Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy

The diagnosis of primary mitochondrial myopathy is often delayed by years due to non-specific clinical symptoms as well as variable testing of mitochondrial disorders. The aim of this review is to summarize and discuss the collective findings and novel insights regarding the diagnosing, testing, and clinical presentation of primary mitochondrial myopathy (PMM). PMM results from a disruption of the oxidative phosphorylation (OXPHOS) chain in mitochondria due to mutations in mitochondrial DNA (mtDNA) or nuclear DNA (nDNA). Although there are many named syndromes caused by mitochondrial mutations, this review will focus on PMM, which are mitochondrial disorders mainly affecting, but not limited to, the skeletal muscle. Clinical presentation may include muscle weakness, exercise intolerance, myalgia, and rhabdomyolysis. Although skeletal muscle and respiratory function are most frequently affected due to their high energy demand, multisystem dysfunction may also occur, which may lead to the inclusion of mitochondrial myopathies on the differential. Currently, there are no effective disease-modifying treatments, and treatment programs typically only focus on managing the symptomatic manifestations of the disease. Although the field has a large unmet need regarding treatment options, diagnostic pathways are better understood and can help shorten the diagnostic journey to aid in disease management and clinical trial enrollment.

BackgroundThis study aims to evaluate the effect of subcutaneous (SC) elamipretide dosing on exercise performance using the 6 min walk test (6MWT), patient‐reported outcomes measuring fatigue, functional assessments, and safety to guide the development of the Phase 3 trial.MethodsMMPOWER‐2 was a randomized, double‐blind, placebo‐controlled, crossover trial that enrolled participants (N = 30) with genetically confirmed primary mitochondrial myopathy. Participants were randomly assigned (1:1) to 40 mg/day SC elamipretide for 4 weeks followed by placebo SC for 4 weeks, separated by a 4‐week washout period, or the opposite sequence. The primary endpoint was the distance walked on the 6MWT.ResultsThe distance walked on the 6MWT by the elamipretide‐treated participants was 398.3 (±134.16) meters compared with 378.5 (±125.10) meters in the placebo‐treated group, a difference of 19.8 m (95% confidence interval, −2.8, 42.5; P = 0.0833). The results of the Primary Mitochondrial Myopathy Symptom Assessment Total Fatigue and Total Fatigue During Activities scores showed that participants treated with elamipretide reported less fatigue and muscle complaints compared with placebo (P = 0.0006 and P = 0.0018, respectively). Additionally, the Neuro‐QoL Fatigue Short Form and Patient Global Assessment showed reductions in symptoms (P = 0.0115 and P = 0.0421, respectively). In this 4‐week treatment period, no statistically significant change was observed in the Physician Global Assessment (P = 0.0636), the Triple Timed Up and Go (P = 0.8423) test, and wrist/hip accelerometry (P = 0.9345 and P = 0.7326, respectively). Injection site reactions were the most commonly reported adverse events with elamipretide (80%), the majority of which were mild. No serious adverse events or deaths were reported.ConclusionsParticipants who received a short‐course treatment of daily SC elamipretide for 4 weeks experienced a clinically meaningful change in the 6MWT, which did not achieve statistical significance as the primary endpoint of the study. Secondary endpoints were suggestive of an elamipretide treatment effect compared with placebo. Nominal statistically significant and clinically meaningful improvements were seen in patient‐reported outcomes. The results of this trial provided an efficacy signal and data to support the initiation of MMPOWER‐3, a 6‐month long, Phase 3 treatment trial in patients with primary mitochondrial myopathy.

