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Blood. 2018 Oct 15. pii: blood-2018-08-872465. doi: 10.1182/blood-2018-08-872465. [Epub ahead of print]

Targeted inhibition of PI3Kα/δ is synergistic with BCL-2 blockade in genetically defined subtypes of DLBCL.

Author information

1
Department of Experimental Hematology, Institute of Hematology and Transfusion Medicine, Warsaw, Poland.
2
Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, United States.
3
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, United States.
4
Department of Immunology, Medical University of Warsaw, Warsaw, Poland.
5
Department of Hematology and Oncology, University Medical Center, Gottingen, Germany.
6
Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, United States; margaret_shipp@dfci.harvard.edu.

Abstract

Inhibition of the B-cell receptor (BCR) signaling pathway is a promising treatment strategy in multiple B-cell malignancies. However, the role of BCR blockade in diffuse large B-cell lymphoma (DLBCL) remains undefined. We recently characterized primary DLBCL subsets with distinct genetic bases for perturbed BCR/PI3K signaling and dysregulated BCL-2 expression. Herein, we explore the activity of PI3K inhibitors and BCL-2 blockade in a panel of functionally and genetically characterized DLBCL cell line models. A PI3K inhibitor with predominant α/δ activity, copanlisib, exhibited the highest cytotoxicity in all BCR-dependent DLBCLs. The pro-apoptotic effect of copanlisib was associated with DLBCL subtype-specific dysregulated expression of BCL-2 family members including HRK and its anti-apoptotic partner BCL-xL, BFL-1, MCL-1 and BIM. Using functional BH3 profiling, we found that the cytotoxic activity of copanlisib was primarily mediated through BCL-xL and MCL-1-dependent mechanisms that might complement BCL-2 blockade. For these reasons, we evaluated single agent activity of venetoclax in the DLBCLs and identified a subset with limited sensitivity to BCL-2 blockade despite having genetic bases of BCL-2 dysregulation. As these were largely BCR-dependent DLBCLs, we hypothesized that combined inhibition of PI3Kα/δ and BCL-2 would perturb BCR-dependent and BCL2-mediated survival pathways. Indeed, we observed synergistic activity of copanlisib/venetoclax in BCR-dependent DLBCLs with genetic bases for BCL-2 dysregulation in vitro and confirmed these findings in a xenograft model. These results provide pre-clinical evidence for the rational combination of PI3Kα/δ and BCL-2 blockade in genetically defined DLBCLs.

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