Open-Label Evaluation of Eteplirsen in Patients with Duchenne Muscular Dystrophy Amenable to Exon 51 Skipping: PROMOVI Trial

Study design

PROMOVI (ClinicalTrials.org identifier: NCT02255552) was a 96-week, multicenter, open-label, non-randomized trial evaluating the efficacy and safety of eteplirsen in patients with DMD and genetic deletions amenable to exon 51 skipping, with an intended control group of patients with DMD and genetic deletions not amenable to exon 51 skipping. The trial was conducted at 40 sites in the United States between November 2017 and June 2019.

Independent ethics committees or institutional review boards at each site approved the protocol. The trial was conducted in accordance with the ethical principles of Good Clinical Practice, according to the International Council for Harmonisation Tripartite Guideline [20]. Written informed consent was obtained from each patient’s parent(s) or legal guardian(s), and informed assent was obtained from patients where applicable.

Patients

Eligible patients were male, aged 7–16 years, with DMD and genotypically confirmed mutations amenable to exon 51 skipping (eteplirsen-treated group) or with genotypically confirmed mutations not amenable to exon 51 skipping (untreated control group). Patients were required to have stable pulmonary function (percent predicted forced vital capacity [FVC%p]≥50%, not requiring nocturnal ventilation, and unlikely to decompensate over the duration of the study), be on a stable dose of oral corticosteroids for at least 24 weeks before study entry and be able to walk≥300 m on the 6-minute walk test (6MWT). Patients may or may not have been genotyped prior to the screening period. For those who were not previously genotyped, screening procedures (other than informed consent) and treatment group assignment were not conducted until after genotype results were received.

Exclusion criteria included use of any pharmacologic treatment, other than corticosteroids, that may have had an effect on muscle strength or function within 12 weeks of study entry; previous treatment with ezutromid at any time and treatment with drisapersen within the last 3 months; previous treatment with any other RNA antisense agent or any gene therapy within the last 6 months, or participation in any other DMD interventional clinical study within 12 weeks of study entry. Also excluded were patients with left ventricular ejection fraction of < 50%, based on the screening echocardiogram (ECHO) or QT interval corrected by Fridericia’s formula (QTcF) ≥450 ms based on the screening electrocardiogram (ECG).

Treatment

Patients in the treated group received a weekly intravenous (IV) infusion of 30 mg/kg eteplirsen, administered over approximately 35–60 minutes, from baseline (Week 1) until the end of the study (Week 96).

Assessments

The effect on ambulation, endurance, and muscle function was assessed using the 6MWT; the 6MWT was performed by standardized procedures, in which patients were asked to walk a set course of 25 m for 6 minutes and the distance walked was recorded, as previously described [21]. The North Star Ambulatory Assessment (NSAA) scale, performed on 2 consecutive days, was used to assess patient performance on 17 different functional activities [22]. Patients were graded as follows: 2 = normal, no obvious modification of activity; 1 = modified method but achieves goal independent of physical assistance from another; and 0 = unable to achieve goal independently. Ability to rise independently from the floor (without external support) was defined as an NSAA subscore of 2 or 1. Loss of ambulation (LOA) was defined as: i) an NSAA walk subscore of 0; ii) or NSAA was not done due to reason related to nonambulation; or iii) if 6MWT was not done with any reason related to permanent nonambulation. It was also required that no later data showed the patient was still ambulatory. Respiratory muscle function was evaluated as FVC%p using standard spirometry procedures. FVC%p was calculated using the Hankinson formula [23], and calculations were based on the use of both standing height (measured with shoes off) and ulnar-calculated height (the ulna was measured with an anthropometer or calipers and height was calculated as: height [cm] = 4.605×ulnar length [cm] + 1.308×patient age [years] + 28.003). Patients in the eteplirsen-treated group underwent muscle biopsy at baseline and were randomized to a muscle biopsy at either Week 24, Week 48, Week 72, or Week 96 in a 1:2:1:1 ratio. Muscle biopsies were analyzed for quantity of dystrophin protein expression using Western blot, intensity of dystrophin expression and percentage of dystrophin-positive fibers using immunofluorescence histochemistry (IHC), and exon 51 skipping using quantitative digital droplet polymerase chain reaction (ddPCR) assay. All expression analyses were performed as previously described [8].

