Long-term Safety and Dosing of OnabotulinumtoxinA: A Prospective, Observational Study.

BACKGROUND: Although therapeutic treatments are intended to help alleviate symptoms associated with disease, safety must be carefully considered and monitored to confirm continued positive benefit/risk balance. The objective of MOBILITY was to study the long-term safety of onabotulinumtoxinA for treatment of various therapeutic indications. METHODS: A prospective, multicenter, observational, Phase IV Canadian study in patients treated with onabotulinumtoxinA for a therapeutic indication. Dosing was determined by the participating physician. Adverse events (AEs) were recorded throughout the study. RESULTS: Patients (n = 1372) with adult focal spasticity, blepharospasm, cerebral palsy, cervical dystonia, hemifacial spasm, hyperhidrosis, or "other" diagnoses were enrolled into the safety cohort. Eighty-three patients (6%) reported 209 AEs; 44 AEs in 24 patients (2%) were considered treatment-related AEs. Seventy-two serious AEs were reported by 38 patients (3%); 10 serious AEs in 5 patients (0.4%) were considered treatment related. Most commonly reported treatment-related AEs were muscular weakness (n = 7/44) and dysphagia (n = 6/44). CONCLUSIONS: In patients with follow-up for up to six treatments with onabotulinumtoxinA, treatment-related AEs were reported in <2% of the safety population over the course of nearly 5 years. Our findings from MOBILITY provide further evidence that onabotulinumtoxinA treatment is safe for long-term use across a variety of therapeutic indications.

Dosage et sécurité à long terme de l'onabotulinumtoxinA : une étude prospective et observationnelle. Contexte : Bien que les traitements thérapeutiques soient destinés à soulager les symptômes associés à une maladie, il importe d'examiner avec grand soin leur sécurité et d'en assurer un suivi afin de maintenir un rapport bénéfice/risque qui soit positif. L'objectif de MOBILITY a donc été d'étudier la sécurité à long terme de l'onabotulinumtoxinA dans le traitement de plusieurs indications thérapeutiques. Méthodes : Nous avons ainsi fait appel à une étude canadienne prospective et observationnelle menée dans plusieurs centres de santé. Dans cette étude de phase IV, des patients ont été traités avec l'onabotulinumtoxinA en vertu d'indications thérapeutiques. Ce sont des médecins participants qui en avaient déterminé le dosage. De plus, tout événement indésirable a été noté en cours d'étude. Résultats : Au total 1372 patients ont été inclus dans cette cohorte (n = 1372). Ces patients étaient atteints des troubles suivants : spasticité focale chez l'adulte, blépharospasme, infirmité motrice cérébrale, dystonie cervicale, spasmes hémifaciaux, hyperhidrose, etc. On a signalé chez 83 patients, soit 6 % d'entre eux, des événements indésirables. On a aussi estimé que 44 événements indésirables ayant affecté 24 patients (2 %) étaient reliés au traitement proprement dit. Ajoutons que 38 patients (3 %) ont signalé avoir été victimes d'événements indésirables et que 10 événements indésirables ont été reliés au traitement chez 5 patients (0,4 %). Enfin, les événements indésirables les plus communément signalés ont été la faiblesse musculaire (n = 7/44) et la dysphagie (n = 6/44). Conclusions : Dans le cas de patients ayant bénéficié de six traitements ou moins avec l'onabotulinumtoxinA, des événements indésirables ont été signalés chez < 2 % d'entre eux au cours des presque cinq prochaines années. Tirés de MOBILITY, nos résultats apportent une preuve additionnelle que les traitements avec l'onabotulinumtoxinA sont à long terme sécuritaires dans le cas de nombreuses indications thérapeutiques.

Real-World, Long-Term Quality of Life Following Therapeutic OnabotulinumtoxinA Treatment.

