Micro-dystrophin and follistatin co-delivery restores muscle function in aged DMD model.

Pharmacologic strategies have provided modest improvement in the devastating muscle-wasting disease, Duchenne muscular dystrophy (DMD). Pre-clinical gene therapy studies have shown promise in the mdx mouse model; however, studies conducted after disease onset fall short of fully correcting muscle strength or protecting against contraction-induced injury. Here we examine the treatment effect on muscle physiology in aged dystrophic mice with significant disease pathology by combining two promising therapies: micro-dystrophin gene replacement and muscle enhancement with follistatin, a potent myostatin inhibitor. Individual treatments with micro-dystrophin and follistatin demonstrated marked improvement in mdx mice but were insufficient to fully restore muscle strength and response to injury to wild-type levels. Strikingly, when combined, micro-dystrophin/follistatin treatment restored force generation and conferred resistance to contraction-induced injury in aged mdx mice. Pre-clinical studies with miniature dystrophins have failed to demonstrate full correction of the physiological defects seen in mdx mice. Importantly, the addition of a muscle enhancement strategy with delivery of follistatin in combination with micro-dystrophin gene therapy completely restored resistance to eccentric contraction-induced injury and improved force. Eccentric contraction-induced injury is a pre-clinical parameter relevant to the exercise induced injury that occurs in DMD patients, and herein, we demonstrate compelling evidence for the therapeutic potential of micro-dystrophin/follistatin combinatorial therapy.

Regulated neuronal neuromodulation via spinal cord expression of the gene for the inwardly rectifying potassium channel 2.1 (Kir2.1).

BACKGROUND: Neuromodulation is used to restore neural function in disorders that stem from an imbalance in the activity of specific neural networks when they prove refractory to pharmacological therapy. The Kir2.1 gene contributes to stabilizing the resting potential below the threshold of activation of voltage-gated sodium channels and action potentials. Therefore, the delivery of the Kir2.1 gene to neuronal cells could reduce the probability of action potential generation, inhibiting excessive neural activity. OBJECTIVE: To address the hypothesis that overexpression of the inwardly rectifying potassium channel 2.1 (Kir2.1) gene could inhibit motor neuron activity and therefore be therapeutically used in gene-based neuromodulation. METHODS: To induce expression of Kir2.1, the inducible RheoSwitch promoter was used and controlled by ligand. In vivo gene expression was accomplished by an adenoviral vector to deliver unilaterally into the lumbar spinal cord of rats. RESULTS: Behavioral assays demonstrated that neuromuscular inhibition was exclusive to rats that received the ligand. Histological analysis also showed evidence of some motor neuron loss in these animals. Behavioral effects of Kir2.1 expression were completely reversible, arguing that the behavioral effect did not result from motor neuron death. CONCLUSION: Delivery of the gene for Kir2.1 inhibits neurons by resisting depolarization to the action potential threshold. Regulated neuronal expression of Kir2.1 may provide an elegant means for neuromodulation in a selected neuronal population.

Characterization of a murine model of SMA.

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disease, which is the leading genetic cause of mortality in children. To date no effective treatment exists for SMA. The genetic basis for SMA has been well documented as a mutation in the gene for survival of motor neuron (SMN). Because there is an understanding of which gene needs to be replaced (SMN) and where it needs to be replaced (spinal motor systems), SMA is an ideal target for gene replacement via gene therapy. While a variety of animal models for SMA exist, they are either too fulminant to realistically test most gene delivery strategies, or too mild to provide a robust read out of the therapeutic effect. The field, therefore, requires a robust model with a slower symptomatic progression. A conditional knockout of SMN in neuronal cell types, giving a phenotype of functional motor defects, weight loss and reduced life expectancy partially satisfies this need (Frugier, Tiziano et al. 2000). This Cre/LoxP mediated neuron specific model presents an attractive alternative. In the present manuscript, we characterize the functional motor deficits of the model. We observed a decline in locomotor ability, as assessed by open field testing. The finer functions of motor skills such as righting reflex and grip strength were also observed to degenerate in the SMA mice. The decline in motor function that we observed here correlates with the anatomical decline in motor neurons and motor axons presented in the literature (Ferri, Melki et al. 2004). This work adds to our understanding and knowledge base of this Cre/LoxP model and provides a basis from which functional recovery, following interventions can be assessed.

