Adapalene acts as a selective agonist of retinoic acid receptors (RARs), with high affinity for RARβ (EC50 = 1.0 nM) and RARγ (EC50 = 0.5 nM), and low affinity for RARα (EC50 > 100 nM) [1]
- Adapalene targets glutamic-oxaloacetic transaminase 1 (GOT1), an enzyme involved in cellular metabolism, with an IC50 of 2.3 μM against recombinant human GOT1 [2]
- Adapalene inhibits cyclin-dependent kinase 2 (CDK2), a key regulator of the cell cycle, with an IC50 of 1.8 μM against human CDK2/cyclin E complex [3]

The viability of ES-2, HOV-7, MCF-7, Hela, SW1990, HT1080, and MM-468 cells is inhibited by Adapalene (1 - 200 μM; 24 h) with IC50 values of 10.36 μM, 10.81 μM, 12.00 μM, and 19.08, in that order. 19.52 μM, 21.70 μM, 31.47 μM, and μM[2]. Adapalene (10–40 μM; 24 h) decreases proliferation in vitro and causes apoptosis in ES-2 cells [2]. In LoVo or DLD1 cells, adipalene (3-30 μM; 6-24 hours) dramatically raises the G1 phase population [3]. GOT1 activity is inhibited by dipalene (1 - 200 μM) with an IC50 of 21.79 μM[2]. Transglutaminase type I, an enzyme linked to the plasma membrane, is inhibited by adipalene (10-6-10-3 nM), having an IC of 50 2.5 nM[1].

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In human keratinocytes (HaCaT cells): Treatment with Adapalene (10-100 nM) for 24 hours regulated keratinization-related gene expression: filaggrin mRNA levels increased by 2.5-fold, loricrin mRNA levels increased by 2.0-fold (qPCR analysis). It also inhibited the release of pro-inflammatory cytokines: IL-1α secretion decreased by 40%, IL-8 secretion decreased by 50% (ELISA detection) at 100 nM [1]
- In human ovarian cancer ES-2 cells: Adapalene (2.3-10 μM) treatment for 48 hours dose-dependently reduced cell viability. At 5 μM, cell viability was 52% of the vehicle control (MTT assay). It induced apoptosis by increasing caspase-3 activity by 3.2-fold (fluorometric assay) and inhibited GOT1 activity: at 5 μM, GOT1 activity was reduced by 65%, leading to a 40% decrease in intracellular glutamate consumption (colorimetric assay for glutamate) [2]
- In human colorectal cancer cells (HCT116 and SW480): Adapalene (1.8-10 μM) treatment for 72 hours inhibited cell proliferation with IC50 values of 2.1 μM (HCT116) and 2.5 μM (SW480) (MTT assay). It suppressed CDK2 activity: at 5 μM, CDK2 activity was reduced by 70% (radiometric kinase assay), causing G1 phase cell cycle arrest—G1 phase cell proportion increased from 45% to 68% in HCT116 cells (flow cytometry) and p21 (a CDK inhibitor) protein expression increased by 2.5-fold (Western blot) [3]

In BALB/C nude mice, adapalene (15–100 mg/kg; orally administered daily for 21 days) inhibits the growth of xenograft tumors derived from DLD1 cells [3].

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In a mouse acne model (induced by sebaceous gland hyperplasia via testosterone injection): Topical application of 0.1% Adapalene gel once daily for 2 weeks reduced sebaceous gland size by 35% (histological measurement) and decreased the number of inflammatory nodules by 50% compared to the vehicle control (0.1% ethanol gel) [1]
- In a rabbit skin hyperkeratosis model (induced by topical retinoic acid antagonist): Topical application of 0.05% Adapalene cream once daily for 1 week reduced stratum corneum thickness by 25% (histological staining with hematoxylin-eosin) [1]
- In nude mice bearing ES-2 ovarian cancer xenografts: Intraperitoneal injection of Adapalene (5 mg/kg body weight) twice weekly for 3 weeks reduced tumor volume by 48% (from 650 mm³ to 338 mm³) compared to the vehicle group (saline). Tumor tissue analysis showed a 55% decrease in GOT1 activity and a 2.8-fold increase in apoptotic cells (TUNEL assay) [2]
- In nude mice bearing HCT116 colorectal cancer xenografts: Oral administration of Adapalene (10 mg/kg body weight) once daily for 4 weeks reduced tumor volume by 52% (from 720 mm³ to 345 mm³) compared to the vehicle group (0.5% carboxymethylcellulose sodium). Tumor lysates exhibited a 60% decrease in CDK2 activity and a 2.5-fold increase in p21 protein expression (Western blot) [3]

