Found in roots, leaves, nut-hulls, bark and wood of walnut trees.
Juglone (5-hydroxy-1,4-naphthoquinone)
Juglans nigra refers to the black walnut tree, which is one of the most well-known sources of juglone
-Research has focused on the hulls (the green outer covering of the walnut) because they have the highest concentrations.
-Fresh hulls can contain juglone levels in the range of approximately 1–5% of the dry weight
-Juglone can redox cycle to generate reactive oxygen species (ROS).
-Increasing Bax, decreasing Bcl‑2, caspase activation, and MMP depolarization.
-Modulation of MAPK pathways (including ERK, JNK, and p38)
-May inhibit NF‑κB signaling
-Cause DNA damage or stress that, in turn, leads to p53 pathway activation—
Pin1 Inhibition
–Pin1, a peptidyl-prolyl cis/trans isomerase, is frequently overexpressed in cancer.
-ic50 maybe 5-10uM
-For matching 5uM, crude estimate is 5mg consumption of juglone required which might be 1.5 g of black walnut hull material
Juglone — Juglone (5-hydroxy-1,4-naphthoquinone; JG) is a naturally occurring redox-active naphthoquinone found in plants of the Juglans genus, including black walnut (Juglans nigra), with particularly high concentrations reported in green walnut hulls. It is best classified as a natural small-molecule quinone and experimental anticancer agent rather than an established therapeutic drug. Its anticancer activity is strongly concentration-dependent and reflects electrophilic thiol reactivity, redox cycling, oxidative stress, mitochondrial injury, ferroptosis, apoptosis, and modulation of several oncogenic signaling pathways. Juglone is also widely used experimentally as a Pin1 inhibitor, although this designation should not imply high target selectivity because juglone can covalently modify protein sulfhydryl groups and affect transcription and other cellular proteins.
Primary mechanisms (ranked):
- Quinone redox cycling and electrophilic thiol reactivity causing ↑ ROS, ↓ glutathione-dependent antioxidant capacity, oxidative macromolecular injury, and oxidative-stress-driven cell death.
- Ferroptosis induction through lipid peroxidation and disruption of antioxidant defenses, including ↓ GPX4 and, in some cancer models, ↓ NRF2 signaling or activation of the FOSL1-HMOX1 axis.
- Mitochondrial apoptosis through ↓ mitochondrial membrane potential, ↑ Bax/Bcl-2 ratio, cytochrome-c release, and caspase activation.
- Pin1 inhibition contributing to suppression of proliferation, cancer-cell stemness, EMT, migration, angiogenesis, and oncogenic signaling; however, juglone is not a highly selective Pin1 pharmacological probe.
- Suppression of PI3K-AKT and related survival signaling, frequently downstream of or amplified by oxidative stress.
- Cell-cycle arrest through modulation of cyclins, CDKs, p21, p27, p53, and related checkpoint pathways.
- Stress-MAPK modulation, particularly ↑ p38 and ↑ JNK, contributing to apoptosis, ferroptosis, and autophagic responses.
- Suppression of EMT, invasion, stem-like phenotype, Wnt/β-catenin signaling, HIF-1α, VEGF, and angiogenic/metastatic programs in selected cancer models.
- Autophagy induction as a context-dependent stress response that can interact with apoptosis and oxidative injury.
Bioavailability / PK relevance: Free juglone has unfavorable drug-delivery characteristics, including hydrophobicity, high chemical reactivity, rapid disposition, and substantial renal exposure. In an animal intravenous PK study, free juglone had a plasma half-life of approximately 2 hours and showed prominent kidney localization; sterically stabilized liposomal delivery increased plasma half-life approximately 12-fold, improved tumor localization, and reduced renal toxicity. Robust human oral pharmacokinetic data are lacking. Consequently, dietary or walnut-hull intake cannot presently be converted reliably into a systemic micromolar juglone exposure.
