J Clin Neurol.  2006 Dec;2(4):213-224. 10.3988/jcn.2006.2.4.213.

Therapeutic Strategies in Huntington's Disease

• Kanazawa I

• KMID: 1980460
• DOI: http://doi.org/10.3988/jcn.2006.2.4.213

Abstract

This article provides an overview of the therapeutic strategies, from ordinary classical drugs to the modern molecular strategy at experimental level, for Huntington's disease. The disease is characterized by choreic movements, psychiatric disorders, striatal atrophy with selective small neuronal loss, and autosomal dominant inheritance. The genetic abnormality is CAG expansion in huntingtin gene. Mutant huntingtin with abnormally long glutamine stretch aggregates and forms intranuclear inclusions. In this review, I summarize the results of previous trials from the following aspects; 1. symptomatic/palliative therapies including drugs, stereotaxic surgery and repetitive transcranial magnetic stimulation, 2. anti-degenerative therapies including anti-excitotoxicity, reversal of mitochondrial dysfunction and anti-apoptosis, 3. restorative/reparative therapies including neural trophic factors and tissue or stem cell transplantation, and 4. molecular targets in specific and radical therapies including inhibition of truncation of huntingtin, inhibition of aggregate formation, normalization of transcriptional dysregulation, enhancement of autophagic clearance of mutant huntingtin, and specific inhibition of huntingtin expression by sRNAi. Although the strategies mentioned in the latter two categories are mostly at laboratory level at present, we are pleased that one can discuss such "therapeutic strategies", a matter absolutely impossible before the causal gene of Huntington's disease was identified more than 10 years ago. It is also true, however, that some of the "therapeutic strategies" mentioned here would be found difficult to implement and abandoned in the future.

Keyword

Huntington's Disease; Huntingtin; Cell therapy; Gene therapy; Aggregation; Autophagy; RNA interference

MeSH Terms

Atrophy
Autophagy
Cell- and Tissue-Based Therapy
Chorea
Genetic Therapy
Glutamine
Huntington Disease*
Intranuclear Inclusion Bodies
Neurons
RNA Interference
Stem Cell Transplantation
Transcranial Magnetic Stimulation
Wills
Glutamine

Figure

• 

  Figure 1 Schematic diagram of molecular targets in "therapeutic strategies" for HD. The outer square represents a cell (neuron) and the interior circle is the nucleus. "hht" indicates huntingtin. ①~⑧ represent individual processes that could be the molecular target in HD therapy in the future. The processes are designed to: ① inhibit expression of hht in each cell, ② inhibit hht truncation, ③ block transfer of truncated hht into nucleus, ④ inhibit aggregation formation, ⑤ shift the reaction toward histone acetylation, ⑥ enhance clearance of degraded hht through autophagy, ⑦ normalize transcriptional dysregulation, and ⑧ promote normal protein folding.

• 

  Figure 2 The relative amount of huntingtin (normal and expanded) expressed in 10 single neurons obtained from one HD patient. Putaminal neurons and Purkinje cells are analyzed because the former are the most severely affected, and the latter least affected. A single neuron was dissected from a freeze-dried brain tissue of HD patient, using an Eximer-Laser-Microdissector. Total amount of mRNA in a single neuron was processed quantitatively by RT-PCR, in order to keep the relative amounts of normal and mutant huntingtin and to amplify them in the form of cDNA. The amplified cDNAs were electrophoresed and densitometrically quantitated. When comparedwith least affected Purkinje cells, most vulnerable putaminal neurons expressed relatively more expanded huntingtin than normal sized huntingtin. This subtle but definite difference in the relative amount of expressed huntingtin (normal and mutant) might explain the neuronal selectivity in HD brain pathology, and more importantly, might provide an excellent hint for a molecular target in HD. Data shown are unpublished results of experiments conducted by Dr. Jeoung Seon-Yong, a brilliant post-doctoral fellow in my CREST team (1996-2001).

