Properly scaled and targeted AAV2-NRTN (neurturin) to the substantia nigra is safe, effective and causes no weight loss: support for nigral targeting in Parkinson's disease

The Role of Striatal Cav1.3 Calcium Channels in Therapeutics for Parkinson's Disease

Parkinson's disease (PD) is a relentlessly progressive neurodegenerative disorder with typical motor symptoms that include rigidity, tremor, and akinesia/bradykinesia, in addition to a host of non-motor symptoms. Motor symptoms are caused by progressive and selective degeneration of dopamine (DA) neurons in the SN pars compacta (SNpc) and the accompanying loss of striatal DA innervation from these neurons. With the exception of monogenic forms of PD, the etiology of idiopathic PD remains unknown. While there are a number of symptomatic treatment options available to individuals with PD, these therapies do not work uniformly well in all patients, and eventually most are plagued with waning efficacy and significant side-effect liability with disease progression. The incidence of PD increases with aging, and as such the expected burden of this disease will continue to escalate as our aging population increases (Dorsey et al. Neurology 68:384-386, 2007). The daunting personal and socioeconomic burden has pressed scientists and clinicians to find improved symptomatic treatment options devoid side-effect liability and meaningful disease-modifying therapies. Federal and private sources have supported clinical investigations over the past two-plus decades; however, no trial has yet been successful in finding an effective therapy to slow progression of PD, and there is currently just one FDA approved drug to treat the antiparkinsonian side-effect known as levodopa-induced dyskinesia (LID) that impacts approximately 90% of all individuals with PD. In this review, we present biological rationale and experimental evidence on the potential therapeutic role of the L-type voltage-gated Cav1.3 calcium (Ca2+) channels in two distinct brain regions, with two distinct mechanisms of action, in impacting the lives of individuals with PD. Our primary emphasis will be on the role of Cav1.3 channels in the striatum and the compelling evidence of their involvement in LID side-effect liability. We also briefly discuss the role of these same Ca2+ channels in the SNpc and the longstanding interest in Cav1.3 in this brain region in halting or delaying progression of PD.

Gene Therapy Approach with an Emphasis on Growth Factors: Theoretical and Clinical Outcomes in Neurodegenerative Diseases

The etiology of many neurological diseases affecting the central nervous system (CNS) is unknown and still needs more effective and specific therapeutic approaches. Gene therapy has a promising future in treating neurodegenerative disorders by correcting the genetic defects or by therapeutic protein delivery and is now an attraction for neurologists to treat brain disorders, like Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, spinal muscular atrophy, spinocerebellar ataxia, epilepsy, Huntington's disease, stroke, and spinal cord injury. Gene therapy allows the transgene induction, with a unique expression in cells' substrate. This article mainly focuses on the delivering modes of genetic materials in the CNS, which includes viral and non-viral vectors and their application in gene therapy. Despite the many clinical trials conducted so far, data have shown disappointing outcomes. The efforts done to improve outcomes, efficacy, and safety in the identification of targets in various neurological disorders are also discussed here. Adapting gene therapy as a new therapeutic approach for treating neurological disorders seems to be promising, with early detection and delivery of therapy before the neuron is lost, helping a lot the development of new therapeutic options to translate to the clinic.

Adeno-Associated Viral Vectors as Versatile Tools for Parkinson's Research, Both for Disease Modeling Purposes and for Therapeutic Uses

It is without any doubt that precision medicine therapeutic strategies targeting neurodegenerative disorders are currently witnessing the spectacular rise of newly designed approaches based on the use of viral vectors as Trojan horses for the controlled release of a given genetic payload. Among the different types of viral vectors, adeno-associated viruses (AAVs) rank as the ones most commonly used for the purposes of either disease modeling or for therapeutic strategies. Here, we reviewed the current literature dealing with the use of AAVs within the field of Parkinson’s disease with the aim to provide neuroscientists with the advice and background required when facing a choice on which AAV might be best suited for addressing a given experimental challenge. Accordingly, here we will be summarizing some insights on different AAV serotypes, and which would be the most appropriate AAV delivery route. Next, the use of AAVs for modeling synucleinopathies is highlighted, providing potential readers with a landscape view of ongoing pre-clinical and clinical initiatives pushing forward AAV-based therapeutic approaches for Parkinson’s disease and related synucleinopathies.

Long-term post-mortem studies following neurturin gene therapy in patients with advanced Parkinson's disease

We performed post-mortem studies on two patients with advanced Parkinson’s disease 8 and10 years following AAV2-neurturin (CERE120) gene therapy, the longest post-mortem trophic factor gene therapy cases reported to date. CERE120 was delivered to the putamen bilaterally in one case (10 years post-surgery), and to the putamen plus the substantia nigra bilaterally in the second (8 years post-surgery). In both patients there was persistent, albeit limited, neurturin expression in the putamen covering ∼3–12% of the putamen. In the putamen, dense staining of tyrosine hydroxylase-positive fibres was observed in areas that contained detectable neurturin expression. In the substantia nigra, neurturin expression was detected in 9.8–18.95% and 22.02–39% of remaining melanin-containing neurons in the patient with putamenal and combined putamenal and nigral gene delivery, respectively. Melanized neurons displayed intense tyrosine hydroxylase and RET proto-oncogene expression in nigral neurons in the patient where CERE120 was directly delivered to the nigra. There was no difference in the degree of Lewy pathology in comparison to untreated control patients with Parkinson’s disease, and α-synuclein aggregates were detected in neurons that also stained for neurturin, RET, and tyrosine hydroxylase. These changes were not associated with antiparkinsonian benefits likely due to the limited neurturin expression. This study provides the longest term evidence of persistent transgene expression following gene delivery to the CNS and the first human results when targeting both the terminal fields in the putamen as well as the originating nigral neurons.

Gene Therapy for Parkinson's Disease, An Update

The current mainstay treatment of Parkinson's disease (PD) consists of dopamine replacement therapy which, in addition to causing several side effects, does not delay disease progression. The field of gene therapy offers a potential means to improve current therapy. The present review gives an update of the present status of gene therapy for PD. Both non-disease and disease modifying transgenes have been tested for PD gene therapy in animal and human studies. Non-disease modifying treatments targeting dopamine or GABA synthesis have been successful and promising at improving PD symptomatology in randomized clinical studies, but substantial testing remains before these can be implemented in the standard clinical treatment repertoire. As for disease modifying targets that theoretically offer the possibility of slowing the progression of disease, several neurotrophic factors show encouraging results in preclinical models (e.g., neurturin, GDNF, BDNF, CDNF, VEGF-A). However, so far, clinical trials have only tested neurturin, and, unfortunately, no trial has been able to meet its primary endpoint. Future clinical trials with neurotrophic factors clearly deserve to be conducted, considering the still enticing goal of actually slowing the disease process of PD. As alternative types of gene therapy, opto- and chemogenetics might also find future use in PD treatment and novel genome-editing technology could also potentially be applied as individualized gene therapy for genetic types of PD.

