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Children’s Hospital of Eastern Ontario Research Institute; Division of Neurology, Department of Medicine, The Ottawa Hospital; and Brain and Mind Research Institute, University of Ottawa, Ottawa, Canada
GSK3β is an intracellular regulatory kinase that is dysregulated in multiple tissues in type 1 myotonic dystrophy, a rare neuromuscular disorder that manifests at any age. AMO-02 (tideglusib) inhibits GSK3β activity in preclinical models of type 1 myotonic dystrophy and promotes cellular maturation as well as normalizes aberrant molecular and behavioral phenotypes. This phase 2 study assessed the pharmacokinetics, safety and tolerability, and preliminary efficacy of AMO-02 in adolescents and adults with congenital and childhood-onset type 1 myotonic dystrophy.
Methods
Sixteen subjects (aged 13 to 34 years) with congenital and childhood-onset type 1 myotonic dystrophy received 12 weeks of single-blind fixed-dose oral treatment with either 400 mg (n = 8) or 1000 mg (n = 8) AMO-02 (NCT02858908). Blood samples were obtained for pharmacokinetic assessment. Safety assessments, such as laboratory tests and electrocardiograms, as well as efficacy assessments of syndromal, cognitive, and muscular functioning, were obtained.
Results
AMO-02 plasma concentrations conformed to a two-compartment model with first-order absorption and elimination, and dose-dependent increases in exposure (area under the curve) were observed. AMO-02 was generally safe and well-tolerated. No early discontinuations due to adverse events or dose adjustments of AMO-02 occurred. The majority of subjects manifested clinical improvement in their central nervous system and neuromuscular symptoms after 12 weeks of treatment compared with the placebo baseline, with a larger response noted at the 1000 mg/day dose level. AMO-02 exposure (cumulative area under the curve) was significantly correlated (P < 0.01) with change from baseline on several key efficacy assessments.
Conclusion
AMO-02 has favorable pharmacokinetic and clinical risk/benefit profiles meriting further study as a potential treatment for congenital and childhood-onset type 1 myotonic dystrophy.
Myotonic dystrophy type 1 (DM1) is a rare, genetically determined neuromuscular disorder affecting individuals across the lifespan. DM1 occurs secondary to an expansion triplicate repeat in the untranslated 3′ region of the DMPK gene located on chromosome 19; this leads to the production of dysfunctional RNA, which increases the total levels of GSK3β and active GSK3β, an intracellular regulatory kinase, as confirmed in studies of brain and muscle tissue of transgenic mouse models as well as in patient tissues.
GSK3β activation causes mis-splicing of downstream effectors responsible for the differentiation of muscle tissue and the formation of synapses in the central nervous system. Recent evidence indicates that correction of GSK3β activation with AMO-02 (tideglusib) in DM1 transgenic mice reduces the mutant RNA associated with the DMPK expansion triplicate repeat and subsequently improves the postnatal survival of these mice.
From a clinical perspective, patients with DM1 experience substantial impairment in cognition, sleep regulation, communication skills, muscle functioning, and quality of life. DM1 is a familial disorder, and genetic anticipation occurs across generations, with congenital and childhood-onset presentations often accompanied by life-threatening features such as muscular weakness and compromised respiration at birth that can culminate in early mortality. Intellectual disability and co-occurring features of autism spectrum disorder are also common in this population.
Although mexiletine was recently approved in the European Union for the symptomatic treatment of myotonia in adults, there is no approved treatment for other aspects of DM1 or for younger individuals affected with this disorder.
The congenital and childhood-onset forms of DM1 are typically associated with significant medical morbidity, and there is no treatment available that can ameliorate the key pathologic features of this condition. Furthermore, there have been no previous clinical trials devoted to individuals affected by early-onset DM1. The goal of this study was to assess the pharmacokinetics as well as the initial safety, tolerability, and efficacy of AMO-02 (tideglusib), a novel, orally administered GSK3β enzyme inhibitor, as a potential treatment for adolescents and adults with congenital and childhood-onset DM1.
