SLU-PP-332: ERR Agonist Research Guide 2026

Almost every compound on a research menu is a peptide. SLU-PP-332 is not. It is a 290-dalton small molecule that acts on a nuclear receptor family rather than a cell-surface GPCR, and that single structural fact changes what the literature can show, what the mechanism looks like, and — most practically — what a certificate of analysis has to prove before the material is worth anything in an experiment.

It also occupies an unusual position in the research market: a compound with a clean academic provenance, a well-characterised molecular target, a small but real peer-reviewed literature, and no clinical development programme whatsoever. Everything published about it lives in cell culture and rodent models.

All research described below is in-vitro or preclinical. No human data exist for this compound. Nothing here describes or implies use in humans.

1. Molecular Profile

SLU-PP-332 is not a peptide, and framing it as one — as several vendor listings do — is the first error to avoid.

• Compound: SLU-PP-332
• CAS number: 303760-60-3
• Molecular formula: C18H14N2O2
• Molecular weight: ~290.32 g/mol
• Chemical class: N-acylhydrazone (aroyl hydrazone)
• Chemical name: 4-hydroxy-N’-(naphthalen-2-ylmethylidene)benzohydrazide
• Sequence: none — this is a synthetic small molecule, not an amino acid chain
• Target class: estrogen-related receptors (ERRα, ERRβ, ERRγ) — orphan nuclear receptors
• Reported potency: EC50 ≈ 98 nM (ERRα), ≈ 230 nM (ERRβ), ≈ 430 nM (ERRγ)
• Regulatory status: not approved by FDA, EMA, or any other authority for any indication; not in registered clinical development

The name is a laboratory designation, not a trade name: the compound emerged from the laboratory of Thomas P. Burris at Saint Louis University — hence SLU — with subsequent work continuing at Washington University in St. Louis and the University of Florida.

Structurally it is two aromatic rings — a 2-naphthaldehyde-derived end and a 4-hydroxybenzoyl end — joined by a C=N–NH acylhydrazone bridge. That bridge is the whole compound’s analytical story, and Section 6 returns to it.

2. Mechanism

The estrogen-related receptors are orphan nuclear receptors: constitutively active transcription factors with no established endogenous ligand. Despite the name, they do not bind estradiol. Their activity is governed primarily by how much coactivator protein is available to them, and the coactivators in question are the PGC-1 family.

Vincent Giguère’s review in Endocrine Reviews (2008) is the standard reference for this architecture. ERRα and ERRγ function as the principal transcriptional conduits for PGC-1α and PGC-1β activity, and together they occupy the promoters of gene networks governing oxidative phosphorylation, fatty acid oxidation, the tricarboxylic acid cycle, and mitochondrial biogenesis. When PGC-1α is induced, ERRs are a large part of how that induction becomes transcription.

SLU-PP-332 has been studied as a direct agonist at this node. Rather than raising coactivator levels indirectly, it binds the ERR ligand-binding domain and has been reported to stabilise the receptor–coactivator interaction, driving ERR-dependent transcription. It is a pan-agonist across all three isoforms with the highest reported potency at ERRα.

Two properties of that mechanism are worth stating precisely, because they are what makes the compound scientifically interesting rather than merely marketable:

It is transcriptional, not signalling. There is no second messenger cascade, no receptor internalisation, no acute cAMP or calcium response to measure. The readouts are gene expression time courses and downstream mitochondrial phenotype. Effects are slow to appear and slow to reverse relative to GPCR-directed compounds.

It is pan-isoform. ERRα, ERRβ, and ERRγ have overlapping but distinct tissue distributions and target genes. A pan-agonist does not permit clean attribution of any observed effect to a single isoform without genetic controls — which is exactly why the primary published study went to the trouble of using ERRα-null models.

The mechanism is described here at pathway and receptor level only. SLU-PP-332 has been studied for effects on ERR-dependent transcriptional programmes in defined experimental systems. That is the entirety of the claim.

