Inhibition of BCL6-dependent gene expression in Philadelphia chromosome positive acute lymphoblastic leukemia

The Philadelphia chromosome (Ph) encodes the oncogenic BCR-ABL1 tyrosine kinase, which defines a subset of acute lymphoblastic leukemia (ALL) with a particularly unfavorable prognosis. Tyrosine kinase inhibitors (TKI) are widely used to treat patients with leukemia driven by BCR-ABL1 and other oncogenic tyrosine kinases. In response to TKI-treatment, BCR-ABL1 ALL cells upregulate BCL6 protein levels by ~90-fold, i.e. to similar levels as in diffuse large B cell lymphoma (DLBCL) with BCL6 translocations. In this study, we analyzed the gene expression changes after treatment with Imatinib or Imatinib + RI-BPI. Three Ph+ ALL cell lines (BV-173, SUP-B15 and TOM-1) were treated in the presence or absence of 10 μM STI571 (Imatinib) or in the presence of both 10 μM STI571 and 20 μM RI-BPI for 24 hours.