Intracranial delivery of proteins and peptides as a therapy for neurodegenerative diseases

Failure of Glial Cell-Line Derived Neurotrophic Factor (GDNF) in Clinical Trials Orchestrated By Reduced NR4A2 (NURR1) Transcription Factor in Parkinson's Disease. A Systematic Review

Parkinson’s disease (PD) is one of the most common neurodegenerative maladies with unforeseen complex pathologies. While this neurodegenerative disorder’s neuropathology is reasonably well known, its etiology remains a mystery, making it challenging to aim therapy. Glial cell-line derived neurotrophic factor (GDNF) remains an auspicious therapeutic molecule for treating PD. Neurotrophic factor derived from glial cell lines is effective in rodents and nonhuman primates, but clinical findings have been equivocal. Laborious exertions have been made over the past few decades to improve and assess GDNF in treating PD (clinical studies). Definitive clinical trials have, however, failed to demonstrate a survival advantage. Consequently, there seemed to be a doubt as to whether GDNF has merit in the potential treatment of PD. The purpose of this cutting edge review is to speculate as to why the clinical trials have failed to meet the primary endpoint. We introduce a hypothesis, “Failure of GDNF in clinical trials succumbed by nuclear receptor-related factor 1 (Nurr1) shortfall.” We demonstrate how Nurr1 binds to GDNF to induce dopaminergic neuron synthesis. Due to its undisputable neuro-protection aptitude, we display Nurr1 (also called Nr4a2) as a promising therapeutic target for PD.

Long-term, stable, targeted biodelivery and efficacy of GDNF from encapsulated cells in the rat and Goettingen miniature pig brain

Delivering glial cell line-derived neurotrophic factor (GDNF) to the brain is a potential treatment for Parkinson's Disease (PD). Here we use an implantable encapsulated cell technology that uses modified human clonal ARPE-19 ​cells to deliver of GDNF to the brain. In vivo studies demonstrated sustained delivery of GDNF to the rat striatum over 6 months. Anatomical benefits and behavioral efficacy were shown in 6-OHDA lesioned rats where nigral dopaminergic neurons were preserved in neuroprotection studies and dopaminergic fibers were restored in neurorecovery studies. When larger, clinical-sized devices were implanted for 3 months into the putamen of Göttingen minipigs, GDNF was widely distributed throughout the putamen and caudate producing a significant upregulation of tyrosine hydroxylase immunohistochemistry. These results are the first to provide clear evidence that implantation of encapsulated GDNF-secreting cells deliver efficacious and biologically relevant amounts of GDNF in a sustained and targeted manner that is scalable to treat the large putamen in patients with Parkinson's disease.

Widespread Striatal Delivery of GDNF from Encapsulated Cells Prevents the Anatomical and Functional Consequences of Excitotoxicity

Methods

Human ARPE-19 cells engineered to secrete high levels of the glial cell line-derived neurotrophic factor (GDNF) were encapsulated into hollow fiber membranes. The devices were implanted into the rat striatum 1 week prior to striatal quinolinic acid injections. Animals were evaluated using a battery of validated motor tests, and histology was performed to determine the extent of GDNF diffusion and associated prevention of neuronal cell loss and behavioral deficits.

Results

Encapsulated cell-based delivery of GDNF produced widespread distribution of GDNF throughout the entire implanted striatum. Stereological estimates of striatal neuron number and volume of lesion size revealed that GDNF delivery resulted in near complete neuroprotection.

Conclusions

Delivery of neurotrophic molecules such as GDNF using encapsulated cells has reached a technological point where clinical evaluation is justified. Because GDNF has been effective in animal models of Parkinson's disease, stroke, epilepsy, and Huntington's disease, among other debilitating neurodegenerative diseases, encapsulated cell-based delivery of GDNF might represent one innovative means of slowing the neural degeneration seen in a myriad of currently untreatable neurological diseases.

Methodology and effects of repeated intranasal delivery of DNSP-11 in awake Rhesus macaques

BACKGROUND

To determine if the intranasal delivery of neuroactive compounds is a viable, long-term treatment strategy for progressive, chronic neurodegenerative disorders, such as Parkinson's disease (PD), intranasal methodologies in preclinical models comparable to humans are needed.

NEW METHOD

We developed a methodology to evaluate the repeated intranasal delivery of neuroactive compounds on the non-human primate (NHP) brain, without the need for sedation. We evaluated the effects of the neuroactive peptide, DNSP-11 following repeated intranasal delivery and dose-escalation over the course of 10-weeks in Rhesus macaques. This approach allowed us to examine striatal target engagement, safety and tolerability, and brain distribution following a single ¹²⁵I-labeled DNSP-11 dose.

