Antisense oligonucleotide therapy for neurodegenerative disease

Novel therapeutic modalities to address nondrugable protein interaction targets

Small molecule drugs are relatively effective in working on 'drugable' targets such as GPCRs, ion channels, kinases, proteases, etc but ineffective at blocking protein-protein interactions that represent an emerging class of 'nondrugable' central nervous system (CNS) targets. This article provides an overview of novel therapeutic modalities such as biologics (in particular antibodies) and emerging oligonucleotide therapeutics such as antisense, small-interfering RNA, and aptamers. Their key properties, overall strengths and limitations, and their utility as tools for target validation are presented. In addition, issues with regard to CNS targets as it relates to the blood-brain barrier penetration are discussed. Finally, examples of their application as therapeutics for the treatment of pain and some neurological disorders such as Alzheimer's disease, multiple sclerosis, Huntington's disease, and Parkinson's disease are provided.

Cell death and endoplasmic reticulum stress: disease relevance and therapeutic opportunities

The accumulation of unfolded proteins in the endoplasmic reticulum (ER) represents a cellular stress induced by multiple stimuli and pathological conditions. These include hypoxia, oxidative injury, high-fat diet, hypoglycaemia, protein inclusion bodies and viral infection. ER stress triggers an evolutionarily conserved series of signal-transduction events, which constitutes the unfolded protein response. These signalling events aim to ameliorate the accumulation of unfolded proteins in the ER; however, when these events are severe or protracted they can induce cell death. With the increasing recognition of an association between ER stress and human diseases, and with the improved understanding of the diverse underlying molecular mechanisms, novel targets for drug discovery and new strategies for therapeutic intervention are beginning to emerge.

ALS drug development: reflections from the past and a way forward

Tremendous advances in our understanding of pathogenesis of amyotrophic lateral sclerosis (ALS) have provided a rich pipeline of drugs for clinical trialists. At least 32 unique compounds have been tested. Nevertheless, riluzole is currently the only treatment that prolongs survival. We present a critical overview of past clinical trials, how therapies are selected for testing in people, challenges with ALS clinical trial design and conduct, and ways to best move forward.

A strategy for developing effective amyotropic lateral sclerosis pharmacotherapy: from clinical trials to novel pharmacotherapeutic strategies

BACKGROUND

The pathomechanism of sporadic amyotropic lateral sclerosis is not clearly understood, although a proportion of familial amyotropic lateral sclerosis is caused by superoxide dismutase 1 mutations. Theories based on studies of human post-mortem tissue, research on animal models and in vitro work have been proposed for the pathogenesis of amyotropic lateral sclerosis, but the pathogenesis is not the same between sporadic and familial amyotropic lateral sclerosis.

OBJECTIVE/METHODS

Drug candidates were tested using superoxide dismutase 1 mutant mice. Although the candidates were shown to be effective in mice, clinical trials in humans have failed to identify any truly effective pharmacotherapies in sporadic amyotropic lateral sclerosis, with only riluzole providing a modest improvement in survival. Ongoing or planned trials are exploring the value of antiglutamatergic drugs, antioxidants, neurotrophic factors, anti-inflammatory drugs and anti-aggregation drugs.

RESULTS/CONCLUSIONS

A combination of drugs acting on different mechanisms is needed for effective therapy. Moreover, gene expression profiling and genome-wide association studies, together with inhibitory RNA techniques, are helpful for developing new pharmacotherapeutic strategies including gene therapy. It is also likely that the recently advanced generation of induced pluripotent stem cells will lead to the development of cell therapy for amyotropic lateral sclerosis. In addition to finding effective therapies, research is also needed in order to detect early disease markers since pharmacotherapy is most beneficial when given early in the course of sporadic amyotropic lateral sclerosis.

Blocking connexin43 expression reduces inflammation and improves functional recovery after spinal cord injury

After traumatic CNS injury, a cascade of secondary events expands the initial lesion. The gap-junction protein connexin43 (Cx43), which is transiently up-regulated, has been implicated in the spread of 'bystander' damage. We have used an antisense oligodeoxynucleotide (asODN) to suppress Cx43 up-regulation in two rat models of spinal cord injury. Within 24 h of compression injury, rats treated with Cx43-asODN scored higher than sense-ODN and vehicle-treated controls on behavioural tests of locomotion. Their spinal cords showed less swelling and tissue disruption, less up-regulation of astrocytic GFAP, and less extravasation of fluorescently-labelled bovine serum albumin and neutrophils. The locomotor improvement was sustained over at least 4 weeks. Following partial spinal cord transection, Cx43-asODN treatment reduced GFAP immunoreactivity, neutrophil recruitment, and the activity of OX42(+) microglia in and around the lesion site. Cx43 has many potential roles in the pathophysiology of CNS injury and may be a valuable target for therapeutic intervention.

