Kylo-0603 enters Phase 2a testing in MASLD with a liver-fat endpoint at the center
A new Phase 2a study is preparing to test Kylo-0603, an oral thyroid hormone receptor beta agonist designed for liver targeting, in adults with metabolic dysfunction-associated steatotic liver disease and overweight or obesity. The trial is not yet recruiting, but its design is already clinically clear: investigators are trying to determine whether selective activation of hepatic THRβ can reduce intrahepatic fat while limiting the peripheral thyroid-related effects that have complicated this drug class elsewhere.
The study is multicenter, randomized, double-blind, and placebo-controlled. About 120 participants will be assigned in a 1:1:1:1 ratio to once-daily oral Kylo-0603 at 8 mg, 12 mg, or 16 mg, or to placebo for 12 weeks. The primary endpoint is the percentage change from baseline in liver fat content measured by MRI-PDFF at Week 12.
Why a liver-selective THRβ agonist matters in steatotic liver disease
MASLD sits at the intersection of excess hepatic lipid storage, insulin resistance, and metabolic stress. Its clinical burden is large, with progression in some patients to metabolic dysfunction-associated steatohepatitis, fibrosis, cirrhosis, and end-stage liver disease. The cardiovascular risk attached to this disease is part of the same biology: hepatic lipid overload rarely stays confined to the liver.
THRβ is predominantly expressed in the liver, which makes it a rational therapeutic target for steatotic liver disease. Agonism at this receptor can regulate hepatic lipid metabolism, reduce fat accumulation, and suppress inflammatory and fibrotic signaling in the liver. The therapeutic logic is straightforward. If the receptor can be activated in the liver without driving systemic thyroid effects, the drug may lower liver fat in a way that is both mechanistically plausible and clinically useful.
Kylo-0603 is built around that idea. The compound is described as a liver-targeted, highly selective THRβ agonist modified with GalNAc to enrich hepatic exposure and reduce peripheral effects. In practical terms, the design aims to shift drug distribution toward the organ that matters most in MASLD while avoiding the adverse consequences that come from nonselective thyroid receptor stimulation.
A 12-week liver-fat readout will test dose response
The trial uses a short, focused treatment period, which is appropriate for a Phase 2a study centered on hepatic fat reduction rather than long-term outcomes. Twelve weeks is enough time to see whether a pharmacologic signal emerges in liver fat content, especially when MRI-PDFF is used as the biomarker. That imaging method is well suited to quantifying steatosis without the variability and invasiveness of repeated biopsy.
The dosing scheme is intentionally simple: 8 mg, 12 mg, and 16 mg once daily, compared with placebo. This structure should allow investigators to determine whether a dose-response relationship appears across the three active arms. A clean separation in MRI-PDFF from placebo would support the biological premise of the drug. A flat response across doses would raise harder questions about exposure, receptor engagement, or the limits of THRβ modulation in this population.
The study’s estimated enrollment is 120 participants, which is modest but typical for early efficacy work. At this stage, the goal is not to settle the MASLD treatment question. It is to determine whether the signal is strong enough to justify a larger trial with longer follow-up and more durable liver and metabolic endpoints.
Eligibility criteria define a metabolically stressed but noncirrhotic population
The inclusion criteria shape a population with meaningful hepatic steatosis but without advanced liver failure. Eligible participants must be 18 to 70 years old, have MRI-PDFF of at least 10% at screening, and show liver stiffness between 8 and 15 kPa on FibroScan. Body mass index must fall between 25.0 and 40.0 kg/m², and body weight must be stable in the 6 weeks before screening.
Several exclusions narrow the sample further. Patients with other chronic liver diseases, cirrhosis, portal hypertension, hepatic encephalopathy, or prior liver transplantation are excluded. So are those with significant alcohol exposure, thyroid disease, major uncontrolled metabolic abnormalities, or recent use of drugs that could independently alter hepatic steatosis or confound the study drug’s effect.
The protocol also excludes recent use of insulin, GLP-1 receptor agonists, GIP receptor agonists, or glucagon receptor agonists, along with recent weight-loss medications and recent or current MASH therapies. This matters because those therapies can change liver fat, body weight, and glycemic control on their own. By removing them from the equation, the study is trying to isolate the effect of Kylo-0603 with fewer competing metabolic forces in the background.
Safety monitoring will be especially sensitive to thyroid and cardiometabolic issues
Because the investigational agent acts through the thyroid hormone pathway, the exclusion criteria around thyroid function are extensive. Participants with thyroid disease, abnormal thyroid function tests, or thyroid-related antibodies are not eligible. The protocol excludes abnormal TSH, FT3, FT4, TT3, TT4, and positive TPOAb, TRAb, or TGAb results. That level of screening reflects the need to avoid enrolling patients in whom thyroid biology is already unstable.
Cardiovascular and metabolic safety also receive careful attention. Poorly controlled hypertension, recent congestive heart failure, unstable coronary disease, stroke, transient ischemic attack, renal failure, and other major systemic illness are all exclusionary. The study also excludes clinically significant ECG abnormalities, including QTcF thresholds of 450 msec in men and 470 msec in women. These are not cosmetic details. They are the boundary markers that separate a focused metabolic liver trial from a broader safety risk.
The liver chemistry thresholds are similarly strict. Screening excludes ALT or AST greater than 5 times the upper limit of normal, ALP at least 2 times the upper limit, total bilirubin above 1.5 times the upper limit, INR at least 1.3, eGFR below 60 mL/min/1.73 m², or platelets below the lower limit of normal. Those limits remove patients with more advanced hepatic dysfunction and reduce the chance that baseline injury will be mistaken for a drug-related problem.
What this trial can and cannot answer
This study is designed to answer a narrow but important question: can a liver-targeted THRβ agonist reduce hepatic fat over 12 weeks in adults with MASLD and overweight or obesity? It will not determine whether Kylo-0603 prevents fibrosis progression, reduces cirrhosis, or lowers cardiovascular events. It will not establish whether a liver-fat reduction translates into symptom relief or long-term histologic benefit.
The trial is also limited by its size and duration. With approximately 120 participants and a 12-week treatment window, the study can generate a pharmacodynamic signal, but it cannot resolve the full clinical value of the drug class. Even so, the design is well matched to the question being asked. If the MRI-PDFF endpoint shifts meaningfully away from placebo, the result would support the logic of hepatic THRβ selectivity and justify larger studies in more advanced disease.
A negative result would be just as instructive. It would suggest that liver targeting alone is not enough, or that the selected doses and duration are insufficient to move hepatic steatosis in a measurable way. Either outcome would carry real value for a field still searching for effective, durable therapies in MASLD.