ABSTRACT
Drug-resistant forms of acute lymphoblastic leukaemia (ALL) are a leading cause of death from disease in children. Up to 25% of patients with T-cell ALL (T-ALL) develop resistance to chemotherapeutic agents, particularly to glucocorticoids (GCs), a class of drug to which resistance is one of the strongest indicators of poor clinical outcome. Despite their clinical importance, the molecular mechanisms that underpin GC resistance and leukaemia relapse are not well understood. Recently, we demonstrated that GC-resistance is associated with a proliferative metabolism involving the up-regulation of glycolysis, oxidative phosphorylation and cholesterol biosynthesis. Here we confirm that resistance is directly associated with a glycolytic phenotype and show that GC-resistant T-ALL cells are able to shift between glucose bioenergetic pathways. We evaluated the potential for targeting these pathways in vitro using a glycolysis inhibitor, 2-deoxyglucose (2DG), and the oxidative phosphorylation inhibitor oligomycin in combination with methylprednisolone (MPRED). We found that oligomycin synergized with MPRED to sensitize cells otherwise resistant to GCs. Similarly we observed synergy between MPRED and simvastatin, an inhibitor of cholesterol metabolism. Collectively, our findings suggest that dual targeting of bioenergetic pathways in combination with GCs may offer a promising therapeutic strategy to overcome drug resistance in ALL.
Subject(s)
Antineoplastic Agents/pharmacology , Drug Resistance, Neoplasm , Precursor T-Cell Lymphoblastic Leukemia-Lymphoma/metabolism , Antineoplastic Agents/therapeutic use , Apoptosis/drug effects , Cell Line, Tumor , Cell Proliferation , Drug Synergism , Galactose/metabolism , Glucocorticoids/pharmacology , Glucocorticoids/therapeutic use , Glycolysis/drug effects , Humans , Hydroxymethylglutaryl-CoA Reductase Inhibitors/pharmacology , Methylprednisolone/pharmacology , Methylprednisolone/therapeutic use , Mitochondria/drug effects , Mitochondria/metabolism , Oligomycins/pharmacology , Precursor T-Cell Lymphoblastic Leukemia-Lymphoma/drug therapy , Signal Transduction/drug effectsABSTRACT
BACKGROUND: Rearrangement of the mixed-lineage leukemia gene (MLL) is found in 80% of infant acute lymphoblastic leukemia (ALL) and is associated with poor prognosis and resistance to glucocorticoids (GCs). We have recently observed that GC resistance in T-ALL cell lines is associated with a proliferative metabolism and reduced expression of MLL. In this study we have further explored the relationship between MLL status and GC sensitivity. RESULTS: Negative correlation of MLL expression with GC resistance in 15 T-ALL cell lines was confirmed by quantitative RT-PCR. The absence of MLL-rearrangements suggested that this relationship represented expression of wild-type MLL. Analysis of MLL expression patterns revealed a negative relationship with cellular metabolism, proliferation and anti-apoptotic transcriptional networks. In silico analysis of published data demonstrated that reduced levels of MLL mRNA are associated with relapse and prednisolone resistance in T-ALL patients and adverse clinical outcome in children with MLL-rearranged ALL. RNAi knockdown of MLL expression in T-ALL cell lines significantly increased resistance to dexamethasone and gamma irradiation indicating an important role for wild-type MLL in the control of cellular apoptosis. CONCLUSIONS: The data suggests that reduced expression of wild-type MLL can contribute to GC resistance in ALL patients both with and without MLL-translocations.
