1. What Is Trans-ISRIB?
Trans-ISRIB (Integrated Stress Response Inhibitor, trans-isomer) is a first-in-class small molecule that allosterically activates the guanine nucleotide exchange factor eIF2B, thereby reversing the translational blockade imposed by stress-induced phosphorylation of eukaryotic initiation factor 2α (p-eIF2α). Discovered in 2013 through a high-throughput phenotypic screen at the Walter Lab (UCSF) and published in eLife (Sidrauski et al.), ISRIB has since become one of the most important tool compounds in translational control research, neurodegeneration, and cognitive neuroscience — with over 500 citations across its landmark papers and a cryo-EM structure resolved at 4.1 Å resolution (PDB: 6EZO).
Unlike conventional kinase inhibitors that block upstream stress sensors (PERK, GCN2, PKR, HRI), ISRIB operates at the convergence point of all four eIF2α kinases — directly targeting the eIF2B decameric complex at the β-δ regulatory subunit interface. This unique mechanism allows ISRIB to selectively restore cap-dependent translation in stressed cells without affecting global transcription, mRNA stability, or translation in non-stressed cells — a critical selectivity feature that distinguishes it from general translation inhibitors like cycloheximide or harringtonine.
The trans stereochemistry is essential: trans-ISRIB is 100-fold more potent (IC₅₀ = 5 nM) than its cis counterpart (IC₅₀ = 600 nM), confirming that the compound's interaction with eIF2B is stereospecific. This high potency, combined with excellent blood-brain barrier penetration (plasma t₁/₂ ≈ 8 h) and oral bioavailability, has positioned ISRIB at the center of preclinical programs targeting traumatic brain injury, vanishing white matter disease, prion disorders, and age-related cognitive decline.
1.1 Discovery & Key Milestones
eIF2B Allosteric Activator
Binds at β-δ regulatory interface, stabilizing eIF2B in its active decameric conformation — not a kinase inhibitor, but a translational "brake release."
100× Stereospecific Potency
Trans-isomer (IC₅₀ = 5 nM) is 100-fold more potent than cis-isomer (IC₅₀ = 600 nM); stereochemistry validated by cryo-EM and mutagenesis.
Cryo-EM Resolved (PDB 6EZO)
Binding pose confirmed at 4.1 Å resolution; mutagenesis of β/δ interface residues alters ISRIB analog sensitivity in hierarchical fashion.
2. Physicochemical Specifications
| Parameter | Specification |
|---|---|
| Compound Name | ISRIB (trans-isomer); Trans-ISRIB |
| Full Chemical Name | N,N'-trans-1,4-Cyclohexanediylbis[2-(4-chlorophenoxy)acetamide] |
| CAS Number | 1597403-47-8 |
| MDL Number | MFCD27952932 |
| PubChem CID | 1011240 |
| Empirical Formula | C₂₂H₂₄Cl₂N₂O₄ |
| Molecular Weight | 451.34 g/mol |
| Chemical Class | Symmetrical bis-amide; trans-1,4-cyclohexane-bridged bis(4-chlorophenoxyacetamide) |
| Appearance | White to off-white crystalline powder |
| Purity | ≥99% (HPLC, C18 reversed-phase, UV 254 nm); identity confirmed by ¹H-NMR, ¹³C-NMR, and HR-LC-MS |
| Predicted Density | 1.3±0.1 g/cm³ |
| Predicted Boiling Point | 719.0±60.0 °C at 760 mmHg |
| Predicted Flash Point | 388.6±32.9 °C |
| Solubility (in vitro) | DMSO: ~4–38 mg/mL (8.8–84 mM; sonication + warming to 37–60°C recommended); Water: insoluble; Ethanol: insoluble |
| Solubility (in vivo) | 0.5% CMC-Na suspension: ≥5 mg/mL (homogeneous); 50% PEG300 + 50% saline: ~0.83 mg/mL (sonicate + warm) |
| SMILES | O=C(N[C@@H]1CC[C@@H](NC(COC2=CC=C(Cl)C=C2)=O)CC1)COC3=CC=C(Cl)C=C3 |
| InChI Key | HJGMCDHQPXTGAV-UHFFFAOYSA-N |
| Storage (Powder) | −20°C, protected from light and moisture, 36 months |
| Storage (Solution) | −80°C, 12 months; −20°C, 6 months (DMSO stock, single-use aliquots) |
3. Mechanism of Action
The integrated stress response (ISR) is an evolutionarily conserved signaling network activated by diverse cellular insults — ER stress, viral infection, amino acid deprivation, heme deficiency, and oxidative damage — each sensed by one of four stress kinases (PERK, GCN2, PKR, HRI). These kinases converge on a single substrate: serine 51 of eIF2α. Phosphorylated eIF2α (p-eIF2α) acts as a competitive inhibitor of eIF2B, the guanine nucleotide exchange factor (GEF) responsible for recycling eIF2-GDP to eIF2-GTP for translation initiation. When p-eIF2α binds eIF2B, global cap-dependent translation is attenuated while selective translation of stress-adaptive mRNAs (notably ATF4) is paradoxically enhanced.
