表观遗传学药物的研究进展

随着表观遗传学研究的不断深入,表观遗传学药物的研究取得了巨大进展。目前已有研究并批准上市的表观遗传学药物主要针对DNA异常甲基化和组蛋白的异常修饰。潜在的药物有DNA甲基转移酶抑制剂、赖氨酸去甲基化酶抑制剂、蛋白质甲基转移酶抑制剂、组蛋白去乙酰化酶抑制剂、组蛋白乙酰基转移酶抑制剂、含溴结构域蛋白抑制剂及甲基化组蛋白结合蛋白的抑制剂等。该文综述了近年来表观遗传学治疗在药理学上的进展,以期为疾病防治和基础研究提供一些新的思路。     

5-Azacytidine for the treatment of myelodysplastic syndromes

Introduction: 5-Azacytidine is a pyrimidine nucleoside analog of cytidine that undergoes incorporation into DNA and blocks DNA methyltransferase leading to hypomethylation and potentially beneficial re-expression of abnormally silenced genes. It is the first agent approved for use in patients with myelodysplastic syndromes (MDSs) based on its improvement in overall survival as monotherapy. Evidence of efficacy in combination with other agents is also accumulating.

Areas covered: Key information on mechanisms of action is presented. Development, synthesis, and pharmacokinetics are also outlined. Key safety, tolerability, and efficacy data from clinical trials of 5-azacytidine as monotherapy as well as in combination are also presented.

Expert opinion: Our understanding of the molecular basis and pathogenesis of MDS continues to evolve rapidly. 5-Azacytidine has been shown to improve both overall survival and quality of life in patients with high-risk MDS. Currently, the oral route of administration is undergoing evaluation in clinical trials. Used as a monotherapy and also in novel combinations, 5-azacytidine has the potential to further improve the prognosis of some patients with MDS.     

LSD1 inhibition: a therapeutic strategy in cancer?

Introduction: The role of epigenetic dysfunction in cancer is increasingly appreciated. This has raised the question as to whether enzymes that regulate the structure and function of chromatin might represent novel therapeutic targets. The histone demethylase LSD1 is one such candidate and novel, potent inhibitors are under development.

Areas covered: The literature on LSD1 (also known as KDM1A, AOF2, BHC110 or KIAA0601) was identified in Pubmed and is herein discussed. Areas covered include the structure and enzymatic activity of LSD1, its role in chromatin regulatory complexes, its functional roles in normal and malignant tissue, pharmacological inhibitors of its activity and their putative therapeutic roles.

Expert opinion: Pre-clinical data supporting a therapeutic role for LSD1 inhibitors are most encouraging in acute myeloid leukaemia, although optimal dosing strategies and beneficial combinations with other agents remain unclear. Studies making use of potent, selective LSD1 inhibitors active in the nanomolar range are required to establish therapeutic indications in other subtypes of haematological malignancy, and in solid tumours.     

Valproic acid and its derivatives enhanced estrogenic activity but not androgenic activity in a structure dependent manner

Steroid hormones affect metabolic pathways and cellular functions. Valproic acid (VPA), used as antiepileptic drug, inhibits histone deacetylases and interacts with intracellular receptors. We analyzed the impact of VPA and VPA derivatives on activation of estrogen and androgen receptors (ER and AR) using reporter gene assays. VPA and its long-chain derivatives 2-(2-propynyl)-hexanoic acid [butyl-4-yn-VPA], 2-(2-propynyl)-heptanoic acid [S-pentyl-4-yn-VPA] and 2-(2-propynyl)-nonanoic acid [heptyl-4-yn-VPA] enhanced 17β-estradiol-induced ERα and ERβ activation partly synergistically with a structure–activity correlation. The extent of this effect regarding to ERα activation increased with prolongation of the aliphatic side chain. Regarding AR activation, VPA, S-pentyl-4-yn- and heptyl-4-yn-VPA slightly induced AR activity when tested alone. In combination with the AR agonist 5α-dihydrotestosterone, VPA, S-pentyl-4-yn- and heptyl-4-yn-VPA showed anti-androgenic effects without an apparent structural relation. Our results indicate that VPA and its derivatives affect estrogen signaling with a structural specificity, while the (anti-)androgenic effects of these compounds are not structurally correlated.     

