Paper Details

ABSTRACT

Background: Many leukemias and lymphomas depend on oxidative phosphorylation (OXPHOS), creating vulnerabilities to perturbation of mitochondrial bioenergetics. Inhibitors of mitochondrial translation such as tigecycline show preclinical anti-leukemic activity but have failed clinically, underscoring the need for more potent, selective agents. Elatol, a halogenated sesquiterpene from the red alga Laurencia microcladia, was previously identified as an eIF4A1 inhibitor with anti-tumor activity in non-Hodgkin lymphoma and primary chronic lymphocytic leukemia (CLL), while exhibiting favorable in vivo tolerability. In addition, elatol induced an integrated stress response (ISR), although the underlying mechanism remained unclear. We recently identified a bioenergetic checkpoint in which matrix guanine nucleotide (GTP) availability couples OXPHOS to mitochondrial translation. Here, we show that elatol pharmacologically engages this checkpoint, leading to potent anti-leukemic activity.

Methods: Mitochondrial translation was assessed by ³⁵S-methionine labeling in whole cells (with emetine) and isolated mitochondria, mitoribosome profiling, and cryo-EM of purified mitoribosomes. Mitochondrial bioenergetics were evaluated by TMRM staining (mitochondrial membrane potential, ΔΨm), oligomycin-sensitive ATPase activity, and matrix ATP bioluminescence measurements, using cells treated with FCCP, adenine-nucleotide-translocase (ANT) inhibitors, and expressing a yeast mitochondrial GTP transporter (ScGgc1). ISR signaling was mapped by kinase knockdown/knockout and DELE1 fractionation. A leukemia panel comprising K-562 (CML), HL-60 (APL), MOLT-4 and RS4;11 (ALL), together with peripheral blood mononuclear cells (PBMCs), was tested for viability, apoptosis (Annexin V), reactive oxygen species (ROS), lipid peroxidation (C11-BODIPY), glutathione, and GPX4/FTH1, and for synergy with venetoclax (Bliss model).

Results: Elatol rapidly arrested mitochondrial translation at concentrations that spared cytosolic translation, without binding or destabilizing the mitoribosome (no cryo-EM density; loss of stabilizing polyamines, and preserved activity in chloramphenicol-resistant cells). This effect required an intact inner membrane potential, as it was abolished by FCCP-mediated depolarization and in mutants with low ΔΨm. Mechanistically, elatol inhibited the F₁F_o-ATP synthase, inducing ΔΨm hyperpolarization that restricted ANT-mediated ATP import, collapsed matrix ATP, and secondarily depleted matrix GTP. Restoring GTP import via ScGgc1 rescued mitochondrial translation, whereas oligomycin and apoptolidin A phenocopied elatol. This bioenergetic stress activated the OMA1-DELE1-HRI axis and the ISR (p-eIF2α, ATF4, CHOP). Leukemia cells showed 3-to-6-fold higher mtDNA content, greater mitochondrial mass, and roughly 3-fold higher ΔΨm than PBMCs, and were correspondingly hypersensitive. Across all leukemia cell lines, elatol was more potent than tigecycline, killing even tigecycline-resistant K-562 and RS4;11 cells. Cell death involved both apoptosis and ferroptosis, characterized by increased ROS, lipid peroxidation, glutathione depletion, and GPX4/FTH1 loss, with the strongest responses observed in MOLT-4 and HL-60. In contrast, PBMCs were largely spared, defining a bioenergetically based therapeutic window. Finally, elatol synergized with venetoclax (Bliss scores 27.3 in MOLT-4, 16.4 in HL-60, and 12.3 in K-562; additive in RS4;11), supporting a promising combination strategy for clinical translation.

Conclusions: Elatol is a natural-product inhibitor of mitochondrial ATP synthase that engages a newly defined matrix-nucleotide bioenergetic checkpoint, arresting mitochondrial translation, triggering the ISR, and inducing apoptotic and ferroptotic death selectively in OXPHOS-reliant leukemia cells while sparing normal PBMCs. Its greater potency than tigecycline and its synergy with venetoclax support elatol as a lead for mitochondria-directed therapy in hematologic malignancies.