ISRIB does not inhibit any eIF2α kinase or phosphatase. Instead, it binds directly to eIF2B — specifically at the interface between the β and δ regulatory subunits — and allosterically stabilizes the active decameric conformation. This stabilization reduces eIF2B's affinity for p-eIF2α, effectively uncoupling the stress signal from translational output. The result: cap-dependent mRNA translation resumes, ATF4 production is suppressed, and stress granules disassemble — all without interfering with the upstream phosphorylation machinery.
3.1 The ISR Signaling Cascade & ISRIB Intervention Point
(Thapsigargin)
Activation
(Ser51-P)
Inhibition
Attenuation
Interface
Decamer Stabilized
Restored
Red = stress-driven suppression | Green = ISRIB rescue | ⊘ = step bypassed by ISRIB
3.2 Downstream Consequences of eIF2B Reactivation
Once ISRIB reactivates eIF2B, four key downstream effects occur simultaneously:
| Downstream Event | Effect of ISRIB | Molecular Mechanism | Functional Outcome |
|---|---|---|---|
| ATF4 Translation | ↓ Suppressed | Restored scanning ribosomes bypass uORF2 in ATF4 5'UTR, eliminating preferential ATF4 translation | Fibrogenic gene programs (liver), CHOP-mediated apoptosis, and ISR transcriptional output all inhibited |
| Cap-Dependent Translation | ↑ Restored | eIF2-GDP → eIF2-GTP recycling resumes; ternary complex (eIF2-GTP-tRNAiMet) formation normalized | Global protein synthesis restored; synaptic plasticity proteins (e.g., BDNF, Arc) re-expressed |
| Stress Granule Assembly | ↓ Inhibited | Restored translation prevents accumulation of stalled 48S preinitiation complexes that nucleate SGs | G3BP1/TIA-1 aggregation blocked; mRNA released from stalled complexes for active translation |
| ISR Transcriptional Program | ↓ Attenuated | Reduced ATF4 → lower CHOP, GADD34, TRIB3, and ASNS expression; negative feedback loop broken | Cell survival during chronic ER stress context-dependent: protective in some settings, pro-apoptotic in ER-stressed cancer cells |
3.3 Structural Basis: Cryo-EM of ISRIB-eIF2B Complex
The 4.1 Å cryo-EM structure (Zyryanova et al., 2018, Science; PDB: 6EZO) revealed that ISRIB binds within a deep hydrophobic pocket formed at the interface of the eIF2B β and δ regulatory subunits — a region distant from both the catalytic site (ε-subunit) and the p-eIF2α binding surface. This allosteric site does not overlap with the p-eIF2α contact region; instead, ISRIB stabilizes the active eIF2B decamer conformation, functionally antagonizing p-eIF2α binding. Mutagenesis of residues lining this pocket (notably eIF2Bδ L179F and eIF2Bβ H160D) alters cellular sensitivity to ISRIB analogs in a hierarchical manner, providing an orthogonal chemical-genetic validation of the binding site.
3.4 Stereospecificity: Why Trans Matters
The striking 100-fold potency difference between trans-ISRIB (IC₅₀ = 5 nM) and cis-ISRIB (IC₅₀ = 600 nM) arises from the compound's symmetrical, rigid trans-1,4-cyclohexane core. The trans configuration positions both 4-chlorophenoxyacetamide arms in an extended, roughly linear conformation that optimally spans the β-δ interface pocket. The cis isomer's bent geometry cannot achieve this productive binding pose, as confirmed by both cellular ATF4 reporter assays and cryo-EM density fitting. This stereochemical requirement has important practical implications: researchers must verify the trans configuration of their ISRIB source to ensure expected potency.
