SLU-PP-332 Peptide

SLU-PP-332 is a small-molecule pan-agonist of the estrogen-related receptors (ERRs), a subfamily of orphan nuclear receptors comprising three isoforms: ERRα (NR3B1), ERRβ (NR3B2), and ERRγ (NR3B3). Developed in the laboratory of Thomas Burris at Saint Louis University, SLU-PP-332 emerged from a medicinal chemistry program aimed at producing selective, drug-like ERR activators with sufficient potency and pharmacokinetic stability for preclinical investigation. It is currently classified as a research chemical and is not approved for human use, diagnosis, or treatment.

Chemically, SLU-PP-332 belongs to a series of acyl-hydrazide-derived ERR agonists. It demonstrates nanomolar agonist activity at ERRα and ERRγ, with somewhat lower activity at ERRβ. In cell-based reporter assays, SLU-PP-332 induces robust transcriptional activation of ERR-responsive promoter elements (ERREs) without engaging classical estrogen receptors (ERα/ERβ), distinguishing it pharmacologically from estrogenic ligands.

SLU-PP-332 is widely described in the literature as an "exercise mimetic" because it activates many of the same transcriptional programs that are induced by sustained endurance exercise. Whereas previously studied exercise-mimetic compounds such as AICAR (an AMPK activator) and GW501516 (a PPARδ agonist) act on energy-sensing kinases or peroxisome-proliferator–activated receptors, SLU-PP-332 operates upstream through the ERR axis. ERRs are highly expressed in tissues with high oxidative demand—skeletal muscle, cardiac muscle, brown adipose tissue, kidney, and liver—where they coordinate the transcription of nuclear-encoded mitochondrial genes in cooperation with the coactivators PGC-1α and PGC-1β.

Key reported features of SLU-PP-332 in preclinical models include:

• Receptor pharmacology: Direct agonist of ERRα and ERRγ, with EC50 values in the high nanomolar range in cell-based assays.
• Tissue selectivity bias: Pronounced transcriptional effects in skeletal muscle and adipose tissue, consistent with ERR expression patterns.
• Pharmacokinetics: Reasonable oral and parenteral exposure in rodents; reported plasma half-life sufficient for once- or twice-daily dosing in mouse studies.
• Metabolic phenotype in mice: Increased running endurance, enhanced oxidative fiber profile, improved glucose handling, and resistance to diet-induced obesity.

From a research standpoint, SLU-PP-332 is a valuable chemical biology tool for dissecting the ERR transcriptional network in vitro and in vivo. It provides investigators with a pharmacological alternative to genetic models (e.g., ERRα-knockout or muscle-specific PGC-1α overexpression) for probing how ERR activity contributes to mitochondrial biogenesis, substrate utilization, and exercise adaptation. It is also being explored mechanistically in models of obesity, heart failure, and pulmonary hypertension, where ERR-driven mitochondrial function appears to be a relevant therapeutic node.

Importantly, SLU-PP-332 should not be confused with peptide hormones or with selective androgen receptor modulators (SARMs), despite occasionally being grouped with them in informal discussions. It is a non-steroidal, non-peptide small molecule whose biology is mediated entirely through ERR-dependent transcriptional reprogramming. As with all early-stage research compounds, the long-term safety profile, off-target effects, and translational relevance of SLU-PP-332 remain to be established, and its use is strictly limited to laboratory research in qualified, regulated settings.

SLU-PP-332 exerts its effects by binding directly to the ligand-binding domain (LBD) of the estrogen-related receptors ERRα and ERRγ, stabilizing an active receptor conformation that promotes recruitment of transcriptional coactivators. Unlike classical nuclear receptors, ERRs were long considered "orphan" because endogenous high-affinity ligands have not been definitively identified; instead, their activity in vivo is governed largely by coactivator availability—particularly PGC-1α and PGC-1β. SLU-PP-332 effectively bypasses this constraint by acting as a synthetic agonist that locks the receptor in a coactivator-competent state, increasing transcription of ERR target genes even under basal metabolic conditions.

Once activated, ERRα/γ bind to ERR-response elements (ERREs) in the promoters and enhancers of nuclear-encoded mitochondrial genes. The downstream transcriptional program overlaps substantially with the adaptations induced by endurance training and includes:

• Mitochondrial biogenesis: Upregulation of NRF1, NRF2 (GABP), and TFAM, driving replication of mitochondrial DNA and assembly of new mitochondria.
• Oxidative phosphorylation: Increased expression of electron transport chain subunits across complexes I–V, raising maximal respiratory capacity.
• Fatty acid oxidation: Induction of CPT1b, MCAD, LCAD, and other β-oxidation enzymes, enhancing reliance on lipid substrates.
• TCA cycle flux: Upregulation of citrate synthase, isocitrate dehydrogenase, and succinate dehydrogenase components.
• Fiber-type remodeling: Shift toward fatigue-resistant Type I (slow oxidative) and Type IIa (fast oxidative-glycolytic) fibers at the expense of Type IIb glycolytic fibers.

