Benzazepinones and benzoxazepinones as antagonists of inhibitor of apoptosis proteins (IAPs) selective for the second baculovirus IAP repeat (BIR2) domain.

XIAP is a key regulator of apoptosis, and its overexpression in cancer cells may contribute to their survival. The antiapoptotic function of XIAP derives from its BIR domains, which bind to and inhibit pro-apoptotic caspases. Most known IAP inhibitors are selective for the BIR3 domain and bind to cIAP1 and cIAP2 as well as XIAP. Pathways activated upon cIAP binding contribute to the function of these compounds. Inhibitors selective for XIAP should exert pro-apoptotic effects through competition with the terminal caspases. This paper details our synthetic explorations of a novel XIAP BIR2-selective benzazepinone screening hit with a focus on increasing BIR2 potency and overcoming high in vivo clearance. These efforts led to the discovery of benzoxazepinone 40, a potent BIR2-selective inhibitor with good in vivo pharmacokinetic properties which potentiates apoptotic signaling in a manner mechanistically distinct from that of known pan-IAP inhibitors.

Optimization of benzodiazepinones as selective inhibitors of the X-linked inhibitor of apoptosis protein (XIAP) second baculovirus IAP repeat (BIR2) domain.

The IAPs are key regulators of the apoptotic pathways and are commonly overexpressed in many cancer cells. IAPs contain one to three BIR domains that are crucial for their inhibitory function. The pro-survival properties of XIAP come from binding of the BIR domains to the pro-apoptotic caspases. The BIR3 domain of XIAP binds and inhibits caspase 9, while the BIR2 domain binds and inhibits the terminal caspases 3 and 7. While XIAP BIR3 inhibitors have previously been reported, they also inhibit cIAP1/2 and promote the release of TNFα, potentially limiting their therapeutic utility. This paper will focus on the optimization of selective XIAP BIR2 inhibitors leading to the discovery of highly potent benzodiazepinone 36 (IC50 = 45 nM), which has high levels of selectivity over XIAP BIR3 and cIAP1 BIR2/3 and shows efficacy in a xenograft pharmacodynamic model monitoring caspase activity while not promoting the release of TNFα in vitro.

The discovery of NVP-LAQ824: from concept to clinic.

The natural products trapoxin B and trichostatin A, as well as the novel marine natural product psammaplin A (PSMA) were found in a cell-based screen for compounds that induced the expression of the cyclin dependent kinase inhibitor p21(waf1). The mechanism of p21(waf1) induction for these compounds was via histone deacetylase (HDAC) inhibition. Of these compounds, PSMA was of interest because of its novel structure, but the physiological stability of it, and its analogs was poor. Thus, a directed medicinal chemistry effort was undertaken to prepare analogs of the simple HDAC inhibitor dimethylaminobenzamidylcaprylic hydroxamate (DBCH), which led to chromenone amide 9. This compound was efficacious in the HCT116 colon xenograft assay, but was difficult to formulate in pharmaceutically acceptable vehicles. In parallel with these efforts, a screen of the Novartis compound archive for novel HDAC inhibitors uncovered the cinnamyl hydroxamic acid NVP-LAK974. This compound had good enzyme and cellular potency, but poor efficacy in vivo. A systematic structural exploration of cinnamyl hydroxamates based on NVP-LAK974 was undertaken with the goal of finding a novel, well-tolerated and efficacious HDAC inhibitor. Several derivatives were found to be efficacious in the xenograft assay. Of those compounds, NVP-LAQ824 distinguished itself due to its tolerability, efficacy and potency. Based, in part, on these properties, NVP-LAQ824 is currently undergoing human clinical trials as a novel anti-cancer agent.

N-hydroxy-3-phenyl-2-propenamides as novel inhibitors of human histone deacetylase with in vivo antitumor activity: discovery of (2E)-N-hydroxy-3-[4-[[(2-hydroxyethyl)[2-(1H-indol-3-yl)ethyl]amino]methyl]phenyl]-2-propenamide (NVP-LAQ824).

A series of N-hydroxy-3-phenyl-2-propenamides were prepared as novel inhibitors of human histone deacetylase (HDAC). These compounds were potent enzyme inhibitors, having IC(50)s < 400 nM in a partially purified enzyme assay. However, potency in cell growth inhibition assays ranged over 2 orders of magnitude in two human carcinoma cell lines. Selected compounds having cellular IC(50) < 750 nM were tested for maximum tolerated dose (MTD) and for efficacy in the HCT116 human colon tumor xenograft assay. Four compounds having an MTD > or = 100 mg/kg were selected for dose-response studies in the HCT116 xenograft model. One compound, 9 (NVP-LAQ824), had significant dose-related activity in the HCT116 colon and A549 lung tumor models, high MTD, and low gross toxicity. On the basis, in part, of these properties, 9 has entered human clinical trials in 2002.

Psammaplins from the sponge Pseudoceratina purpurea: inhibition of both histone deacetylase and DNA methyltransferase.

Four novel bisulfide bromotyrosine derivatives, psammaplins E (9), F (10), G (11), and H (12), and two new bromotyrosine derivatives, psammaplins I (13) and J (14), were isolated from the sponge Pseudoceratina purpurea, along with known psammaplins A (4), B (6), C (7), and D (8) and bisaprasin (5). The structures of psammaplins E (9) and F (10), which each contain an oxalyl group rarely found in marine organisms, were determined by spectroscopic analysis. Compounds 4, 5, and 10 are potent histone deacetylase inhibitors and also show mild cytotoxicity. Furthermore, compounds 4, 5, and 11 are potent DNA methyltransferase inhibitors. The biogenetic pathway previously proposed for the psammaplins class is also revisited.

Recent advances in the discovery of small molecule histone deacetylase inhibitors.

The reversible acetylation of lysine amino groups in nuclear histones is an important mechanism by which gene expression is regulated, and may act by disrupting higher order chromatin structure. In normal cells, the competing activities of two enzyme classes, the histone acetyl transferases (HATs) and histone deacetylases (HDACs), result in cell-specific patterns of gene expression. Aberrant patterns of histone acetylation have been linked to cancer, and natural and synthetic HDAC inhibitors (HDAIs) have shown antiproliferative effects on tumor cells in culture. Thus, there has been an increasing interest in histone deacetylase inhibitors as novel anticancer agents, with clinical investigation underway for several molecules. This review summarizes recent progress in the development of new HDAIs and their reported activities.

Inhibitors of human histone deacetylase: synthesis and enzyme and cellular activity of straight chain hydroxamates.

Inhibitors of histone deacetylase (HDAC) have been shown to induce terminal differentiation of human tumor cell lines and to have antitumor effects in vivo. We have prepared analogues of suberoylanilide hydroxamic acid (SAHA) and trichostatin A and have evaluated them in a human HDAC enzyme inhibition assay, a p21(waf1) (p21) promoter assay, and in monolayer growth inhibition assays. One compound, 4-(dimethylamino)-N-[7-(hydroxyamino)-7-oxoheptyl]-benzamide, was found to affect the growth of a panel of eight human tumor cell lines differentially.