4. Core Advantages
4.1 ISRIB vs Conventional ISR Intervention Strategies
| Parameter | Trans-ISRIB | PERK Inhibitors (GSK2606414) | eIF2α Phosphatase Activators (Salubrinal) |
|---|---|---|---|
| Target | eIF2B (β-δ interface) | PERK kinase domain (ATP-competitive) | GADD34/PP1 phosphatase complex |
| Level of Action | Convergence point — blocks all 4 kinase outputs | Upstream — only PERK branch of ISR | Upstream — phosphatase activation; global eIF2α dephosphorylation |
| IC₅₀ | 5 nM | ~1–30 nM (PERK) | ~15 μM (GADD34/PP1) |
| Selectivity | Stress-conditional; no effect in non-stressed cells | PERK-specific; GCN2/PKR/HRI branches unaffected | Non-specific; dephosphorylates all eIF2α pools |
| BBB Penetration | Yes — validated; CNS/plasma ratio ~1 | Limited (P-gp substrate) | Not reported / minimal |
| Plasma t₁/₂ | ~8 h (mouse) | ~2–4 h | Not well characterized |
| Cognitive Enhancement | Validated — spatial + fear memory (0.25 mg/kg i.p.) | Not reported | Not reported |
| Structural Validation | Cryo-EM (4.1 Å, PDB 6EZO) + mutagenesis | X-ray crystallography (kinase domain only) | No structural data |
| TBI Recovery | Validated — spine dynamics + working memory (mouse, zebrafish) | Not evaluated for TBI | Not evaluated for TBI |
| Clinical Development | Preclinical; VWM organoid data (2025) | Phase I (discontinued — pancreatic toxicity) | Preclinical only |
4.2 Why Choose Trans-ISRIB?
Single Convergence Point
One compound blocks output from ALL four eIF2α kinases (PERK, GCN2, PKR, HRI). No need for kinase-specific inhibitors or combination strategies.
Stress-Conditional Activity
Zero effect on translation, transcription, or mRNA stability in non-stressed cells. Active ONLY when and where p-eIF2α is present — ideal for disease models with localized ISR activation.
BBB Penetrant + CNS Bioavailable
Plasma t₁/₂ = 8 h; rapidly equilibrates across the blood-brain barrier (CNS/plasma ~1). Orally bioavailable; suitable for chronic i.p. or p.o. dosing in rodent models.
Cryo-EM Validated Binding
Mechanism confirmed at atomic resolution (PDB 6EZO). Binding site mapped by mutagenesis. Structure-guided SAR enables rational analog design.
Multi-Indication Preclinical Track Record
Positive efficacy data across TBI, prion disease, VWM leukodystrophy, liver fibrosis, and cognitive aging — all with the same tool compound.
Economical Research Supply
≥99% HPLC purity, 1G at $50 — one of the most accessible prices for any IC₅₀ = 5 nM tool compound. Enables large-scale in vivo studies at practical budgets.
5. Research Applications
TBI & Concussion Recovery
ISRIB reverses post-TBI cognitive deficits by normalizing aberrant cortical spine dynamics. Chou et al. (2017, PNAS) demonstrated restored working memory within 24 h of treatment (2.5 mg/kg i.p., days 14–18 post-CHI); effects persisted after washout. Validated in both mouse (CHI model) and zebrafish (telencephalic injury, Ilyin et al., 2025, Brain Res). ISRIB also attenuates NCOA4-mediated ferritinophagy and white matter injury post-TBI (Zhou et al., 2024, Neurochem Int).
Prion Disease & Alzheimer's
ISRIB prevents translational shutdown and cognitive decline in prion-diseased mice (Halliday et al., 2015, 2017). In tauopathy and amyloidosis models, ISRIB mitigates ER stress-associated learning and memory impairment (eNeuro, 2017). Ongoing work explores ISRIB in ALS, Huntington's, and Parkinson's disease where ISR activation is a convergent pathological feature.
Vanishing White Matter (VWM)
Yan et al. (2025, CNS Neurosci Ther) demonstrated that ISRIB rescues myelination defects, restores mature oligodendrocyte and astrocyte populations, and suppresses UPR hyperactivation in VWM patient iPSC-derived cerebral organoids — the first human-cell evidence supporting ISRIB as a VWM therapeutic candidate.
Memory Enhancement & Aging
ISRIB enhances hippocampus-dependent spatial and fear-associated learning at just 0.25 mg/kg i.p. (Sidrauski et al., 2013). Effects are long-lasting; cognitive benefits persist beyond compound washout, suggesting durable synaptic remodeling. Relevant to age-related cognitive decline and "cognitive resilience" research.
Liver Fibrosis & Stellate Cells
Yang et al. (2025) showed that ISRIB suppresses ATF4-driven fibrogenic EMT gene transcription in hepatic stellate cells and attenuates liver fibrosis in vivo — expanding ISRIB's utility beyond neuroscience into fibrotic disease models.