• 

  Figure 3 (a) A schematic drawing of the construct used in the in vitro experiments and target position of siRNA; siRNA-HDExon1. The constructed expression vector contains HD gene exon 1. Cytomegalovirus promoter [P (CMV)] was ligated at the 5' end of exon 1 gene, and a set of the sequence for GFP [EGFP] ligated at the 3'end as a reporter. Two groups of constructs were used in terms of the length of CAG repeats: normal HD exon 1 containing 17 CAG repeats and mutant HD exon 1 containing 72 CAG repeats.79 (b) Nucleotide sequence of the siRNA-HDExon1. This sequence was second best in terms of "specificity" or "uniqueness" based on BLAST search, but best in its "efficacy" on silencing the huntingtin gene.79

• 

  Figure 4 Fluorescence images of COS-7 cells transfected with construct ligated with EGFP shown in Fig. 3. Upper panel (a): cells transfected with the construct inserted with HD exon 1 containing normal sized 17 CAG repeats. Lower panel (b): cells transfected with the construct inserted with HD exon 1 containing mutant sized 72 CAG repeats. Left columns: cells transfected with HD gene construct alone. Right columns: cells co-transfected with HD gene construct and siRNA-HDExon1 (40 nM). Note that cells transfected with the construct of mutant sized CAG repeats exhibit intracellular aggregation formation. In addition, note that HD gene is strongly suppressed in siRNA co-transfected cells compared with cells without siRNA.79

• 

  Figure 5 A mouse (R6/2) model of HD generated by Bates et al in 1996 and purchased from Jackson Laboratory. Brains from 8-week-old mice were immunostained with antibody against mutant huntingtin (MAB5374) that recognizes the N-terminal portion of this human protein. Note the abundant presence of neuronal intranuclear inclusions of mutant huntingtin in the striatum of mock-treated and untreated mice, and in contrast, a clear decrease in the number of cells with intranuclear inclusions in the striatum of siRNSHDExon1-treated mice. Scale bar: 200 µm for the upper panel (magnification x40) and 30 µm for the lower panel (magnification x100).80

• 

  Figure 6 Effects of siRNA-HDExon1 on the survival rate of R6/2 mice model of HD. Kaplan-Meier survival curves showing that siRNA-HDExon1 treatment significantly extended the longevity of R6/2 mice (p< 0.0001 by log-rank test, siRNA-treated, n=39; mock-treated, n=9; untreated, n=65). Wild-type mice that had received sham treatment had a normal lifespan (data not shown).80

Reference

1. Perry TL, Hansen S, Kloster M. Huntington's chorea. Deficiency of gamma-aminobutyric acid in brain. N Engl J Med. 1973. 288:337–342.

2. Spokes EG. Neurochemical alterations in Huntington's chorea: A study of post-mortem brain tissue. Brain. 1980. 103:179–210.

3. Gusella JF, Wexler NS, Conneally PM, Naylor SL, Anderson MA, Tanzi RE, et al. A polymorphic DNA marker genetically linked to Huntington's disease. Nature. 1983. 306:234–238.

4. The Huntington's disease collaborative research group. A novel gene containing a trinucleotide repeat that is expanded and unstable on Huntington's disease chromosomes. Cell. 1993. 72:971–983.

5. Davies SW, Turmaine M, Cozens BA, DiFiglia M, Sharp AH, Ross CA, et al. Formation of neuronal intranuclear inclusions underlies the neurological dysfunction in mice transgenic for the hd mutation. Cell. 1997. 90:537–548.

6. Trushina E, Heldebrant MP, Perez-Terzic CM, Bortolon R, Kovtun IV, Badger JD, et al. Microtubule destabilization and nuclear entry are sequential steps leading to toxicity in Huntington's disease. Proc Natl Acad Sci USA. 2003. 100:12171–12176.

7. Shoulson I, Chase TN, Roberts E, Van Balgooy JN. Letter: Huntington's disease: Treatment with imidazole-4-acetic acid. N Engl J Med. 1975. 293:504–505.

8. Shoulson I, Kartzinel R, Chase TN. Huntington's disease: Treatment with dipropylacetic acid and gamma-amino-butyric acid. Neurology. 1976. 26:61–63.

9. Shoulson I, Goldblatt D, Charlton M, Joynt RJ. Huntington's disease: Treatment with muscimol, a gaba-mimetic drug. Ann Neurol. 1978. 4:279–284.

10. Perry TL, Wright JM, Hansen S, Thomas SM, Allan BM, Baird PA, et al. A double-blind clinical trial of isoniazid in Huntington disease. Neurology. 1982. 32:354–358.

11. Shoulson I, Odoroff C, Oakes D, Behr J, Goldblatt D, Caine E, et al. A controlled clinical trial of baclofen as protective therapy in early Huntington's disease. Ann Neurol. 1989. 25:252–259.

