SLU-PP-332

What is SLU-PP-332?

SLU-PP-332 is a synthetic small-molecule pan-agonist of all three Estrogen-Related Receptors (ERRα, ERRβ, and ERRγ) — orphan nuclear receptors that function as master regulators of mitochondrial biogenesis, fatty acid oxidation, and oxidative metabolism. Developed at St. Louis University (hence 'SLU'), SLU-PP-332 was the first compound to demonstrate that pharmacological ERR pan-activation can replicate the transcriptional signature of acute aerobic exercise in skeletal muscle, earning it the designation of 'exercise mimetic.' In mouse models, it increased exercise endurance, enhanced fatty acid oxidation, promoted type IIa oxidative muscle fiber formation, and alleviated metabolic syndrome markers — all without physical training.

Molecular Composition

SLU-PP-332 is a synthetic small molecule built on a naphthalene-based scaffold, not a peptide. Its molecular structure was designed to fit the ligand-binding domain of all three ERR subtypes (α, β, γ) simultaneously — a pan-agonist profile that distinguishes it from earlier ERR-selective compounds. The naphthalene core provides hydrophobic interactions with the receptor binding pocket, while functional groups on the scaffold enable hydrogen bonding with key residues in the ERRα AF-2 helix. Structural optimization studies have identified that the naphthalene group is critical for ERRγ binding, while ERRα activity can be preserved with modifications that reduce ERRγ engagement — providing a roadmap for next-generation selective analogs. SLU-PP-332 is supplied as a lyophilized research powder requiring reconstitution for in vitro or in vivo research applications.

How Does It Work?

SLU-PP-332 acts as a pan-agonist at all three Estrogen-Related Receptors (ERRα, ERRβ, ERRγ) — orphan nuclear receptors that are constitutively active and do not require endogenous ligands for baseline activity. Upon SLU-PP-332 binding, ERR activity is amplified, driving the transcription of target genes involved in mitochondrial biogenesis, fatty acid β-oxidation, and oxidative phosphorylation. The primary downstream effector is PGC-1α (Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha) — the master regulator of mitochondrial biogenesis. ERRα directly binds to ERR Response Elements (ERREs) in the promoters of PGC-1α target genes, creating a positive feedback loop: PGC-1α coactivates ERRα, and ERRα drives PGC-1α target gene expression. Key downstream targets include DDIT4 (a direct ERRα target gene that regulates the acute aerobic exercise genetic program), SLC25A25 (mitochondrial calcium transport), ALAS2 (heme biosynthesis), and genes encoding components of the electron transport chain. Critically, the effects of SLU-PP-332 on exercise endurance enhancement were completely abolished in skeletal muscle-specific ERRα knockout mice, demonstrating that ERRα is the primary mediator of its exercise-mimetic effects. SLU-PP-332 also shifts skeletal muscle fiber composition toward type IIa oxidative fibers (the 'endurance fiber' phenotype), increases mitochondrial density, and enhances cellular respiration in C2C12 myocytes. In metabolic syndrome models, it increases whole-body energy expenditure, enhances fatty acid oxidation, reduces adiposity, and improves insulin sensitivity — replicating the metabolic adaptations of endurance exercise training.

Key Research Pathways

Key Findings from the Literature

• SLU-PP-332 enhanced exercise endurance in mice by ~50% after 14 days of treatment (50 mg/kg b.i.d., i.p.), an effect completely abolished in skeletal muscle-specific ERRα knockout mice, confirming ERRα as the primary mediator (Billon et al., 2023, PMC11584170)
• In mouse models of obesity and metabolic syndrome, SLU-PP-332 administration increased energy expenditure, enhanced fatty acid oxidation, reduced adiposity, and improved insulin sensitivity — replicating the metabolic benefits of endurance exercise without physical training (Billon et al., J Pharmacol Exp Ther 2024; PMID 37739806)
• SLU-PP-332 induced a transcriptional signature in skeletal muscle that closely matched the acute aerobic exercise genetic program, including upregulation of DDIT4, SLC25A25, PER1, ALAS2, and multiple electron transport chain components
• The compound increased type IIa oxidative skeletal muscle fiber content and enhanced mitochondrial respiration in C2C12 myocytes, demonstrating direct effects on muscle fiber phenotype and mitochondrial function
• Novel ERR pan-agonists derived from SLU-PP-332's scaffold demonstrated cardioprotective effects in heart failure models by boosting cardiac fatty acid metabolism and mitochondrial function (Hegazy et al., 2022, bioRxiv)
• Chemical optimization of SLU-PP-332 has produced orally bioavailable analogs (SLU-PP-915 and related compounds) that retain exercise-mimetic activity with improved pharmacokinetic profiles, validating the ERR pan-agonist approach for drug development

Important Research Context