Methods
This phase 2 proof-of-concept clinical trial enrolled individuals with congenital or childhood-onset DM1. All subjects had preceding diagnostic confirmation of DM1 via genetic testing as well as documentation of the onset of symptoms during infancy or early childhood. The subjects with congenital DM1 had a history of one or more of the following signs or symptoms that was evident within the first week after birth: hypotonia, generalized weakness, respiratory insufficiency, feeding difficulties, and/or clubfoot or another musculoskeletal deformity. The subjects with childhood-onset DM1 had at least two signs or symptoms (not caused by another, unrelated condition) that were evident before age 12 years and that could be clearly assigned to DM1, including muscle weakness, myotonia, difficulty using hands (including fine motor problems), excessive daytime sleepiness, problems with upper or lower gastrointestinal functioning, problems with concentration or focusing (including symptoms of attention-deficit/hyperactivity disorder), and learning difficulties (including dyslexia).
The subjects were all enrolled at a single investigative site, a specialty center for DM1 in the United Kingdom. The subjects were ambulatory and had a Clinical Global Impressions of Severity score of 4 (moderately ill) or greater upon entry to the study. The subjects were not receiving any stimulant medications, and other treatments, and therapies had to be stable for at least four weeks before the commencement of the single-blinded placebo run-in. A history of clinically significant renal, hepatic, cardiovascular, endocrine, or respiratory disease was exclusionary.
Treatment involved a two-week single-blind placebo period and 12 weeks of fixed-dose oral treatment with either 400 mg (n = 8) or 1000 mg (n = 8) AMO-02 administered once each morning. A two-week follow-up period occurred after the study medication was discontinued. Subjects were enrolled into the 1000 mg arm first and then the 400 mg arm, so the investigator and study personnel were not unaware of the dose. The study medication, including the placebo, was packaged in sachets of 400 and 600 mg dose strengths that, at the time of dosing, were opened and mixed in water by caregivers. The contents were stirred vigorously before being ingested as a liquid suspension by the subjects.
Outcome measures included plasma levels (for pharmacokinetic assessment), standard safety assessments, and efficacy rating scales completed by clinicians, caregivers, and subjects, as well as performance-based/functional measures that are often used in the routine clinical assessment of individuals with neuromuscular disorders. Safety and tolerability were assessed via laboratory assessments, vital signs, and electrocardiograms, and with open-ended queries for adverse events (AEs).
Blood samples were taken for pharmacokinetic analysis after two and 12 weeks of treatment with AMO-02. On the days when pharmacokinetic blood samples were drawn, the study medication was administered in the clinic, and predose and postdose blood levels were obtained, separated by at least two hours. Lymphocytes were collected from blood samples obtained before, during, and after treatment with AMO-02 to analyze the levels of GSK3β protein and other associated kinases.
A population pharmacokinetic model that included prior information from a prior AMO-02 phase I trial in healthy subjects was used to estimate pharmacokinetic parameters of the enrollees in this study. Individual area under the curve (AUC), Cmax, and CSS values were derived from simulated profiles using posthoc parameter estimates in a rich sampling scheme (i.e., a sample every five minutes). Select pharmacokinetic parameters (i.e., AUC and Cmax) were used to assess potential correlations between systemic exposure and treatment response based on several measures of efficacy.
The efficacy assessments utilized in this study could be classified into four categories: muscle function (10-m walk/run test, handgrip strength and relaxation time, lung function, actigraphy, timed nine-hole peg test, dual-energy x-ray absorptiometry), clinician-completed rating scales (Clinical Global Impressions Severity and Improvement, Clinician-Completed Domain Specific Causes for Concern Visual Analogue Scale [VAS]: Myotonic Dystrophy), assessments of cognitive functioning and associated neurodevelopmental symptoms (Ohio State University Autism Rating Scale, Ohio State University Autism Rating Scale Clinician Global Impressions-Improvement [CGI-I], Peabody Picture Vocabulary Test), and subject- or caregiver-completed rating scales (Top 3 Concerns).
AE data were summarized as frequencies and percentages and described in terms of severity and relationship to the study treatment. AEs were summarized separately for nontreatment emergent events (e.g., during placebo run-in) and treatment emergent events (during active treatment). Objective safety assessments (e.g., laboratory values) were summarized by visit. Changes in safety parameters over time were evaluated, and shift tables at time points of interest were generated. The safety and tolerability data were reviewed on a serial basis (e.g., every three months) by an independent data safety and monitoring committee.