12. O'Suilleabhain P, Dewey RB Jr. A randomized trial of amantadine in Huntington disease. Arch Neurol. 2003. 60:996–998.

13. Bonelli RM, Wenning GK. Pharmacological management of Huntington's disease: An evidence-based review. Curr Pharm Des. 2006. 12:2701–2720.

14. Huntington Study Group. Tetrabenazine as antichorea therapy in Huntington disease: A randomized controlled trial. Neurology. 2006. 66:366–372.

15. Puri BK, Leavitt BR, Hayden MR, Ross CA, Rosenblatt A, Greenamyre JT, et al. Ethyl-epa in Huntington disease: A double-blind, randomized, placebo-controlled trial. Neurology. 2005. 65:286–292.

16. NarabayashiH SM, Ohye C. Experience with stereotaxic surgery on choreic movements with some physiological interpretations. Adv Neurol. 1973. 1:789–793.

17. Priori A, Berardelli A, Inghilleri M, Polidori L, Manfredi M. Electromyographic silent period after transcranial brain stimulation in Huntington's disease. Mov Disord. 1994. 9:178–182.

18. Brusa L, Versace V, Koch G, Bernardi G, Iani C, Stanzione P, et al. Improvement of choreic movements by 1 hz repetitive transcranial magnetic stimulation in Huntington's disease patients. Ann Neurol. 2005. 58:655–656.

19. Huntington Study Group. Dosage effects of riluzole in Huntington's disease: A multicenter placebo-controlled study. Neurology. 2003. 61:1551–1556.

20. Browne SE, Ferrante RJ, Beal MF. Oxidative stress in Huntington's disease. Brain Pathol. 1999. 9:147–163.

21. Huntington Study Group. A randomized, placebo-controlled trial of coenzyme Q10 and remacemide in Huntington's disease. Neurology. 2001. 57:397–404.

22. Ryu H, Rosas HD, Hersch SM, Ferrante RJ. The therapeutic role of creatine in Huntington's disease. Pharmacol Ther. 2005. 108:193–207.

23. Hersch SM, Gevorkian S, Marder K, Moskowitz C, Feigin A, Cox M, et al. Creatine in Huntington disease is safe, tolerable, bioavailable in brain and reduces serum 8oh2'dg. Neurology. 2006. 66:250–252.

24. Chen M, Ona VO, Li M, Ferrante RJ, Fink KB, Zhu S, et al. Minocycline inhibits caspase-1 and caspase-3 expression and delays mortality in a transgenic mouse model of Huntington disease. Nat Med. 2000. 6:797–801.

25. Bonelli RM, Hodl AK, Hofmann P, Kapfhammer HP. Neuroprotection in Huntington's disease: A 2-year study on minocycline. Int Clin Psychopharmacol. 2004. 19:337–342.

26. Keene CD, Rodrigues CM, Eich T, Chhabra MS, Steer CJ, Low WC. Tauroursodeoxycholic acid, a bile acid, is neuroprotective in a transgenic animal model of Huntington's disease. Proc Natl Acad Sci USA. 2002. 99:10671–10676.

27. Ravikumar B, Berger Z, Vacher C, O'Kane CJ, Rubinsztein DC. Rapamycin pre-treatment protects against apoptosis. Hum Mol Genet. 2006. 15:1209–1216.

28. Zuccato C, Ciammola A, Rigamonti D, Leavitt BR, Goffredo D, Conti L, et al. Loss of huntingtin-mediated bdnf gene transcription in Huntington's disease. Science. 2001. 293:493–498.

29. Popovic N, Maingay M, Kirik D, Brundin P. Lentiviral gene delivery of gdnf into the striatum of r6/2 Huntington mice fails to attenuate behavioral and neuropathological changes. Exp Neurol. 2005. 193:65–74.

30. Jin K, LaFevre-Bernt M, Sun Y, Chen S, Gafni J, Crippen D, et al. FGF-2 promotes neurogenesis and neuroprotection and prolongs survival in a transgenic mouse model of Huntington's disease. Proc Natl Acad Sci USA. 2005. 102:18189–18194.

31. Emerich DF, Thanos CG. Intracompartmental delivery of cntf as therapy for Huntington's disease and retinitis pigmentosa. Curr Gene Ther. 2006. 6:147–159.