Gene therapy: a potential approach for cancer pain.

Chronic pain is experienced by as many as 90% of cancer patients at some point during the disease. This pain can be directly cancer related or arise from a sensory neuropathy related to chemotherapy. Major pharmacological agents used to treat cancer pain often lack anatomical specificity and can have off-target effects that create new sources of suffering. These concerns establish a need for improved cancer pain management. Gene therapy is emerging as an exciting prospect. This paper discusses the potential for viral vector-based treatment of cancer pain. It describes studies involving vector delivery of transgenes to laboratory pain models to modulate the nociceptive cascade. It also discusses clinical investigations aimed at regulating pain in cancer patients. Considering the prevalence of pain among cancer patients and the growing potential of gene therapy, these studies could set the stage for a new class of medicines that selectively disrupt nociceptive signaling with limited off-target effects.

Pain in amyotrophic lateral sclerosis: a neglected aspect of disease.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder marked by progressive loss of motor neurons, muscle wasting, and respiratory dysfunction. With disease progression, secondary symptoms arise creating new problematic conditions for ALS patients. Amongst these is pain. Although not a primary consequence of disease, pain occurs in a substantial number of individuals. Yet, studies investigating its pathomechanistic properties in the ALS patient are lacking. Therefore, more exploratory efforts into its scope, severity, impact, and treatment should be initiated. Several studies investigating the use of Clostridial neurotoxins for the reduction of pain in ALS patients suggest the potential for a neural specific approach involving focal drug delivery. Gene therapy represents a way to accomplish this. Therefore, the use of viral vectors to express transgenes that modulate the nociceptive cascade could prove to be an effective way to achieve meaningful benefit in conditions of pain in ALS.

AAV4-mediated expression of IGF-1 and VEGF within cellular components of the ventricular system improves survival outcome in familial ALS mice.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by motor neuron cell death in the cortex, brainstem, and spinal cord. Extensive efforts have been made to develop trophic factor-based therapies to enhance motor neuron survival; however, achievement of adequate therapeutic delivery to all regions of the corticospinal tract has remained a significant challenge. Here, we show that adeno-associated virus serotype 4 (AAV4)-mediated expression of insulin-like growth factor-1 (IGF-1) or vascular endothelial growth factor (VEGF)-165 in the cellular components of the ventricular system including the ependymal cell layer, choroid plexus [the primary cerebrospinal fluid (CSF)-producing cells of the central nervous system (CNS)] and spinal cord central canal leads to trophic factor delivery throughout the CNS, delayed motor decline and a significant extension of survival in SOD1(G93A) transgenic mice. Interestingly, when IGF-1- and VEGF-165-expressing AAV4 vectors were given in combination, no additional benefit in efficacy was observed suggesting that these trophic factors are acting on similar signaling pathways to modestly slow disease progression. Consistent with these findings, experiments conducted in a recently described in vitro cell culture model of ALS led to a similar result, with both IGF-1 and VEGF-165 providing significant motor neuron protection but in a nonadditive fashion. These findings support the continued investigation of trophic factor-based therapies that target the CNS as a potential treatment of ALS.

Inhibition of myostatin with emphasis on follistatin as a therapy for muscle disease.