Analyses of changes in efficacy variables from baseline to each time point were performed using mixed effect model repeated measures with baseline value as a covariate, dose group and visit as fixed effects, and a treatment-by-visit interaction. Adjusted least square mean estimates were produced by dose group and study visit and were analyzed with two-sided 95% confidence intervals and P values.
In addition, a concordant trend analysis was completed in which 10 predefined efficacy variables included in the study were analyzed simultaneously to determine the likelihood of the pattern of efficacy results representing a false-positive finding (an example of this analytic approach is found in Glaze et al.).
Because this was a phase 2 proof-of-concept study in a clinical population that had not previously been studied in a clinical trial context, with no prior information available on potential or expected magnitudes of change from baseline in efficacy measures in association with treatment, no corrections were made for multiple comparisons when P values were generated. In this regard, the study was posited to be hypotheses-generating, and the goal of diminishing the risk of a type 2 error was prioritized over the risk of encountering a type 1 error.
The study was approved by a central ethics committee in the United Kingdom. Consent was obtained for all subjects before screening; in most cases consent was provided by the subject’s parent or legally authorized representative, where the subjects were younger than 16 years or did not have the capacity to consent for themselves. Assent was obtained from all subjects who could not consent for themselves. The study was registered on Clinicaltrials.gov (NCT02858908) and on the EU Clinical Trials Register (2016-000067-16).
Results
Sixteen subjects between the ages 13 and 34 years were enrolled in the study, including 10 males and six females with an overall mean age of 21 years and an S.D. of 5.8 years. Fourteen of these individuals had the congenital form of DM1, whereas two had the childhood-onset form.
The pharmacokinetic profile of AMO-02 was best described by a two-compartment model with first-order absorption and elimination. Estimated clearance and the volume of distribution parameters remained the same across the two dose levels evaluated in this study, indicating that the pharmacokinetics of AMO-02 are generally linear (see Table 1). There was no evidence of accumulation, metabolic inhibition, or induction observed during treatment. Body weight was a covariate effect on clearance and volume of distribution. Previous phase I studies indicated that higher plasma concentrations and exposures occur when AMO-02 is coadministered with a fatty meal. However, in this study, the timing of last food intake did not appear to influence systemic exposure, as assessed by AUC and Cmax.
TABLE 1AMO-02 Pharmacokinetic Parameters (Median, 5th, and 95th Quantiles)
Dose (mg)
1000 mg
400 mg
Cmax (ng/mL)
1170.95 (573.3-1450.16)
513.54 (342.95-615.45)
Cmin (ng/mL)
5.65 (3.47-16.21)
4.17 (2.16-11.34)
CSS (ng/mL)
141.62 (68.83-220.29)
56.89 (30.71-74.47)
tmax (h)
0.7 (0.6-1.22)
0.75 (0.3-0.99)
t1/2 (h)
1.7 (1.04-2.56)
2.05 (1.31-5.45)
AUC (0-12) (ng/mL·h)
3145.76 (1571.4-5109.46)
1218.16 (660.3-1713.85)
AUC (0-24) (ng/mL·h)
3398.68 (1651.9-5287.1)
1365.54 (737.21-1787.29)
Abbreviations:
AUC = Total area under the serum drug concentration-time curve both up to 12 hours (0 to 12) and 24 hours (0 to 24) after AMO-02 administration
All subjects completed the study, and no subject required dose adjustments of the study medication at any point in time. AMO-02 was generally safe and well-tolerated, with no early discontinuations due to AEs. The most common on-treatment AE was nasopharyngitis, mild in severity, which was experienced by 31% of subjects. All AEs were mild or moderate in severity, except one event of bilateral knee pain at the 400 mg/day dose level, considered unrelated to the study drug. There were no serious AE. One subject in each dose group experienced on-treatment elevations in alanine aminotransferase where values were higher than 1.5 times the upper limit of the normal reference range, above baseline. All liver function test elevations were not deemed to be clinically significant by the investigator and typically self-resolved while treatment was still ongoing. No patient experienced elevated bilirubin values or associated symptoms.
