title: The combination regimen of idarubicin and taxotere is effective against human drug-resistant leukemic cell lines.
abstract: Up-regulation of Bcl-2 protein may contribute to drug resistance, by decreasing apoptosis after treatment, in pre-B and B-cell leukemias in pediatric patients. By contrast, augmented caspase-3 activity, an effector caspase, may be indicative of drug sensitivity due to increased cellular apoptosis. We have reported the development of an in vitro human T-lymphoblastic leukemia model resistant to ara-C and/or native E. coli L-asparaginase (ASNase), mimicking the drug resistance to the Capizzi II regimen. We have investigated the potential drug synergism between Idarubicin (IDA) and Taxotere (TXR) that may be active in the ara-C and ASNase double drug-resistant cell lines. The additive or synergistic activity between IDA and TXR is drug concentration-dependent in inducing caspase-3 activation and cellular apoptosis. We exposed two human drug-resistant cell lines that do not express the MDRI phenotype, one resistant to ASNase alone (CEM/ASNase-1-3) and the other resistant to both ara-C and ASNase (CEM/ara-C/I/ASNase-0.5-2), to physiologically achievable concentrations of IDA, TXR, or their combination. Both lines showed either synergistic drug activity to the combination regimen in comparison to either drug used alone, as determined by MTT assay, or additivity as demonstrated by flow cytometry after Annexin V and propidium iodide (PI) staining. After exposure of the ASNase-resistant line to various concentrations, the intracellular levels of Bcl-2 protein decreased to near zero relative to untreated control cells. The Bcl-2 protein reductions in these cells ranged from 30% to <1%, 49% to <1%, and 27% to 3% when treated with IDA or TXR as a single drug or IDA + TXR combination, respectively. Similarly, intracellular Bcl-2 levels in the double-resistant cell line decreased with reductions ranging from 24% to <1%, 87% to <1%, and 46% to <1% of the untreated control after treatment with IDA, TXR, or their combination, respectively. Conversely, the caspase-3 activity increased in a dose-dependent manner and inversely-correlated with loss of cell viability (r= 0.91) after exposure to IDA + TXR combination in the double drug-resistant line to both ara-C and ASNase. We conclude that the combination of the IDA + TXR regimen is highly synergistic or additive in drug resistant human leukemic cell clones. The molecular mechanism of action is due to the down-regulation of Bcl-2 protein and up-regulation of caspase-3 activity. This drug combination warrants further investigation for use in the treatment of patients with ara-C and/or ASNase refractory leukemias.
authors.affiliation: Department of Pediatrics, USC School of Medicine, Childrens Hospital Los Angeles, California 90027, USA.
authors.forename: F
authors.initials: F
authors.lastname: Majlessipour
authors.forename: I A
authors.initials: IA
authors.lastname: Avramis
authors.forename: R
authors.initials: R
authors.lastname: Kwock
authors.forename: K I
authors.initials: KI
authors.lastname: Weinberg
authors.forename: V I
authors.initials: VI
authors.lastname: Avrami
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001215:Asparaginase / Q000494:pharmacology; D053148:Caspase 3; D020169:Caspases / Q000096:biosynthesis / Q000235:genetics; D002470:Cell Survival / Q000187:drug effects; D002999:Clone Cells; D003561:Cytarabine / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D004789:Enzyme Activation; D006801:Humans; D015255:Idarubicin / Q000008:administration & dosage; D015458:Leukemia, T-Cell / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000235:genetics; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2; D003561:Cytarabine; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D001215:Asparaginase; D015255:Idarubicin