Continuous intranigral infusion is not associated with observable behavioral deficits or marked pathology: a preclinical safety study

OBJECTIVE

A better understanding of the effects of chronically delivering compounds to the substantia nigra and nearby areas is important for the development of new therapeutic approaches to treat alpha-synucleinopathies, like Parkinson's disease. Whether chronic intranigral delivery of an infusate could be achieved without causing motor dysfunction or marked pathology remains unclear. The authors evaluated the tolerability of continuously delivering an infusate directly into the rhesus monkey substantia nigra via a programmable pump coupled to a novel intraparenchymal needle-tip catheter surgically implanted using MRI-guided techniques.

METHODS

The MRI contrast agent gadopentetate dimeglumine (Magnevist, 5 mM) was used to noninvasively evaluate catheter patency and infusion volume associated with 2 flow rates sequentially tested in each of 3 animals: 0.1 µl/min for 14 days into the right substantia nigra and 0.1 µl/min for 7 days plus 0.2 µl/min for an additional 7 days into the left substantia nigra. Flow rate tolerability was assessed via clinical observations and a microscopic examination of the striatum and midbrain regions.

RESULTS

Evaluation of postsurgical MRI indicated that all 6 catheters remained patent throughout the study and that the volume of distribution achieved in the left midbrain region at a rate of up to 0.2 µl/min (2052 ± 168 mm3) was greater than that achieved in the right midbrain region at a constant rate of 0.1 µl/min (1225 ± 273 mm3) by nearly 2-fold. Both flow rates provided sufficient infusate coverage of the rhesus (and possibly the human) midbrain region. There were no indications of observable deficits in behavior. Histopathological evaluations confirmed that all catheter tips were placed in or near the pars compacta region of the substantia nigra in all animals. There was no evidence of infection at any of the 6 catheter sites. Mild to moderate microglial reactions were observed at most catheter track sites and were comparable between the 2 infusion rates. Finally, there was neither observable decrease of tyrosine hydroxylase staining in the striatum nor detectable necrosis of neurons in the pars compacta region of the substantia nigra in any of the animals.

CONCLUSIONS

The data from this study support the feasibility of using a pump-and-catheter system for chronic intranigral infusion and lay the foundation for using this approach to treat Parkinson's disease or other related degenerative diseases that would benefit from targeted drug delivery to the substantia nigra or to other brainstem regions.

Targeting bone morphogenetic protein signalling in midbrain dopaminergic neurons as a therapeutic approach in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease, characterized by the degeneration of midbrain dopaminergic (mDA) neurons and their axons, and aggregation of α-synuclein, which leads to motor and late-stage cognitive impairments. As the motor symptoms of PD are caused by the degeneration of a specific population of mDA neurons, PD lends itself to neurotrophic factor therapy. The goal of this therapy is to apply a neurotrophic factor that can slow down, halt or even reverse the progressive degeneration of mDA neurons. While the best known neurotrophic factors are members of the glial cell line-derived neurotrophic factor (GDNF) family, their lack of clinical efficacy to date means that it is important to continue to study other neurotrophic factors. Bone morphogenetic proteins (BMPs) are naturally secreted proteins that play critical roles during nervous system development and in the adult brain. In this review, we provide an overview of the BMP ligands, BMP receptors (BMPRs) and their intracellular signalling effectors, the Smad proteins. We review the available evidence that BMP-Smad signalling pathways play an endogenous role in mDA neuronal survival in vivo, before outlining how exogenous application of BMPs exerts potent effects on mDA neuron survival and axon growth in vitro and in vivo. We discuss the molecular mechanisms that mediate these effects, before highlighting the potential of targeting the downstream effectors of BMP-Smad signalling as a novel neuroprotective approach to slow or stop the degeneration of mDA neurons in PD.

AAV Vector-Mediated Gene Delivery to Substantia Nigra Dopamine Neurons: Implications for Gene Therapy and Disease Models

Gene delivery using adeno-associated virus (AAV) vectors is a widely used method to transduce neurons in the brain, especially due to its safety, efficacy, and long-lasting expression. In addition, by varying AAV serotype, promotor, and titer, it is possible to affect the cell specificity of expression or the expression levels of the protein of interest. Dopamine neurons in the substantia nigra projecting to the striatum, comprising the nigrostriatal pathway, are involved in movement control and degenerate in Parkinson’s disease. AAV-based gene targeting to the projection area of these neurons in the striatum has been studied extensively to induce the production of neurotrophic factors for disease-modifying therapies for Parkinson’s disease. Much less emphasis has been put on AAV-based gene therapy targeting dopamine neurons in substantia nigra. We will review the literature related to targeting striatum and/or substantia nigra dopamine neurons using AAVs in order to express neuroprotective and neurorestorative molecules, as well as produce animal disease models of Parkinson’s disease. We discuss difficulties in targeting substantia nigra dopamine neurons and their vulnerability to stress in general. Therefore, choosing a proper control for experimental work is not trivial. Since the axons along the nigrostriatal tract are the first to degenerate in Parkinson’s disease, the location to deliver the therapy must be carefully considered. We also review studies using AAV-α-synuclein (α-syn) to target substantia nigra dopamine neurons to produce an α-syn overexpression disease model in rats. Though these studies are able to produce mild dopamine system degeneration in the striatum and substantia nigra and some behavioural effects, there are studies pointing to the toxicity of AAV-carrying green fluorescent protein (GFP), which is often used as a control. Therefore, we discuss the potential difficulties in overexpressing proteins in general in the substantia nigra.

Trophic factors for Parkinson's disease: To live or let die

Trophic factors show great promise in laboratory studies as potential therapies for PD. However, multiple double-blind, clinical trials have failed to show benefits in comparison to a placebo control. This article will review the scientific rationale for testing trophic factors in PD, the results of the different clinical trials that have been performed to date, and the possible explanations for these failed outcomes. We will also consider future directions and the likelihood that trophic factors will become a viable therapy for patients with PD.

Applications of CRISPR/Cas9 for Gene Editing in Hereditary Movement Disorders

Gene therapy is a potential therapeutic strategy for treating hereditary movement disorders, including hereditary ataxia, dystonia, Huntington’s disease, and Parkinson’s disease. Genome editing is a type of genetic engineering in which DNA is inserted, deleted or replaced in the genome using modified nucleases. Recently, clustered regularly interspaced short palindromic repeat/CRISPR associated protein 9 (CRISPR/Cas9) has been used as an essential tool in biotechnology. Cas9 is an RNA-guided DNA endonuclease enzyme that was originally associated with the adaptive immune system of Streptococcus pyogenes and is now being utilized as a genome editing tool to induce double strand breaks in DNA. CRISPR/Cas9 has advantages in terms of clinical applicability over other genome editing technologies such as zinc-finger nucleases and transcription activator-like effector nucleases because of easy in vivo delivery. Here, we review and discuss the applicability of CRISPR/Cas9 to preclinical studies or gene therapy in hereditary movement disorders.

