BIIB 021

BIIB 021 binds in the ATP-binding pocket of Hsp90, interferes with Hsp90 chaperone function, and results in client protein degradation and tumor growth inhibition. BIIB 021 inhibits tumor cell (BT474, MCF-7, N87, HT29, H1650, H1299, H69 and H82) proliferation (IC50 of 0.06-0.31 μM). BIIB 021 induces the degradation of Hsp90 client proteins including HER-2, Akt, and Raf-1 and up-regulated expression of the heat shock proteins Hsp70 and Hsp27. BIIB 021 inhibits Hodgkin's lymphoma cells (KM-H2, L428, L540, L540cy, L591, L1236 and DEV) (IC50 of 0.24-0.8 μM). BIIB 021 shows low activity in lymphocytes from healthy individuals. BIIB 021 inhibits the constitutive activity of NF-κB despite defective IκB. BIIB 021 induces the expression of ligands for the activating NK cell receptor NKG2D on Hodgkin's lymphoma cells resulting in an increased susceptibility to NK cell–mediated killing. BIIB 021 enhanced the in vitro radiosensitivity of HNSCCA cell lines (UM11B and JHU12) with a corresponding reduction in the expression of key radioresponsive proteins, increased apoptotic cells and enhance G2 arrest. BIIB 021 is considerably more active than 17-AAG against adrenocortical carcinoma H295R, both in vitro and in vivo. The cytotoxic activity of BIIB 021 is not influenced by loss of NQO1 or Bcl-2 overexpression, molecular lesions that do not prevent client loss but are nonetheless associated with reduced cell killing by 17-AAG. BIIB 021 is also active in 17-AAG resistant cell lines (NIH-H69, MES SA Dx5, NCI-ADR-RES, Nalm6 and etc.).