Pharmacotherapeutic group: Bile and liver therapy, liver therapy, ATC code: A05BA11.
Mechanism of action
Resmetirom is a liver-directed partial agonist for the thyroid hormone receptor beta (THR-β). Resmetirom produced 83.8% of the maximum response compared to triiodothyronine (T3), with an EC50 of 0.21 μM in an in vitro functional assay for THR-β activation. The same functional assay for thyroid hormone receptor alpha (THR-α) agonism showed 48.6% efficacy for resmetirom relative to T3, with an EC50 of 3.74 μM. THR-β is the predominant form of THR in the liver. Stimulation of THR-β in the liver improves mitochondrial function and lipid metabolism, and increases fatty acid β-oxidation, thereby reducing lipotoxic liver fat, inflammation and liver fibrosis. Resmetirom's liver directed THR-β agonism is particularly relevant in the treatment of MASH and leads to minimal off-target activity on THR-α in tissues such as heart and bone.
Pharmacodynamic effects
Liver fat content
Resmetirom decreases liver fat content as measured by magnetic resonance imaging-proton density fat fraction (MRI-PDFF) or FibroScan controlled attenuation parameter (CAP). Reductions in liver fat content by MRI-PDFF were observed at 16 (the first assessment) and 52 weeks of treatment. Reductions in liver fat content by CAP were observed at 52 weeks of treatment.
Reductions in lipids
Resmetirom reduces blood low density lipoprotein (LDL) cholesterol, apolipoprotein B, lipoprotein (a) and triglyceride levels. Reductions in all lipid endpoints were observed initially after 4 weeks (the first assessment) and sustained at 24 and through 52 weeks of treatment.
Prohormone FT4
Decreased concentrations of prohormone FT4 were observed at the first assessment at 4 weeks of treatment. Similar decreases in FT4 were observed during treatment.
Sex hormone binding globulin (SHBG)
Resmetirom increased concentrations of sex hormone binding globulin (SHBG) at the first assessment at 4 weeks of treatment and at longer durations of treatment; by week 52, SHBG increased from baseline 145% (95% CI: 128, 160%) for 80 mg, 205% (95% CI: 182, 229%) for 100 mg and -0.4% (95% CI: -4, 2%) for placebo. No known adverse reactions were associated with SHBG elevations..
Cardiac electrophysiology
At a dose of 200 mg given for 7 days, resmetirom did not prolong the QT interval, PR interval, QRS interval, or alter heart rate in a study in healthy subjects.
Clinical efficacy and safety
The efficacy of resmetirom was studied in one multicentre, randomised, double-blind, placebo-controlled, clinical study in patients with MASH with liver fibrosis (MAESTRO-NASH). The 54-month outcomes portion of MAESTRO-NASH remains ongoing. The dual primary endpoints of the 52-week analysis were the effects of resmetirom versus placebo on: 1) the percentage of patients with resolution of NASH (ballooning 0, inflammation 0,1) associated with at least a 2-point reduction in NAFLD Activity Score (NAS) and without worsening of fibrosis by liver biopsy, and 2) the histological improvement from baseline demonstrated by at least a 1-point improvement in fibrosis (NASH Clinical Research Network [CRN] system) by liver biopsy with no worsening of NAS (total of three NAS components: ballooning, inflammation and steatosis).
Patients with metabolic risk factors were included in MAESTRO-NASH who had a baseline or recent historic liver biopsy showing NASH with a NAS of at least 4 and fibrosis stage 2 or 3.
The 52-week assessment included 917 patients with F2 or F3 fibrosis who received resmetirom 80 mg (n=306), resmetirom 100 mg (n=308), or placebo (n=303) once daily, in addition to lifestyle counselling on diet and exercise. Patients were on stable doses of medicinal products for diabetes, dyslipidaemia and hypertension. Patients were stratified by baseline type-2 diabetes status (present/absent) and fibrosis stage.
Demographics and baseline disease characteristics were balanced between treatment arms. The mean (SD) age at baseline was 57 (11) years. 25% of patients were older than 65 years, and 2% of patients were 75 years of age or older. Overall, 56% were female, ethnicity was 21% Hispanic, and races included 89% White, 3% Other, 3% Asian and 2% Black. The mean BMI was 36 (7) and mean body weight was 101 (23) kg. The baseline disease and comorbidity characteristics are shown in Table 2.
Table 2: Baseline disease and comorbidity characteristics in F2 and F3 patients enrolled in MAESTRO-NASH
| | Overall (N=917) |
| Type 2 diabetes, n (%) | 614 (67) |
| Hypertension, n (%) | 715 (78) |
| Dyslipidaemia, n (%) | 652 (71) |
| Statin use, n (%) | 441 (48) |
| Thyroxine use, n (%) | 124 (14) |
| FibroScan VCTE (kPa), median (Q1, Q3) | 12 (10, 15) |
| FibroScan CAP (dB/m), median (Q1, Q3) | 350 (321, 378) |
| MRI-PDFF (% ), median (Q1, Q3) | 17 (13, 22) |
| Fibrosis stage |
| F2, n (%) | 319 (35) |
| F3, n (%) | 583 (64) |
| NAS at Screening ≥ 5, n (%) | 770 (84) |
| ELF score (n = 905), median (Q1, Q3) | 9.7 (9.2, 10.4) |
| Fib-4 index (n = 915), median (Q1, Q3) | 1.3 (1.0, 1.8) |
Note: Patients who were rescored F4 at baseline were considered F3 for the purposes of stratification and analysis and are included in F3 numbers.