AMO-02 rendered clinical benefit to the majority of subjects after 12 weeks of treatment, with a larger magnitude of response generally apparent at the 1000 mg/day dose level. Improvements were most evident in the subjects’ cognitive functioning, fatigue, and ability to perform activities of daily living, as well as in the neuromuscular symptoms of several of the subjects. In addition, co-occurring autism symptoms improved in several subjects (see Fig 1B). The heatmaps in Fig 2 and Fig 3 visualize the changes to symptoms in all subjects with variable phenotypes at baseline.
FIGURE 1Clinical Global Impression-Improvement Scale (A) and the Ohio State University Autism Rating Scale Clinician Global Impression-Improvement (B) values comparing the 400 and 1000 mg/day dosages at end of placebo (week 0), midtreatment (week 6), and end of treatment (week 12). Data are mean ± SEM from the mixed effect model repeated measures analysis with N = 8 subjects per dose group.
FIGURE 2Each colored area shows the change relative to baseline for the Clinician-Completed Domain Specific Causes for Concern Visual Analogue Scale: Myotonic Dystrophy. White represents data points where no baseline deficit was detected, gray represents data points where a baseline deficit was recorded and no benefit was detected, red represents data points where a baseline deficit was recorded and a treatment response above the threshold for minimally clinically meaningful benefit was shown (change of 10% or greater), and amber represents data points where a baseline deficit was recorded and a treatment response trending to the threshold for minimally clinically meaningful benefit was shown (change of 5% to 10%). (A) Cohort 1: 1000 mg; (B) Cohort 2: 400 mg.
FIGURE 3Each colored area shows the change relative to baseline for the Caregiver Top 3 Concerns Visual Analogue Scale. White represents data points where no baseline deficit was detected, gray represents data points where a baseline deficit was recorded and no benefit was detected, red represents data points where a baseline deficit was recorded and a treatment response above the threshold for minimally clinically meaningful benefit was shown (change of 10% or greater), and amber represents data points where a baseline deficit was recorded and a treatment response trending to the threshold for minimally clinically meaningful benefit was shown (change of 5% to 10%). (A) Cohort 1: 1000 mg; (B) Cohort 2: 400 mg.
There were no statistically significant effects of placebo treatment during the two-week baseline placebo run-in period (data not shown). The clinician-completed and caregiver-completed rating scales (shown in FIGURE 1, FIGURE 4, FIGURE 5, FIGURE 6 and Table 2) revealed large treatment-associated effects, these effects being statistically significant across the period of treatment with AMO-02.
FIGURE 4Change from end of placebo baseline in the Clinician-Completed Domain Specific Causes for Concern Visual Analogue Scale: Myotonic Dystrophy total score in centimeters comparing both 400 and 1000 mg/day dosages. Data are mean ± SEM from the mixed effect model repeated measures analysis with P values compared with end of placebo, which coincides with start of treatment at week 0, with data analyzed at mid-treatment (week 6) and end of treatment (week 12).
FIGURE 5Individual Subject Clinician-Completed Domain Specific Causes for Concern Visual Analogue Scale (VAS): Myotonic Dystrophy with Week 12 Clinician Global Impressions-Improvement (CGI-I) score in the legend.
FIGURE 6Change from end of placebo baseline in the Caregiver Top 3 Concerns Rating Scale Visual Analogue Scale total score in centimeters comparing both 400 and 1000 mg/day dosages. Data are mean ± SEM from the mixed effect model repeated measures analysis with P values compared with end of placebo, which coincides with start of treatment at week 0, with data analyzed at midtreatment (week 6) and end of treatment (week 12).
