BIIB021 is a potent, orally-available inhibitor of Hsp90 (Ki = 1.7 nM) that induces the degradation of oncoproteins, including HER2 (EC50 = 38 nM), while up-regulating the expression of Hsp70 and Hsp27. It is cytotoxic to cancer cells and, when administered orally to mice, inhibits growth of xenograft tumors. BIIB021 suppresses growth in various lymphoma cells but not in normal lymphocytes and induces apoptosis in a myelodysplastic syndrome cell line.
