- Email: [email protected]
S.27.03 Neuroprotection therapies for Huntington's disease
S.27. Basal ganglia disease; Li~ing geues to ueuroprotee~ou
S.27. Basal ganglia disease: Linking genes to neuroproteetion ~
Neuroprotection therapies for Huntington's disease
E. Bmuillet, C. Jacquard, P liantraye. UR4 CEA-CNIRS 2210,
CEA, 5fgTd Department of Medical iResearc~, Orsay, France Huntington's disease (liD) is an inherited autoaomal dominant neurological disorder which is characterized by choreiform abnormal movements, cognitive deficits and psychiatric manifestations associated with progressive atrophy of the atriatum and cerebral cortex (Brouillet et ah, 1999). The mutation responsible for this disorder is an expansion of a polyglutamine (polyQ) stretch in the N-terminal part of a high molecular weight protein called huntingtin (htt). Cell death produced by mutated htt is likely due to a toxic gain-of-function, and, in addition, the possibility of an additive loss of function of normal htt has been demonstrated. How the "simple" expansion of the polyglutamine stretch in mutated htt can lead neurons to die is still unknown and there is no effective therapy to slow disease progression. Restorative strategies using the call transplantation approach showed promising results in Phase I clinical trials. However, the source of cells to be grafted is a major limitation. Current researches on stem celia may allow overcoming this difflcul W, We will focus our discussion on neuroprotective strategies which aim at slowing the progression of symptoms by inhibiting neuronal cell death mechanisms. As it is the case for the other neurodegenerative disorders, therapeutic targets for l i d are defined from the cellular mechanisms underlying neuron dysfunction and death. Since the cloning of htt, the number of cell pathways potentially involved in l i d has tremendously increased. In contrast, our understanding of the pathology remains limited and it is generally considered that HD pathogenesis involves complex-multifactorial mechanisrm affecting severn functions playing a key role in cell survival such as transcription, vesicle trafficking, Ca2+ homeostasis, energy metabolism and free radicals production. HD pathogenesis may be separated in two phases: 1) an upstream "initiation" phase where mutated htt (or a fragment of the protein) through a highly specific molecular mechanism produces a disruption of cellular homeostasis, and 2) an %xecution" phase where death pathways (possibly seen in other physiological and pathological conditions) such as excitotoxicit~/necrosis, apoptosis and/or autophagy would lead to cell demise. All the steps identified as important events in cell death cascade in HD constitute potential therapeutic targets to slow disease progression. For example, the neuroprotective strategy acting the most "upstream" in the cell death cascade consists in blocking the expression of mutated htt using selective "small interfering RNA" which could selectively bind rnRNAs of mutated htt, leading to their rapid degradation. This approach showed convincing results in cell culture model of liD. Abnormal transcription is probably a key "upstream" events underlying HID. There are several mechanisms associated with abnormal transcription in t-ID. Of therapeutic interest is the finding that inhibitors of histone deace~lase (acetylation of histones increase transcription) could improve the pathology in animal models of HD. These therapeutic strategies acting "upstream" are, at present experimental. Clinical trials concern molecules which are though to act more downstream is cell death cascade undelying HID. The detrimental role of glutamate, which possibly triggers excitotoxicity in liD, could be inhibited by selective pharmacological antagonists. Similarly, the potential therapeutic interest of molecules
$167
(scavengem) which decrease radical oxygen species (ROS) was strongly supported by studies in cultured ceils and animal models of HD. Creatine supplementation which improves brain energy metabolism also showed impressive neuroprotective effects in animals models of HD. Unfortunatdy, whereas these approaches provided encouraging results in models of HD, n o n e of the free radical scavengers, vitamins nor anti-glutamate molecules tested in large cohorts of patients were markedly efficacious. Recently, the potential neuroprotective effect of minocycline (a wall-known antibiotic) has been suggested in one transgenic modal of liD. Dased o n this encouraging results, and despite the fact that the underlying mechanisrm of minocycline were unclear, a clinical trial with minocycline in l i d was launched. In the meantime., the neuroprotective effects of minocycline in the transgenic models of I-]D was the subject of recent controversies. Another important research field deals with new methods to deliver potential neuroproteotive agents (such as siRNA, trophic factors, inhibitory peptides) to the living brain. One interesting approach is to use viral vectors which could, after intraoerebral injection, infect neurons or glial cells, allowing long term expression of a therapeutic transgene. Infection of the striatum using lentivirus encoding the trophic factors CNTF of DDNF provides neuroprotection in animal models of striatal degeneration. Another possibili~, is to use cells encapsulated into bio-compatible polymers and genetically engineered to express the trophio factors. Such strategy has been developed and tested in a non-human primate model of HD and is currently studied in a Phase I clinical trial (Bachoud-Levi et al., 2000). At present, research efforts focus on developing high through put methods for the screening of compound libraries. Screening is made in cultured cells expressing the human mutant htt. Candidate drugs are also rapidly evaluated using transgenic models developed in worms or flies. The best candidates (leads) are tested in transgenic mouse mode.is of HD. These high through put methods represent an important hope for the rapid discovery of new efficient drugs. In addition, these methods can also provide new insights into the molecular mechanisms involved in liD (Pollitt et al., 2003). Although pharmacology and molecular biology provided promising results, research efforts are still required to improve the cultured cell and animal models of HI). The "relevance" of the experimental HD models to can be in certain case debated. We have to keep in mind that there is a huge gap in terms of physiology between the mouse and human brain. Genetic models in larger animals may be necessary for the %cale up" of news therapeutic strategies before launching clinical trials.
