In vivo suppression of Bcl-XL expression facilitates chemotherapy-induced leukaemia cell death in a SCID/NOD-Hu model.
Bcl-XL, a member of the Bcl-2-related anti-apoptosis protein family, antagonizes a diverse range of apoptosis-inducing stimuli by preventing mitochondrial permeability transition, release of apoptogenic factors including cytochrome C, and caspase activation. We have tested the hypothesis that the susceptibility of Bcl-XL-expressing leukaemic cells to apoptosis induced by VP16 (etoposide) can be enhanced by pharmacological downregulation of Bcl-XL in vivo. Two subcutaneous xenograft models of B-cell leukaemia-employing SEMK-2 and BV173 cell lines were established in severe combined immunodeficient/non-obese diabetic mice followed by 14 d of continuous subcutaneous administration of Bcl-XL-specific second generation oligonucleotides ISIS 16009 or ISIS 15999. Tumours were disaggregated, enabling investigation of Bcl-XL expression and apoptosis susceptibility at single-cell resolution using cytofluorimetry. Marked sequence-specific reduction of Bcl-XL was associated with sequence-specific enhancement of VP16-induced mitochondrial permeability transition, caspase-3 activation and loss of membrane asymmetry. A negative correlation between Bcl-XL expression and apoptosis susceptibility was observed, together with a positive correlation with respect to a reduced redox state. Bcl-XL downregulation reduces the threshold for VP16-induced apoptosis by potentiating mitochondrial dysfunction and its sequelae, and therefore presents a novel therapeutic strategy for reversing chemoresistance.
Fennell
D A
DA
Department of Experimental Haematology, St Bartholomew's and The Royal London School of Medicine & Dentistry, Turner Street, London E1 2AD, UK.
Corbo
M V
MV
Dean
N M
NM
Monia
B P
BP
Cotter
F E
FE
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D003131:Combined Modality Therapy; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D004789:Enzyme Activation; D005047:Etoposide / Q000494:pharmacology; D005434:Flow Cytometry / Q000379:methods; D015316:Genetic Therapy / Q000379:methods*; D006801:Humans; D051379:Mice; D016376:Oligonucleotides, Antisense / Q000008:administration & dosage*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics*; D016511:Severe Combined Immunodeficiency / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured; D051020:bcl-X Protein
C494811:BCL2L1 protein, human; C494812:Bcl2l1 protein, mouse; D016376:Oligonucleotides, Antisense; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; D005047:Etoposide; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases