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.In  atro-118Q transgenic mice, neuronal expression of the mutant humanatrophin-1 protein containing an expanded stretch of 118 polyQ results in severalneurodegenerative phenotypes that are commonly seen in DRPLA patients.Symp-toms include ataxia, tremors, and other motor defects.Biochemical analysisof these mice also revealed histone H3 hypo-acetylation in brain tissue [197].Furthermore, histone hypo-acetylation has also been demonstrated in transgenicALS mice [198].Friedreich s ataxia (FRDA) is the result of a GAA·TTC triplet hyper-expansionin an intron of the frataxin (FXN) gene that leads to transcriptional silencing.Frataxin is an essential mitochondrial protein and the resultant FXN insufficiencyresults in progressive spinocerebellar neurodegeneration and cardiomyopathy,leading to a progressive lack of motor coordination, incapacity, and death, usuallyin early adulthood.Interference with transcription due to the high GAA content ofthe mutated gene as well as the ability of expanded GAA·TTC regions to favor aheterochromatin assembly has been implicated as the reason for the observedtranscriptional silencing [199].Histones H3 and H4 of the FXN gene were notedto be hypo-acetylated in transformed lymphoid cell lines taken from an FRDApatient and a concomitant upregulation of trimethylated H3K9 has been observed.These findings imply a repressed heterochromatin state [200].The effects onboth H3 and H4 acetylation and FXN mRNA levels were assessed using valproicacid (21, Fig.8), TSA (2, Fig.1), SAHA (1, Fig.1), and suberoyl bishydroxamicacid (52, Fig.14) with variable results that were confounded by the cellulartoxicity of these compounds.However, the benzamide derivative BML-210 (53,Fig.14) did indeed increase FXN mRNA without showing cytotoxicity at theconcentration tested.Furthermore, treatment with an analog of BML-210, pimelicHH HO HHNN NNHO NN OHnH OO OOOH2NH2N52(suberoyl bishydroxamic acid, 53 n = 2 (BML-210) 55SBHA) (compound 106)54 n = 1 (compound 4b)Fig.14 Structure of SBHA (52), BML-210 (53), and analogs 54 and 55The Role of Histone Deacetylases in Neurodegenerative Diseases 27diphenylamide 54, resulted in a 2.5-fold enhancement of FXN mRNA (5 mM),acetylation of H3K14, H4K5, and H4K12 in the chromatin region immediatelyupstream of the GAA repeats, and an approximate 3.5-fold increase in FXNprotein levels (2.5 mM) [200].A subsequent short pharmacodynamic study showed that a very close analog of54, the tolyl derivative 55, corrected the frataxin deficiency in a Friedreich s ataxiamouse model [201].These mice carry a homozygous (GAA)230 expansion in thefirst intron of the mouse FXN gene (KI/KI mice).Biochemical analysis revealedthat these mice carry the same heterochromatin marks, close to the GAA repeat asthose detected in patient cell lines and have mildly but significantly reducedfrataxin mRNA and protein levels.However, they show no overt phenotype.Once a day treatment with compound 55 at 150 mg/kg subcutaneously for 3 daysincreased global brain tissue histone acetylation as well as histone acetylation closeto the GAA repeat and restored frataxin levels in the nervous system and heart(determined by qPCR and semiquantitative western blot analysis).Reversion ofother differentially expressed genes toward wild-type levels was also observed.Thecompound showed no apparent toxicity.HDAC inhibitor 54 has also demonstrated a therapeutic effect in the R6/2Huntington s disease model, which expressed the Exon 1 Htt protein with anexpanded polyglutamine region of ~300 repeats, and shows a more delayed pheno-type than the R6/2 model with shorter polyQ expansions [202].Again, a shortpharmacodynamic trial (once a day subcutaneous treatment with 150 mg/kg for3 days) successfully ameliorated gene expression abnormalities as detected bymicroarray analysis in these mice and showed increased histone H3 acetylationin association with selected downregulated genes.For a chronic efficacy trial, theTFA salt of compound 54 was solubilized in 2-hydroxypropyl-b-cyclodextrin anddissolved in drinking water to an estimated dosage of 150 mg/kg/day and adminis-tered to mice from 4 months of age [ Pobierz caÅ‚ość w formacie PDF ]