Synergistic induction of apoptosis in high-risk DLBCL by BCL2 inhibition with ABT-199 combined with pharmacologic loss of MCL1.

Abstract

Better treatments are needed for patients with diffuse large B-cell lymphoma (DLBCL) at high risk of failing standard therapy. Avoiding apoptosis is a hallmark of cancer, and in DLBCL the redundantly functioning anti-apoptotic proteins BCL2 and MCL1 are frequently expressed. Here, we explore drugs that cause loss of MCL1, particularly the potent new cyclin-dependent kinase inhibitor dinaciclib, which knocks down MCL1 by inhibiting CDK9. Dinaciclib induces apoptosis in DLBCL cells but is completely overcome by increased activity of BCL2. We find clinical samples have frequent co-expression of MCL1 and BCL2, suggesting therapeutic strategies targeting only one will lead to treatment failures due to activity of the other. The BH3 mimetic ABT-199 potently and specifically targets BCL2. Single-agent ABT-199 had modest anti-tumor activity against most DLBCL lines and resulted in compensatory up-regulation of MCL1 expression. ABT-199 synergized strongly, however, when combined with dinaciclib and with other drugs affecting MCL1, including standard DLBCL chemotherapy drugs. We show potent anti-tumor activities of these combinations in xenografts and in a genetically accurate murine model of MYC-BCL2 double-hit lymphoma. In sum, we reveal a rational treatment paradigm to strip DLBCL of its protection from apoptosis and improve outcomes for high-risk patients.