Biplob Dass

The role of α-synuclein in Parkinson's disease: insights from animal models

The abnormal accumulations of fibrillar α-synuclein in Lewy bodies and the mutations in the gene for α-synuclein in familial forms of Parkinsons disease have led to the belief that this protein has a central role in a group of neurodegenerative diseases known as the synucleinopathies. Our understanding of the biology of α-synuclein has increased significantly since its discovery in 1997, and recently developed animal models of the synucleinopathies have contributed to this understanding. The information gleaned from animal models has the potential to provide a framework for continuing the development of rational therapeutic strategies.

Delivery of neurturin by AAV2 (CERE‐120)‐mediated gene transfer provides structural and functional neuroprotection and neurorestoration in MPTP‐treated monkeys

We tested the hypothesis that gene delivery of the trophic factor neurturin could preserve motor function and protect nigrostriatal circuitry in hemiparkinsonian monkeys.

Striatal delivery of CERE‐120, an AAV2 vector encoding human neurturin, enhances activity of the dopaminergic nigrostriatal system in aged monkeys

Neurturin (NTN) is a potent survival factor for midbrain dopaminergic neurons. CERE‐120, an adeno‐associated virus type 2 (AAV2) vector encoding human NTN (AAV2‐NTN), is currently being developed as a potential therapy for Parkinsons disease. This study examined the bioactivity and safety/tolerability of AAV2‐NTN in the aged monkey model of nigrostriatal dopamine insufficiency. Aged rhesus monkeys received unilateral injections of AAV2‐NTN into the caudate and putamen, with each animal therefore serving as its own control. Robust expression of NTN within the nigrostriatal system was observed 8 months postadministration. 18F‐fluorodopa imaging using positron emission tomography revealed statistically significant increases in 18F‐fluorodopa uptake in the injected striatum compared with the uninjected side at 4 and 8 months. In addition, at 8 months postadministration, a significant enhancement in tyrosine hydroxylase immunoreactive fibers and an increase in the number of tyrosine hydroxylase immunoreactive cells was observed in the AAV2‐NTN injected striatum compared with the uninjected side. Robust activation of phosphorylated extracellular signal‐regulated kinase immunoreactivity in the substantia nigra was also observed. Histopathological analyses revealed no adverse effects of AAV2‐NTN in the brain. Collectively, these results are consistent with the neurotrophic effects of NTN on the dopaminergic nigrostriatal system and extend the growing body of evidence supporting the concept that AAV2‐NTN may have therapeutic benefit for Parkinsons disease.

Transgene Expression, Bioactivity, and Safety of CERE-120 (AAV2-Neurturin) Following Delivery to the Monkey Striatum

Neurturin (NTN) is a neurotrophic factor for dopaminergic neurons that may be therapeutic for patients with Parkinsons disease (PD). As a crucial component in a series of nonclinical translational studies aimed at testing whether CERE-120 should advance into clinical trials in PD subjects, we characterized the expression, bioactivity and safety of CERE-120, an adeno-associated virus type-2 (AAV2) vector encoding NTN, following delivery to the striatum of nonhuman primates. Monkeys received bilateral injections of CERE-120 across a tenfold range of doses (6 x 10(10) to 6 x 10(11) vector genomes per animal) or formulation buffer (FB) control. We report here, for the first time, a dose-related: increase in NTN protein expression within the striatum and substantia nigra (SN) pars compacta of nonhuman primates; increase in nigrostriatal tyrosine hydroxylase (TH), (the rate-limited enzyme for dopamine); and activation of phosphorylated signal-regulated kinase (a common neurotrophic signaling event). Additionally, extensive toxicology testing revealed no adverse effects of CERE-120 on in-life measures, neurotoxicity (in any site throughout the brain) or systemic pathology (in any organ or tissue) across the tenfold range of doses. Collectively, these data provide substantial novel evidence for the potential utility of CERE-120 as a novel treatment for PD and support ongoing clinical trials testing CERE-120 in PD patients.

Gene therapy approaches for the treatment of Parkinson's disease.

Publisher Summary Levodopa is considered gold-standard treatment by which all other therapies for the long-term treatment of PD patients are compared. Despite being an outstanding therapy, levodopa loses its usefulness because benefit is accompanied by debilitating side-effects that limit its utility. This chapter describes gene therapy approaches for the treatment of Parkinsons disease. When considering a gene therapy strategy to treat any human disease, there are two major unknowns that must be conquered. These are: (1) the safety of the gene transfer itself, and (2) the efficacy of the transgene product. Gene therapies can drive the dose of the therapeutic molecule by placing the vectors in site-specific loci and thus does not affect an unintended brain region that makes delivery of therapeutic genes superior to the delivery of pharmacological agents. For prodopaminergic gene therapy approaches, the postcommissural putamen are regarded the most critical site. Rigorous screening of patients must be conducted before the commencement of gene therapy. Some of the candidates for gene therapy in PD include trophic factors and dopamine-synthesizing enzymes. The transfection of trophic factors offer the greatest benefit, as it can prevent the progressive degeneration of the dopaminergic nigrostriatal system, while enhancing the function of surviving neurons.

947. Effects of Natural Pre-Existing Humoral Immunity to AAV on Administration of AAV2-NTN to the Brain of Non-Human Primates

The prevalence of antibodies (ab) to wild type AAV2 in humans is estimated to be 50-90%, with 30% developing neutralizing ab (Nab). In an attempt to mimic pre-existing immunity in animal models, many groups have immunized naive animals in order to study its effect on gene transfer. One limitation of this approach is that direct inoculation with high titers of AAV with adjuvant does not mimic the natural course of infection of the wild type virus. Therefore, the nature and intensity of the immune response may differ considerably from that generated by mucosal exposure. In addition, gene transfer is often attempted during the acute phase of the immune response. In contrast, human AAV2 seroconversion typically occurs in childhood, while AAV gene transfer is often performed in adults.