BIIB021, an orally available, fully synthetic small-molecule inhibitor of the heat shock protein Hsp90.

Inhibition of heat shock protein 90 (Hsp90) results in the degradation of oncoproteins that drive malignant progression, inducing cell death, making Hsp90 a target of substantial interest for cancer therapy. BIIB021 is a novel, fully synthetic inhibitor of Hsp90 that binds competitively with geldanamycin in the ATP-binding pocket of Hsp90. In tumor cells, BIIB021 induced 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. BIIB021 treatment resulted in growth inhibition and cell death in cell lines from a variety of tumor types at nanomolar concentrations. Oral administration of BIIB021 led to the degradation of Hsp90 client proteins measured in tumor tissue and resulted in the inhibition of tumor growth in several human tumor xenograft models. Studies to investigate the antitumor effects of BIIB021 showed activity on both daily and intermittent dosing schedules, providing dose schedule flexibility for clinical studies. Assays measuring the HER-2 protein in tumor tissue and the HER-2 extracellular domain in plasma were used to show interdiction of the Hsp90 pathway and utility as potential biomarkers in clinical trials for BIIB021. Together, these data show that BIIB021 is a promising new oral inhibitor of Hsp90 with antitumor activity in preclinical models.

Rationally designed high-affinity 2-amino-6-halopurine heat shock protein 90 inhibitors that exhibit potent antitumor activity.

Heat shock protein 90 (Hsp90) is a molecular chaperone protein implicated in stabilizing the conformation and maintaining the function of many cell-signaling proteins. Many oncogenic proteins are more dependent on Hsp90 in maintaining their conformation, stability, and maturation than their normal counterparts. Furthermore, recent data show that Hsp90 exists in an activated form in malignant cells but in a latent inactive form in normal tissues, suggesting that inhibitors selective for the activated form could provide a high therapeutic index. Hence, Hsp90 is emerging as an exciting new target for the treatment of cancer. We now report on a novel series of 2-amino-6-halopurine Hsp90 inhibitors exemplified by 2-amino-6-chloro-9-(4-iodo-3,5-dimethylpyridin-2-ylmethyl)purine (30). These highly potent inhibitors (IC50 of 30 = 0.009 microM in a HER-2 degradation assay) also display excellent antiproliferative activity against various tumor cell lines (IC50 of 30 = 0.03 microM in MCF7 cells). Moreover, this class of inhibitors shows higher affinity for the activated form of Hsp90 compared to our earlier 8-sulfanylpurine Hsp90 inhibitor series. When administered orally to mice, these compounds exhibited potent tumor growth inhibition (>80%) in an N87 xenograft model, similar to that observed with 17-allylamino-17-desmethoxygeldanamycin (17-AAG), which is a compound currently in phase I/II clinical trials.

Orally active purine-based inhibitors of the heat shock protein 90.

Orally active Hsp90 inhibitors are of interest as potential chemotherapeutic agents. Recently, fully synthetic 8-benzyladenines and 8-sulfanyladenines such as 4 were disclosed as Hsp90 inhibitors, but these compounds are not water soluble and consequently have unacceptably low oral bioavailabilities. We now report that water-solubility can be achieved by inserting an amino functionality in the N(9) side chain. This results in compounds that are potent, soluble in aqueous media, and orally bioavailable. In an HER-2 degradation assay, the highest potency was achieved with the neopentylamine 42 (HER-2 IC(50) = 90 nM). In a murine tumor xenograft model (using the gastric cancer cell line N87), the H(3)PO(4) salts of the amines 38, 39, and 42 induced tumor growth inhibition when administered orally at 200 mg/kg/day. The amines 38, 39, and 42 are the first Hsp90 inhibitors shown to inhibit tumor growth upon oral dosage.

7'-substituted benzothiazolothio- and pyridinothiazolothio-purines as potent heat shock protein 90 inhibitors.

We report on the discovery of benzo- and pyridino- thiazolothiopurines as potent heat shock protein 90 inhibitors. The benzothiazole moiety is exceptionally sensitive to substitutions on the aromatic ring with a 7'-substituent essential for activity. Some of these compounds exhibit low nanomolar inhibition activity in a Her-2 degradation assay (28-150 nM), good aqueous solubility, and oral bioavailability profiles in mice. In vivo efficacy experiments demonstrate that compounds of this class inhibit tumor growth in an N87 human colon cancer xenograft model via oral administration as shown with compound 37 (8-(7-chlorobenzothiazol-2-ylsulfanyl)-9-(2-cyclopropylamino-ethyl)-9H- purin-6-ylamine).

EC144 is a potent inhibitor of the heat shock protein 90.

Alkyne 40, 5-(2-amino-4-chloro-7-((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)-7H-pyrrolo[2,3-d]pyrimidin-5-yl)-2-methylpent-4-yn-2-ol (EC144), is a second generation inhibitor of heat shock protein 90 (Hsp90) and is substantially more potent in vitro and in vivo than the first generation inhibitor 14 (BIIB021) that completed phase II clinical trials. Alkyne 40 is more potent than 14 in an Hsp90α binding assay (IC(50) = 1.1 vs 5.1 nM) as well as in its ability to degrade Her-2 in MCF-7 cells (EC(50) = 14 vs 38 nM). In a mouse model of gastric tumors (N87), 40 stops tumor growth at 5 mg/kg and causes partial tumor regressions at 10 mg/kg (po, qd × 5). Under the same conditions, 14 stops tumor growth only at 120 mg/kg, and does not induce partial regressions. Thus, alkyne 40 is approximately 20-fold more efficacious than 14 in mice.

Preparation of 8-(arylsulfanyl)adenines with diazonium salts under mild, aerobic conditions.

8-(Arylsulfanyl)adenines 11 were prepared in up to 75% yield by reacting the 8-thionoadenine 6 (acetic acid 3-(6-amino-8-thioxo-7,8-dihydropurin-9-yl)propyl ester) with benzenediazonium tetrafluoroborates in DMSO. Benzenediazonium ions carrying an electron-withdrawing substituent gave the highest yields. The reaction proceeded smoothly at room temperature without any base and could be performed under air atmosphere. The extremely mild conditions are compatible with a wide range of functional groups.