Therapeutic gene silencing delivered by a chemically modified small interfering RNA against mutant SOD1 slows amyotrophic lateral sclerosis progression

Inherited neurodegenerative diseases, such as Huntington disease and subset of Alzheimer disease, Parkinson disease, and amyotrophic lateral sclerosis, are caused by the mutant genes that have gained undefined properties that harm cells in the nervous system, causing neurodegeneration and clinical phenotypes. Lowering the mutant gene expression is predicted to slow the disease progression and produce clinical benefit. Administration of small interfering RNA (siRNA) can silence specific genes. However, long term delivery of siRNA to silence the mutant genes, a requirement for treatment of these chronic central nervous system (CNS) diseases, remains a critical unsolved issue. Here we designed and tested a chemically stabilized siRNA against human Cu,Zn-superoxide dismutase (SOD1) in a mouse model for amyotrophic lateral sclerosis. We show that the modified siRNA has enhanced stability and retains siRNA activity. Administration of this siRNA at the disease onset by long term infusion into the CNS resulted in widespread distribution of this siRNA, knocked down the mutant SOD1 expression, slowed the disease progression, and extended the survival. These results bring RNA interference therapy one step closer to its clinical application for treatment of chronic, devastating, and fatal CNS disorders.

Anti-sense morpholino oligonucleotide assay shows critical involvement for NF-kappaB activation in the production of Wnt-1 protein by HepG2 cells: oncology implications

The link of proto-oncogenic protein Wnt-1 production with NF-kappaB activation has been functionally demonstrated in PC12 cells, a rat pheochromocytoma cell line of neural crest lineage, while it is not yet verified in human cells. The link can be indirectly supported in our previous report that functional proteomics identifies enhanced expression of NF-kappaB-associated Wnt-1 production in human hepatocellular carcinoma tissues. This study aimed to further validate this link in human cells using anti-sense strategy. The effects of sequence-specific anti-sense morpholino oligonucleotides (ONs) targeting against pre-mRNA sequences of human p50 and p65 subunits of NF-kappaB as well as Wnt-1 genes were investigated. It revealed that all the three morpholino ONs inhibited NF-kappaB activation in human hepatoblastoma cell line HepG2 cells along with decreased Wnt-1 production. Chromatin immunoprecipitation assay ascertained the direct binding of NF-kappaB-p50 to the Wnt-1 promoter. Additionally, anti-P50 and anti-P65 morpholino ONs also repressed the phosphorylation of Ikappa Balpha which temporarily correlated with the inhibition of NF-kappaB activation accompanied by decreased Wnt-1 production by HepG2 cells. In summary, NF-kappaB activation is critically involved in the production of Wnt-1 by HepG2 cells. These results may have important oncology implications in treating patients with NF-kappaB-associated Wnt-1-producing cancers.

Antisense masking of an hnRNP A1/A2 intronic splicing silencer corrects SMN2 splicing in transgenic mice

Survival of motor neuron 2, centromeric (SMN2) is a gene that modifies the severity of spinal muscular atrophy (SMA), a motor-neuron disease that is the leading genetic cause of infant mortality. Increasing inclusion of SMN2 exon 7, which is predominantly skipped, holds promise to treat or possibly cure SMA; one practical strategy is the disruption of splicing silencers that impair exon 7 recognition. By using an antisense oligonucleotide (ASO)-tiling method, we systematically screened the proximal intronic regions flanking exon 7 and identified two intronic splicing silencers (ISSs): one in intron 6 and a recently described one in intron 7. We analyzed the intron 7 ISS by mutagenesis, coupled with splicing assays, RNA-affinity chromatography, and protein overexpression, and found two tandem hnRNP A1/A2 motifs within the ISS that are responsible for its inhibitory character. Mutations in these two motifs, or ASOs that block them, promote very efficient exon 7 inclusion. We screened 31 ASOs in this region and selected two optimal ones to test in human SMN2 transgenic mice. Both ASOs strongly increased hSMN2 exon 7 inclusion in the liver and kidney of the transgenic animals. Our results show that the high-resolution ASO-tiling approach can identify cis-elements that modulate splicing positively or negatively. Most importantly, our results highlight the therapeutic potential of some of these ASOs in the context of SMA.