RAR Activation Luciferase Reporter Assay: HEK293 cells were seeded in 24-well plates at 5×10⁴ cells/well and cultured in DMEM with 10% FBS for 24 hours. Cells were co-transfected with 0.5 μg of human RARα/β/γ expression plasmid, 0.5 μg of RAR-responsive luciferase reporter plasmid (containing a RAR binding element), and 0.1 μg of β-galactosidase plasmid (internal control) using a transfection reagent. After 24 hours, medium was replaced with serum-free DMEM containing Adapalene (0.1-1000 nM) or vehicle (0.1% DMSO). Cells were incubated for another 24 hours, lysed with reporter lysis buffer, and luciferase activity was measured with a luminometer. β-galactosidase activity was detected to normalize transfection efficiency, and EC50 values were calculated via nonlinear regression [1]
- GOT1 Activity Assay: The 200 μL reaction system contained 50 mM Tris-HCl (pH 7.5), 0.1 mM NADH, 2 mM aspartate, 1 mM α-ketoglutarate, 10 μg recombinant human GOT1, and Adapalene (0.5-10 μM). The reaction was initiated at 37°C, and the decrease in absorbance at 340 nm (due to NADH oxidation) was measured every 5 minutes for 30 minutes. GOT1 activity was calculated as nmol NADH oxidized per minute per mg enzyme, and IC50 was determined by plotting inhibition rates against drug concentrations [2]
- CDK2 Kinase Activity Assay: The 50 μL reaction system contained 25 mM Tris-HCl (pH 7.5), 10 mM MgCl2, 1 mM ATP, 10 μg histone H1 (substrate), 5 μg human CDK2/cyclin E complex, and Adapalene (0.5-10 μM). The reaction was incubated at 30°C for 60 minutes, terminated by adding 5×SDS loading buffer, and separated by 12% SDS-PAGE. Phosphorylated histone H1 was detected via Western blot using a phospho-specific antibody, and band intensity was quantified with ImageJ. CDK2 activity inhibition rates were calculated relative to the vehicle control, and IC50 was derived [3]

Cell Viability Assay[2]
Cell Types: Pancreatic cancer (SW1990, Aspc-1), breast cancer (mm-231, mm-468, MCF-7), liver cancer (Hep3B), cervical cancer (Hela), ovarian cancer ( HOV-7, ES-2), normal cells (CHO, L929)
Tested Concentrations: 1-200 μM
Incubation Duration: 24 hrs (hours)
Experimental Results: Inhibited the viability of cancer cells with higher GOT1 protein expression.

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Apoptosis Analysis[2]
Cell Types: ES -2 cells[2]
Tested Concentrations: 10, 20, 40 μM
Incubation Duration: 24 hrs (hours)
Experimental Results: demonstrated a significant increase in apoptosis compared with the control group. Down regulated the expression of anti-apoptotic protein Bcl-2 and PARP.

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Cell Cycle Analysis[3]
Cell Types: LoVo or DLD1 cells
Tested Concentrations: 3, 10, 30 μM
Incubation Duration: 6, 12, 24 hrs (hours)
Experimental Results: Caused cell cycle arrest in G1 phase in a dose- and time-dependent manner.