Hyposensitivity to Gamma-Aminobutyric Acid in the Ventral Tegmental Area During Alcohol Withdrawal: Reversal by Histone Deacetylase Inhibitors

Putative dopaminergic (pDAergic) ventral tegmental area (VTA) neurons have an important role in alcohol addiction. Acute ethanol increases the activity of pDAergic neurons, and withdrawal from repeated ethanol administration produces a decreased sensitivity of pDAergic VTA neurons to GABA. Recent studies show that behavioral changes induced by chronic alcohol are reversed by inhibitors of histone deacetylases (HDACs). Whether HDAC-induced histone modifications regulate changes in GABA sensitivity of VTA pDAergic neurons during withdrawal is unknown. Here, we investigated modulation of withdrawal-induced changes in GABA sensitivity of pDAergic VTA neurons by HDAC inhibitors (HDACi), and also measured the levels of HDAC2, histone (H3-K9) acetylation, and GABA-Aα1 receptor (GABA (A-α1) R) subunit in VTA during ethanol withdrawal. Mice were injected intraperitoneally (ip) with either ethanol (3.5 g/kg) or saline twice daily for 3 weeks. In recordings from pDAergic VTA neurons in brain slices from ethanol-withdrawn mice, sensitivity to GABA (50–500 μM) was reduced. In brain slices from ethanol-withdrawn mice incubated with the HDACi SAHA (vorinostat) or trichostatin A (TSA) for 2 h, the hyposensitivity of pDAergic VTA neurons to GABA was significantly attenuated. There was no effect of TSA or SAHA on GABA sensitivity of pDAergic VTA neurons from saline-treated mice. In addition, ethanol withdrawal was associated with an increase in levels of HDAC2 and a decrease in histone (H3-K9) acetylation and levels of GABA (A-α1) R subunits in the VTA. Therefore, blockade of upregulation of HDAC2 by HDACi normalizes GABA hyposensitivity of pDAergic neurons developed during withdrawal after chronic ethanol treatment, which suggests the possibility that inhibition of HDACs can reverse ethanol-induced neuroadaptational changes in reward circuitry.     

Histone deacetylase inhibitors

Sustained efforts towards identifying novel histone deacetylase (HDAC) inhibitors as suitable therapies for the treatment of cancer and other human diseases has been a goal for the pharmaceutical industry during the last decade. In the second half of 2006 these efforts culminated in the FDA granting approval for the first HDAC inhibitor, suberoylanilide hydroxamic acid; also known as vorinostat, for once-daily oral treatment of advanced cutaneous T cell lymphoma. This review provides a summary of the published patent literature from mid-2005 until the end of 2006.     

Panobinostat for the treatment of multiple myeloma

Introduction : Multiple myeloma (MM) is a B-cell malignancy characterized by proliferation of monoclonal plasma cells in the bone marrow. Although new therapeutic options have been introduced and response rates have improved in recent years, MM still remains incurable and new treatment options are urgently needed. The histone deacetylase inhibitors (HDACi) are a new class of anticancer agents in early clinical development in many malignancies including MM. HDACi target the enzyme histone deacetylase (HDAC) involved in the deacetylation of histone and non-histone cellular proteins that play important roles in epigenetic regulation of gene expression inducing death, apoptosis and cell cycle arrest in cancer cells. Panobinostat (LBH589) is a highly potent HDACi with demonstrated antitumor activities at low nanomolar concentration in several preclinical studies and its clinical efficacy is currently under investigation in several clinical trials.

Area covered : In this review the authors discuss the role of HDACs in the regulation of gene expression and the biological mechanisms mediating the anticancer effects of HDACi with particular focus on the recent development of panobinostat as anti-MM agent in preclinical and clinical studies.

Expert opinion : As a ‘multi-target' drug, panobinostat appears attractive as potential anti-MM therapeutic for its ability to modulate a variety of biological pathways essential in MM biology. This ‘multi-target' property of panobinostat may also be one its major shortcomings, and a better understanding of its mechanisms of action and targets will permit to identify the best combination therapies that will ultimately overcome and improve outcomes in MM patients.     

Interferon regulatory factor-1 mediates the release of high mobility group box-1 in endotoxemia in mice

Background The extracellular release of the danger signal high mobility group box-1 (HMGB1) has been implicated in the pathogenesis and outcomes of sepsis.Understanding the mechanisms responsible for H...