TABLE 2Age at Enrolment, Disease Severity (CGI-S), and the Mode Number (the Most Common Repeat Length at Sampling) of CTG Repeats at Baseline
Subject ID
Age (Years)
CGI-S at Baseline
Number of CTG Repeats at Baseline
Clinician-Completed Domain Specific Causes for Concern VAS: Myotonic Dystrophy Total Score
Baseline
Week 12
Change From Baseline
Cohort 1 (1000 mg)
001-001
23
6
1680
50.7
47.8
−2.9
001-002
34
5
1011
49.5
49.7
0.2
001-003
18
4
456
60.8
49.1
−11.7
001-005
17
6
1141
69.1
66.1
−3
001-006
22
4
1139
49.9
45.1
−4.8
001-010
23
4
1172
73.6
59.4
−14.2
001-012
19
6
1113
58.1
54.7
−3.4
001-016
18
4
711
44.2
37.6
−6.6
Cohort 2 (400 mg)
001-017
22
6
1381
52.4
50.5
−1.9
001-019
26
4
330
47.9
40.8
−7.1
001-022
32
4
726
50.8
47.5
−3.3
001-024
17
5
600
68
62.9
−5.1
001-025
15
5
1763
74.2
74.5
0.3
001-027
16
4
1085
54.2
49
−5.2
001-029
13
6
1401
99
94
−5
001-030
21
5
875
54.7
55
0.3
Abbreviations:
CGI-S = Clinician Global Impressions of Severity
VAS = Visual Analogue Scale
Clinician-Completed Domain Specific Causes for Concern Visual Analogue Scale: Myotonic Dystrophy total score at baseline, end of treatment (week 12), and change from baseline.
Phenotypic variability at baseline was the norm rather than the exception in the group of subjects enrolled in this study. A wide range of values at baseline contributed to greater-than-expected intrasubject and intersubject variability in the performance-based/functional neuromuscular assessments, and accordingly, this limited the informativeness of these assessments. Results from the functional neuromuscular assessments are summarized in Table 3. Some symptoms, such as myotonia (handgrip relaxation), were not present in all subjects, therefore rendering average change from baseline ineffective at detecting improvement, which was evident in some subjects (see Fig 7).
TABLE 3Summary of Unadjusted Mean and S.D. at Baseline and End of Treatment (12 Weeks) for Functional Neuromuscular Assessments
Analysis completed on adjusted treatment means (least squares means) for change from baseline were statistically significant at the P < 0.05 level. Actigraphy is not included because device wear time was not consistently sufficient across all subjects to produce interpretable data.
Analysis completed on adjusted treatment means (least squares means) for change from baseline were statistically significant at the P < 0.05 level. Actigraphy is not included because device wear time was not consistently sufficient across all subjects to produce interpretable data.
Analysis completed on adjusted treatment means (least squares means) for change from baseline were statistically significant at the P < 0.05 level. Actigraphy is not included because device wear time was not consistently sufficient across all subjects to produce interpretable data.
25.76 (11.08)
23.59 (8.26)
−2.17
400 mg
25.71 (4.53)
24.76 (3.83)
−0.95
Peabody picture vocabulary test (age-based standard score)
1000 mg
63.9 (20.17)
63.8 (15.81)
−0.1
400 mg
80.9 (20.92)
79.8 (22.23)
−1.1
DXA: total lean muscle mass (kg)
1000 mg
37.86 (8.11)
38.27 (8.27)
0.41
400 mg
37.35 (8.66)
37.74 (8.48)
0.39
Abbreviations:
DXA = Dual-energy x-ray absorptiometry
EOT = End of treatment
∗ Analysis completed on adjusted treatment means (least squares means) for change from baseline were statistically significant at the P < 0.05 level. Actigraphy is not included because device wear time was not consistently sufficient across all subjects to produce interpretable data.
FIGURE 7Average time taken from three attempts to relax dominant handgrip on a myometer from maximum contraction at baseline and after 12 weeks of treatment.
The concordant trend analysis confirmed these findings by revealing a clear dose-response relationship that favored the 1000 mg over the 400 mg dose.
A pharmacokinetic/pharmacodynamic analysis revealed that AUC significantly correlated (P < 0.01) with the CGI-I scores and change from baseline for both the Caregiver Top 3 Concerns and the Clinician-Completed Domain Specific Causes for Concern VAS: Myotonic Dystrophy. In addition, a greater on-treatment reduction in lymphocyte GSK3β levels was observed in subjects classified as responders versus nonresponders, as defined by CGI-I scores.
