translocation juxtaposes the 5Ј end of the bcr gene with the 3Ј end of the abl gene, resulting in a unique 210-kd fusion protein, p210 bcr/abl . 1,2 This constitutively active cytoplasmic kinase is capable of not only transforming murine fibroblasts and hematopoietic cell lines, but also causing a chronic myeloproliferative disorder resembling CML on transduction into mouse marrow. 3,4 This p210 bcr/abl -induced transformation appears to involve the activation of signaling through the Ras-Raf and phosphatidylinositol-3 kinase/Akt pathways as well as transcription mediated by signal transducer and activator of transcription 5 (Stat5) and nuclear factor B (NFB). 1,5 Collectively, these events result in the up-regulation of antiapoptotic proteins, including Bcl-x L , 6 the X-linked inhibitor of apoptosis protein (XIAP), and survivin, 7 contributing to the resistance of p210 bcr/abl -expressing cells to a variety of apoptotic stimuli. 6,8,9 Until recently, treatment options for CML, which included the use of hydroxyurea, ␣-interferon with or without cytarabine, or stem cell transplantation, were less than satisfactory. 10,11 The almost universal presence of the p210 bcr/abl kinase in CML, coupled with evidence implicating this kinase in the pathogenesis of the disorder, made this fusion protein an attractive target for CMLdirected therapy. Previous efforts identified multiple p210 bcr/abl kinase inhibitors. [12][13][14][15][16] The most widely studied p210 bcr/abl inhibitor is STI571 (formerly known as CGP 57148), 17 a reversible inhibitor that occupies the adenosine triphosphate-binding pocket of p210 bcr/abl and stabilizes the kinase in an inactive conformation. 18 Preclinical studies demonstrated that STI571 also inhibits the kinase activities of c-abl, platelet-derived growth factor receptor, and the c-kit receptor. 15,19,20 Phase 1 studies suggest that STI571 has impressive activity against chronic-phase CML 21 but more limited activity against p190 bcr/abl -expressing acute lymphocytic leukemia and the blast crisis phase of CML. 22 Recent studies have demonstrated that mutation and amplification of p210 bcr/abl are observed in samples from patients who have relapsed after STI571 therapy. 23 Additional preclinical and clinical studies of STI571, alone and in combination with conventional cytotoxic agents, are ongoing. 7,24,25 An alternative approach to inhibiting protein kinases involves the use of small molecules that alter the binding of peptide substrates rather than adenosine triphosphate. A chemically diverse group of agents, generically termed tyrphostins, has been synthesized and evaluated as potential tyrosine kinase inhibitors. 26 The tyrphostin AG957 has previously been reported to inhibit p210 bcr/abl activity in immune complex kinase assays 14 and to cause decreased For personal use only. on May 10, 2018. by guest www.bloodjournal.org From p...

Different target range and cytotoxic specificity of adaphostin and 17-allylamino-17-demethoxygeldanamycin in imatinib-resistant and sensitive cell lines

“…In contrast, the absence of BcrAbl does not confer insensitivity to adaphostin on 32D cells, as their mean IC 50 for this drug was not significantly different (P40.05; Mann-Whitney test) from that of 32D/BCR-ABL/GFP clone x6(1.03 and 1.92 mM, respectively). Our findings are in agreement with those of others, 10,18 who found a similar lack of selectivity for cell death induced by adaphostin in murine cell lines.…”

“…In this work we show that adaphostin is capable of inducing the rapid downregulation of multiple cell signalling proteins, in addition to its previously reported inhibitory effects upon expression of p210 Bcr-Abl10, 18,19,25 Raf-1 21 and cyclin D1. 21 The affected peptides were a tyrosine kinase (wild-type Abl), serine-threonine kinases (Akt and wild-type Bcr) and a transcription factor (STAT5a).…”

“…8 Indeed, there is evidence to suggest that the cytotoxic effects of adaphostin on CML cells are not mediated via inhibition of Bcr-Abl. 18,19 In contrast to imatinib, which rapidly abolishes tyrosine kinase activity and induces apoptosis gradually in the CML cell line K562, adaphostin induces rapid apoptosis and inhibits tyrosine phosphorylation more slowly. 18 Moreover, adaphostin has been reported to induce cell death in cell lines that do not express Bcr-Abl, including T-cell lymphoblastic leukaemia cells (Jurkat and CEM) 18,20,21 and murine myeloid cell lines such as FDC-P1 18 and Ba/F3.…”

“…18,19 In contrast to imatinib, which rapidly abolishes tyrosine kinase activity and induces apoptosis gradually in the CML cell line K562, adaphostin induces rapid apoptosis and inhibits tyrosine phosphorylation more slowly. 18 Moreover, adaphostin has been reported to induce cell death in cell lines that do not express Bcr-Abl, including T-cell lymphoblastic leukaemia cells (Jurkat and CEM) 18,20,21 and murine myeloid cell lines such as FDC-P1 18 and Ba/F3. 10 Paradoxically, adaphostin does not exhibit selectivity for murine cell lines transformed with Bcr-Abl but does cause selective growth inhibition of CML granulocyte colony-forming units relative to normal progenitors.…”

“…10 Paradoxically, adaphostin does not exhibit selectivity for murine cell lines transformed with Bcr-Abl but does cause selective growth inhibition of CML granulocyte colony-forming units relative to normal progenitors. 18 Although the mechanisms underlying the apparent selectivity of adaphostin for primary CML cells remain elusive, it is still considered to have potential as an antileukaemic agent.…”