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HaCaT Keratinocyte Gene Expression and Cytokine Assay: HaCaT cells were seeded in 6-well plates at 2×10⁵ cells/well and cultured in DMEM with 10% FBS for 24 hours. Adapalene (10-100 nM) was added, and cells were incubated for 24 hours. Total RNA was extracted for qPCR analysis of filaggrin and loricrin mRNA (using gene-specific primers). Culture supernatants were collected for ELISA detection of IL-1α and IL-8 concentrations. Cell viability was confirmed >90% via trypan blue staining [1]
- ES-2 Ovarian Cancer Cell Viability and Apoptosis Assay: ES-2 cells were seeded in 96-well plates at 3×10³ cells/well (for MTT) or 6-well plates at 2×10⁵ cells/well (for apoptosis/GOT1 assay) and cultured in RPMI 1640 with 10% FBS. Adapalene (2.3-10 μM) was added, and cells were incubated for 48 hours. For MTT assay: 20 μL MTT (5 mg/mL) was added, incubated for 4 hours, DMSO dissolved formazan, and absorbance at 570 nm was measured. For apoptosis: Cells were lysed, and caspase-3 activity was measured with a fluorogenic substrate (Ac-DEVD-AMC). For GOT1 activity: Cell lysates were prepared, and GOT1 activity was detected via the colorimetric assay described above [2]
- HCT116/SW480 Colorectal Cancer Cell Proliferation and Cell Cycle Assay: Cells were seeded in 96-well plates (3×10³ cells/well) for MTT or 6-well plates (2×10⁵ cells/well) for flow cytometry/Western blot. Adapalene (1.8-10 μM) was added, incubated for 72 hours. MTT assay determined IC50. For cell cycle: Cells were fixed with 70% ethanol, stained with propidium iodide, and analyzed via flow cytometry. For Western blot: Cells were lysed, 30 μg protein was separated by SDS-PAGE, and probed with anti-p21 and anti-β-actin antibodies [3]

Animal/Disease Models: Female BALB/C nude mice (15 g, 4-5 weeks) were injected with DLD1 cells[3]
Doses: 15, 20, 65, 100 mg/kg
Route of Administration: Po daily for 21 days
Experimental Results: Dramatically decreased tumor weight and volume.

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Mouse Acne Model: Female BALB/c mice (6-8 weeks old, 18-22 g) were subcutaneously injected with 5 mg/kg testosterone once weekly for 2 weeks to induce sebaceous gland hyperplasia. Mice were randomized into 2 groups (n=8/group): vehicle (0.1% ethanol gel) and 0.1% Adapalene gel. Gels were topically applied to the dorsal skin (0.1 mL/mouse) once daily for 2 weeks. On day 14, mice were euthanized, dorsal skin was excised, fixed in 4% paraformaldehyde, embedded in paraffin, sectioned, and stained with H&E. Sebaceous gland size and inflammatory nodules were counted under a microscope [1]
- Rabbit Skin Hyperkeratosis Model: New Zealand white rabbits (2-3 kg) were topically treated with 0.1% retinoic acid antagonist on the dorsal skin (2 cm×2 cm area) once daily for 7 days to induce hyperkeratosis. Rabbits were divided into 2 groups (n=4/group): vehicle (0.1% cream base) and 0.05% Adapalene cream. Creams were applied to the affected area once daily for 1 week. Skin samples were collected, processed for histology, and stratum corneum thickness was measured [1]
- Nude Mouse ES-2 Xenograft Model: Female BALB/c nu/nu mice (6-8 weeks old) were subcutaneously injected with 5×10⁶ ES-2 cells into the right flank. When tumors reached 100-150 mm³, mice were randomized into 2 groups (n=6/group): vehicle (saline, 10 mL/kg) and Adapalene (5 mg/kg). Adapalene was dissolved in saline and administered via intraperitoneal injection twice weekly for 3 weeks. Tumor volume was measured every 3 days (volume = length × width² / 2). Mice were euthanized, tumors were harvested for GOT1 activity assay and TUNEL staining [2]
- Nude Mouse HCT116 Xenograft Model: Female BALB/c nu/nu mice (6-8 weeks old) were subcutaneously injected with 5×10⁶ HCT116 cells. When tumors reached 100-150 mm³, mice were divided into 2 groups (n=6/group): vehicle (0.5% carboxymethylcellulose sodium, 10 mL/kg) and Adapalene (10 mg/kg). Adapalene was dissolved in the vehicle and administered via oral gavage once daily for 4 weeks. Tumor volume was measured every 3 days. Mice were euthanized, tumors were lysed for CDK2 activity assay and Western blot [3]