ObjectiveTo assess the safety and efficacy of elamipretide, an aromatic-cationic tetrapeptide that readily penetrates cell membranes and transiently localizes to the inner mitochondrial membrane where it associates with cardiolipin, in adults with primary mitochondrial myopathy (PMM).MethodsA Study Investigating the Safety, Tolerability, and Efficacy of MTP-131 for the Treatment of Mitochondrial Myopathy (MMPOWER) was a phase I/II multicenter, randomized, double-blind, placebo-controlled trial of elamipretide in 36 participants with genetically confirmed PMM. Participants were randomized to intravenous elamipretide (0.01, 0.1, and 0.25 mg/kg/h or placebo for 2 hours in a dose-escalating sequence). The primary efficacy measure was the change in distance walked in the 6-minute walk test (6MWT) after 5 days of treatment. Other efficacy measures included changes in cardiopulmonary exercise testing parameters, in participant-reported symptoms, and in serum and urinary biomarkers. Safety, tolerability, and pharmacokinetics were also measured.ResultsParticipants who received the highest dose of elamipretide walked a mean of 64.5 m farther at day 5 compared to a change of 20.4 m in the placebo group (p = 0.053). In addition, there was a dose-dependent increase in distance walked on the 6MWT with elamipretide treatment (p = 0.014). In a model that adjusted for additional covariates possibly affecting response, the adjusted change for the highest dose of elamipretide was 51.2 vs 3.0 m in the placebo group (p = 0.0297). No significant differences were observed in other efficacy and safety endpoints.ConclusionsElamipretide increased exercise performance after 5 days of treatment in patients with PMM without increased safety concerns. These findings, as well as additional functional and patient-reported measures, remain to be tested in larger trials with longer treatment periods to detect other potential therapeutic benefits in individuals affected by this condition.Classification of evidenceThis trial provides Class I evidence that for patients with PMM, elamipretide improved the distance walked on the 6MWT.

ObjectiveTo determine whether a set of functional tests, clinical scales, patient-reported questionnaires, and specific biomarkers can be considered reliable outcome measures in patients with primary mitochondrial myopathy (PMM), we analyzed a cohort of Italian patients.MethodsBaseline data were collected from 118 patients with PMM, followed by centers of the Italian network for mitochondrial diseases. We used the 6-Minute Walk Test (6MWT), Timed Up-and-Go Test (x3) (3TUG), Five-Times Sit-To-Stand Test (5XSST), Timed Water Swallow Test (TWST), and Test of Masticating and Swallowing Solids (TOMASS) as functional outcome measures; the Fatigue Severity Scale and West Haven-Yale Multidimensional Pain Inventory as patient-reported outcome measures; and FGF21, GDF15, lactate, and creatine kinase (CK) as biomarkers.ResultsA total of 118 PMM cases were included. Functional outcome measures (6MWT, 3TUG, 5XSST, TWST, and TOMASS) and biomarkers significantly differed from healthy reference values and controls. Moreover, functional measures correlated with patients' perceived fatigue and pain severity. Patients with either mitochondrial or nuclear DNA point mutations performed worse in functional measures than patients harboring single deletion, even if the latter had an earlier age at onset but similar disease duration. Both the biomarkers FGF21 and GDF15 were significantly higher in the patients compared with a matched control population; however, there was no relation with severity of disease.ConclusionsWe characterized a large cohort of PMM by evaluating baseline mitochondrial biomarkers and functional scales that represent potential outcome measures to monitor the efficacy of treatment in clinical trials; these outcome measures will be further reinvestigated longitudinally to define the natural history of PMM.

Primary mitochondrial myopathy (PMM) is a genetic condition characterized by life-limiting symptoms such as muscle weakness, fatigue, and pain. Because these symptoms are best reported by individuals with PMM, the objective of this qualitative research study was to develop a PMM-specific patient-reported outcome (PRO) questionnaire. Individuals with PMM were interviewed, identifying the most salient symptoms of PMM and assessing the resulting questionnaire's relevance and comprehensibility. Developed based on patient interviews, the 10-item Primary Mitochondrial Myopathy Symptom Assessment assesses patients' symptom experiences at their worst in the last 24 hours. Individuals with PMM confirmed the concepts of the questionnaire as relevant and comprehensive to their symptom experiences and responded to the items consistently with developers' intentions. The Primary Mitochondrial Myopathy Symptom Assessment is a content-valid PRO questionnaire with qualitative and quantitative support as a valuable tool to evaluate and monitor the day-to-day experience of PMM symptoms from the patient perspective.

