Astellas (TYO: 4503) Enhances ASP2957 Safety with the Launch of the 'EXCEL' Observational Study
Subheading: Addressing the Genetic Limitations of XLMTM and the Need to Define Hepatic Complications
Astellas Pharma (Astellas Pharma, TYO: 4503), through its Astellas Gene Therapies division, has initiated the 'EXCEL' (NCT06581146) clinical trial, a non-interventional observational study designed to monitor liver health in pediatric patients with X-linked Myotubular Myopathy (XLMTM). XLMTM is a rare genetic disorder caused by mutations in the MTM1 gene, affecting approximately 1 in 40,000 to 50,000 male newborns. In addition to muscle weakness, it is often associated with severe liver and biliary diseases, including cholestasis. The primary objective of this study is to characterize and document the natural history of liver cell dysfunction and biliary complications resulting from MTM1 protein deficiency.
Subheading: 'EXCEL' Clinical Design and Data Tracking with Advanced Diagnostic Equipment
The 'EXCEL' trial is designed to enroll 50 pediatric patients with XLMTM under the age of 18 and will track their natural history for approximately 48 weeks (1 year) without any treatment modifications. Patients will undergo liver and gallbladder health assessments approximately every six weeks, with a focus on precise monitoring using tools such as FibroScan (transient elastography) to assess liver fibrosis. This initiative is expected to standardize clinical indicators of liver function in this rare patient population, potentially revolutionizing patient management in the future.
Subheading: Past AT132 Clinical Trial Deaths and the Regulatory Need for Enhanced Safety
Astellas previously discontinued the development of its previous-generation gene therapy candidate, AT132 (Resglistogene Bilparvovec), after four patients in a Phase 1/2 clinical trial died from progressive cholestatic liver failure. The U.S. Food and Drug Administration (FDA) issued clinical hold orders in 2020 and 2021. The cause was determined to be toxicity resulting from the administration of high doses of gene therapy to patients with pre-existing liver disease. Therefore, establishing a protocol to screen for pre-existing liver and biliary conditions in patients before the start of clinical trials is essential to prevent potentially fatal toxicities associated with gene therapy and to establish a robust safety profile.
Subheading: Development of Next-Generation Gene Therapy ASP2957 and Activation of the Global Market
Astellas plans to leverage the natural history data from this study to improve the success rate of clinical development for its next-generation gene therapy candidate, ASP2957, which was acquired from Kate Therapeutics. ASP2957 utilizes a highly muscle-specific MyoAAV capsid, significantly reducing the administered dose and the potential for hepatotoxicity. A Phase 1/2 VALOR trial is currently underway in patients aged three years and younger. With the global myotubular myopathy treatment market estimated at approximately $1.26 billion in 2025, Astellas is poised to strengthen its market-leading position, particularly with the discontinuation of competing candidates such as Dynacure's DYN101.
The global myotubular myopathy treatment market is valued at $1.26 billion in 2025 and is projected to grow to $1.95 billion by 2033, representing a high-value rare disease area with continued growth potential. With the failure of competing candidates such as Dynacure's DYN101, Astellas Pharma has a high probability of achieving a dominant market position. Following the four deaths in the previous AT132 clinical trial, the regulatory hurdles for demonstrating the safety of gene therapies, particularly regarding hepatotoxicity, have increased significantly. Therefore, securing safety data through the 'EXCEL' observational study will be a critical strategy for overcoming regulatory approvals. In the short term, it will contribute to defining the toxicity monitoring criteria for the ongoing Phase 1/2 VALOR trial of the next-generation pipeline, ASP2957. In the long term, it is expected to promote the standardization of pre-existing cholestasis screening, expanding into a broader guideline for preventing adverse events in AAV-based gene therapies.
Source: ClinicalTrials.gov (api_ct)