A Study of a Thyroid Hormone Receptor Beta Isoform (THRβ) Agonist and an Semicarbazide Sensitive Amine Oxidase (SSAO) Inhibitor, Alone and in Combination, in Adults With Presumed Metabolic Dysfunction-associated Steatohepatitis (MASH)

The primary objective of this trial is to evaluate the dose-dependent and comparative effects of ECC4703 (low and high dose), ECC0509 (low and high dose), and their combination on hepatic fat reduction as assessed by change in magnetic resonance imaging proton density fat fraction (MRI-PDFF) at Week 12.

Inclusion Criteria: 1. Adults between 18 and 75 years of age, inclusive, who can provide written informed consent and comply with study procedures. 2. Diagnosis of presumed MASH based on: liver biopsy within 180 days prior to screening showing an NAFLD activity score (NAS) of ≥3 and a fibrosis score (F) of F1-3 OR FibroScan® CAP \>280 dB/m at screening with presence of metabolic risk factors. 3. Evidence of hepatic steatosis confirmed by FibroScan® LSM \> 7 kPa and \< 20 kPa and MRI-PDFF \>8% at screening. 4. BMI \>25 kg/m\^2 to \5× Upper Limit of Normal (ULN) or ALP \>2×ULN at screening. 4. Clinically significant thyroid or adrenal dysfunction, including uncontrolled hypothyroidism, hyperthyroidism, or adrenal disorders. 5. Type 1 diabetes, HbA1c \>9.5%, or unstable type 2 diabetes requiring medication changes within 90 days. 6. Use of medications that affect liver fat or fibrosis (e.g., Glucagon-Like Peptide-1 Receptor Agonists (GLP-1 RAs) not on a stable dose, pioglitazone, obeticholic acid, high-dose vitamin E, hepatotoxic drugs) within protocol-specified washout periods. 7. Significant alcohol use within 1 year prior to screening. 8. Recent cardiovascular events, including myocardial infraction (MI), stroke, unstable angina, heart failure (New York heart association \[NYHA III-IV\]), or uncontrolled arrhythmia. 9. Current or recent serious psychiatric illness, including psychosis, active suicidal ideation, or suicide attempt within 5 years. 10. Pregnancy, breastfeeding, or conditions that increase risk or interfere with study procedures, including MRI contraindications or other investigator-determined safety concerns.