Dantrolene normalizes serum creatine kinase in MDX mice

Repurposing Dantrolene for Long-Term Combination Therapy to Potentiate Antisense-Mediated DMD Exon Skipping in the mdx Mouse

Duchenne muscular dystrophy (DMD) is caused by mutations in DMD, resulting in loss of dystrophin, which is essential to muscle health. DMD “exon skipping” uses anti-sense oligo-nucleotides (AONs) to force specific exon exclusion during mRNA processing to restore reading frame and rescue of partially functional dystrophin protein. Although exon-skipping drugs in humans show promise, levels of rescued dystrophin protein remain suboptimal. We previously identified dantrolene as a skip booster when combined with AON in human DMD cultures and short-term mdx dystrophic mouse studies. Here, we assess the effect of dantrolene/AON combination on DMD exon-23 skipping over long-term mdx treatment under conditions that better approximate potential human dosing. To evaluate the dantrolene/AON combination treatment effect on dystrophin induction, we assayed three AON doses, with and without oral dantrolene, to assess multiple outcomes across different muscles. Meta-analyses of the results of statistical tests from both the quadriceps and diaphragm assessing contributions of dantrolene beyond AON, across all AON treatment groups, provide strong evidence that dantrolene modestly boosts exon skipping and dystrophin rescue while reducing muscle pathology in mdx mice (p < 0.0087). These findings support a trial of combination dantrolene/AON to increase exon-skipping efficacy and highlight the value of combinatorial approaches and Food and Drug Administration (FDA) drug re-purposing for discovery of unsuspected therapeutic application and rapid translation.

High throughput screening in duchenne muscular dystrophy: from drug discovery to functional genomics

Centers for the screening of biologically active compounds and genomic libraries are becoming common in the academic setting and have enabled researchers devoted to developing strategies for the treatment of diseases or interested in studying a biological phenomenon to have unprecedented access to libraries that, until few years ago, were accessible only by pharmaceutical companies. As a result, new drugs and genetic targets have now been identified for the treatment of Duchenne muscular dystrophy (DMD), the most prominent of the neuromuscular disorders affecting children. Although the work is still at an early stage, the results obtained to date are encouraging and demonstrate the importance that these centers may have in advancing therapeutic strategies for DMD as well as other diseases. This review will provide a summary of the status and progress made toward the development of a cure for this disorder and implementing high-throughput screening (HTS) technologies as the main source of discovery. As more academic institutions are gaining access to HTS as a valuable discovery tool, the identification of new biologically active molecules is likely to grow larger. In addition, the presence in the academic setting of experts in different aspects of the disease will offer the opportunity to develop novel assays capable of identifying new targets to be pursued as potential therapeutic options. These assays will represent an excellent source to be used by pharmaceutical companies for the screening of larger libraries providing the opportunity to establish strong collaborations between the private and academic sectors and maximizing the chances of bringing into the clinic new drugs for the treatment of DMD.

Effects of Dantrolene Therapy on Disease Phenotype in Dystrophin Deficient mdx Mice

Dystrophin deficiency causes contraction-induced injury and damage to the muscle fiber, resulting in sustained increase in intracellular calcium levels, activation of calcium-dependent proteases and cell death. It is known that the Ryanodine receptor (RyR1) on the sarcoplasmic reticular (SR) membrane controls calcium release. Dantrolene, an FDA approved skeletal muscle relaxant, inhibits the release of calcium from the SR during excitation-contraction and suppresses uncontrolled calcium release by directly acting on the RyR complex to limit its activation. This study examines whether Dantrolene can reduce the disease phenotype in the mdx mouse model of muscular dystrophy. We treated mdx mice (4 weeks old) with daily intraperitoneal injections of 40mg/kg of Dantrolene for 6 weeks and measured functional (grip strength, in vitro force contractions), behavioral (open field digiscan), imagining (optical imaging for inflammation), histological (H&E), and molecular (protein and RNA) endpoints in a blinded fashion. We found that treatment with Dantrolene resulted in decreased grip strength and open field behavioral activity in mdx mice. There was no significant difference in inflammation either by optical imaging analysis of cathepsin activity or histological (H&E) analysis. In vitro force contraction measures showed no changes in EDL muscle-specific force, lengthening-contraction force deficit, or fatigue resistance. We found Dantrolene treatment significantly reduces serum CK levels. Further, Dantrolene-treated mice showed decreased SERCA1 but not RyR1 expression in skeletal muscle. These results suggest that Dantrolene treatment alone has no significant beneficial effects at the tested doses in young mdx mice.