32. Isacson O, Brundin P, Gage FH, Bjorklund A. Neural grafting in a rat model of Huntington's disease: Progressive neurochemical changes after neostriatal ibotenate lesions and striatal tissue grafting. Neuroscience. 1985. 16:799–817.

33. Bachoud-Levi AC, Gaura V, Brugieres P, Lefaucheur JP, Boisse MF, Maison P, et al. Effect of fetal neural transplants in patients with Huntington's disease 6 years after surgery: A long-term follow-up study. Lancet Neurol. 2006. 5:303–309.

34. Dunnett SB, Rosser AE. Cell therapy in Huntington's disease. NeuroRx. 2004. 1:394–405.

35. Lee ST, Chu K, Park JE, Lee K, Kang L, Kim SU, Kim M. Intravenous administration of human neural stem cells induces functional recovery in Huntington's disease rat model. Neurosci Res. 2005. 52:243–249.

36. DiFiglia M, Sapp E, Chase KO, Davies SW, Bates GP, Vonsattel JP, et al. Aggregation of huntingtin in neuronal intranuclear inclusions and dystrophic neurites in brain. Science. 1997. 277:1990–1993.

37. Perutz MF, Johnson T, Suzuki M, Finch JT. Glutamine repeats as polar zippers: Their possible role in inherited neurodegenerative diseases. Proc Natl Acad Sci USA. 1994. 91:5355–5358.

38. Hazeki N, Tsukamoto T, Yazawa I, Koyama M, Hattori S, Someki I, et al. Ultrastructure of nuclear aggregates formed by expressing an expanded polyglutamine. Biochem Biophys Res Commun. 2002. 294:429–440.

39. Gines S, Seong IS, Fossale E, Ivanova E, Trettel F, Gusella JF, et al. Specific progressive camp reduction implicates energy deficit in presymptomatic Huntington's disease knock-in mice. Hum Mol Genet. 2003. 12:497–508.

40. Cattaneo E, Rigamonti D, Goffredo D, Zuccato C, Squitieri F, Sipione S. Loss of normal huntingtin function: New developments in Huntington's disease research. Trends Neurosci. 2001. 24:182–188.

41. Kim M, Lee HS, LaForet G, McIntyre C, Martin EJ, Chang P. Mutant huntingtin expression in clonal striatal cells: Dissociation of inclusion formation and neuronal survival by caspase inhibition. J Neurosci. 1999. 19:964.

42. Graham RK, Deng Y, Slow EJ, Haigh B, Bissada N, Lu G, et al. Cleavage at the caspase-6 site is required for neuronal dysfunction and degeneration due to mutant huntingtin. Cell. 2006. 125:1179–1191.

43. Cariello L, de Cristofaro T, Zanetti L, Cuomo T, Di Maio L, Campanella G, et al. Transglutaminase activity is related to cag repeat length in patients with Huntington's disease. Hum Genet. 1996. 98:633–635.

44. Chun W, Lesort M, Tucholski J, Faber PW, MacDonald ME, Ross CA, et al. Tissue transglutaminase selectively modifies proteins associated with truncated mutant huntingtin in intact cells. Neurobiol Dis. 2001. 8:391–404.

45. Karpuj MV, Becher MW, Springer JE, Chabas D, Youssef S, Pedotti R, et al. Prolonged survival and decreased abnormal movements in transgenic model of Huntington disease, with administration of the transglutaminase inhibitor cystamine. Nat Med. 2002. 8:143–149.

46. Wang X, Sarkar A, Cicchetti F, Yu M, Zhu A, Jokivarsi K, et al. Cerebral pet imaging and histological evidence of transglutaminase inhibitor cystamine induced neuroprotection in transgenic r6/2 mouse model of Huntington's disease. J Neurol Sci. 2005. 231:57–66.

47. Zhang X, Smith DL, Meriin AB, Engemann S, Russel DE, Roark M, et al. A potent small molecule inhibits polyglutamine aggregation in Huntington's disease neurons and suppresses neurodegeneration in vivo. Proc Natl Acad Sci USA. 2005. 102:892–897.

48. Bodner RA, Outeiro TF, Altmann S, Maxwell MM, Cho SH, Hyman BT, et al. Pharmacological promotion of inclusion formation: A therapeutic approach for Huntington's and parkinson's diseases. Proc Natl Acad Sci USA. 2006. 103:4246–4251.

