title: Effect of all-trans retinoic acid on chemotherapy induced apoptosis and down-regulation of Bcl-2 in human myeloid leukaemia CD34 positive cells.
abstract: Acute myeloid leukaemia (AML) is a heterogeneous malignant disease in which disease progression at the level of CD34 positive cells has a major impact in drug resistance and relapse. The multi-drug resistance (MDR1) gene product, P-glycoprotein is expressed mainly in CD34 positive AML cells and Bcl-2 is expressed simultaneously with several putative drug resistance parameters in these cells. Bcl-2 over-expression is associated with CD34 positivity, poor response to chemotherapy and reduced overall survival in AML patients. Recently, all-trans retinoic acid (RA) has been reported to enhance cytarabine-induced apoptosis and downregulate Bcl-2 in several human myeloid leukaemia CD34 negative cells. The two CD34 positive human myeloid leukaemia cell lines: KG1 and KGla have the unique feature of expressing significant functional P-glycoprotein. Thus, the efficacy of RA in enhancing cytrabine- and fludarabine-induced apoptosis and overcoming the resistance was examined in both KG1 (CD34+CD7-) and KGla (CD34+CD7+) human myeloid leukaemia cells in the present study. Both cytarabine and fludarabine induced a dose dependent increase in the number of apoptotic cells in both CD34 positive cell types. Interestingly, the cytarabine-induced apoptosis was significantly more than fludarabine-induced apoptosis in both cell types. All-trans RA alone failed to induce apoptosis or inhibit proliferation of either of the two human CD34 positive leukaemia cell types. However, RA enhanced cytarabine- or fludarabine-induced apoptosis and inhibition of proliferation in KG1 CD34+CD7- but not in KGla CD34+CD7+ myeloid leukaemia cells. As single agents, RA, cytarabine and fludarabine reduced Bcl-2 expression in a dose dependent manner in both cell types. Using a quantitative ELISA assay, the Bcl-2 protein concentration was reduced by 86 or 100%, after 72 h of treatment with 10 microM cytarabine or fludarabine, respectively, in both CD34 positive leukaemia cell types. The addition of RA to cytarabine enhanced its induced reduction of Bcl-2 in KG1 CD34+CD7- but not in KGla CD34+CD7+ human myeloid leukaemia cells. Meanwhile, RA failed to augment fludarabine-induced reduction of Bcl-2 in both cell types. In conclusion, the present results suggest a potential role for the combination of RA and cytarabine in the treatment of refractory and/or relapsed AML patients with CD34+CD7- but not CD34+CD7+ blast cells.
authors.affiliation: Division of Biomedical Sciences, School of Health Sciences, University of Wolverhampton, UK.
authors.forename: N
authors.initials: N
authors.lastname: Ahmed
authors.forename: L
authors.initials: L
authors.lastname: Laverick
authors.forename: J
authors.initials: J
authors.lastname: Sammons
authors.forename: K R
authors.initials: KR
authors.lastname: Baumforth
authors.forename: H T
authors.initials: HT
authors.lastname: Hassan
mesh_terms: D018952:Antigens, CD34 / Q000276:immunology*; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D003561:Cytarabine / Q000494:pharmacology; D006801:Humans; D007951:Leukemia, Myeloid / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D014212:Tretinoin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D014740:Vidarabine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D018952:Antigens, CD34; D000964:Antimetabolites, Antineoplastic; D019253:Proto-Oncogene Proteins c-bcl-2; D003561:Cytarabine; D014212:Tretinoin; D014740:Vidarabine; C024352:fludarabine