BACKGROUND: OnabotulinumtoxinA is an efficacious treatment option for patients with various conditions. Although studies have reported on the efficacy of onabotulinumtoxinA, quality of life (QoL) data are limited. This study evaluated QoL in patients treated with onabotulinumtoxinA across various therapeutic indications. METHODS: MDs on BOTOX Utility (MOBILITY) was a prospective, multicenter, observational Canadian study in patients initiating (naïve) or receiving ongoing (maintenance) onabotulinumtoxinA treatment. Health utility was the primary outcome measure and was obtained from the Short Form-12 Health Survey using the Short Form-6D at baseline, week 4 posttreatment, and up to five subsequent treatment visits. The safety cohort included patients who received ≥1 onabotulinumtoxinA treatment. RESULTS: The efficacy cohort included 1062 patients; the majority were Caucasian, female, and on maintenance onabotulinumtoxinA treatment. Adult focal spasticity (n=398), blepharospasm (n=81), cerebral palsy (n=22), cervical dystonia (n=234), hemifacial spasm (n=116), and hyperhidrosis (n=211) patients were included. Baseline health utility was generally higher in maintenance versus naïve patients; however, naïve patients showed the greatest improvements over time. Health utility was generally maintained or trended toward improvement across all cohorts, including maintenance patients who had been treated for up to 22 years before study entry. Eighteen of 1222 patients (2%) in the safety cohort reported 28 treatment-related adverse events; eight were serious in four patients. CONCLUSION: MOBILITY is the largest prospective study to date to provide QoL data over a variety of therapeutic indications following treatment with onabotulinumtoxinA. Although the QoL burden varies by disease, data suggest that long-term treatment may help improve or maintain QoL over time.

ATP depletion inhibits the endocytosis of ClC-2.

The chloride channel, ClC-2 is expressed ubiquitously and participates in multiple physiological processes. In particular, ClC-2 has been implicated in the regulation of neuronal chloride ion homeostasis and mutations in ClC-2 are associated with idiopathic generalized epilepsy. Despite the physiological and pathophysiological significance of this channel, its regulation remains incompletely understood. The functional expression of ClC-2 at the cell surface has been shown to be enhanced by depletion of cellular ATP, implicating its possible role in cellular energy sensing. In the present study, biochemical assays of cell surface expression suggest that this gain of function reflects, in part, an increase in channel number due to the reduction in ClC-2 internalization by endocytosis. Cell surface expression of the disease-causing mutant: G715E, thought to lack wild-type nucleotide binding affinity, is similarly affected, suggesting that ATP-depletion modifies the function of proteins in the endocytic pathway rather than ClC-2 directly. Using a combination of immunofluorescence and biochemical studies, we confirmed that ClC-2 is internalized via dynamin-dependent endocytosis and that the change in surface expression evoked by ATP depletion is partially mimicked by inhibition of dynamin function using a dynamin dominant-negative mutant (DynK44A). Furthermore, trafficking via the early endosomal compartment occurs in part through rab5-associated vesicles and recycling of ClC-2 to the cell surface occurs through a rab11 dependent pathway. In summary, we have determined that the internalization of ClC-2 by endocytosis is inhibited by metabolic stress, highlighting the importance for understanding the molecular mechanisms mediating the endosomal trafficking of this channel.

Role of intramolecular and intermolecular interactions in ClC channel and transporter function.

The ClC family of chloride channels and transporters includes several members in which mutations have been associated with human disease. Clearly, an understanding of the structure-function relationships of these proteins will be critical in defining the molecular mechanisms underlying disease pathogenesis. The X-ray crystal structure of prokaryotic ClC proteins provides an exquisite template with which to model molecular aspects of eukaryotic ClC protein function. The dimeric structure of these proteins highlights the pivotal importance of intermolecular interactions in the modulation of channel/transporter activity, while mutagenesis studies implicate a crucial role for intrinsic interdomain interactions in regulated function. In this review, we will initially focus on the channel forming members of this family and discuss interactions within homodimeric channel complexes important for gating. Finally, with regard to both channel and transporter family members, we will discuss the multiple heteromeric interactions which occur with cytosolic proteins, and the putative functional impact of these interactions.

Stable dimeric assembly of the second membrane-spanning domain of CFTR (cystic fibrosis transmembrane conductance regulator) reconstitutes a chloride-selective pore.