BackgroundAs previously published, the MMPOWER-3 clinical trial did not demonstrate a significant benefit of elamipretide treatment in a genotypically diverse population of adults with primary mitochondrial myopathy (PMM). However, the prespecified subgroup of subjects with disease-causing nuclear DNA (nDNA) pathogenic variants receiving elamipretide experienced an improvement in the six-minute walk test (6MWT), while the cohort of subjects with mitochondrial DNA (mtDNA) pathogenic variants showed no difference versus placebo. These published findings prompted additional genotype-specific post hoc analyses of the MMPOWER-3 trial. Here, we present these analyses to further investigate the findings and to seek trends and commonalities among those subjects who responded to treatment, to build a more precise Phase 3 trial design for further investigation in likely responders.ResultsSubjects with mtDNA pathogenic variants or single large-scale mtDNA deletions represented 74% of the MMPOWER-3 population, with 70% in the mtDNA cohort having either single large-scale mtDNA deletions or MT-TL1 pathogenic variants. Most subjects in the nDNA cohort had pathogenic variants in genes required for mtDNA maintenance (mtDNA replisome), the majority of which were in POLG and TWNK. The mtDNA replisome post-hoc cohort displayed an improvement on the 6MWT, trending towards significant, in the elamipretide group when compared with placebo (25.2 ± 8.7 m versus 2.0 ± 8.6 m for placebo group; p = 0.06). The 6MWT results at week 24 in subjects with replisome variants showed a significant change in the elamipretide group subjects who had chronic progressive external ophthalmoplegia (CPEO) (37.3 ± 9.5 m versus − 8.0 ± 10.7 m for the placebo group; p = 0.0024). Pharmacokinetic (exposure–response) analyses in the nDNA cohort showed a weak positive correlation between plasma elamipretide concentration and 6MWT improvement.ConclusionsPost hoc analyses indicated that elamipretide had a beneficial effect in PMM patients with mtDNA replisome disorders, underscoring the importance of considering specific genetic subtypes in PMM clinical trials. These data serve as the foundation for a follow-up Phase 3 clinical trial (NuPOWER) which has been designed as described in this paper to determine the efficacy of elamipretide in patients with mtDNA maintenance-related disorders.Classification of evidenceClass IClinicalTrials.gov identifierNCT03323749

To validate new mitochondrial myopathy serum biomarkers for diagnostic use. We analyzed serum FGF21 (S-FGF21) and GDF15 from patients with (1) mitochondrial diseases and (2) nonmitochondrial disorders partially overlapping with mitochondrial disorder phenotypes. We (3) did a meta-analysis of S-FGF21 in mitochondrial disease and (4) analyzed S-Fgf21 and skeletal muscle Fgf21 expression in 6 mouse models with different muscle-manifesting mitochondrial dysfunctions. We report that S-FGF21 consistently increases in primary mitochondrial myopathy, especially in patients with mitochondrial translation defects or mitochondrial DNA (mtDNA) deletions (675 and 347 pg/mL, respectively; controls: 66 pg/mL, p < 0.0001 for both). This is corroborated in mice (mtDNA deletions 1,163 vs 379 pg/mL, p < 0.0001). However, patients and mice with structural respiratory chain subunit or assembly factor defects showed low induction (human 335 pg/mL, p < 0.05; mice 335 pg/mL, not significant). Overall specificities of FGF21 and GDF15 to find patients with mitochondrial myopathy were 89.3% vs 86.4%, and sensitivities 67.3% and 76.0%, respectively. However, GDF15 was increased also in a wide range of nonmitochondrial conditions. S-FGF21 is a specific biomarker for muscle-manifesting defects of mitochondrial translation, including mitochondrial transfer-RNA mutations and primary and secondary mtDNA deletions, the most common causes of mitochondrial disease. However, normal S-FGF21 does not exclude structural respiratory chain complex or assembly factor defects, important to acknowledge in diagnostics. This study provides Class III evidence that elevated S-FGF21 accurately distinguishes patients with mitochondrial myopathies from patients with other conditions, and FGF21 and GDF15 mitochondrial myopathy from other myopathies.

ObjectivesTo assess natural history and 12-month change of a series of scales and functional outcome measures in a cohort of 117 patients with primary mitochondrial myopathy (PMM).MethodsTwelve months follow-up data of 117 patients with PMM were collected. We analysed the 6-min walk test (6MWT), timed up-and-go test (× 3) (3TUG), five-times sit-to-stand test (5XSST), timed water swallow test (TWST), and test of masticating and swallowing solids (TOMASS) as functional outcome measures; the Fatigue Severity Scale and West Haven-Yale Multidimensional pain inventory as patient-reported outcome measures. PMM patients were divided into three phenotypic categories: mitochondrial myopathy (MiMy) without extraocular muscles involvement, pure chronic progressive external ophthalmoplegia (PEO) and PEO&MiMy. As 6MWT is recognized to have significant test–retest variability, we calculated MCID (minimal clinically important difference) as one third of baseline 6 min walking distance (6MWD) standard deviation.ResultsAt 12-month follow-up, 3TUG, 5XSST and FSS were stable, while TWST and the perceived pain severity (WHYMPI) worsened. 6MWD significantly increased in the entire cohort, especially in the higher percentiles and in PEO patients, while was substantially stable in the lower percentile (< 408 m) and MiMy patients. This increase in 6MWD was considered not significant, as inferior to MCID (33.3 m). NMDAS total score showed a slight but significant decline at 12 months (0.9 point). The perceived pain severity significantly worsened. Patients with PEO performed better in functional measures than patients with PEO&MiMy or MiMy, and had lower values of NMDAS.ConclusionsPMM patients showed a slow global decline valued by NMDAS at 12 months; 6MWT was a more reliable measurement below 408 m, substantially stable at 12 months. PEO patients had better motor performance and lower NMDAS than PEO&MiMy and MiMy also at 12 months of follow-up.