References Baohoud-Levi AC, Deglon N, Nguyen JP, Blooh J, Bourdet C, Winkel L, R~'ny P, Goddard M, Lefau&enr JP, Brugieres i>, Baudio S, Cesaro P, Pesohanski M~ Aebis&er i:: Neuroproteotlve gone therapy for Huntington's disease using a polymer encapsulated BHK cell line engineered to secrete human CNTE Hum Gone Thor. 2000, 11:1723-9. Brouillet E~Cond6 F, Beal M~ Hantraye R Replicating Huntington's disease in experimental animals. Prog Neurobiol 1999; 59:427-458. Pollitt SK, Pallos J, Shao J, Desai UA, Ma AA, Thompson LM, Marsh JL, Diamond MI. A rapid cellular FREq-' assay ofpolyghtamine aggregation identifies a novel inhibitor. Neuron. 2003, 40:685-94.
•
Genetic aetiopathogenesis of Parkinson's disease
Y, Mizuno, 3-unte~do U~ioerso~ ScAoo[ of Medicine, Neurology,
Tokyo, Japan Parkinson's disease (PD) is pathologically characterized by neurodegeneration of dopamine containing neurons in the substan-
S.27. Basal ganglia disease: Linking genes to neuroproteetion ~
Neuroprotection therapies for Huntington's disease
E. Bmuillet, C. Jacquard, P liantraye. UR4 CEA-CNIRS 2210,
CEA, 5fgTd Department of Medical iResearc~, Orsay, France Huntington's disease (liD) is an inherited autoaomal dominant neurological disorder which is characterized by choreiform abnormal movements, cognitive deficits and psychiatric manifestations associated with progressive atrophy of the atriatum and cerebral cortex (Brouillet et ah, 1999). The mutation responsible for this disorder is an expansion of a polyglutamine (polyQ) stretch in the N-terminal part of a high molecular weight protein called huntingtin (htt). Cell death produced by mutated htt is likely due to a toxic gain-of-function, and, in addition, the possibility of an additive loss of function of normal htt has been demonstrated. How the "simple" expansion of the polyglutamine stretch in mutated htt can lead neurons to die is still unknown and there is no effective therapy to slow disease progression. Restorative strategies using the call transplantation approach showed promising results in Phase I clinical trials. However, the source of cells to be grafted is a major limitation. Current researches on stem celia may allow overcoming this difflcul W, We will focus our discussion on neuroprotective strategies which aim at slowing the progression of symptoms by inhibiting neuronal cell death mechanisms. As it is the case for the other neurodegenerative disorders, therapeutic targets for l i d are defined from the cellular mechanisms underlying neuron dysfunction and death. Since the cloning of htt, the number of cell pathways potentially involved in l i d has tremendously increased. In contrast, our understanding of the pathology remains limited and it is generally considered that HD pathogenesis involves complex-multifactorial mechanisrm affecting severn functions playing a key role in cell survival such as transcription, vesicle trafficking, Ca2+ homeostasis, energy metabolism and free radicals production. HD pathogenesis may be separated in two phases: 1) an upstream "initiation" phase where mutated htt (or a fragment of the protein) through a highly specific molecular mechanism produces a disruption of cellular homeostasis, and 2) an %xecution" phase where death pathways (possibly seen in other physiological and pathological conditions) such as excitotoxicit~/necrosis, apoptosis and/or autophagy would lead to cell demise. All the steps identified as important events in cell death cascade in HD constitute potential therapeutic targets to slow disease progression. For example, the neuroprotective strategy acting the most "upstream" in the cell death cascade consists in blocking the expression of mutated htt using selective "small interfering RNA" which could selectively bind rnRNAs of mutated htt, leading to their rapid degradation. This approach showed convincing results in cell culture model of liD. Abnormal transcription is probably a key "upstream" events underlying HID. There are several mechanisms associated with abnormal transcription in t-ID. Of therapeutic interest is the finding that inhibitors of histone deace~lase (acetylation of histones increase transcription) could improve the pathology in animal models of HD. These therapeutic strategies acting "upstream" are, at present experimental. Clinical trials concern molecules which are though to act more downstream is cell death cascade undelying HID. The detrimental role of glutamate, which possibly triggers excitotoxicity in liD, could be inhibited by selective pharmacological antagonists. Similarly, the potential therapeutic interest of molecules
