17-AAG, An Anticancer Antibiotic. 17-AAG is a less toxic and more stable derivative of the antibiotic Geldanamycin. It binds to Hsp90 and regulates its function. Hsp90 regulates the physiology of cells exposed to environmental stress and in maintaining the malignant phenotype of tumor cells. 17-AAG induces apoptosis and displays anti-tumor effects in tumor cells. 17-AAG depletes cancer cells of erbB-1, erbB-2, Raf-1, and Akt and hence inhibits the Ras/Raf/MEK and PI3-kinase signaling pathways. It also downregulates vascular endothelial growth factor (VEGF) expression. 17AAG is currently in phase I clinical trial in several centers worldwide Preliminary data obtained from these trials demonstrate that anti tumor activity is achieved at concentrations below the maximum tolerated dose. Cell Signaling Activators and Inhibitors; Anticancer Compounds.