Dantrolene enhances antisense-mediated exon skipping in human and mouse models of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) causes profound and progressive muscle weakness and loss, resulting in early death. DMD is usually caused by frameshifting deletions in the gene DMD, which leads to absence of dystrophin protein. Dystrophin binds to F-actin and components of the dystrophin-associated glycoprotein complex and protects the sarcolemma from contraction-induced injury. Antisense oligonucleotide-mediated exon skipping is a promising therapeutic approach aimed at restoring the DMD reading frame and allowing expression of an intact dystrophin glycoprotein complex. To date, low levels of dystrophin protein have been produced in humans by this method. We performed a small-molecule screen to identify existing drugs that enhance antisense-directed exon skipping. We found that dantrolene, currently used to treat malignant hyperthermia, potentiates antisense oligomer-guided exon skipping to increase exon skipping to restore the mRNA reading frame, the sarcolemmal dystrophin protein, and the dystrophin glycoprotein complex in skeletal muscles of mdx mice when delivered intramuscularly or intravenously. Further, dantrolene synergized with multiple weekly injections of antisense to increase muscle strength and reduce serum creatine kinase in mdx mice. Dantrolene similarly promoted antisense-mediated exon skipping in reprogrammed myotubes from DMD patients. Ryanodine and Rycal S107, which, like dantrolene, targets the ryanodine receptor, also promoted antisense-driven exon skipping, implicating the ryanodine receptor as the critical molecular target.

Loss of cIAP1 attenuates soleus muscle pathology and improves diaphragm function in mdx mice

The cellular inhibitor of apoptosis 1 (cIAP1) protein is an essential regulator of canonical and noncanonical nuclear factor κB (NF-κB) signaling pathways. NF-κB signaling is known to play important roles in myogenesis and degenerative muscle disorders such as Duchenne muscular dystrophy (DMD), but the involvement of cIAP1 in muscle disease has not been studied directly. Here, we asked whether the loss of cIAP1 would influence the pathology of skeletal muscle in the mdx mouse model of DMD. Double-mutant cIAP1(-/-);mdx mice exhibited reduced muscle damage and decreased fiber centronucleation in the soleus, compared with single-mutant cIAP1(+/+);mdx mice. This improvement in pathology was associated with a reduction in muscle infiltration by macrophages and diminished expression of inflammatory cytokines such as IL-6 and tumor necrosis factor-α. Furthermore, the cIAP1(-/-);mdx mice exhibited reduced serum creatine kinase, and improved exercise endurance associated with improved exercise resilience by the diaphragm. Mechanistically, the loss of cIAP1 was sufficient to drive constitutive activation of the noncanonical NF-κB pathway, which led to increased myoblast fusion in vitro and in vivo. Collectively, these results show that the loss of cIAP1 protects skeletal muscle from the degenerative pathology resulting from systemic loss of dystrophin.

Clenbuterol, a beta 2-agonist, retards wasting and loss of contractility in irradiated dystrophic mdx muscle

Treatment with the adrenergic beta 2-receptor agonist clenbuterol prevented, in dystrophic muscle from mdx mice, a pronounced loss of contractile strength that is observed after blockade of muscle regeneration with gamma irradiation. In addition, muscle mass and myosin content were greater (62-109%) in irradiated hindlimbs from clenbuterol-treated mdx mice, whereas the effects of the beta 2-agonist were relatively smaller (12-21%) in the nonirradiated hindlimbs. Together, these results suggest that beta 2-agonists can antagonize degenerative processes occurring in muscle fibers lacking dystrophin.

Dantrolene ameliorates the metabolic hallmarks of sepsis in rats and improves survival in a mouse model of endotoxemia

