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Blood, 15 March 2005, Vol. 105, No. 6, pp. 2519-2526.
Prepublished online as a Blood First Edition Paper on November 30, 2004; DOI 10.1182/blood-2004-05-2023.
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Submitted May 28, 2004
Accepted November 6, 2004
Dexamethasone resistance in B-cell precursor childhood acute lymphoblastic leukemia occurs downstream of ligand-induced nuclear translocation of the glucocorticoid receptor
Petra S Bachmann, Rosemary Gorman, Karen L MacKenzie, Louise Lutze-Mann, and Richard B Lock*
Children's Cancer Institute Australia for Medical Research, Sydney, Australia; University of New South Wales, Sydney, Australia
Children's Cancer Institute Australia for Medical Research, Sydney, Australia
University of New South Wales, Sydney, Australia
* Corresponding author; email: richard.lock{at}unsw.edu.au.
Glucocorticoids are among the most effective agents used in the treatment of childhood acute lymphoblastic leukemia (ALL), and patient response to treatment is an important determinant of long-term outcome. In spite of its clinical significance, the molecular basis of glucocorticoid resistance in lymphoid malignancies is still poorly understood. We have recently developed a highly clinically relevant experimental model of childhood ALL, in which primary childhood ALL biopsies were established as xenografts in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. The in vivo and in vitro responses of a panel of these xenografts to the glucocorticoid, dexamethasone, reflected the outcome of the patients from whom they were derived. In this report we show that glucocorticoid resistance in B-cell precursor (BCP) ALL xenografts was not due to down-regulation of the glucocorticoid receptor (GR), nor to defective ligand binding of the GR. Moreover, dexamethasone-induced GR translocation from the cytoplasm to the nucleus was comparable in all xenografts. However, glucocorticoid resistance was associated with profoundly attenuated induction of the BH3-only pro-apoptotic protein, Bim, when xenograft cells were exposed to dexamethasone. These results show that dexamethasone resistance in BCP ALL xenografts occurs downstream of ligand-induced nuclear translocation of the GR, but upstream of Bim induction.

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