Structural information is required to define the molecular basis for chloride conduction through CFTR (cystic fibrosis transmembrane conductance regulator). Towards this goal, we expressed MSD2, the second of the two MSDs (membrane-spanning domains) of CFTR, encompassing residues 857-1158 in Sf9 cells using the baculovirus system. In Sf9 plasma membranes, MSD2 migrates as expected for a dimer in non-dissociative PAGE, and confers the appearance of an anion permeation pathway suggesting that dimeric MSD2 mediates anion flux. To assess directly the function and quaternary structure of MSD2, we purified it from Sf9 cells by virtue of its polyhistidine tag and nickel affinity. Reconstitution of MSD2 into liposomes conferred a 4,4'-di-isothiocyanostilbene-2,2'-disulphonate-inhibitable, chloride-selective electrodiffusion pathway. Further, this activity is probably mediated directly by MSD2 as reaction of its single cysteine residue (Cys866) with the thiol modifying reagent, N(alpha)(3-maleimidylpropionyl)biocytin, inhibited chloride flux. Only MSD2 dimers were labelled by N(alpha)(3-maleimidylpropionyl)biocytin, supporting the idea that only dimeric MSD2 can mediate anion flux. As a further test of this hypothesis, we conducted a second purification procedure, wherein purified dimeric and monomeric MSD2 proteins were reconstituted separately. Only proteoliposomes containing stable MSD2 dimers mediated chloride electrodiffusion, providing direct evidence that dimeric MSD2 mediates chloride channel function. In summary, we have shown that the second membrane domain of CFTR can be purified and functionally reconstituted as a chloride channel, providing a tool for probing the structural basis of chloride conduction through CFTR.

Evidence for a functional interaction between the ClC-2 chloride channel and the retrograde motor dynein complex.

The ClC-2 chloride channel has been implicated in essential physiological functions. Analyses of ClC-2 knock-out mice suggest that ClC-2 expression in retinal pigment epithelia and Sertoli cells normally supports the viability of photoreceptor cells and male germ cells, respectively. Further, other studies suggest that ClC-2 expression in neurons may modify inhibitory synaptic transmission via the gamma-aminobutyric acid, type A receptor. However, complete understanding of the physiological functions of ClC-2 requires elucidation of the molecular basis for its regulation. Using cell imaging and biochemical and electrophysiological techniques, we show that expression of ClC-2 at the cell surface may be regulated via an interaction with the dynein motor complex. Mass spectrometry and Western blot analysis of eluate from a ClC-2 affinity matrix showed that heavy and intermediate chains of dynein bind ClC-2 in vitro. The dynein intermediate chain co-immunoprecipitates with ClC-2 from hippocampal membranes suggesting that they also interact in vivo. Disruption of dynein motor function perturbs ClC-2 localization and increases the functional expression of ClC-2 in the plasma membranes of COS7 cells. Thus, cell surface expression of ClC-2 may be regulated by dynein motor activity. This work is the first to demonstrate an in vivo interaction between an ion channel and the dynein motor complex.

The chloride channel ClC-4 contributes to endosomal acidification and trafficking.

Mutations in the gene coding for the chloride channel ClC-5 cause Dent's disease, a disease associated with proteinuria and renal stones. Studies in ClC-5 knockout mice suggest that this phenotype is related to defective endocytosis of low molecular weight proteins and membrane proteins by the renal proximal tubule. In this study, confocal micrographs of proximal tubules and cultured epithelial cells revealed that the related protein ClC-4 is expressed in endosomal membranes suggesting that this channel may also contribute to the function of this organelle. In support of this hypothesis, specific disruption of endogenous ClC-4 expression by transfection of ClC-4 antisense cDNA acidified endosomal pH and altered transferrin trafficking in cultured epithelial cells to the same extent as the specific disruption of ClC-5. Both channels can be co-immunoprecipitated, arguing that they may partially contribute to endosomal function as a channel complex. These studies prompt future investigation of the role of ClC-4 in renal function in health and in Dent's disease. Future studies will assess whether the severity of Dent's disease relates not only to the impact of particular mutations on ClC-5 but also on the consequences of those mutations on the functional expression of ClC-4.