Crystal structure of reduced MsAcg, a putative nitroreductase from Mycobacterium smegmatis and a close homologue of Mycobacterium tuberculosis Acg.

This paper presents the structure of MsAcg (MSMEG_5246), a Mycobacterium smegmatis homologue of Mycobacterium tuberculosis Acg (Rv2032) in its reduced form at 1.6 Å resolution using x-ray crystallography. Rv2032 is one of the most induced genes under the hypoxic model of tuberculosis dormancy. The Acg family turns out to be unusual flavin mononucleotide (FMN)-binding proteins that have probably arisen by gene duplication and fusion from a classical homodimeric nitroreductase such that the monomeric protein resembles a classical nitroreductase dimer but with one active site deleted and the other active site covered by a unique lid. The FMN cofactor is not reduced by either NADH or NADPH, but the chemically reduced enzyme is capable of reduction of nitro substrates, albeit at no kinetic advantage over free FMN. The reduced enzyme is rapidly oxidized by oxygen but without any evidence for a radical state commonly seen in oxygen-sensitive nitroreductases. The presence of the unique lid domain, the lack of reduction by NAD(P)H, and the slow rate of reaction of the chemically reduced protein raises a possible alternative function of Acg proteins in FMN storage or sequestration from other biochemical pathways as part of the bacteria's adaptation to a dormancy state.

Detection of a single DNA base-pair mismatch using an anthracene-tagged fluorescent probe.

A novel anthracene-tagged oligonucleotide can discriminate between a fully-matched DNA target sequence and one with a single mismatching base-pair through a remarkable difference in fluorescence emission intensity upon duplex formation.

The first biosynthetic studies of the azinomycins: acetate incorporation into azinomycin B.

13C-labelled acetate efficiently labels the antitumour natural product azinomycin B, revealing a polyketide origin for the naphthoate fragment, that threonine is the probable precursor of the enol fragment, and that alpha-ketoglutarate is a probable precursor of the aziridine fragment.

Biosynthetic studies on the azinomycins: the pathway to the naphthoate fragment.

Isotopically labelled intermediates in a proposed biosynthesis of the naphthoate fragment of azinomycin B have been made and successfully incorporated by the azinomycin producing organism.

Electrochemical, in vitro and cell culture analysis of integrated redox catalysts: implications for cancer therapy.

Integrated catalysts as redox sensitisers towards cancer.

A brain-permeable small molecule reduces neuronal cholesterol by inhibiting activity of sirtuin 2 deacetylase.

Sirtuin 2 (SIRT2) deacetylase-dependent inhibition mediates neuroprotective reduction of cholesterol biosynthesis in an in vitro Huntington's disease model. This study sought to identify the first brain-permeable SIRT2 inhibitor and to characterize its cholesterol-reducing properties in neuronal models. Using biochemical sirtuin deacetylation assays, we screened a brain-permeable in silico compound library, yielding 3-(1-azepanylsulfonyl)-N-(3-bromphenyl)benzamide as the most potent and selective SIRT2 inhibitor. Pharmacokinetic studies demonstrated brain-permeability but limited metabolic stability of the selected candidate. In accordance with previous observations, this SIRT2 inhibitor stimulated cytoplasmic retention of sterol regulatory element binding protein-2 and subsequent transcriptional downregulation of cholesterol biosynthesis genes, resulting in reduced total cholesterol in primary striatal neurons. Furthermore, the identified inhibitor reduced cholesterol in cultured naïve neuronal cells and brain slices from wild-type mice. The outcome of this study provides a clear opportunity for lead optimization and drug development, targeting metabolic dysfunctions in CNS disorders where abnormal cholesterol homeostasis is implicated.

Evaluation of the benzothiazole aggregation inhibitors riluzole and PGL-135 as therapeutics for Huntington's disease.

Huntington's disease (HD) is an inherited progressive neurological disorder for which there is no effective therapy. It is caused by a CAG/polyglutamine repeat expansion that leads to abnormal protein aggregation and deposition in the brain. Several compounds have been shown to disrupt the aggregation process in vitro, including a number of benzothiazoles. To further explore the therapeutic potential of the benzothiazole aggregation inhibitors, we assessed PGL-135 and riluzole in hippocampal slice cultures derived from the R6/2 mouse, confirming their ability to inhibit aggregation with an EC50 of 40 microM in this system. Preliminary pharmacological work showed that PGL-135 was metabolically unstable, and therefore, we conducted a preclinical trial in the R6/2 mouse with riluzole. At the maximum tolerated dose, we achieved steady-state riluzole levels of 100 microM in brain. However, this was insufficient to inhibit aggregation in vivo and we found no improvement in the disease phenotype.

Minocycline and doxycycline are not beneficial in a model of Huntington's disease.

Huntington's Disease (HD) is an inherited neurological disorder causing movement impairment, personality changes, dementia, and premature death, for which there is currently no effective therapy. The modified tetracycline antibiotic, minocycline, has been reported to ameliorate the disease phenotype in the R6/2 mouse model of HD. Because the tetracyclines have also been reported to inhibit aggregation in other amyloid disorders, we have investigated their ability to inhibit huntingtin aggregation and further explored their efficacy in preclinical mouse trials. We show that tetracyclines are potent inhibitors of huntingtin aggregation in a hippocampal slice culture model of HD at an effective concentration of 30 microM. However, despite achieving tissue levels approaching this concentration by oral treatment of R6/2 mice with minocycline, we observed no clear difference in their behavioral abnormalities, or in aggregate load postmortem. In the light of these new data, we would advise that caution be exercised in proceeding into human clinical trials of minocycline.

Suberoylanilide hydroxamic acid, a histone deacetylase inhibitor, ameliorates motor deficits in a mouse model of Huntington's disease.

Huntington's disease (HD) is an inherited, progressive neurological disorder that is caused by a CAG/polyglutamine repeat expansion and for which there is no effective therapy. Recent evidence indicates that transcriptional dysregulation may contribute to the molecular pathogenesis of this disease. Supporting this view, administration of histone deacetylase (HDAC) inhibitors has been shown to rescue lethality and photoreceptor neurodegeneration in a Drosophila model of polyglutamine disease. To further explore the therapeutic potential of HDAC inhibitors, we have conducted preclinical trials with suberoylanilide hydroxamic acid (SAHA), a potent HDAC inhibitor, in the R6/2 HD mouse model. We show that SAHA crosses the blood-brain barrier and increases histone acetylation in the brain. We found that SAHA could be administered orally in drinking water when complexed with cyclodextrins. SAHA dramatically improved the motor impairment in R6/2 mice, clearly validating the pursuit of this class of compounds as HD therapeutics.