Licorice / HO-1 Cancer Research Results

Licorice — Licorice is the dried root and stolon of Glycyrrhiza species, principally Glycyrrhiza glabra, G. uralensis, and G. inflata, used as a botanical medicine and food ingredient. It is a complex phytochemical mixture rather than a single drug. Major bioactive classes include the triterpenoid saponin glycyrrhizin (glycyrrhizic acid), its intestinal metabolite 18β-glycyrrhetinic acid, and numerous flavonoids and chalcones including liquiritigenin, isoliquiritigenin, glabridin, and species-dependent licochalcones. Standard abbreviations include LE for licorice extract and GL for glycyrrhizin. Anticancer findings are predominantly preclinical and depend strongly on species, extract preparation, constituent composition, and concentration. Glycyrrhizin is particularly important because it directly binds and inhibits extracellular HMGB1 signaling, while several flavonoid constituents contribute additional antiproliferative effects.

Primary mechanisms (ranked):

1. HMGB1 inhibition and suppression of HMGB1-driven inflammatory, proliferative, angiogenic, and metastatic signaling, principally attributable to glycyrrhizin.
2. Suppression of tumor proliferation and cell-cycle progression, including modulation of cyclins/CDKs and, in some models, induction of S-phase or other cell-cycle arrest.
3. Induction of cancer-cell death through mitochondrial apoptosis, caspase activation, altered BAX/BCL-2 balance, autophagy, or necrotic mechanisms depending on extract and tumor model.
4. Suppression of EMT, migration, invasion, and associated TGF-β/SMAD, cadherin, and extracellular-matrix signaling.
5. Suppression of PI3K/AKT/mTOR, STAT3, NF-κB, and related survival/inflammatory signaling in constituent- and model-dependent studies.
6. Oxidative-redox modulation (secondary): some licorice constituents increase tumor-cell ROS sufficiently to promote cell death, whereas licorice can decrease oxidative stress and activate antioxidant defenses including NRF2 in non-malignant tissues.
7. Modulation of DNA-damage responses; glycyrrhizin-HMGB1 inhibition can impair NHEJ-associated DNA repair and increase DNA damage in colorectal cancer models.
8. Anti-angiogenic signaling through reductions in VEGF/HIF-1α and related pathways in selected preclinical systems.

Bioavailability / PK relevance: Oral glycyrrhizin has low systemic exposure as intact glycyrrhizin and undergoes extensive metabolism by intestinal microbiota to glycyrrhetinic acid and additional metabolites. In a human study using a 75-mg oral glycyrrhizin dose, mean glycyrrhizin peak plasma concentration was approximately 25 ng/mL while glycyrrhetinic acid reached approximately 200 ng/mL. Consequently, systemic biology after oral licorice can differ markedly from direct exposure experiments using glycyrrhizin or crude extract. Formulation, intestinal microbiota, biliary transport, species of licorice, glycyrrhizin content, and concomitant botanicals can materially alter exposure.

In-vitro vs systemic exposure relevance: Many anticancer experiments expose cells directly to licorice extracts or purified constituents at tens to hundreds of µg/mL or micromolar concentrations. These exposures frequently exceed circulating concentrations achievable after conventional oral licorice or glycyrrhizin administration. For example, recent whole-extract studies reported substantial antiproliferative effects around 30–200 µg/mL, whereas orally administered glycyrrhizin produces plasma levels in the ng/mL range and is extensively converted to metabolites. Whole-extract in-vitro anticancer potency should therefore not be interpreted as demonstrating equivalent systemic antitumor exposure in humans.

Clinical evidence status: Preclinical for treatment or prevention of cancer. Cell and animal evidence supports several anticancer mechanisms, particularly glycyrrhizin-HMGB1 signaling and constituent-dependent antiproliferative effects. Small human / RCT adjunct evidence exists for supportive care rather than tumor treatment; randomized studies have reported reduced pain and severity of radiotherapy-associated oral mucositis with topical licorice preparations. There is no established clinical evidence that oral licorice treats human malignancy or improves cancer survival.

Safety / translation relevance: Glycyrrhizin-containing licorice has a clinically important dose- and duration-dependent mineralocorticoid-like toxicity. Glycyrrhetinic-acid-related metabolites inhibit renal 11β-HSD2, permitting cortisol activation of mineralocorticoid receptors and potentially causing sodium retention, hypertension, edema, hypokalemia, metabolic alkalosis, arrhythmias, and suppression of renin and aldosterone. Risk increases with prolonged exposure and can be influenced by intestinal microbiota, renal/hepatic function, albumin concentration, age, and interacting medications. Licorice can also alter drug metabolism and should not be assumed pharmacologically inert when used with cancer therapy.

Licorice Mechanistic Profile