Study endpoints

The primary efficacy endpoint was the change from baseline to Week 96 in 6MWT distance. Secondary efficacy endpoints included change from baseline to Week 96 for the ability to rise independently from the floor, LOA, NSAA total score, and FVC%p. In the original study protocol, comparisons were to be made with the untreated group for the primary and secondary endpoints; however, due to inadequate recruitment and retention of untreated patients with mutations not amenable to exon 51 skipping a revised statistical analysis plan was finalized prior to database lock, which specified that only descriptive summaries would be presented for each group. During the time of trial design and initiation, natural history data began to emerge demonstrating disparate disease trajectories for patients with different mutations [11–14]. As these data were confirmed, it became clear that the untreated control group, which consisted entirely of patients with mutations not amenable to exon 51 skipping, did not provide an adequate comparator group, and nonmutation-matched comparisons may be inappropriate.

Biological endpoints included the change from baseline to Week 96 in exon 51 skipping by quantitative digital droplet polymerase chain reaction (ddPCR) and dystrophin protein expression by Western blot. Safety assessments included all adverse events (AEs), vital signs, weight, height and ulnar length, physical examination, ECG, ECHO, and routine clinical laboratory evaluations.

Post-hoc analyses with matched comparators

Post-hoc analyses were performed with genotype- and baseline characteristic-matched comparisons of a subset of PROMOVI data with external natural history control cohorts and data from previous eteplirsen phase 2 studies, 4658-201 [16]/202 [15]. For the 6MWT analysis, a subgroup of PROMOVI patients that matched predefined criteria was compared with patients from studies 201/202 [24]. An external natural history cohort (exon 51 skipping amenable patients from the Italian DMD Telethon Registry [12, 25, 26], and the Leuven NMRC Registry [27]) is also shown to give context to the study results. These registries are based in expert neuromuscular centers that use a standard of care consistent with that used in the United States, where PROMOVI was conducted. The matched subgroup of PROMOVI patients was defined as those in the trial who had baseline 6MWT distance of ≥300–≤450 m, a baseline NSAA total score of ≥17–≤31 and were aged 7–13 years. For the FVC%p analysis, a matched subgroup of PROMOVI patients was compared with data from matched untreated patients (aged 10–18 years) in the Cooperative International Neuromuscular Research Group (CINRG) Duchenne Natural History Study (DNHS) exon 51 cohort [11]; data from studies 201/202 were also used for comparisons with previous reports of eteplirsen treatment effect [28].

Statistical analyses

The efficacy set consisted of all patients in the eteplirsen-treated and untreated control groups who had at least 1 post-baseline functional assessment. The primary efficacy set consisted of all patients in the efficacy set who had a baseline 6MWT distance of≥300–≤450 m. The safety set consisted of all patients who were enrolled in the study and either received at least 1 dose of eteplirsen in the eteplirsen-treated group or had at least 1 post-baseline safety assessment in the untreated group. For patients in the untreated group, any safety assessment on or after the Week 1 visit was considered a post-baseline safety assessment. Changes in 6MWT, ability to rise, LOA, NSAA total score, and FVC%p from baseline were summarized by treatment group using descriptive statistics. Changes in dystrophin protein expression and exon 51 skipping were analyzed using a 1-sample permutation t-test; for all hypothesis testing, significance level was 0.05. Correlation between exon 51 skipping and dystrophin protein expression was analyzed using Pearson’s coefficient and Spearman’s r correlation coefficient. AEs were coded using the Medical Dictionary for Regulatory Activities (MedDRA) Version 17.1 or higher, and treatment-emergent AEs (TEAEs) were summarized using descriptive statistics.

For the post-hoc analyses: FVC%p was compared between PROMOVI and the CINRG DNHS exon 51 cohort using mixed model repeated measures (MMRM) model with age, treatment, and age by treatment interaction as fixed effects and patient as a random effect; the slope of each treatment group is estimated from least square means in the MMRM.

Untreated arm (not amenable to exon 51 skipping)

Study enrollment occurred over a 2.5-year period starting October 1, 2014. A total of 30 patients entered the untreated arm; 15 (50%) completed the study (Fig. 1 and Table 1). As their mutations were not amenable to exon 51 skipping, they could not cross over into the treatment group. This factor contributed to poor retention, which precluded statistically and clinically meaningful comparisons. Because the untreated control group was not mutation-matched, it was also an inappropriate comparator group and was thus not analyzed for efficacy comparisons. Clinical outcomes in the untreated group are shown in Table 2. TEAEs were reported in 25 (83.3%) of these untreated patients and were serious in 2 (6.7%) patients. Of 78 TEAEs, 58 were mild and 20 were moderate.