49. Heiser V, Engemann S, Brocker W, Dunkel I, Boeddrich A, Waelter S, et al. Identification of benzothiazoles as potential polyglutamine aggregation inhibitors of Huntington's disease by using an automated filter retardation assay. Proc Natl Acad Sci USA. 2002. 99:Suppl 4. 16400–16406.

50. Pollitt SK, Pallos J, Shao J, Desai UA, Ma AA, Thompson LM, et al. A rapid cellular fret assay of polyglutamine aggregation identifies a novel inhibitor. Neuron. 2003. 40:685–694.

51. Tanaka M, Machida Y, Niu S, Ikeda T, Jana NR, Doi H, et al. Trehalose alleviates polyglutamine-mediated pathology in a mouse model of Huntington disease. Nat Med. 2004. 10:148–154.

52. Sanchez I, Mahlke C, Yuan J. Pivotal role of oligomerization in expanded polyglutamine neurodegenerative disorders. Nature. 2003. 421:373–379.

53. Miller VM, Nelson RF, Gouvion CM, Williams A, Rodriguez-Lebron E, Harper SQ, et al. Chip suppresses polyglutamine aggregation and toxicity in vitro and in vivo. J Neurosci. 2005. 25:9152–9161.

54. Hockly E, Tse J, Barker AL, Moolman DL, Beunard JL, Revington AP, et al. Evaluation of the benzothiazole aggregation inhibitors riluzole and pgl-135 as therapeutics for Huntington's disease. Neurobiol Dis. 2006. 21:228–236.

55. Wang J, Gines S, MacDonald ME, Gusella JF. Reversal of a full-length mutant huntingtin neuronal cell phenotype by chemical inhibitors of polyglutamine-mediated aggregation. BMC Neurosci. 2005. 6:1–12.

56. Jana NR, Tanaka M, Wang G, Nukina N. Polyglutamine length-dependent interaction of hsp40 and hsp70 family chaperones with truncated n-terminal huntingtin: Their role in suppression of aggregation and cellular toxicity. Hum Mol Genet. 2000. 9:2009–2018.

57. Smith DF, Whitesell L, Nair SC, Chen S, Prapapanich V, Rimerman RA. Progesterone receptor structure and function altered by geldanamycin, an hsp90-binding agent. Mol Cell Biol. 1995. 15:6804–6812.

58. Sittler A, Lurz R, Lueder G, Priller J, Lehrach H, Hayer-Hartl MK, et al. Geldanamycin activates a heat shock response and inhibits huntingtin aggregation in a cell culture model of Huntington's disease. Hum Mol Genet. 2001. 10:1307–1315.

59. Hay DG, Sathasivam K, Tobaben S, Stahl B, Marber M, Mestril R, et al. Progressive decrease in chaperone protein levels in a mouse model of Huntington's disease and induction of stress proteins as a therapeutic approach. Hum Mol Genet. 2004. 13:1389–1405.

60. Gerber HP, Seipel K, Georgiev O, Hofferer M, Hug M, Rusconi S, et al. Transcriptional activation modulated by homopolymeric glutamine and proline stretches. Science. 1994. 263:808–811.

61. Okazawa H. Polyglutamine diseases: A transcription disorder? Cell Mol Life Sci. 2003. 60:1427–1439.

62. Cha JH. Transcriptional dysregulation in Huntington's disease. Trends Neurosci. 2000. 23:387–392.

63. Zhai W, Jeong H, Cui L, Krainc D, Tjian R. In vitro analysis of huntingtin-mediated transcriptional repression reveals multiple transcription factor targets. Cell. 2005. 123:1241–1253.

64. Steffan JS, Bodai L, Pallos J, Poelman M, McCampbell A, Apostol BL, et al. Histone deacetylase inhibitors arrest polyglutamine-dependent neurodegeneration in drosophila. Nature. 2001. 413:739–743.

65. Ferrante RJ, Kubilus JK, Lee J, Ryu H, Beesen A, Zucker B, et al. Histone deacetylase inhibition by sodium butyrate chemotherapy ameliorates the neurodegenerative phenotype in Huntington's disease mice. J Neurosci. 2003. 23:9418–9427.

66. Noda T, Ohsumi Y. Tor, a phosphatidylinositol kinase homologue, controls autophagy in yeast. J Biol Chem. 1998. 273:3963–3966.