Clinical tests of neurotrophic factors for human neurodegenerative diseases, part 1: Where have we been and what have we learned?

Over the past 25years, about 3 dozen clinical reports have been published regarding the safety and possible efficacy of neurotrophic factors in patients with various neurodegenerative diseases. This effort involved a half dozen different neurotrophic factors, using at least 5 different general delivery approaches for ALS (amyolateral sclerosis), peripheral neuropathies, PD (Parkinson's disease) and AD (Alzheimer's disease). While none of these efforts have yet produced efficacy data sufficiently robust or reliable to establish neurotrophic factors as treatments for any human disease, the obstacles encountered and novel information reported, when viewed collectively, provide important insight to help future efforts. Three consistent themes emerge from these publications: (1) unexpected and undesirable side effects, at times serious, have plagued many efforts to deliver neurotrophic factors to humans; (2) the magnitude and consistency of clinical benefit has been disappointing; (3) by far that most consistently proposed reason for the side effects and poor efficacy has been inadequate dosing and delivery. This paper reviews and attempts to synthesize the available data derived from clinical tests of neurotrophic factors for neurodegenerative diseases. The obstacles encountered, the solutions attempted, and the lessons learned are discussed. The vast majority of solutions have involved changes in dosing paradigms and dose levels, which has primarily led to improved safety outcomes. However, lack of adequate efficacy remains a significant issue. While current efforts continue to focus exclusively on still-further changes in dosing parameters, a review of available data argues that it may now be the time to ask whether other, non-dose-related variables should be given more serious consideration as being responsible for the great divide that exists between the robust effects seen in animal models and the relatively weak effects seen in human neurodegenerative patients. Foremost among these appears to be the severe degeneration seen in the majority of patients enrolled in past and current trials testing neurotrophic factors in humans. A companion paper (Bartus and Johnson, 2016), reviews the contemporary data and concludes that compelling empirical evidence already exists for enrolling earlier-stage subjects as likely essential to achieving more robust and reliable benefit.

Neurotrophic Factors and Their Potential Applications in Tissue Regeneration

Neurotrophic factors are growth factors that can nourish neurons and promote neuron survival and regeneration. They have been studied as potential drug candidates for treating neurodegenerative diseases. Since their identification, there are more and more evidences to indicate that neurotrophic factors are also expressed in non-neuronal tissues and regulate the survival, anti-inflammation, proliferation and differentiation in these tissues. This mini review summarizes the characteristics of the neurotrophic factors and their potential clinical applications in the regeneration of neuronal and non-neuronal tissues.

Intranasal gene delivery for treating Parkinson's disease: overcoming the blood-brain barrier

INTRODUCTION

Developing a disease-modifying gene therapy for Parkinson's disease (PD) has been a high priority for over a decade. However, due to the inability of large biomolecules to cross the blood-brain barrier (BBB), the only means of delivery to the brain has been intracerebral infusion. Intranasal administration offers a non-surgical means of bypassing the BBB to deliver neurotrophic factors, and the genes encoding them, directly to the brain.

AREAS COVERED

This review summarizes: i) evidence demonstrating intranasal delivery to the brain of a number of biomolecules having therapeutic potential for various CNS disorders; and ii) evidence demonstrating neuroprotective efficacy of a subset of biomolecules specifically for PD. The intersection of these two spheres represents the area of opportunity for development of new intranasal gene therapies for PD. To that end, our laboratory showed that intranasal administration of glial cell line-derived neurotrophic factor (GDNF), or plasmid DNA nanoparticles encoding GDNF, provides neuroprotection in a rat model of PD, and that the cells transfected by the nanoparticle vector are likely to be pericytes.

EXPERT OPINION

A number of genes encoding neurotrophic factors have therapeutic potential for PD, but few have been tested by the intranasal route and shown to be neuroprotective in a model of PD. Intranasal delivery provides a largely unexplored, promising approach for development of a non-invasive gene therapy for PD.

Neurotensin-polyplex-mediated brain-derived neurotrophic factor gene delivery into nigral dopamine neurons prevents nigrostriatal degeneration in a rat model of early Parkinson's disease

Background

The neurotrophin Brain-Derived Neurotrophic Factor (BDNF) influences nigral dopaminergic neurons via autocrine and paracrine mechanisms. The reduction of BDNF expression in Parkinson’s disease substantia nigra (SN) might contribute to the death of dopaminergic neurons because inhibiting BDNF expression in the SN causes parkinsonism in the rat. This study aimed to demonstrate that increasing BDNF expression in dopaminergic neurons of rats with one week of 6-hydroxydopamine lesion recovers from parkinsonism. The plasmids phDAT-BDNF-flag and phDAT-EGFP, coding for enhanced green fluorescent protein, were transfected using neurotensin (NTS)-polyplex, which enables delivery of genes into the dopaminergic neurons via neurotensin-receptor type 1 (NTSR1) internalization.

Results

Two weeks after transfections, RT-PCR and immunofluorescence techniques showed that the residual dopaminergic neurons retain NTSR1 expression and susceptibility to be transfected by the NTS-polyplex. phDAT-BDNF-flag transfection did not increase dopaminergic neurons, but caused 7-fold increase in dopamine fibers within the SN and 5-fold increase in innervation and dopamine levels in the striatum. These neurotrophic effects were accompanied by a significant improvement in motor behavior.

Conclusions

NTS-polyplex-mediated BDNF overexpression in dopaminergic neurons has proven to be effective to remit hemiparkinsonism in the rat. This BDNF gene therapy might be helpful in the early stage of Parkinson’s disease.

Gene therapy for neurodegenerative diseases

Gene therapy is, potentially, a powerful tool for treating neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), spinal muscular atrophy, Parkinson's disease (PD) and Alzheimer's disease (AD). To date, clinical trials have failed to show any improvement in outcome beyond the placebo effect. Efforts to improve outcomes are focusing on three main areas: vector design and the identification of new vector serotypes, mode of delivery of gene therapies, and identification of new therapeutic targets. These advances are being tested both individually and together to improve efficacy. These improvements may finally make gene therapy successful for these disorders.

Gene delivery of neurturin to putamen and substantia nigra in Parkinson disease: A double-blind, randomized, controlled trial

OBJECTIVE

A 12-month double-blind sham-surgery-controlled trial assessing adeno-associated virus type 2 (AAV2)-neurturin injected into the putamen bilaterally failed to meet its primary endpoint, but showed positive results for the primary endpoint in the subgroup of subjects followed for 18 months and for several secondary endpoints. Analysis of postmortem tissue suggested impaired axonal transport of neurturin from putamen to substantia nigra. In the present study, we tested the safety and efficacy of AAV2-neurturin delivered to putamen and substantia nigra.