The 80 and 100 mg doses of resmetirom achieved both primary endpoints with statistically significant improvement relative to placebo in NASH resolution and fibrosis improvement (by 1 stage) (Table 3). Confidence intervals for other study endpoints were not controlled for multiple determinations. NASH resolution and fibrosis improvement were consistent regardless of age, gender, diabetes status, and baseline fibrosis stage. NASH resolution and fibrosis improvement (combined) and 2-stage reduction in fibrosis also improved with both doses of resmetirom relative to placebo.
Table 3: Effect of resmetirom in F2/F3 patients at week 52 on the primary liver biopsy endpoints of MAESTRO-NASH
| Week 52 Endpoint | Resmetirom 80 mg (N=300) | Resmetirom 100 mg (N=306) | Placebo (N=300) |
| NASH Resolution (%) | 26 | 30 | 10 |
| % difference vs placebo (95% CI) | 16 (11, 22) | 21 (15, 26) | |
| p-value | < 0.0001 | < 0.0001 | |
| Fibrosis Improvement (%) | 27 | 29 | 17 |
| % difference vs placebo (95% CI) | 9 (4, 15) | 12 (6, 18) | |
| p-value | 0.0017 | < 0.0001 | |
Note: Missing data were considered as non-responders. Additionally, 11 patients whose biopsies were delayed outside of the analysis window due to COVID-related issues were excluded.
Decreases from baseline in liver enzymes in resmetirom versus placebo-treated patients were observed at week 12 and continued to decline over 1 year (Table 4).
Table 4: Mean percent change from baseline to week 48 in liver enzymes in F2-F3 patients – ANCOVA with Placebo-based (-CR) Multiple Imputation (Week 52 Modified Intent-to-Treat Population – F2/F3)
| Parameter | Resmetirom 80 mg N = 305 | Resmetirom 100 mg N = 308 | Placebo N = 303 |
| ALT (% CFB) | -17.2 | -22.5 | 1.0 |
| Relative to placebo (95% CI) | -18.2 (-27.0, -9.5) | -23.6 (-32.5, -14.7) | |
| AST (% CFB) | -13.8 | -18.7 | 3.6 |
| Relative to placebo (95% CI) | -17.4 (-25.7, -9.1) | -22.2 (-30.7, -13.8) | |
| GGT (% CFB) | -21.8 | -27.4 | 5.7 |
| Relative to placebo (95% CI) | -27.5 (-36.8, - 18.1) | -32.0 (-42.7, -23.4) | |
ANCOVA = analysis of covariance; %CFB = percent change from baseline; CI = confidence interval; CR=copy reference
Note: n = number of patients used to compute LSM after imputation (imputation was not done for patients with no baseline data).
Note: Patients that were F3 at eligibility and re-evaluated as F4 at baseline by either pathologist are included in this analysis
% CFB = percent change from baseline
For a number of NASH biomarkers, in patients with increased baseline, greater improvements from baseline to week 52 were observed in resmetirom versus placebo-treated patients, including CK-18, ELF score, PIIINP, TIMP-1, and Hyaluronic Acid (HA).
The results of imaging endpoints overall showed support of the primary evaluation as shown in the following table (Table 5).
Table 5: Mean change from baseline for Imaging Endpoints at Week 52 in F2/F3 patients– ANCOVA with Placebo-based (CR) Multiple Imputation (Week 52 Modified Intent-to-Treat Population – F2/F3)
| Parameter | Resmetirom 80 mg | Resmetirom 100 mg | Placebo |
| N | 294 | 299 | 290 |
| Fibroscan VCTE (kPa) (CFB) | -2.3 | -3.0 | -1.5 |
| Relative to placebo (95% CI) | -0.82 (-1.7, 0.01) | -1.5 (-2.4, -0.7) | |
| N | 291 | 298 | 289 |
| Fibroscan CAP (dB/m) (CFB) | -36.0 | -37.1 | -15.0 |
| Relative to placebo (95% CI) | -21.0 (-30.5, -11.6) | -22.2 (-31.4, -12.9) | |
ANCOVA = analysis of covariance; CFB = change from baseline; CI = confidence interval; CR=Copy Reference
Note: n = number of patients used to compute LSM after imputation (imputation was not done for patients with no baseline data).
Note: Patients that were F3 at eligibility and re-evaluated as F4 at baseline by either pathologist are included in this analysis
Resmetirom reduced lipid and lipoprotein particles to a greater extent than placebo (Table 6). At week 24, resmetirom significantly reduced LDL-C, the key secondary endpoint of MAESTRO-NASH, at both studied doses.
Table 6: Mean percent change from baseline to week 52 in LDL-C in F2/F3 patients
| Parameter | Resmetirom 80 mg | Resmetirom 100 mg | Placebo |
| N | 305 | 308 | 303 |
| LDL-C (% CFB) | -13.3 | -17.6 | 0 |
| Relative to placebo | -13.5 (-17.9, -9.5) | -17.9 (-22.0, -13.8) | |
Note: N is based on 917 total patients minus one patient in the Resmetirom 80 mg group who did not have a baseline LDL-C value.
Note: Missing data imputed with Placebo-based (CR) Multiple Imputation
Paediatric population
The Medicines and Healthcare products Regulatory Agency has deferred the obligation to submit the results of studies with resmetirom in one or more subsets of the paediatric population in the treatment of metabolic dysfunction-associated steatohepatitis (see section 4.2 for information on paediatric use).
Conditional approval
This medicinal product has been authorised under a so-called 'conditional approval' scheme. This means that further evidence on this medicinal product is awaited. The Medicines and Healthcare products Regulatory Agency will review new information on this medicinal product at least every year and this SmPC will be updated as necessary.