In the landmark preclinical study by Billon and colleagues (2024), administration of SLU-PP-332 to sedentary mice produced a marked increase in treadmill running time and distance—approximately 45–50% greater than vehicle controls—without any concurrent exercise training. Histological analysis of soleus and gastrocnemius muscles revealed a significant increase in oxidative fiber proportion, accompanied by elevated mitochondrial content and citrate synthase activity. Importantly, these adaptations occurred without measurable hypertrophy, indicating that the effect is metabolic and transcriptional rather than anabolic.

Beyond skeletal muscle, ERR activation by SLU-PP-332 has been investigated in adipose tissue and cardiac muscle. In diet-induced obese mice, the compound reduced fat mass, improved insulin sensitivity, and increased whole-body energy expenditure, consistent with enhanced oxidative metabolism in brown and beige adipocytes. In cardiac models, ERR signaling supports the high mitochondrial density required for sustained contractile function, and ERR agonism has been proposed as a strategy to restore mitochondrial gene expression in heart failure, where ERR activity is characteristically suppressed.

Mechanistically, SLU-PP-332 also intersects with broader metabolic signaling. ERR activation cooperates with PGC-1α, which itself is induced by exercise-related stimuli such as AMPK activation, calcium/calcineurin signaling, and p38 MAPK. By directly amplifying the ERR arm of this network, SLU-PP-332 produces a coordinated transcriptional output that mimics endurance training without requiring upstream energetic stress. This positions the molecule as a useful pharmacological probe for studying how transcriptional control of mitochondrial function influences endurance, substrate selection, and metabolic flexibility.

Reference: Billon C, Page CL, Idris N, et al. Synthetic ERR agonists reverse obesity and improve glucose tolerance in mice. The Journal of Pharmacology and Experimental Therapeutics. 2024.

SLU-PP-332 is structurally distinct from earlier ERR ligands such as the inverse agonists XCT-790 and DY131, and unlike GSK4716 (an ERRβ/γ-selective agonist), it engages all three ERR isoforms. Its drug-like physicochemical profile and oral bioavailability in rodents make it a preferred chemical probe for ERR biology research.

SLU-PP-332 is a small-molecule pan-ERR agonist supplied as a crystalline lyophilized solid. Unlike peptides, it does not contain disulfide bonds or methionine residues, but its extended conjugated aromatic system and sulfonamide linkage benefit from careful handling to maintain chemical integrity over extended laboratory studies.

Recommended Reconstitution Protocol:

1. Equilibrate the sealed vial to room temperature (approximately 20-25°C) for 20-30 minutes prior to opening to prevent atmospheric moisture condensing onto the cold powder.
2. SLU-PP-332 is poorly soluble in water. The standard laboratory practice is to prepare a stock solution in anhydrous DMSO (dimethyl sulfoxide) at 10-50 mM (approximately 4.88-24.4 mg/mL).
3. Add the calculated volume of DMSO directly down the inner wall of the vial; do not inject into the powder bolus.
4. Cap the vial and gently invert or rotate. Brief, low-power sonication (water bath, 1-2 minutes) may be used to dissolve any residual particulate. Avoid vigorous vortexing.
5. For in vivo dosing solutions, the DMSO stock is typically diluted into a vehicle such as 5-10% DMSO / 40% PEG-400 / 5% Tween-80 / balance saline, as used in published SLU-PP-332 studies.
6. Working dilutions should be prepared fresh on the day of use and protected from light.

Concentration calculation example: 5 mg of SLU-PP-332 dissolved in 0.5 mL anhydrous DMSO yields a 10 mg/mL (~20.5 mM) stock solution.

Compound-specific notes: SLU-PP-332 contains an aromatic sulfonamide and an extended π-system that may be photosensitive over long exposures. Store stock solutions in amber vials or wrap in foil. Avoid repeated freeze-thaw cycles of the DMSO stock; aliquot upon first dissolution.

Proper storage of SLU-PP-332 preserves the integrity of the pan-ERR agonist scaffold and ensures reproducible pharmacological activity across long-term laboratory studies.

Lyophilized / solid powder storage:

• Long-term: Store at -20°C in a sealed, desiccated container. Under these conditions the compound is stable for at least 24 months.
• Short-term (working stock): 2-8°C in a sealed, light-protected container for up to 4 weeks.
• Transit: Stable at ambient temperature (15-25°C) for up to 2 weeks without measurable degradation.

Reconstituted solution storage:

• DMSO stock solutions: stable at -20°C or -80°C for up to 6 months when stored in single-use aliquots in amber tubes. DMSO freezes at approximately 19°C, so aliquots will solidify; thaw fully and mix gently before use.
• Aqueous working dilutions (in vehicle): use within 24 hours; do not refreeze.

Compound-specific stability notes: SLU-PP-332 lacks oxidation-sensitive residues (methionine, cysteine) found in peptides, but its aromatic sulfonamide linkage is susceptible to slow hydrolysis in protic solvents at elevated temperature. Always store in aprotic solvent (DMSO) for stock solutions, protect from prolonged UV exposure, and document any change in solution color (the compound is typically pale yellow to off-white in DMSO; darkening may indicate degradation).