Fig. 1

Participant flow diagram and analysis subsets. Abbreviations: CINRG = Cooperative International Neuromuscular Research Group; DNHS = Duchenne Natural History Study (DNHS); FVC%p = percent predicted forced vital capacity; LOA = loss of ambulation; 6MWT = 6-minute walk test; NSAA = North Star Ambulatory Assessment. ^aEteplirsen studies 201 (NCT01396239) [24] and 202 (NCT01540409) [28]. ^bUntreated patients in the CINRG DNHS exon 51 cohort (age 10–18 years) [11]. ^cItalian DMD Telethon Registry [12, 25, 26] and the Leuven NMRC Registry [27].

Eteplirsen-treated patients

A total of 79 patients were enrolled into the eteplirsen-treated arm, 78 (98.7%) of whom completed 96 weeks of treatment. Mean age at baseline was 9.1 years, and mean time since DMD diagnosis was 53.3 months (Table 3). Patients were ambulatory at baseline.

Biological assessments

With eteplirsen treatment, exon 51 skipping in muscle fibers significantly increased over baseline at the earliest time point assessed (Week 24), continued to increase until Week 72, and was 18.7-fold higher at Week 96 versus baseline (p < 0.001; Fig. 2A). Similarly, dystrophin protein expression increased over time, increasing 7.0-fold over baseline by Week 96 (p < 0.001; Fig. 2B). Positive correlation was observed between exon 51 skipping and protein expression (Pearson coefficient = 0.710 [p < 0.001]; Spearman coefficient = 0.692 [p < 0.001]). IHC analyses indicated that weekly treatment with eteplirsen resulted in a significant mean increase in percentage of dystrophin-positive fibers at Week 96 (p < 0.001) and dystrophin intensity levels (p < 0.001) (Fig. 2C & 2D, respectively).

Fig. 2

Exon 51 skipping by quantitative ddPCR (A), dystrophin protein quantification by western blot (B), percentage of dystrophin-positive fibers by IHC (C) and dystrophin intensity by IHC (D) from Baseline to Week 96 in eteplirsen-treated patients. Abbreviations: SE = standard error. ^*p < 0.05. ^†p < 0.001. ^aMean of individual patient fold changes. ^bp value is based on one-sample permutation t-test.

Efficacy assessments with eteplirsen treatment

Primary and secondary efficacy outcomes for eteplirsen-treated patients are shown in Table 4. Mean 6MWT distance decreased from 374.6 m at baseline to 256.2 m at Week 96. At Week 96, 54.1%of eteplirsen-treated patients were able to rise from the floor independently compared with 86.6% at baseline. The Kaplan-Meier estimate for remaining ambulatory at Week 96 was 81.9%; LOA occurred in 17.9% of eteplirsen-treated patients. The NSAA total score for eteplirsen-treated patients was 14.9 at Week 96 compared with 21.4 at baseline. Mean FVC%p decreased from 90.4% at baseline to 87.3% at Week 96.

Post-hoc analyses

Baseline characteristics of the PROMOVI and studies 201/202 subgroup populations for the 6MWT-matched comparator analysis are shown in Table S1. At Week 96, the 6MWT comparator analysis showed that PROMOVI results were consistent with those of studies 201/202. Mean change from baseline in 6MWT in eteplirsen-treated patients was –68.9 m in PROMOVI compared with –67.3 m in patients from studies 201/202; mean change in external natural history controls (n = 11; Italian DMD Telethon Registry, Leuven NMRC Registry), who were matched to the study 201/202 population, was –133.8 m (Fig. 3A).

Fig. 3

Post-hoc analysis: Mean change from baseline to Week 96 in 6MWT (A), and FVC%p (B) in eteplirsen-treated patients and matched comparisons. Abbreviations: FVC%p = percent predicted forced vital capacity; 6MWT = 6-minute walk test; SE = standard error. ^aAt Weeks 12, 72, and 96 (n = 41). One patient did not have a value at Week 12, but had at later visits. Another patient withdrew after Week 48. ^bEteplirsen studies 201 (NCT01396239) [24] and 202 (NCT01540409) [28]. ^cItalian DMD Telethon Registry [12, 25, 26] and the Leuven NMRC Registry [27]. ^dUntreated patients in the CINRG DNHS exon 51 cohort (age 10–18 years) [11].