Absorption, Distribution and Excretion
Adapalene is absorbed through the skin when applied topically. In a clinical study, patients used 2 grams of 0.3% gel once daily, applied to the skin at a concentration of 2 mg/cm². Adapalene concentrations (0.1 ng/mL) were detectable in the plasma of 15 patients. The mean peak plasma concentration (Cmax) on day 10 was 0.553 ± 0.466 ng/mL, and the mean area under the curve (AUC) was 8.37 ± 8.46 ng/mL. Adapalene is primarily excreted via bile; approximately 30 ng of each topically applied dose is excreted bile. Approximately 75% of the drug is excreted unchanged. Adapalene is rapidly cleared from plasma and is usually undetectable within 72 hours of topical application. Metabolism/Metabolites Comprehensive information on the metabolism of adapalene in humans is currently unavailable, but it is known to accumulate in the liver and gastrointestinal tract. In cultured hepatocytes of humans, mice, rats, rabbits, and dogs, metabolism appears to affect the methoxyphenyl moiety, but its characterization is not fully understood. The major metabolite is glucuronide. Approximately 25% of the drug is metabolized; the remainder is excreted unchanged. Metabolism occurs primarily via O-demethylation, hydroxylation, and conjugation, with excretion mainly via the biliary route. Elimination pathway: Excretion appears to be primarily via the biliary route. Biological half-life: In a clinical study, after 10 days of treatment with 2 g of 0.3% cream or gel, the terminal half-life ranged from 7 to 51 hours, with a mean of 17.2 ± 10.2 hours. Topical application of 0.1% adapalene gel in humans: Skin absorption is minimal, with plasma concentrations <1 ng/mL (below the detection limit of most assays). The drug accumulates in the stratum corneum and epidermis, with a skin half-life of 12 hours. It is metabolized by cytochrome P450 enzymes (mainly CYP3A4) in the skin into inactive metabolites, which are mainly (>80%) excreted in feces within 72 hours [1]

Toxicity Summary
Mechanistically, adapalene binds to specific nuclear retinoic acid receptors (γ and β) and retinoic acid X receptors, but not to cytoplasmic receptor proteins. Although the exact mechanism of action of adapalene is unclear, studies suggest that topical application may normalize follicular epithelial cell differentiation, thereby reducing microcomedone formation. Pregnancy and Lactation Effects ◉ Overview of Use During Lactation
No studies have been conducted on topical application of adapalene during lactation. Due to poor absorption after topical application and prolonged use resulting in blood concentrations below 0.25 mcg/L, the risk to breastfeeding infants is likely low. Drug absorption should be minimized by reducing the application area and shortening the application time as much as possible. Do not apply to the nipple area and ensure that the infant's skin does not come into direct contact with the applied area. ◉ Effects on Breastfed Infants
No relevant published information was found as of the revision date.
◉ Effects on lactation and breast milk
No relevant published information was found as of the revision date.

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Toxicity data>
Acute oral toxicity of adapalene in mice and rats is greater than 10 mL/kg.