Discussion
This is the first clinical trial conducted in the early-onset version of this rare neuromuscular disorder. In this study, AMO-02 was generally safe and well-tolerated, with a fully reversible elevation in alanine aminotransferase being the only notable objective finding in some subjects. AMO-02 improved multiple aspects of the subjects’ symptomatology, including neuromuscular symptoms as well as the cognitive symptoms that are often underappreciated in this condition but that can contribute greatly to the medical morbidity and functional deficits in affected individuals. In addition, co-occurring autism symptoms improved in several subjects, consistent with preliminary finding suggesting that GSK3 inhibitors may be beneficial to individuals with neurodevelopmental disorders.
The most informative assessments of efficacy in this study were the clinician-completed and caregiver-completed rating scales. These rating scales are essentially composite assessments, and they revealed large treatment-associated effects, these effects being statistically significant across the period of AMO-02 treatment. The treatment response data were consistent across the rating scales, reflecting signals of efficacy in multiple symptom domains (e.g., CNS and muscles) that are commonly affected in this condition.
Phenotypic variability is the norm rather than the exception in DM-1, and this study included subjects with both congenital and childhood-onset forms of DM-1. Therefore, rating scales that take into account clinician or caregiver causes for concern appeared to provide a better tool for detecting change than solely functional assessments. The heatmaps (FIGURE 2, FIGURE 3) highlight how some subjects improved in domains where other subjects had no disabling symptoms present at baseline. The functional outcome measures provided objective support to clinician-observed and caregiver-elicited markers of change during treatment.
The Clinician-Completed Domain Specific Causes for Concern VAS used in this study represents an important innovation in this orphan therapeutic area. This scale was derived from a measure previously validated in natural history and intervention studies in DM1,
and is also being validated in an ongoing natural history study in children and adolescents with congenital DM1 (NCT03059264). This rating scale was developed with the collaborative assistance of therapeutic area experts and has been vetted and refined in collaboration with the United States Food and Drug Administration. A refined version of the scale will serve as the primary outcome measure in a forthcoming phase 2/3 study in children and adolescents with congenital DM1 (NCT03692312).
The changes from baseline in the Clinician-Completed Domain Specific Causes for Concern (VAS) scores appear to track with CGI-I scores so that clinically significant improvements (i.e., CGI-I scores of 3 or better) were correlated with reduced scores of 5% to 10% in the Clinician-Completed Domain Specific Causes for Concern (VAS). Due to the small sample size in this proof-of-concept study, an analysis of the influence of potential response modifiers such as age, severity, and number of genetic repeats was not undertaken.
The results from this small phase 2 study indicate that AMO-02 may represent a potential treatment for congenital and childhood-onset DM1. Although this was a relatively small study (n = 16) with no randomized placebo-controlled arm, the initial findings in this rare disease population indicate that the 1000 mg dose may have the best prospect of establishing a consistent efficacy signal. Correlation between AMO-02 exposure and observed efficacy in several end points supports these conclusions. The continuing improvement that was evident toward the end of dosing with AMO-02 suggests that the magnitude of clinical benefit is likely to increase further with a longer dosing period. Accordingly, additional clinical trials appear warranted.
Acknowledgments
The authors would like to thank Dr Gráinne Gorman, Philip Brown and the team at the Clinical Ageing Research Unit (CARU) in Newcastle, UK, and the participants and their caregivers.
References
Jones K.
Wei C.
Iakova P.
et al.
GSK3β mediates muscle pathology in myotonic dystrophy.
Joseph Horrigan, Mike Snape, Alison McMorn, and Stuart Evans are all employees for AMO Pharma, who were the Sponsors of this clinical trial. AMO Pharma funded the positions of Tiago Bernardino Gomes and Sean Oosterholt during the study. Alex Yaroshinsky is an employee of Vital Systems who has a consultancy agreement with AMO Pharma. Hanns Lochmüller has a consultancy agreement with AMO Pharma and also receives support from the Canadian Institutes of Health Research (Foundation Grant FDN-167281), the Canadian Institutes of Health Research and Muscular Dystrophy Canada (Network Catalyst Grant for NMD4C), the Canada Foundation for Innovation (CFI-JELF 38412), and the Canada Research Chairs program (Canada Research Chair in Neuromuscular Genomics and Health, 950-232279). No professional writers were involved in the creation of the manuscript.
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