3. Preclinical Research Data

The foundational in vivo characterisation is Billon and colleagues, ACS Chemical Biology (2023). In mouse skeletal muscle, systemic administration of SLU-PP-332 induced a transcriptional programme resembling the acute response to a single bout of aerobic exercise, including upregulation of ERR target genes such as Ddit4 and Slc25a25. Critically, the response was abolished in ERRα-deficient animals, establishing that the transcriptional effect was receptor-dependent rather than an off-target artefact of the chemotype. The same study reported an increased proportion of type IIa oxidative fibres and increased treadmill running distance and time in treated animals relative to vehicle controls.

That combination — a defined molecular target, a receptor-null control demonstrating dependence, and a physiological readout — is what distinguishes this compound’s evidence base from most of the research market. It is also worth being clear about scale: group sizes were small, the models were mice, and the endpoints were exercise capacity and gene expression, not anything else.

A follow-up study from the same group in the Journal of Pharmacology and Experimental Therapeutics (2024) extended the work into mouse models of metabolic dysfunction, reporting increases in energy expenditure and markers of fatty acid oxidation in diet-induced obese and ob/ob animals. Again: rodents, defined models, transcriptional and metabolic-flux endpoints.

Cell-culture work has focused on C2C12 murine myoblasts, where treatment has been reported to increase pyruvate dehydrogenase kinase 4 (Pdk4) expression, mitochondrial biogenesis markers, and cellular respiration. A 2025 pilot study in Frontiers in Physiology examined ERR targeting in the context of age-related muscle atrophy associated with physical inactivity and reported upregulation of SIRT1, PGC-1α, and ERRα in treated myoblasts alongside markers of mitochondrial biogenesis.

Cardiac work exists but should be weighted appropriately. Pan-ERR agonists including SLU-PP-332 have been examined in transverse aortic constriction models of pressure-overload heart failure in mice, with reported effects on cardiac fatty acid metabolism and mitochondrial gene expression. Much of that material has circulated as a preprint and a conference abstract rather than as a peer-reviewed primary paper, and it should be read as preliminary until it appears in final form.

What the literature does not contain: any human data, any clinical trial, any pharmacokinetic characterisation in humans, and any long-term safety assessment in any species. The compound has been described in the literature and in secondary coverage as an “exercise mimetic.” That phrase describes a transcriptional signature observed in rodent muscle. It is not a demonstrated outcome, and it is certainly not a claim about humans.

4. Published Literature

Real, verifiable sources for the mechanism and preclinical record:

• Billon C, Sitaula S, Banerjee S, et al. “Synthetic ERRα/β/γ Agonist Induces an ERRα-Dependent Acute Aerobic Exercise Response and Enhances Exercise Capacity.” ACS Chemical Biology. 2023;18(4):756–771. — Primary in vivo characterisation; ERRα-dependence established genetically.
• Billon C, Schoepke E, et al. “A Synthetic ERR Agonist Alleviates Metabolic Syndrome.” Journal of Pharmacology and Experimental Therapeutics. 2024. — Rodent metabolic models; energy expenditure and fatty acid metabolism endpoints.
• Giguère V. “Transcriptional Control of Energy Homeostasis by the Estrogen-Related Receptors.” Endocrine Reviews. 2008;29(6):677–696. — Standard reference for ERR/PGC-1 transcriptional biology.
• Frontiers in Physiology. “Targeting ERRs to counteract age-related muscle atrophy associated with physical inactivity: a pilot study.” 2025. — Myoblast-level ERR targeting; SIRT1/PGC-1α/ERRα expression.
• Zhang Z, Le GNT, Ge Y, et al. “Isomerization of bioactive acylhydrazones triggered by light or thiols.” Nature Chemistry. 2023;15:1285–1295. — Not about SLU-PP-332, but directly relevant to its chemical class and to how it must be handled and analysed.

