BCL6 enables Ph+ acute lymphoblastic leukaemia cells to survive BCR–ABL1 kinase inhibition

Targeted cancer therapies are often associated with drug resistance, a phenomenon that has been observed with tyrosine kinase inhibitors (TKIs), widely used to treat leukaemia driven by BCR–ABL1 mutations. Markus Mueschen and colleagues describe a novel BCL6-dependent mechanism of drug resistance in leukaemia through which TKI-induced upregulation of BCL6 allows leukemia cells to cope with acute oncogene withdrawal. Targeted inhibition of BCL6 reduces the number of drug-resistant and self-renewing leukaemia-initiating cells. In xenograft models of acute lymphoblastic leukaemia cells carrying BCR–ABL1 mutations, dual inhibition of BCR–ABL1 and BCL6 prevents resistance and improves the anticancer response. Tyrosine kinase inhibitors (TKIs) are widely used to treat patients with leukaemia driven by BCR–ABL1 (ref. 1) and other oncogenic tyrosine kinases2,3. Recent efforts have focused on developing more potent TKIs that also inhibit mutant tyrosine kinases4,5. However, even effective TKIs typically fail to eradicate leukaemia-initiating cells (LICs)6,7,8, which often cause recurrence of leukaemia after initially successful treatment. Here we report the discovery of a novel mechanism of drug resistance, which is based on protective feedback signalling of leukaemia cells in response to treatment with TKI. We identify BCL6 as a central component of this drug-resistance pathway and demonstrate that targeted inhibition of BCL6 leads to eradication of drug-resistant and leukaemia-initiating subclones.