Inhibiting pathways involved in B‐cell development enhances sensitivity of B‐cell acute lymphoblastic leukemia to glucocorticoids

Abstract

Glucocorticoids, such as dexamethasone (dex), are used in combination chemotherapy for leukemias and lymphomas. Dex activates the glucocorticoid receptor (GR), which in turn regulates genes that induce cell death. Although dex is a remarkably effective therapeutic, some patients are insensitive to it, and others develop resistance. From among the thousands of GR‐regulated genes, it is not known which are required to induce cell death, nor how resistance arises in most cases. To understand which GR regulated genes drive lymphoid cell death, and which signaling pathways modulate dex‐sensitivity, we took an integrated functional genomic approach. We first identified sets of dex‐regulated genes by measuring differential gene expression in a panel of childhood B‐cell acute lymphoblastic leukemia (B‐ALL) primary samples and cell lines. We then performed a next‐generation genome‐wide shRNA screen to identify genes that affect growth and sensitivity to dex in B‐ALL. By comparing regulation and effect on sensitivity we essentially validated all genes en masse in B‐ALL, and were able to show that only 10% of dex‐regulated genes contributed to cell death. These genes predominantly function in transcription regulation and B‐cell development. This screen also identified cellular pathways that modulate dex‐induced death, including the B‐cell receptor pathway (BCR), a key checkpoint in B‐cell development. By integrating the gene expression and shRNA data sets we identified a double‐negative feedback loop between GR and PI3Kδ, a lynchpin in the BCR and IL7R pathways. Inhibition of PI3Kδ attenuated phosphorylation of GR, enhanced dex‐induced gene regulation, and restored sensitivity to even highly resistant B‐ALL specimens. Thus, this work elaborates with high resolution fundamental mechanistic details of GR function, and, in doing so, identifies numerous opportunities for enhanced lymphoid‐specific combination chemotherapy.Support or Funding InformationNIH, NSF, Carver Charitable Trust, V Foundation