Primary mitochondrial myopathies (PMMs), a group of genetic mitochondrial oxidative phosphorylation disorders, primarily affect skeletal muscle function. No approved treatments for PMM exist, and patient information is limited. The international RePOWER registry (NCT03048617) assessed genotypic and phenotypic relationships in PMM and identified patients for MMPOWER-3 (elamipretide Phase 3 study). RePOWER enrolled screened and ambulatory patients aged 16-80 years. With signs and/or symptoms of PMM (N = 376; 60.4% female; mean [SD] age 42.6 [14.4] years; ~75% with an mtDNA variant and ~25% with an nDNA variant). Baseline information, current symptoms, qualityoflife, and functional assessments (6-Minute Walk Test [6MWT], Triple-Timed Up-and-Go [3TUG] Test, and 5-Times Sit-to-Stand Test [5XSST]) were captured. Accredited laboratory and genetic testing methods were available to most patients. The majority of enrolled PMM patients presented with progressive external ophthalmoplegia and fatigue. US patients were observed to use more medical interventions. Compared to non-US patients, US patients did not perform as well on the 6MWT (mean 364.6 vs. 375.2 m) and 5XSST (mean 21.6 vs. 18.6 s); US patients performed better on the 3TUG test (mean 40.2 vs. 45.0 s). The RePOWER registry provided data on patients with genetically confirmed PMM, thereby improving our understanding of PMM diagnosis and treatment and the differences in global mitochondrial clinical practice.

Mitochondrial disorders are the most common inherited conditions, characterized by defects in oxidative phosphorylation and caused by mutations in nuclear or mitochondrial genes. Due to its high energy request, skeletal muscle is typically involved. According to the International Workshop of Experts in Mitochondrial Diseases held in Rome in 2016, the term Primary Mitochondrial Myopathy (PMM) should refer to those mitochondrial disorders affecting principally, but not exclusively, the skeletal muscle. The clinical presentation may include general isolated myopathy with muscle weakness, exercise intolerance, chronic ophthalmoplegia/ophthalmoparesis (cPEO) and eyelids ptosis, or multisystem conditions where there is a coexistence with extramuscular signs and symptoms. In recent years, new therapeutic targets have been identified leading to the launch of some promising clinical trials that have mainly focused on treating muscle symptoms and that require populations with defined genotype. Advantages in next-generation sequencing techniques have substantially improved diagnosis. So far, an increasing number of mutations have been identified as responsible for mitochondrial disorders. In this review, we focused on the principal molecular genetic alterations in PMM. Accordingly, we carried out a comprehensive review of the literature and briefly discussed the possible approaches which could guide the clinician to a genetic diagnosis.

Biallelic mutations in the C1QBP gene have been associated with mitochondrial cardiomyopathy and combined respiratory-chain deficiencies, with variable onset (including intrauterine or neonatal forms), phenotypes, and severity. We studied two unrelated adult patients from consanguineous families, presenting with progressive external ophthalmoplegia (PEO), mitochondrial myopathy, and without any heart involvement. Muscle biopsies from both patients showed typical mitochondrial alterations and the presence of multiple mitochondrial DNA deletions, whereas biochemical defects of the respiratory chain were present only in one subject. Using next-generation sequencing approaches, we identified homozygous mutations in C1QBP. Immunoblot analyses in patients' muscle samples revealed a strong reduction in the amount of the C1QBP protein and varied impairment of respiratory chain complexes, correlating with disease severity. Despite the original study indicated C1QBP mutations as causative for mitochondrial cardiomyopathy, our data indicate that mutations in C1QBP have to be considered in subjects with PEO phenotype or primary mitochondrial myopathy and without cardiomyopathy.

