Dopamine gene therapy for Parkinson's disease in a nonhuman primate without associated dyskinesia.

In Parkinson's disease, degeneration of specific neurons in the midbrain can cause severe motor deficits, including tremors and the inability to initiate movement. The standard treatment is administration of pharmacological agents that transiently increase concentrations of brain dopamine and thereby discontinuously modulate neuronal activity in the striatum, the primary target of dopaminergic neurons. The resulting intermittent dopamine alleviates parkinsonian symptoms but is also thought to cause abnormal involuntary movements, called dyskinesias. To investigate gene therapy for Parkinson's disease, we simulated the disease in macaque monkeys by treating them with the complex I mitochondrial inhibitor 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, which induces selective degeneration of dopamine-producing neurons. In this model, we demonstrated that injection of a tricistronic lentiviral vector encoding the critical genes for dopamine synthesis (tyrosine hydroxylase, aromatic L-amino acid decarboxylase, and guanosine 5'-triphosphate cyclohydrolase 1) into the striatum safely restored extracellular concentrations of dopamine and corrected the motor deficits for 12 months without associated dyskinesias. Gene therapy-mediated dopamine replacement may be able to correct Parkinsonism in patients without the complications of dyskinesias.

Silencing mutant SOD1 using RNAi protects against neurodegeneration and extends survival in an ALS model.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease resulting in the selective death of motor neurons in the brain and spinal cord. Some familial cases of ALS are caused by dominant mutations in the gene encoding superoxide dismutase (SOD1). The emergence of interfering RNA (RNAi) for specific gene silencing could be therapeutically beneficial for the treatment of such dominantly inherited diseases. We generated a lentiviral vector to mediate expression of RNAi molecules specifically targeting the human SOD1 gene (SOD1). Injection of this vector into various muscle groups of mice engineered to overexpress a mutated form of human SOD1 (SOD1(G93A)) resulted in an efficient and specific reduction of SOD1 expression and improved survival of vulnerable motor neurons in the brainstem and spinal cord. Furthermore, SOD1 silencing mediated an improved motor performance in these animals, resulting in a considerable delay in the onset of ALS symptoms by more than 100% and an extension in survival by nearly 80% of their normal life span. These data are the first to show a substantial extension of survival in an animal model of a fatal, dominantly inherited neurodegenerative condition using RNAi and provide the highest therapeutic efficacy observed in this field to date.