METHODS

We performed a 15- to 24-month, multicenter, double-blind trial in patients with advanced Parkinson disease (PD) who were randomly assigned to receive bilateral AAV2-neurturin injected bilaterally into the substantia nigra (2.0 × 10(11) vector genomes) and putamen (1.0 × 10(12) vector genomes) or sham surgery. The primary endpoint was change from baseline to final visit performed at the time the last enrolled subject completed the 15-month evaluation in the motor subscore of the Unified Parkinson's Disease Rating Scale in the practically defined off state.

RESULTS

Fifty-one patients were enrolled in the trial. There was no significant difference between groups in the primary endpoint (change from baseline: AAV2-neurturin, -7.0 ± 9.92; sham, -5.2 ± 10.01; p = 0.515) or in most secondary endpoints. Two subjects had cerebral hemorrhages with transient symptoms. No clinically meaningful adverse events were attributed to AAV2-neurturin.

INTERPRETATION

AAV2-neurturin delivery to the putamen and substantia nigra bilaterally in PD was not superior to sham surgery. The procedure was well tolerated, and there were no clinically significant adverse events related to AAV2-neurturin.

Viral vector delivery of neurotrophic factors for Parkinson's disease therapy

Parkinson's disease (PD) is a neurodegenerative disorder characterised by the progressive loss of midbrain dopaminergic neurons, which causes motor impairments. Current treatments involve dopamine replacement to address the disease symptoms rather than its cause. Factors that promote the survival of dopaminergic neurons have been proposed as novel therapies for PD. Several dopaminergic neurotrophic factors (NTFs) have been examined for their ability to protect and/or restore degenerating dopaminergic neurons, both in animal models and in clinical trials. These include glial cell line-derived neurotrophic factor, neurturin, cerebral dopamine neurotrophic factor and growth/differentiation factor 5. Delivery of these NTFs via injection or infusion to the brain raises several practical problems. A new delivery approach for NTFs involves the use of recombinant viral vectors to enable long-term expression of these factors in brain cells. Vectors used include those based on adenoviruses, adeno-associated viruses and lentiviruses. Here we review progress to date on the potential of each of these four NTFs as novel therapeutic strategies for PD, as well as the challenges that have arisen, from pre-clinical analysis to clinical trials. We conclude by discussing recently-developed approaches to optimise the delivery of NTF-carrying viral vectors to the brain.

Gene transfer provides a practical means for safe, long-term, targeted delivery of biologically active neurotrophic factor proteins for neurodegenerative diseases

Efforts to develop neurotrophic factors to restore function and protect dying neurons in chronic neurodegenerative diseases like Alzheimer's (AD) and Parkinson's (PD) have been attempted for decades. Despite abundant data establishing nonclinical proof-of-concept, significant delivery issues have precluded the successful translation of this concept to the clinic. The development of AAV2 viral vectors to deliver therapeutic genes has emerged as a safe and effective means to achieve sustained, long-term, targeted, bioactive protein expression. Thus, it potentially offers a practical means to solve those long-standing delivery/translational issues associated with neurotrophic factors. Data are presented for two AAV2 viral vector constructs expressing one of two different neurotrophic factors: nerve growth factor (NGF) and neurturin (NRTN). One (AAV2-NGF; aka CERE-110) is being developed as a treatment to improve the function and delay further degeneration of cholinergic neurons in the nucleus basalis of Meynert, the degeneration of which has been linked to cognitive deficits in AD. The other (AAV2-NRTN; aka CERE-120) is similarly being developed to treat the degenerating nigrostriatal dopamine neurons and major motor deficits in PD. The data presented here demonstrate: (1) 2-year, targeted, bioactive-protein in monkeys, (2) persistent, bioactive-protein throughout the life-span of the rat, and (3) accurately targeted bioactive-protein in aged rats, with (4) no safety issues or antibodies to the protein detected. They also provide empirical guidance to establish parameters for human dosing and collectively support the idea that gene transfer may overcome key delivery obstacles that have precluded successful translation of neurotrophic factors to the clinic. More specifically, they also enabled the AAV-NGF and AAV-NRTN programs to advance into ongoing multi-center, double-blind clinical trials in AD and PD patients.

Convection-enhanced delivery of AAV2-PrPshRNA in prion-infected mice

Prion disease is caused by a single pathogenic protein (PrP^Sc), an abnormal conformer of the normal cellular prion protein PrP^C. Depletion of PrP^C in prion knockout mice makes them resistant to prion disease. Thus, gene silencing of the Prnp gene is a promising effective therapeutic approach. Here, we examined adeno-associated virus vector type 2 encoding a short hairpin RNA targeting Prnp mRNA (AAV2-PrP-shRNA) to suppress PrP^C expression both in vitro and in vivo. AAV2-PrP-shRNA treatment suppressed PrP levels and prevented dendritic degeneration in RML-infected brain aggregate cultures. Infusion of AAV2-PrP-shRNA-eGFP into the thalamus of CD-1 mice showed that eGFP was transported to the cerebral cortex via anterograde transport and the overall PrP^C levels were reduced by ∼70% within 4 weeks. For therapeutic purposes, we treated RML-infected CD-1 mice with AAV2-PrP-shRNA beginning at 50 days post inoculation. Although AAV2-PrP-shRNA focally suppressed PrP^Sc formation in the thalamic infusion site by ∼75%, it did not suppress PrP^Sc formation efficiently in other regions of the brain. Survival of mice was not extended compared to the untreated controls. Global suppression of PrP^C in the brain is required for successful therapy of prion diseases.

Neuroprotective potential of pleiotrophin overexpression in the striatonigral pathway compared with overexpression in both the striatonigral and nigrostriatal pathways

Intrastriatal injection of recombinant adeno-associated viral vector serotype 2/1 (rAAV2/1) to overexpress the neurotrophic factor pleiotrophin (PTN) provides neuroprotection for tyrosine hydroxylase immunoreactive (THir) neurons in the substantia nigra pars compacta (SNpc), increases THir neurite density in the striatum (ST) and reverses functional deficits in forepaw use following 6-hydroxydopamine (6-OHDA) toxic insult. Glial cell line-derived neurotrophic factor (GDNF) gene transfer studies suggest that optimal neuroprotection is dependent on the site of nigrostriatal overexpression. The present study was conducted to determine whether enhanced neuroprotection could be accomplished via simultaneous rAAV2/1 PTN injections into the ST and SN compared with ST injections alone. Rats were unilaterally injected in the ST alone or injected in both the ST and SN with rAAV2/1 expressing either PTN or control vector. Four weeks later, all rats received intrastriatal injections of 6-OHDA. Rats were euthanized 6 or 16 weeks relative to 6-OHDA injection. A novel selective total enumeration method to estimate nigral THir neuron survival was validated to maintain the accuracy of stereological assessment. Long-term nigrostriatal neuroprotection and functional benefits were only observed in rats in which rAAV2/1 PTN was injected into the ST alone. Results suggest that superior preservation of the nigrostriatal system is provided by PTN overexpression delivered to the ST and restricted to the ST and SN pars reticulata and is not improved with overexpression of PTN within SNpc neurons.

