Marine sponge-derived xestoquinones suppress HIF signaling and disrupt cellular respiration in human breast tumor cells
The organic extract of a marine sponge Petrosia alfiani selectively inhibited iron chelator-induced hypoxia-inducible factor-1 (HIF-1) activation in a human breast tumor T47D cell-based reporter assay. Bioassay-guided fractionation yielded seven xestoquinones (1 - 7) including three new compounds 14-hydroxymethylxestoquinone (1), 15-hydroxymethylxestoquinone (2), and 14,15-dihydroxestoquinone (3). Compounds 1 - 7 were evaluated for their effects on HIF-1 signaling, mitochondrial respiration, and tumor cell proliferation/viability. The known metabolites adociaquinones A (5) and B (6), that possess a 3,4-dihydro-2H-1,4-thiazine-1,1-dioxide moiety, potently and selectively inhibited iron chelator-induced HIF-1 activation in T47D cells, each with an IC50 value of 0.2µM. Mechanistic studies revealed that adociaquinones promote oxygen consumption without affecting mitochondrial membrane potential. Compound 1 both enhances respiration and decreases mitochondrial membrane potential, suggesting that it acts as a protonophore that uncouples mitochondrial respiration.