Sepsis is the systemic inflammatory response resulting from serious infection and is the most common cause of death in intensive care units. Intracellular free calcium concentration ([Ca2+]i) is an important regulator of numerous cellular processes and when increased excessively may act as a potent cellular toxin. To determine if [Ca2+]i is responsible for the major metabolic changes which are hallmarks of sepsis, we examined if sodium dantrolene, a drug which decreases release of calcium from sarcoplasmic reticulum, affected the metabolic abnormalities in plasma and epitrochlearis muscles of rats made septic by cecal ligation and perforation. Dantrolene when added in vitro or when given in vivo decreases many of the metabolic hallmarks of sepsis--i.e., muscle protein breakdown approximately 30%, muscle glucose transport approximately 38%, muscle lactate formation approximately 28%, and plasma lactate approximately 29% (P < 0.05). In addition, we examined the ability of dantrolene to improve survival in a mouse model of endotoxemia. Dantrolene caused > 2-fold improvement in survival when it was administered concurrently with endotoxin (54% vs. 20% survival in dantrolene-treated and control mice, respectively (P < 0.001). Our results are consistent with the hypothesis that an increase in [Ca2+]i plays an important role in the metabolic abnormalities which occur during sepsis and that dantrolene administration may be an effective therapeutic strategy.

Brain creatine kinase activity during ontogeny of the cichlid fish oreochromis mossambicus and the clawed toad Xenopus laevis, influence of gravity?

The development of creatine kinase (CK) activity was studied in the brain of cichlid fish and clawed toads. The activity of CK in the whole brain of the fish decreases immediately after hatching (stage 6) from values of about 135 nmol substrate cleaved/mg protein/min to a value of about 105 at stage 8 (5 days post hatch at 20 degrees C). With the exception of a significant peak (125 nmol) between stages 9 and 10 (7 and 9 days respectively, post hatch at 20 degrees C) and a small intermediate peak at stages 12 and 13 (about 10 days post hatch at 20 degrees C) a constant level of about 100 nmol cleaved substrate is maintained until maturity. In contrast, CK activity was determined to be 3-fold higher in the whole brain of the clawed toad. With the exception of two significant peaks at stages 47 and 49 (5 and 12 days respectively, post fertilization at 23 degrees C) a value of about 360 nmol was found during larval development and metamorphosis, as well as in the adult brain. In investigating the possible influence of gravity on CK activity during early ontogeny of the brain both animal species were exposed to hyper-gravity (3 +/- 1 g) for 7 days. A significant decrease of total CK activity of 20% was found in the fish brain and of about 5% in the toad.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations of protein degradation and 2-D protein pattern in muscle cells of MDX and DMD origin

Intracellular protein turnover of MDX, DMD and normal muscle was determined by [35S]methionine pulse-chase experiments and subsequent high resolution 2-D gel electrophoresis. In MDX myotubes intracellular degradation of short-lived and long-lived proteins was markedly increased by a factor of 1,4-2,1. In wildtype the rate of degradation of short-lived proteins was approximately 2.6%/h, whereas in MDX these proteins were degraded by 5.7%/h. Long-lived proteins were degraded in wildtype at a rate of 1.8%/h, and in MDX at a rate of 2.5%/h. Furthermore, we have described a 51.000 Da protein with an IEP of 5.1 (p51/5.1), whose net content is highly and specifically reduced in cultured MDX and DMD muscle cells as well as in isolated MDX muscle fibers. Treatment with calcium-channel blockers Dantrolene and Verapamil inhibited the degradation of p51/5.1 in MDX myotubes by more than 90% in contrast to controls.

Effect of dantrolene in Duchenne muscular dystrophy

We have demonstrated that maneuvers capable of reducing Ca influx into cells have beneficial effects in dystrophic hamsters and Duchenne muscular dystrophy. Since dantrolene inhibits Ca release from the sarcoplasmic reticulum, its effects on DMD was studied in 7 patients of 6 to 13 years of age (mean 10.8 years). Patients were studied for 4 years with tri-monthly evaluations of manual muscle testing (MMT), functional activity, and serum CK and aldolase. During the first 2-year period, no medicines were given and served as control. In the second 2-year period, dantrolene 8 mg/kg/d was administered. No side effects were observed. In 1 patient, mild weakness occurred that disappeared when the dose was reduced to 6 mg/kg/d. The 95% confidence limit for the difference in slopes of regression lines from tri-monthly MMT was asymmetric in favor of dantrolene in 5 of 7 patients. Serum CK did not differ between the first and second year of the control and treatment periods, respectively. However, it fell significantly from the second year of control to the first year of treatment (P = 0.003). The fall during the first year of treatment was significantly greater (P less than 0.01) than in age-matched natural history controls during the same length of observation. There was a 3-fold reduction in CK when the pooled values of the first and second year control vs. treatment periods were analyzed. No changes were observed in functional activity and serum aldolase. The data suggest that dantrolene reduces serum CK in DMD associated with a lessening trend in MMT deterioration.