Direct and retrograde transduction of nigral neurons with AAV6, 8, and 9 and intraneuronal persistence of viral particles

Recombinant adeno-associated viral (AAV) vectors of serotypes 6, 8, and 9 were characterized as tools for gene delivery to dopaminergic neurons in the substantia nigra for future gene therapeutic applications in Parkinson's disease. While vectors of all three serotypes transduced nigral dopaminergic neurons with equal efficiency when directly injected to the substantia nigra, AAV6 was clearly superior to AAV8 and AAV9 for retrograde transduction of nigral neurons after striatal delivery. For sequential transduction of nigral dopaminergic neurons, the combination of AAV9 with AAV6 proved to be more powerful than AAV8 with AAV6 or repeated AAV6 administration. Surprisingly, single-stranded viral genomes persisted in nigral dopaminergic neurons within cell bodies and axon terminals in the striatum, and intact assembled AAV capsid was enriched in nuclei of nigral neurons, 4 weeks after virus injections to the substantia nigra. 6-Hydroxydopamine (6-OHDA)-induced degeneration of dopaminergic neurons in the substantia nigra reduced the number of viral genomes in the striatum, in line with viral genome persistence in axon terminals. However, 6-OHDA-induced axonal degeneration did not induce any transsynaptic spread of AAV infection in the striatum. Therefore, the potential presence of viral particles in axons may not represent an important safety issue for AAV gene therapy applications in neurodegenerative diseases.

Transgenic expression of human glial cell line-derived neurotrophic factor from integration-deficient lentiviral vectors is neuroprotective in a rodent model of Parkinson's disease

Standard integration-proficient lentiviral vectors (IPLVs) are effective at much lower doses than other vector systems and have shown promise for gene therapy of Parkinson's disease (PD). Their main drawback is the risk of insertional mutagenesis. The novel biosafety-enhanced integration-deficient lentiviral vectors (IDLVs) may offer a significant enhancement in biosafety, but have not been previously tested in a model of a major disease. We have assessed biosafety and transduction efficiency of IDLVs in a rat model of PD, using IPLVs as a reference. Genomic insertion of lentivectors injected into the lesioned striatum was studied by linear amplification-mediated polymerase chain reaction (PCR), followed by deep sequencing and insertion site analysis, demonstrating lack of significant IDLV integration. Reporter gene expression studies showed efficient, long-lived, and transcriptionally targeted expression from IDLVs injected ahead of lesioning in the rat striatum, although at somewhat lower expression levels than from IPLVs. Transgenic human glial cell line-derived neurotrophic factor (hGDNF) expression from IDLVs was used for a long-term investigation of lentivector-mediated, transcriptionally targeted neuroprotection in this PD rat model. Vectors were injected before striatal lesioning, and the results showed improvements in nigral dopaminergic neuron survival and behavioral tests regardless of lentiviral integration proficiency, although they confirmed lower expression levels of hGDNF from IDLVs. These data demonstrate the effectiveness of IDLVs in a model of a major disease and indicate that these vectors could provide long-term PD treatment at low dose, combining efficacy and biosafety for targeted central nervous system applications.

Treating Parkinson's disease in the 21st century: can stem cell transplantation compete?

The characteristic and selective degeneration of a unique population of cells—the nigrostriatal dopamine (DA) neurons—that occurs in Parkinson’s disease (PD) has made the condition an iconic target for cell replacement therapies. Indeed, transplantation of fetal ventral mesencephalic cells into the DA-deficient striatum was first trialled nearly 30 years ago, at a time when other treatments for the disease were less well developed. Over recent decades standard treatments for PD have advanced, and newer biological therapies are now emerging. In the 21st century, stem cell technology will have to compete alongside other sophisticated treatments, including deep brain stimulation and gene therapies. In this review we examine how stem cell–based transplantation therapies compare with these novel and emerging treatments in the management of this common condition. J. Comp. Neurol. 522:2802–2816, 2014.

Gene therapy for Parkinson's disease: state-of-the-art treatments for neurodegenerative disease

Pharmacological and surgical treatments offer symptomatic benefits to patients with Parkinson's disease; however, as the condition progresses, patients experience gradual worsening in symptom control, with the development of a range of disabling complications. In addition, none of the currently available therapies have convincingly shown disease-modifying effects - either in slowing or reversing the disease. These problems have led to extensive research into the possible use of gene therapy as a treatment for Parkinson's disease. Several treatments have reached human clinical trial stages, providing important information on the risks and benefits of this novel therapeutic approach, and the tantalizing promise of improved control of this currently incurable neurodegenerative disorder.

Differential effects of two MRI contrast agents on the integrity and distribution of rAAV2 and rAAV5 in the rat striatum

Intraoperative magnetic resonance imaging (MRI) has been proposed as a method to optimize intracerebral targeting and for tracking infusate distribution in gene therapy trials for nervous system disorders. We thus investigated possible effects of two MRI contrast agents, gadoteridol (Gd) and galbumin (Gab), on the distribution and levels of transgene expression in the rat striatum and their effect on integrity and stability of recombinant adeno-associated virus (rAAV) particles. MRI studies showed that contrast agent distribution did not predict rAAV distribution. However, green fluorescent protein (GFP) immunoreactivity revealed an increase in distribution of rAAV5-GFP, but not rAAV2-GFP, in the presence of Gd when compared with viral vector injected alone. In contrast, Gab increased the distribution of rAAV2-GFP not rAAV5-GFP. These observations pointed to a direct effect of infused contrast agent on the rAAV particles. Negative-stain electron microscopy (EM), DNAase treatment, and differential scanning calorimetry (DSC) were used to monitor rAAV2 and rAAV5 particle integrity and stability following contrast agent incubation. EMs of rAAV2-GFP and rAAV5-GFP particles pretreated with Gd appear morphologically similar to the untreated sample; however, Gab treatment resulted in surface morphology changes and aggregation. A compromise of particle integrity was suggested by sensitivity of the packaged genome to DNAase treatment following Gab incubation but not Gd for both vectors. However, neither agent significantly affected particle stability when analyzed by DSC. An increase in T m was observed for AAV2 in lactated Ringer's buffer. These results thus highlight potential interactions between MRI contrast agents and AAV that might affect vector distribution and stability, as well as the stabilizing effect of lactated Ringer's solution on AAV2.