ER Stress Sensitization
ISRIB reduces viability of cells under chronic PERK-dependent ER stress (Sidrauski et al., 2013). Synergizes with proteasome inhibitors and ER stress-inducing chemotherapeutics in multiple myeloma and pancreatic cancer models. Also impairs ubiquitin-proteasome system under proteotoxic stress (Nature Commun Biol, 2024).
ER Stress & UPR Toolkit
Essential tool compound for ISR/UPR research: blocks ATF4 induction without affecting XBP1 splicing (IRE1 branch intact). Enables branch-specific dissection of UPR signaling. Used in combination with thapsigargin, tunicamycin, or brefeldin A for mechanistic ER stress studies.
HTS Hit Validation & Benchmarking
Gold-standard positive control for ISR-targeted drug discovery. Well-characterized pharmacokinetics, cryo-EM binding mode, and orthogonal chemical-genetic validation (ISRIB-resistant eIF2B mutants) make ISRIB ideal as a reference compound in screening cascades.
6. Packaging, Storage & Logistics Compliance
6.1 Storage Conditions
| Form | Temperature | Duration | Notes |
|---|---|---|---|
| Dry Powder | −20°C | 36 months | Sealed, light-protected, desiccated container |
| Dry Powder | 4°C | 24 months | Sealed, light-protected |
| DMSO Stock | −80°C | 12 months | Single-use aliquots; avoid freeze-thaw cycles |
| DMSO Stock | −20°C | 6 months | Amber vial; single-use aliquots recommended |
| CMC-Na Suspension | 2–8°C | Prepare fresh | Use within 24 h; vortex before each administration |
6.2 Solubility & Formulation Guidelines
| Application | Solvent/Vehicle | Maximum Solubility | Preparation Notes |
|---|---|---|---|
| In vitro (stock) | DMSO (anhydrous) | 4–38 mg/mL (8.8–84 mM) | Sonicate + warm to 37–60°C; use anhydrous, freshly opened DMSO; hygroscopic DMSO significantly reduces solubility |
| In vitro (working) | Culture medium | Dilute from DMSO stock | Final DMSO ≤0.1%; vortex thoroughly; avoid precipitation upon dilution |
| In vivo (oral/i.p.) | 0.5% CMC-Na in water | ≥5 mg/mL homogeneous suspension | Sonicate to disperse; vortex immediately before each dose; store at 2–8°C |
| In vivo (i.p.) | 50% PEG300 + 50% saline | ~0.83 mg/mL | Sequential addition: dissolve in PEG300 first, then add saline; sonicate + warm |
| NOT recommended | Water, PBS, ethanol | Insoluble | Do not attempt aqueous dissolution without co-solvent; precipitation guaranteed |
6.3 Regulatory & Shipping Status
Non-Controlled Substance
Trans-ISRIB is NOT listed on any controlled substance or scheduled chemical registry (DEA, CFDA, EMA, TGA). It is not a narcotic, psychotropic, or precursor chemical.
Ambient Shipping (Powder)
Dry powder is stable at ambient temperature during transit (validated by stability studies). Shipped in sealed, light-protective containers. Cold-chain shipping available upon request.
Customs Documentation
Full commercial invoice, packing list, COA, and MSDS (GHS-compliant) provided with international shipments. HS code: 2924.29 (cyclic amides). Customs clearance support available for all destinations.
6.4 GHS Hazard Classification
6.5 Packaging Options
| Pack Size | Container | Price | Typical Use Case |
|---|---|---|---|
| 1 G | Amber glass vial, PTFE-lined cap | $50.00 | Standard research unit; multi-dose in vivo study |
| 5 G | Amber glass bottle, argon-flushed | Contact for quote | Multi-group in vivo study; laboratory stock |
| 10 G | Amber glass bottle, argon-flushed | Contact for quote | Institutional supply; HTS campaigns |
| 50 G+ (bulk) | Custom; contact for specifications | Contact for quote | Multi-site consortium studies; long-term programs |
7. Frequently Asked Questions
Q: What is ISRIB and what does it stand for?
ISRIB stands for Integrated Stress Response Inhibitor. It is a small molecule that allosterically activates eIF2B, the guanine nucleotide exchange factor for eIF2, thereby reversing the translational blockade caused by stress-induced eIF2α phosphorylation. It was discovered at UCSF (Sidrauski et al., 2013, eLife) and its molecular target and cryo-EM structure (PDB 6EZO) have been fully validated.
Q: Why is the trans-isomer important? Can I use cis-ISRIB?
