Pharmacology of a central nervous system delivered 2'-O-methoxyethyl-modified survival of motor neuron splicing oligonucleotide in mice and nonhuman primates

SMN2 splice modulators enhance U1-pre-mRNA association and rescue SMA mice

Spinal muscular atrophy (SMA), which results from the loss of expression of the survival of motor neuron-1 (SMN1) gene, represents the most common genetic cause of pediatric mortality. A duplicate copy (SMN2) is inefficiently spliced, producing a truncated and unstable protein. We describe herein a potent, orally active, small-molecule enhancer of SMN2 splicing that elevates full-length SMN protein and extends survival in a severe SMA mouse model. We demonstrate that the molecular mechanism of action is via stabilization of the transient double-strand RNA structure formed by the SMN2 pre-mRNA and U1 small nuclear ribonucleic protein (snRNP) complex. The binding affinity of U1 snRNP to the 5' splice site is increased in a sequence-selective manner, discrete from constitutive recognition. This new mechanism demonstrates the feasibility of small molecule-mediated, sequence-selective splice modulation and the potential for leveraging this strategy in other splicing diseases.

Spinal muscular atrophy--recent therapeutic advances for an old challenge

In the past decade, improved understanding of spinal muscular atrophy (SMA) aetiopathogenesis has brought us to a historical turning point: we are at the verge of development of disease-modifying treatments for this hitherto incurable disease. The increasingly precise delineation of molecular targets within the survival of motor neuron (SMN) gene locus has led to the development of promising therapeutic strategies. These novel avenues in treatment for SMA include gene therapy, molecular therapy with antisense oligonucleotides, and small molecules that aim to increase expression of SMN protein. Stem cell studies of SMA have provided an in vitro model for SMA, and stem cell transplantation could be used as a complementary strategy with a potential to treat the symptomatic phases of the disease. Here, we provide an overview of established data and novel insights into SMA pathogenesis, including discussion of the crucial function of the SMN protein. Preclinical evidence and recent advances from ongoing clinical trials are thoroughly reviewed. The final remarks are dedicated to future clinical perspectives in this rapidly evolving field, with a broad discussion on the comparison between the outlined therapeutic approaches and the remaining open questions.

The Cancer Genome Atlas Analysis Predicts MicroRNA for Targeting Cancer Growth and Vascularization in Glioblastoma

Using in silico analysis of The Cancer Genome Atlas (TCGA), we identified microRNAs associated with glioblastoma (GBM) survival, and predicted their functions in glioma growth and progression. Inhibition of two "risky" miRNAs, miR-148a and miR-31, in orthotopic xenograft GBM mouse models suppressed tumor growth and thereby prolonged animal survival. Intracranial tumors treated with uncomplexed miR-148a and miR-31 antagomirs exhibited reduced proliferation, stem cell depletion, and normalized tumor vasculature. Growth-promoting functions of these two miRNAs were, in part, mediated by the common target, the factor inhibiting hypoxia-inducible factor 1 (FIH1), and the downstream pathways involving hypoxia-inducible factor HIF1α and Notch signaling. Therefore, miR-31 and miR-148a regulate glioma growth by maintaining tumor stem cells and their niche, and providing the tumor a way to activate angiogenesis even in a normoxic environment. This is the first study that demonstrates intratumoral uptake and growth-inhibiting effects of uncomplexed antagomirs in orthotopic glioma.

