Echinomycin, a Potential Binder of FKBP12, Shows Minor Effect on Calcineurin Activity

Echinomycin, a member of the quinoxaline family of antibiotics, is known to be a small-molecule inhibitor of hypoxia inducible factor–1 (HIF-1) DNA binding activity. Recently, it has been shown to suppress mammalian target of rapamycin (mTOR) signaling and growth in leukemia cell lines. In this study, we investigated whether echinomycin interacts with the FKBP12 protein. Molecular docking was used, and the predicted binding energy was −10.61 kcal/mol. Moreover, surface plasmon resonance imaging and fluorescence quenching techniques were used to validate this interaction. Echinomycin binds to FKBP12 with a strong binding affinity comparable with rapamycin. Furthermore, the echinomycin-FKBP12 complex has been shown to affect calcineurin activity when tested in a calcineurin phosphatase inhibition assay. All of these studies have shown that echinomycin may have a double impact on HIF signaling by direct inhibition and through mTOR.