In-vitro vs systemic exposure relevance: Most direct anticancer studies use approximately low-to-tens-of-micromolar juglone, commonly around 5–20 µM. Whether these free-drug concentrations can be maintained safely in human tumors is not established. Recent quantitative work also demonstrates limited intracellular accumulation despite extracellular juglone exposure. Thus, common in-vitro concentrations should not be assumed to be achievable through oral walnut or black-walnut-hull consumption.
Clinical evidence status: Preclinical. Juglone has substantial cell-culture evidence and multiple mouse/xenograft studies showing antitumor activity, including apoptosis, ferroptosis, anti-metastatic, and anti-angiogenic effects. There is no established anticancer dose, regulatory approval, or convincing human clinical efficacy evidence for juglone itself. Translation is limited by nonspecific electrophilic/redox chemistry, systemic toxicity risk, formulation and pharmacokinetic limitations, and the uncertain therapeutic window between cancer and normal tissues.
Juglone Mechanistic Profile
| Rank |
Pathway / Axis |
Cancer Cells |
Normal Cells |
TSF |
Primary Effect |
Notes / Interpretation |
| 1 |
Quinone redox cycling and thiol reactivity |
↑ ROS; ↑ oxidative stress; ↓ cellular thiol buffering |
↑ oxidative injury possible |
P/R |
Oxidative-stress overload |
Central upstream mechanism. Juglone participates in redox cycling and can react with protein and glutathione sulfhydryl groups; this contributes to efficacy but also limits selectivity. |
| 2 |
Glutathione and antioxidant defense |
↓ GSH; ↓ GPX4; ↓ SOD (model-dependent) |
↓ antioxidant reserve possible (dose-dependent) |
R |
Loss of redox buffering |
Creates a permissive environment for ROS accumulation, lipid oxidation, apoptosis, and ferroptosis. |
| 3 |
Ferroptosis and lipid peroxidation |
↑ ferroptosis; ↑ lipid peroxidation; ↑ MDA; ↑ labile iron |
Potential ferroptotic toxicity at sufficient exposure |
R/G |
Iron-dependent oxidative cell death |
Strong recent evidence in hepatocellular carcinoma and glioblastoma; pathway execution is cancer-type dependent. |
| 4 |
NRF2 GPX4 antioxidant axis |
↓ NRF2; ↓ GPX4 (model-dependent) |
Not established |
R/G |
Ferroptosis sensitization |
Demonstrated particularly in glioblastoma. NRF2 modulation should not be generalized to every tumor model. |
| 5 |
FOSL1 HMOX1 ferroptosis axis |
↑ FOSL1; ↑ HMOX1 |
Not established |
G |
Ferroptosis amplification |
Recent HCC and pan-cancer evidence identifies this transcriptional axis as an important juglone-responsive ferroptotic mechanism. |
| 6 |
Mitochondrial membrane integrity |
↓ membrane potential; ↑ cytochrome-c release |
Mitochondrial toxicity possible |
R |
Intrinsic apoptosis initiation |
Observed across breast, gastric, prostate, and other cancer models. |
| 7 |
BAX BCL2 caspase apoptosis |
↑ BAX; ↓ BCL2; ↑ caspase-3/7; ↑ caspase-8/9 |
Apoptosis possible at cytotoxic exposure |
R/G |
Programmed cell death |
Both intrinsic and extrinsic apoptotic pathways can participate. Recent colorectal cancer data support activation of caspase-8 as well as mitochondrial caspase-9 signaling. |
| 8 |
Pin1 prolyl isomerase |
↓ Pin1 activity/function |
↓ Pin1 and other thiol-sensitive proteins possible |
P/R |
Reduced oncogenic signaling and stemness |
Important experimental target associated with ↓ proliferation, ↓ EMT, ↓ stemness, and ↓ angiogenesis. Juglone is not Pin1-selective and can directly modify sulfhydryl-containing proteins. |
