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Phase 2b Randomized Double‑Blind Study of ALN‑CIDEB in Adults with Metabolic Dysfunction‑Associated Steatohepatitis (MASH)

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What is this trial about?

A plain-language summary of the goals, design and what participants do

The study focuses on adults with Metabolic Dysfunction-Associated Steatohepatitis (MASH), a condition where excess fat builds up in the liver and causes scarring. Participants will receive a subcutaneous injection of the investigational drug ALN-CIDEB or a matching placebo. The medication is given under the skin in a liquid form.

The purpose of the study is to evaluate whether ALN-CIDEB can lower the amount of fat in the liver. Over several months, participants will attend regular clinic visits where they will have imaging scans, blood tests, and a brief liver assessment. Liver fat will be measured using a specialized scan called MRI-PDFF, which provides a picture of how much fat is present, and stiffness will be checked with a non‑invasive test called FibroScan. A small tissue sample (liver biopsy) may be taken at the start and end of the study to look at scarring.

Safety will be monitored by recording any side effects and by checking routine blood enzymes such as AST and ALT. The study lasts for a defined period, after which the data will be analyzed to see if the drug reduced liver fat compared with the placebo.

The research process

The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Randomization and Baseline Assessments

    After joining the study, you will be randomly assigned to receive either ALN-CIDEB or a matching placebo. The assignment is unknown to both you and the study team.

    Baseline examinations will be performed, including a magnetic resonance imaging‑derived proton density fat fraction (MRI‑PDFF) scan to measure liver fat, a liver biopsy to evaluate tissue changes, blood tests for liver enzymes (AST and ALT), and a FibroScan examination to assess liver stiffness and fat content.

  2. Step 2

    First Dose Administration

    You will receive the first dose of the study medication as a subcutaneous injection. The drug is supplied as a solution for injection; the exact amount per injection is defined by the study protocol.

    If you are assigned to the placebo group, you will receive an injection of a solution that looks identical but contains no active substance.

  3. Step 3

    Regular Injection Visits During Treatment Period

    You will return to the clinic at scheduled intervals for additional subcutaneous injections. Each visit includes a brief safety check, during which you will be asked about any new symptoms or side effects.

    The frequency of these visits follows the study schedule, which is consistent for all participants throughout the treatment phase.

  4. Step 4

    Mid‑Study Imaging and Laboratory Assessments

    Approximately halfway through the treatment period, another MRI‑PDFF scan will be performed to evaluate changes in liver fat.

    Additional blood tests and a repeat FibroScan will be conducted to monitor liver enzymes, liver stiffness, and fat content.

    The study team will also review any adverse events you may have experienced.

  5. Step 5

    End‑of‑Treatment Assessments

    At the conclusion of the treatment phase, a final set of assessments will be carried out, including a repeat MRI‑PDFF scan, a liver biopsy to determine any improvement in fibrosis, and comprehensive blood tests.

    All safety information collected during the study will be evaluated to determine the overall tolerability of the medication.

  6. Step 6

    Follow‑Up Visit

    A follow‑up visit will be scheduled after the end‑of‑treatment assessments to ensure that any delayed effects are identified. This visit may include a brief physical examination and a final safety questionnaire.

Who can join the trial?

5 criteria

  • Have a confirmed diagnosis of MASH (Metabolic Dysfunction‑Associated Steatohepatitis) in your medical records, or your doctor suspects you have it based on simple blood tests called biomarkers and risk factors, and you have at least one sign of metabolic syndrome (such as high blood pressure, high blood sugar, extra belly fat, high triglycerides, or low “good” cholesterol).
  • Undergo a small needle liver sample called a percutaneous liver biopsy that shows a NAFLD Activity Score (NAS) of 4 or higher and a fibrosis stage of F2 or F3. (The NAS is a number doctors use to measure inflammation and damage in the liver, and the fibrosis stage describes how much scarring is present.)
  • Have a FibroScan test result with a FAST score greater than 0.35, measured either at the first screening visit or within about three months before that. (FibroScan is an ultrasound‑based test that measures liver stiffness; the FAST score combines this with a blood enzyme called Aspartate aminotransferase to estimate disease severity.)
  • Be between 18 and 75 years old, inclusive, at the first screening visit.
  • Meet any other requirements that the study protocol specifies.

Who cannot join the trial?

6 criteria

  • Having a long‑lasting liver problem (chronic liver disease) that is not the specific condition being studied, called Metabolic dysfunction‑Associated steatotic Liver Disease (MASLD).
  • Having had or currently having suspected or confirmed liver damage caused by medicines (drug‑induced liver injury) within about one year before the first screening visit.
  • Having a history of liver transplantation, being on a waiting list for a liver transplant, or having a MELD score (a number doctors use to measure how sick the liver is) higher than 12.
  • Having a known history of alcohol or other substance abuse within the last year, or at any time during screening, as judged by the doctor or shown by a score of 8 or more on the AUDIT questionnaire (a set of questions that checks alcohol use).
  • Having used, currently using, or planning to use a medicine called a Glucagon‑Like Peptide‑1 (GLP‑1) receptor agonist (a type of drug that helps control blood sugar) or any drug approved to treat MASH (the liver condition being studied), unless the medicine has been taken at a stable dose for at least three months with no expected changes.
  • Any other reasons defined by the study protocol that would prevent participation.
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Investigated drugs

ALN-CIDEB is an experimental medication being studied to see if it can lower the amount of fat in the liver of adults who have a condition called metabolic dysfunction‑associated steatohepatitis (MASH) with fibrosis. In the trial, the drug is given as a liquid that is injected under the skin (subcutaneous injection). Researchers are measuring changes in liver fat using MRI scans to determine whether the medication helps improve the liver condition.

What is already known about the treatment

ALN-CIDEB - This medication is given as a subcutaneous injection of a clear solution. It is still investigational and is being studied in clinical trials, with limited data in the medical literature so far. The drug is being tested for treating Metabolic Dysfunction‑Associated Steatohepatitis (MASH), a liver disease that involves fat buildup and scarring. ALN‑CIDEB works by using a small piece of genetic material to silence the CIDEB gene in liver cells, which helps reduce the amount of fat stored in the liver, and it belongs to the class of RNA‑interference (siRNA) therapies.

Investigated diseases

Metabolic Dysfunction-Associated Steatohepatitis (MASH) - Metabolic Dysfunction-Associated Steatohepatitis (MASH) is a condition where excess fat accumulates in the liver together with inflammation caused by metabolic problems such as obesity or insulin resistance. The disease begins with simple fatty liver and then develops inflammation that damages liver cells. Over time, this damage can lead to the formation of scar tissue, known as fibrosis. As fibrosis progresses, the liver’s ability to perform its normal functions gradually declines. Without changes in the underlying metabolic state, the condition can continue to advance from mild to more extensive scarring.
Trial detailsLast updated 2 Nov 2026
Age18+ yearsPhasePhase IITrial ID2026-525916-33-00Protocol codeALN-CIDEB-MASH-2603Estimated enrolment142 patientsSponsorRegeneron Pharmaceuticals Inc.

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