RESULTS

Our initial data support that repeated intranasal delivery and dose-escalation of DNSP-11 resulted in bilateral, striatal target engagement based on neurochemical changes in dopamine (DA) metabolites-without observable, adverse behavioral effects or weight loss in NHPs. Furthermore, a ¹²⁵I-labeled DNSP-11 study illustrates diffuse rostral to caudal distribution in the brain including the striatum-our target region of interest.

COMPARISON WITH EXISTING METHODS

The results of this study are compared to our experiments in normal and 6-OHDA lesioned rats, where DNSP-11 was repeatedly delivered intranasally using a micropipette with animals under light sedation.

CONCLUSIONS

The results from this proof-of-concept study support the utility of our repeated intranasal dosing methodology in awake Rhesus macaques, to evaluate the effects of neuroactive compounds on the NHP brain. Additionally, results indicate that DNSP-11 can be safely and effectively delivered intranasally in MPTP-treated NHPs, while engaging the DA system.

Current Neurogenic and Neuroprotective Strategies to Prevent and Treat Neurodegenerative and Neuropsychiatric Disorders

The adult central nervous system is commonly known to have a very limited regenerative capacity. The presence of functional stem cells in the brain can therefore be seen as a paradox, since in other organs these are known to counterbalance cell loss derived from pathological conditions. This fact has therefore raised the possibility to stimulate neural stem cell differentiation and proliferation or survival by either stem cell replacement therapy or direct administration of neurotrophic factors or other proneurogenic molecules, which in turn has also originated regenerative medicine for the treatment of otherwise incurable neurodegenerative and neuropsychiatric disorders that take a huge toll on society. This may be facilitated by the fact that many of these disorders converge on similar pathophysiological pathways: excitotoxicity, oxidative stress, neuroinflammation, mitochondrial failure, excessive intracellular calcium and apoptosis. This review will therefore focus on the most promising achievements in promoting neuroprotection and neuroregeneration reported to date.

Stem cells and regenerative therapies for Parkinson's disease

Currently the mainstay of Parkinson's disease (PD) therapy is the pharmacological replacement of the loss of the dopaminergic nigrostriatal pathway using drugs such as dopamine agonists and levodopa. Whilst these drugs effectively ameliorate some of the motor features of PD, they do not improve many of the nonmotor features that arise secondary to pathology outside of this system, nor do they slow the progressive neurodegeneration that is a characteristic of the disease. Regenerative therapies for PD seek to fill this therapeutic gap, with cell transplantation being the most explored approach to date. A number of different cell sources have been used in this therapeutic approach, but to date, the most successful has been the use of fetal ventral mesencephalic (VM) tissue that contains within it the developing nigral dopaminergic cells. Cell transplantation for PD was pioneered in the 1980-1990s, with several successful open-label trials of fetal VM transplantation in patients with relatively advanced PD. Whilst these findings were not replicated in two subsequent double-blind sham-surgery controlled trials, there were reasons to explain this outside of the one drawn at the time that these therapies are ineffective. Indeed all these studies have provided evidence that following the transplantation of fetal VM tissue, dopaminergic cells can survive long term, produce dopamine, and bring about clinical improvements in younger patients over many years. The use of fetal tissue, irrespective of its true efficacy, will never become a widely available therapy for PD for a host of practical and ethical reasons, and thus much work has been put in recently to exploring the utility of stem cells as a source of nigral dopaminergic neurons. In this respect, the advent of embryonic stem cell and induced pluripotent cells has heralded a new era in cell therapy for PD, and several groups have now demonstrated that these cells can form dopaminergic neurons which improve functional deficits in animal models of PD. Whilst encouraging, problems with respect to the immunogenicity and tumorigenicity of these cells means that they will need to be used in the clinic cautiously. Other regenerative therapies in PD have been tried over the years and include the use of trophic factors. This has primarily involved glial cell line-derived neurotrophic factor (GDNF) and again has produced mixed clinical effects, and in order to try and resolve this, a new trial of intraputamenal GDNF is now being planned. In addition, a new trial for platelet derived growth factor as a treatment for PD has just completed recruitment, and PYM50028 (Cogane) an oral agent shown in animal models to reduce the effects of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) lesioning by the induction of growth factors is currently under investigation in a multicentre Phase II trial. Overall, there are a number of promising new regenerative therapies being developed and tested in PD, although the true long-term efficacy of any of these in large numbers of patients is still not known.

