Targeting autophagy augments the anticancer activity of the histone deacetylase inhibitor SAHA to overcome Bcr-Abl–mediated drug resistance

Abstract

Novel therapeutic strategies are needed to address the emerging problem of imatinib resistance. The histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA) is being evaluated for imatinib-resistant chronic myelogenous leukemia (CML) and has multiple cellular effects, including the induction of autophagy and apoptosis. Considering that autophagy may promote cancer cell survival, we hypothesized that disrupting autophagy would augment the anticancer activity of SAHA. Here we report that drugs that disrupt the autophagy pathway dramatically augment the antineoplastic effects of SAHA in CML cell lines and primary CML cells expressing wild-type and imatinib-resistant mutant forms of BcrAbl, including T315I. This regimen has selectivity for malignant cells and its efficacy was not diminished by impairing p53 function, another contributing factor in imatinib resistance. IntroductionImatinib (Gleevec; STI-571), a targeted competitive inhibitor of the Bcr-Abl tyrosine kinase, revolutionized the clinical treatment of chronic myelogenous leukemia (CML). 1 However, acquired imatinib resistance during the accelerated and blast crisis phases of the disease is an emerging problem and has been linked to gene amplification, to point mutations in Bcr-Abl that impede drug binding or structurally preclude adoption of the inactive conformation, and to loss of p53 function. [2][3][4] Two novel inhibitors of Bcr-Abl, dasatinib and nilotinib, have been evaluated to address this problem. 5,6 Both agents produce clinical responses in many imatinib-refractory patients but not in those carrying the most drug-resistant T315I mutation, which confers cross-resistance to nilotinib and dasatinib. 7,8 The lack of effective therapeutic regimens for T315I patients thus highlights the dire need for novel therapeutic strategies that are effective in treating these patients.Histone deacetylase (HDAC) inhibitors represent a novel class of anticancer agents currently under investigation in preclinical models and in phase 1/2 clinical trials. [9][10][11][12] Suberoylanilide hydroxamic acid (SAHA) is an orally bioavailable, well-tolerated pan-HDAC inhibitor with anticancer activity in hematologic and solid malignancies. 12,13 SAHA's anticancer effects have been linked to the generation of reactive oxygen species (ROS) and to the induction of apoptosis, growth arrest, polyploidy, and autophagy. 14-17 Whether SAHA's ability to augment autophagy affects its anticancer activity remains unclear. Here we tested the hypotheses that disruption of the autophagy pathway would significantly enhance the anticancer activity of SAHA and that this would prove effective in killing imatinib-resistant CML. Patients, materials, and methods Cells and cell cultureBa/F3 cells and Ba/F3 cells engineered to express comparable levels of wild-type (p210) and mutant forms of Bcr-Abl (E255K, M351T, and T315I) were maintained as previously described. 2 K562 and LAMA 84 CML cells were maintained in RPMI-1640 media with 10% heat-inactivated fetal bovine serum at 3...

Autophagy Inhibition Promotes Gambogic Acid-induced Suppression of Growth and Apoptosis in Glioblastoma Cells

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Autophagy-active beclin-1 correlates with favourable clinical outcome in non-Hodgkin lymphomas

“…Yet another investigation has shown that inhibition of autophagy by chloroquine enhances the pro-apoptotic effects of the histone deacetylase suberoylanide hydroxamic acid in primary chronic myelogenous leukaemia cells from patients clinically refractory to imatinib. 43 Interestingly, the pro-death synergism between these two drugs was associated with disruption of lysosomal membrane integrity and cathepsin D-mediated degradation of thioredoxin, a key regulator of cellular redox status. 43 These findings underscore the complexity of the role(s) of autophagy in anticancer drug response, which likely depend on the actual level of autophagy in the cell and the cytotoxic mechanism of the therapeutic drug.…”

“…43 Interestingly, the pro-death synergism between these two drugs was associated with disruption of lysosomal membrane integrity and cathepsin D-mediated degradation of thioredoxin, a key regulator of cellular redox status. 43 These findings underscore the complexity of the role(s) of autophagy in anticancer drug response, which likely depend on the actual level of autophagy in the cell and the cytotoxic mechanism of the therapeutic drug.…”

PAWR-mediated suppression of BCL2 promotes switching of 3-azido withaferin A (3-AWA)-induced autophagy to apoptosis in prostate cancer cells

“…Indeed, inhibition of autophagy can sensitize tumor cells to a wide selection of drugs. 32,33 In essence, autophagy-dependent mechanisms that contribute to the maintenance of cellular homeostasis could indirectly postpone the onset of apoptosis, for example, by recycling or eliminating damaged organelles and cytotoxic protein aggregates. 34,35 As the parent withaferin A strongly induces endogenous PAWR for prostate cancer cell sensitization to apoptosis, 10 we therefore sought to investigate the role of the more potent derivative 3-AWA in mediating PAWR activation in the autophagy-apoptosis switching cascade in CaP cells.…”