Pharmacological Modulation of Autophagy Can Sensitize Acute Lymphoblastic Leukemia Cell Lines to Dexamethasone.

backgroundThe potent synthetic glucocorticoid (GC), dexamethasone (DEX), is a highly effective component of conventional chemotherapy for acute lymphoblastic leukemia (ALL). However, cases of GC resistance require elucidation of the underlying mechanisms and the development of new strategies to overcome them. GC-induced autophagy can play a dual role in GC resistance: it often acts as a salvage mechanism in resistant cells, while in sensitive cells, it is a mechanism leading to cell death.

methodsIn the present study, cell death and autophagy, as well as their dependence on glucocorticoid receptors (GRs), were simultaneously monitored in DEX-treated ALL cell lines, both sensitive and resistant to GCs.

resultsIn GC-resistant cell lines, no changes in autophagy levels were observed after DEX treatment, whereas in GC-sensitive cell lines, autophagy elevation was associated with cell death. Blockade of GC receptors completely abolished DEX cytotoxicity in CCRF-CEM cells but not in RS4;11 cells, suggesting the participation of distinct, cell line-specific mechanisms. Furthermore, we investigated how pharmacological modulation of autophagy, both induction and inhibition, affects GC sensitivity. Autophagy induction with tamoxifen (TAM) successfully sensitized most cell lines to DEX. In CCRF-CEM cells, the sensitization effect was shown to correlate with increased apoptosis. In other cell lines, no increase in cell death was observed, suggesting decreased cell proliferation.

conclusionsThese results suggest that each ALL cell line may have an optimal basal level of autophagy, and targeted dysregulation of this level may be an effective strategy for enhancing GC sensitivity.