Combining glial cell line-derived neurotrophic factor gene delivery (AdGDNF) with L-arginine decreases contusion size but not behavioral deficits after traumatic brain injury

Our laboratory has previously demonstrated that viral administration of glial cell line-derived neurotrophic factor (AdGDNF), one week prior to a controlled cortical impact (CCI) over the forelimb sensorimotor cortex of the rat (FL-SMC) is neuroprotective, but does not significantly enhance recovery of sensorimotor function. One possible explanation for this discrepancy is that although protected, neurons may not have been functional due to enduring metabolic deficiencies. Additionally, metabolic events following TBI may interfere with expression of therapeutic proteins administered to the injured brain via gene therapy. The current study focused on enhancing the metabolic function of the brain by increasing cerebral blood flow (CBF) with l-arginine in conjunction with administration of AdGDNF immediately following CCI. An adenoviral vector harboring human GDNF was injected unilaterally into FL-SMC of the rat immediately following a unilateral CCI over the FL-SMC. Within 30min of the CCI and AdGDNF injections, some animals were injected with l-arginine (i.v.). Tests of forelimb function and asymmetry were administered for 4weeks post-injury. Animals were sacrificed and contusion size and GDNF protein expression measured. This study demonstrated that rats treated with AdGDNF and l-arginine post-CCI had a significantly smaller contusion than injured rats who did not receive any treatment, or injured rats treated with either AdGDNF or l-arginine alone. Nevertheless, no amelioration of behavioral deficits was seen. These findings suggest that AdGDNF alone following a CCI was not therapeutic and although combining it with l-arginine decreased contusion size, it did not enhance behavioral recovery.

Functional effects of AAV2-GDNF on the dopaminergic nigrostriatal pathway in parkinsonian rhesus monkeys

We investigated the safety and neuroregenerative potential of an adeno-associated virus (AAV2) containing human glial cell line-derived neurotrophic factor (GDNF) in an MPTP primate model of Parkinson's disease. Dopaminergic function was evaluated by positron emission tomography with 6-[(18)F]fluoro-l-m-tyrosine (FMT) before and after AAV2-GDNF or phosphate-buffered saline infusion bilaterally into the putamen. FMT uptake was significantly increased bilaterally in the putamen of AAV2-GDNF but not phosphate-buffered saline-treated animals 6 months after infusion, indicating increased dopaminergic activity in the nigrostriatal pathways. AAV2-GDNF-treated animals also showed clinical improvement without adverse effects. These findings are consistent with our previous report in aged nonhuman primates that showed evidence of enhanced use of striatal dopamine and dopaminergic nigrostriatal innervation. Clinical improvement and evidence of functional recovery in the nigrostriatal pathway, and the absence of adverse effects, support the safety of this approach for the delivery of GDNF over a 6-month period.

Mitochondrial toxins in Basal Ganglia disorders: from animal models to therapeutic strategies

Current knowledge of the pathogenesis of basal ganglia disorders, such as Huntington's disease (HD) and Parkinson's disease (PD) appoints a central role to a dysfunction in mitochondrial metabolism. The development of animal models, based upon the use of mitochondrial toxins has been successfully introduced to reproduce human disease, leading to important acquisitions. Most notably, experimental evidence supports the existence, within basal ganglia, of a peculiar regional vulnerability to distinct mitochondrial toxins. MPTP and rotenone, both selective inhibitors of mitochondrial complex I have been extensively used to mimic PD. Accordingly, in human PD, a specific dysfunction of complex I activity was found in vulnerable dopaminergic neurons of the substantia nigra. Conversely, in HD a selective impairment of mitochondrial succinate dehydrogenase, key enzyme in complex II activity was found in medium spiny neurons of the caudate-putamen. The relevance of such finding is further demonstrated by the evidence that toxins able to primarily target mitochondrial complex II, such as malonic acid and 3-nitropropionic acid (3-NP), strikingly reproduce the main phenotypic and pathological features of HD.Despite the advances obtained from these experimental models, a deeper understanding of the molecular and cellular mechanisms underlying such neuronal vulnerability is lacking.The present review provides a brief survey of currently utilized animal models of mitochondrial intoxication, in attempt to address the cellular mechanisms triggered by energy metabolism failure and to identify potential therapeutic targets.

Purified mouse dopamine neurons thrive and function after transplantation into brain but require novel glial factors for survival in culture

Cell replacement therapy in Parkinson's disease depends on a reliable source of purified dopamine (DA) neurons (PDN) and the identification of factors relevant to their survival. Our goal was to genetically tag and purify by flow cytometry embryonic midbrain DA neurons from a transgenic mouse line carrying 11 kb of human tyrosine hydroxylase promoter driving expression of the enhanced green fluorescent protein (GFP) for studies in vivo and in vitro. A 99% purification of GFP(+) cells was achieved. When transplanted into 6-hydroxydopamine-treated rat striatum, PDN survived, became well-integrated and produced recovery from amphetamine-induced motor behaviors. However, when grown in culture, PDN died within days of plating. No known growth factors prevented PDN death as did incubation with novel factors in glia/glial-conditioned media. We conclude that GFP-tagged DA neurons can be purified to homogeneity and can survive and function when grown with glial factors in vitro or after transplantation in vivo.