67. Ravikumar B, Stewart A, Kita H, Kato K, Duden R, Rubinsztein DC. Raised intracellular glucose concentrations reduce aggregation and cell death caused by mutant huntingtin exon 1 by decreasing mtor phosphorylation and inducing autophagy. Hum Mol Genet. 2003. 12:985–994.

68. Ravikumar B, Vacher C, Berger Z, Davies JE, Luo S, Oroz LG, et al. Inhibition of mtor induces autophagy and reduces toxicity of polyglutamine expansions in fly and mouse models of Huntington disease. Nat Genet. 2004. 36:585–595.

69. Yamamoto A, Cremona ML, Rothman JE. Autophagy-mediated clearance of huntingtin aggregates triggered by the insulin-signaling pathway. J Cell Biol. 2006. 172:719–731.

70. Haque NS, Borghesani P, Isacson O. Therapeutic strategies for Huntington's disease based on a molecular understanding of the disorder. Mol Med Today. 1997. 3:175–183.

71. Yamamoto A, Lucas JJ, Hen R. Reversal of neuropathology and motor dysfunction in a conditional model of Huntington's disease. Cell. 2000. 101:57–66.

72. Boado RJ, Kazantsev A, Apostol BL, Thompson LM, Pardridge WM. Antisense-mediated down-regulation of the human huntingtin gene. J Pharmacol Exp Ther. 2000. 295:239–243.

73. Nellemann C, Abell K, Norremolle A, Lokkegaard T, Naver B, Ropke C, et al. Inhibition of Huntington synthesis by antisense oligodeoxynucleotides. Mol Cell Neurosci. 2000. 16:313–323.

74. Yen L, Strittmatter SM, Kalb RG. Sequence-specific cleavage of huntingtin mRNA by catalytic DNA. Ann Neurol. 1999. 46:366–373.

75. Fire A, Xu S, Montgomery MK, Kostas SA, Driver SE, Mello CC. Potent and specific genetic interference by double-stranded RNA in caenorhabditis elegans. Nature. 1998. 391:806–811.

76. Hannon GJ. RNA interference. Nature. 2002. 418:244–251.

77. Elbashir SM, Lendeckel W, Tuschl T. RNA interference is mediated by 21- and 22-nucleotide RNAs. Genes Dev. 2001. 15:188–200.

78. Elbashir SM, Harborth J, Lendeckel W, Yalcin A, Weber K, Tuschl T. Duplexes of 21-nucleotide RNAs mediate RNA interference in cultured mammalian cells. Nature. 2001. 411:494–498.

79. Liu WZ, Wang YL, Murata M, Wada K, Kanazawa I. Specific inhibition of Huntington's disease gene expression by siRNAs in cultured cells. Proc Japan Acad. 2003. 79:239–298.

80. Wang YL, Liu W, Wada E, Murata M, Wada K, Kanazawa I. Clinico-pathological rescue of a model mouse of Huntington's disease by siRNA. Neurosci Res. 2005. 53:241–249.

81. Harper SQ, Staber PD, He X, Eliason SL, Martins IH, Mao Q, et al. RNA interference improves motor and neuropathological abnormalities in a Huntington's disease mouse model. Proc Natl Acad Sci USA. 2005. 102:5820–5825.

82. Rodriguez-Lebron E, Denovan-Wright EM, Nash K, Lewin AS, Mandel RJ. Intrastriatal raav-mediated delivery of anti-huntingtin shRNAs induces partial reversal of disease progression in r6/1 Huntington's disease transgenic mice. Mol Ther. 2005. 12:618–633.

83. Machida Y, Okada T, Kurosawa M, Oyama F, Ozawa K, Nukina N. Raav-mediated shRNA ameliorated neuropathology in Huntington disease model mouse. Biochem Biophys Res Commun. 2006. 343:190–197.

84. Grimm D, Streetz KL, Jopling CL, Storm TA, Pandey K, Davis CR, et al. Fatality in mice due to oversaturation of cellular microRNA/short hairpin RNA pathways. Nature. 2006. 441:537–541.

85. Aronin N. Target selectivity in mRNA silencing. Gene Ther. 2006. 13:509–516.

86. Nguyen T, Hamby A, Massa SM. Clioquinol down-regulates mutant huntingtin expression in vitro and mitigates pathology in a Huntington's disease mouse model. Proc Natl Acad Sci USA. 2005. 102:11840–11845.