Abstract 3784: BTM-3655 co-opts mitochondrial quality control pathways to induce apoptosis, and complete tumor regression in DLBCL cell lines, xenografts and PDX models
Authors: Schwarzer Adrian , Oliveira Matheus , Kleppa Marc-Jens , Anantha Andy , Cooper Alan , Hembrough Todd , Levine Jedd , Luther Michael , Stocum Michael , Liesa-Roig Marc , Kostura Matt 
Published: June 2022

Abstract
Cellular integrated stress response (ISR) pathways are induced by multiple triggers - viral RNA, nutrient deprivation, protein misfolding and disruption of mitochondrial homeostasis -that lead to phosphorylation of eIF2α, blockade of translation and activation of transcription factor ATF4 allowing the cell to recover or become apoptotic. These pathways are emerging as important targets in oncology, and here we demonstrate that mitochondrial homeostatic pathways can be co-opted to induce apoptosis in tumor cells and complete tumor regression in xenograft and PDX models. Diffuse large B-cell lymphoma (DLBCL) is a highly heterogeneous tumor, for which novel therapies are needed. We recently described BTM-3566, a small molecule which induces apoptosis in DLBCL cell lines, including double- and triple-hit subtypes. In xenograft models BTM-3566 induces complete and durable regression in all tumor-bearing animals, importantly, no regrowth is seen through 21 days post therapy. In an expanded panel of high-risk human DLBCL PDX models BTM-3566 demonstrated a 100% response rate, and complete tumor regression in 6 of 8 PDX models. Molecular analysis revealed that BTM-3566 activates the mitochondrial protease OMA1, leading to activation of HRI kinase, phosphorylation of the eIF2a -ATF4 pathway and apoptosis in DLBCL cell lines. CRISPR-Cas9 depletion of OMA1 eliminates BTM-3566’s apoptotic activity. Substrates of OMA1 include dynamin, OPA1 and DELE1, a protein of unknown function but which has recently been shown to act as a sensor for mitochondrial dysfunction and signals through HRI kinase and ATF4. Transfection of BJAB cells with a cleavage resistant OPA1 mutant has no effect on BTM-3566 induced apoptosis. In contrast, KO of DELE1 suppresses BTM-3566 mediated apoptosis. Interestingly, knockout of the ATF4 gene has a partial effect, delaying onset of apoptosis. BTM-3566 activates OMA1 in a manner unrelated to changes in mitochondrial ATP synthesis, reactive oxygen species generation or electron transport chain inhibition. Instead, BTM-3566 induces OMA1 activity through a novel mechanism regulated by the mitochondrial protein FAM210B. FAM210B expression is negatively correlated with response to BTM-3566, and overexpression of FAM210B blocks OMA1 activation and causes complete resistance to BTM-3566 induced apoptosis. Thus, FAM210B expression is a strong predictor of sensitivity to BTM-3566 and reveals a novel mechanism of regulation of OMA1 activation. Taken together, these data support a novel antitumor mechanism in DLBCL, where BTM3566 induces mitochondrial stress, activating the OMA1-DELE1-HRI-eIF2a-ATF4 pathway leading to apoptosis and tumor regression. An Investigational New Drug application for BTM3566 in B-cell malignancies will be submitted by early Q1 2022 with initiation of first in human clinical trials the first half of 2022.
Citation Format: Adrian Schwarzer, Matheus Oliveira, Marc-Jens Kleppa, Andy Anantha, Alan Cooper, Todd Hembrough, Jedd Levine, Michael Luther, Michael Stocum, Marc Liesa-Roig, Matt Kostura. BTM-3655 co-opts mitochondrial quality control pathways to induce apoptosis, and complete tumor regression in DLBCL cell lines, xenografts and PDX models [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 3784.