Targeting mitochondrial metabolism by the mitotoxin bromoxib as a therapeutic approach for the treatment of leukemia and lymphoma

Targeting mitochondrial metabolism represents a promising approach for cancer treatment. Here, we investigated the mitotoxic potential of the polybrominated diphenyl ether bromoxib, a natural compound isolated from the marine sponge Dysidea family. We could show that bromoxib comprised strong cytotoxicity in different leukemia and lymphoma cell lines (such as HL60, HPBALL, Jurkat, K562, KOPTK1, MOLT4, SUPB15 and Ramos), but also in solid tumor cell lines (such as glioblastoma cell lines SJ-GBM2 and TP365MG). Bromoxib activated the mitochondrial death pathway as evidenced by the rapid translocation of Bax to mitochondria and subsequent mitochondrial release of Smac. Accordingly, bromoxib-induced apoptosis was blocked in caspase-9 deficient Jurkat cells and Jurkat cells overexpressing antiapoptotic Bcl-2. In addition, we could show that bromoxib functioned as a protonophore in similar rapid kinetics as CCCP concerning the breakdown of the mitochondrial membrane potential (ΔΨm), processing of the dynamin-like GTPase OPA1 and subsequent fragmentation of mitochondria. Beyond that, bromoxib strongly abrogated ATP production via glycolysis as well as oxidative phosphorylation (OXPHOS) by targeting electron transport chain complexes II, III, and ATP-synthase in Ramos lymphoma cells. Thus, bromoxib's potential to act on both cytosolic glycolysis and mitochondrial respiration renders it a promising agent for the treatment of leukemia and lymphoma.