Effects on murine behavior and lifespan of selectively decreasing expression of mutant huntingtin allele by supt4h knockdown

Production of protein containing lengthy stretches of polyglutamine encoded by multiple repeats of the trinucleotide CAG is a hallmark of Huntington's disease (HD) and of a variety of other inherited degenerative neurological and neuromuscular disorders. Earlier work has shown that interference with production of the transcription elongation protein SUPT4H results in decreased cellular capacity to transcribe mutant huntingtin gene (Htt) alleles containing long CAG expansions, but has little effect on expression of genes containing short CAG stretches. zQ175 and R6/2 are genetically engineered mouse strains whose genomes contain human HTT alleles that include greatly expanded CAG repeats and which are used as animal models for HD. Here we show that reduction of SUPT4H expression in brains of zQ175 mice by intracerebroventricular bolus injection of antisense 2'-O-methoxyethyl oligonucleotides (ASOs) directed against Supt4h, or in R6/2 mice by deletion of one copy of the Supt4h gene, results in a decrease in mRNA and protein encoded specifically by mutant Htt alleles. We further show that reduction of SUPT4H in mouse brains is associated with decreased HTT protein aggregation, and in R6/2 mice, also with prolonged lifespan and delay of the motor impairment that normally develops in these animals. Our findings support the view that targeting of SUPT4H function may be useful as a therapeutic countermeasure against HD.

Rescue of gene-expression changes in an induced mouse model of spinal muscular atrophy by an antisense oligonucleotide that promotes inclusion of SMN2 exon 7

Spinal muscular atrophy (SMA) is a neuromuscular disease caused by disruption of the survival motor neuron 1 (SMN1) gene, partly compensated for by the paralogous gene SMN2. Exon 7 inclusion is critical for full-length SMN protein production and occurs at a much lower frequency for SMN2 than for SMN1. Antisense oligonucleotide (ASO)-mediated blockade of an intron 7 splicing silencer was previously shown to promote inclusion of SMN2 exon 7 in SMA mouse models and mediate phenotypic rescue. However, downstream molecular consequences of this ASO therapy have not been defined. Here we characterize the gene-expression changes that occur in an induced model of SMA and show substantial rescue of those changes in central nervous system tissue upon intracerebroventricular administration of an ASO that promotes inclusion of exon 7, with earlier administration promoting greater rescue. This study offers a robust reference set of preclinical pharmacodynamic gene expression effects for comparison of other investigational therapies for SMA.

Motor neuron cell-nonautonomous rescue of spinal muscular atrophy phenotypes in mild and severe transgenic mouse models

Survival of motor neuron (SMN) deficiency causes spinal muscular atrophy (SMA), but restoring SMN in motor neurons only partially rescues SMA in mouse models. Hua et al. address the relative importance of SMN restoration in the CNS versus peripheral tissues in mouse models by using a therapeutic splice-switching antisense oligonucleotide to restore SMN and a complementary decoy oligonucleotide to neutralize its effects in the CNS. Increasing SMN exclusively in peripheral tissues completely rescued necrosis in mild SMA mice and robustly extended survival in severe SMA mice, with significant improvements in vulnerable tissues and motor function.

Survival of motor neuron (SMN) deficiency causes spinal muscular atrophy (SMA), but the pathogenesis mechanisms remain elusive. Restoring SMN in motor neurons only partially rescues SMA in mouse models, although it is thought to be therapeutically essential. Here, we address the relative importance of SMN restoration in the central nervous system (CNS) versus peripheral tissues in mouse models using a therapeutic splice-switching antisense oligonucleotide to restore SMN and a complementary decoy oligonucleotide to neutralize its effects in the CNS. Increasing SMN exclusively in peripheral tissues completely rescued necrosis in mild SMA mice and robustly extended survival in severe SMA mice, with significant improvements in vulnerable tissues and motor function. Our data demonstrate a critical role of peripheral pathology in the mortality of SMA mice and indicate that peripheral SMN restoration compensates for its deficiency in the CNS and preserves motor neurons. Thus, SMA is not a cell-autonomous defect of motor neurons in SMA mice.

Splicing modulation therapy in the treatment of genetic diseases

Antisense-mediated splicing modulation is a tool that can be exploited in several ways to provide a potential therapy for rare genetic diseases. This approach is currently being tested in clinical trials for Duchenne muscular dystrophy and spinal muscular atrophy. The present review outlines the versatility of the approach to correct cryptic splicing, modulate alternative splicing, restore the open reading frame, and induce protein knockdown, providing examples of each. Finally, we outline a possible path forward toward the clinical application of this approach for a wide variety of inherited rare diseases.