5. Research Applications

Reported in-vitro and preclinical contexts for this compound class:

• ERR transcriptional profiling — RNA-seq or targeted qPCR time courses in myotube and cardiomyocyte cultures to map ERR-dependent gene networks.
• Mitochondrial phenotyping — extracellular flux analysis (oxygen consumption rate, spare respiratory capacity), mitochondrial DNA copy number, and biogenesis marker quantification in C2C12 and related lines.
• Receptor-dependence controls — pairing treatment with ERRα knockout or knockdown systems to distinguish on-target transcription from chemotype artefact.
• Coactivator interaction assays — biochemical or cell-based assays measuring ERR ligand-binding-domain association with PGC-1 coactivator peptides.
• Nuclear receptor selectivity panels — counter-screening across the broader nuclear receptor family, which is standard diligence for any compound of this class.

All of the above are laboratory applications in cells and preclinical models.

6. How to Evaluate a Source

This compound has a specific analytical problem that peptides do not, and it deserves to be understood before purchase.

The acylhydrazone bridge is labile. N-acylhydrazones hydrolyse back to their two precursors — here, 2-naphthaldehyde and 4-hydroxybenzohydrazide — under acidic conditions. They are comparatively stable near neutral pH but degrade under strongly acidic and strongly alkaline conditions. A COA that reports purity at manufacture tells you nothing about what the material looks like after storage in a plasticiser-permeable container, in solution, or at ambient temperature.

It exists as E and Z isomers. Acylhydrazones favour one geometry in the ground state due to intramolecular hydrogen bonding, but the Woolley group’s 2023 Nature Chemistry work demonstrated that this class isomerises in response to light and on exposure to thiols — the latter being significant, given that biological buffers and cell culture media routinely contain reduced thiols. E/Z ratio is a genuine identity variable for this scaffold, not a footnote, and a chromatographic method that does not resolve the isomers cannot report on it.

Practical evaluation criteria:

• HPLC purity reported with the actual chromatogram, stated column, mobile phase, and gradient — not a bare percentage. On this scaffold you want to see whether the method separates the isomers and the two hydrolysis precursors.
• LC-MS identity with the expected 290.32 Da parent. Note that the two hydrolysis fragments have distinct, lower masses; their presence is directly detectable.
• Residual solvent and starting material data. This is a synthetic small molecule, so unreacted 2-naphthaldehyde and synthesis solvents are the relevant impurity classes — different questions entirely from the deletion sequences and deamidation products that dominate peptide COAs.
• Heavy metals by ICP-MS.
• Batch-specific documentation, dated, tied to the lot number on the vial. A generic “representative” COA is not a COA.
• Storage guidance appropriate to a photosensitive, hydrolysis-prone compound.

Regulatory context, briefly. SLU-PP-332 is a small molecule, not a peptide, and is therefore outside the FDA’s Section 503A bulk drug substances proceedings — it was not among the seven peptides reviewed at the July 2026 PCAC meeting, nor among those scheduled for the review due before the end of February 2027. That does not place it outside enforcement attention generally. The FDA has issued warning letters through 2025 and 2026 to vendors whose research-use-only labelling was contradicted by advertising that indicated intent for human use. Research-use-only is a posture that has to be real in practice, not a line of small print.

7. PYXAX Verification Standard

PYXAX uses accredited independent laboratories in its verification network, including ILS Labs, Krause Analytical, and Janoshik. The current per-batch panel covers purity by HPLC, potency against label claim, and identity by LC-MS. A lot-specific COA is published in the COA Library before dispatch and names the laboratory that tested that batch. Endotoxin, heavy-metals, and final-vial sterility screening are not part of the current panel.

The testing panel:

• Purity by HPLC — with the chromatogram and method published, not a summary figure.
• Identity by LC-MS — confirming the expected parent mass.
• Endotoxin (USP <85> LAL) — for material intended for cell-based work.
• Heavy metals by ICP-MS.

Available lot-specific COAs are published in the PYXAX COA Library and name the laboratory that tested each batch. A published COA is required before any batch is dispatched.

For a compound of this chemical class, the chromatogram matters more than the number printed on top of it. We publish the trace.

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All PYXAX compounds are supplied strictly for in-vitro and preclinical laboratory research use only. Not for human consumption. Not for veterinary use. Not for diagnostic procedures. These statements have not been evaluated by the FDA. Researchers are responsible for compliance with all applicable laws and regulations governing the use of research compounds in their jurisdiction.