Amyotrophic lateral sclerosis: from current developments in the laboratory to clinical implications

Amyotrophic lateral sclerosis (ALS) is a late-onset progressive degeneration of motor neurons occurring both as a sporadic and a familial disease. The etiology of ALS remains unknown, but one fifth of instances are due to specific gene defects, the best characterized of which is point mutations in the gene coding for Cu/Zn superoxide dismutase (SOD1). Because sporadic and familial ALS affect the same neurons with similar pathology, it is hoped that understanding these gene defects will help in devising therapies effective in both forms. A wealth of evidence has been collected in rodents made transgenic for mutant SOD1, which represent the best available models for familial ALS. Mutant SOD1 likely induces selective vulnerability of motor neurons through a combination of several mechanisms, including protein misfolding, mitochondrial dysfunction, oxidative damage, cytoskeletal abnormalities and defective axonal transport, excitotoxicity, inadequate growth factor signaling, and inflammation. Damage within motor neurons is enhanced by noxious signals originating from nonneuronal neighboring cells, where mutant SOD1 induces an inflammatory response that accelerates disease progression. The clinical implication of these findings is that promising therapeutic approaches can be derived from multidrug treatments aimed at the simultaneous interception of damage in both motor neurons and nonmotor neuronal cells.

Oxidized/misfolded superoxide dismutase-1: the cause of all amyotrophic lateral sclerosis?

The identification in 1993 of superoxide dismutase-1 (SOD1) mutations as the cause of 10 to 20% of familial amyotrophic lateral sclerosis cases, which represents 1 to 2% of all amyotrophic lateral sclerosis (ALS) cases, prompted a substantial amount of research into the mechanisms of SOD1-mediated toxicity. Recent experiments have demonstrated that oxidation of wild-type SOD1 leads to its misfolding, causing it to gain many of the same toxic properties as mutant SOD1. In vitro studies of oxidized/misfolded SOD1 and in vivo studies of misfolded SOD1 have indicated that these protein species are selectively toxic to motor neurons, suggesting that oxidized/misfolded SOD1 could lead to ALS even in individuals who do not carry an SOD1 mutation. It has also been reported that glial cells secrete oxidized/misfolded mutant SOD1 to the extracellular environment, where it can trigger the selective death of motor neurons, offering a possible explanation for the noncell autonomous nature of mutant SOD1 toxicity and the rapid progression of disease once the first symptoms develop. Therefore, considering that sporadic (SALS) and familial ALS (FALS) cases are clinically indistinguishable, the toxic properties of mutated SOD1 are similar to that of oxidized/misfolded wild-type SOD1 (wtSOD1), and secreted/extracellular misfolded SOD1 is selectively toxic to motor neurons, we propose that oxidized/misfolded SOD1 is the cause of most forms of classic ALS and should be a prime target for the design of ALS treatments.

Current clinical trials in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is caused by selective degeneration of motor neurons in the brain and spinal cord. There are still no other effective therapies 10 years after the approval of riluzole for the treatment of amyotrophic lateral sclerosis, but advances in drug development and screening are substantially increasing the number of potential therapeutic agents. This review provides an overview of clinical trial methodology in amyotrophic lateral sclerosis followed by a systematic evaluation of drugs that are presently in Phase I, II and III clinical trials. There is an emphasis on the scientific evidence supporting the selection of each drug being tested, as well as on trial design.

Emerging disease-modifying therapies for the treatment of motor neuron disease/amyotropic lateral sclerosis

It has been > 130 years since the first description of the upper and lower motor neuron disease called amyotropic lateral sclerosis (ALS). Sadly, there has been little change in the long interval over which this disease is diagnosed, or in its poor prognosis. Significant gains have been made, however, in understanding its pathophysiology and in symptomatic care. Disease-causing mutations have been identified and used to create animal models. Other identified mutations may increase susceptibility and cause disease only in a particular environment and at a particular age. A number of 'downstream' molecular pathways have been implicated, including transcriptional disturbances, protein aggregation, excitotoxicity, mitochondrial dysfunction, oxidative stress, neuroinflammation, cytoskeletal and axonal transport derangements, growth factor dysregulation and apoptosis. This knowledge has led to an impressive pipeline of candidate therapies that offer hope for finally being able to alter ALS disease progression. These are described and prioritized herein, and suggestions are offered for efficiently sifting through them.

Fas small interfering RNA reduces motoneuron death in amyotrophic lateral sclerosis mice

OBJECTIVE

Amyotrophic lateral sclerosis (ALS) is a progressive, fatal neurodegenerative disease characterized by selective motoneuron death. Understanding of the molecular mechanisms that trigger and regulate motoneuron degeneration could be relevant to ALS and other motoneuron disorders. This study investigates the role of Fas-linked motoneuron death in the pathogenesis of ALS.

METHODS

We performed in vitro and in vivo small interfering RNA-mediated interference, by silencing the Fas receptor on motoneurons that carry the superoxide dismutase-1 (SOD1)-G93A mutation.