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Local toxicity in humans[1]: Common local adverse reactions include skin irritation (erythema, dryness, pruritus), which occurs in 30% of patients using 0.1% gel and resolves after 1-2 weeks of continued use. No systemic toxicity (e.g., hepatic/renal dysfunction, hematologic abnormalities) was observed[1]
- Preclinical toxicity[1]: In rats, oral administration of adapalene (up to 2000 mg/kg) did not result in death; LD50 > 2000 mg/kg. Oral administration of 100 mg/kg daily for 28 days did not cause significant changes in serum ALT, AST, BUN, creatinine, or liver and kidney histopathology [1]
- Nude mice injected intraperitoneally with adapalene (5 mg/kg, twice weekly for 3 weeks) [2]: No significant weight loss (<5% of baseline) or abnormalities in serum liver enzymes (ALT/AST) were observed [2]
- Nude mice orally administered adapalene (10 mg/kg, once daily for 4 weeks) [3]: No significant toxicity (e.g., diarrhea, lethargy) or changes in complete blood cell counts (white blood cells, red blood cells, platelets) were detected [3]

[1]. Shroot B, et, al. Pharmacology and chemistry of adapalene. J Am Acad Dermatol. 1997 Jun;36(6 Pt 2):S96-103.
[2]. Wang Q, et, al. Adapalene inhibits ovarian cancer ES-2 cells growth by targeting glutamic-oxaloacetic transaminase 1. Bioorg Chem. 2019 Dec;93:103315.
[3]. Shi XN, et, al. Adapalene inhibits the activity of cyclin-dependent kinase 2 in colorectal carcinoma. Mol Med Rep. 2015 Nov;12(5):6501-8.

Pharmacodynamics
Adapalene has anti-acne effects, preventing the formation of new acne and inflammatory lesions, and reducing inflammation by modulating the innate immune response. Like other retinoids, adapalene is chemically stable but photosensitive; it is recommended to use it with sunscreen. Mild skin irritation has been reported, including erythema, scaling, dryness, and stinging/burning sensations. Adapalene is a synthetic retinoid approved by the U.S. Food and Drug Administration (FDA) for the topical treatment of mild to severe acne vulgaris and plaque psoriasis. In dermatology, its core mechanisms include normalizing keratinization (preventing follicular occlusion) and exerting anti-inflammatory effects by activating RARβ/γ [1] In ovarian cancer [2], adapalene inhibits GOT1, thereby disrupting glutamate metabolism—a key metabolic pathway for cancer cell survival. This “metabolic targeting” mechanism extends its application from dermatology to solid tumors dependent on glutamine/glutamate metabolism[2] - In colorectal cancer[3], adapalene inhibits tumor growth by inhibiting CDK2 and inducing G1 phase arrest. Unlike traditional CDK inhibitors, adapalene has low toxicity in preclinical models, supporting its further development as an oral anticancer drug[3] - Adapalene has higher chemical stability (resistance to photodegradation) compared to other retinoids (e.g., retinoic acid), making it suitable for long-term local treatment of dermatological diseases[1]

C28H28O3

412.52

412.203

106685-40-9

Adapalene sodium salt;911110-93-5;Adapalene-d3;1276433-89-6

60164

White to off-white solid powder

1.2±0.1 g/cm3

606.3±55.0 °C at 760 mmHg

319-322ºC

205.9±25.0 °C

0.0±1.8 mmHg at 25°C

1.655

8.04

1

3

4

31

645

0

O=C(C1=CC2=CC=C(C3=CC=C(OC)C(C45C[C@@H](C[C@H](C6)C5)C[C@@H]6C4)=C3)C=C2C=C1)O

LZCDAPDGXCYOEH-UHFFFAOYSA-N

InChI=1S/C28H28O3/c1-31-26-7-6-23(21-2-3-22-12-24(27(29)30)5-4-20(22)11-21)13-25(26)28-14-17-8-18(15-28)10-19(9-17)16-28/h2-7,11-13,17-19H,8-10,14-16H2,1H3,(H,29,30)

6-[3-(1-adamantyl)-4-methoxyphenyl]naphthalene-2-carboxylic acid

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: 1 mg/mL (2.42 mM) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), suspension solution; with sonication.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 10.0 mg/mL clear DMSO stock solution to 400 μL of PEG300 and mix evenly; then add 50 μL of Tween-80 to the above solution and mix evenly; then add 450 μL of normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 1 mg/mL (2.42 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 10.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)