Abstract A07: BTM 3566, a novel activator of the mitochondrial stress response promotes robust therapeutic responses in vitro and in vivo in diffuse large B-cell lymphoma

Abstract Relapsed/refractory diffuse large B-cell lymphomas (r/r-DLBCL) are a therapeutic challenge as they are highly heterogeneous both clinically and molecularly, which imposes a pressing need to develop novel therapies to improve outcomes in patients independently of the molecular subtype. We describe here BTM-3566, a first-in-class, orally active compound with activity against DLBCL. BTM-3566 induces apoptosis and complete cell killing in DLBCL lines a with an IC50 of ~200 – 500 nM. Responsive DLBCL cell lines include ABC, GCB, and double-hit and triple-hit lymphoma type. Pharmacokinetic studies in mice showed suitability for once daily dosing, with > 50% oral bioavailability and ~6 hours of serum half-life. In xenograft models using the double-hit DLBCL line SU-DHL-10, BTM-3566 treatment resulted in complete response in all tumor-bearing animals and durable remission in 50% of animals with no tumor growth occurring for 2 weeks after dose cessation. Expansion studies into human DLBCL PDX models harboring a range of high-risk genomic alterations demonstrated response in 100% of the lines with complete response in 6 of 9 PDX models tested. Dose scheduling studies indicate that 7 days of continuous dosing is sufficient to induce tumor regression and maintenance of a complete response. The therapeutic activity of BTM-3566 is related to a novel effect on mitochondrial proteostasis and a robust induction of the ATF4 ISR. Of the four eIF2α -kinases in the human genome we determined that HRI was uniquely required for BTM-3566 activity in DLBCL. HRI is activated by mitochondrial-related stress resulting in activation of the mitochondrial protease OMA1. Molecular analysis revealed that BTM-3566 activates OMA1, leading to induction of the ATF4 ISR pathway and apoptosis in DLBCL cell lines. Deletion of OMA1 reduces the ability of BTM-3566’s to induce apoptosis in DBLCL. Substrates of OMA1 include the dynamin OPA1 and DELE1, a protein recently shown to signal mitochondrial dysfunction through activation of HRI kinase and ATF4. Transfection of BJAB cells with a cleavage resistant OPA1 mutant has no effect on BTM-3566 induced apoptosis. In contrast, DELE1 KO suppresses BTM-3566 mediated apoptosis. BTM-3566 activates OMA1 without acting as a classical mitochondrial toxin. 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. 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 in Q2 2022 with initiation of first in human clinical trials planned for fall 2022. Citation Format: Adrian Schwarzer, Matheus Oliveira, Marc-Jens Kleppa, Andy Anantha, Alan Cooper, Mark Hannink, Todd Hembrough, Jedd Levine, Michael Luther, Michael Stocum, Linsey Stiles, Marc Liesa-Roig, Matthew Kostura. BTM 3566, a novel activator of the mitochondrial stress response promotes robust therapeutic responses in vitro and in vivo in diffuse large B-cell lymphoma [abstract]. In: Proceedings of the Third AACR International Meeting: Advances in Malignant Lymphoma: Maximizing the Basic-Translational Interface for Clinical Application; 2022 Jun 23-26; Boston, MA. Philadelphia (PA): AACR; Blood Cancer Discov 2022;3(5_Suppl):Abstract nr A07.