This article highlights the updates from preclinical and clinical studies into the field of wasting disorders that were presented at the 11th Cachexia Conference held in Maastricht, the Netherlands, in December 2018. Herein, we summarize the biological and clinical significance of different markers and new diagnostic tools and cut‐offs for the detection of skeletal muscle wasting, including micro‐RNAs, siRNAs, epigenetic targets, the ubiquitin–proteasome system, mammalian target of rapamycin signalling, news in body composition analysis including the D3‐creatine dilution method, and electrocardiography that was modified to enable segmental impedance spectroscopy. Of particular interest were the beneficial effects of BIO101 on muscle cell differentiation, hypertrophy of myofibers associated with mammalian target of rapamycin pathways activation, and the effect of metal ion transporter ZIP14 loss that reduces cancer‐induced cachexia. The potential of anti‐ZIP14 antibodies and zinc chelation as anti‐cachexia therapy should be tested in patients with cancer cachexia. Big randomized studies were presented such as RePOWER (observational study of patients with primary mitochondrial myopathy), STRAMBO (influence of physical performance assessed as score and clinical testing), MMPOWER (treatment of elamipretide in subjects with primary mitochondrial myopathy), FORCE (examined differences in relative dose intensity and moderate and severe chemotherapy‐associated toxicities between a strength training intervention and a control group), and SPRINTT (effectiveness of exercise training in healthy aging). Effective treatments were urothelin A, rapamycin analogue treatment, epigenetic factor BRD 4 and epigenetic protein BET, and the gut pathobiont Klebsiella oxytoca. Clinical studies that investigated novel approaches, including urolithin A, the role of gut microbiota, metal ion transporter ZIP14, lysophosphatidylcholine and lysophosphatidylethanolamine, and BIO101, were described. It remains a fact, however, that effective treatments of cachexia and wasting disorders are urgently needed in order to improve patients' quality of life and their survival.

This article highlights preclinical and clinical studies in the field of wasting disorders that were presented at the 12th Cachexia Conference held in Berlin, Germany, in December 2019. Herein, we summarize the biological and clinical significance of different strategies including antibodies that target Fn14, Spsb 1, SAA1 treatment, ZIP14, a MuRF1 inhibitor, and new diagnostic tools like T‐cell communication targets and cut‐offs for the detection of skeletal muscle wasting. Of particular interest were the transplantation of mesenchymal stromal cells and muscle stem cell communication. Importantly, one presentation discussed the effect of metal ion transporter ZIP14 loss that reduces cancer‐induced cachexia. The potential of anti‐ZIP14 antibodies and zinc chelation as anti‐cachexia therapy may require testing in patients with cancer cachexia. Large clinical studies were presented such as RePOWER (observational study of patients with primary mitochondrial myopathy), MMPOWER (treatment with elamipretide in patients with primary mitochondrial myopathy), and ACT‐ONE as well as new mouse models like the KPP mouse. Promising treatments include rapamycin analogue treatment, anamorelin, elanapril, glucocorticoids, SAA1, antibodies that target Fn14, and a MuRF1 inhibitor. Clinical studies investigated novel approaches, including the role of exercise. It remains a fact, however, that effective treatments for cachexia and wasting disorders are urgently needed in order to improve patients' quality of life and their survival.

In the article “Randomized dose-escalation trial of elamipretide in adults with primary mitochondrial myopathy” by A. …

Primary mitochondrial myopathies (PMM) are a clinically and genetically highly heterogeneous group that, in some cases, may manifest exclusively as fatigue and exercise intolerance, with minimal or no signs on examination. On these occasions, the symptoms can be confused with the much more common chronic fatigue syndrome (CFS). Nonetheless, other possibilities must be excluded for the final diagnosis of CFS, with PMM being one of the primary differential diagnoses. For this reason, many patients with CFS undergo extensive studies, including extensive genetic testing and muscle biopsies, to rule out this possibility. This study evaluated the diagnostic performance of growth differentiation factor-15 (GDF-15) as a potential biomarker to distinguish which patient with chronic fatigue has a mitochondrial disorder. We studied 34 adult patients with symptoms of fatigue and exercise intolerance with a definitive diagnosis of PMM (7), CFS (22), or other non-mitochondrial disorders (5). The results indicate that GDF-15 can accurately discriminate between patients with PMM and CFS (AUC = 0.95) and between PMM and patients with fatigue due to other non-mitochondrial disorders (AUC = 0.94). Therefore, GDF-15 emerges as a promising biomarker to select which patients with fatigue should undergo further studies to exclude mitochondrial disease.