Abstract 5377: Decitabine sensitizes diffuse large B cell lymphoma cells to venetoclax
Authors: Davids Matthew S. , Zhu Fen , Chong Stephen J. , Crombie Jennifer , Hackett Liam , Collins May C. 
Published: June 2022

Abstract
Introduction: Despite recent advances in the therapy of diffuse large B cell lymphoma (DLBCL), many patients are still not cured, and therefore new therapeutic combinations are needed. The anti-apoptotic B cell lymphoma 2 (BCL-2) gene is commonly dysregulated in DLBCL due to various mechanisms such as chromosomal translocation t(14;18)(q32.3;q21.3), copy number alterations and gene amplifications; however, targeting BCL-2 with a selective inhibitor, venetoclax, led to response in only a minority of patients. Thus, we sought to identify a novel combination partner for venetoclax to improve response to therapy. Previously with dynamic BH3 profiling, we found that DNA hypomethylating agents (HMA) could increase BCL2 dependence in DLBCL cells. Here, we investigate the activity of the HMA decitabine with venetoclax in DLBCL.
Methods: We utilized BH3 profiling, a functional assay to assess the mitochondrial priming of cells for apoptosis and the dependence of cells on various anti-apoptotic BCL-2 family proteins. Other standard techniques included Western blot, cell cycle (BrdU/7-AAD), CellTiter-Glo, and Seahorse XF cell mito stress test. The DLBCL cell lines (TMD8, HBL1, OCI-Ly3, OCI-Ly1, Karpas 422, SUDHL4, Toledo, OCI-Ly7) and double hit lymphoma (DHL) patient-derived xenograft cell lines were used to investigate the in vitro anti-cancer activity of decitabine and venetoclax.
Results: Through BH3 profiling, we found heterogenous dependence of DLBCL, consistent with the variable expression of multiple anti-apoptotic proteins in DLBCL assessed by Western blot. DLBCL cells were less sensitive to single BH3 mimetic treatment (venetoclax, S63 (MCL-1i) and A133 (BCL-xLi)). Using dynamic BH3 profiling (which assesses the change in priming induced by ex vivo drug treatment), we found that decitabine primes DLBCL cells for apoptosis and increases BCL-2 dependence. Consequently, decitabine increases the sensitivity of DLBCL cells to venetoclax, as the combination of decitabine and venetoclax synergistically induces apoptosis and suppresses cell proliferation. Decitabine has previously been shown to increase TGF-β signaling in DLBCL by restoring the expression of a downstream target, SMAD1. Interestingly, we found that inhibition of TGF-β signaling only partially antagonizes the anti-cancer activity of decitabine, implicating other anti-cancer mechanisms of decitabine. Indeed, we found that decitabine also induces DNA damage and leads to cell cycle arrest in DLBCL cells. Furthermore, decitabine promotes activation of the key apoptotic effector proteins, BAK and BAX. Additionally, we found that this combination also suppresses oxidative phosphorylation, thus restricting the energy supply for DLBCL cells.
Conclusions: The HMA decitabine sensitizes DLBCL cells to venetoclax in vitro through increasing apoptotic priming and BCL-2 dependence. This combination is worthy of further study in in vivo model systems.
Citation Format: Matthew S. Davids, Fen Zhu, Stephen J. Chong, Jennifer Crombie, Liam Hackett, May C. Collins. Decitabine sensitizes diffuse large B cell lymphoma cells to venetoclax [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5377.