Parkinson's disease gene therapy: success by design meets failure by efficacy

Over the past decade, nine gene therapy clinical trials for Parkinson's disease (PD) have been initiated and completed. Starting with considerable optimism at the initiation of each trial, none of the programs has yet borne sufficiently robust clinical efficacy or found a clear path toward regulatory approval. Despite the immediately disappointing nature of the efficacy outcomes in these trials, the clinical data garnered from the individual studies nonetheless represent tangible and significant progress for the gene therapy field. Collectively, the clinical trials demonstrate that we have overcome the major safety hurdles previously suppressing central nervous system (CNS) gene therapy, for none produced any evidence of untoward risk or harm after administration of various vector-delivery systems. More importantly, these studies also demonstrated controlled, highly persistent generation of biologically active proteins targeted to structures deep in the human brain. Therefore, a renewed, focused emphasis must be placed on advancing clinical efficacy by improving clinical trial design, patient selection and outcome measures, developing more predictive animal models to support clinical testing, carefully performing retrospective analyses, and most importantly moving forward—beyond our past limits.

Interactions between developing nerves and salivary glands

Our aim is to provide a summary of the field of salivary gland development and regeneration from the perspective of what is known about the function of nerves during these processes. The primary function of adult salivary glands is to produce and secrete saliva. Neuronal control of adult salivary gland function has been a focus of research ever since Pavlov’s seminal experiments on salivation in dogs. Less is known about salivary gland innervation during development and how the developing nerves influence gland organogenesis and regeneration. Here, we will review what is known about the communication between the autonomic nervous system and the epithelium of the salivary glands during organogenesis. An important emerging theme is the instructive role of the nervous system on the epithelial stem/progenitor cells during development as well as regeneration after damage. We will provide a brief overview of the neuroanatomy of the salivary glands and discuss recent literature that begins to integrate neurobiology with epithelial organogenesis, which may provide paradigms for exploring these interactions in other organ systems.

AAV2-neurturin (CERE-120) for Parkinson's disease

INTRODUCTION

Parkinson's disease (PD) is a common and chronic movement disorder with no therapy yet proven to alter the underlying advancing pathology. Gene delivery of trophic factors, which have shown disease modifying potential in preclinical PD models, are now being evaluated in early clinical trials.

AREAS COVERED

This review discusses early experiences with glial-derived neurotrophic factor in PD, the initial studies using AAV2-neurturin in PD patients, the lessons learned from these studies and the future directions of this therapy.

EXPERT OPINION

Gene therapy has emerged as a potential breakthrough in the treatment of PD and early clinical trials using AAV2-neurturin, a trophic factor that has shown the ability to protect dopaminergic degeneration in preclinical PD models, are underway. While trophic protection of dopamine neurons would be a significant breakthrough, PD remains a widespread disorder that involves neurodegeneration across multiple cellular types. We believe that these initial studies with AAV2-neurturin are significant steps toward the realization of gene delivery of trophic factors as a viable therapy, though the ultimate goal must be that of comprehensive neurorestoration.

Enhanced neurotrophic distribution, cell signaling and neuroprotection following substantia nigral versus striatal delivery of AAV2-NRTN (CERE-120)

This paper reassesses the currently accepted viewpoint that targeting the terminal fields (i.e. striatum) of degenerating nigrostriatal dopamine neurons with neurotrophic factors in Parkinson's disease (PD) is sufficient for achieving an optimal neurotrophic response. Recent insight indicating that PD is an axonopathy characterized by axonal transport deficits prompted this effort. We tested whether a significantly greater neurotrophic response might be induced in SN neurons when the neurotrophic factor neurturin (NRTN) is also targeted to the substantia nigra (SN), compared to the more conventional, striatum-only target. While recognizing the importance of maintaining the integrity of nigrostriatal fibers and terminals (especially for achieving optimal function), we refocused attention to the fate of SN neurons. Under conditions of axonal degeneration and neuronal transport deficits, this component of the nigrostriatal system is most vulnerable to the lack of neurotrophic exposure following striatal-only delivery. Given the location of repair genes induced by neurotrophic factors, achieving adequate neurotrophic exposure to the SN neurons is essential for an optimal neurotrophic response, while the survival of these neurons is essential to the very survival of the fibers. Two separate studies were performed using the 6-OHDA model of nigrostriatal degeneration, in conjunction with delivery of the viral vector AAV2-NRTN (CERE-120) to continuously express NRTN to either striatum or nigra alone or combined striatal/nigral exposure, including conditions of ongoing axonopathy. These studies provide additional insight for reinterpreting past animal neurotrophic/6-OHDA studies conducted under conditions where axon transport deficiencies were generally not accounted for, which suggested that targeting the striatum was both necessary and sufficient. The current data demonstrate that delivering NRTN directly to the SN produces 1) expanded NRTN distribution within the terminal field and cell bodies of targeted nigrostriatal neurons, 2) enhanced intracellular neurotrophic factor signaling in the nigrostriatal neurons, and 3) produced greater numbers of surviving dopamine neurons against 6-OHDA-induced toxicity, particularly under the conditions of active axonopathy. Thus, these data provide empirical support that targeting the SN with neurotrophic factors (in addition to striatum) may help enhance the neurotrophic response in midbrain neurons, particularly under conditions of active neurodegeneration which occurs in PD patients.

Safety/feasibility of targeting the substantia nigra with AAV2-neurturin in Parkinson patients

OBJECTIVE

In an effort to account for deficiencies in axonal transport that limit the effectiveness of neurotrophic factors, this study tested the safety and feasibility, in moderately advanced Parkinson disease (PD), of bilaterally administering the gene therapy vector AAV2-neurturin (CERE-120) to the putamen plus substantia nigra (SN, a relatively small structure deep within the midbrain, in proximity to critical neuronal and vascular structures).

METHODS

After planning and minimizing risks of stereotactically targeting the SN, an open-label, dose-escalation safety trial was initiated in 6 subjects with PD who received bilateral stereotactic injections of CERE-120 into the SN and putamen.

RESULTS

Two-year safety data for all subjects suggest the procedures were well-tolerated, with no serious adverse events. All adverse events and complications were expected for patients with PD undergoing stereotactic brain surgery.

CONCLUSIONS

Bilateral stereotactic administration of CERE-120 to the SN plus putamen in PD is feasible and this evaluation provides initial empirical support that it is safe and well-tolerated.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that bilateral neurturin gene delivery (CERE-120) to the SN plus putamen in patients with moderately advanced PD is feasible and safe.

