Open-Label Extension Study on Long-Term Safety of Zagociguat in MELAS Patients Post TIS6463-203 Completion

The primary objective of this study is to evaluate the long-term **safety** and tolerability of zagociguat in participants with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). This is clinically relevant as it aims to ensure that the therapeutic use of zagociguat does not result in adverse effects over extended periods, which is crucial for patient safety and treatment adherence.

Secondary objectives include evaluating the long-term effects of zagociguat on various clinical parameters:

• Safety measurements
• Bone density and turnover
• Systemic lupus erythematosus (SLE) manifestations
• Disease progression and pathophysiology
• Clinicians’ impression of disease
• Renal and cardiac function
• Average blood glucose levels
• Exploratory pharmacokinetics to assess zagociguat plasma pharmacokinetics

The clinical trial involves a total of **30 participants** diagnosed with **Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS)**. The study population includes both male and female subjects, with an age range that encompasses both children and adults. Participants were selected based on their completion of a prior treatment phase, and the trial includes individuals who are considered part of a vulnerable population. The health status of participants is characterized by their existing diagnosis of MELAS, and they are required to adhere to specific contraceptive measures if of reproductive potential. The trial does not specify particular lifestyle considerations such as diet or physical activity. The selection criteria ensure that participants have provided informed consent and meet specific reproductive health requirements, but further details on lifestyle or health status are not provided by the sponsor.

The clinical trial is designed as an **open-label extension study** to evaluate the long-term safety and tolerability of **zagociguat** in participants with **Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS)** who have completed a prior study, TIS6463-203. The trial is categorized as a Phase 4 study and is not considered low intervention. The study will involve oral administration of zagociguat in tablet form, with a maximum daily dose of 15 mg and a total treatment period of up to 156 weeks. The primary endpoint is the incidence of treatment-emergent adverse events (TEAEs), while secondary endpoints include various clinical assessments and biomarker measurements at scheduled timepoints.

Participants will be involved in the study from the screening visit through to the end-of-study visit, with the estimated recruitment start date being January 31, 2025, and the estimated end date being September 29, 2028. The sequence of study visits includes an initial screening visit to confirm eligibility, followed by regular follow-up visits to monitor safety and efficacy parameters, and a final end-of-study visit to conclude participation. The expected length of participant involvement is approximately three years, contingent upon the completion of all required visits and assessments.

Inclusion criteria require participants to have completed the previous study, TIS6463-203, and to have signed an informed consent form approved by an Institutional Review Board (IRB) or Independent Ethics Committee (IEC). Female participants must meet specific reproductive criteria, and both male and female participants of reproductive potential must agree to use highly effective contraception methods during the study and for a specified period after the final dose. Conditions that may lead to early termination from the study include the occurrence of significant adverse events or non-compliance with study procedures.

The clinical trial involves the administration of **zagociguat**, a chemical compound developed by Tisento Therapeutics Inc. The experimental medication is provided in the form of a **tablet** with a dosage strength of 15 mg. The route of administration is **oral use**, and the medication is to be taken once daily. The maximum daily dose is 15 mg, with a total maximum dose of 16,380 mg over the course of the study. The treatment period extends up to 156 days. The active substance in zagociguat is chemically synthesized and is also known by its synonyms, IW-6463 and 8-(2-fluorobenzyl)-6-(3-(trifluoromethyl)-1H-1,2,4-triazol-5-yl)imidazo[1,2-a]pyrazine.

In this open-label extension study, the primary objective is to evaluate the long-term safety and tolerability of zagociguat in participants with **MELAS** who have completed a previous study, TIS6463-203. No non-experimental treatments, such as standard-of-care therapy, placebo, or comparator treatments, are specified for this trial. Participant compliance with the dosing schedule will be monitored throughout the study to ensure adherence to the prescribed regimen.

The efficacy of zagociguat in the clinical trial will be assessed through a series of secondary endpoints. These include measurements of vital signs, ECG assessments, and clinical laboratory tests, which will be conducted at each scheduled timepoint. Additionally, the trial will evaluate the concentrations of various biomarkers, such as CTX, P1NP, lactate, GDF-15, FGF-21, B2M, serum amyloid P component, TNFR-2, vWF, ICAM-1, NfL, and VCAM-1, at each scheduled timepoint. The trial will also assess the **NMDAS** item scores and the CGI-C overall MELAS scale score at each scheduled timepoint to determine symptom improvement.

Further efficacy assessments will include the measurement of DEXA hip and lumbar spine BMD, eGFR, UACR, HbA1c levels, and concentrations of troponin I, NT-proBNP, and creatine kinase (CK)-MB at each scheduled timepoint. Exploratory pharmacokinetics will be evaluated by measuring the concentrations of zagociguat at each scheduled timepoint. The incidence of SLE and the time to first SLE from Day 1 will also be recorded. These parameters will be collected and analyzed to provide a comprehensive evaluation of the drug's efficacy in participants with MELAS.