Comparative mutagenicity of apicidin and apicidin derivatives (SD-0203 and SD-2007), histone deacetylase inhibitors

SIRT2 Inhibition Rescues Neurodegenerative Pathology but Increases Systemic Inflammation in a Transgenic Mouse Model of Alzheimer's Disease

Sirtuin 2 (SIRT2) has been proposed to have a central role on aging, inflammation, cancer and neurodegenerative diseases; however, its specific function remains controversial. Recent studies propose SIRT2 pharmacological inhibition as a therapeutic strategy for several neurodegenerative diseases including Alzheimer's disease (AD). Surprisingly, none of these published studies regarding the potential interest of SIRT2 inhibition has assessed the peripheral adverse side consequences of this treatment. In this study, we demonstrate that the specific SIRT2 inhibitor, the compound 33i, does not exhibit genotoxic or mutagenic properties. Moreover, pharmacological treatment with 33i, improved cognitive dysfunction and long-term potentiation, reducing amyloid pathology and neuroinflammation in the APP/PS1 AD mouse model. However, this treatment increased peripheral levels of the inflammatory cytokines IL-1β, TNF, IL-6 and MCP-1. Accordingly, peripheral SIRT2 inhibition with the blood brain barrier impermeable compound AGK-2, worsened the cognitive capacities and increased systemic inflammation. The analysis of human samples revealed that SIRT2 is increased in the brain but not in the serum of AD patients. These results suggest that, although SIRT2 pharmacological inhibition may have beneficial consequences in neurodegenerative diseases, its pharmacological inhibition at the periphery would not be recommended and the systemic adverse side effects should be considered. This information is essential to maximize the therapeutic potential of SIRT2 inhibition not only for AD but also for other neurodegenerative diseases.

Histone-deacetylase inhibitors produce positive results in the GADD45a-GFP GreenScreen HC assay

Histone-deacetylase inhibitors (HDACi) are able to induce cell-cycle arrest, apoptosis and differentiation in a variety of tumour cell lines. The mechanisms leading to these cellular outcomes are not fully understood, however, it is has been proposed that induction of cell-cycle arrest might be a result of genotoxic stress. Despite the potential for genotoxic activity of this class of compounds, there are very few data available to provide evidence for this, either in vitro or in vivo. In this study, four HDACi, viz. trichostatin A, sodium butyrate, APHA compound 8 and apicidin, were tested in the human lymphoblastoid TK6 cell line-hosted GADD45a-GFP assay, which has high sensitivity and specificity in the detection of genotoxic carcinogens and in vivo genotoxicants. All four compounds produced positive genotoxicity results within the acceptable toxic dose range of the assay, with APHA compound 8 producing the weakest response. Taken alongside recent evidence demonstrating that GADD45a is not induced by non-genotoxic apoptogens, this study suggests that genotoxicity contributes to the anti-tumour activity of HDACi drugs.

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

Nonclinical safety assessment of the histone deacetylase inhibitor vorinostat

Vorinostat (SAHA, Zolinza), a histone deacetylase inhibitor, is assessed in nonclinical studies to support its approval for cutaneous T-cell lymphoma. Vorinostat is weakly mutagenic in the Ames assay; is clastogenic in rodent (ie, CHO) cells but not in normal human lymphocytes; and is weakly positive in an in vivo mouse micronucleus assay. No effects are observed on potassium ion currents in the hERG assay up to 300 microM (safety margin approximately 300-fold the approximately 1 microM serum concentration associated with the 400 mg/d maximum recommended human dose. No rat respiratory or central nervous system effects are found at 150 mg/kg (>2-fold maximum recommended human dose). No cardiovascular effects, including effects on QTc interval, are observed after a single oral dose (150 mg/kg) in dogs. Vorinostat is orally dosed daily in rats (controls, 20, 50, or 150 mg/kg/d) and dogs (controls, 60, 80, or 100/125/160 mg/kg/d) for 26 weeks with a 4-week recovery. Rat vorinostat-related adverse findings are decreased food consumption, weight loss, and hematologic changes; a no observed adverse effects level is not established. In dogs, adverse effects are primarily gastrointestinal; the no observed adverse effects level is 60 mg/kg/d (approximately 6-fold maximum recommended human dose). Toxicities are reversible and can be monitored in the clinic.

Toxicological evaluation of an apicidin derivative, histone deacetylase inhibitor SD-2007 in mice

SD-2007 is a new derivative of apicidin, an anti-parasitic agent and a histone deacetylase (HDAC) inhibitor. A subacute toxicological evaluation of SD-2007 was investigated for 2 weeks in ICR mice. After oral administration of SD-2007 (0, 0.2, 1, 5 or 25 mg/mouse), the clinical signs, mortalities, body weight changes, blood biochemical parameters, absolute and relative organ weights were examined. One day after the administration of SD-2007, excretion of soft feces in 1 and 5 mg/head groups, and one male in 25 mg/mouse group developed diarrhea, but theses complications were disappeared two days after administration. No mortalities were observed in animals up to 25 mg/mouse (LD(50), >25 mg/kg), but absolute and relative weights of testes were significantly lower at the highest dose group (25 mg/mouse) and serum LDH and glucose levels were elevated in male mice. In addition, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP) activities were reduced in female mice at all dosages. These data suggest that SD- 2007 may be sex specific and be toxic to the male reproductive organ, and thus our findings require further investigation and in particular chronic toxicological investigations should be investigated.

Histone deacetylase inhibitors--turning epigenic mechanisms of gene regulation into tools of therapeutic intervention in malignant and other diseases

Histone deacetylase inhibitors reside among the most promising targeted anticancer agents that are potent inducers of growth arrest, differentiation, and/or apoptotic cell death of transformed cells. In October 2006, the US Food and Drug Administration approved the first drug of this new class, vorinostat (1, Zolinza, Merck). Several histone deacetylase (HDAC) inhibitors more are in clinical trials. HDAC inhibitors have shown significant activity against a variety of hematological and solid tumors at doses that are well tolerated by patients, both in monotherapy as well as in combination therapy with other drugs. This paper reviews the most recent developments in HDAC inhibitor design, particularly in the context of anticancer therapy, and other possible pharmaceutical applications.