Baseline characteristics of the PROMOVI, studies 201/202, and CINRG DNHS subgroup populations for the matched FVC%p comparator analysis are shown in Table S2. Eteplirsen-treated patients experienced a significant, clinically meaningful attenuation in pulmonary function decline (p < 0.001) compared with the untreated CINRG DNHS exon 51 cohort (Fig. 3B). In PROMOVI, the annual rate of decline in FVC%p was 3.3% based on ulnar length calculated height and 3.1% based on standing height, approximately half of the natural history decline in the matched CINRG DNHS group (–6.0%).

The proportion of PROMOVI patients with LOA at Week 96 (17.9%) was comparable to results from the phase 2 studies 201/202 at that timepoint (year 2, 17%) [24].

Safety assessment

The majority of the TEAEs reported were mild or moderate in severity, and there were no treatment-related discontinuations due to TEAEs (Table 5). Infusion-related reactions occurred in 45 of 79 (57.0%) patients; of these, headache (15/79; 19.0%) and vomiting (13/79; 16.5%) were the most common infusion-related reactions. Most infusion-related reactions were mild and all resolved. One treatment-related serious AE of urticaria was observed approximately 15–20 minutes after infusion and resolved approximately 1 hour after an IV steroid and antihistamine were administered; although the patient continued on eteplirsen without subsequent events and without corticosteroid pretreatment, the event was considered related to eteplirsen by the investigator and may reflect drug hypersensitivity. Overall, 8 eteplirsen-treated patients (10.1%) experienced renal TEAEs; each as proteinuria, which resolved by end of study in all but one individual. Proteinuria did not result in eteplirsen interruption or require treatment for any patient. Eteplirsen did not appear to adversely affect clinical laboratory values, vital signs, ECGs, or ECHOs. Percentages of patients with low, normal, or high serum chemistry, hematology, and urinalysis values were generally comparable at baseline and the last post-baseline measurement. No clinically significant mean changes in ECHOs were observed, and medical review found no clinically important changes in ECG parameters. One infected venous port serious AE was reported as severe and unrelated to treatment, and the patient recovered after removal of the port and antibiotic treatment.

PROMOVI trial principal clinical investigators

Hoda Z. Abdel-Hamid (UPMC Children’s Hospital of Pittsburgh, Pittsburgh, PA, USA); Gyula Acsadi (Connecticut Children’s Medical Center, Hartford, CT, USA); Susan Apkon (Seattle Children’s Hospital, Seattle, WA, USA); Ibrahim Binalsheikh (Carolinas Medical Center, Charlotte, NC, USA); William B. Burnette (Vanderbilt University Medical Center, Nashville, TN, USA); Russell Butterfield (University of Utah, Salt Lake City, UT, USA); Barry Byrne (University of Florida Health, Shands Hospital, Gainesville, FL, USA); Emma Ciafaloni (University of Rochester Clinical Research Center, Rochester, NY, USA); Anne M. Connolly (Washington University in St Louis, St Louis, MO, US); Basil Darras (Harvard Medical School, Boston Children’s Hospital, Boston, MA, USA); John Day (Stanford University School of Medicine, Stanford, CA, USA); Darryl C. De Vivo (Columbia University Irving Medical Center, New York, NY, USA); Erika Finanger (Shriners Hospitals for Children, Portland, OR, USA); Richard Finkel (Nemours Children’s Hospital, Orlando, FL, USA); Carla Grosmann (Rady Children’s Hospital, University of California at San Diego, San Diego, CA, USA); Susan Iannaccone (Children’s Medical Center of Dallas, Dallas, TX, USA); Huiyuan Jiang (Wayne State University, Detroit, MI, USA); Ashutosh Kumar (Pennsylvania State University, Hershey, PA, USA); Nancy Kuntz (Ann and Robert H. Lurie Children’s Hospital of Chicago, Chicago, IL, USA); Tim Lotze (Texas Children’s Hospital, Houston, TX, USA); Katherine Mathews (University of Iowa Children’s Hospital, Iowa City, IA, USA); Craig M. McDonald (University of California Davis Health System and School of Medicine, Sacramento, CA, USA); Jerry R. Mendell (Nationwide Children’s Hospital, Columbus, OH, USA); Julie Parsons (Children’s Hospital Colorado, Aurora, CO, USA); Han C. Phan (Rare Disease Research, Atlanta, GA, USA); Gerald Raymond (University of Minnesota, Minneapolis, MN, USA); Ben Renfroe (Northwest Florida Clinical Research Group, Gulf Breeze, FL, USA); Perry B. Shieh (David Geffen School of Medicine at UCLA, Los Angeles, CA, USA); Kumarswamy Sivakumar (Neuromuscular Research Center, Phoenix, AZ, USA); Cuixia Tian (Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA); Mathula Thangarajh (Children’s National Health System, Washington D.C., USA); Kathryn R. Wagner (Kennedy Krieger Institute, Baltimore, MD, USA); David Wolf (Emory University, Atlanta, GA, USA).

