Abstract 3775: Inhibition of mitochondrial translation by the marine natural product elatol shows potent antileukemia activity

Abstract

Abstract Targeted signaling inhibitors for hematologic malignancies may lead to limited clinical efficacy due to the outgrowth of subpopulations with alternative pathways independent of the drug target. Recent studies have shown that some forms of hematologic malignancies (Ashton et al., 2018) and solid tumors (Molina et al., 2018) have an energy metabolism highly dependent on mitochondrial oxidative phosphorylation. Tigecycline, a US FDA approved antibiotic, has been shown to inhibit synthesis of mitochondrion-encoded proteins leading to selective lethality in hematologic malignancies reliant on oxidative phosphorylation (Norberg et al., 2017). Combination treatment with the tyrosine-kinase inhibitor (TKI) imatinib and tigecycline eradicated therapy-resistant chronic myelogenous leukemia (CML), both in vitro and in vivo (Kuntz et al., 2017). We have previously reported that elatol, the major compound from algae Laurencia microcladia, is effective against several non-Hodgkin lymphomas and primary CML cells (Peters et al., 2018). In vitro studies showed that elatol inhibits eIF4A1 helicase activity, suppressing cytoplasmic cap-dependent translation initiation. Further assessments using 35-S-methionine incorporation in HEK293T cells treated with single-digit micromolar concentrations of elatol for short periods revealed strong downregulation of mitochondrion-encoded proteins (no transcriptional effect). This was confirmed in CML and acute lymphoblastic leukemia (ALL) cell lines whose 24-hour elatol LD50 ranged from high nanomolar to low micromolar concentrations. This potency was 2-10x higher than for tigecycline in side-by-side comparisons across several leukemia cell lines. Through sedimentation property analysis using sucrose gradients, we established that elatol does not affect integrity of small and large mitochondrial ribosomal units. Although the specific target on the mitochondrial translation apparatus remains elusive, we have uncovered that its mechanism of action differs from that of chloramphenicol, which inhibits translation elongation. Moreover, elatol treatment leads to activation of the integrated stress response (ISR) evidenced by induction of ATF4 and CHOP. We found that elatol activates the ISR through mitochondrial stress in which cleaved DELE1 binds to HRI to phosphorylate eIF2α, a mechanism described in Fessler et al., 2020. In summary, we have performed proof-of-concept studies using HEK293T and HeLa cell lines, isolated mitochondria, and CML and ALL cell lines to reveal that elatol is a potent inhibitor of mitochondrial protein synthesis and mechanistically different from chloramphenicol. Tigecycline’s compelling preclinical data in combination with TKI informed design of a pending clinical trial (NCT02883036). Elatol’s greatly improved potency provides a potential starting point for further optimization of this paradigm. Citation Format: Tyler A. Cunningham, Priyanka Maiti, Antonio Barrientos, Jonathan H. Schatz. Inhibition of mitochondrial translation by the marine natural product elatol shows potent antileukemia activity [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 3775.