Neurotrophic molecules in the treatment of neurodegenerative disease with focus on the retina: status and perspectives

Neurotrophic factors are operationally defined as molecules that promote the survival and differentiation of neurons. Chemically, they belong to divergent classes of molecules but most of the classic neurotrophic factors are proteins. Together with stem cells, viral vectors and genetically engineered cells, they constitute important tools in neuroprotective and regenerative neurobiology. Protein neurotrophic molecules signal through receptors located on the cell membrane. Their downstream signaling exploits pathways that are often common to chemically different factors and frequently target a relatively restricted set of transcription factors, RNA interference and diverse molecular machinery involved in the life vs. death decisions of neurons. Application of neurotrophic factors with the aim of curing or, at least, improving the outcome of neurodegenerative diseases requires (1) profound knowledge of the complex molecular pathology of the disease, (2) the development of animal models as closely as possible resembling the human disease, (3) the identification of target cells to be addressed, (4) intense efforts in chemical engineering to ensure the stability of molecules or to design carriers and small analogs with the ability to cross the blood-brain barrier and (5) scrutinity with regard to possible side effects. Last, but not least, engineering efforts to optimize administration, e.g., by designing the right canulae and infusion devices, are important for the successful translation of preclinical advances into clinical benefit. This article presents selected examples of neurotrophic factors that are currently being tested in animal models or developed for transfer to the clinic, with a major focus on factors with the potential of becoming applicable in various forms of retinal degeneration.

Nigral GFRα1 infusion in aged rats increases locomotor activity, nigral tyrosine hydroxylase, and dopamine content in synchronicity

Delivery of exogenous glial cell line-derived neurotrophic factor (GDNF) increases locomotor activity in rodent models of aging and Parkinson's disease in conjunction with increased dopamine (DA) tissue content in substantia nigra (SN). Striatal GDNF infusion also increases expression of GDNF's cognate receptor, GFRα1, and tyrosine hydroxylase (TH) ser31 phosphorylation in the SN of aged rats long after elevated GDNF is no longer detectable. In aging, expression of soluble GFRα1 in the SN decreases in association with decreased TH expression, TH ser31 phosphorylation, DA tissue content, and locomotor activity. Thus, we hypothesized that, in aged rats, replenishing soluble GFRα1 in SN could reverse these deficits and increase locomotor activity. We determined that the quantity of soluble GFRα1 in young adult rat SN is ~3.6 ng. To replenish age-related loss, which is ~30 %, we infused 1 ng soluble GFRα1 bilaterally into SN of aged male rats and observed increased locomotor activity compared to vehicle-infused rats up to 4 days following infusion, with maximal effects on day 3. Five days after infusion, however, neither locomotor activity nor nigrostriatal neurochemical measures were significantly different between groups. In a separate cohort of male rats, nigral, but not striatal, DA, TH, and TH ser31 phosphorylation were increased 3 days following unilateral infusion of 1 ng soluble GFRα1into SN. Therefore, in aged male rats, the transient increase in locomotor activity induced by replenishing age-related loss of soluble GFRα1is temporally matched with increased nigral dopaminergic function. Thus, expression of soluble GFRα1 in SN may be a key component in locomotor activity regulation through its influence over TH regulation and DA biosynthesis.

RING finger protein 11 (RNF11) modulates susceptibility to 6-OHDA-induced nigral degeneration and behavioral deficits through NF-κB signaling in dopaminergic cells

Chronic activation of the NF-κB pathway is associated with progressive neurodegeneration in Parkinson's disease (PD). Given the role of neuronal RING finger protein 11 (RNF11) as a negative regulator of the NF-κB pathway, in this report we investigated the function of RNF11 in dopaminergic cells in PD-associated neurodegeneration. We found that RNF11 knockdown in an in vitro model of PD mediated protection against 6-OHDA-induced toxicity. In converse, over-expression of RNF11 enhanced 6-OHDA-induced dopaminergic cell death. Furthermore, by directly manipulating NF-κB signaling, we showed that the observed RNF11-enhanced 6-OHDA toxicity is mediated through inhibition of NF-κB-dependent transcription of TNF-α, antioxidants GSS and SOD1, and anti-apoptotic factor BCL2. Experiments in an in vivo 6-OHDA rat model of PD recapitulated the in vitro results. In vivo targeted RNF11 over-expression in nigral neurons enhanced 6-OHDA toxicity, as evident by increased amphetamine-induced rotations and loss of nigral dopaminergic neurons as compared to controls. This enhanced toxicity was coupled with the downregulation of NF-κB transcribed GSS, SOD1, BCL2, and neurotrophic factor BDNF mRNA levels, in addition to decreased TNF-α mRNA levels in ventral mesenchephalon samples. In converse, knockdown of RNF11 was associated with protective phenotypes and increased expression of above-mentioned NF-κB transcribed genes. Collectively, our in vitro and in vivo data suggest that RNF11-mediated inhibition of NF-κB in dopaminergic cells exaggerates 6-OHDA toxicity by inhibiting neuroprotective responses while loss of RNF11 inhibition on NF-κB activity promotes neuronal survival. The decreased expression of RNF11 in surviving cortical and nigral tissue detected in PD patients, thus implies a compensatory response in the diseased brain to PD-associated insults. In summary, our findings demonstrate that RNF11 in neurons can modulate susceptibility to 6-OHDA toxicity through NF-κB mediated responses. This neuron-specific role of RNF11 in the brain has important implications for targeted therapeutics aimed at preventing neurodegeneration.

Gene therapy for psychiatric disorders

Gene therapy has become of increasing interest in clinical neurosurgery with the completion of numerous clinical trials for Parkinson disease, Alzheimer disease, and pediatric genetic disorders. With improved understanding of the dysfunctional circuitry mediating various psychiatric disorders, deep brain stimulation for refractory psychiatric diseases is being increasingly explored in human patients. These factors are likely to facilitate development of gene therapy for psychiatric diseases. Because delivery of gene therapy agents would require the same surgical techniques currently being employed for deep brain stimulation, neurosurgeons are likely to lead the development of this field, as has occurred in other areas of clinical gene therapy for neurologic disorders. We review the current state of gene therapy for psychiatric disorders and focus specifically on particular areas of promising research that may translate into human trials for depression, drug addiction, obsessive-compulsive disorder, and schizophrenia. Issues that are relatively unique to psychiatric gene therapy are also discussed.

Bone marrow-derived mesenchymal stem cells increase dopamine synthesis in the injured striatum

Previous studies showed that tyrosine hydroxylase or neurturin gene-modified cells transplanted into rats with Parkinson’s disease significantly improved behavior and increased striatal dopamine content. In the present study, we transplanted tyrosine hydroxylase and neurturin gene-modified bone marrow-derived mesenchymal stem cells into the damaged striatum of Parkinson’s disease model rats. Several weeks after cell transplantation, in addition to an improvement of motor function, tyrosine hydroxylase and neurturin proteins were up-regulated in the injured striatum, and importantly, levels of dopamine and its metabolite 3,4-dihydroxyphenylacetic acid increased significantly. Furthermore, the density of the D2 dopamine receptor in the postsynaptic membranes of dopaminergic neurons was decreased. These results indicate that transplantation of tyrosine hydroxylase and neurturin gene-modified bone marrow-derived mesenchymal stem cells increases dopamine synthesis and significantly improves the behavior of rats with Parkinson’s disease.

