Stockholm-based Atrogi AB has dosed the first subjects in clinical trial evaluating the muscle physiological effects of its oral β2-adrenergic receptor therapy ATR-258 in overweight male volunteers, as per a company announcement. ATR-258 is a first-in-class, GRK-biased, long-acting β2-adrenergic receptor agonist designed to mimic the metabolic effects of exercise — driving fat loss while preserving or increasing skeletal muscle mass. The 8-week investigator-initiated study, led by Associate Professor Morten Hostrup at the University of Copenhagen, will measure the extent to which ATR-258 recapitulates the muscle-building effects of classical β2-agonists through biased downstream signaling. The trial is registered as NCT07421024 and is also listed on AllSci.
The study plans to enrol 10 participants receiving daily oral dosing of Atrogi ATR-258, with endpoints focused on molecular and physiological readouts in skeletal muscle. A primary completion date of December 2026 is listed. This trial builds on a completed 69-subject Phase 1 study in healthy volunteers and patients with type 2 diabetes, the results of which were published in Cell in June 2025 and demonstrated safety and tolerability. Atrogi describes ATR-258 as an exercise mimicking drug with potential across metabolic disease and muscle atrophic conditions including sarcopenia, immobilization-induced wasting, and muscle loss during weight-loss therapy.
Research context: β2-adrenergic signaling for muscle-sparing weight loss
The β2-adrenergic receptor is a GPCR expressed in skeletal muscle and other tissues. Traditional β2-agonists such as clenbuterol are known to promote muscle hypertrophy and fat oxidation, but their clinical use for metabolic indications has been precluded by cardiovascular toxicity — tachycardia, arrhythmias, and desensitization with chronic dosing. ATR-258 is engineered to exploit biased agonism, preferentially engaging GRK-mediated signaling pathways rather than classical G protein coupling. The principle that selective pathway activation at GPCRs can separate therapeutic from adverse effects is well established in receptor pharmacology, as reviewed in literature on β2-adrenergic receptor activation. Atrogi’s Cell publication provided validation that GRK2-biased β2-AR agonism can decouple the metabolic and muscle-related benefits from cardiovascular risk, a result that underpins the current trial’s rationale. The Copenhagen study is designed to interrogate the specific downstream effectors — GRK, cAMP/PKA, and β-arrestin pathways — in human muscle tissue, generating mechanistic data that would be difficult to obtain outside a dedicated physiology-focused trial.
The obesity treatment landscape has been reshaped by incretin-based therapies. Semaglutide (Wegovy, Novo Nordisk), approved in 2021, and tirzepatide (Zepbound, Eli Lilly), approved in 2023, deliver 15–22% body weight reductions. An oral formulation of semaglutide for obesity was approved in December 2025. All current pharmacotherapies operate primarily through appetite suppression and caloric intake reduction. None specifically target muscle preservation. Studies indicate that 25%-40% of total weight lost with GLP-1 agonists can be lean body mass, raising concerns about sarcopenia, frailty, and metabolic deterioration, particularly in older adults. No pharmacotherapy is currently approved for sarcopenia itself. ATR-258, as an oral obesity treatment that aims to simultaneously promote fat loss and muscle gain through a mechanistically distinct pathway, would address a gap that existing incretin therapies do not.
No other GRK-biased β2-adrenergic receptor agonists are in active clinical development for obesity or muscle-sparing weight loss, according to public data. The closest conceptual competitor addressing muscle loss during weight reduction is bimagrumab, an anti-activin type II receptor antibody acquired by Eli Lilly. Bimagrumab operates through an entirely different mechanism — blocking myostatin/activin signaling to prevent muscle catabolism — and requires intravenous infusion. A Phase II trial combining bimagrumab with semaglutide showed lean mass preservation, but Lilly terminated one of its Phase II studies for the molecule in 2025 for strategic reasons. The broader obesity pipeline remains dominated by incretin-based approaches: Eli Lilly’s retatrutide (a triple GIP/GLP-1/glucagon agonist) is in late-phase development, and multiple companies are advancing oral GLP-1 formulations. These programs pursue appetite and energy balance modulation rather than direct muscle anabolism. ATR-258 potentially occupies a distinct position as an oral small molecule that attempts to achieve both fat loss and muscle gain through a single mechanism.