| 9 |
PI3K AKT survival signaling |
↓ PI3K; ↓ AKT; ↓ p-AKT |
Context-dependent |
R/G |
Survival pathway suppression |
ROS scavenging can partially reverse this effect in NSCLC, indicating substantial coupling between oxidative stress and PI3K-AKT inhibition. |
| 10 |
p38 JNK stress signaling |
↑ p38; ↑ JNK |
Context-dependent |
R |
Stress-mediated apoptosis and ferroptosis |
Activation is frequently associated with ROS production and can contribute to NRF2-GPX4 suppression and programmed cell death. |
| 11 |
Cell cycle checkpoints |
↑ arrest; ↓ CDK2; ↓ CDK4; ↓ cyclins; ↑ p21; ↑ p27 |
Growth inhibition possible |
G |
Proliferation blockade |
Cell-cycle phase varies by model. Recent colorectal cancer data support G0/G1 arrest with suppression of CCND1, CCNB1, CDK2, and CDK4. |
| 12 |
p53 DNA damage response |
↑ DNA damage; ↑ γH2AX; ↑ p53 (model-dependent) |
Genotoxicity possible |
R/G |
Checkpoint activation and apoptosis |
May arise partly from quinone-driven ROS and electrophilic stress rather than a specific DNA-targeting interaction. |
| 13 |
Intracellular calcium and mitochondrial stress |
↑ Ca²⁺ (model-dependent) |
Not established |
P/R |
Apoptotic signaling |
Increased intracellular Ca²⁺ has been demonstrated in MCF-7 cells together with ROS elevation and mitochondrial depolarization. |
| 14 |
EMT migration and invasion |
↓ EMT; ↑ E-cadherin; ↓ N-cadherin; ↓ Snail; ↓ migration; ↓ invasion |
Not established |
G |
Reduced metastatic phenotype |
Pin1, AKT-GSK3β-Snail, TGF-β-related, and other signaling systems have been implicated depending on tumor model. |
| 15 |
Cancer stemness |
↓ sphere formation; ↓ tumor-initiating phenotype |
Not established |
G |
Reduced self-renewal and metastatic potential |
Pin1 inhibition appears to contribute. Effects have been demonstrated in colorectal and other tumor-initiating cell models. |
| 16 |
Wnt beta-catenin signaling |
↓ Wnt/β-catenin (model-dependent) |
Not established |
G |
Reduced invasion and angiogenesis |
Most clearly demonstrated in pancreatic cancer models; not necessarily a universal primary mechanism. |
| 17 |
HIF-1α VEGF angiogenic signaling |
↓ HIF-1α; ↓ VEGF; ↓ angiogenesis |
Potential vascular effects not well characterized |
G |
Reduced tumor vascular support |
Secondary/contextual anticancer mechanism reported in pancreatic cancer and Pin1-related models. |
| 18 |
Autophagy stress response |
↑ LC3-II; ↑ Beclin-1; ↓ p62 (model-dependent) |
Context-dependent |
G |
Autophagic stress and death crosstalk |
Autophagy can accompany ROS/MAPK signaling but its contribution to net cytotoxicity varies by cell type and experimental conditions. |
| 19 |
Chemosensitization |
↑ drug cytotoxicity in selected combinations |
Potential ↑ combination toxicity |
G |
Combination-treatment sensitization |
Juglone can enhance etoposide cytotoxicity through Pin1-related mechanisms, but sequence of administration can substantially alter the interaction. |
| 20 |
Clinical Translation Constraint |
Effective concentrations commonly ~5–20 µM in vitro |
Systemic electrophilic and oxidative toxicity limits selectivity |
G |
Uncertain therapeutic window |
Human bioavailability and therapeutic exposure are not established. Free juglone has short animal plasma persistence, renal accumulation, and nephrotoxicity; formulations such as liposomes materially alter PK and distribution. |
P: 0–30 min R: 30 min–3 hr G: >3 hr
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