BIIB021 is a potent HSP90 inhibitor (IC₅₀ = 30 nM HER-2 degradation).¹ It inhibited the proliferation of MCF7 and BT474 breast cancer cell lines (IC₅₀ = 100 nM for each).  BIIB021 has shown efficacy as a therapeutic in multiple cancer models.^2-5

References:

1. Kasibhatla et al. (2007), Rationally designed high-affinity 2-amino-6-halopurine heat shock protein 90 inhibitors that exhibit potent antitumor activity; J. Med. Chem. 50 2767
2. Lundgren et al. (2009), BIIB021, an orally available, fully synthetic small-molecule inhibitor of the heat shock protein Hsp90; Mol. Cancer Ther. 8 921
3. Boll et al. (2009), Heat shock protein 90 inhibitor BIIB021 (CNF2024) depletes NF-kappaB and sensitizes Hodgkin’s lymphoma cells for natural killer cell-mediated cytotoxicity; Clin. Cancer Res. 15 5108
4. Zhang et al. (2010), BIIB021, a synthetic Hsp90 inhibitor, has broad application against tumors with acquired multidrug resistance; Int. J. Cancer 126 1226
5. Wang et al. (2014), BIIB021, a novel Hsp90 inhibitor, sensitizes esophageal squamous cell carcinoma to radiation; Biochem. Biophys. Res. Commun. 452 945