Towards a therapy for Angelman syndrome by targeting a long non-coding RNA

Angelman syndrome (AS) is a single gene disorder characterized by intellectual disability, developmental delay, behavioral uniqueness, speech impairment, seizures, and ataxia^1,2. It is caused by maternal deficiency of the imprinted gene UBE3A, encoding an E3 ubiquitin ligase^3-5. All patients carry at least one copy of paternal UBE3A, which is intact but silenced by a nuclear-localized long non-coding RNA, UBE3A antisense transcript (UBE3A-ATS)^6-8. Murine Ube3a-ATS reduction by either transcription termination or topoisomerase I inhibition increased paternal Ube3a expression^9,10. Despite a clear understanding of the disease-causing event in AS and the potential to harness the intact paternal allele to correct disease, no gene-specific treatment exists for patients. Here we developed a potential therapeutic intervention for AS by reducing Ube3a-ATS with antisense oligonucleotides (ASOs). ASO treatment achieved specific reduction of Ube3a-ATS and sustained unsilencing of paternal Ube3a in neurons in vitro and in vivo. Partial restoration of UBE3A protein in an AS mouse model ameliorated some cognitive deficits associated with the disease. Although additional studies of phenotypic correction are needed, for the first time we developed a sequence-specific and clinically feasible method to activate expression of the paternal Ube3a allele.

Spinal muscular atrophy: journeying from bench to bedside

Spinal muscular atrophy (SMA) is a frequently fatal neuromuscular disorder and the most common inherited cause of infant mortality. SMA results from reduced levels of the survival of motor neuron (SMN) protein. Although the disease was first described more than a century ago, a precise understanding of its genetics was not obtained until the SMA genes were cloned in 1995. This was followed in rapid succession by experiments that assigned a role to the SMN protein in the proper splicing of genes, novel animal models of the disease, and the eventual use of the models in the pre clinical development of rational therapies for SMA. These successes have led the scientific and clinical communities to the cusp of what are expected to be the first truly promising treatments for the human disorder. Yet, important questions remain, not the least of which is how SMN paucity triggers a predominantly neuromuscular phenotype. Here we review how our understanding of the disease has evolved since the SMA genes were identified. We begin with a brief description of the genetics of SMA and the proposed roles of the SMN protein. We follow with an examination of how the genetics of the disease was exploited to develop genetically faithful animal models, and highlight the insights gained from their analysis. We end with a discussion of ongoing debates, future challenges, and the most promising treatments to have emerged from our current knowledge of the disease.

Allele-specific suppression of mutant huntingtin using antisense oligonucleotides: providing a therapeutic option for all Huntington disease patients

Huntington disease (HD) is an inherited, fatal neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin gene. The mutant protein causes neuronal dysfunction and degeneration resulting in motor dysfunction, cognitive decline, and psychiatric disturbances. Currently, there is no disease altering treatment, and symptomatic therapy has limited benefit. The pathogenesis of HD is complicated and multiple pathways are compromised. Addressing the problem at its genetic root by suppressing mutant huntingtin expression is a promising therapeutic strategy for HD. We have developed and evaluated antisense oligonucleotides (ASOs) targeting single nucleotide polymorphisms that are significantly enriched on HD alleles (HD-SNPs). We describe our structure-activity relationship studies for ASO design and find that adjusting the SNP position within the gap, chemical modifications of the wings, and shortening the unmodified gap are critical for potent, specific, and well tolerated silencing of mutant huntingtin. Finally, we show that using two distinct ASO drugs targeting the two allelic variants of an HD-SNP could provide a therapeutic option for all persons with HD; allele-specifically for roughly half, and non-specifically for the remainder.