title: Elevated Bcr-Abl expression levels are sufficient for a haematopoietic cell line to acquire a drug-resistant phenotype.
abstract: A characteristic feature of chronic myeloid leukaemia (CML) is the inevitable advancement from a treatable chronic phase to a fatal, drug-resistant stage referred to as blast crisis. The molecular mechanisms responsible for this disease transition remain unknown. As increased expression of Bcr-Abl has been associated with blast crisis CML, we have established transfectants in 32D cells that express low and high levels of Bcr-Abl, and assessed their drug sensitivity. Cells with high Bcr-Abl expression levels are resistant to conventional cytotoxic drugs, and also require higher levels of STI571 (an inhibitor of Bcr-Abl), to induce cell death. Co-treatment with cytotoxic drugs and STI571 increased the sensitivity of the drug-resistant cells. Despite the drug-resistant phenotype, high Bcr-Abl levels concomitantly increased the expression of p53, p21, Bax and down-regulated Bcl-2. These cells maintain a survival advantage irrespective of a reduced proportion of cycling cells and the pro-apoptotic shift in gene expression. In addition, the level of Bcr-Abl expression (high or low) does not alter the growth factor independence and elevated Bcl-xL expression observed. Our study indicates that drug resistance can be primarily attained by increased Bcr-Abl expression, and highlights the potential of therapy which combines STI571 with conventional cytotoxic drugs.
authors.affiliation: Department of Biochemistry, University College Cork, Ireland.
authors.forename: K
authors.initials: K
authors.lastname: Keeshan
authors.forename: K I
authors.initials: KI
authors.lastname: Mills
authors.forename: T G
authors.initials: TG
authors.lastname: Cotter
authors.forename: S L
authors.initials: SL
authors.lastname: McKenna
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001549:Benzamides; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016044:Fusion Proteins, bcr-abl / Q000096:biosynthesis* / Q000378:metabolism; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D000068877:Imatinib Mesylate; D007377:Interleukin-3 / Q000494:pharmacology; D010641:Phenotype; D010879:Piperazines / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D014162:Transfection
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D004791:Enzyme Inhibitors; D007377:Interleukin-3; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D011505:Protein-Tyrosine Kinases; D016044:Fusion Proteins, bcr-abl