Macbecin I is an ansamycin antibiotic compound that inhibits Hsp90 activity (IC50 = 2 μM) by binding to the ATP-binding site. Macbecin I exhibits antitumor and cytocidal activities (IC50 ~ 0.4 μM) by causing degradation of key oncogenic client proteins such as ErbB2 and cRaf1. Macbecin I displays higher potency and affinity than geldanamycin.