Italian DMD telethon registry study group investigators

Antonella Pini (IRCCS Istituto delle Scienze Neurologiche di Bologna, Bologna, Italy); Maria A. Donati, Michele Sacchini (Ospedale Pediatrico Meyer, Florence, Italy); Maria P. Sormani (University of Genoa, Genoa, Italy); Claudio Bruno (IRCCS ‘Giannina Gaslini’, Genoa, Italy); Sonia Messina, Gianluca Vita (University of Messina, Messina, Italy); Giovanni Baranello, Maria T. Arnoldi (IRCCS Istituto Neurologico ‘Carlo Besta’, Milan, Italy); Giacomo P. Comi, Francesca Magri, Yvan Torrente (University of Milan and IRCSS Fondazione Ca’ Granda Ospedale Maggiore Policlinico, Milan, Italy); Luisa Politano (Seconda Università di Napoli, Naples, Italy); Stefano C. Previtali (University of Campania Luigi Vanvitelli, Naples, Italy); Elena Pegoraro (University of Padua, Padua, Italy); Angela Berardinelli (IRCCS ‘C. Mondino’ Fondazione, Pavia, Italy); Roberta Battini, Silvia Frosini (Stella Maris Institute, Pisa, Italy); Enrico Bertini, Adele D’Amico (Bambino Gesù Children’s Hospital, Rome, Italy); Claudia Brogna, Giorgia Coratti, Lavinia Fanelli, Elena S. Mazzone, Giulia Norcia, Concetta Palermo, Marika Pane (Catholic University of Sacred Heart, Rome, Italy); Tiziana Mongini, Enrica Rolle, Francesca Rossi (University of Turin, Turin, Italy).

Leuven NMRC registry investigator

Marleen van den Hauwe (University Hospitals Leuven, Leuven, Belgium).

Cooperative International Neuromuscular Research Group (CINRG) investigators

Alberto Dubrovsky (Instituto de Neurosciencias Fundacion Favaloro, Buenos Aires, Argentina); Andrew Kornberg, Monique Ryan (Royal Children’s Hospital, Melbourne, Victoria, Australia); Richard Webster (Children’s Hospital at Westmead, Sydney, New South Wales, Australia); Jean K. Mah (Alberta Children’s Hospital, Calgary, Alberta, Canada); Hanna Kolski (University of Alberta, Edmonton, Alberta, Canada); W. Douglas Biggar, Laura C. McAdam (Holland Bloorview Kids Rehab Hospital, Toronto, Ontario, Canada); S. Chidambaranathan, V. Viswanathan (Sundaram Medical Foundation and Apollo Children’s Hospital, Chennai, India); Yoram Nevo (Hadassah Hebrew University Hospital, Jerusalem, Israel); Ksenija Gorni (University of Pavia and Niguarda Ca’ Granda Hospital, Milan, Italy); Jose Carlo (University of Puerto Rico, San Juan, Puerto Rico); Mar Tulinius (Queen Silvia Children’s Hospital, Gothenburg, Sweden); Richard T. Abresch, Erik K. Henricson, Nanette C. Joyce, Craig M. McDonald (University of California Davis Health System and School of Medicine, Sacramento, CA, USA); Avital Cnaan, Tina Duong, Robert Leshner, Lauren P. Morgenroth, Carolina Tesi-Rocha, Mathula Thangarajh (Children’s National Medical Center, Washington, DC, USA); John W. Day, Peter Karachunski (University of Minnesota, Minneapolis, MN, USA); Sherilyn Driscoll, Nancy Kuntz (Mayo Clinic, Rochester, MN, USA); Anne M. Connolly, Alan Pestronk (Washington University in St Louis, St Louis, MO, USA); Hoda Z. Abdel-Hamid, Paula R. Clemens (UPMC Children’s Hospital of Pittsburgh, Pittsburgh, PA, USA); Tulio E. Bertorini (University of Tennessee, Memphis, TN, USA); Timothy Lotze (Texas Children’s Hospital Houston, TX, USA); Amy D. Harper, Jean Teasley (Children’s Hospital of Virginia, Richmond, VA, USA).