Abstract 2803: Pharmacokinetics and pharmacodynamics of the novel OMA1 activator BTM 3566 in a mouse model of diffuse large B-cell lymphoma
Authors: Bagherzadeh Azadeh , Baker Jennifer , Bennett Charlotte , Lee Mi-Young , Pacheco Natalia , Patel Bhavisha , Stewart Kevin , Travers Jon , Stocum Michael , Hembrough Todd , Kostura Matthew 
Published: April 2023

Abstract
We have previously described a novel compound, BTM-3566, that exhibits robust single agent activity in xenograft and PDX models of DLBCL. BTM-3566 is effective on all types of DLBCL, independent of cell of origin (COO) or genotype. Drug activity depends on activation of the mitochondrial protease OMA1 followed by activation of HRI and induction of the ATF4 ISR. To ascertain whether ATF4 ISR induction occurs in vivo, we determined the pharmacokinetics (PK) and pharmacodynamic (PD) responses of BTM-3566 in mouse xenograft models of DLBCL using the double hit lymphoma SU-DHL-10. To establish PK parameters, tumor bearing mice were dosed orally for 1 or 5 consecutive days with 20 mg/kg BTM-3566 and blood sampled over 28 hours. Plasma levels of BTM-3566 were determined and analyzed using a non-compartment model. Half-life in blood plasma was 5.4 and 4.5 hours on days 1 and 5 respectively. Total exposure (AUCinf) was 524164 and 429485 hr*nM on day 1 and day 5 respectively. Drug AUCinf in tumor after a single oral dose of BTM-3566 was 151260 hr*nM. Free drug was estimated to be above the free IC90 for approximately 16 hours post-dose in both plasma and tumor. PD responses to BTM-3566 treatment were determined by measuring biomarkers of the therapeutic cascade: OPA1 cleavage is used as a surrogate for target engagement and activation of OMA1; increased phosphorylation of eIF2α represents pathway activation; induction of ATF4 regulated transcripts and the decrease in the anti-apoptotic protein MCL1 represent pathway effect. A single 20/mg/kg dose of BTM-3566 on day 1 resulted in cleavage of OPA1 by 0.5 hour, with maximal cleavage seen by 12 hours. Phosho-eIF2α was observed by 0.5 hours, peaking at 6 hours. Induction of the ATF4 transcripts ATF4, DDIT3, TRIB3, and CDKN1A was observed within 2 hours with a maximum at 6-12 hours followed by a reduction in transcript levels. MCL1 protein levels were reduced consistent with suppression of translation and protein turnover. By day 5, repeat dosing shows evidence of cumulative pathway effects: OPA1 is extensively cleaved; despite generally depressed levels, phosphorylation of eIF2α remains dynamic and MCL1 levels are markedly suppressed. Induction of ATF4 transcripts, however, follow largely the same kinetics as seen on day 1. The data suggests that in vivo anti-tumor activity of BTM-3566 is associated with activation of the mitochondrial protease OMA1 and induction of the ATF4 ISR. Robust tumor regression is correlated with both blood plasma levels of BTM-3566 and induction of the ATF4 ISR pathway. The data support the use of both ATF4 transcripts and OPA1 cleavage as robust PD markers of target engagement and pathway effect in human clinical trials. An Investigational New Drug application for BTM3566 in B-cell malignancies has been approved with initiation of first in human clinical trials planned for spring 2023.
Citation Format: Azadeh Bagherzadeh, Jennifer Baker, Charlotte Bennett, Mi-Young Lee, Natalia Pacheco, Bhavisha Patel, Kevin Stewart, Jon Travers, Michael Stocum, Todd Hembrough, Matthew Kostura. Pharmacokinetics and pharmacodynamics of the novel OMA1 activator BTM 3566 in a mouse model of diffuse large B-cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2803.