$167
(scavengem) which decrease radical oxygen species (ROS) was strongly supported by studies in cultured ceils and animal models of HD. Creatine supplementation which improves brain energy metabolism also showed impressive neuroprotective effects in animals models of HD. Unfortunatdy, whereas these approaches provided encouraging results in models of HD, n o n e of the free radical scavengers, vitamins nor anti-glutamate molecules tested in large cohorts of patients were markedly efficacious. Recently, the potential neuroprotective effect of minocycline (a wall-known antibiotic) has been suggested in one transgenic modal of liD. Dased o n this encouraging results, and despite the fact that the underlying mechanisrm of minocycline were unclear, a clinical trial with minocycline in l i d was launched. In the meantime., the neuroprotective effects of minocycline in the transgenic models of I-]D was the subject of recent controversies. Another important research field deals with new methods to deliver potential neuroproteotive agents (such as siRNA, trophic factors, inhibitory peptides) to the living brain. One interesting approach is to use viral vectors which could, after intraoerebral injection, infect neurons or glial cells, allowing long term expression of a therapeutic transgene. Infection of the striatum using lentivirus encoding the trophic factors CNTF of DDNF provides neuroprotection in animal models of striatal degeneration. Another possibili~, is to use cells encapsulated into bio-compatible polymers and genetically engineered to express the trophio factors. Such strategy has been developed and tested in a non-human primate model of HD and is currently studied in a Phase I clinical trial (Bachoud-Levi et al., 2000). At present, research efforts focus on developing high through put methods for the screening of compound libraries. Screening is made in cultured cells expressing the human mutant htt. Candidate drugs are also rapidly evaluated using transgenic models developed in worms or flies. The best candidates (leads) are tested in transgenic mouse mode.is of HD. These high through put methods represent an important hope for the rapid discovery of new efficient drugs. In addition, these methods can also provide new insights into the molecular mechanisms involved in liD (Pollitt et al., 2003). Although pharmacology and molecular biology provided promising results, research efforts are still required to improve the cultured cell and animal models of HI). The "relevance" of the experimental HD models to can be in certain case debated. We have to keep in mind that there is a huge gap in terms of physiology between the mouse and human brain. Genetic models in larger animals may be necessary for the %cale up" of news therapeutic strategies before launching clinical trials.
References Baohoud-Levi AC, Deglon N, Nguyen JP, Blooh J, Bourdet C, Winkel L, R~'ny P, Goddard M, Lefau&enr JP, Brugieres i>, Baudio S, Cesaro P, Pesohanski M~ Aebis&er i:: Neuroproteotlve gone therapy for Huntington's disease using a polymer encapsulated BHK cell line engineered to secrete human CNTE Hum Gone Thor. 2000, 11:1723-9. Brouillet E~Cond6 F, Beal M~ Hantraye R Replicating Huntington's disease in experimental animals. Prog Neurobiol 1999; 59:427-458. Pollitt SK, Pallos J, Shao J, Desai UA, Ma AA, Thompson LM, Marsh JL, Diamond MI. A rapid cellular FREq-' assay ofpolyghtamine aggregation identifies a novel inhibitor. Neuron. 2003, 40:685-94.
•
Genetic aetiopathogenesis of Parkinson's disease
Y, Mizuno, 3-unte~do U~ioerso~ ScAoo[ of Medicine, Neurology,
Tokyo, Japan Parkinson's disease (PD) is pathologically characterized by neurodegeneration of dopamine containing neurons in the substan-