Advancing neurotrophic factors as treatments for age-related neurodegenerative diseases: developing and demonstrating "clinical proof-of-concept" for AAV-neurturin (CERE-120) in Parkinson's disease

Neurotrophic factors have long shown promise as potential therapies for age-related neurodegenerative diseases. However, 20 years of largely disappointing clinical results have underscored the difficulties involved with safely and effectively delivering these proteins to targeted sites within the central nervous system. Recent progress establishes that gene transfer can now likely overcome the delivery issues plaguing the translation of neurotrophic factors. This may be best exemplified by adeno-associated virus serotype-2-neurturin (CERE-120), a viral-vector construct designed to deliver the neurotrophic factor, neurturin to degenerating nigrostriatal neurons in Parkinson's disease. Eighty Parkinson's subjects have been dosed with CERE-120 (some 7+ years ago), with long-term, targeted neurturin expression confirmed and no serious safety issues identified. A double-blind, controlled Phase 2a trial established clinical "proof-of-concept" via 19 of the 24 prescribed efficacy end points favoring CERE-120 at the 12-month protocol-prescribed time point and all but one favoring CERE-120 at the 18-month secondary time point (p = 0.007 and 0.001, respectively). Moreover, clinically meaningful benefit was seen with CERE-120 on several specific protocol-prescribed, pairwise, blinded, motor, and quality-of-life end points at 12 months, and an even greater number of end points at 18 months. Because the trial failed to meet the primary end point (Unified Parkinson's Disease Rating Scale motor-off, measured at 12 months), a revised multicenter Phase 1/2b protocol was designed to enhance the neurotrophic effects of CERE-120, using insight gained from the Phase 2a trial. This review summarizes the development of CERE-120 from its inception through establishing "clinical proof-of-concept" and beyond. The translational obstacles and issues confronted, and the strategies applied, are reviewed. This information should be informative to investigators interested in translational research and development for age-related and other neurodegenerative diseases.

Concordant signaling pathways produced by pesticide exposure in mice correspond to pathways identified in human Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease in which the etiology of 90 percent of the patients is unknown. Pesticide exposure is a major risk factor for PD, and paraquat (PQ), pyridaben (PY) and maneb (MN) are amongst the most widely used pesticides. We studied mRNA expression using transcriptome sequencing (RNA-Seq) in the ventral midbrain (VMB) and striatum (STR) of PQ, PY and paraquat+maneb (MNPQ) treated mice, followed by pathway analysis. We found concordance of signaling pathways between the three pesticide models in both the VMB and STR as well as concordance in these two brain areas. The concordant signaling pathways with relevance to PD pathogenesis were e.g. axonal guidance signaling, Wnt/β-catenin signaling, as well as pathways not previously linked to PD, e.g. basal cell carcinoma, human embryonic stem cell pluripotency and role of macrophages, fibroblasts and endothelial cells in rheumatoid arthritis. Human PD pathways previously identified by expression analysis, concordant with VMB pathways identified in our study were axonal guidance signaling, Wnt/β-catenin signaling, IL-6 signaling, ephrin receptor signaling, TGF-β signaling, PPAR signaling and G-protein coupled receptor signaling. Human PD pathways concordant with the STR pathways in our study were Wnt/β-catenin signaling, axonal guidance signaling and G-protein coupled receptor signaling. Peroxisome proliferator activated receptor delta (Ppard) and G-Protein Coupled Receptors (GPCRs) were common genes in VMB and STR identified by network analysis. In conclusion, the pesticides PQ, PY and MNPQ elicit common signaling pathways in the VMB and STR in mice, which are concordant with known signaling pathways identified in human PD, suggesting that these pathways contribute to the pathogenesis of idiopathic PD. The analysis of these networks and pathways may therefore lead to improved understanding of disease pathogenesis, and potential novel therapeutic targets.

Translating the therapeutic potential of neurotrophic factors to clinical 'proof of concept': a personal saga achieving a career-long quest

While the therapeutic potential of neurotrophic factors has been well-recognized for over two decades, attempts to translate that potential to the clinic have been disappointing, largely due to significant delivery obstacles. Similarly, gene therapy (or gene transfer) emerged as a potentially powerful, new therapeutic approach nearly two decades ago and despite its promise, also suffered serious setbacks when applied to the human clinic. As advances continue to be made in both fields, ironically, they may now be poised to complement each other to produce a translational breakthrough. The accumulated data argue that gene transfer provides the 'enabling technology' that can solve the age-old delivery problems that have plagued the translation of neurotrophic factors as treatments for chronic central nervous system diseases. A leading translational program applying gene transfer to deliver a neurotrophic factor to rejuvenate and protect degenerating human neurons is CERE-120 (AAV2-NRTN). To date, over two dozen nonclinical studies and three clinical trials have been completed. A fourth (pivotal) clinical trial has completed all dosing and is currently evaluating safety and efficacy. In total, eighty Parkinson's disease (PD) subjects have thus far been dosed with CERE-120 (some 7 years ago), representing over 250 cumulative patient-years of exposure, with no serious safety issues identified. In a completed sham-surgery, double-blinded controlled trial, though the primary endpoint (the Unified Parkinson's Disease Rating Scale (UDPRS) motor off score measured at 12 months) did not show benefit from CERE-120, several important motor and quality of life measurements did, including the same UPDRS-motor-off score, pre-specified to also be measured at a longer, 18-month post-dosing time point. Importantly, not a single measurement favored the sham control group. This study therefore, provided important, well-controlled evidence establishing 'clinical proof of concept' for gene transfer to the CNS and the first controlled evidence for clinical benefit of a neurotrophic factor in a human neurodegenerative disease. This paper reviews the development of CERE-120, starting historically with the long-standing interest in the therapeutic potential of neurotrophic factors and continuing with selective accounts of past efforts to translate their potential to the clinic, eventually leading to the application of gene transfer and its role as the 'enabling technology'. Because of growing interest in translational R&D, including its practice in industry, the paper is uniquely oriented from the author's personal, quasi-autobiographic perspective and career-long experiences conducting translational research and development, with a focus on various translational neurotrophic factor programs spanning 30+ years in Big Pharma and development-stage biotech companies. It is hoped that by sharing these perspectives, practical insight and information might be provided to others also interested in translational R&D as well as neurotrophic factors and gene therapy, offering readers the opportunity to benefit from some of our successes, while possibly avoiding some of our missteps.