Tyrosine kinase inhibitors (TKIs) have revolutionised the treatment of chronic myeloid leukemia (CML), however, fail to cure the disease due to the persistence of a refractory fraction of stem/progenitor cells. Autophagy is a recycling mechanism utilised by the cell as a survival mechanism under stressful conditions, and its induction has been suggested to have a cytoprotective role in cancer cells. In this study we demonstrate that autophagy is triggered in CML upon TKI-mediated inhibition of BCR-ABL, and protects from cell death. In order to evaluate if specific autophagy inhibition enhances TKI effects, we stably transduced primary CML stem/progenitor cells with a vector carrying a short-hairpin against the key autophagy gene ATG7. Knock-down of basal ATG7/autophagy levels in CML stem/progenitor cells inhibited by approximately 50% the survival of the cells in a clonogenic assay, and reduced by 75% their erythroid differentiation potential. Furthermore, ATG7 knock-down enhanced the effects of TKIs imatinib (IM; 1st), dasatinib (DAS; 2nd), nilotinib (NIL; 2nd) and ponatinib (PON; 3rd generation), reducing by 92-98% the survival of these cells in a clonogenic assay. In contrast, ATG7 knock-down in normal stem cells, with or without TKI treatment, did not have a significant effect on survival and proliferation. ATG7 was also knocked-down in final disease stage, blast crisis (BC), patient-derived K562 and KCL22 cell lines. Both cell lines appeared to depend significantly on autophagy for survival as indicated by high apoptosis levels (70-100%) after ATG7 knock-down. Interestingly, ATG7 knock-down cells appeared to be more differentiated compared to the control (scrambled shRNA). Our findings suggest a role for basal autophagy in the survival, differentiation decisions and clonogenicity of CML cells, and support the combined use of autophagy inhibition with TKIs for the eradication of CML stem/progenitor cells. This could be partially attributed to a bypass of the differentiation block upon autophagy inhibition, which facilitates TKI-targeting. We underline the necessity for the development of specific autophagy inhibitors that in combination with TKIs could potentially eradicate the fraction of persistent CML stem/progenitor cells and offer a curative option for CML patients.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:572184 |
| Date | January 2013 |
| Creators | Karvela, Maria |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/4271/ |
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