In most cases, pharmacologic strategies to treat genetic muscle disorders and certain acquired disorders, such as sporadic inclusion body myositis, have produced modest clinical benefits. In these conditions, inhibition of the myostatin pathway represents an alternative strategy to improve functional outcomes. Preclinical data that support this approach clearly demonstrate the potential for blocking the myostatin pathway. Follistatin has emerged as a powerful antagonist of myostatin that can increase muscle mass and strength. Follistatin was first isolated from the ovary and is known to suppress follicle-stimulating hormone. This raises concerns for potential adverse effects on the hypothalamic-pituitary-gonadal axis and possible reproductive capabilities. In this review we demonstrate a strategy to bypass off-target effects using an alternatively spliced cDNA of follistatin (FS344) delivered by adeno-associated virus (AAV) to muscle. The transgene product is a peptide of 315 amino acids that is secreted from the muscle and circulates in the serum, thus avoiding cell-surface binding sites. Using this approach our translational studies show increased muscle size and strength in species ranging from mice to monkeys. Adverse effects are avoided, and no organ system pathology or change in reproductive capabilities has been seen. These findings provide the impetus to move toward gene therapy clinical trials with delivery of AAV-FS344 to increase size and function of muscle in patients with neuromuscular disease.

Increased glial glutamate transporter EAAT2 expression reduces visceral nociceptive response in mice.

Visceral hypersensitivity is the leading complaint of functional bowel disorders. Central sensitization mediated by glutamate receptor activation is implicated in pathophysiology of visceral pain. The glial glutamate transporter EAAT2 is the principal mediator of glutamate clearance to terminate glutamate-mediated responses. Transgenic mice overexpressing human EAAT2 (EAAT2 mice), which exhibited a twofold enhanced glutamate uptake, showed 39% less writhing response to intraperitoneal acetic acid than nontransgenic littermates. Moreover, EAAT2 transgenic mice showed a 53-64% reduction in visceromotor response (VMR) to colorectal distension (CRD) in assessments of the response to graded increase in pressures. Corroborating the involvement of enhanced glutamate uptake, wild-type mice treated for 1 wk with ceftriaxone, an EAAT2 expression activator, showed a 49-70% reduction in VMR to CRD. Moreover, systemic pretreatment with the selective EAAT2 transporter blocker dihydrokainate reversed the ceftriaxone-blunted nociceptive response to CRD. However, the enhanced VMR to CRD produced by intracolonic ethanol was not significantly attenuated by 1-wk ceftriaxone pretreatment. The data suggest that enhanced glutamate uptake provides protective effects against colonic distension-induced nociception and represents an exciting new mechanistic approach leading to better therapeutic options to visceral pain disorders.

Follistatin gene delivery enhances muscle growth and strength in nonhuman primates.

Antagonists of myostatin, a blood-borne negative regulator of muscle growth produced in muscle cells, have shown considerable promise for enhancing muscle mass and strength in rodent studies and could serve as potential therapeutic agents for human muscle diseases. One of the most potent of these agents, follistatin, is both safe and effective in mice, but similar tests have not been performed in nonhuman primates. To assess this important criterion for clinical translation, we tested an alternatively spliced form of human follistatin that affects skeletal muscle but that has only minimal effects on nonmuscle cells. When injected into the quadriceps of cynomolgus macaque monkeys, a follistatin isoform expressed from an adeno-associated virus serotype 1 vector, AAV1-FS344, induced pronounced and durable increases in muscle size and strength. Long-term expression of the transgene did not produce any abnormal changes in the morphology or function of key organs, indicating the safety of gene delivery by intramuscular injection of an AAV1 vector. Our results, together with the findings in mice, suggest that therapy with AAV1-FS344 may improve muscle mass and function in patients with certain degenerative muscle disorders.

Long-term enhancement of skeletal muscle mass and strength by single gene administration of myostatin inhibitors.

Increasing the size and strength of muscles represents a promising therapeutic strategy for musculoskeletal disorders, and interest has focused on myostatin, a negative regulator of muscle growth. Various myostatin inhibitor approaches have been identified and tested in models of muscle disease with varying efficacies, depending on the age at which myostatin inhibition occurs. Here, we describe a one-time gene administration of myostatin-inhibitor-proteins to enhance muscle mass and strength in normal and dystrophic mouse models for >2 years, even when delivered in aged animals. These results demonstrate a promising therapeutic strategy that warrants consideration for clinical trials in human muscle diseases.