Selective Small-Molecule AdipoR1 Agonist 3-Hydroxy Pterocarpan Salt (CDRI-1709S) Ameliorates Skeletal Muscle Atrophy

Skeletal muscle atrophy is a frequent comorbidity of metabolic disorders and chronic diseases, and despite its high prevalence, no pharmacological therapy is available, representing a major unmet clinical need. Adiponectin and its receptors are key regulators of skeletal muscle metabolism, mitochondrial function and myogenesis, yet clinical translation has been hindered by the lack of receptor-selective agonists with favourable pharmacological and safety profiles. Here, we report the identification and characterization of CDRI-1709S, the first small-molecule AdipoR1-selective agonist and evaluate its myogenic and anti-atrophy efficacy.

A PGC-1α luciferase reporter-based screen in AdipoR1/AdipoR2-transfected, AdipoR-low HEK293T cells identified CDRI-1709S as an AdipoR1 agonist. Adiponectin-associated signalling events were evaluated by immunoblotting in AdipoR1/2-overexpressing HEK293T cells and AdipoR-abundant C2C12 myotubes, with receptor specificity confirmed using RNA interference. Myogenic potential was assessed by morphometric analysis and immune detection of myogenic factors. Fibre-type composition and metabolic capacity were evaluated using immunoblotting and extracellular flux analysis. Anti-atrophy effects were examined in vitro using various assault-induced models of myotube atrophy, and in vivo using rat models of dexamethasone (Dex) and sciatic nerve denervation-induced muscle atrophy.

CDRI-1709S selectively activated AdipoR1 with high potency (EC₅₀: 414.7pM) and, at a pharmacologically relevant concentration (100 nM), induced rapid adiponectin-associated signalling, including phosphorylation of AMPK, AKT and p38-MAPK, along with upregulation of its downstream skeletal muscle metabolic targets PGC-1α, GLUT4 and UCP3 in an AdipoR1-dependent manner (p < 0.05). CDRI-1709S promoted C2C12 myoblast differentiation into mature myotubes, accompanied by increased expression of MyoD and myogenin (p < 0.05). Treated myotubes were protected against cytokine-, Dex- and nutrient-deprivation-induced atrophy through suppression of atrogenes Atrogin-1 and MuRF-1 (p < 0.01), restoration of myogenic markers (p < 0.05) and prevention of Dex-induced fibre-type switching toward glycolytic MyHC-IIB, with concomitant induction of slow (MyHC-I) and fast (MyHC-IIA) oxidative fibres (p < 0.05). CDRI-1709S also reversed Dex-mediated impairments in oxidative and glycolytic capacity (p < 0.05). Oral administration of CDRI-1709S (10 mg/kg/day) in Dex- and denervation-induced rat models restored atrogene expression, myogenic markers, local adiponectin signalling and myofibrillar architecture to normalcy (p < 0.05 to p < 0.0001). CDRI-1709S prevented Dex-induced enrichment of glycolytic fibres and preserved oxidative fibre composition (p < 0.05). The structural/molecular improvements translated into significant functional enhancements, including toe-spread reflex in denervated limbs (p < 0.05) and increased grip strength (p < 0.0001) plus prolonged wire-hang duration (p < 0.01) in Dex-treated animals.

CDRI-1709S is the first AdipoR1-selective small-molecule agonist that induced myogenesis and robustly ameliorated skeletal muscle atrophy, establishing the proof-of-concept for AdipoR1-targeting as a promising therapeutic strategy for sarcopenia and skeletal muscle atrophy.