Unlocking the Potential of BTM-3566: A Breakthrough in Mitochondrial Stress Response for Diffuse Large B-Cell Lymphoma Therapy

Difficulties in treating relapsed or refractory diffuse large B-cell lymphoma (r/r-DLBCL) are highlighted, particularly for patients unable to undergo high-dose chemotherapy, stem cell transplants, or CAR-T-cell therapy. The heterogeneity of r/r-DLBCL demands innovative treatments to improve patient outcomes regardless of molecular subtypes. BTM-3566, a novel compound, shows significant efficacy against B-cell malignancies, notably in DLBCL. It triggers the mitochondrial integrated stress response (ISR) via the mitochondrial protein FAM210B, leading to apoptosis in DLBCL cell lines and complete tumor regression in vivo in patient-derived xenograft (PDX) mouse models with poor-prognosis genetic alterations.

BTM-3566, an oral small molecule with a pyrazolothiazol backbone, is developed for DLBCL treatment. It induces apoptosis and cell death in DLBCL lines with an IC50 of ~200 - 500 nM, affecting ABC, GCB, and high-risk lymphoma lines. Mice pharmacokinetic studies indicate suitability for daily dosing, with over 50% oral bioavailability and a serum half-life close to 6 hours. 14-day dosing in mice and dogs showed excellent tolerability at therapeutic doses, and BTM-3566 demonstrated stability in human hepatocytes and a favorable safety profile. In xenograft models with the double-hit DLBCL line SU-DHL-10, BTM-3566 led to complete regression in all animals, with no tumor growth for two weeks post-therapy, suggesting durable remission. In human DLBCL PDX models with high-risk genomic alterations, BTM-3566 elicited a 100% response rate with complete tumor regression in 6 of 8 tested models.

Analyses of transcriptome and proteome data show BTM-3566's strong activation of the ATF4-ISR, evidenced by eIF2α phosphorylation and ATF4 upregulation. CRISPR-Cas9 gene depletion identified HRI as crucial for BTM-3566's ISR and apoptosis induction. HRI is activated by mitochondrial stressors, such as heme depletion or mitochondrial ATP synthesis blockage, which increase mitochondrial proteostasis and activate protease OMA1. BTM-3566 uniquely activates OMA1 without being a classical mitochondrial toxin, inducing OMA1-dependent processes and mitochondrial fragmentation rapidly without affecting oxygen consumption or membrane potential.

Gene expression profiling across over 400 cancer cell lines revealed that FAM210B, a mitochondrial protein, negatively correlates with BTM-3566 sensitivity. Overexpression of FAM210B prevents OMA1 activation and induces resistance to BTM-3566-induced apoptosis, making it a strong predictor of sensitivity and revealing a new OMA1 regulation mechanism.

In conclusion, BTM-3566 is a potent activator of the mitochondrial ISR, well-tolerated in animals, with favorable pharmacokinetics and robust DLBCL regression in vivo. An IND application for B-cell malignancies is expected in early 2022, with clinical trials planned for the first half of 2022.