Trans-ISRIB (IC₅₀ = 5 nM) is 100-fold more potent than cis-ISRIB (IC₅₀ = 600 nM). The trans-1,4-cyclohexane core positions both chlorophenoxyacetamide arms in the correct extended conformation to span the eIF2B β-δ interface pocket. The cis isomer cannot adopt this productive binding pose. For reproducible, high-potency results, always use the trans-isomer.
Q: Does ISRIB inhibit PERK directly?
No. Despite being commonly described as a "PERK inhibitor" in some databases, ISRIB does not bind to or inhibit PERK (or any other eIF2α kinase). It acts downstream — at the eIF2B level — uncoupling p-eIF2α from its inhibitory effect on eIF2B. This means ISRIB blocks the output of all four ISR kinases (PERK, GCN2, PKR, HRI), not just PERK.
Q: Will ISRIB affect translation in non-stressed cells?
No. ISRIB is stress-conditional — it restores translation only in cells where p-eIF2α has accumulated. In non-stressed cells without p-eIF2α, ISRIB has no detectable effect on translation rates, transcription, or mRNA stability (Sidrauski et al., 2013, 2015). This selectivity is a key advantage over general translation inhibitors.
Q: How do I dissolve ISRIB for in vitro experiments?
Use anhydrous DMSO (freshly opened) at 10–50 mM stock concentration. Sonicate and warm to 37–60°C until fully dissolved. Important: hygroscopic DMSO (old/exposed bottles) significantly reduces solubility — always use dry, freshly opened DMSO. Dilute stock into culture medium to final DMSO ≤0.1%. Do not attempt aqueous dissolution without co-solvent — ISRIB is insoluble in water, PBS, and ethanol.
Q: What is the recommended in vivo formulation?
0.5% carboxymethylcellulose sodium (CMC-Na) in water produces a homogeneous suspension at ≥5 mg/mL. Sonicate to disperse, vortex immediately before each dose. For lower volumes: 50% PEG300 + 50% saline yields ~0.83 mg/mL. Oral gavage, i.p. injection, and dietary administration have all been validated. ISRIB crosses the BBB efficiently (CNS/plasma ≈ 1).
Q: Is ISRIB a controlled or regulated substance?
No. Trans-ISRIB is not listed on any DEA, CFDA, EMA, TGA, or FDA controlled substance schedule. It is sold exclusively as a research chemical — not approved for human therapeutic use. International shipping is permitted without import/export permits.
Q: How should I store ISRIB?
Powder: −20°C, sealed, protected from light and moisture — stable for 36 months. DMSO stocks: aliquot into single-use vials, store at −80°C (12 months) or −20°C (6 months). Do NOT refreeze thawed aliquots. ISRIB powder is stable at room temperature for short periods (shipping) but should be returned to −20°C upon receipt.
Q: What purity level do you supply and how is it verified?
≥99% by HPLC (C18 reversed-phase, UV 254 nm). Identity confirmed by ¹H-NMR, ¹³C-NMR, and HR-LC-MS. Trans/cis isomer ratio is verified by chiral HPLC or ¹H-NMR. Each batch ships with a full COA including residual solvents (ICH Q3C), heavy metals (ICP-MS), and water content (Karl Fischer).
Q: Has ISRIB been used in human clinical trials?
Not yet. All ISRIB data to date are preclinical (in vitro, rodent, zebrafish, and human iPSC-derived organoids). However, the VWM organoid data (Yan et al., 2025) provides compelling human-cell evidence, and the favorable PK/BBB profile has attracted significant interest for clinical translation. Researchers should monitor ClinicalTrials.gov for upcoming trials.
Q: What documentation is provided with each order?
Every shipment includes: Certificate of Analysis (COA) with batch-specific HPLC chromatogram, NMR spectrum, and LC-MS trace; Material Safety Data Sheet (MSDS, GHS-compliant); commercial invoice; and packing list. Additional documentation (stability data, residual solvent report, heavy metals analysis, chiral purity certificate) is available upon request.
Q: Is bulk or custom packaging available?
Yes. Beyond the 1G standard unit ($50), we offer 5G, 10G, 50G, and custom bulk quantities with dedicated batch reservation and tailored packaging. Volume discounts apply. Contact our procurement team for multi-gram pricing and delivery timelines.
Source High-Purity Trans-ISRIB for Your Research
≥99% HPLC purity, batch-specific COA with full spectroscopic characterization, flexible packaging from 1G ($50) to bulk scale, and global shipping with customs support. Contact our team for pricing, technical documentation, or a custom quotation.