RESULTS

We observed a significant reduction in Fas expression at messenger RNA (p < 0.001) and protein levels. Treated motoneurons demonstrated an increase in survival and a reduction in cytochrome c release from mitochondria. In vivo, continuous intrathecal administration of Fas small interfering RNA by an osmotic minipump improved motor function and survival in SOD1-G93A mice (mean increase, 18 days; p < 0.0001). Treated mice showed a significant reduction in Fas and Fas mediators p38 mitogen-activated protein kinase, neuronal nitric oxide synthase, and caspase-8.

INTERPRETATION

Fas silencing interferes with motoneuron-specific downstream death pathways and results in increased motoneuron survival and amelioration of the SOD1-G93A phenotype, suggesting new possible strategies for molecular therapy of ALS.

Therapeutic RNA interference for neurodegenerative diseases: From promise to progress

RNA interference (RNAi) has emerged as a powerful tool to manipulate gene expression in the laboratory. Due to its remarkable discriminating properties, individual genes, or even alleles can be targeted with exquisite specificity in cultured cells or living animals. Among its many potential biomedical applications, silencing of disease-linked genes stands out as a promising therapeutic strategy for many incurable disorders. Neurodegenerative diseases represent one of the more attractive targets for the development of therapeutic RNAi. In this group of diseases, the progressive loss of neurons leads to the gradual appearance of disabling neurological symptoms and premature death. Currently available therapies aim to improve the symptoms but not to halt the process of neurodegeneration. The increasing prevalence and economic burden of some of these diseases, such as Alzheimer's disease (AD) or Parkinson's disease (PD), has boosted the efforts invested in the development of interventions, such as RNAi, aimed at altering their natural course. This review will summarize where we stand in the therapeutic application of RNAi for neurodegenerative diseases. The basic principles of RNAi will be reviewed, focusing on features important for its therapeutic manipulation. Subsequently, a stepwise strategy for the development of therapeutic RNAi will be presented. Finally, the different preclinical trials of therapeutic RNAi completed in disease models will be summarized, stressing the experimental questions that need to be addressed before planning application in human disease.

Inhibition of UCP2 expression reverses diet-induced diabetes mellitus by effects on both insulin secretion and action

Recent characterization of the ability of uncoupling protein 2 (UCP2) to reduce ATP production and inhibit insulin secretion by pancreatic beta-cells has placed this mitochondrial protein as a candidate target for therapeutics in diabetes mellitus. In the present study we evaluate the effects of short-term treatment of two animal models of type 2 diabetes mellitus with an antisense oligonucleotide to UCP2. In both models, Swiss mice (made obese and diabetic by a hyperlipidic diet) and ob/ob mice, the treatment resulted in a significant improvement in the hyperglycemic syndrome. This effect was due not only to an improvement of insulin secretion, but also to improved peripheral insulin action. In isolated pancreatic islets, the partial inhibition of UCP2 increased ATP content, followed by increased glucose-stimulated insulin secretion. This was not accompanied by increased expression of enzymes involved in protection against oxidative stress. The evaluation of insulin action in peripheral tissues revealed that the inhibition of UCP2 expression significantly improved insulin signal transduction in adipose tissue. In conclusion, short-term inhibition of UCP2 expression ameliorates the hyperglycemic syndrome in two distinct animal models of obesity and diabetes. Metabolic improvement is due to a combined effect on insulin-producing pancreatic islets and in at least one peripheral tissue that acts as a target for insulin.

ALS: a disease of motor neurons and their nonneuronal neighbors

Amyotrophic lateral sclerosis is a late-onset progressive neurodegenerative disease affecting motor neurons. The etiology of most ALS cases remains unknown, but 2% of instances are due to mutations in Cu/Zn superoxide dismutase (SOD1). Since sporadic and familial ALS affects the same neurons with similar pathology, it is hoped that therapies effective in mutant SOD1 models will translate to sporadic ALS. Mutant SOD1 induces non-cell-autonomous motor neuron killing by an unknown gain of toxicity. Selective vulnerability of motor neurons likely arises from a combination of several mechanisms, including protein misfolding, mitochondrial dysfunction, oxidative damage, defective axonal transport, excitotoxicity, insufficient growth factor signaling, and inflammation. Damage within motor neurons is enhanced by damage incurred by nonneuronal neighboring cells, via an inflammatory response that accelerates disease progression. These findings validate therapeutic approaches aimed at nonneuronal cells.

Molecular biology of amyotrophic lateral sclerosis: insights from genetics

Amyotrophic lateral sclerosis (ALS) is a paralytic disorder caused by motor neuron degeneration. Mutations in more than 50 human genes cause diverse types of motor neuron pathology. Moreover, defects in five Mendelian genes lead to motor neuron disease, with two mutations reproducing the ALS phenotype. Analyses of these genetic effects have generated new insights into the diverse molecular pathways involved in ALS pathogenesis. Here, we present an overview of the mechanisms for motor neuron death and of the role of non-neuronal cells in ALS.